Investigating the microstructure and mechanical properties of 316L/TiB2 composites fabricated by laser cladding additive manufacturing

Abstract

In this paper, the 316L stainless steel matrix composite strengthened by TiB2 was successfully fabricated using laser cladding additive manufacturing technology. The microstructures of 316L/TiB2 with the addition of TiB2 (mass fractions of 0, 3 and 6, respectively) were characterised. Hardness tests and tensile tests were conducted to evaluate the physical and mechanical properties of the samples. The results indicated that all prepared samples exhibit a complex cellular microstructure composed of sub-grains. The matrix phase was verified as γ austenite with a honeycomb-like reinforcement phases forming along the boundaries. Further analysis revealed the net-like reinforcements were (Fe,Cr)2B and M3B2 (M is Cr, Fe, Mo, Ni, Ti) phases. The Microhardness of the samples with 0 wt%,3 wt% and 6 wt% of TiB2 were 148 HV, 170 HV and 186 HV, respectively. The addition of 3 wt% and 6 wt% TiB2 composites increased the yield strength by 22 % and 29 %, respectively, compared to 316L composite. Also, the tensile strength and modulus of elasticity of the reinforcement composites were improved by 8 % and 13 %, respectively. However, the elongation of the reinforcement composites was reduced by 36 % and 47 %, respectively. The reinforcement with high strength and modulus is formed in 316L/TiB2 composite, which leads to a reduction in grain size while enhancing the density of large-angle grain boundaries. Multiple strengthening effects dominated by Orowan strengthening were simultaneously experienced during the preparation process, which improved the mechanical properties of the composites.

Keywords

• Additive manufacturing
• 316L stainless steel
• TiB2
• Metal matrix composites
• Microstructure