激光喷丸强化TC6钛合金的振动疲劳寿命及断口分析

发布时间：2018-04-24 17:42

本文选题：激光喷丸 + TC6钛合金　；参考：《江苏大学》2017年硕士论文

【摘要】：激光喷丸强化技术(Laser Peening,LP)是使用高功率脉冲激光照射工件表层,诱导产生超过材料屈服极限的冲击波压力,从而引起工件表层发生剧烈塑性变形、使材料晶粒细化并产生高密度的位错组织。激光喷丸强化技术能显著改善材料的应力分布状态和微观组织,更好地抑制材料中裂纹源的萌生、扩展,从而提高航空关键部件的使用寿命。本文采用不同的激光功率密度与喷丸次数对TC6航空钛合金进行激光喷丸,探索激光工艺参数对激光喷丸强化材料表面完整性的影响,研究激光喷丸强化TC6钛合金的振动疲劳寿命,结合断裂力学对振动疲劳断口进行分析,根据振动疲劳失效过程中不同阶段的断口形貌,研究激光喷丸强化工艺对TC6钛合金的疲劳延寿增益机制。本文的主要研究内容有:研究激光喷丸诱导残余压应力的产生过程及估算模型;结合振动疲劳失效及疲劳断裂理论,分别从疲劳极限、裂纹扩展门槛值、应力强度因子等几个方面研究激光喷丸强化工艺对TC6钛合金疲劳裂纹扩展速率的改善机理。使用高功率Nd:YAG固体激光器对TC6航空钛合金试样进行激光喷丸强化实验,并对试样表面方向及深度方向进行残余应力测定和显微硬度测试。综合使用激光共聚焦显微镜、扫描电子显微镜和透射电子显微镜等实验手段研究激光喷丸前后试样的微观组织,包括α/β相形态、晶粒尺寸以及位错形态等。利用振动疲劳实验系统测定激光喷丸强化TC6航空钛合金试样的振动疲劳寿命,研究激光功率密度与喷丸次数对试样振动疲劳寿命的影响规律。用扫描电子显微镜观测振动疲劳试样的断口形貌,针对断口中的裂纹源区、裂纹扩展区和最终断裂区,研究激光喷丸强化对TC6航空钛合金振动疲劳断口形貌的影响,通过疲劳条带间距对TC6航空钛合金的振动疲劳裂纹扩展速率进行分析。
[Abstract]:Laser peening technique (LP) is a method of irradiating the surface layer of the workpiece with high power pulse laser, which induces shock wave pressure beyond the material yield limit, thus causing severe plastic deformation of the surface layer of the workpiece. The grain size of the material is refined and high density dislocation structure is produced. Laser shot peening can improve the stress distribution and microstructure of the material, restrain the initiation and propagation of the crack source, and improve the service life of the key components of aviation. In this paper, laser shot peening of TC6 aeronautical titanium alloy was carried out with different laser power density and shot peening times, and the effect of laser processing parameters on surface integrity of laser shot peening strengthened material was explored. The vibration fatigue life of TC6 titanium alloy strengthened by laser shot peening was studied. The vibration fatigue fracture was analyzed in combination with fracture mechanics. According to the fracture morphology of different stages in the process of vibration fatigue failure, the vibration fatigue life of TC6 titanium alloy strengthened by laser shot peening was studied. The fatigue life extension gain mechanism of TC6 titanium alloy by laser shot peening was studied. The main contents of this paper are as follows: to study the process and estimation model of residual compressive stress induced by laser shot peening, to combine the theory of vibration fatigue failure and fatigue fracture, to analyze the fatigue limit and crack growth threshold, respectively. The improvement mechanism of laser shot peening on fatigue crack growth rate of TC6 titanium alloy was studied in several aspects such as stress intensity factor. High power Nd:YAG laser was used to test the laser shot peening of TC6 aeronautical titanium alloy samples. The residual stress and microhardness of the samples were measured in the direction of surface and depth. The microstructures of the samples before and after laser shot peening were studied by means of laser confocal microscope, scanning electron microscope and transmission electron microscope, including 伪 / 尾 phase morphology, grain size and dislocation morphology. The vibration fatigue life of TC6 aeronautical titanium alloy specimens strengthened by laser shot peening was measured by vibration fatigue test system. The effects of laser power density and shot peening times on the vibration fatigue life of the samples were studied. The fracture morphology of TC6 aeronautical titanium alloy was observed by scanning electron microscope (SEM). The effect of laser shot peening on the vibration fatigue fracture morphology of TC6 aeronautical titanium alloy was studied according to the crack source, crack propagation zone and final fracture zone. The vibration fatigue crack propagation rate of TC6 aeronautical titanium alloy was analyzed by fatigue strip spacing.
【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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