Effect of milling time on structure and mechanical properties of porous nickel-free austenitic stainless steels processed by mechanical alloying and sintering

In this paper, the microstructure and mechanical properties of biocompatible Cr–Mn–N austenitic stainless steels produced by powder metallurgy are investigated. Processing is conducted by mechanical alloying of 74Fe–18Cr–8Mn (wt.%) powder mixture under a nitrogen atmosphere, followed by sintering at 1100 °C for 20 h. The prepared materials are characterized by X-ray diffraction, scanning and transmission electron microscopy, suggesting the development of nanostructures with micron-sized spherical pores. It is also found that by increasing the milling time from 48 to 120 h, the densification is retarded; however, the hardness and compressive yield strength of the nanomaterials are enhanced. Moreover, the yield strength of matrix is estimated by valid empirical and plasticity-based relations.