奥氏体不锈钢1Cr18Ni9Ti激光冲击强化研究

对奥氏体不锈钢１Ｃｒ１８Ｎｉ９Ｔｉ进行激光冲击强化,观察了激光冲击强化层显微组织与结构的变化并测定了激光冲击强化层内的显微硬度和残余应力。结果表明：１Ｃｒ１８Ｎｉ９Ｔｉ激光冲击强化层中有高密度的位错和大量的孪晶,显微硬度显著提高并产生较高的残余压应力,１Ｃｒ１８Ｎｉ９Ｔｉ激光冲击强化区还发生了形变诱发马氏体相变。     

激光冲击对TC11钛合金组织和力学性能的影响

对TC11钛合金进行激光冲击强化处理,通过透射电子显微镜观察不同参数下TC11钛合金的微观组织变化,用显微硬度计和X射线应力测试仪分别测试材料表层硬度和残余应力,并通过TC11钛合金标准疲劳试片高周振动疲劳试验验证激光冲击对其疲劳性能的影响.试验结果表明:激光冲击波作用后表面组织结构发生明显变化,当冲击次数增加,先后出现了高密度位错、位错胞和纳米级晶粒等微观组织特征.冲击10次后,表面残余应力最高达到-632.5MPa,相应的塑性变形层深度达到1500μm左右;同时表面硬度在冲击1次即可提高19%,硬度影响深度为700μm,随着次数增加而提高,但幅度不大.经3次冲击处理的TC11钛合金标准疲劳试片的疲劳极限由原始483MPa提高到593MPa.      

钢制叶片激光冲击强化与渗铝的组合应用

采用扫描电子显微镜(SEM),X射线衍射(XRD)等手段研究了激光冲击强化(LSP)对钢制叶片渗铝层的影响,结果表明渗铝后进行激光冲击强化会对渗铝层造成破环,而在渗铝之前进行激光冲击强化则能提高渗层质量.从残余应力和显微组织变化两方面分析了渗铝高温作用对不锈钢材料激光冲击强化效果的影响,激光冲击强化产生的残余压应力在510℃渗铝温度环境下保温150min仍有-295MPa稳定存在,晶粒细化组织也没有明显长大,激光冲击不锈钢材料的残余应力和微观组织具有良好的热稳定性.振动疲劳对比试验结果验证了“LSP+渗铝”组合工艺对不锈钢材料的强化效果,在660MPa应力水平下,采用该组合工艺试片的疲劳寿命为3.98×106,为原渗铝试片疲劳寿命的14倍左右.      

激光冲击提高航空铝合金疲劳寿命的研究

分析了激光冲击改善航空铝合金疲劳性能的机理；讨论了涂层及约束层的重要作用。对２０２４和７４７５铝合金进行了优化激光冲击试验。结果表明：提高了这些铝合金的疲劳寿命，获得了均匀稳定的位错显微组织和表面残余压应力。     

LY2铝合金的激光冲击强化区硬度和残余应力测试分析

为了研究激光冲击处理对LY2航空铝合金力学性能的影响,采用Nd:YAG激光器对航空铝合金LY2进行了激光冲击强化处理,测定其显微硬度和残余应力.结果表明,经过激光冲击处理后,试样表面没有受强脉冲激光和冲击波的破坏,而显微硬度和残余压应力明显提高,激光冲击处理后的强化区与光斑相当,深度约为1.2mm.     

浅齿轮齿根激光冲击强化试验和仿真研究

为探究激光冲击强化对高强度钢齿轮齿根表面及内部残余应力的影响,使用ABAQUS软件对齿轮齿根进行了激光冲击强化模拟仿真,并通过试验对该仿真模型进行了验证。结果表明,所建立的齿轮齿根激光冲击强化有限元模型可以较好地预测实际激光冲击强化结果,准确揭示激光冲击强化作用规律。同时,根据残余应力分布情况可知,激光冲击强化可使高强度钢齿轮齿根产生明显的残余压应力层,但不同方向残余压应力分布略有不同,平行于齿根路径方向的平均残余压应力大于垂直于齿根路径方向的平均残余压应力。     

