激光喷丸强化TC4钛合金抗氢脆性能及机理

发布时间：2018-05-19 09:59

本文选题：激光喷丸 + TC4钛合金　；参考：《江苏大学》2017年硕士论文

【摘要】：钛合金是海洋、航天工程中常用的金属材料,服役环境对其抗氢脆性能提出了更高的要求。目前常采用表面改性方法来提高其表面机械性能。激光喷丸是利用激光冲击波效应在合金表层引入残余压应力从而实现表面改性的一项新技术,其具有强化效果更优、可控性强且加工更为柔性化等优点。本文以典型TC4钛合金为研究材料,开展激光喷丸及电解充氢试验,通过研究激光喷丸对TC4钛合金充氢前后表层显微硬度、微观组织、拉伸力学性能及宏观微观断口形貌的影响,探讨激光喷丸TC4钛合金抗氢脆机理,其核心研究内容如下:(1)从理论上分析了激光冲击波作用于合金表面的强化机理,研究了TC4钛合金在高应变率强烈塑性变形条件下的微观结构响应机理,制定激光喷丸TC4钛合金的喷丸路径和试验参数,揭示了氢扩散行为及其影响因素,探讨了激光喷丸抗氢脆机理。(2)比较了喷丸与未喷丸TC4钛合金在电解充氢前后微观组织和显微硬度的差异。根据激光喷丸强化引入残余压应力分布原理,分析激光喷丸对氢渗透影响机制。结果显示:激光喷丸在TC4钛合金表层引入幅值较大的残余压应力,并使TC4钛合金表层晶粒细化,电解充氢过程中进入试样的氢浓度随晶粒尺寸的减小而降低,合金氢脆敏感性降低;激光喷丸后合金的硬度提高,经电解充氢处理后出现氢致硬化现象,并且随着激光功率密度增加,氢致硬化率增速趋缓,激光喷丸受氢的影响变小,激光喷丸提高了TC4钛合金抗氢脆性能。(3)对喷丸与未喷丸的TC4钛合金在电解充氢前后进行室温慢拉伸试验,研究其力学性能变化。试验结果表明:激光喷丸提高了TC4钛合金抗拉强度及延伸率,并且随激光功率密度的增加,其抗拉强度及延伸率也增加;经电解充氢处理后,TC4钛合金抗拉强度及延伸率均降低,并且随激光功率密度的增加,氢致延伸率损失降低,TC4钛合金氢脆敏感性随激光功率密度的提高逐渐减小。观察试样断口形貌,发现其微观断口均为典型韧窝形貌,激光喷丸后韧窝更深且更大并且均匀,显示出更好的韧性;经电解充氢处理后,未喷丸的TC4钛合金出现准解理断裂,韧性变差,但喷丸后的TC4钛合金依然呈现出较好的韧性。
[Abstract]:Titanium alloy is a common metal material in marine and aerospace engineering. At present, surface modification is often used to improve the surface mechanical properties. Laser shot peening is a new technology which uses laser shock wave effect to introduce residual compressive stress into the surface of alloy to achieve surface modification. It has the advantages of better strengthening effect, better controllability and more flexible processing. In this paper, laser shot peening and electrolytic hydrogen charging experiments were carried out on typical TC4 titanium alloy. The effects of laser shot peening on the microhardness, microstructure, tensile mechanical properties and macroscopic microfracture morphology of TC4 titanium alloy before and after hydrogen filling were studied. The anti-hydrogen embrittlement mechanism of laser shot peening TC4 titanium alloy is discussed. The key research contents are as follows: (1) the strengthening mechanism of laser shock wave acting on alloy surface is analyzed theoretically. The microstructure response mechanism of TC4 titanium alloy under the condition of high strain rate and strong plastic deformation was studied. The shot peening path and test parameters of laser shot peening TC4 titanium alloy were established, and the hydrogen diffusion behavior and its influencing factors were revealed. The anti-hydrogen embrittlement mechanism of laser shot peening was discussed. The differences of microstructure and microhardness between shot peening and non-shot peening TC4 titanium alloy before and after electrolytic hydrogen charging were compared. The influence mechanism of laser shot peening on hydrogen permeation was analyzed according to the principle of residual compressive stress distribution in laser shot peening. The results show that laser shot peening induces large residual compressive stress on the surface of TC4 titanium alloy and refines the surface grain of TC4 titanium alloy. The concentration of hydrogen entering the sample decreases with the decrease of grain size in the process of electrolytic hydrogen charging. The hydrogen embrittlement sensitivity of the alloy was decreased, the hardness of the alloy was increased after laser shot peening, the phenomenon of hydrogen induced hardening appeared after electrolytic hydrogen charging, and with the increase of laser power density, the growth rate of hydrogen induced hardening slowed down, and the effect of laser shot peening on hydrogen became smaller. The hydrogen embrittlement resistance of TC4 titanium alloy was improved by laser shot peening. The mechanical properties of TC4 titanium alloy with shot peening and without shot peening were studied by slow tensile test at room temperature before and after electrolytic hydrogen filling. The results showed that laser shot peening increased the tensile strength and elongation of TC4 titanium alloy, and with the increase of laser power density, the tensile strength and elongation also increased, and the tensile strength and elongation of TC4 titanium alloy decreased after electrolytic hydrogen charging. With the increase of laser power density, the hydrogen embrittlement sensitivity of TC4 titanium alloy decreases with the increase of laser power density. By observing the fracture morphology of the sample, it was found that the microfracture was typical dimple morphology, the dimple was deeper, bigger and more uniform after laser shot peening, which showed better toughness, and after electrolytic hydrogen charging, the TC4 titanium alloy without shot peening appeared quasi cleavage fracture. The toughness became worse, but the TC4 titanium alloy still showed good toughness after shot peening.
【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】：TG668;TG146.23

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