Metals, Vol. 15, Pages 1185: Microstructure and Properties of Gas-Nitrided Ti-6Al-4V Alloy

Metals doi: 10.3390/met15111185

Authors:
Qiang Li
Yichun Zhu
Sancai Du
Xuyan Liu
Rongbin Li
Yuqing Miao

To enhance its surface properties, the Ti-6Al-4V alloy was subjected to a nitrogen atmosphere at elevated temperatures. An orthogonal experiment was employed to investigate the effects of nitriding temperature, nitriding duration, and nitrogen flow rate on the surface hardness and the thickness of the nitrided layer. Mechanical properties were assessed using a micro-Vickers hardness tester and a universal material testing machine. Accelerated corrosion tests were performed by immersing the samples in solutions with varying HF concentrations, while wear resistance was evaluated via a circumferential dry sliding wear test. The results indicate that after nitriding, the subsurface region is primarily composed of TiN, Ti2N, and Ti2AlN. Nitriding temperature exerts the greatest influence on the thickness of the nitrided layer, whereas nitrogen flow rate has the least impact. Conversely, nitrogen flow rate shows the strongest effect on surface hardness, with nitriding temperature having the weakest influence. After nitriding, the microstructure becomes coarse with a decrease in substrate hardness. As nitriding temperature and time increase, the thickness of the nitrided layer grows, but both the tensile strength and percentage elongation after fracture decline. The sample nitrided at 850 °C for 2 h under a nitrogen flow rate of 20 mL·min−1 exhibits favorable overall properties. Compared with the as-received sample, its surface hardness increases noticeably, though both the tensile strength and percentage elongation after fracture decrease. In comparison to the continuous weight loss of the as-received sample when immersed in HF solution, the nitrided sample exhibits an initial mass loss of nearly zero, which suggests that the nitrided layer has a protective efficacy. After nitriding, the wear rate is reduced to no more than 3% of that of the as-received sample. Therefore, gas nitriding is considered a feasible technique for improving the surface properties of Ti-6Al-4V in complex environments.

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