Nano-indentation

Accurately predicting the fatigue behavior of spot welds remains challenging due to varying material properties across weld zones. This study investigates the fatigue behavior of spot welds in DC04 steel through experimental testing and finite element modeling (FEM). Four modeling approaches-Solid Element (SE), MPC Beam Element (MBE), Quad RBE3, and Triangular RBE3 Elements (T-RE)-were used to simulate the weld nugget, with material properties of the base metal (BM), heat-affected zone (HAZ), and fusion zone (FZ) characterized using a novel indentation method. Fatigue life predictions were conducted using multiaxial criteria, including Morrow, Brown-Miller-Morrow (BMM), and Smith-Watson-Topper (SWT). Microhardness and microstructural analyses identified a decarburized "pale halo line" at the FZ/HAZ interface, resulting in a notable reduction in hardness. Experimental fatigue tests validated the numerical models, with simulations using SE providing the most accurate predictions of fatigue life and fracture behavior. Among the fatigue criteria, BMM predictions were the most conservative, while Morrow and SWT showed closer agreement at higher stress levels. This research highlights the effectiveness of advanced modeling and material characterization techniques in improving the accuracy of fatigue life predictions for spot welds in the automotive industry.

The hardness of the metals in the bulk forming operations, such as upsetting increases, when the material is compressed. The increase in the level of strain improves the hardness of the billets in the upsetting tests. Issues like anisotropy may arise depending on the class of material and effect of the anisotropy on the metallic hardness is an interesting study for the effective utilization of material. Three sets of AA2014 billets solutionized at 502 C and aged for 9 h, 13 h, and 18 h at a temperature of 150 C were considered for the investigation. The effect of the material constant (C 1) on the variations in hardness was studied. Billets aged for 18 h were upset by employing three different lubricants namely grease, molybdenum disulphide, and white grease to study the effect of lubrication on anisotropy. The effect of anisotropy on hardness was studied by modeling Hill's criteria for anisotropy with the hardness. The empirical results of hardness values were compared with the values of experimental hardness for validity.

The higher order relationships of the Pentastomida have historically been tenuous. In one early and influential study, analysis of extracted chitin implicated that pentastomids possess β-chitin, a paradoxical finding given that the α allomorph is found uniformly in the cuticles of all arthropods and is considered as an apomorphic character of the Ecdysozoa. This result was further used to support the idea that the enigmatic pentastomids might be a wholly independent clade. More recent studies, however, firmly place the pentastomids within the Ecdysozoa, suggesting that the state of its chitin should be reexamined. In this study, we extracted high-quality chitin from the pentastomid, Leiperia cincinnalis, and carried out diagnostic analyses. Fourier Transform Infrared Spectroscopy (FT-IR) and ThermoGravimetric Analysis (TGA) demonstrated the conspicuous features of α-chitin but not β-chitin. Furthermore, transmission electron microscopy (TEM) of the cuticle of the anterior part of a specimen revealed nanofibres organized largely in a parallel configuration and scanning electron microscopy (SEM) of isolated cuticular chitin exhibited well-defined chitin bundles, these observations being more consistent with the known characteristics of αchitin. Collectively, our analyses demonstrate the clear existence of α-chitin in a pentastomid and clarify a contentious issue using modern methods of analysis.

Berkovich nanoindentation experiments were conducted on Zr 55 Cu 30 Al 10 Ni 5 bulk metallic glass under a constant loading rate. Indentation hardness decreased linearly with contact depth, which defied the direct application of conventional indentation size effect model for crystalline material. Elastic modulus remained invariant under small loads, but decreased linearly under large loads. The scaling relationships between indentation variables such as contact depth, permanent depth, the maximum indentation displacement, plastic energy, the total work of indentation and their ratios were investigated. The area of shear band circle, the projected contact area at the maximum load, and the residual projected area were all found to be proportional to one another. A new methodology to determine fracture toughness was proposed based on the total work of indentation, provided that the critical indentation displacement at the onset of fracture corresponds to zero value of elastic modulus extrapolated from curve fitting.

The effect of Nb in the glue site of the cluster-plus-glue atom model formula on the microstructure and mechanical properties of Ti-Mo alloy was investigated. Phase and microstructural analysis were performed by X-ray diffraction and electron backscatter diffraction. Tensile properties were also examined. A small amount of secondary martensitic α” and ωath nano particles were precipitated in the β matrix of both alloys, due to to the inhomogeneous distribution of Mo and/ or Nb caused by segregation, which formed local regions with high- and low-stability of the β phase. The elastic modulus was significantly reduced to 56.9 ± 3.08 GPa, while the elastic admissible strain was substantially improved. The increased β stability and suppression of the ωath phase led to no significant change in both the yield and ultimate tensile strengths, and the brittle fracture behavior. The alloy can be a potential alternative of the conventional orthopedic implant materials in orthopedic applications.

