激光冲击对不锈钢焊接接头残余应力场的影响

针对不锈钢焊接接头存在残余应力且分布不均匀、容易发生应力腐蚀的问题,采用激光冲击强化对其进行处理,探究激光功率密度和冲击次数对表面残余应力状态的优化作用,并通过应力腐蚀试验验证优化效果。结果表明:随着功率密度增加,表面残余应力明显下降,但下降幅度逐渐减小,功率密度4.24GW/cm2与2.83GW/cm2冲击产生的残余应力相差不大,熔合区还存在残余拉应力,说明高功率密度不足以消除表面残余拉应力;随着冲击次数增加,残余拉应力显著降低,2.83GW/cm2冲击3次之后,残余拉应力完全消除,局部最高应力梯度从54.7 MPa/mm下降到11.7 MPa/mm,获得了高数值、分布均匀的残余压应力层。激光冲击强化后,焊接试样的应力腐蚀断裂时间提高了33.48%,激光冲击强化产生的残余压应力是其应力腐蚀抗性提高的重要原因。     

强激光冲击铝合金改性处理研究

利用新型聚偏1.1-二氟乙烯（PVDF）压电传感器,实现了对激光引发的冲击波压力的实时测量,得到激光引发的冲击波峰压在铝中成指数型的衰减规律;观测了不同约束层材料在铝靶表面产生的激光冲击波,研究了不同约束层对冲击效果的影响;最后用激光冲击强化装置对7050-T7451航空铝合金结构材料进行了冲击强化处理,对试件激光冲击区存在的残余压应力及位错密度进行了测量。结果显示经激光冲击处理的试件表面具有极高的残余压应力,可达-200MPa以上。激光冲击处理后铝合金的位错密度得到显著的提高,疲劳寿命提高到175％～428％。这些重要结果对激光冲击改性处理技术的实际应用具有指导性作用。     

大耕深旋耕刀激光冲击强化残余应力研究

研究了激光冲击强化对回转半径为350mm大耕深旋耕刀残余应力的影响,利用ANSYS对旋耕刀进行理论应力分析,发现应力集中在刀柄外弯角处,同时进行了激光冲击强化模拟,得到理论残余应力引入值。利用X射线衍射法对激光冲击强化前后旋耕刀表面进行了残余应力测试。结果表明,ANSYS模拟激光冲击强化引入的残余应力值与试验实测的结果吻合得较好,相比未经处理的旋耕刀,激光冲击强化后刀具表面残余应力明显增大,最大残余压应力达412.25 MPa,增幅达166%,残余压应力的引入可消除旋耕刀工作的应力集中,提高了刀具使用寿命。研究结果为进一步提高和优化大耕深旋耕刀制造工艺提供了新的参考依据。     

激光冲击7075-T6铝合金焊缝的残余应力场数值模拟

针对激光冲击强化铝合金焊缝过程中存在多场耦合导致残余应力变化幅度大、实时表征难的问题,采用ABAQUS非线性有限元软件建立了激光冲击强化7075-T6铝合金板材焊接件的有限元模型,模拟计算焊缝在激光冲击强化前后的残余应力场分布,重点分析了激光冲击强化对焊缝的横、纵向残余应力场的影响规律,并对焊缝的激光冲击强化工艺参数进行优化。研究结果表明,焊缝表面为残余拉应力场并且分布不均,激光冲击强化使得焊缝的拉应力状态转变为高幅压应力状态;优化激光冲击强化工艺参数(如激光能量、激光光斑尺寸、搭接率),可以明显改善焊缝区域和热影响区的残余应力分布;当激光光斑搭接率为50%至70%时,残余应力分布趋于均匀,可以有效消除"残余应力洞"现象。     

放大自发辐射对激光冲击处理7050铝合金的影响

 利用高功率钕玻璃激光器对7050铝合金表面进行了冲击处理,保持泵浦功率不变,用压电传感器和示波器测试了激光冲击产生的压力波形,用X射线应力测量仪测量了激光冲击后铝合金表面的残余应力,并用非接触式光学轮廓仪分析了激光冲击后铝合金的表面形貌,研究了放大自发辐射强度对激光冲击处理7050铝合金冲击压力、残余应力和粗糙度影响的微观机理。研究结果表明:在泵浦功率不变前提下,放大自发辐射强度的增大降低了激光冲击波压力,铝合金表面残余压应力也随之降低,同时铝合金表面粗糙度增大。     

