The effect of solid state heat treatment at 913 K on extruded XD Al/TiC metal matrix composite wi... more The effect of solid state heat treatment at 913 K on extruded XD Al/TiC metal matrix composite with 0.7 and 4.0 /nm particle sizes has been investigated. The interfaces between Al and TiC after extrusion were atomically abrupt, as observed by HRTEM. On holding at 913 K, the composite with submicron particle size showed substantial changes in the phases present due to reaction between Al and TiC at 913 K. The stable reaction products are Al 3 Ti and A1 4 C 3 . A substantial increase in Young's modulus occurs. The room and elevated temperature strength and hardness of the composite with submicron particles also increase significantly with time of heat treatment, but at the expense of ductility. The effect of heat treatment over the time range investigated is limited to the interfaces for the 4.0 /xm TiC particle size composite due to longer diffusion paths.
The in-situ Al-4.5Cu-5TiB 2 composite plates were processed by stir casting through mixed salt ro... more The in-situ Al-4.5Cu-5TiB 2 composite plates were processed by stir casting through mixed salt route process involving K 2 TiF 6 and KBF 4 salts. Mushy state rolling has been carried out at temperatures above the solidus of the alloy matrix, corresponding to the presence of 10, 20 and 30 volume percent liquid to obtain 2.5, 5, 7.5 and 10 percent reduction in thickness. Alligatoring has been noticed during mushy state rolling of the as cast composites, except when the liquid content is 30 volume percent and thickness reduction is 2.5 and 5 percent. Prior hot rolling leading to chemical homogenization accompanied by modification of dendritic microstructure into that with equiaxed grains has led to the prevention of alligatoring during mushy-state rolling of the composite for reduction in thickness of less than 10%. Study of microstructural evolution and its effect on hardness as well as minimization of rolling defects in the products has been carried out. The wear properties of as-cast and mushy state rolled composites were also investigated, and correlated with microstructure.
The transient stage during isothermal oxidation of Mo 76 Si 14 B 10 has been studied at 1150°C. T... more The transient stage during isothermal oxidation of Mo 76 Si 14 B 10 has been studied at 1150°C. The maximum mass loss is found to occur by volatilization of MoO 3 within the first 480 s of exposure, which is considered to be the transient period. Scanning electron microscopic studies have revealed that a glassy borosilicate layer flows to cover the top surface, and thereby it acts as a protective coating. The thickness of the borosilicate layer increases with exposure time following a parabolic relationship. The mechanism of oxidation during transient period has been discussed with the help of an analytical model.
Mechanically alloyed Al 65 Cu 20 Ti 15 amorphous alloy powder with 10 wt.% nano-TiO 2 dispersion ... more Mechanically alloyed Al 65 Cu 20 Ti 15 amorphous alloy powder with 10 wt.% nano-TiO 2 dispersion was consolidated by high pressure sintering (HPS) at room temperature and/or 300-450 o C for about 1 min using a uniaxial pressure of 8GPa. The sintered material was examined by XRD and TEM. Excellent hardness and strength were obtained in selected sintered samples of 8.34 GPa and 1600 MPa respectively, although ductility was very low (< 1%).
Nickel based superalloy Post-solutionizing cooling rate Low cycle fatigue Precipitates Bilinear C... more Nickel based superalloy Post-solutionizing cooling rate Low cycle fatigue Precipitates Bilinear Coffin-Manson relationship Cyclic stress-strain behavior a b s t r a c t
Oxidation behavior of hot pressed (HP) and arc melted (AMI) Mo76Si14B10 alloy has been studied at... more Oxidation behavior of hot pressed (HP) and arc melted (AMI) Mo76Si14B10 alloy has been studied at 1150 °C in different partial pressures of oxygen to explore the mechanism of protection against degradation. Microstructure of both the differently prepared alloy consists of Moss, Mo3Si and Mo5SiB2 phases with varying morphologies. The size of Moss phase is 3 times bigger in AMI alloy compared to that in the HP alloy. Cyclic oxidation of the HP alloy shows 1.5 and 4 times lower mass loss compared to that of the AMI alloy during exposure in air ( = 0.21 atm.) and oxygen ( = 1 atm.), respectively due to microstructural refinement in the latter alloy. The top surfaces of the oxide scales that forms over both the differently prepared alloys after six cycles of oxidation in air are found to be smooth and shows the viscous flow of borosilicate glass, whereas, round pores have been observed in case of both HP and AMI alloys oxidized in oxygen. A dark grey uppermost borosilicate layer followed...
