In-situ additive manufacturing of high strength yet ductility titanium composites with gradient layered structure using N₂

Abstract

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 TiN/Ti gradient layered structure (GLSTi) composites by using different N2-Ar ratios during the LPBF process. We systematically investigated the mechanisms of in-situ synthesis TiN, 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 N2 concentration and the volume fraction of LPBF in-situ synthesized TiN. 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 1.5 times 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 TiN/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 N2 in-situ synthesis layer. Our study provides a new concept for the structure-performance digital customization of 3D-printed Ti-based composites.

An overview of additively manufactured metal matrix composites: preparation, performance, and challenge

“…Recently, a novel method for fabricating TMCs using reactive atmosphere during the LPBF process was developed [70, [294][295][296]. For the conventional LPBF process, the reinforcements are prepared in the feedstock in advance, regardless of whether they are pre-alloyed powder or mixed powder.…”

“…For the conventional LPBF process, the reinforcements are prepared in the feedstock in advance, regardless of whether they are pre-alloyed powder or mixed powder. Xiao et al [295,296] produced TiN/Ti and TiN/Ti6Al4V composites with spatial heterostructures by LPBF under a nitrogen-containing atmosphere. The produced composites show increased mechanical strength without a significant decrease in ductility.…”

Editorial for the Special Issue on Laser Additive Manufacturing: Design, Materials, Processes, and Applications, 2nd Edition

“…Building on the work in the first edition [ 11 ] and sincere cooperation with the Guest Editors [ 12 ], the second edition will continue to concentrate on laser additive manufacturing, including macro- to micro-scale additive manufacturing with lasers, including structure design/material design [ 13 ], fabrication [ 14 ], modeling and simulation; in situ characterization of additive manufacturing processes [ 15 ]; and ex situ material characterization and performances [ 16 ], with an overview of various applications [ 17 ] in aerospace, biomedicine, optics, transportation, energy, etc.…”