Densification kinetics of P/M austenitic (316L) stainless steels processed by rapid microwave hybrid heating method at various conditions

Microwave sintering of powder metals is recognised for better process advantages, namely, less process time, rapid densification, uniform volumetric and selective heating characteristics. There are certain theoretical analyses to explain the mass transport mechanisms during microwave sintering. The current study reports on an investigation of densification kinetics in austenitic (316 L) stainless steel powder compacts processed by microwave hybrid heating method at solidus and super-solidus temperatures. The analysis of densification kinetics and sintering mechanisms were studied using the grain growth exponential and time-temperature plots. The results revealed that the major densification is achieved through bulk diffusion (viscous mass flow) at a higher temperature (1250 degrees C-1300 degrees C) under the super-solidus region while grain boundary retardation is the mechanism for the reduced grain growth at a lower sintering temperature (1100 degrees C-1200 degrees C) under solidus region. The apparent activation energies are calculated using the Arrhenius plot and classical grain growth analysis simultaneously. The activation energies of 42 +/- 3 kJ/mol and 24 +/- 2 kJ/mol are observed for the samples sintered at a lower temperature. The higher activation energies of 219 +/- 8 kJ/mol and 254 +/- 7 kJ/mol are obtained for the samples sintered at 1250 degrees C-1300 degrees C for both analyses.