Influence of addition of TiAl particles on microstructural and mechanical property development in a selectively laser melted stainless steel

Abstract

316L stainless steel is well known for its excellent corrosion resistance and ductility. However, its relatively low strengths restrict its application in many load-bearing fields. In this study, Ti–48Al–2Cr–2Nb powder particles were mixed with 316L powder particles and then processed by selective laser melting (SLM) with the aim of developing intermetallic nano-particles reinforced 316L. It was found that the addition of 2 wt.% TiAl particles led to formation of numerous nano-sized cuboidal γ-TiAl precipitates in the austenite matrix and ferrite in the bottom regions of solidified melt pools. The majority of ferrite shows no particular orientation relationships with austenite that are characteristic of austenite → ferrite (γ-Fe → α-Fe) solid phase transformation, indicating that they should have formed during solidification. The α-Fe domains and surrounding γ-Fe regions were found to have experienced significant dynamic recrystallization during thermal cycling, resulting in fine α-Fe and γ-Fe equiaxed grains and massive twins in the γ-Fe. The addition of TiAl has moderately improved 0.2% yield strength and significantly increased ultimate tensile strength, thanks to the refined grain structure and massive γ-TiAl nano-particles which have acted as effective dislocation motion barriers. Some un-melted TiAl particles acted as preferential crack initiation and propagation sites during deformation, leading to reduction in ductility.