表面超声滚压处理对高速列车车轴钢疲劳性能的影响

对EA4T型高速列车车轴钢棒状旋转弯曲疲劳试样实验段磨削加工后进行了表面超声滚压处理。观察了处理前后试样的表面形貌及表层微观组织,测量了处理前后试样的表面粗糙度、表层硬度及表层残余应力。利用旋转弯曲疲劳实验得到处理前后试样的疲劳极限。结果表明:表面超声滚压处理后,试样的疲劳极限由352MPa提高到401MPa。疲劳极限的提高主要由于表面超声滚压处理后试样表面粗糙度降低、表层强度及残余压应力增加。     

Ti-6Al-4V表面超声滚压制备Al_2O_3膜层的微观组织及性能研究

运用超声滚压处理(USRP)的方法,在Ti-6Al-4V合金表面制得一层Al2O3薄膜。利用SEM、XRD、光学干涉仪及显微硬度计分析了超声滚压处理后试样表面层的微观组织和性能。结果表明:加入Al2O3粉末进行USRP后可以在基体金属表面形成厚度约为7μm的Al2O3膜层,且结合处基体金属存在残余压应力和塑性变形。相对于母材,处理后试样表面粗糙度降低50%,表面硬度提高98%。同时,处理后试样表面层存在残余压应力场,最大压应力值为-687MPa,位于最表层,残余压应力深度为420μm。加入Al2O3粉末的USRP后的试样,既利用表面Al2O3的加入进一步提高其表面硬度,同时保留了USRP的优势。     

喷丸处理对6151-T6铝合金旋转弯曲疲劳性能的影响

对经过电解抛光、喷丸处理和喷丸处理再抛光的三种6151-T6铝合金试样的表面粗糙度及喷丸处理后试样表面硬化层的硬度进行测试。对三种表面状态不同的铝合金材料进行旋转弯曲疲劳实验。研究喷丸处理试样表面残余应力随疲劳实验的变化情况,以及喷丸处理对该铝合金疲劳性能的影响。结果表明:喷丸处理对材料疲劳性能的影响与加载的压应力水平有关。当加载的压应力与表面残余压应力之和不超过材料表面硬化层的循环屈服强度时,硬化层中的残余压应力在疲劳过程中不发生应力松弛,疲劳寿命得到大幅度提高;反之,将发生应力松弛现象,疲劳寿命的提高程度受残余压应力松弛程度的影响。此外,喷丸处理造成的材料表面粗糙度的增加,在全应力幅范围,使材料的疲劳寿命略有降低。     

复合喷丸对铝-铜-镁合金表面形貌和硬度的影响

对铝-铜-镁合金试样进行复合喷丸处理,通过观察喷丸处理后试样的表面形貌和测量试样的表面粗糙度、残余应力、衍射峰半峰宽及显微硬度等参数,分析了复合喷丸处理对铝-铜-镁合金表面形貌和力学性能的影响。结果表明:铝-铜-镁合金试样经复合喷丸处理后表面粗糙度变化不大,由0.70μm增加到2.97μm,试样表面整体细密、均匀,完整性较高,表面质量较好;引入较深的残余压应力场,最大残余压应力为306 MPa,且压应力场整体分布均匀,能够起到很好的强化效果;表面衍射半峰宽增大,为0.275°;表面显微硬度增大,为180.8 HV,比基体的硬度120 HV增加了50%。     

喷丸强度对不同粗糙度表面超高强度钢疲劳性能的影响

不同方式加工的高强度钢零件具有不同的表面状态,对其采用相同的喷丸工艺是否合理尚不明确。对不同表面粗糙度23Co14Ni12Cr3Mo E超高强度钢作不同强度的喷丸强化。采用扫描电镜及白光干涉仪观察了喷丸试样的表面形貌,采用金相显微镜观察喷丸试样的表面组织,采用旋弯疲劳试验机测试了喷丸试样的疲劳性能,采用X射线衍射残余应力测试仪测试喷丸试样的残余应力。研究了喷丸强度对不同表面粗糙度超高强度钢的表面组织、形貌、残余应力场及疲劳性能的影响。结果表明:喷丸过程可以细化表面组织,引入残余压应力场,改变表面形貌特征,从而引起表面应力集中状况的改变,其改善效果与原始表面状态有关;对于初始表面粗糙度Ra≤0.4μm的表面,喷丸强化过程能有效提高材料的疲劳寿命,促使疲劳裂纹源内移;随表面粗糙度的提高,当应力集中状况过于严重时,表面组织细化和残余压应力对疲劳性能的提升作用会被抑制,喷丸工艺对疲劳寿命的提升效果大幅下降,疲劳裂纹源均位于表面。     