The present paper aims at providing a fine-scale analysis of the Ti-4.5Al-2.5Fe-0.25Si α+α'+β retained microstructures to give insight into the link between the microstructural characteristics of the alloy (phase fraction and chemistry, grain size, etc.) and the deformation mechanisms at play. These microstructures were found to exhibit outstanding work-hardening capabilities that have the great potential to be obtained simultaneously with a high yield strength when the microstructural features are carefully optimized. Ex-situ analyses coupled with TEM revealed the simultaneous occurrence of Reorientation Induced Plasticity (RIP) into the self-accommodated Feenriched α' martensite, TRansformation Induced Plasticity (TRIP) of the β retained phase and TWinning Induced Plasticity (TWIP) of the α phase that add to dislocation glide. The Fe-enriched martensite has the remarkable capability to induce reorientation through two distinctive mechanisms: by the motion upon deformation of the intervariant boundary associated to the [4 5 1 3] α ′ Type II twin, a rather classical mechanism although not often reported into α'; but more surprisingly into such a fine phase, by the creation and growth upon deformation of {1012}1011 α ′ twins. A 3-scale mechanical contrast is proposed to explain the remarkable work-hardening rates achieved. Reorientation is shown to be a key microstructural feature for the development of Ti alloys with superior mechanical properties.

ABSTRACTDepth sensing nano-indentation investigations have been performed to determine the radial dependence of the hardness through the cross section of a Fe-based bulk glassy rod. We have found the hardness of the material decreases along radius from the centre to the outermost surface. This phenomenon is attributed to the ‘cooling rate induced surface softening’. Furthermore, a significant change (~15 %) in elastic modulus is noticed along the radius as well.

equation 1 6 , 1 7) , whi ch has al so been well known for 70 years, also 1 needed to be modified in order to be able to apply it to submicron-1 structured materials as well. 1 An important factor in the plasticity of polycrystalline metals is the 1 grain size , which c an strongly affect the mechanism of deformation. 1 The mechanism maps for fcc-structured Ni and Al summarized 40 years 1 ago in t he much-cited, almost handbook " Maps of Deformation 1 Mechanisms" written by Frost and Ashby 1 8) were edited for the smallest 1 grain sizes of 1 and 10 μ m, r espectively. The much lower grain size of 2 200 nm and 1μ m obt ained by using the mentioned SPD techniques have 2 resulted in new phenomena, as strong twinning 1 9) or intense grain 2 boundary sliding at room temperature 1 1) in UFG Ni and Al, respectively. because of some typical problems. Firstly, the value of parameter K i n 1 Eq. (1) paradoxically changes in the case of s ubmicron grain sizes 3 4-1 3 8). Secondly, Eq. (1) is no longer valid at all at grain sizes below Recent experimental results 5 6) , howe ver, have shown t hat the ISE 2 effect is not experienced at all in submicron Al and Cu having average 2 grain size of about 100-120 nm. Mechanical properties of different 2 composition Al-Cu layers having thickness of ~1.7 μ m wer e studied by 2 using depth-sensing indentation. Figur e 3 shows the hardness obtained 2

The cuticle of arthropods (jointed-limb animals), and especially of insects is, by biological standards, a relatively simple composite. It is a single external layer of material forming the skeleton and many sense organs. The fibrous phase is crystalline chitin making nanofibrils of about 3 nm diameter, a few hundreds of nanometers long and a modulus probably in excess of 150 GPa. At least two surfaces of the nanofibril can have silk-like protein attached through specific H-bonds; the rest of the protein is globular. The protein matrix stiffens through dehydration controlled by the introduction of hydrophobic phenolics. Crustacea add up to 40% calcium salts. The stiffness of cuticle can range from tens of GPa to 1 kPa. It can be hardened by the addition of Zn or Mn. It can form springs and change its stiffness and plasticity under the control of the animal.

Due to high solubility of oxygen and nitrogen in titanium alloys, the influence of the diffusion zone on the macroscopic tensile properties of pre-oxidized annealed Ti-6Al-4V tensile specimens was examined at room temperature. Thin microtensile specimens were prepared with different thicknesses ranging from 100 µm to 500 µm and then exposed at 750°C for durations between 5 and 200h. A dedicated gripping technique was developed in the present study to investigate the brittleness of such pre-oxidized and ultrathin specimens at room temperature. Tensile testing was paired with digital image correlation techniques to assess both macroscopic deformation and full-field strain maps. High temperature pre-oxidation treatments significantly decreased the ductility of the specimen and the tensile strength of the materials (yield strength and ultimate tensile strength). Fractographic examinations revealed typical brittle fracture features in the oxygen/nitrogen-affected diffusion zone in the pe...

This study investigated the effect of heat treatment processes on the dry sliding wear resistance of the TC21 Ti-alloy at several levels of normal load and sliding speed. Response Surface Methodology (RSM) has been used as a design of the experiment procedure. OM and FESEM besides XRD analysis were used for results justification. Highest hardness of 49 HRC was recorded for WQ + Aging specimens due to the plenty of α″ which decomposed to αs and the more αs, while the lowest hardness of 36 HRC was reported for WQ specimens. The results revealed that specimens subjected to water quenching and aging (WQ + Aging) under extreme load and speed conditions (50 N and 3 m/s), possessed the poorest wear resistance although they had the highest hardness. While those left in the annealed condition revealed the highest wear resistance although they had much lower hardness when compared to other conditions. A mathematical polynomial model for wear resistance expressed in wear rate was developed, va...

