激光冲击强化对Ti6Al4V钛合金表面完整性和四点弯曲疲劳性能的影响

研究了激光冲击强化对Ti6Al4V合金表面完整性和四点弯曲疲劳性能的影响,采用扫描电镜、显微硬度仪、X射线应力测量仪及透射电镜等仪器对材料表面完整性进行了分析,采用MTS疲劳试验机对试样进行了疲劳性能测试,并采用扫描电镜分析了疲劳断口,并探讨了激光冲击强化机制。结果表明：采用功率密度为15.9 GW/cm2的激光处理试样后,其四点弯曲疲劳中值寿命较未强化试样提高了4.2～23.5倍;且激光功率密度越大,试样的疲劳中值寿命越长。激光冲击强化表现出比喷丸强化更优的疲劳寿命增益效果。分析发现：经激光冲击强化后,Ti6Al4V合金表面形成了深度约为600~1400 μm的残余压应力场,表面硬度比未强化区域提高了约10%,而亚表层内部的位错密度比未强化试样显著提高,以上表层性能和微观组织的变化对四点弯曲疲劳寿命的提高具有重要作用。     

激光冲击强化对Ti-6Al-4V合金表面完整性及疲劳性能的影响

研究了激光冲击强化处理对Ti-6Al-4V合金表面完整性及疲劳性能的影响。采用表面粗糙度仪、显微硬度计和X射线衍射残余应力仪分别对激光冲击强化前后Ti-6Al-4V合金表面完整性进行了表征。在PQ-6旋转弯曲疲劳试验机上测试了经激光冲击强化处理的Ti-6Al-4V合金107周次条件下的疲劳极限,用扫描电镜分析了疲劳断口形貌,探讨激光冲击强化机制。结果表明,激光功率密度越大,表面粗糙度越小,表面残余压应力和表面硬度值越大,残余压应力层和硬化层深度越深;与原始试样相比,激光冲击强化试样的疲劳极限提高了33.3%,原因是激光冲击强化可以显著降低合金表面的粗糙度,改善合金的表面完整性,产生深层的残余压应力场和表面硬化层,将疲劳裂纹源由表层转移到次表层,有效地抑制了疲劳裂纹的萌生和扩展,从而提升合金的疲劳抗力。     

Ti6Al4V合金表面热氧化/真空扩散处理及耐磨性研究

Ti6Al4V合金经800℃、1 h和900℃、15 min热氧化后,分别进行850℃、20 h真空扩散,并将900℃、15 min热氧化+850℃、20 h真空扩散后的试样在25℃和400℃下进行磨损试验,比较真空扩散后的显微硬度分布及处理前后的磨损量,通过XRD、SEM、EDS等分析手段对氧化、氧化/扩散及磨损后的结构和形貌进行测试分析。结果表明:Ti6Al4V合金经热氧化后,表面形成钛氧化物,再经真空扩散后,TiO2发生了分解,在表层和基体间形成了氧扩散层,增加了两者间的结合力,产生了硬化效应,同时形成一定数量的Al3Ti,在不同温度和载荷下,磨损量均比未处理试样的小;经900℃、15 min热氧化+850℃、20 h真空扩散后的Ti6Al4V合金,耐磨性可得以显著提高。     

用氢细化Ti—6Al—4V合金显微组织的研究

本文介绍了用氢细化Ti—6Al—4V合金显微组织的方法。利用氢在钛中的可逆性,作临时性的合金化元素,可改善铸造钛合金的粗大魏氏组织,强化力学性能,提高疲劳寿命。     

激光熔丝Ti6Al4V合金成形工艺、微观组织及强韧性研究

采用激光熔丝增材制造技术制备了单道多层的Ti6Al4V合金试样,系统研究了激光功率、扫描速度及送丝速度对Ti6Al4V合金的组织形貌、拉伸性能和冲击性能的影响。单道多层沉积试样的组织由马氏体α’、α集束和网篮状α构成。激光功率提高使β晶粒尺寸增大和马氏体α’分解程度增加,激光功率从3 000 W提升至3 500 W时试样抗拉强度下降了约4%,但延伸率上升了50%,冲击韧性提高了约6%。送丝速度的提高增大了试样的β晶粒平均尺寸,随着送丝速度从10 mm/s增加至30 mm/s,抗拉强度下降了2%,延伸率提高了67%,冲击韧性提高了11%。扫描速度提高会增加试样内的未熔合缺陷和残留马氏体α’,扫描速度6 mm/s试样相比扫描速度4 mm/s的试样延伸率提高了约45%,抗拉强度下降了2%,冲击韧性提高了11%。     

