湿喷丸强化Ti-6Al-4V合金的微动磨损和微动疲劳行为及其机理研究

发布时间：2018-04-25 03:06

本文选题：Ti-6Al-4V合金 + 湿喷丸处理　；参考：《大连理工大学》2016年博士论文

【摘要】：Ti-6Al-4V合金因其具有比强度高和耐腐蚀等特点,一直是生产航空涡轮发动机叶片的重要材料。然而,由于Ti-6Al-4V合金硬度低、抗疲劳性能差等缺点严重影响其航空工件的使用寿命。特别是涡轮叶片与压气机盘的榫头—榫槽连接部位的微动磨损将大大降低钛合金叶片的疲劳寿命。同时,这种微小幅度的损伤又具有极强的隐蔽性,常常会造成灾难的发生。随着航空工业的飞速发展,微动损伤越来越引起人们的重视,并且航空工业对微动损伤防护方面的要求也越来越高。在微动损伤防护方面,喷丸处理技术以其成本低、易操作、效率高等优点而成为目前航空领域最普遍的表面处理方法。本文利用湿喷丸技术对Ti-6Al-4V进行表面强化处理,并对比分析湿喷丸表面强化对微动损伤及疲劳损伤的影响,综合湿喷丸强化机制和微动损伤机制,系统地研究了湿喷丸强化作用对Ti-6Al-4V合金微动损伤的影响规律。主要研究内容包括：(1)采用湿喷丸技术对Ti-6Al-4V合金进行表面强化处理,利用XRD技术、纳米压痕技术、扫描电镜以及透射电镜技术对合金强化层的残余应力、硬度以及微观组织进行测试分析。结果表明,强化层的残余压应力和硬度均随深度增加而减小,影响深度分别为160和80μm。利用修正的硬度与屈服关系公式对Ti-6Al-4V合金湿喷丸强化层作了定量描述,计算表明,表层屈服强度由820 MPa提高至约1165 MPa并在0-80μm范围内线性降低。通过对强化层的微观组织观察探讨了湿喷丸晶粒细化机制,并根据晶粒细化机制提出了残余应力的形成模型,即喷丸引起的残余压应力是以晶粒之间未释放的弹性能形式存在。(2) Ti-6A1-4V合金试样的常规疲劳性能试验结果表明,湿喷丸处理能显著提高Ti-6Al-4V合金的疲劳寿命。显微组织观察发现,湿喷丸强化改变了疲劳裂纹萌生机制,强化层内的细晶强化和位错强化导致疲劳裂纹萌生位置由表面转移至试样内部,同时,湿喷丸引入的残余压应力对裂纹扩展起到有效的阻碍作用。(3)通过微动磨损的对比试验,研究湿喷丸处理对Ti-6Al-4V合金微动磨损行为的影响规律。结果表明,湿喷丸处理对Ti-6Al-4V合金在粘着状态和滑移状态时的微动磨损行为影响不明显,但是在部分滑移状态时,湿喷丸强化可以对微动磨痕内塑性变形积累区的微裂纹萌生起到有效的阻止作用。通过计算,湿喷丸处理后强化层局部屈服强度的提高是防止局部疲劳损伤的主要因素。(4)利用自主设计的微动疲劳试验装置进行Ti-6Al-4V合金试样的微动疲劳试验。与常规疲劳结果相比,湿喷丸处理对合金微动疲劳损伤的防护作用远高于常规疲劳损伤。通过显微组织观察,提出了湿喷丸处理前后试样的微动疲劳失效机制,即未喷丸试样微动区有局部疲劳微裂纹,出现裂纹尖端效应；湿喷丸试样微动区以磨损为主。湿喷丸强化层对微动区裂纹萌生的阻碍作用是导致试样微动疲劳失效机制不同的主要原因。此外,残余压应力的引入又能阻碍裂纹的扩展。因此,湿喷丸处理对钛合金微动疲劳抗性的提高是由强化层内硬度的增加和残余压应力的引入共同导致的。
[Abstract]:Because of its high specific strength and corrosion resistance, Ti-6Al-4V alloy has always been an important material for the production of aero turbine engine blades. However, the low hardness of the Ti-6Al-4V alloy and poor fatigue resistance have seriously affected the service life of its aeronautical workpiece. Dynamic wear will greatly reduce the fatigue life of titanium alloy blades. At the same time, this small amplitude damage is very strong concealment and often causes disaster. With the rapid development of the aviation industry, the microdynamic damage has attracted more and more attention, and the aviation industry is becoming more and more demanding on the protection of micro damage. With the advantages of low cost, easy operation and high efficiency, the shot peening technology has become the most common surface treatment method in the field of aviation. This paper uses wet shot peening technology to strengthen the surface of Ti-6Al-4V, and compares and analyzes the influence of the surface hardening of the wet shot peening on the microdynamic damage and fatigue damage. The strengthening mechanism of pellets and the mechanism of microdynamic damage have been studied systematically. The main contents of the study are as follows: (1) the surface hardening of Ti-6Al-4V alloys by wet shot peening technology, XRD technology, nano indentation, scanning electron microscopy and transmission electron microscopy are used to strengthen the alloy strength. The residual stress, hardness and microstructure of the layer are tested and analyzed. The results show that the residual compressive stress and hardness of the reinforced layer decrease with