High strain rate micromechanical testing can assist researchers in elucidating complex deformation mechanisms in advanced material systems. In this work, the interactions of atomic-scale chemistry and strain rate in affecting the deformation response of a Zr-based metallic glass was studied by varying the concentration of oxygen dissolved into the local structure. Compression of micropillars over six decades of strain rate uncovered a remarkable reversal of the strain rate sensitivity from negative to positive above ~ 5 s−1 due to a delocalisation of shear transformation events within the pre-yield linear regime for both samples, while a higher oxygen content was found to generally decrease the strain rate sensitivity effect. It was also identified that the shear band propagation speed increases with the actuation speed, leading to a transition in the deformation behaviour from serrated to apparent non-serrated plastic flow at ~ 5 s−1. Graphic abstract

Due to high solubility of oxygen and nitrogen in titanium alloys, the influence of the diffusion zone on the macroscopic tensile properties of pre-oxidized annealed Ti-6Al-4V tensile specimens was examined at room temperature. Thin microtensile specimens were prepared with different thicknesses ranging from 100 µm to 500 µm and then exposed at 750°C for durations between 5 and 200h. A dedicated gripping technique was developed in the present study to investigate the brittleness of such pre-oxidized and ultrathin specimens at room temperature. Tensile testing was paired with digital image correlation techniques to assess both macroscopic deformation and full-field strain maps. High temperature pre-oxidation treatments significantly decreased the ductility of the specimen and the tensile strength of the materials (yield strength and ultimate tensile strength). Fractographic examinations revealed typical brittle fracture features in the oxygen/nitrogen-affected diffusion zone in the pe...

This study investigated the effect of heat treatment processes on the dry sliding wear resistance of the TC21 Ti-alloy at several levels of normal load and sliding speed. Response Surface Methodology (RSM) has been used as a design of the experiment procedure. OM and FESEM besides XRD analysis were used for results justification. Highest hardness of 49 HRC was recorded for WQ + Aging specimens due to the plenty of α″ which decomposed to αs and the more αs, while the lowest hardness of 36 HRC was reported for WQ specimens. The results revealed that specimens subjected to water quenching and aging (WQ + Aging) under extreme load and speed conditions (50 N and 3 m/s), possessed the poorest wear resistance although they had the highest hardness. While those left in the annealed condition revealed the highest wear resistance although they had much lower hardness when compared to other conditions. A mathematical polynomial model for wear resistance expressed in wear rate was developed, va...

Cu 59.6 Zr 36.9 Al 3.5 alloy are prepared by laserinduced combustion synthesis technology. The microstructure and phases formed of the product is studied by XRD and TEM. The product consists of mixtures of amorphous and crystalline phases, mainly(a-Zr, Zr 2 Cu, Zr 10 Cu 7 and Cu 8 Zr 3. The amorphous and nanocrystalline phases content over 50% in volume estimated from the broad peak in the XRD spectrum. TEM and HRTEM results show that the microstructure is characterized by inhomogeneously distributed amorphous, nano Zr 2 Cu, relatively gross (~100 nm) Zr 2 Cu, and large grain Cu 10 Zr 7 .

This study investigated the effect of heat treatment processes on the dry sliding wear resistance of the TC21 Ti-alloy at several levels of normal load and sliding speed. Response Surface Methodology (RSM) has been used as a design of the experiment procedure. OM and FESEM besides XRD analysis were used for results justification. Highest hardness of 49 HRC was recorded for WQ + Aging specimens due to the plenty of α″ which decomposed to α s and the more α s , while the lowest hardness of 36 HRC was reported for WQ specimens. The results revealed that specimens subjected to water quenching and aging (WQ + Aging) under extreme load and speed conditions (50 N and 3 m/s), possessed the poorest wear resistance although they had the highest hardness. While those left in the annealed condition revealed the highest wear resistance although they had much lower hardness when compared to other conditions. A mathematical polynomial model for wear resistance expressed in wear rate was developed, validated then used to get the optimum parameters.

Biomechanics is gaining relevance as complementary discipline to structural and cellular biology. The response of cells to mechanical stimuli determines cell type and function, while the spatial distribution of mechanical forces within the cells is crucial to understand cell activity. The experimental methodologies to approach cell mechanics are diverse but either they are effective in few cases or they rule out the innate cell complexity. In this regard, we have developed a simple scanning probebased methodology that overcomes the limitations of the available methods. Stress relaxation, the decay of the force exerted by the cell surface at constant deformation, has been used to extract relaxational responses at each cellular sublocalisation and generate maps. Surprisingly, decay curves exerted by test cells are fully described by a generalized viscoelastic model that accounts for more than one simultaneously occurring relaxations. Within the range of applied forces (0.5-4 nN) a slow and a fast relaxation with characteristic times of 0.1 and 1 s have been detected and assigned to rearrangements of cell membrane and cytoskeleton, respectively. Relaxation time mapping of entire cells is thus promising to simultaneously detect non-uniformities in membrane and cytoskeleton and as identifying tool for cell type and disease.

The effect of rare-earth (Sm) microalloying on the thermal stability and phase selection along with the effect of nanocrystallization on the mechanical properties of amorphous melt-spun ribbons of Zr 50 Cu 40 Al 10 , Zr 49 Cu 39.2 Al 9.8 Sm 2 and Zr 48 Cu 38.4 Al 9.6 Sm 4 alloys were investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), Vickers and nanoindentation hardness tests and micropillar compression analysis. XRD and TEM analyses showed that all samples were fully amorphous in as-spun state; however, crystallization sequences for the Sm-free and the Sm micro-alloyed samples were different during devitrification. Combined study of XRD, DSC and TEM on melt-spun ribbons show that Zr 48 Cu 38.4 Al 9.6 Sm 4 have nanocrystallization of Cu 2 Sm phase with an average diameter of 10 nm, which was absent in Zr 50 Cu 40 Al 10 , prior to crystallization of Cu 10 Zr 7 phase. The nanoindentation and micropillar compression tests revealed Cu 2 Sm nanocrystals embedded in Zr 48 Cu 38.4 Al 9.6 Sm 4 alloy improves strength and hardness. On the other hand, presence of these nanocrystals deteriorate shear band stability and thus result in a catastrophic brittle fracture through a single shear band burst.

