Dynamic mechanical properties and machinability characteristics of selective laser melted and forged Ti6Al4V

Titanium alloys are widely used in aerospace, medical devices and other fields, but titanium alloy parts with complex structures are difficult to be produced through traditional process route. Additive manufacturing (AM) technology provides the new process route. But for AM parts, machining is usually required to obtain high precision and surface quality. The microstructure and material properties of selective laser melted (SLM) and forged Ti6Al4V are obviously different, which will greatly affect the machinability. Acicular martensite increases the strength and hardness of SLM Ti6Al4V, and reduces plasticity. The dynamic mechanical properties were obtained by Split Hopkinson Pressure Bar (SHPB) tests. The flow stress of SLM Ti6Al4V decreases greatly at high temperature and high strain rate, but the effect of strain rate on the dynamic mechanical properties of forged Ti6Al4V is not significant. Milling experiments with CVD diamond coated tools were carried out under dry and minimum lubrication (MQL) conditions. When the cutting speed reaches 80m/min, the cutting force of SLM Ti6Al4V is significantly reduced, the cutting stability and surface quality are improved. After milling, the residual compressive stress of SLM Ti6Al4V is anisotropic, and the value is greater than that of forged Ti6Al4V. Under MQL condition, the cutting force decreases slightly, the milling is more stable, and the depth of residual compressive stress increases.