Experimental study of the Fe–Ni–Ti system

Intermetallics, 2006

While the main features of the Fe-Ni-Ti system are well known at low Ti content, literature review of the Ti-rich corner revealed inconsistencies between experimental reports. This investigation presents new experimental results, defined to remove the uncertainties concerning melting behavior and solid-state phase equilibria of the (Ni,Fe)Ti 2 phase with the adjacent (Fe,Ni)Ti (B2, CsCl-type structure) and β-Ti (A2, W-type) phases. Six samples have been prepared and examined by differential thermal analysis performed in yttria and alumina crucibles, and by scanning electron microscopy in the as-cast state as well as equilibrated at 900 °C.

Journal of Phase Equilibria and Diffusion

Fe-Ni-Te alloys have been experimentally studied using isothermal heat treatments with SEM-EDS and WDS, XRD, and DTA in order to add phase diagram data for a thermodynamic assessment. This is for the application of fission product-induced corrosion of the stainless steel cladding of nuclear fuel pins, where Te is a key element. Phase diagram data are presented at 700 and 800 C, together with the solidus and liquidus temperatures from 44 to 80 at.% Te. Metallographic and XRD analysis show that the b2 phase forms as a Widmanstätten structure, preferentially precipitated in the s phase. SEM images show unidentified precipitates in several samples. Keywords isothermal equilibration Á microstructure Á phase diagram Á phase transformation Á thermal analysis Á ternary phase diagram

Journal of Solid State Chemistry, 2000

The experimental evaluation of phase equilibria in the Ti+Ni+Al+N and Ti+Ni+Al+O phase diagrams are based on alloy samples, which were prepared of elemental powder blends by argon-levitation melting in a Hukin crucible. The experimental investigation employed X-ray powder di4raction, metallography, SEM, and EMPA techniques in the as-cast state as well as after annealing at 9003C. Two quaternary compounds Ti 3 NiAl 2 N and Ti 3 NiAl 2 O deriving from the 5lled Ti 2 Ni type (phase) were observed. The novel phases are in equilibrium with the Ti 2 Ni-type solid solution phase (Ti 1؊x Al x) 2 Ni, which exhibits a maximum solubility of 14 at.% Al in binary Ti 2 Ni. Atom order in all these phases was monitored by quantitative X-ray powder di4raction (Rietveld analyses). The di4erence of X-ray spectra among the various phases deriving from parent Ti 2 Ni type was analyzed and the complex atom site occupation mode was discussed in terms of the general classi5cation scheme for phases.

Journal of Phase Equilibria and Diffusion, 2008

The homogeneity ranges of the Laves phases and phase relations concerning the Laves phases in the quaternary system Ti-Fe-Ni-Al at 900°C were defined by x-ray powder diffraction (XPD) data and electron probe microanalysis (EPMA). Although at higher temperatures the Laves phase forms a continuous solid solution, two separate homogeneity fields of TiFe 2-based (denoted by k Fe) and Ti(TiNiAl) 2-based (denoted by k Ni) Laves phases appear at 900°C. The relative locations of Laves phases, G phase, Heusler phase, and CsCl-type phase as well as the associated tie-tetrahedra were experimentally established in the quaternary for 900°C and presented in three-dimensional (3D) view. Furthermore, a partial isothermal section TiFe 2-TiAl 2-TiNi 2 was constructed, and a connectivity scheme, derived for equilibria involving Laves phases in the Ti-Fe-Ni-Al quaternary system at 900°C was derived. As a characteristic feature of the quaternary phase diagram, the solid solubility of fourth elements in both the TiFe 2-based and Ti(NiAl) 2-based Laves phases is limited at 900°C and is dependent on the ternary Laves phase composition. A maximum solubility of about 8 at.% Ni is reached for composition Ti 33.3 Fe 33.3 Al 33.4. Structural details have been evaluated from powder x-ray and neutron diffraction data for (i) the Ti-Fe-Ni ternary and the Ti-Fe-Ni-Al quaternary Laves phases (MgZn 2-type, space group: P6 3 /mmc) and (ii) the quaternary G phase. Atom site occupation behavior for all phases from the quaternary system corresponds to that of the ternary systems. For the quaternary Laves phase, Ti occupies the 4f site and additional Ti (for compositions higher than 33.3 at.%Ti) preferably enters the 6h site. Aluminum and (Fe,Ni) share the 6h and the 2a sites. The compositional dependence of unit cell dimensions, atomic coordinates, and interatomic distances for the Laves phases from the quaternary system is discussed. For the quaternary cubic G phase, a centrosymmetric as well as a noncentrosymmetric variety was observed depending on the composition: from combined x-ray and neutron powder diffraction measurements Ti 33.33 Fe 13.33 Ni 10.67 Al 42.67 was found to adopt the lower symmetry with space groupF " 43m.

