Effects of Oxygen Content on Microstructure and Mechanical Properties of TC4 Titanium Alloy Deposited by Laser Directional Energy Deposition

TC4 titanium alloy samples were prepared by laser energy deposition. The correlation of different oxygen content on the microstructure, phase composition, oxygen concentration and properties of titanium alloy was studied with OM, SEM, electron probe quantitative analysis, X-ray diffraction and so on. The results show that the intensity of the diffraction peak increases slightly with the increase of oxygen content. The intensity of the (002) diffraction peak obviously reaches the maximum in the medium oxygen environment, and then weakens. With the increase of oxygen content, the strength and hardness of the material increase 115 MPa and 58 HV respectively, the elongation decreases to 8.71%, and the section shrinkage decreases to 6.6%. The fracture failure mechanism changes from ductile fracture to compound fracture of quasi-cleavage and ductile fracture with the increase of oxygen content. The macrostructure is mainly columnar grain and acicular martensite, and the transformation structure of martensite is α' and β_T after heat treatment. The interstitial solid solution is formed in different oxygen content environment, which leads to the increase of lattice constant, then leads to lattice expansion.With the increase of the interface energy, the high density dislocation phenomenon is formed at the grain boundary, which further strengthens the pinning and increases the strength, but decreases the plasticity of the sample.