Oxidation behavior of hot pressed (HP) and arc melted (AMI) Mo76Si14B10 alloy has been studied at... more Oxidation behavior of hot pressed (HP) and arc melted (AMI) Mo76Si14B10 alloy has been studied at 1150 °C in different partial pressures of oxygen to explore the mechanism of protection against degradation. Microstructure of both the differently prepared alloy consists of Moss, Mo3Si and Mo5SiB2 phases with varying morphologies. The size of Moss phase is 3 times bigger in AMI alloy compared to that in the HP alloy. Cyclic oxidation of the HP alloy shows 1.5 and 4 times lower mass loss compared to that of the AMI alloy during exposure in air ( = 0.21 atm.) and oxygen ( = 1 atm.), respectively due to microstructural refinement in the latter alloy. The top surfaces of the oxide scales that forms over both the differently prepared alloys after six cycles of oxidation in air are found to be smooth and shows the viscous flow of borosilicate glass, whereas, round pores have been observed in case of both HP and AMI alloys oxidized in oxygen. A dark grey uppermost borosilicate layer followed...
Transactions of the Indian Institute of Metals, 2009
In situ Al-4.5Cu-5TiB2 composite has been processed through stir casting method, in which, the Ti... more In situ Al-4.5Cu-5TiB2 composite has been processed through stir casting method, in which, the TiB2 particles have been precipitated in situ by mixed salt route involving reactions between K2TiF6 and KBF4.The as-cast specimens containing 20 volume percent liquid content have been subjected to three mushy state roll passes, each leading to 5 percent reduction in thickness. The grain structure has
ABSTRACT The metal-ceramic interface in an XDTM Al/TiCp metal matrix composite has been character... more ABSTRACT The metal-ceramic interface in an XDTM Al/TiCp metal matrix composite has been characterized in as-extruded, recrystallized, and high temperature heat-treated conditions. In both the as-extruded and recrystallized composite, the interface is atomically abrupt. Localized orientation relationships exist between Al and Tic that lead to some degree of coherency at the interface. Recrystallization produces semicoherent interfaces by formation of subgrains in the Al adjacent to the Tie particles. Few interfaces show cracking, even after extensive deformation. Lack of cracking together with the direct contact down to atomic level, observed between the two phases are evidence for excellent bonding between the carbide particles and the aluminum matrix. Heat treating samples at 913 k for 24 hours produces reaction products like Al3Ti and Al4C3. These reactions are explained on the basis of thermodynamic data.
In-situ Al-4.5Cu-5TiB 2 composite plates were stir cast with TiB 2 particles formed through mixed... more In-situ Al-4.5Cu-5TiB 2 composite plates were stir cast with TiB 2 particles formed through mixed salt route. The as-cast samples with 30 volume percent liquid content were rolled in mushy state down to 2.5 and 5 percent reduction in thickness per pass. The rolled products found to be defect-free after the first pass were subjected to multiple roll passes in mushy state with identical experimental conditions, adding up to seven. The wear properties of as-cast and mushy state rolled composites were also investigated, and correlated with microstructure.
A comparative study has been carried out on dry sliding wear behavior of in situ Al-4.5Cu-5TiB 2 ... more A comparative study has been carried out on dry sliding wear behavior of in situ Al-4.5Cu-5TiB 2 composite subjected to single or multiple mushy state roll passes, each to 5% thickness reduction at 626 • C (temperature for 20% liquid). The results of wear tests using a pin-on-disc machine under normal loads of 20 or 40 N have been analyzed to determine wear rate, friction and wear coefficients. It has been found that wear resistance of rolling surface is superior to that of long-transverse surface, and improves on subjecting composites to higher number of roll passes, which cause enhancement of hardness through grain refinement and particle redistribution. Studies of surfaces and cross-sections of worn specimens as well as wear debris have shown evidence of Fe-enrichment, plastic deformation and work hardening. Surface roughness and friction coefficients depend on wear mechanisms, which appear to be influenced by applied load and specimen hardness.