Journal of Alloys and Compounds, 2014

Several issues are related to casting large ingots of Ni-Ti alloys, as well as to their post-processes (hot and cold working, machining). On the other hand, the effects and benefits of the rapid solidification on these materials are known. Very high solidification rates, such as 10 6 -10 7 K/s, obtained by melt spinning and planar flow casting, were mainly explored up to now, but these processes have severe limitations. The aim of this research is to analyze the effects of the cooling rate in the lower regime of the rapid solidification (10 2 -10 3 K/s), which is much more suitable for industrial processes. For this purpose, cone shaped samples of a near equiatomic Ni 51 Ti 49 alloy were obtained by rapid solidification in a water cooled copper mold. The conical shape of the samples allows the comparison among different cooling rates. The thermal and metallographic analyzes showed that a cooling rate within the explored range is effective to tailor the microstructure and the characteristic temperatures of the alloy. The thermal analysis revealed that the phase transformation temperatures are inclined to be lower as the cooling rate increases. On the other hand, a refinement of the microstructure, as well as a reduction in the amount of the precipitates can be obtained. Oxygen is present inside the Ni-Ti-O phase and these crystals are smaller if the cooling rate increases.

Acta Materialia, 2005

In the context of the development of high-strength Fe 3 Al-based alloys, phase equilibria among a-Fe(Al, Cr, Ti), liquid and TiC phases in the Fe-Al-Cr-TiC quinary system and the formation of TiC were determined. A pseudo-eutectic trough (L () a + L + TiC) exists at 1470°C at around Fe-26Al-5Cr-2Ti-1.7C on the vertical section between Fe-26Al-5Cr (a) and Ti-46C (TiC) in at.%. Large faceted TiC precipitates form from the melt after the formation of primary a phase even in hypoeutectic alloys. The TiC formation is thought to be due to the composition change of the liquid towards the hypereutectic compositions by solidification of the primary a. In order to remove the faceted TiC, which are unfavourable for strengthening the material, two different processing routes have been successfully tested: (i) solidification with an increased rate to reduce the composition variation of the liquid during solidification, and (ii) unidirectional solidification to separate the light TiC precipitates from the melt.

Journal of Electronic Materials, 2015

The calculated liquidus projection of the Ag-Bi-Ni ternary system has been experimentally examined. Alloys were prepared by induction melting, and their microstructure studied by scanning electron microscopy coupled with energy dispersive x-ray spectroscopy. Of the primary solidification phases, (Ni) solidifies over the largest concentration range, although it was found to be narrower than calculated. The range in which Bi 3 Ni is the primary solidification phase was found to be broader than calculated. Also, the liquid miscibility gap is broader than predicted from assessed thermodynamic parameters. Differential thermal analysis was used to study temperatures of phase transitions of as-cast alloys, and recorded temperatures of melting of Bi 3 Ni and BiNi phases in ternary alloys agree well with those calculated.

Metallurgical Transactions A, 1985

Esomat 2009 - 8th European Symposium on Martensitic Transformations, 2009

The high temperature transformations (e.g. liquidus, ordering temperature) of the alloys were studied for the practical melting and annealing purposes. At first the chemical compositions (SEM-EDS) and the martensitic and magnetic transition temperatures (DSC, ac magnetic susceptibility) of the alloys were determined. High temperature DSC measurements were made in argon with 10 K/min. Two first measurements were carried out in the solid state (301 -1273 K) and in the third measurement the material was melted (max meas. temp. 1573 K). The ordering temperature was obtained from the measurements in the solid state. As the e/a ratio was above 7.53 the ordering temperature was in the range of 1019-1039 K, otherwise a clear change was observed. The variation in heating and cooling was less than 5 K with small quaternary additions, but alloying of 8% Fe increased this difference to 18 K. Alloys with close Ni/Mn/Ga-ratio showed only minor differences in solidus and liquidus temperatures, but if there was a clear change in the Ni/Mn-ratio even those alloys having close e/a ratios showed a clear difference in melting behavior. When Ni/Mn is 1.5-with higher values not clear region could be determined.