Effects of cryogenic treatment on microstructures, mechanical properties, and wear resistance of selective laser melted Ti-6Al-4V

The microstructural analysis of Ti-6Al-4V (TC4) fabricated by Selective Laser Melting (SLM) reveals a predominance of needle-like alpha' martensite, which results in lower ductility. Annealing is employed to induce the transformation of the alpha' phase to enhance the plasticity of SLM TC4 but leading to a decrease in tensile strength. The effects of cryogenic treatment on the microstructures, mechanical properties, and wear resistance of SLM TC4 were investigated in this work. The results demonstrate that cryogenic treatment (0-48 h) induces phase transformation of the SLM TC4, where the supersaturated needle-like martensite alpha' phase transforms into short rod-shaped alpha phase and nano-sized (3 phase particles (alpha'-*alpha+(3). The mechanical properties of SLM TC4 initially increase and then decrease as the time of cryogenic treatment is extended. The hardness, ultimate tensile strength, yield strength, and elongation of the cryogenically treated specimens reached their peak after 36 hours of treatment, and increased by 5.4 %, 11.2 %, 17.3 %, and 36.7 % compared with that of the untreated samples, respectively. With the extension of cryogenic treatment time, the wear resistance of SLM TC4 continuously improves. The specimens treated for 48 hours display the lowest wear rate, reducing by 23.4 % compared to that of untreated specimens.