On the spark plasma sintering of Mo-and-Cu containing low-density stainless steel: influence of sintering parameters on microstructure, densification and hardness considerations

This work investigates the microstructural and mechanical behaviour of Fe–Mn–Al–Cr–C-based low-density stainless steels produced via mechanical alloying and spark plasma sintering (SPS). Fe-Mn-Al-Cr-C based low-density stainless-steel alloys with Mo and Cu were produced using commercially available elemental powders. Spark plasma sintering was used to obtain four alloys with different compositions, Fe-30.9Mn-4.9Al-4.5Cr-0.4 C, Fe-21.3Mn-7.6Al-4.3Cr-1 C, Fe-30.9Mn-4.9Al-4.5Cr-0.4 C-3Mo-3Cu and Fe-21.3Mn-7.6Al-4.3Cr-1 C-3Mo-3Cu. The alloys were sintered at different optimised parameters, temperature (900–1100 °C) and pressure (40 and 50 MPa). Hardness studies were conducted using the strain gradient plasticity approach in accordance with Nix and Gao Model. SEM-BSE and XRD were used to characterise the alloy powder and sintered alloys. The density of the alloys was calculated to be between 91 and 98% with porosity range between 2.38 and 5.77%. The alloys had similar sintering behaviour under the same sintering parameters. Microhardness studies showed density and porosity affects the hardness of the alloy. Hardness increases with increasing density. Microstructural analysis revealed a dual-phase structure primarily composed of γ-austenite (FCC) and α-ferrite (BCC), with Cr-rich and Mo-rich precipitates. Alloy 2 A, Fe-21.3Mn-7.6Al-4.3Cr-1 C, demonstrated the best mechanical performance, with low porosity, high density, enhanced dislocation resistance and the most uniform microstructure. A positive correlation exists between hardness and dislocation density. Hardness measurements interpreted using the Nix–Gao model, showed the impact of the indentation size effect, with true hardness (H₀) being lower than measured hardness.