Ti-6Al-4V合金表面超声振动滚压强化研究

采用超声振动滚压加工技术对Ti-6Al-4V合金表面进行处理,探究该项技术对Ti-6Al-4V合金表面质量的影响。通过对该工艺加工前后的Ti-6Al-4V合金进行表面粗糙度参数、XRD图谱、截面微观形貌、表层残余应力及显微硬度的对比分析,结果表明:经该工艺处理后的合金表面各项粗糙度参数皆有明显降低;加工后的合金表面XRD图谱的衍射峰减弱且宽化,衍射角向高角度方向偏移;加工后的合金表层β相组织相较加工前明显细化,且随着深度增加β相组织逐渐增大;在距离表面约50μm位置的残余应力值最大可达到-967 MPa;加工后的合金表面显微硬度可达到421HV,且在0~140μm的深度范围内,显微硬度随着深度的增加逐渐减小至与基体硬度一致。经超声振动滚压加工后的Ti-6Al-4V合金表面质量显著提高,有利于提高其零部件的使用性能。     

喷丸强化对2XXX铝合金疲劳寿命的影响

研究喷丸对2XXX铝合金拉-拉疲劳性能的影响。对未喷丸试样和喷丸强化试样的微观组织、显微硬度、残余应力和拉-拉疲劳性能进行对比分析。结果表明:喷丸处理后,试样的组织和微结构未发现明显变化,但其粗糙度、残余压应力和显微硬度有所提高,分别是未喷丸试样的6.25倍,3.85倍和1.12倍;拉-拉疲劳性能显著提高,其中值疲劳寿命是未喷丸的1.67倍。在99.9%存活率下,喷丸试样的安全寿命是未喷丸试样的1.45倍。且表面喷丸强化后疲劳裂纹源由多个变为一个。     

氮等离子体浸没离子注入技术改善轴承钢滚动接触疲劳寿命和机械性能的研究

研究了氮等离子体浸没离子注入(N-PIII)技术处理后GCr15轴承钢表面的滚动接触疲劳特征和机械性能。测试了改性前后试样的滚动接触疲劳寿命和磨痕光学形貌、摩擦磨损行为及纳米压痕硬度。结果表明,处理后试样的最大显微硬度较基体增大近一倍,摩擦系数从0.95下降到0.15。在赫兹接触应力为5.1 GPa,90%置信区间下的L10和L50寿命分别增加了99.6%和236.3%。分析不同处理参数下的Weibull分布曲线和光学显微形貌可知,脉冲偏压、材料内部缺陷、基体表面粗糙度、注入时间和N离子注入剂量对疲劳寿命均有很大影响。疲劳寿命和相关机械性能的改善主要源于N-PIII处理所导致的氮化物强化相和残余压应力的共同作用。     

纵-扭复合超声对滚齿面强化机理及表面特性研究

为了强化齿面,提高齿轮表面的使役性能,使用一种新的纵-扭复合强化加工方法对齿轮进行强化。首先,基于赫兹接触理论和齿轮啮合理论,建立了纵-扭超声滚压齿面等效应力的理论模型;其次采用有限元仿真技术对该加工方式进行了模拟;最后利用已经搭建好的试验平台进行了一系列的纵-扭超声对滚齿面强化试验。通过对比仿真与理论结果对比,施加纵-扭超声后可以有效的提高接触应力,中有无超声振动接触应力提高约1.7倍～2倍,致使齿轮表面材料发生屈服进而完成。试验结果进一步表明纵-扭超声滚强化压改善了齿面的表面特性。当施加纵-扭复合超声振动时,齿面残余应力随阻尼力矩增大而增加,沿齿廓方向残余应力呈现先增大后减小趋势,在节圆处残余应力值最大。齿面的显微硬度HV_1.0数值沿齿廓呈现时变特性,超声滚压强化加工可以改善齿面表面形貌。与传统滚压相比,超声滚压强化后表面峰谷间距加宽,粗糙度降幅可达45%～55%。因此,纵-扭超声对滚强化加工可以实现齿面强化、改善齿面特性,提高残余压应力和显微硬度、降低表面粗糙度并提高齿面质量。     

钛合金疲劳试样加工残余应力的表征及其对低周疲劳寿命的影响

目的 探究钛合金TC4低周疲劳试样加工过程中残余应力的变化及残余应力对低周疲劳寿命的影响.方法 采用X射线衍射法分别对车、磨、抛后的试样进行表面残余应力的表征,分析加工工艺对其的影响,利用液压伺服万能试验机进行低周疲劳试验,分析其表面残余应力对寿命的影响.结果 经过粗车、精车、磨削、纵抛,试样加工表面的残余应力不断减小...     