粉末冶金Ti6Al4V合金的研究

采用Ti粉、AlV中间合金粉,通过模压和真空烧结制备了Ti6Al4V合金,并通过随后的锻造和热处理来改变其组织和性能.通过金相显微镜、X射线衍射(XRD)仪、扫描电镜(SEM)及力学性能检测等分析手段,系统研究了压制压力对Ti6Al4V烧结体密度的影响,以及试样状态(烧结态及烧结淬火态)、锻造温度、淬火温度及时效温度等工艺参数对粉末冶金Ti6Al4V合金组织和性能的影响.结果表明:通过模压和烧结可制备出相对密度达97.4%的Ti6Al4V合金;Ti6Al4V烧结态及烧结淬火态合金经过锻造后,相对密度接近100%;通过不同热处理工艺得到不同组织和性能,能获得等轴组织,其α晶粒尺寸在5μm左右.     

电化学抛光对选区激光熔化成形Ti6Al4V牙冠表面质量及耐蚀性能的影响

研究了电化学抛光过程中电解液比例、电压、电解时间等参数对选区激光熔化成形Ti6Al4V牙冠表面质量及耐蚀性能的影响。结果表明，选区激光熔化成形的Ti6Al4V牙冠表面粗糙度较大，有明显的熔池边界及台阶，试样表面粘结大量粉末颗粒，初始粗糙度高达30μm。在体积比1:8的高氯酸和醋酸电解液中进行电化学抛光，当电压较小（10 V）时，只能去除表面粘附的粉末颗粒，抛光效果不明显；当抛光电压较高（50 V）或高氯酸和醋酸比例较大时，表面抛光过度，导致局部凹凸不平，粗糙度明显上升。在30 V电压下抛光30 min后，表面质量较好，表面粗糙度约为1μm，达到使用要求。经抛光处理后的Ti6Al4V牙冠表面的耐蚀性能大大提升，相比于未进行表面处理的牙冠，其耐蚀性能提高近一个数量级。     

Ti6Al4V合金热浸铝研究

采用热浸镀法在Ti6Al4V合金表面制备出TiAl3金属间化合物涂层,并在不同温度下对浸镀后的试样进行热扩散处理.通过XRD、SEM等分析手段对涂层结构和成分进行测试分析,探讨涂层形成机理.结果表明:Ti6Al4V合金经750℃ 5 min热浸铝后,在其表面形成了由纯铝和TiAl3组成的涂层,TiAl3合金层厚约1.5 μm;经550℃退火5h后,TiAl3含量增多而纯铝层含量则相应减少,纯铝层几近消失,合金层厚度约为40μm,涂层致密;经930℃退火5h后,表面的涂层转化为单相的TiAl3,产物纯净,但涂层中出现了较多的孔洞,自涂层表面到钛合金基体,孔洞浓度呈梯度变化.     

Ti-2Al-2.5Zr合金低温下单向与循环变形行为

采用管材试样研究了低温下 (- 196℃ )Ti 2Al 2 .5Zr合金的循环变形行为。分析了应力比、应力幅、循环周次、加载速率等对合金循环变形行为和疲劳性能的影响。建立了循环和单调加载方式下合金的应力—应变曲线方程和疲劳寿命预测方程。根据不同循环周次下疲劳试样的金相分析和断口观察 ,讨论了合金的循环变形规律和疲劳断口特征     

粉末冶金Ti6Al4V合金的研制进展

Ti6Al4V合金具有良好的力学性能和广阔的应用领域.该文作者在阅读大量新、老文献的基础上,综述了采用传统粉末冶金法和粉末冶金新技术制备Ti6Al4V合金的历史及现状,并将粉末冶金Ti6Al4V合金的力学性能与相应的铸造和锻造合金性能进行对比.结果表明,采用传统和新的粉末冶金技术制备Ti6Al4V合金,都能在降低成本的同时,使合金性能满足应用要求;随着近净成形技术的发展,制品性能和成本都将进一步优化.还对粉末冶金法制备多孔Ti6Al4V材料的研究进展进行了论述,认为粉末冶金法能进一步扩大Ti6Al4V合金在医学领域的应用范围.     