Modified 9Cr-1Mo steel Finish rolling temperature Upper shelf energy Ductile-to-brittle transitio... more Modified 9Cr-1Mo steel Finish rolling temperature Upper shelf energy Ductile-to-brittle transition temperature (DBTT). a b s t r a c t A modified 9Cr-1Mo steel received in normalized and tempered condition has been subjected to four different hot-rolling treatments at different rolling temperatures (1050 1C, 1000 1C, 950 1C and 875 1C) applying a constant true strain of $ 0.7. The rolled plates were tempered and tested for tensile and Charpy impact properties following standard procedures. Hot-rolling increased the strength by more than 100 MPa, but reduced the ductility of the steel by more than 10%. The ductile-to-brittle transition temperature (DBTT) was found to increase by more than 25 1C after hot-rolling as compared to As-received steel. Among the rolled samples, the plates rolled at 950 1C and 1050 1C showed higher upper shelf energy (comparable to Asreceived steel), whilst the plate rolled at 1050 1C showed the lowest DBTT. In terms of superior strengthtoughness combination rolling at 1050 1C can be considered to be optimum. The results have been analyzed considering the effect of rolling on parameters related to the microstructure and crystallographic texture of the steel, such as, effective grain size, ferrite fraction, fraction of low-angle boundaries, fraction of cleavage planes on the main fracture plane and the fraction of slip planes along the 451 to the main fracture plane.
A modified 9Cr-1Mo steel has been exposed to three separate normalization treatments i.e. at 950 ... more A modified 9Cr-1Mo steel has been exposed to three separate normalization treatments i.e. at 950 1C, 1025 1C and 1100 1C from As-received (normalized at 1050 1C and tempered at 750 1C) condition. After subsequent tempering treatment the impact toughness in terms of upper shelf energy (USE) and ductileto-brittle transition temperature (DBTT) has been evaluated using Charpy impact testing (with 10 mm  10 mm  55 mm specimens) following ASTM E23 procedures. A substantial improvement in USE ( $ 20 J) and reduction in DBTT ( $ 20 1C) has been noticed for the 1025 1C treatment. The result has been analysed in terms of change in yield strength and ductility evaluated with tensile tests. Further, effects of microstructure, precipitate and texture on the change of DBTT have been studied with TEM and EBSD analyses. The results have been attributed to the smaller 'effective grain size', higher fraction of high-angle boundaries, presence of beneficial γ-fibre texture and dissolution of the pre-existing coarse precipitates in the reheated sample as compared to As-received material.
The 9Cr-1Mo steel used in fast breeder reactor is exposed to irradiation during service which sev... more The 9Cr-1Mo steel used in fast breeder reactor is exposed to irradiation during service which severely affects the dynamic fracture resistance by increasing the ductile to brittle transition temperature (DBTT). Thus, even at room temperature, the steel can become brittle and prone to cracking. The microstructural features especially prior austenite grain size (PAGS), martensitic lath and packet size originating from prior processing routes has an effect on the toughness properties of 9Cr-1Mo steel, which is yet to be understood fully. In the present investigation, three different austenitizing temperatures (950°C, 1025°C and 1100°C for 1 h) have been selected to vary the PAGS. Impact energy, lateral expansion, dynamic yield stress as the function of temperature has been estimated from Charpy impact tests carried out on normalized and tempered specimens. The results show lower DBTT for the samples reheated at 1025°C followed by tempering.
A comparative study on the microstructure-mechanical property relationships in the molybdenum and... more A comparative study on the microstructure-mechanical property relationships in the molybdenum and niobium silicide based composites has been carried out with emphasis on the role of the ductile and brittle phase constituents at ambient and elevated temperatures. The MoSi 2 , MoSi 2 -20 vol.% SiC and -Mo-Mo 3 Si-Mo 5 SiB 2 composites have been prepared by powder metallurgy processing. Furthermore, the niobium silicide based composites, having a eutectic of Nb solid solution (Nb ss ) and (Nb,Mo) 5 Si 3 , and either Nbss or (Nb,Mo) 5 Si 3 as the primary phase in the hypoeutectic or hypereutectic compositions, respectively, have been processed by arc melting. The increase in fracture toughness with respect to that of MoSi 2 is modest in the MoSi 2 -SiC composites, and more significant in the multiphase Mo-Mo 3 Si-Mo 5 SiB 2 and Nb ss -(Nb,Mo) 5 Si 3 based in-situ composites with ductile reinforcements. The ductile phase, either Mo or Nb ss aids in toughening chiefly through crack arrest and bridging, and undergoes plastic yielding under constraint during deformation, leading to a higher energy of fracture. In the MoSi 2 and MoSi 2 -SiC composites, the matrix grain size has a significant role in high temperature strength retention and strain hardening behaviour. In the ductile phase reinforced composites, the hard silicide-based intermetallic phases contribute to elevated temperature strength, while the constrained plastic deformation of the -Mo or Nb ss is responsible for much higher rate of strain hardening than in the MoSi 2 and MoSi 2 -SiC composites.