The applicability of various hardness-yield strength (H À y) relationships currently available in the literature for bulk metallic glasses (BMGs) is investigated. Experimental data generated on ZrHf-based BMGs in this study and those available elsewhere on other BMG compositions are used to validate the models. A modified expanding-cavity model, proposed earlier by the authors, is extended to propose a new H À y relationship. Unlike previous models, the proposed model takes into account, not only the indenter geometry and the material properties, but also the pressure sensitivity index of the BMGs. The influence of various model parameters is systematically analyzed. It is shown that there is a good correlation between the model predictions and experimental data for a wide range of BMG compositions.

Al-Zn alloys with different Zn concentrations between 2 and 30 wt.% were processed by high-pressure torsion (HPT) to produce ultrafine-grained (UFG) materials. Microstructural and mechanical and properties of these UFG alloys were then investigated using depth-sensing indentations (DSI), focused ion beam (FIB), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Emphasis was placed on the decomposition due to the HPT process, as well as on its effects on the mechanical properties of the UFG alloys. For low Zn contents, HPT gave strengthening due to grain refinement while for the highest Zn concentration the decomposition of the microstructure yielded an abnormal softening at room temperature. The microstructure decomposition led also to the formation of a Zn-rich phase, which wets the Al/Al grain boundaries and enhanced the role of grain boundary sliding with unusually high strain rate sensitivity. The occurrence of intensive sliding in these UFG alloys a...

Dedicated to Professor Terence G. Langdon on the occasion of his 80 th birthday Herein, the characterization of microstructures and mechanical properties of Al-Zn alloys ultrafine-grained (UFG) by using high pressure torsion (HPT) is surveyed. Emphasis is placed on the decomposition of the solid solution structures due to the HPT process, leading to unique mechanical and plastic properties of the UFG alloys. The decomposed microstructures, the grain boundaries wetted by Zn-rich layers, as well as the softening, grain boundary sliding (GBS) with usually high strain rate sensitivity and super-ductility of the HPT-processed samples are described and discussed. Furthermore, the innovation potential of intensive GBS at room temperature is briefly considered.

Most ultrafine-grained (UFG) materials produced by severe plastic deformation (SPD) exibit only limited ductility which is correlated with the low strain rate sensitivity (SRS) of these materials. Recently, it was demonstrated that SPD is capable of increasing the room temperature ductility of aluminum-based alloys attaining elongations up to 150%, together with relatively high strain rate sensitivity. In the present work, additional results and discussions are presented on the effect of grain boundary sliding (GBS) and SRS on the ductility of some UFG metals and alloys. The characteristics of constitutive equations describing the steady-state deformation process are quantitatively analyzed for a better understanding of the effects of grain boundaries and strain rate sensitivity. Recently, we demonstrated the room temperature super-ductility of a UFG Al-30Zn alloy in which GBS takes place with relatively high SRS [7]. In this work, the effect of GBS taking place in different materials is discussed and related to the SRS. Additional results are presented to demonstrate the role of diffusion-controlled GBS on the ductility of UFG materials.

Bulk metallic glass (BMG) matrix composites with crystalline dendrites as reinforcements exhibit a wide variance in their microstructures (and thus mechanical properties), which in turn can be attributed to the processing route employed, which affects the size and distribution of the dendrites. A critical investigation on the microstructure and tensile properties of Zr/Ti-based BMG composites of the same composition, but produced by different routes, was conducted so as to identify "structure-property" connections in these materials. This was accomplished by employing four different processing methods-arc melting, suction casting, semi-solid forging and induction melting on a water-cooled copper boat-on composites with two different dendrite volume fractions, V d. The change in processing parameters only affects microstructural length scales such as the interdendritic spacing, k, and dendrite size, d, whereas compositions of the matrix and dendrite are unaffected. Broadly, the composite's properties are insensitive to the microstructural length scales when V d is high ($75%), whereas they become process dependent for relatively lower V d ($55%). Larger d in arc-melted and forged specimens result in higher ductility (7-9%) and lower hardening rates, whereas smaller dendrites increase the hardening rate. A bimodal distribution of dendrites offers excellent ductility at a marginal cost of yield strength. Finer k result in marked improvements in both ductility and yield strength, due to the confinement of shear band nucleation sites in smaller volumes of the glassy phase. Forging in the semi-solid state imparts such a microstructure.

Understanding the structural characteristics in bulk metallic glass forming alloys is important in order to understand the atomic origin of its high glass forming ability and associated physio-chemical properties. Zr 60 Cu 10 Al 15 Ni 15 alloy was cast in a water cooled copper mold. Due to difference in cooling rate the bottom regions of the cast rod shows amorphous phase with randomly oriented short range ordered domains while in the top part of the cast rod having faceted or dentritic crystals of cF96 Zr 2 Ni and tP20 Zr 3 Al 2 phases were observed. The size of the short/medium range ordered domains is~0.3 nm. Complete structural analysis of the crystalline phases indicates that complex interconnected polyhedral order exists in the crystalline phases which are related to Bernal deltahedra and Frank-Kasper polyhedra. Correlation with the size of short range ordered regions indicates that similar polyhedra may also exist in the liquid, the specific interaction of which leads to the formation of short range ordered domains and crystal nuclei. Morphology of the crystalline phases indicates strong interplay of solid-liquid interfacial energy; break down of solid-liquid planar interface and solute segregation during solidification and crystal nucleation.