激光冲击强化技术研究及其在钛合金中的应用

激光冲击强化（LSP）通过高功率（GW／cm2级）、短脉冲（ns级）强激光诱导的冲击波在金属材料表层引入残余压应力,从而抑制疲劳裂纹的萌生和发展,是一种新型的金属表面强化技术。阐述了激光诱导冲击波的机理以及残余应力场的形成。分析了激光冲击的影响因素,论述了激光冲击强化的特点及其在钛合金中的应用,展望了激光冲击强化的应用前景和发展。     

Effects of laser-shock processing on the microstructure and surface mechanical properties of hadfield manganese steel

The effects of laser-shock processing (LSP) on the microstructure, hardness, and residual stress of Hadfield manganese (1 pct C and 14 pct Mn) steels were studied. Laser-shock processing was performed using a Nd: glass phosphate laser with 600 ps pulse width and up to 120 J/pulse energy at power density above 10¹² W/cm². The effects of cold rolling and shot peening were also studied for comparison. Laser-shock processing caused extensive formation of ε hexagonal close-packed (hep) martensite (35 vol pct), producing up to a 130 pct increase of surface hardness. The surface hardness increase was 40 to 60 pct for the shot-peened specimen and about 60 pct for the cold-rolled specimen. The LSP strengthening effect on Hadfield steel was attributed to the combined effects of the partial dislocation/stacking fault arrays and the grain refinement due to the presence of the ε-hcp martensite. For the cold-rolled and shot-peened specimens, the strengthening was a result of ε-hcp martensite and twins with dislocation effects, respectively. Shot peening resulted in a relatively higher compressive residual stress throughout the specimen than LSP.     

Effect of Treatment Area on Residual Stress and Fatigue in Laser Peened Aluminum Sheets

Two 2.0-mm-thick aluminum sheets were laser peened and the resulting residual stresses were measured using incremental hole drilling, surface X-ray diffraction, and synchrotron X-ray diffraction techniques. Laser peening was applied to two samples using the same laser peening parameters, but one of the samples has a larger peened area. The aim of this research was to discover the effect of peen area on residual stress, for application in aerospace structures for fatigue life enhancement. It was found that a larger peened area has higher and deeper compressive stresses in the crack-opening direction, leading to greater enhancement of fatigue life.     

Effects of CeO2 nanoparticles on microstructure and properties of laser cladded NiCoCrAlY coatings

CeO2 nanoparticles(nano-CeO2p) were added into laser cladded NiCoCrAlY coatings on Ni-based superalloy substrate to improve the microstructure and properties.Scanning electron microscope(SEM),X-ray diffractometer(XRD),micro-hardness tester,and heat treatment furnace were employed to investigate their morphologies,phases,micro-hardness and thermal shock resistance,compared with the coating without nanoparticles added.The results showed that the microstructure and properties of the coatings with the addition ...     

Effects of sodium chloride and shot peening on corrosion fatigue of AISI 6150 steel

Reversed-bending fatigue tests of quenched and tempered AISI 6150 steel were conducted in dry air and in aqueous 3 pct NaCl. The 3 pct NaCl environment drastically reduced fatigue life but two different shot peening treatments were found to improve the corrosion fatigue life over that of unpeened samples. Multiple fatigue crack initiation occurred at very distinct locations in both the unpeened and the peened specimens fatigued in 3 pct NaCl. Fatigue crack propagation from each initiation site occurred first on flat facets normal to the stress axis and then by a more ductile mechanism after the initiation facets had linked. The average size of the corrosion fatigue initiation facets in the peened specimens was much smaller than that of the unpeened specimens; however, the number of initiation sites was greater in the peened specimens. It is believed that the beneficial effect of the shot peening results from significantly reduced early fatigue crack propagation rates in the compressive residual stress layer at the surface. Formerly Research Assistant, Materials Department, University of Wisconsin-Milwaukee     

Effects of stress‐ and/or warm peening of AISI 4140 on fatigue life

Using a new system shot peening and/or stress peening in an air blast machine at elevated temperatures is feasible. The effects of conventional shot peening, stress peening, warm peening and stress peening at elevated temperatures on the characteristics of regions close to the surface, on the stability of residual stresses and on the fatigue strength of a quenched and tempered AISI 4140 steel (German grade 42 CrMo 4) are presented. The alternating bending strength is increased by stress peening, warm peening and especially the combination of both compared to conventional shot peening. These effects are due to the residual stresses induced and the stability of the dislocation structure, which is highly affected by strain ageing effects.     