激光冲击对E690高强钢激光熔覆修复微观组织的影响

为研究激光冲击对E690高强钢激光熔覆修复层微观组织的影响,选用专用金属粉末对E690高强钢试样预制凹坑进行激光熔覆修复,并使用脉冲激光对激光熔覆层进行冲击强化处理,同时采用扫描电镜、透射电镜和X射线应力分析仪分别对激光冲击前后激光熔覆层的微观组织和表面残余应力进行检测。结果表明:激光熔覆修复后,激光熔覆层组织为等轴晶,熔覆层与E690高强钢基体之间冶金结合良好,其表面残余应力为均匀分布的压应力。经激光冲击后,激光熔覆层截面晶粒得到细化,并观察到大量的形变孪晶,互相平行的孪晶界分割熔覆层粗大晶粒,在激光熔覆层的晶粒细化过程中发挥着重要作用;试样表层位错在{110}滑移面上发生交滑移,在晶界周围形成了位错缠结。经激光冲击后,激光熔覆层冲击区域表面残余压应力数值相较于冲击前提升了1.1倍。     

阵列式压电振子超声复合喷丸强化*

为了进一步改善超声喷丸强化质量,提升工件表面残余应力和显微硬度的均匀性,对压电振子阵列型超声喷丸强化加工系统进行了改进,提出了在强化加工过程中辅助工件往复运动的方法。对改进后的压电振子阵列型超声喷丸强化加工原理进行了阐述,分析了激振片的振动特性并进行了结构尺寸优化,应用Abaqus对工件往复运动下超声喷丸强化过程进行了仿真研究,分析了在不同的工件往复运动频率下,工件表面残余应力分布情况。实验测试了在不同喷丸强化时间及工件往复运动频率下超声喷丸强化加工质量,探究了喷丸时间和工件往复运动频率对工件表面显微硬度的影响。结果表明：在压电振子阵列型超声喷丸强化过程中辅助工件往返运动,可以有效提高工件表面残余应力和显微硬度分布的均匀性,工件表面强化质量得到提升。     

激光喷丸改善TC6钛合金组织和力学性能

为了使激光冲击强化技术能较好地应用于TC6钛合金的发动机叶片,对TC6钛合金进行试验研究。通过X射线衍射仪、透射电子显微镜等测试技术分析了不同参数下TC6钛合金的微观组织变化,用显微硬度计和残余应力测试仪分别表征表层硬度和残余应力变化,并测试材料冲击后的振动高周疲劳性能。试验结果表明:激光冲击材料后表面组织得到明显细化,随着冲击次数的增加,先后出现了高密度位错、位错胞、亚晶和纳米晶。性能方面,表面硬度在冲击一次即可提高19%,硬度影响深度达到700 m;与此同时表面残余应力最高达到-608.5 MPa,在500 m深度上仍具有-100 MPa左右的应力存在。经三次冲击后,标准疲劳试片的疲劳极限提高近20%。     

2A02铝合金中强激光冲击诱导的位错组态分析

利用输出波长为1064 nm、脉冲宽度为20 ns的钕玻璃YAG激光器,对2A02铝合金进行了表面冲击强化试验.测定了激光冲击后材料的表面硬度和残余应力,用快速傅里叶逆变换(IFFT)方法分析了铝合金激光冲击诱导的晶内亚结构及其演变行为.结果表明,激光冲击强化可使2A02铝合金表面硬度提高50%以上,残余压应力达到12...     

激光喷丸对TC4钛合金抗氢脆性能的影响

通过性能测试分析,研究了激光喷丸(LP)技术对TC4钛合金抗氢脆性能的影响。结果表明,LP试样表面产生了-327 MPa的残余压应力;电化学充氢后,试样表面残余压应力降低了9.17%,喷丸与未喷丸试样的表面显微硬度分别提高了5.07%和7.08%,而延伸率分别降低了2.25%和4.84%。LP处理可提高TC4钛合金的韧性,降低其氢脆敏感性。     

2024铝合金激光多次冲击诱导残余应力状态分布规律

采用高功率激光器多次冲击2024铝合金,用X射线衍射技术分析了冲击区域的残余应力,研究了冲击残余应力状态分布规律,并用其评价激光冲击强化效果。研究表明,随着冲击次数增加,塑变量及塑性应变梯度逐渐减小,测点是双向压应力状态,而4次冲击时,塑性应变梯度增大,光斑中心是单向压应力状态,其他点是双向压应力状态。当激光功率密度为2.8 GW/cm2时,3次冲击强化效果最佳,材料是二向压应力状态,残余最大主应力及应力强度的均值最大,方差最小,分布基本均匀,塑性应变梯度较小。     

Effects of processing parameters on fatigue properties of LY2 Al alloy subjected to laser shock processing

We address the effects of processing parameters on residual stresses and fatigue properties of LY2 Al alloy by laser shock processing (LSP). Results show that compressive residual stresses are generated near the surface of samples due to LSP. The maximum compressive residual stress at the surface by two LSP impacts on one side is higher than that by one LSP impact. The maximum value of tensile residual stress is found at the mid-plane of samples subjected to two-sided LSP. Compared with fatigue lives of samples treated by single-sided LSP, lives of those treated by two-sided LSP are lower. However, these are higher than untreated ones.     