Soda lime silica glasses were investigated by continuous indentation tests. The load indentation depth curves were taken during the loading as well as the unloading period by a computer controlled MTS machine. It was found that the loading force is a quadratic finction of the indentation depth during both the loading and unloading stage of the deformation. The validity of the quadratic relationship in the case of the unloading stage seems to be characteristic only for glasses. Taking into account the elastic relaxation of the indentation depth an estimation is given for the size of the hydrostatic core which is necessary to symmetrize the stress field around the indenter. Using the measured length of the radial cracks started frpm the corners of the Vickers indentation pattern the K,, values were calculated.

Microstructure evolution and phase transformation of metallic glasses (MGs) could occur under heating condition or mechanical deformation. The cross-section of as-cast Zr 55 Cu 30 Ni 5 Al 10 MG rod was impacted by the solid particles when subjected to erosion in slurry flow. The surface microstructure was observed by XRD before and after slurry erosion. And the stress-driven de-vitrification increases with the increase of erosion time. A microstructure evolution layer with 1~2 μ thickness was formed on the topmost eroded surface. And a short range atomic ordering prevails in the microstructure evolution layer with crystalline size around 2~3 nm embedded in the amorphous matrix. The XPS analysis reveals that most of the metal elements in the MG surface, except for Cu, were oxidized. And a composite layer with ZrO 2 and Al 2 O 3 phases were formed in the topmost surface after slurry erosion. The cooling rate during solidification of MG has a strong influence on the slurry

The effect of heat treatment on microstructure and tensile properties as well as wear behavior on TC21 (Ti-6Al-2Sn-2Zr-3Mo-1Cr-2Nb-Si, wt.%) Ti-alloy was investigated. The samples were solution treated at 900˚C for 15 min followed by furnace cooling to 800˚C with a cooling rate 1˚C/min and holding for 20 min, then the samples cooled down to room temperature either using water quenching (WQ) or air cooling (AC). Consequently, aging treatment was applied at 575˚C for 4 hr. The microstructure feature showed a secondary α phase (α s) precipitated in residual β phase due to the step cooling from 900˚C to 800˚C inside furnace as well as the aging treatment. The highest wear rate was obtained for WQ samples due to increasing in volume fraction of α p (58%). However, the lowest wear rate was reported for WQ + Aging samples due to the high hardness. Optimum mechanical properties of the studied TC21 Ti-alloy were obtained for AC + Aging condition. A better combination of hardness, tensile properties, and wear resistance was achieved for AC + Aging samples, although their wear resistance was found to be slightly lower than that of WQ + Aging samples.

Over the last two decades, particular interest has been paid to the preparation of bulk metallic glasses (BMGs) due to their unique and original properties. [1,2] Ball-milling (BM) of blended pure elements or pre-alloyed compounds is an efficient technique for producing glassy powders. [3] Combined with the powder consolidation within the supercooled liquid region, bulk samples with amorphous structures can be easily formed. [4,5] However, the crystallization of amorphous alloys under ball-milling, which is considered as mechanically induced crystallization (MIC), has been observed extensively in a number of alloy systems, i.e., Al-, Fe-, Ti-and Zr-based ones. [6-14] In particular, a cyclic crystalline-glassy-crystalline phase transformation induced by BM has been reported in CoÀTi, ZrÀNi, ZrÀAlÀNi and ZrÀAlÀNiÀCuÀPd systems. [12-15] These previous works have shown that the crystallization process and the corresponding procedures under ball-milling are significantly different from those obtained under conventional thermal crystallization, indicating that the MIC cannot be attributed only to the local temperature rise. [8,9] The exact mechanisms of MIC are not fully understood but have been suggested to be related to the effects-possibly combined-of pressure and mechanically induced defects. [7-11,16] This manuscript gives the first results of an ongoing research project set up to improve the understanding of MIC in Zr-based BMGs. To this end, the crystallization behaviors of Zr 65 Al 7.5 Ni 10 Cu 17.5 (Z1) and Zr 58 Al 16 Ni 11 Cu 15 (Z2) BMGs under ball-milling and thermal cycles are here compared. Experimental BMG Preparation Master ingots with nominal compositions Zr 65 Al 7.5-Ni 10 Cu 17.5 and Zr 58 Al 16 Ni 11 Cu 15 (at-%) were prepared by arc melting under an argon atmosphere. The levels of purity for the different constituting elements are 99.9 wt-% for Zr, 99.999 wt-% for Al, and 99.99 wt-% for Cu and Ni.

The mechanical properties of ex-situ and in-situ metallic glass matrix composites (MGMCs) have proven to be both scientifically unique and of potentially important for practical applications. However, the underlying deformation mechanisms remain to be studied. In this article, we review the development, fabrication, microstructures, and properties of MGMCs, including the room-temperature, cryogenic-temperature, and high-temperature mechanical properties upon quasi-static and dynamic loadings. In parallel, the deformation mechanisms are experimentally and theoretically explored. Moreover, the fatigue, corrosion, and wear behaviors of MGMCs are discussed. Finally, the potential applications and important unresolved issues are identified and discussed.