激光冲击强化对加力燃烧室火焰探测器焊缝的影响

为了研究激光冲击强化(LSP)后加力燃烧室火焰探测器焊缝位置异常开裂原因,采用X射线衍射方法和金相方法对激光冲击强化效果进行分析,并利用扫描电子显微镜对断口进行了观察。在Abaqus有限元分析软件中建立了与观察到的焊缝缺陷相似的有限元模型,对焊缝缺陷的LSP处理及冲击波传播过程进行了模拟分析。试验结果表明:具有较好材料完整性的区域经LSP处理后,表面会预置较大残余压应力,同时表面金属晶粒得到细化,疲劳裂纹会在焊缝缺陷位置萌生和扩展。有限元分析结果表明:存在分层缺陷的焊缝经LSP强化后,冲击波会在分层缺陷处产生反射,造成分层位置发生开裂,形成裂纹源造成疲劳开裂。根据试验和仿真分析结果,为提升火焰探测器焊缝激光冲击抗疲劳效果,建议优化焊接工艺,提高焊接质量。     

激光冲击强化对TC17钛合金模拟叶片疲劳极限的影响

通过振动疲劳试验探究了激光冲击强化(LSP)对带根部倒圆的TC17钛合金叶片一阶弯曲疲劳极限的影响,结合疲劳断口、组织观察和残余应力测试等方法分析了激光冲击强化提高叶片疲劳极限的强化机制。结果表明,激光冲击强化对TC17钛合金叶片的一阶弯曲振动频率无影响,但显著提高了叶片的疲劳极限(约8%)。冲击强化后叶片的金相组织无显著变化,但表层晶粒组织明显细化,并在距离材料表面50μm的深度范围内形成剧烈塑性变形区,材料表面产生了不小于466 MPa的残余压应力。晶粒细化和残余压应力是叶片疲劳极限提高的直接原因。     

激光冲击强化7075铝合金熔焊接头的疲劳性能

激光冲击强化（LSP）技术具有残余压应力场深、冷作硬化程度低和强化区域可控等优点,在焊接结构表面改性方面应用前景广阔。对2 mm厚度的7075-T6铝合金激光-电弧复合焊接接头实施了激光冲击强化处理,对比分析了强化前后接头的硬度、残余应力、疲劳寿命以及疲劳裂纹形核机制。结果表明,焊缝中心的最高硬度由强化前的152 HV提高到强化后的175 HV,有效强化层深度约为100 μm;经激光冲击强化后,焊缝区呈现残余压缩应力,最大残余压应力为-200 MPa;9组焊接接头试样的平均疲劳寿命为675 937周,约为强化前疲劳寿命（262 297周）的2.6倍;疲劳裂纹萌生位置从具有高度应力集中的表面缺陷转移至强化层以下的亚表面,进而有效地提高了疲劳裂纹的形核寿命。     

激光冲击强化提高压气机叶片疲劳性能研究

根据1Cr11Ni2W2MoV不锈钢材料性能,确定了激光冲击强化参数;并通过标准试片疲劳试验,验证了该参数条件下激光冲击强化提高不锈钢材料振动疲劳寿命的有效性.设计了不锈钢叶片振动疲劳试验,确定了叶片冲击强化部位和方式,对强化叶片进行了型面检查、一阶弯曲振动疲劳试验和强化机理研究.结果表明:激光冲击强化后的叶片各个截面尺寸在设计范围之内,强化后叶片的应力-循环次数(S-N)曲线往上移动,提高了叶片的疲劳强度,在660MPa应力水平下,叶片的振动中值疲劳寿命提高70%;激光冲击强化引起的残余应力和表层微观组织变化是疲劳强度提高的主要原因.      

Investigation of Surface Integrity on TC17 Titanium Alloy Treated by Square-spot Laser Shock Peening

Laser shock peening(LSP) is an innovative surface treatment method,which has been shown to greatly improve the fatigue life of many metallic components.This work investigates surface integrity of TC17 titanium alloy treated by LSP with innovative square laser spot.Nd:glass laser with duration of 30 ns and spot size of 4 mm×4 mm is applied.The surface morphology and surface residual stress of the TC17 titanium alloy,treated with varying peening parameters such as laser power density and overlapping ratio,have been studied in detail.The results show that laser pulse energy greatly influences surface morphology and surface residual stress around single-spot treated areas,and compressive residual stresses are saturated as laser pulse energy is over 55 J.There are significantly different surface morphologies and residual stress distributions at the overlapped areas with different overlapping ratios.A relative smooth surface is produced with uniform compressive residual stress distribution at an overlapping ratio of 8 %.The experiment of residual stress relaxation is implemented by measuring residual stress at the center of four overlapped spots and by four point bending fatigue test at the frequency of 105 Hz.The compressive residual stresses induced by LSP are found to relax quite slowly under cyclic fatigue loading.     

