基于微观结构的热喷涂WC/Co涂层裂纹生长模拟
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摘要
涂层微观结构特征直接影响涂层的寿命,基于涂层微观结构研究涂层裂纹扩展特征成为评价热喷涂层性能的重要问题.本文基于WC/Co涂层微观结构建立了有限元模型,并采用XFEM方法研究了单应力状态预存裂纹行了模拟,获得了涂层微观裂纹扩展的损伤规律.研究表明:在拉应力作用下,沿着WC-Co边界产生的应力集中是涂层裂纹产生的根源;WC/Co涂层浅表面(0.125b,b为涂层厚度)的水平裂纹对垂直拉应力敏感、吸收能量快,0.78b处的裂纹扩展后对应力响应迅速,因此0.125b与0.78b是WC/Co涂层裂纹生长的关键深度;在0.78b处,当初始裂纹角度0°～45°时,扩展位移逐渐减小,扩展偏转角增大,45°时存在能量积累导致角度快速偏转.在周期应力作用时,WC/Co涂层的疲劳周期随应变幅值增加而减小;应变幅值相同时,WC/Co涂层的疲劳周期随频率增加而增加.
Since the microstructure characteristics of a coating have direct effects on the life of the coating, it is important to study the crack growth characteristics based on the microstructure of coatings for evaluating the properties of the thermal sprayed coatings. In this paper, a finite element model is established based on the microstructure of WC/Co coatings. The crack propagation in single stress state was simulated by XFEM method and the damage rules of the microscopic crack growth were obtained. Results show that the stress concentration along the WC-Co boundary under tensile stress was the root of cracks in the coatings. The horizontal cracks on the surface of WC/Co coatings(0.125b, b is the thickness of coatings) were sensitive to vertical tensile stress and they absorbed energy faster. The crack growth at 0.78b had a rapid response to stress, so 0.125b and 0.78b were critical depths of crack damage in WC/Co coatings. At 0.78b, when the initial crack angle was 0°～45°, the expansion displacement gradually decreased and the expansion deflection angle increased. When the initial crack angle was 45°, the energy accumulation caused the angle deflecting rapidly. Under cyclic stress, the fatigue cycle of WC/Co coatings decreased with the increase of strain amplitude. At the same strain amplitude, the fatigue cycle of WC/Co coatings increased with increasing strain.
Since the microstructure characteristics of a coating have direct effects on the life of the coating, it is important to study the crack growth characteristics based on the microstructure of coatings for evaluating the properties of the thermal sprayed coatings. In this paper, a finite element model is established based on the microstructure of WC/Co coatings. The crack propagation in single stress state was simulated by XFEM method and the damage rules of the microscopic crack growth were obtained. Results show that the stress concentration along the WC-Co boundary under tensile stress was the root of cracks in the coatings. The horizontal cracks on the surface of WC/Co coatings(0.125b, b is the thickness of coatings) were sensitive to vertical tensile stress and they absorbed energy faster. The crack growth at 0.78b had a rapid response to stress, so 0.125b and 0.78b were critical depths of crack damage in WC/Co coatings. At 0.78b, when the initial crack angle was 0°～45°, the expansion displacement gradually decreased and the expansion deflection angle increased. When the initial crack angle was 45°, the energy accumulation caused the angle deflecting rapidly. Under cyclic stress, the fatigue cycle of WC/Co coatings decreased with the increase of strain amplitude. At the same strain amplitude, the fatigue cycle of WC/Co coatings increased with increasing strain.
引文
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[3] 冯剑军,薛雷,刘芬,等.TiN涂层中表面裂纹产生的机理研究[J].机械科学与技术,2016,35(5):1125-1131.FENG Jianjun,XUE Lei,LIU Fen,et al.Study on mechanism of surface cracks in TiN coating[J].Mechanical Science and Technology for Aerospace Engineering,2016,35(5):1125-1131.DOI:10.13433/j.cnki.1003-8728.2016.0723
[4] 徐滨士,王海斗,朴钟宇,等.再制造的热喷涂合金涂层的结构完整性与服役寿命预测研究[J].金属学报,2011,47(11):1355-1361.XU Binshi,WANG Haidou,PIAO Zhongyu,et al.Investigation of structural integrity and life time prediction of the thermal sprayed alloy coating for remanufacturing [J].Acta Metallurgica Sinica,2011,47(11):1355-1361.
[5] 王文昌,盛天原,孔德军,等.等离子喷涂 WC-12Co 涂层表面-界面性能[J].材料热处理学报,2015,36(12):190-196.WANG Wenchang,SHENG Tianyuan,KONG Dejun,et al.Surface and interface properties of WC-12Co coating by plasma spraying[J].Transactions of Materials and Heat Treatment,2015,36(12):190-196.DOI:10.13289/j.issn.1009-6264.2015.12.033
[6] 查柏林,高双林,袁晓静,等.厚度对HVOF喷涂WC-12Co涂层结构的影响[J].稀有金属材料与工程,2017,46(2):509-514.ZHA Bailin,GAO Shuanglin,YUAN Xiaojing,et al.Effect of thickness on microstructure of HVOF sprayed WC-12Co coatings [J].Rare Metal Materials and Engineering,2017,46(2):509-514.
[7] TOBI A L M,SHIPWAY P H,LEEN S B.Finite element modelling of brittle fracture of thick coatings under normal and tangential loading[J].Tribology International,2013,58(2):29-39.
[8] OLIVEIRA S A G,BOWER A F.An analysis of fracture and delamination in thin coatings subjected to contact loading[J].Wear,1996,198(1/2):15-32.
[9] VABEN R,GIESEN S,ST?VERD.Lifetime of plasma-sprayed thermal barrier coatings:comparison of numerical and experimental results[J].Journal of Thermal Spray Technology,2009,18(5/6):835-845.
[10] 王东,赵军,李安海.WC-Co 硬质合金微观结构随机分布模型与弹性性能预报[J].材料热处理学报,2013,34(3):160-165.WANG Dong,ZHAO Jun,LI Anhai.Random distribution model of microstructure and elastic properties prediction of WC-Co cemented carbides[J].Transactions of Materials and Heat Treatment,2013,34(3):160-165.
[11] GUPTA M,SKOGSBERG K,NYLéN P.Influence of topcoat-bondcoat interface roughness on stresses and lifetime in thermal barrier coatings[J].Journal of Thermal Spray Technology,2014,23(1/2):170-181.
[12] TILLMANN W,KLUSEMANN B,NEBEL J,et al.Analysis of the mechanical properties of an arc-sprayed WC-FeCSiMn coating:nanoindentation and simulation[J].Journal of Thermal Spray Technology,2011,20(1/2):328-335.
[13] BELYTSCHKO T,BLACK T.Elastic crack growth in finite elements with minimal remeshing[J].International Journal for Numerical Methods in Engineering,1999,45(5):601-620.
[14] DIMITRI R,FANTUZZIN,LI Yong,et al.Numerical computation of the crack development and SIF in composite materials with XFEM and SFEM[J].Composite Structures,2017,160(3):468-490.
[15] WEN Longfei,TIAN Rong.Improved XFEM:accurate and robust dynamic crack growth simulation [J].Computer Methods in Applied Mechanics and Engineering,2016,308(15):256-285.