Indentation and scratching tests are carried out on a ZrCuAlNi bulk metallic glass. The bonded interface technique is used to characterize the plasticity mechanisms underneath the indentation. Finite-element analyses are conducted with a Drucker-Prager behaviour law to challenge the indentation experimental data. The relevance of the bonded interface technique, in terms of quantitative evaluation, is discussed. It is also reported that the angle value, for which radial bands intersect at the surface or underneath it, is not a constant value and depends on the indenter geometry. Finally, it is shown that a simple Drucker-Prager model can describe most of the indentation mechanical response but fails in predicting completely the indentation morphology.

The influence of partial crystallization on the evolution of the characteristic temperatures, i.e. of the glass transition and the onset of crystallization, the density, and the mechanical properties of the bulk metallic glass Pt 49.95 Si 6.4 B 24 Ge 3 Cu 16.65 is investigated. Partial crystallization is introduced by annealing the alloy in a stabilized salt bath at 350°C and for different times and quantified by the residual heat of crystallization as measured in differential scanning calorimetry. It is found that the crystalline regions are enriched in platinum and the remaining amorphous phase is enriched in copper. The evolution of T g and T x of the remaining amorphous phase can be quantitatively linked to the degree of copper enrichment of the amorphous phase as crystallization advances. Hardness increases steadily with the degree of crystallization from 570 HV in the as-cast state to 750 HV in the fully crystallized state. In contrast, compressive strength drops steadily with increasing crystallinity due to increasing brittleness.

Understanding the structural characteristics in bulk metallic glass forming alloys is important in order to understand the atomic origin of its high glass forming ability and associated physio-chemical properties. Zr 60 Cu 10 Al 15 Ni 15 alloy was cast in a water cooled copper mold. Due to difference in cooling rate the bottom regions of the cast rod shows amorphous phase with randomly oriented short range ordered domains while in the top part of the cast rod having faceted or dentritic crystals of cF96 Zr 2 Ni and tP20 Zr 3 Al 2 phases were observed. The size of the short/medium range ordered domains is~0.3 nm. Complete structural analysis of the crystalline phases indicates that complex interconnected polyhedral order exists in the crystalline phases which are related to Bernal deltahedra and Frank-Kasper polyhedra. Correlation with the size of short range ordered regions indicates that similar polyhedra may also exist in the liquid, the specific interaction of which leads to the formation of short range ordered domains and crystal nuclei. Morphology of the crystalline phases indicates strong interplay of solid-liquid interfacial energy; break down of solid-liquid planar interface and solute segregation during solidification and crystal nucleation.

Partially vitrified Zr 60 Cu 10 Al 15 Ni 15 bulk metallic glass has been synthesized using water cooled copper mold drop casting technique. Kinetically favorable microstructures having different morphologies are observed throughout the volume of the bulk metallic glass sample. X-ray diffraction studies indicate formation of hard intermetallic compounds such as Zr 3 Al 2 and Zr 2 Ni in certain regions along with amorphous structures. Microindentation studies carried out in different regions of the sample reveal microstructure dependent deformation behavior. Highest hardness is observed in the fully crystallized regions compared to pure glassy regions in the same sample. Further nanoindenation in the same sample is used to understand dynamic mechanical properties of microstructures in different regions. The pileup morphologies around the indent and differences in load-displacement curves provide vital information on deformation behavior of sample in different microstructure sensitive regions.

Bulk metallic glass (BMG) matrix composites with crystalline dendrites as reinforcements exhibit a wide variance in their microstructures (and thus mechanical properties), which in turn can be attributed to the processing route employed, which affects the size and distribution of the dendrites. A critical investigation on the microstructure and tensile properties of Zr/Ti-based BMG composites of the same composition, but produced by different routes, was conducted so as to identify "structure-property" connections in these materials. This was accomplished by employing four different processing methods-arc melting, suction casting, semi-solid forging and induction melting on a water-cooled copper boat-on composites with two different dendrite volume fractions, V d. The change in processing parameters only affects microstructural length scales such as the interdendritic spacing, k, and dendrite size, d, whereas compositions of the matrix and dendrite are unaffected. Broadly, the composite's properties are insensitive to the microstructural length scales when V d is high ($75%), whereas they become process dependent for relatively lower V d ($55%). Larger d in arc-melted and forged specimens result in higher ductility (7-9%) and lower hardening rates, whereas smaller dendrites increase the hardening rate. A bimodal distribution of dendrites offers excellent ductility at a marginal cost of yield strength. Finer k result in marked improvements in both ductility and yield strength, due to the confinement of shear band nucleation sites in smaller volumes of the glassy phase. Forging in the semi-solid state imparts such a microstructure.

This review reports on the use of the atomic force microscopy in the investigation of the mechanical properties of cells. It is shown that the technique is able to deliver information about the cell surface properties (e.g., topography), the Young modulus, the viscosity, and the cell the relaxation times. Another aspect that this short review points out is the utilization of the atomic force microscope to investigate basic questions related to materials physics, biology, and medicine. The review is written in a chronological way to offer an overview of phenomenological facts and quantitative results to the reader. The final section discusses in detail the advantages and disadvantages of the Hertz and JKR models. A new implementation of the JKR model derived by Dufresne is presented.