Engineering the residual stress state and microstructure of stainless steel with mechanical surface treatments

Four mechanical surface treatments have been considered for the application to austenitic stainless steel structures. Shot peening (SP), laser shock peening (LSP), ultrasonic impact treatment (UIT) and water jet cavitation peening (WJCP), also known as cavitation shotless peening (CSP), have been applied to 8 mm thick Type 304 austenitic stainless steel coupons. This study considers the merits of each of these mechanical surface treatments in terms of their effect on the surface roughness, microstructure, level of plastic work and through thickness residual stress distribution. Microstructural studies have revealed the formation of martensite close to the treated surface for each process. Residual stress measurements in the samples show compressive stresses to a significantly greater depth for the LSP, UIT and WJCP samples compared to the more conventional SP treated sample.     

Effect of an absorbent overlay on the residual stress field induced by laser shock processing on aluminum samples

Laser shock processing (LSP) or laser shock peening is a new technique for strengthening metals. This process induces a compressive residual stress field, which increases fatigue crack initiation life and reduces fatigue crack growth rate. Specimens of 6061-T6 aluminum alloy are used in this investigation. A convergent lens is used to deliver 2.5 J, 8 ns laser pulses by a Q-switch Nd:YAG laser, operating at 10 Hz. The pulses are focused to a diameter of 1.5 mm onto aluminum samples. Density of 2500 pulses/cm² with infrared (1064 nm) radiation was used. The effect of an absorbent overlay on the residual stress field using this LSP setup and this energy level is evaluated. Residual stress distribution as a function of depth is assessed by the hole drilling method. It is observed that the overlay makes the compressive residual stress profile move to the surface. This effect is explained on the basis of the vaporization of the coat layer suppressing thermal effects on the metallic substrate. The effect of coating the specimen surface before LSP treatment may have advantages on improving wear and contact fatigue properties of this aluminum alloy.     

Effect of laser shot peening on precipitation hardened aluminum alloy 6061-T6 using low energy laser

Mechanical properties of engineering material can be improved by introducing compressive residual stress on the material surface and refinement of their microstructure. Variety of mechanical process such as shot peening, water jet peening, ultrasonic peening, laser shot peening were developed in the last decades on this contrast. Among these, lasers shot peening emerged as a novel industrial treatment to improve the crack resistance of turbine blades and the stress corrosion cracking (SCC) of austenic stainless steel in power plants. In this study we successfully performed laser shot peening on precipitation hardened aluminum alloy 6061-T6 with low energy (300 mJ, 1064 nm) Nd:YAG laser using different pulse densities of 22 pulses/mm² and 32 pulses/mm². Residual stress evaluation based on X-ray diffraction sin² ψ method indicates a maximum of 190% percentage increase on surface compressive stress. Depth profile of micro-hardness shows the impact of laser generated shock wave up to 1.2 mm from the surface. Apart from that, the crystalline size and micro-strain on the laser shot peened surfaces have been investigated and compared with the unpeened surface using X-ray diffraction in conjunction with line broadening analysis through the Williamson-Hall plot.     

激光冲击波对5B05铝合金表面应力状态的调整

采用X射线衍射仪分别对光斑中心及其边界点冲击前后3个方向上的残余应力进行测量。根据主应力及其方向角的计算公式,计算出了各测试点冲击前后的主应力值和主应力方向角,分析了其分布特性。结果表明,激光冲击波不仅能调整5B05铝合金表面残余主应力值,还能调整其方向。最大主应力增幅最大点与最小主应力增幅最大点并不在同一点上。5B05铝合金经激光冲击波作用后,表面应力状态得到了改善,应力分布变得分散,应力域变大。     

Laser Shock Processing of 6061-T6 Al alloy with 1064 nm and 532 nm wavelengths

Laser Shock Processing (LSP) has been proposed as a competitive alternative technology to classical treatments for improving fatigue and wear resistance of metals. We present a configuration and results in the LSP concept for metal surface treatments in underwater laser irradiation at 532 nm and 1064 nm. The purpose of the work is to compare the effect of both wavelengths on the same material. A convergent lens is used to deliver 1.2 J/pulse (1064 nm) and 0.9 J/pulse (532 nm) in a 8 ns laser FWHM pulse produced by 10 Hz Q-switched Nd:YAG laser with spots of a 1.5 mm in diameter moving forward along the work piece. A LSP configuration with experimental results using a pulse density of 2500 pulses/cm² and 5000 pulses/cm² in 6061-T6 aluminum samples are presented. High level compressive residual stresses are produced using both wavelengths. It has been shown that surface residual stress level is comparable to that achieved by conventional shot peening, but with greater depths. This method can be applied to surface treatment of final metal products.