A detailed study was conducted of the microstructure and particle-matrix interfaces in Al/TiCp me... more A detailed study was conducted of the microstructure and particle-matrix interfaces in Al/TiCp metal matrix composites prepared by the XD process and subsequent extrusion. A study of the morphology of the TiC particles showed that the surfaces are low index and planes, the former being more common. Direct contact on an atomic scale is established between Al and TiC, allowing chemical bonds to form. Young's modulus is in the range expected for a composite of Al and TiC with good interfacial bonding and load transfer to the particles. No third element has been detected at the interfaces, showing that they are clean. Both incoherent and semicoherent interfaces are seen. The interface character depends on the size of the particles and their orientation with respect to the neighboring Al grains. "Special" interfaces with evidence for nearly periodic dislocations were observed in both XD Al/TiC and Al/TiB 2 composites, indicating the general tendency of in situ composites to lower their interfacial energy by forming such boundaries.
The oxidation behaviour of a molybdenum disilicide (MoSi2) composite, reinforced with 20 vol.-% s... more The oxidation behaviour of a molybdenum disilicide (MoSi2) composite, reinforced with 20 vol.-% silicon carbide (SiC), at 500 a C has been investigated and the results have been compared to those of hot pressed monolithic MoSi2 and other MoSi2 based composites. The MoSi2-SiC composite was processed by reaction hot pressing an Mo, Si, and SiC powder mixture at 1500 a C, and the composite had around 98% of the theoretical density. The presence of SiC particles does not affect the oxidation behaviour, except the interfaces oxidised at higher rates. The oxidation rate is slow enough in dense composites to prevent pest disintegration. The oxidation products are either an after which MoOJ whiskers and Si02 phases become predominant. The oxide layer thickness was found to be 10·0 J.lm,at the most, after 250 h exposure at 500 a C.
The effect of solid state heat treatment at 913 K on extruded XD Al/TiC metal matrix composite wi... more The effect of solid state heat treatment at 913 K on extruded XD Al/TiC metal matrix composite with 0.7 and 4.0 /nm particle sizes has been investigated. The interfaces between Al and TiC after extrusion were atomically abrupt, as observed by HRTEM. On holding at 913 K, the composite with submicron particle size showed substantial changes in the phases present due to reaction between Al and TiC at 913 K. The stable reaction products are Al 3 Ti and A1 4 C 3 . A substantial increase in Young's modulus occurs. The room and elevated temperature strength and hardness of the composite with submicron particles also increase significantly with time of heat treatment, but at the expense of ductility. The effect of heat treatment over the time range investigated is limited to the interfaces for the 4.0 /xm TiC particle size composite due to longer diffusion paths.
The in-situ Al-4.5Cu-5TiB 2 composite plates were processed by stir casting through mixed salt ro... more The in-situ Al-4.5Cu-5TiB 2 composite plates were processed by stir casting through mixed salt route process involving K 2 TiF 6 and KBF 4 salts. Mushy state rolling has been carried out at temperatures above the solidus of the alloy matrix, corresponding to the presence of 10, 20 and 30 volume percent liquid to obtain 2.5, 5, 7.5 and 10 percent reduction in thickness. Alligatoring has been noticed during mushy state rolling of the as cast composites, except when the liquid content is 30 volume percent and thickness reduction is 2.5 and 5 percent. Prior hot rolling leading to chemical homogenization accompanied by modification of dendritic microstructure into that with equiaxed grains has led to the prevention of alligatoring during mushy-state rolling of the composite for reduction in thickness of less than 10%. Study of microstructural evolution and its effect on hardness as well as minimization of rolling defects in the products has been carried out. The wear properties of as-cast and mushy state rolled composites were also investigated, and correlated with microstructure.
The transient stage during isothermal oxidation of Mo 76 Si 14 B 10 has been studied at 1150°C. T... more The transient stage during isothermal oxidation of Mo 76 Si 14 B 10 has been studied at 1150°C. The maximum mass loss is found to occur by volatilization of MoO 3 within the first 480 s of exposure, which is considered to be the transient period. Scanning electron microscopic studies have revealed that a glassy borosilicate layer flows to cover the top surface, and thereby it acts as a protective coating. The thickness of the borosilicate layer increases with exposure time following a parabolic relationship. The mechanism of oxidation during transient period has been discussed with the help of an analytical model.
