High-Temperature Oxidation Behavior of Al-Modified Boronized Coating Prepared on Ti-6Al-4V by Thermal Diffusion
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High-Temperature Oxidation Behavior of Al-Modified Boronized Coating Prepared on Ti-6Al-4V by Thermal Diffusion Yangguang Liu, Xiaojing Xu, Yishui Xiao, Tianqing Niu, Vitus Tabie, Chong Li, and Chen Li (Submitted June 13, 2020; in revised form September 6, 2020; Accepted: 8 September 2020) The Al-modified boronized coating on Ti-6Al-4V was successfully fabricated to protect the alloy from oxidation by the neutral salt bath method. The thickness of the Al-modified boronized coating (69.8 ± 2 lm) is 36% thicker than that of the simple-boronized coating (51.3 ± 1.5 lm). To evaluate the oxidation resistance, the high-temperature oxidation behavior was analyzed by the high-temperature oxidation experiment at 700 and 900 °C. The results show that after oxidation, the Al-modified boronized coating was mainly comprised of TiO2, Al2O3, Al3Ti, Ti3B4 and TiS phases, and the surface of the Almodified boronized coating is smoother and denser. The thickness of the oxide layer of the Al-modified boronized coating is the minimum, which is 11 ± 0.3 lm and 13 ± 0.5 lm at 700 and 900 °C for 60 h, respectively. The average oxidation rate of the Al-modified boronized coating is 2 0.003 and 0.022 mg cm22 h21 due to the formation of Al2O3 on the surface. Therefore, adding Al into the simpleboronized coating is beneficial for the high-temperature oxidation resistance. Keywords
Ti-6Al-4V, high-temperature oxidation, microstructure, the Al-modified boronized coating, thermal diffusion
1. Introduction Due to specific strength and YoungÕs modulus and other good properties, Ti materials have been widely used in aerospace, military and industrial fields (Ref 1). Among them, Ti-6A1-4V with excellent properties, such as lightweight (Ref 2), high specific strength (Ref 3), high tensile strength (Ref 4) and fatigue resistance (Ref 5), has attracted more attention because of a + b dual phase, but its oxidation resistance declines sharply over 600 °C, which limits its application (Ref 6-10). The addition of trace elements (Ref. 11) and surface modification are two main ways to broaden the application of Ti-6Al-4V in extreme environments, such as elevated temperature. Adding element may worsen the mechanical properties of the alloy, but surface modification is a powerful tool, which can promote surface properties without damaging bulk materials (Ref 12). At present, there are many surface modification methods, including CVD (Ref 13) (chemical vapor deposition), PVD (Ref 14) (physical vapor deposition), LC (Ref 15) (laser cladding) and TRD (Ref 16) (thermal reactive diffusion). CVD, PVD and LC techniques require costly and complex equipment operating in vacuum or inert gas situation (Ref 17, 18). However, TRD has been widely used in coating preparation Yangguang Liu, Xiaojing Xu, Yishui Xiao, Tianqing Niu, Vitus Tabie, Chong Li, and Chen Li, Institute for Advanced Manufacturing and Modern Equipment Technology, Jiangsu University, Zhenjiang 212013 Jiangsu, PeopleÕs Republic of China. Contact e-mail: [email protected].
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