激光冲击对TC11钛合金力学性能与热腐蚀性能影响研究

发布时间：2018-11-11 20:37

【摘要】：钛合金是当前高性能制造产业中使用最多的耐高温合金结构材料。钛合金常被用来制作航空发动机上的叶片、压气机盘、涡轮盘等关键零部件,在发动机的实际使用环境中,叶片等关键部件容易发生疲劳裂纹、疲劳断裂以及表面腐蚀,因此改善钛合金的结构性能和抗腐能力具有重要意义。作为一种表面改性的高新技术,激光冲击能够成功地优化金属的综合力学特性,增强其耐腐蚀性。本文以TC11钛合金为研究目标,通过激光冲击、热腐蚀、性能测试等实验,证实了激光冲击(LSP)增强TC11钛合金力学性能以及耐热腐蚀能力的可行性,分析总结了强化机理和耐腐蚀增强的机理。论文的研究内容及结论如下:(1)分析了激光冲击波从保护层、约束层再到金属表面的能量转化和冲击作用过程,通过理论分析和推导,优化了强化处理TC11钛合金的实验参数。(2)探究了不同冲击次数作用下,TC11钛合金的表面残余应力、截面残余应力、表面粗糙度、三维形貌及显微硬度等力学性能的变化。阐述了冲击强化改善合金综合力学性能的原理。研究结果表明:经过强化处理后,残余压应力的最大测量值出现在材料最上层,强化的次数越多,影响层越深;强化的次数达到某一数值后,激光冲击对显微硬度的影响削弱;强化次数增加,合金表面的凹痕加深,导致粗糙度值变大。(3)研究了激光冲击后TC11钛合金内部位错运动及晶粒细化的过程。结果表明:激光冲击后表面发生塑性变形,分布不均匀的位错会不断繁殖,由于位错之间的相互作用就会形成位错缠结、位错胞、位错墙等位错结构。位错运动继续发展,会继续演化为亚晶界,新的组织结构会切割原始的晶粒组织,使晶粒逐渐被细化,直到内部能量稳定后,晶粒细化完成。(4)讨论了腐蚀温度和持续时间对热腐蚀性能的影响,并证实了冲击处理增强TC11钛合金的耐热腐蚀性的有效性。实验结果表明:激光冲击后,TC11钛合金热腐蚀过程的孕育期增长,合金的失重加速度减小;热腐蚀过程中会形成氧化层和腐蚀层。激光冲击后,表面氧化层更加紧密完整,腐蚀表面的裂纹、凹坑和剥落得到了抑制;随着持续时间或腐蚀温度的增加,不仅表面腐蚀加剧,而且出现严重的表面裂纹、凹坑和脱落。(5)研究了TC11钛合金的热腐蚀形貌变化及激光冲击增强其耐腐蚀性的机理。研究结果表明:热腐蚀现象是氧化膜从产生到出现裂纹、凹坑,最终脱落的一个过程。激光冲击后,产生的残余压应力可以减少裂纹的产生,增加氧化物与基体表面的粘附力,减少应力腐蚀,防止腐蚀加剧;合金内部的位错运动使内部的晶粒组织不断被分割细化,生成大量的细晶组织。位错运动产生的内部缺陷和晶粒细化提高了合金的力学性能及表面结构稳定性,使腐蚀过程中生成的氧化物均匀紧密,可塑性增强,从而提高抗腐蚀性能。
[Abstract]:Titanium alloy is the most widely used high-temperature alloy structural material in high-performance manufacturing industry. Titanium alloy is often used to make the key parts such as blade, compressor disk, turbine disk and so on the aero-engine. In the actual service environment of the engine, the key parts such as blade are prone to fatigue crack, fatigue fracture and surface corrosion. Therefore, it is of great significance to improve the structural properties and corrosion resistance of titanium alloys. As a new technology of surface modification, laser impact can successfully optimize the comprehensive mechanical properties of metals and enhance their corrosion resistance. In this paper, TC11 titanium alloy is taken as the research object, and the feasibility of enhancing the mechanical properties and thermal corrosion resistance of TC11 titanium alloy by laser shock (LSP) is proved by the experiments of laser shock, hot corrosion and property test, etc. The strengthening mechanism and the mechanism of corrosion resistance enhancement are analyzed and summarized. The research contents and conclusions are as follows: (1) the energy conversion and impact process of laser shock wave from protective layer, confinement layer to metal surface are analyzed. The experimental parameters of strengthening TC11 titanium alloy were optimized. (2) the changes of surface residual stress, cross-section residual stress, surface roughness, 3D morphology and microhardness of TC11 titanium alloy under different impact times were investigated. The principle of improving the comprehensive mechanical properties of the alloy by impact strengthening is described. The results show that the maximum measurement value of residual compressive stress appears at the top of the material after strengthening treatment, the more times of strengthening, the deeper the influence layer is, and the effect of laser impact on microhardness is weakened when the number of strengthening times reaches a certain value. With the increase of strengthening times, the indentation on the surface of the alloy becomes deeper, which leads to the increase of roughness value. (3) the dislocation motion and grain refinement process of TC11 titanium alloy after laser shock are studied. The results show that plastic deformation occurs on the surface after laser shock, and dislocations with uneven distribution will continue to propagate. Dislocation entanglement, dislocation cell, dislocation wall and other dislocation structures will be formed due to the interaction between dislocations. The dislocation motion will continue to evolve into the subcrystalline boundary, and the new structure will cut the original grain structure, so that the grain will be refined gradually until the internal energy is stable. (4) the effects of corrosion temperature and duration on the thermal corrosion properties were discussed, and the effectiveness of impact treatment to enhance the thermal corrosion of TC11 titanium alloy was confirmed. The experimental results show that the incubation period of hot corrosion process of TC11 titanium alloy increases and the acceleration of weight loss decreases after laser shock, and the oxide layer and corrosion layer will be formed during the hot corrosion process. After laser shock, the oxide layer on the surface becomes more compact and complete, and the cracks, pits and spalling of the corroded surface are restrained. With the increase of the duration or the corrosion temperature, not only the surface corrosion intensifies, but also serious surface cracks, pits and shedding occur. (5) the thermal corrosion morphology of TC11 titanium alloy and the mechanism of laser shock strengthening its corrosion resistance are studied. The results show that the hot corrosion is a process from the appearance of oxide film to the appearance of cracks, pits and finally falling off. After laser shock, the residual compressive stress can reduce the occurrence of cracks, increase the adhesion between oxide and matrix surface, reduce stress corrosion and prevent corrosion. The dislocation movement in the alloy makes the grain structure of the alloy continuously divided and refined, resulting in a large number of fine grain structure. The internal defects and grain refinement caused by dislocation movement can improve the mechanical properties and surface structure stability of the alloy, make the oxide formed in the corrosion process uniform and compact, enhance the plasticity and improve the corrosion resistance.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.23;TG665

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