Ti-6Al-4V合金表面渗层制备及空蚀性能研究

目的利用化学热处理对钛合金表面进行扩渗处理,制备硬质表面渗层,以提高钛合金抗空蚀能力。方法采用氮气气氛下渗铝工艺对Ti-6Al-4V合金退火试样进行表面处理,获得硬质表面渗层。利用X射线衍射仪、扫描电子显微镜、能谱分析仪和显微硬度计表征分析表面渗层的物相组成、微观结构、元素分布及力学性能。利用超声波振动空蚀试验机,按照ASTM G32标准,测试表面渗层在去离子水中的空蚀性能,并结合空蚀后表面形貌和元素分布,研究分析其空蚀机理。结果扩渗处理在Ti-6Al-4V合金表面生成了具有较高显微硬度的表面渗层,其由最外面的化合物层和内部的扩散层构成。在1023 K温度下处理1 h的试样,其表面渗层均匀、致密、无微裂纹,在去离子水中空蚀12 h的累积质量损失最小,为未处理试样的18%,抗空蚀性能最好。随着处理时间的延长和处理温度的升高,渗层表面变得不平整,且表面凸出的硬质陶瓷颗粒物增多。硬质陶瓷颗粒物虽显著增加试样的显微硬度,但易诱发空泡生成,使抗空蚀性能变差。结论氮气下渗铝处理在Ti-6Al-4V合金表面获得的表面渗层可以改善合金的抗空蚀性能,而表面凸出的大小不均的硬质陶瓷颗粒物使表面渗层的抗空蚀性能减弱。

Preparation and Cavitation Erosion of Surface Diffusion Coating on Ti-6Al-4V Alloy

The work aims to prepare a surface diffusion coating on Ti-6Al-4V alloy by means of diffusion treatment on the titanium alloy surface through chemical heat treatment, and improve cavitation erosion resistance of the alloy. The surface of annealed Ti-6Al-4V alloy sample was treated by aluminizing in nitrogen atmosphere to obtain a hard surface infiltration layer. Phase constituents, microstructure, element distribution and mechanical properties of the diffusion coating were characterized by X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy and Vickers microhardness tests. Subsequently, cavitation erosion tests were performed by an ultrasound vibration testing apparatus in accordance with ASTM G32 standard to explore the cavitation erosion resistance of the diffusion coating in combination with the surface morphology and element distribution after cavitation erosion. The results indicated that the diffusion treatment produced surface infiltration layer with higher microhardness on the surface of Ti-6Al-4V alloy. The coating consisted of the outermost compound layer and the inner diffusion layer. After 1 h of treatment at 1023 K, its surface infiltration layer was dense, uniform and microcrack-free. After 12 h of cavitation, the specimen treated at 1023 K for 1 h had the least cumulative volume loss was 18% of that of the untreated sample, so it had the best cavitation resistance. With the increase of treatment time and temperature, the surface of the diffusion coating with the hard ceramic particles became uneven and there were more and more hard ceramic particles protruding from the surface. The hard ceramic particles could significantly increase the surface microhardness of the treated specimen, but it was likely to induce the formation of cavitation and reduction of cavitation resistance. In summary, aluminizing treatment in nitrogen atmosphere can considerably improve the cavitation erosion behavior of Ti-6Al-4V alloy. The hard ceramic particles with uneven size protruding from the surface weaken the cavitation erosion resistance of the surface infiltration layer.