激光冲击残余应力场的有限元分析

建立模拟激光冲击残余应力场的非线性弹塑性有限元模型,预测AISI 304奥氏体不锈钢厚、薄靶材经激光冲击后表面以及内部的残余应力场分布.模拟过程中,考虑材料高应变率(106s-1)下的力学性能和激光诱导冲击波的精确加载,分析激光功率密度、激光光斑尺寸、激光脉宽、激光冲击次数、激光单面与双面冲击等激光冲击参数以及初始残余应力等因素对不锈钢靶材残余应力分布的影响.数值模拟结果与X射线衍射法测量值吻合较好.在有初始残余拉应力(250MPa)存在的情况下,激光冲击仍能使304奥氏体不锈钢靶材形成残余压应力层,说明激光冲击工艺可提高奥氏体不锈钢焊接构件的抗应力腐蚀开裂能力.     

Laser Shock Peening of Aluminum Alloy 7050 for Fatigue Life Improvement

The effects of laser shock peening (LSP) on improving fatigue life of aluminum alloy 7050 are investigated.Surface hardness is increased corresponding to a high dislocation density induced by LSP.The X-ray diffraction stress measurement shows that LSP results in prominent increase of surface compressive stress,quasi-symmetrically distributed in the laser peened region.The fatigue life of the alloy 7050 in rivet fastener hole structure is notably improved owing to LSP.The sequence of LSP and fastener hole preparation also influence the fatigue cycle life of the alloy.     

一次预过载对铝合金喷丸前后缺口疲劳强度的影响

预过载拉伸可提高铝合金缺口疲劳寿命,但效果不及喷丸;过载量太大还使寿寿命趋于子下降。预过载压缩降低缺口疲劳寿命;喷丸后经过载压缩,寿命降低幅度更大,均与缺口残余应力及亚结构变化有关。     

激光冲击强化铝合金小孔构件的疲劳寿命研究

研究了激光冲击强化对7050-T7451铝合金小孔件疲劳寿命和断口形貌的影响。采用ABAQUS对峰值压力2.7GPa下小孔构件孔壁与表面上的应力分布进行了研究,并基于仿真结果对试样进行激光冲击强化试验和疲劳拉伸试验。结果显示,激光双面冲击强化在板料两侧形成一定深度的残余压应力影响层,而在中心形成一定范围的残余拉应力层,这也是导致疲劳源由孔角向孔壁中心转移的主要原因;在应力水平165.8MPa、195.0MPa和275.4MPa下,试样的疲劳寿命分别平均可增大451%、216%、116%;经激光冲击强化后,试样的疲劳源位置由孔角转移至孔壁内部,且疲劳裂纹扩展区面积明显增大。研究表明,激光冲击强化能明显改善铝合金小孔构件的疲劳性能,但强化效果随外加载荷的增加逐渐减小。     

Influence of laser shock peening on surface integrity and tensile property of high strength low alloy steel

Laser Shock Peening (LSP) is a well-established surface treatment commonly used to improve mechanical properties of material's surfaces. To further understand the relationship between tensile property and fatigue life improvement of high strength low alloy steel in the LSP process, LSP treatment of 32CrNi high strength low alloy steel was carried out by YAG laser with pulse energy of 15 J, and tensile property was tested by electronic universal material testing machine. Surface morphology, residual stress and tensile fracture of the specimens before and after LSP were observed by white light interferometer (WLI), X-ray measuring apparatus and scanning electron microscope (SEM). Result shows that LSP did not change tensile strength of 32CrNi steel but cause yield characteristic transform from obvious yield point to no yield phenomenon which is the only factor benefiting fatigue life, indicating that the increment of fatigue life was probably related to the disappearance of yield phenomenon. Formation mechanisms of tensile fractures and yield phenomenon induced by LSP at room temperature were also discussed and completely revealed. Deeper compressive residual stress and flat grains contributed to the transition of yield characteristic and lower elongation rate of 32CrNi steel subjected to LSP.