Mechanically alloyed Al 65 Cu 20 Ti 15 amorphous alloy powder with 10 wt.% nano-TiO 2 dispersion ... more Mechanically alloyed Al 65 Cu 20 Ti 15 amorphous alloy powder with 10 wt.% nano-TiO 2 dispersion was consolidated by high pressure sintering (HPS) at room temperature and/or 300-450 o C for about 1 min using a uniaxial pressure of 8GPa. The sintered material was examined by XRD and TEM. Excellent hardness and strength were obtained in selected sintered samples of 8.34 GPa and 1600 MPa respectively, although ductility was very low (< 1%).
Nickel based superalloy Post-solutionizing cooling rate Low cycle fatigue Precipitates Bilinear C... more Nickel based superalloy Post-solutionizing cooling rate Low cycle fatigue Precipitates Bilinear Coffin-Manson relationship Cyclic stress-strain behavior a b s t r a c t
Oxidation behavior of hot pressed (HP) and arc melted (AMI) Mo76Si14B10 alloy has been studied at... more Oxidation behavior of hot pressed (HP) and arc melted (AMI) Mo76Si14B10 alloy has been studied at 1150 °C in different partial pressures of oxygen to explore the mechanism of protection against degradation. Microstructure of both the differently prepared alloy consists of Moss, Mo3Si and Mo5SiB2 phases with varying morphologies. The size of Moss phase is 3 times bigger in AMI alloy compared to that in the HP alloy. Cyclic oxidation of the HP alloy shows 1.5 and 4 times lower mass loss compared to that of the AMI alloy during exposure in air ( = 0.21 atm.) and oxygen ( = 1 atm.), respectively due to microstructural refinement in the latter alloy. The top surfaces of the oxide scales that forms over both the differently prepared alloys after six cycles of oxidation in air are found to be smooth and shows the viscous flow of borosilicate glass, whereas, round pores have been observed in case of both HP and AMI alloys oxidized in oxygen. A dark grey uppermost borosilicate layer followed...
Oxidation behavior of hot pressed (HP) and arc melted (AMI) Mo76Si14B10 alloy has been studied at... more Oxidation behavior of hot pressed (HP) and arc melted (AMI) Mo76Si14B10 alloy has been studied at 1150 °C in different partial pressures of oxygen to explore the mechanism of protection against degradation. Microstructure of both the differently prepared alloy consists of Moss, Mo3Si and Mo5SiB2 phases with varying morphologies. The size of Moss phase is 3 times bigger in AMI alloy compared to that in the HP alloy. Cyclic oxidation of the HP alloy shows 1.5 and 4 times lower mass loss compared to that of the AMI alloy during exposure in air ( = 0.21 atm.) and oxygen ( = 1 atm.), respectively due to microstructural refinement in the latter alloy. The top surfaces of the oxide scales that forms over both the differently prepared alloys after six cycles of oxidation in air are found to be smooth and shows the viscous flow of borosilicate glass, whereas, round pores have been observed in case of both HP and AMI alloys oxidized in oxygen. A dark grey uppermost borosilicate layer followed...
Transactions of the Indian Institute of Metals, 2009
In situ Al-4.5Cu-5TiB2 composite has been processed through stir casting method, in which, the Ti... more In situ Al-4.5Cu-5TiB2 composite has been processed through stir casting method, in which, the TiB2 particles have been precipitated in situ by mixed salt route involving reactions between K2TiF6 and KBF4.The as-cast specimens containing 20 volume percent liquid content have been subjected to three mushy state roll passes, each leading to 5 percent reduction in thickness. The grain structure has
ABSTRACT The metal-ceramic interface in an XDTM Al/TiCp metal matrix composite has been character... more ABSTRACT The metal-ceramic interface in an XDTM Al/TiCp metal matrix composite has been characterized in as-extruded, recrystallized, and high temperature heat-treated conditions. In both the as-extruded and recrystallized composite, the interface is atomically abrupt. Localized orientation relationships exist between Al and Tic that lead to some degree of coherency at the interface. Recrystallization produces semicoherent interfaces by formation of subgrains in the Al adjacent to the Tie particles. Few interfaces show cracking, even after extensive deformation. Lack of cracking together with the direct contact down to atomic level, observed between the two phases are evidence for excellent bonding between the carbide particles and the aluminum matrix. Heat treating samples at 913 k for 24 hours produces reaction products like Al3Ti and Al4C3. These reactions are explained on the basis of thermodynamic data.
