Nanocrystalline B2 aluminide (FeAl and NiAl) powders were synthesized using high energy ball mill... more Nanocrystalline B2 aluminide (FeAl and NiAl) powders were synthesized using high energy ball milling and were consolidated using three different sintering methods: conventional pressureless sintering, microwave sintering and spark plasma sintering. The particle-particle contacts after sintering were found to have compositional gradient from interior to surface leading to formation of an Al-O rich phase. This Al-O rich phase formation is primarily attributed to oxygen pick-up during handling of powders and during sintering, leading to formation of amorphous alumina. The formation of amorphous phase is explained by examining the defect concentrations and their interactions. The composite developed with amorphous alumina as a second phase in an ordered B2 matrix can be of great interest for potential structural applications.
The densification kinetics during spark plasma sintering (SPS) of FeAl and NiAl powders were anal... more The densification kinetics during spark plasma sintering (SPS) of FeAl and NiAl powders were analyzed using a model proposed by Bernard-Granger and Guizard [10]. Creep parameters obtained through densification data are in good agreement with those obtained from conventional creep experiments. Validity of the model was illustrated for aluminides in the form of deformation mechanism maps. This validation assures plausible confidence to predict creep behavior using densification data obtained during pressure assisted sintering of metallic alloys.
The grain size dependency of lattice parameter during high-energy ball milling of W has been inve... more The grain size dependency of lattice parameter during high-energy ball milling of W has been investigated. The lattice parameter varies non-monotonically with grain size during milling with a lattice contraction initially followed by an expansion. The lattice parameters were calculated in view of the non-equilibrium grain boundary structure that evolved during milling using excess free volume and the interfacial stresses at the grain boundaries. The calculated lattice parameters closely match the experimentally observed values.
Joule heating as a primary heating source mechanism was probed during spark plasma sintering (SPS... more Joule heating as a primary heating source mechanism was probed during spark plasma sintering (SPS) of pure metal powders (Fe, Ni and Cu). Resistance to electric path was estimated from voltage–current measurements obtained online during these experiments. Resistance was observed to saturate at the same value irrespective of the type of metal powder, after attaining a sintering temperature of ∼0.3Tm. This saturation in resistance is attributed primarily to the Joule heating that occurs at the graphite-foil and punch in an SPS system.
Synthesis and Characterization of Spark Plasma Sintered FeAl and In situ FeAl–Al2O3 Composite, May 23, 2013
In the present work, nanocrystalline FeAl and FeAl–Al2O3 composite were synthesized by high energ... more In the present work, nanocrystalline FeAl and FeAl–Al2O3 composite were synthesized by high energy ball milling and subsequent compaction by spark plasma sintering. Microstructural changes during all stages of processing are studied using X-ray analysis. After 20 h of milling, the disordered FeAl and some amount of Fe rich solid solution was obtained in both of these compositions. Subsequent heat treatment results in formation of ordered FeAl. However, disordering of FeAl was observed in both compositions after spark plasma sintering. Nanocrystallinity is retained in both the compositions even after sintering at high temperature of 1,000 °C. Very high hardness of ~575 HV1 and ~600 HV1 was exhibited by FeAl and FeAl–Al2O3 composite.
Nanocrystalline B2 aluminide (FeAl and NiAl) powders were synthesized using high energy ball mill... more Nanocrystalline B2 aluminide (FeAl and NiAl) powders were synthesized using high energy ball milling and were consolidated using three different sintering methods: conventional pressureless sintering, microwave sintering and spark plasma sintering. The particle-particle contacts after sintering were found to have compositional gradient from interior to surface leading to formation of an Al-O rich phase. This Al-O rich phase formation is primarily attributed to oxygen pick-up during handling of powders and during sintering, leading to formation of amorphous alumina. The formation of amorphous phase is explained by examining the defect concentrations and their interactions. The composite developed with amorphous alumina as a second phase in an ordered B2 matrix can be of great interest for potential structural applications.
The densification kinetics during spark plasma sintering (SPS) of FeAl and NiAl powders were anal... more The densification kinetics during spark plasma sintering (SPS) of FeAl and NiAl powders were analyzed using a model proposed by Bernard-Granger and Guizard [10]. Creep parameters obtained through densification data are in good agreement with those obtained from conventional creep experiments. Validity of the model was illustrated for aluminides in the form of deformation mechanism maps. This validation assures plausible confidence to predict creep behavior using densification data obtained during pressure assisted sintering of metallic alloys.
The grain size dependency of lattice parameter during high-energy ball milling of W has been inve... more The grain size dependency of lattice parameter during high-energy ball milling of W has been investigated. The lattice parameter varies non-monotonically with grain size during milling with a lattice contraction initially followed by an expansion. The lattice parameters were calculated in view of the non-equilibrium grain boundary structure that evolved during milling using excess free volume and the interfacial stresses at the grain boundaries. The calculated lattice parameters closely match the experimentally observed values.
Joule heating as a primary heating source mechanism was probed during spark plasma sintering (SPS... more Joule heating as a primary heating source mechanism was probed during spark plasma sintering (SPS) of pure metal powders (Fe, Ni and Cu). Resistance to electric path was estimated from voltage–current measurements obtained online during these experiments. Resistance was observed to saturate at the same value irrespective of the type of metal powder, after attaining a sintering temperature of ∼0.3Tm. This saturation in resistance is attributed primarily to the Joule heating that occurs at the graphite-foil and punch in an SPS system.
Synthesis and Characterization of Spark Plasma Sintered FeAl and In situ FeAl–Al2O3 Composite, May 23, 2013
In the present work, nanocrystalline FeAl and FeAl–Al2O3 composite were synthesized by high energ... more In the present work, nanocrystalline FeAl and FeAl–Al2O3 composite were synthesized by high energy ball milling and subsequent compaction by spark plasma sintering. Microstructural changes during all stages of processing are studied using X-ray analysis. After 20 h of milling, the disordered FeAl and some amount of Fe rich solid solution was obtained in both of these compositions. Subsequent heat treatment results in formation of ordered FeAl. However, disordering of FeAl was observed in both compositions after spark plasma sintering. Nanocrystallinity is retained in both the compositions even after sintering at high temperature of 1,000 °C. Very high hardness of ~575 HV1 and ~600 HV1 was exhibited by FeAl and FeAl–Al2O3 composite.
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Papers by Niraj Chawake