In-situ additive manufacturing of high strength yet ductility titanium composites with gradient layered structure using N_(2)

It has always been challenging work to reconcile the contradiction between the strength and plasticity of titanium materials.Laser powder bed fusion(LPBF) is a convenient method to fabricate innovative composites including those inspired by gradient layered materials.In this work,we used LPBF to selectively prepare Ti N/Ti gradient layered structure(GLSTi)composites by using different N_(2)–Ar ratios during the LPBF process.We systematically investigated the mechanisms of in-situ synthesis Ti N,high strength and ductility of GLSTi composites using microscopic analysis,TEM characterization,and tensile testing with digital image correlation.Besides,a digital correspondence was established between the N_(2) concentration and the volume fraction of LPBF in-situ synthesized Ti N.Our results show that the GLSTi composites exhibit superior mechanical properties compared to pure titanium fabricated by LPBF under pure Ar.Specifically,the tensile strength of GLSTi was more than 1.5times higher than that of LPBF-formed pure titanium,reaching up to 1100 MPa,while maintaining a high elongation at fracture of 17%.GLSTi breaks the bottleneck of high strength but low ductility exhibited by conventional nanoceramic particle-strengthened titanium matrix composites,and the hetero-deformation induced strengthening effect formed by the Ti N/Ti layered structure explained its strength-plasticity balanced principle.The microhardness exhibits a jagged variation of the relatively low hardness of 245 HV0.2 for the pure titanium layer and a high hardness of 408 HV0.2 for the N_(2) in-situ synthesis layer.Our study provides a new concept for the structure-performance digital customization of 3D-printed Ti-based composites.

Microstructure and Mechanical Properties of AlSi10Mg Alloy Manufactured by Laser Powder Bed Fusion Under Nitrogen and Argon Atmosphere

In order to study the effect of gas atmosphere on forming performance of laser powder bed fusion(LPBF),AlSi10 Mg alloy was prepared by direct forming and in situ laser remelting under the shielding gas of argon and nitrogen in this study,and its micro structure and properties were characterized and tested,respectively.The results show that the forming performance of AlSi10 Mg under nitrogen atmosphere is better than that of argon.Moreover,in situ laser remelting method can effectively enhance the relative density and mechanical properties of AlSi10 Mg,in which the densification is increased to 99.5%.In terms of mechanical properties,after in situ remelting,ultimate tensile strength under argon protection increased from444.85±8.73 to 489.45±3.20 MPa,and that under nitrogen protection increased from 459.21±13.77 to 500.14±5.15 MPa.In addition,the elongation is nearly doubled and the micro-Vickers hardness is increased by 20%.The research results provide a new regulation control method for the customization of AlSi10 Mg properties fabricated by LPBF.