In-situ Al-4.5Cu-5TiB 2 composite plates were stir cast with TiB 2 particles formed through mixed... more In-situ Al-4.5Cu-5TiB 2 composite plates were stir cast with TiB 2 particles formed through mixed salt route. The as-cast samples with 30 volume percent liquid content were rolled in mushy state down to 2.5 and 5 percent reduction in thickness per pass. The rolled products found to be defect-free after the first pass were subjected to multiple roll passes in mushy state with identical experimental conditions, adding up to seven. The wear properties of as-cast and mushy state rolled composites were also investigated, and correlated with microstructure.
A comparative study has been carried out on dry sliding wear behavior of in situ Al-4.5Cu-5TiB 2 ... more A comparative study has been carried out on dry sliding wear behavior of in situ Al-4.5Cu-5TiB 2 composite subjected to single or multiple mushy state roll passes, each to 5% thickness reduction at 626 • C (temperature for 20% liquid). The results of wear tests using a pin-on-disc machine under normal loads of 20 or 40 N have been analyzed to determine wear rate, friction and wear coefficients. It has been found that wear resistance of rolling surface is superior to that of long-transverse surface, and improves on subjecting composites to higher number of roll passes, which cause enhancement of hardness through grain refinement and particle redistribution. Studies of surfaces and cross-sections of worn specimens as well as wear debris have shown evidence of Fe-enrichment, plastic deformation and work hardening. Surface roughness and friction coefficients depend on wear mechanisms, which appear to be influenced by applied load and specimen hardness.
Modified 9Cr-1Mo steel Finish rolling temperature Upper shelf energy Ductile-to-brittle transitio... more Modified 9Cr-1Mo steel Finish rolling temperature Upper shelf energy Ductile-to-brittle transition temperature (DBTT). a b s t r a c t A modified 9Cr-1Mo steel received in normalized and tempered condition has been subjected to four different hot-rolling treatments at different rolling temperatures (1050 1C, 1000 1C, 950 1C and 875 1C) applying a constant true strain of $ 0.7. The rolled plates were tempered and tested for tensile and Charpy impact properties following standard procedures. Hot-rolling increased the strength by more than 100 MPa, but reduced the ductility of the steel by more than 10%. The ductile-to-brittle transition temperature (DBTT) was found to increase by more than 25 1C after hot-rolling as compared to As-received steel. Among the rolled samples, the plates rolled at 950 1C and 1050 1C showed higher upper shelf energy (comparable to Asreceived steel), whilst the plate rolled at 1050 1C showed the lowest DBTT. In terms of superior strengthtoughness combination rolling at 1050 1C can be considered to be optimum. The results have been analyzed considering the effect of rolling on parameters related to the microstructure and crystallographic texture of the steel, such as, effective grain size, ferrite fraction, fraction of low-angle boundaries, fraction of cleavage planes on the main fracture plane and the fraction of slip planes along the 451 to the main fracture plane.
A modified 9Cr-1Mo steel has been exposed to three separate normalization treatments i.e. at 950 ... more A modified 9Cr-1Mo steel has been exposed to three separate normalization treatments i.e. at 950 1C, 1025 1C and 1100 1C from As-received (normalized at 1050 1C and tempered at 750 1C) condition. After subsequent tempering treatment the impact toughness in terms of upper shelf energy (USE) and ductileto-brittle transition temperature (DBTT) has been evaluated using Charpy impact testing (with 10 mm  10 mm  55 mm specimens) following ASTM E23 procedures. A substantial improvement in USE ( $ 20 J) and reduction in DBTT ( $ 20 1C) has been noticed for the 1025 1C treatment. The result has been analysed in terms of change in yield strength and ductility evaluated with tensile tests. Further, effects of microstructure, precipitate and texture on the change of DBTT have been studied with TEM and EBSD analyses. The results have been attributed to the smaller 'effective grain size', higher fraction of high-angle boundaries, presence of beneficial γ-fibre texture and dissolution of the pre-existing coarse precipitates in the reheated sample as compared to As-received material.