Fatigue characteristics of SAE52100 steel via ultrasonic nanocrystal surface modification technology

Ultrasonic nanocrystal surface modification (UNSM) technology is a novel surface modification technology that can improve the mechanical and tribological properties of interacting surfaces in relative motion. UNSM treatment was utilized to improve the wear resistance fatigue strength of slim bearing rings made of SAE52100 bearing steel without damaging the raceway surfaces. In this study, wear and fatigue results that were subjected to different impact loads of the UNSM treatment were investigated and compared with those of the untreated specimen. The microhardness of the UNSM-treated specimens increased by about 20%, higher than that of the untreated specimens. The X-ray diffraction analysis showed that a compressive residual stress of more than 1,000 MPa was induced after the UNSM treatment. Also, electron backscatter diffraction analysis was used to study the surface structure and nanograin refinement. The results showed that the rolling contact fatigue life and the rotary bending fatigue strength of the UNSM-treated specimens increased by about 80% and 31%, respectively, compared to those of the untreated specimen. These results might be attributed to the increased microhardness, the induced compressive residual stress, and the nanocrystal structure modification after the UNSM treatment. In addition, the fracture surface analysis showed that the fish eye crack initiation phenomenon was observed after the UNSM treatment.     

Experimental and numerical rolling contact fatigue study on the 32CrMoV13 steel

The aim of this work is to study pure rolling contact fatigue in 32CrMoV13 quenching and tempering steel. The study involves both experimental and numerical work. The influence of the roughness and the residual stresses on the mechanisms and zones of cracking were studied. The results show a rapid reduction in roughness during the first minute of test but even so there will be specimen deterioration. The residual stress profile after rolling contact tests have high compression values in the surface and at a depth of approximately 240 μm, which is related with the Hertzian maximal shear stress. The numerical simulation of the Hertzian loading was used both to determine the elastic shakedown of the material and to apply a high‐cycle multiaxial fatigue criterion. The three‐dimensional finite element analysis used in the numerical calculation includes elastic‐linear kinematic hardening plastic material and allows the introduction of an initial residual stress state. Taking into account the elastoplastic load induced by the Hertz pressure, low‐cycle fatigue tests were used to characterize the mechanical properties of the material. In order to validate the numerical simulation, the results of the calculation after elastic shakedown were compared with the values measured by X‐ray diffraction after rolling contact tests. The results showed a reasonable agreement between calculated and measured stresses. The Dang Van high‐cycle multiaxial fatigue criterion showed a good relationship with the experimental findings.     

Machining residual stresses

As part of an extended investigation into the effects of pre-and post-processing on shot peening residual stresses, residual stresses due to a controlled turning process were investigated in the aircraft alloy 817M40. Cylindrical specimens were produced on a centre lathe with all machine parameters fixed except for feedrate. A variation in the feedrate was used to produce different surface roughnesses varying from 1·2 to 6·6 μm R_a. The residual stress field resulting from the varying feedrate was established by the well known centre hole drilling method, albeit with a modification which assisted in determining the variation of residual stresses with depth. The results indicated a definite variation in axial residual stress distribution with surface roughness, with a rough surface showing higher tensile residual stresses. This variation was however not duplicated for hoop or circumferential stresses. Maximum tensile residual stress varied from 90 MN m^?2 in the 6·6 μm R_a surface to 50 MN m^?2 in the 1·2 μm R_a surface. Although residual stresses are generally ignored in design, either because of a lack of experimental results or for ease of application, the results indicate that some consideration must be given to machining residual stresses as these can enhance or reduce the fatigue life of engineering components. The study also indicates that turning operations associated with large plastic deformations are encountered during the machining process.

