Tisov Oleksandr, Yurchuk Alina, Pashechko Mykhaylo, Pohreliuk Iryna, Chocyk Dariusz, Kindrachuk Myroslav
School of Aerospace Engineering, Xi'an Jiaotong University, West Xianning Road 28, Xi'an 710049, China.
Department of Air Transport Organization, Faculty of Transport, Management and Logistics, National Aviation University, Lubomyra Huzara Ave. 1, 03058 Kyiv, Ukraine.
Materials (Basel). 2023 May 23;16(11):3900. doi: 10.3390/ma16113900.
This paper studies the microstructure, phase composition and tribological response of BT22 bimodal titanium alloy samples, which were selectively laser-processed before nitriding. Laser power was selected to obtain a maximum temperature just a little above the α↔β transus point. This allows for the formation of a nano-fine cell-type microstructure. The average grain size of the nitrided layer obtained in this study was 300-400 nm, and 30-100 nm for some smaller cells. The width of the "microchannels" between some of them was 2-5 nm. This microstructure was detected on both the intact surface and the wear track. XRD tests proved the prevailing formation of TiN. The thickness of the nitride layer was 15-20 μm between the laser spots, and 50 μm below them, with a maximum surface hardness of 1190 HV. Microstructure analyses revealed nitrogen diffusion along the grain boundaries. Tribological studies were performed using a PoD tribometer in dry sliding conditions, with a counterpart fabricated from untreated titanium alloy BT22. The comparative wear test indicates the superiority of the laser+nitrided alloy over the one that was only nitrided: the weight loss was 28% lower, with a 16% decrease in the coefficient of friction. The predominant wear mechanism of the nitrided sample was determined to be micro-abrasive wear accompanied by delamination, while that of the laser+nitrided sample was micro-abrasive wear. The cellular microstructure of the nitrided layer obtained after the combined laser-thermochemical processing helps to withstand substrate deformations and provide better wear-resistance.
本文研究了在氮化之前进行选择性激光加工的BT22双峰钛合金样品的微观结构、相组成和摩擦学响应。选择激光功率以获得刚好略高于α↔β转变温度的最高温度。这有利于形成纳米细晶胞型微观结构。本研究中获得的氮化层的平均晶粒尺寸为300 - 400 nm，一些较小的晶胞为30 - 100 nm。其中一些之间的“微通道”宽度为2 - 5 nm。在完整表面和磨损轨迹上均检测到这种微观结构。XRD测试证明了TiN的主要形成。激光光斑之间的氮化物层厚度为15 - 20μm，其下方为50μm，表面硬度最高为1190 HV。微观结构分析揭示了氮沿晶界的扩散。摩擦学研究是在干滑动条件下使用PoD摩擦计进行的，配对材料由未处理的钛合金BT22制成。对比磨损试验表明，激光 + 氮化合金优于仅氮化的合金：重量损失降低了28%，摩擦系数降低了16%。氮化样品的主要磨损机制确定为伴有分层的微磨料磨损，而激光 + 氮化样品的主要磨损机制为微磨料磨损。激光 - 热化学联合处理后获得的氮化层的胞状微观结构有助于承受基体变形并提供更好的耐磨性。