Effect of Shot Blasting and Shot Peening Parameters on Residual Stresses Induced in Connecting Rod

This paper investigates the effect of shot blasting and shot peening parameters on residual stresses induced in connecting rod. Compressive residual stresses are induced using shot peening to increase fatigue life of connecting rod. Shot peening is also responsible for increase in surface roughness. Surface roughness is detrimental for fatigue life of the connecting rod. This necessitates shot blasting to reduce surface roughness. Shot peening and shot blasting processes are analysed to find optimum process parameters which will induce required value of compressive residual stress on the surface of connecting rod. Compressive residual stresses induced in the connecting rod specimen have been experimentally measured using X-ray stress analyser. The experimental results have been analysed using grey relational analysis to find optimum values of process parameters for target value of compressive residual stress and surface roughness. The experimental investigation and the analysis of it have resulted in achieving the desired value of compressive residual stress, which is 10.5% higher over the existing connecting rod. Surface roughness also decreases to 3.84 Ra which is 8.5% lesser than specified value to achieve better fatigue life.     

奥氏体钢四点弯曲疲劳行为的数值模拟与试验

采用有限元方法对奥氏体钢四点弯曲疲劳试验的加载过程进行了数值模拟,分析了疲劳试样的应力分布与疲劳寿命,确定了受力分布相对均匀的试样的合理尺寸范围,并对一种Cr-Mn奥氏体钢进行了四点弯曲疲劳试验研究,对比分析了有限元模拟与试验结果间的差别与原因。结果表明,试样尺寸不同,两加载辊之间的应力分布规律不同;当t/h(材料厚度/加载辊距)1.4时,最大应力出现在靠近加载辊的内侧,距加载辊0.4~0.5 mm;当t/h=1.2~1.4时,两加载辊之间的应力分布比较均匀,最大模拟应力与加载应力(理论值)的误差小于5%;当t/h1.2时,最大应力出现在两加载辊中间,其中t/h=0.7~0.8时,模拟值最大应力与加载应力比较接近,但应力分布均匀性较低;采用t/h≈1.3的试样进行疲劳试验研究,试验后的疲劳裂纹均产生在两加载辊中间,在加载辊外侧未发现疲劳裂纹,这与模拟结果相一致;模拟疲劳极限为498 MPa,循环4.0×10~6周次,试验测定疲劳极限为505MPa,循环3.6×106周次,模拟值略小于试验值,可见有限元方法可以较准确地预测材料的疲劳寿命。     

干喷工艺对高速钢 M42-弹簧钢D6A 金属带锯条性能的影响

通过二元影像测量仪观察锯条干喷处理后的表面压应力、覆盖率、齿尖状况,不磨合锯切GCr15棒材的齿尖崩刃情况和锯切45^#钢和空转疲劳寿命试验研究表面处理干喷砂工艺参数（压缩空气压力0.1~0.4MPa,运行速度4~1m/min）对M42（/%:1.08C,1.5W,9.4Mo,3.8Cr,1.2V,8.0Co）-D6A（/%:0.48C,1.0Mo,1.1Cr,0.1V,0.6Ni）双金属带锯条性能的影响。结果表明,锯条经合适的参数-压缩空气压力0.3MPa和运行速度3m/min,背部表面覆盖率达到100%,干喷后,齿尖形成稳定的圆角,承受切割和振动的冲击力,以提高锯条齿尖的耐磨性,齿部的平均使用寿命提高66%,背部疲劳试验寿命提高45%~70%。     

Effects of Fine Particle Peening Conditions on the Rotational Bending Fatigue Strength of a Vacuum-Carburized Transformation-Induced Plasticity-Aided Martensitic Steel

The effects of fine particle peening conditions on the rotational bending fatigue strength of a vacuum-carburized transformation-induced plasticity-aided martensitic steel with a chemical composition of 0.20 pct C, 1.49 pct Si, 1.50 pct Mn, 0.99 pct Cr, 0.02 pct Mo, and 0.05 pct Nb were investigated for the fabrication of automotive drivetrain parts. The maximum fatigue limit, resulting from high hardness and compressive residual stress in the surface-hardened layer caused by the severe plastic deformation and the strain-induced martensite transformation of the retained austenite during fine particle peening, was obtained by fine particle peening at an arc height of 0.21 mm (N). The high fatigue limit was also a result of the increased martensite fraction and the active plastic relaxation via the strain-induced martensite transformation during fatigue deformation, as well as preferential crack initiation on the surface or at the subsurface.