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.