MST/3230     

Relation between fatigue threshold and fatigue limit for surface-rolled specimens

After cylinder notch fatigue specimens of 40 CrNiMo steel were rolled, their fatigue limit increased by 41%. The rolled specimens did not fracture, even though they had been loaded for 10⁷ cycles under fatigue limit stress, but a non-propagating fatigue crack was generated. Thus the value of the fatigue limit depends on the fatigue threshold value ΔK_th of the metal of the rolled layer. Plastic deformation increased ΔK_th in these experiments. It can be inferred that ΔK_th of the rolled layer increases from the occurrence of plastic deformation and microvoids on the layer. Calculation of the effect of residual stress in the crack wake on the stress intensity factor ΔK indicates that residual compression stress decreases ΔK by 21.5 MPa √M. It was calculated that rolling induced both the length of the non-propagating crack and the increase of fatigue limit. The calculated values are in accord with experiment. Analysis and calculations indicate that the non-propagating crack is generated on the rolled layer. Thus the fatigue limit is improved because rolling produces residual compression stress in the layer (which decreases the stress intensity factor), and increases ΔK_th of the layer.     

高强度合金抗疲劳应用技术研究与发展

评述了超高强度钢、高强度Al合金和Ti合金表面完整性抗疲劳应用技术的研究和发展。高强度合金疲劳性能对应力集中敏感，不适当的加工工艺和切削热等造成的表面损伤和高拉应力使其疲劳和应力腐蚀性能损失殆尽。先进的表面完整性加工尤其是表面改性可显著提高疲劳性能，如激光冲击使7475-T761拉-拉疲劳寿命提高约89％，7075-T6裂纹扩展速率降低到原来的1／1500；超声喷丸使超高强度钢低周疲劳强度提高约50％，Ti7Al4Mo合金高周疲劳强度提高约15％；表面超硬化可使Vasco X-2M齿轮钢接触疲劳寿命提高30～35倍等。     

Influence of surface integrity on fatigue strength of 40CrNi2Si2MoVA steel

Influence of surface integrity (including surface roughness, residual stresses, and microstructure in surface) on fatigue limit of 40CrNi2Si2MoVA steel specimens is investigated comprehensively in this work according to a systematic consideration. The surface integrity of specimens is changed due to several widely used manufacturing procedures: heat-treatment, grinding, electro-polishing, hard chromium plating and shot peening. In comparison with specimen electro-polished after grinding, the specimen without polishing has 10% lower fatigue limit due to higher surface roughness; while shot peening improves the fatigue limit for about 36% due to inducing of compressive residual stress field in the surface and transferring the fatigue crack source from surface to interior. The fatigue limit of specimen with decarburized layer after grinding is lower about 13%, but the shot peening can eliminate its detrimental effect. Hard chromium plating decreases the fatigue limit dramatically. The shot peening carried before plating can improve the fatigue limit of specimen and cause it to get to a level even higher than that of specimen without plating.     

Relationship between decarburisation and fatigue strength of through hardened and carburising steels

Abstract

The effect of surface decarburisation upon the fatigue strength in rotating bending of a through hardened low alloy steel and a carburised carburising steel was investigated. The relationships between surface carbon content, depth of decarburisation, microhardness, residual stress, surface finish, and fatigue limit were examined. Whereas the fatigue limit was found to be independent of the depth of decarburisation over the range investigated (up to 1 mm), linear relationships were found between fatigue limit and surface carbon concentration and micro hardness. Furthermore, the presence of residual tensile stresses at the surface were found to lead to a reduction of fatigue limit. The fatigue limit of the rough machined specimens was found not to be significantly lower than that of the polished specimens.

MST/1179     

疲劳损伤过程中45~＃钢剩余力学性能的变化特征

通过对疲劳不同阶段４５~＃钢试样的宏观力学性能测试、表面显微硬度测量及位错结构与显微断口分析，研究了疲劳损伤过程中材料的宏观与细观力学性能随疲劳损伤的变化规律，以及剩余力学性能变化与材料内部位错结构演变及断裂特征变化的关系     

再次喷丸周期对TC18钛合金疲劳寿命的影响

研究了再次喷丸对于经过预先喷丸的TC18钛合金残余应力和室温疲劳寿命的影响。使用X射线衍射仪和旋转弯曲疲劳机测定了再次喷丸后的合金的表面残余应力以及总疲劳寿命。结果表明,疲劳试验会使预先喷丸的TC18钛合金疲劳试样表面残余压应力松弛30%～50%,而再次喷丸可以使由于疲劳而松弛的表面残余压应力回复到疲劳试验前试样的50%～70%。此外,相比未经过再次喷丸的试样,选择合适的再次喷丸周期可使TC18钛合金的总疲劳服役寿命提高了75%。