Exposed regions of the arthropod exoskeleton have specialized structure and mineral composition. Their study can provide insights into the evolutionary optimization of the cuticle as a material. We determined the structural and compositional features of claws in the crustacean Ligia pallasii using X-ray micro-computed tomography, scanning electron microscopy (SEM), and analytical scanning transmission electron microscopy (STEM). In addition, we used nanoindentation to determine how these features fine-tune the mechanical properties of the claw cuticle. We found that the inner layer of the claw cuticle—the endocuticle—contains amorphous calcium phosphate, while the outer layer—the exocuticle—is not mineralized and contains elevated amounts of bromine. While the chitin–protein fibers in crustacean exoskeletons generally shift their orientation, they are aligned axially in the claws of L. pallasii. As a consequence, the claw cuticle has larger elastic modulus and hardness in the axial ...

We measured the stress relaxation of mouse fibroblast NIH3T3 cells with an atomic force microscope (AFM) using a sharp silicon tip and a silica bead with a radius of ~1 µm as an indenter. The decay of loading force was clearly observed in NIH3T3 cells at a small initial loading force of ~0.4 nN and was well fitted to the stretched exponential function rather than to a single exponential function. The stretching exponent parameter was ~0.5 for both indenters, indicating that the stress relaxation observed in NIH3T3 cells consisted of multiple relaxation processes. The time-domain AFM technique described in this report allows us to measure directly the relaxation process of living cells in a range from milliseconds to seconds.

Nanoindentation measurements were performed on as-cast and torsionally deformed Zr 44 Ti 11 Cu 10 Ni 10 Be 25 bulk metallic glass samples. Distribution of the measured hardness values shows peak-increasing and widening as an effect of the plastic pre-deformation. Variation in the strength of the deformation affected material and the origin of strain hardening is explained by key characteristics of shear transformation zones in bulk metallic glasses.

Bottom-up modeling of American lobster (Homarus americanus) cuticle explains architecture and function ab initio, from first principles, starting with synthesis of component polymers and progressively building composite structure that should explain observed properties. A top-down perspective decomposes the lobster cuticle starting at the top level of structural complexity and function aiming to descend to the finest detail. Both approaches aim to ultimately model the same cuticle structure. Current bottom-up models of the cuticle do not succeed in explaining key structural and functional detail identified by top-down approaches. Top-down identified structures and associated functions are valuable as bases for potential vulnerabilities to microbial attack. An immediate objective is to inform the bottom-up approach of top-down identified model components critical to cuticle function. Top-down features include detail of protein expression and mineral heterogeneity and their function i...

Nano-and micro-indentation studies were carried out to characterise a plasticity mechanism through the evolution of localised shear bands that drive material's deformation at sub-micron length scale. Initial deformation of Zr-based bulk metallic glass (BMG) was investigated with nanoindentation tests using a spherical indenter. The indentation cycle reflects an elastic deformation with the yielding load of approx. 3 mN. For designed cycling indentation, hardening and softening phenomena were observed in nano-and microindentations, respectively. High-precision dynamic mechanical relaxation measurements were performed using a Dynamic Mechanical Analyzer (DMA), on decreasing frequency from 160 Hz to 0.1 Hz. A mechanical response of the BMG surface to a concentrated impact load was also studied. The obtained results indicated that the studied Zr-based BMG behaved as an elastic-perfectly plastic material at macroscale with discrete plasticity events at smaller length scales.

Experimental investigation of thermodynamic behavior and mechanical properties of bulk Zr/Hf-based amorphous alloys revealed that crystallization and glass transition temperatures, hardness and modulus increased with increasing Hf content. It is postulated that the observed strengthening might result from the microstructural changes with addition of Hf in place of Zr.

The relationship between the oscillatory force and the depth-response during dynamic indentation was analyzed mathematically and investigated experimentally in ultrafine-grained Al-Zn alloys processed by high-pressure torsion. We have shown for the first time that the phase shift between the local oscillatory force and depth signal, caused by the internal friction, is correlated to the strain-rate sensitivity, which is a key parameter indicating the ductility of materials. This correlation enables a new application of dynamic nanoindentation for studying the ratedependent deformation-mechanisms of materials from a novel aspect.

The variations in local yield strength and plasticity of a Zr-based bulk metallic glass at different fictive temperatures (T f) are studied. To probe the size and distribution of microscopic carriers of plasticity, spherical-tip nanoindentation and microindentation are employed. With nanoindentation, events signifying the departure from Hertzian elastic contact, which manifest as pop-ins in the load-displacement response and correspond to incipient plasticity, are recorded and analyzed. Results indicate that with increasing T f , the incipient plastic event and the number of subsequent pop-ins increases. Using statistical analysis of the scatter in strength, the activation parameters for shear transformation zones (STZs) in all specimens are determined. By considering the linear accumulation of STZs to form a shear band, the increase in shear yield strength along with plasticity, with increasing T f , is explained.

Causal factors leading to epizootic shell disease (ESD) lesions in American lobster, Homarus americanus H. Milne-Edwards, 1837, are not well understood. We explore the structural and physiological bases for development of ESD from preclinical stages invisible to unaided eye to early visible stages. We present a lobster shell model, which develops structural functional vulnerability and suggests plausible routes to ESD. Medallions of carapace cuticle were obtained from carapace fixed with protocols to minimize movement of mineral and macromolecular components. Rapid processing of medallions was used to encourage large sample sizes compatible with environmental surveys. One-and two-dimensional analytic maps of polished sections of the cuticle, obtained with an electron microprobe, described the composite mineral and polymeric structures. Micro-Raman spectroscopy was used to identify bond properties of phosphates and carbonates, as well as signatures of organic structures. The frequency and properties of structures identified can be monitored through the lobster molting cycle using a high throughput application of micro-computed tomography (μCT). We observed density differences in the calcite layer, exocuticle, and endocuticle, and the frequency and structure of CaCO 3 structures in the endocuticle and membranous layer of carapace cuticle during chosen stages of the molting cycle. The correlative microscopy and μCT of shell structures provides improved understanding of the lobster cuticle structure. Detailed structural differences quantified through development and under different environmental conditions can provide insight into causes and vulnerabilities associated with ESD. American lobster, Homarus americanus H. Milne-Edwards, 1837, populations experienced increased and variable incidence of epizootic shell disease (ESD)

