Influence of Powder Particle Size on the Compaction Behavior and Mechanical Properties of a High-Alloy Austenitic CrMnNi TRIP Steel During Spark Plasma Sintering

In this study, varying powder particle size fractions (<25, 25 to 45, 45 to 63 µm) of a TRIP steel powder were compacted by spark plasma sintering (SPS). Densification initiated at a slightly lower temperature with decreasing particle size due to increasing green density. With decreasing powder particle size fraction, the as-sintered materials exhibited smaller grain sizes. Compression tests revealed a slight decrease of the compressive yield strength with increasing particle size and, accordingly, larger grain size. A few large deformation bands formed in bigger grains, while many thin deformation bands were formed in smaller grains. α′-Martensite nuclei formed successively inside the deformation bands, reducing the mean free path of (partial) dislocation slip. Due to the size of the deformation bands, α′-martensite formation started at lower strains with increasing particle size. When α′-martensite formation was initiated, work hardening was influenced more by α′-martensite formation than by the grain size of the steel matrix. Hence, work hardening increased with increasing particle size.