The 9Cr-1Mo steel used in fast breeder reactor is exposed to irradiation during service which sev... more The 9Cr-1Mo steel used in fast breeder reactor is exposed to irradiation during service which severely affects the dynamic fracture resistance by increasing the ductile to brittle transition temperature (DBTT). Thus, even at room temperature, the steel can become brittle and prone to cracking. The microstructural features especially prior austenite grain size (PAGS), martensitic lath and packet size originating from prior processing routes has an effect on the toughness properties of 9Cr-1Mo steel, which is yet to be understood fully. In the present investigation, three different austenitizing temperatures (950°C, 1025°C and 1100°C for 1 h) have been selected to vary the PAGS. Impact energy, lateral expansion, dynamic yield stress as the function of temperature has been estimated from Charpy impact tests carried out on normalized and tempered specimens. The results show lower DBTT for the samples reheated at 1025°C followed by tempering.
A comparative study on the microstructure-mechanical property relationships in the molybdenum and... more A comparative study on the microstructure-mechanical property relationships in the molybdenum and niobium silicide based composites has been carried out with emphasis on the role of the ductile and brittle phase constituents at ambient and elevated temperatures. The MoSi 2 , MoSi 2 -20 vol.% SiC and -Mo-Mo 3 Si-Mo 5 SiB 2 composites have been prepared by powder metallurgy processing. Furthermore, the niobium silicide based composites, having a eutectic of Nb solid solution (Nb ss ) and (Nb,Mo) 5 Si 3 , and either Nbss or (Nb,Mo) 5 Si 3 as the primary phase in the hypoeutectic or hypereutectic compositions, respectively, have been processed by arc melting. The increase in fracture toughness with respect to that of MoSi 2 is modest in the MoSi 2 -SiC composites, and more significant in the multiphase Mo-Mo 3 Si-Mo 5 SiB 2 and Nb ss -(Nb,Mo) 5 Si 3 based in-situ composites with ductile reinforcements. The ductile phase, either Mo or Nb ss aids in toughening chiefly through crack arrest and bridging, and undergoes plastic yielding under constraint during deformation, leading to a higher energy of fracture. In the MoSi 2 and MoSi 2 -SiC composites, the matrix grain size has a significant role in high temperature strength retention and strain hardening behaviour. In the ductile phase reinforced composites, the hard silicide-based intermetallic phases contribute to elevated temperature strength, while the constrained plastic deformation of the -Mo or Nb ss is responsible for much higher rate of strain hardening than in the MoSi 2 and MoSi 2 -SiC composites.
A detailed study was conducted of the microstructure and particle-matrix interfaces in Al/TiCp me... more A detailed study was conducted of the microstructure and particle-matrix interfaces in Al/TiCp metal matrix composites prepared by the XD process and subsequent extrusion. A study of the morphology of the TiC particles showed that the surfaces are low index and planes, the former being more common. Direct contact on an atomic scale is established between Al and TiC, allowing chemical bonds to form. Young's modulus is in the range expected for a composite of Al and TiC with good interfacial bonding and load transfer to the particles. No third element has been detected at the interfaces, showing that they are clean. Both incoherent and semicoherent interfaces are seen. The interface character depends on the size of the particles and their orientation with respect to the neighboring Al grains. "Special" interfaces with evidence for nearly periodic dislocations were observed in both XD Al/TiC and Al/TiB 2 composites, indicating the general tendency of in situ composites to lower their interfacial energy by forming such boundaries.
The oxidation behaviour of a molybdenum disilicide (MoSi2) composite, reinforced with 20 vol.-% s... more The oxidation behaviour of a molybdenum disilicide (MoSi2) composite, reinforced with 20 vol.-% silicon carbide (SiC), at 500 a C has been investigated and the results have been compared to those of hot pressed monolithic MoSi2 and other MoSi2 based composites. The MoSi2-SiC composite was processed by reaction hot pressing an Mo, Si, and SiC powder mixture at 1500 a C, and the composite had around 98% of the theoretical density. The presence of SiC particles does not affect the oxidation behaviour, except the interfaces oxidised at higher rates. The oxidation rate is slow enough in dense composites to prevent pest disintegration. The oxidation products are either an after which MoOJ whiskers and Si02 phases become predominant. The oxide layer thickness was found to be 10·0 J.lm,at the most, after 250 h exposure at 500 a C.
Uploads
Papers by Rahul Mitra