Dynamic mechanical relaxation is a fundamental tool to understand the mechanical and physical properties of viscoelastic materials like glasses. Mechanical spectroscopy shows that the high-entropy bulk metallic glass (La 30 Ce 30 Ni 10 Al 20 Co 10) exhibits a distinct β-relaxation feature. In the present research, dynamic mechanical analysis and thermal creep were performed using this bulk metallic glass material at a temperature domain around the β relaxation. The components of total strain, including ideal elastic strain, anelastic strain, and viscous-plastic strain, were analyzed based on the model of shear transformation zones (STZs). The stochastic activation of STZ contributes to the anelastic strain. When the temperature or external stress is high enough or the timescale is long enough, the interaction between STZs induces viscous-plastic strain. When all the spectrum of STZs is activated, the quasi-steady-state creep is achieved.

The discontinuous creep of Cd-0.08 at~ Sn alloy single crystals was studied. Contrary to some other metals discontinuous creep curves have been observed at rather high temperatures (starting at 0.6 of the melting point). This result was combined with the investigation of Sn atoms distribution and explained in terms of the Portevin-Le Chatelier effect.

The scales of the arapaima (Arapaima gigas), one of the largest freshwater fish in the world, can serve as inspiration for the design of flexible dermal armor. Each scale is composed of two layers: a laminate composite of parallel collagen fibrils and a hard, highly mineralized surface layer. We review the structure of the arapaima scales and examine the functions of the different layers, focusing on the mechanical behavior, including tension and penetration of the scales, with and without the highly mineralized outer layer. We show that the fracture of the mineral and the stretching, rotation and delamination of collagen fibrils dissipate a significant amount of energy prior to catastrophic failure, providing high toughness and resistance to penetration by predator teeth. We show that the arapaima's scale has evolved to minimize damage from penetration by predator teeth through a Bouligand-like arrangement of successive layers, each consisting of parallel collagen fibrils with different orientations. This inhibits crack propagation and restricts damage to an area adjoining the penetration. The flexibility of the lamellae is instrumental to the redistribution of the compressive stresses in the underlying tissue, decreasing the severity of the concentrated load produced by the action of a tooth. The experimental results, combined with small-angle Xray scattering characterization and molecular dynamics simulations, provide a complete picture of the mechanisms of deformation, delamination and rotation of the lamellae during tensile extension of the scale.

The micro/macro mechanical properties of the metastable β-Ti-29Nb-14Ta-4.5Zr (TNTZ) alloys reinforced by various nano-sized second phases of α'', α and ω have been studied. The variation in Young modulus, nano-hardness, ultimate strength, and the ductility have been assessed through conducting nano-indentation and uniaxial tensile tests. The lowest Young
modulus has been obtained for the specimen which contains α'' second phase. The highest hardness, Young's modulus, and strength have been also achieved through the precipitation of the ω phase in the β matrix. However, the elongation to fracture of ω containing specimens
decreases down to ~1%. The formation of the α phase has no significant effect on Young's modulus and the ultimate strength of the β matrix. The detailed microstructural studies reveal that the single β phase accommodates the applied strain through the formation of zigzagshaped
{112}<111> deformation nano-twins, martensite/omega phase transformation, and dislocation slip. These are introduced as the main reason for high hardenability and elongation to fracture of this structure. The initial/secondary martensite laths in the β+α'' specimen cannot operate as an effective obstacle against the dislocation movement. This well justifies the lowers hardness, strength and higher ductility of α'' containing specimen. In the case of β+α microstructure, high the population of the moving dislocation is accumulated behind α precipitates, and then cause the shear displacement of the lamella. Due to the appreciable volume fraction of high hardness ω phase in the β matrix, the β+ω specimen shows a complete brittleness and extremely high ultimate strength (~964 MPa).

The capability of one-step and two-step quenching and partitioning processes (Q&P) to treat the microstructure of a low alloyed TRIP-assisted steel was considered. The treated microstructures primarily consisted of lath martensite, retained austenite, lower bainite, and fresh martensite. Two various types of retained austenite in respect of size and morphologies were observed: blocky and film-like retained austenite. Short holding times were appropriate for carbon enrichment of the retained austenite. However, the volume fraction and carbon concentration of retained austenite vs. partitioning time followed an opposite trends in two step processed microstructures. This was attributed to the competitive processes of bainite or epsilon carbide formation at the specified partitioning temperature. The nano indentation experiments were employed to assess the local mechanical properties of individual phases specifically martensite and enriched retained austenite. The frequent pop-in in load-displacement curves indicated the capability of enriched austenite for martensitic transformation. Owning to the higher diffusion rate, the carbon concentration was relatively higher in two-step processed microstructures. In addition, film like or lamellar morphologies (which hold higher population in partitioned structures at 400°C) possessed better transformation stability rather than a blocky type, which tends to transform to martensite under higher amount of strain. The evolution of mechanical properties was discussed relying on the variations of volume fraction, morphology and carbon concentration of retained austenite.