Stainless steel foams made through powder metallurgy route using NH4HCO3 as space holder

Abstract

Stainless steel (316) foams of varying porosities have been made through powder metallurgy route using NH4HCO3 as a space holder. Green compacts of stainless steel powder with NH4HCO3 were sintered at two different temperatures: 1100°C and 1200°C. At higher sintering temperatures, neighboring stainless steel powders fused together to form polycrystalline grain structure with iron–chromium intermetallic phases segregated along the grain boundaries. Whereas, the fusion of neighboring stainless steel powders was limited around the particle–particle contact only when the green compacts were sintered at 1100°C, which resulted in a larger amount of microporosities in the cell wall. These foams exhibited strain hardening behavior in the plateau region under compressive loading. The yield stress and the flow stress (at lower strain levels) of foams, sintered at 1100°C were higher. But, the reverse is true for the flow stress at higher strain levels. The exponents and the coefficients of the power law relationships varied with sintering temperature and strain levels.