Grain growth kinetics and mechanical properties of spark plasma sintered Fe-15Cr-2W powders

Abstract

In recent years, spark plasma sintering (SPS) technique has emerged as an alternative full density consolidation process as rapid sintering / densification is achieved with restricted grain growth as well as better purification and activation of particle surfaces. In the present investigation, consolidation of mechanically alloyed powder of nominal composition Fe-15Cr-2W at two pressures (50 MPa and 60 MPa) and three sintering temperatures (950 °C, 1025 °C, and 1100 °C) was studied. The consolidated samples were characterized and tested for density, grain size / distribution, hardness, and compressive strength. Consolidated samples were further annealed at 1100 °C for different holding periods (0, 60, and 120 mins) and at different temperatures of 950, 1100, and 1250 °C at a fixed holding period (60 min) to study the grain growth kinetics. The different stages in the displacement profiles during SPS were discussed in depth in view of the densification of the alloys. Pressure was found to be dominant factor in terms of densification at lower sintering temperature (i.e. 950 °C) while at higher temperature (≥1000 °C), temperature activated diffusion was found to be dominant. The grain growth exponent (n) and activation energy (Q) determined for the alloy sintered at 1025 °C and 50 MPa via classical grain growth kinetic equation were 7.34 and 214.9 kJ/mol respectively. The deviation of grain growth exponent from its ideal value (2) has been discussed in light of various attributes of mechanical alloying.