Effect of Ti Addition on the Density–Hardness Trade-Off and Microstructure of Ball-Milled 316L Stainless Steel

This study investigates the influence of titanium (Ti) addition on the densification, hardness, and microstructural evolution of 316L austenitic stainless steel produced by powder metallurgy. Five compositions were examined: pure 316L and 316L with 3, 6, 9, and 12 wt.% Ti. The powder mixtures were prepared by planetary ball milling for 2 h, followed by uniaxial cold compaction at 1400 MPa and sintering at 1200 °C for 60 min in an argon atmosphere. The results reveal a clear density–hardness trade-off as Ti content increases. The relative density decreased from 95.32% for pure 316L to 83.88% for the 12 wt.% Ti composite, indicating that Ti addition reduced densification efficiency during sintering. This reduction is mainly associated with increased porosity, possible oxide-related diffusion barriers, and the formation of heterogeneous Ti-rich regions. In contrast, the hardness showed a non-monotonic response. The addition of 3 wt.% Ti reduced the hardness to 108 HV, mainly due to the dominant effect of porosity. However, further Ti additions increased the hardness substantially, reaching 232 HV at 12 wt.% Ti. This improvement is attributed mainly to the formation of hard Ti-containing intermetallic regions and possible solid-solution effects. Overall, tailoring Ti content provides a promising route for modifying the microstructure and hardness of powder-processed 316L stainless steel, while maintaining the advantages of a conventional press-and-sinter processing route method.