the depth, and the influence depth is 160 and 80 M. respectively. The quantitative description of the wet shot peening layer of Ti-6Al-4V alloy is made by the modified hardness and yield relation formula. The calculation shows that the surface yield can be yielded. The strength is increased from 820 MPa to about 1165 MPa and linearly decreased in the range of 0-80 mu m. The grain refinement mechanism of wet shot peening is discussed by observing the microstructure of the strengthened layer, and the formation model of residual stress is put forward according to the grain refinement mechanism, that is, the residual compressive stress caused by the shot peening is in the form of the unreleased elastic energy between the grains. (2) The normal fatigue test results of Ti-6A1-4V alloy specimens show that the fatigue life of Ti-6Al-4V alloy can be greatly improved by wet shot peening. The microstructure observation shows that wet shot peening has changed the mechanism of fatigue crack initiation, and the fine grain strengthening and dislocation strengthening in the strengthened layer lead to the migration of fatigue crack from the surface to the inside of the specimen. At the same time, the residual compressive stress introduced by the wet shot peening plays an effective hindrance to the crack propagation. (3) the effect of wet shot peening on the fretting wear behavior of Ti-6Al-4V alloy is studied by the contrast test of fretting wear. The results show that the wet shot peening treatment has the microdynamic wear behavior of the Ti-6Al-4V alloy in the adhesion and slip states. It is not obvious that the wet shot peening can effectively prevent the initiation of micro crack initiation in the plastic deformation accumulation area in the fretting wear. By calculation, the improvement of the local yield strength of the reinforced layer after the wet shot peening is the main factor to prevent the local fatigue damage. (4) the self designed micro fatigue test is used. The microdynamic fatigue test of Ti-6Al-4V alloy samples was carried out. Compared with the conventional fatigue results, the protective effect of wet shot peening on the microdynamic fatigue damage of the alloy was much higher than that of the conventional fatigue damage. The microdynamic fatigue failure mechanism of the specimens before and after the wet shot peening was observed. The crack tip effect occurs in the fatigue micro crack, and the fretting zone in the wet shot peening specimen is mainly worn. The hindering effect of the wet shot peening layer on the crack initiation in the microdynamic zone is the main cause of the microfatigue failure mechanism of the specimen. In addition, the introduction of the residual compressive stress can impede the expansion of the crack. The increase of fatigue resistance is caused by the increase of hardness in the strengthened layer and the introduction of residual compressive stress.

【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG146.23;TG668

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