Research on the influence of different heat treatment methods on the performance of titanium alloy (TC4) fasteners

• This study innovatively introduces a mid-process oxygen injection mechanism to accurately simulate actual heat treatment conditions. • Adding a baffle during heat treatment promotes the formation of an oxide layer. • Adding an insulation layer during heat treatment reduces the thickness of the oxide layer. • Adding an insulation layer during heat treatment improves the shear performance of the material. The heat treatment of alloys directly determines their final properties. This research designed four differentiated heat treatment methods and systematically analysed the mechanical properties, microstructure and surface colour of the materials. Combined with molecular dynamics, the mechanical properties and oxygen atom implantation mechanism on Ti-6Al-4 V (TC4) fastener performance were explored during heat treatment. Research results show that TC4 alloy would be aggregated, grew and precipitated equiaxed α phase, that would be distribution like chains and show golden surface after adding insulation. It is because the number of decomposed O atoms is decreased that would be led to reduce bonds probability such as Ti-O or O-O, which would effectively hinder the oxidation. It would be enforced the shear performance but the strength, plasticity and fatigue properties are also affected litter. With the baffle is added into system, it can decompose more O atoms and oxide layer would be thick, and surface shown blue-purple or gray-blue. Adding an insulation layer or baffle can make the oxide layer uniformity. Furthermore, this research provides a new simulation method for mid-way injection of oxygen atoms for TC4 or other materials during heat treatment. Experiments and engineering cases have verified the reliability of this method.