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

Highlights: • Ammonium bicarbonate can be used as excellent space holder for making stainless steel foam • Microarchitecture, microstructures of cell wall and deformation responses are strong functions sintering temperature • The stainless steel foams showed strain hardening during compressive deformation. • The complex carbides formed in the grain boundary of stainless steel foam when sintered at 1200 °C. • Energy absorption is higher when sintered at higher temperature - 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.