40Cr合金钢汽车转向节臂断裂失效分析

针对锻打成形的40Cr合金钢汽车转向节臂在使用过程中的断裂现象进行了失效分析.通过扫SEM、EDS、金相和显微硬度分析等方法分析了转向节臂的断口形貌、断件微观组织及其硬度等.结果表明,Si、Ca和Al元素含量过大形成很多夹杂物,造成应力集中而产生裂纹源,并且在材料外表面出现脱碳层,随着交变应力的作用使得疲劳裂纹萌生和扩展,最终发生双源疲劳断裂.     

涡桨发动机涡轮导向器内环失效分析

分析了一起涡轮螺旋桨发动机涡轮导向器内环多处裂纹故障。通过对裂纹断口进行的宏、微观观察,组织和硬度检查,能谱的半定量分析和综合分析,结果显示,导向器内环裂纹性质为热机械疲劳(TMF),疲劳裂纹起源于叶型槽孔角处。叶型槽孔角加工质量不佳,存在应力集中,是造成内环疲劳裂纹的主要原因;大修时叶型槽局部补焊降低了材料的热疲劳抗力,对裂纹的萌生和扩展也有影响。     

输出齿轮轴试验件的裂纹分析

9310钢制输出齿轮轴试验件进行高周疲劳试验时,其轴肩挖根R处发生开裂且挡边出现剥落。本文采用断口宏、微观分析、显微组织检测、硬度测试、力学性能测试等手段对其失效性质及裂纹萌生原因进行分析。结果表明,该输出齿轮轴开裂性质为疲劳,裂纹源位于轴肩挖根R的表面应力集中处。与之配合的小锥轴承的磨损失效是造成开裂的主要原因,轴肩挖根表面粗糙度过大且局部刀痕尖锐度促进了裂纹的萌生。为了提高输出齿轮轴试验件的疲劳寿命,要合理选用耐磨轴承材料或采取适当的表面处理以提高轴承的耐磨性,要严格控制输出轴的圆角加工质量、降低挖根R处的表面粗糙度。     

循环氢压缩机组主汽轮机轴失效分析

通过硬度检测、金相检验、宏观及微观断口分析, 结合力学分析证实了汽轮机轴失效是由于轴肩变径处加工刀痕导致应力集中,造成多条疲劳 裂纹萌生、扩展及最终的断裂,提出了防止汽轮机轴疲劳断裂的措施.     

球墨铸铁行星架断裂原因分析

球墨铸铁行星架在使用过程中发生断裂,断裂位置位于两行星孔之间。通过宏观观察、微观观察、力学性能等分析手段对行星架进行综合研究和分析,确定了行星架的断裂模式为疲劳断裂,疲劳扩展较充分,未发生局部受力过大的现象,开裂位置存在缩松缺陷。缩松缺陷的存在切断了材料内部的连续性,造成断裂部位的强度降低,使得零件在未达到材料的疲劳强度前就萌生裂纹,尤其是受周期性交变载荷的零件。同时,由于材料缩松严重,在零件表面出现,使得零件表面该缺陷位置的应力集中系数急剧增加,过早地萌生疲劳裂纹,造成零件早期疲劳失效。     

发动机排气阀断裂分析

某汽车发动机排气阀,材料为奥氏体耐热钢,在耐久试验至334 h时发生断裂。对断裂的排气阀进行了宏观及微观断口分析、化学成分分析和硬度测定,以揭示其断裂的原因。结果表明,该排气阀存在易产生应力集中和萌生裂纹的折叠、沟槽等机加工缺陷,加上高温氧化腐蚀作用,最终导致其在耐久试验时发生断裂。     

2024铝合金转动制件的失效分析

采用外观检查、裂纹断口宏微观观察及能谱分析、材料硬度检测、金相检查对2024铝合金转动件出现的裂纹进行了失效分析.结果表明,2024铝合金制件的裂纹失效属低周疲劳开裂,在冲压成型过程中,模具对坯件造成凹坑,产生应力集中加速了疲劳裂纹的萌生与扩展,导致最终失效.提出了严格控制制件的加工工艺的建议,并在装配前严格检查其表面质量.     

火电厂发电机组汽轮机阀杆断裂分析

通过对断裂阀杆进行化学成分分析、宏观检查、金相显微组织观察与分析以及硬度测试,分析汽轮机阀杆的断裂原因。结果表明,受检汽轮机主汽阀杆退刀槽外表面存在明显的加工刀痕,增大了应力集中,并使裂纹源提前产生。材料的有害元素P含量偏高,使材料的抗疲劳强度下降。阀杆在拉压应力和交变热应力的作用下,退刀槽处引起应力集中,导致疲劳裂纹源产生,造成阀杆脆性断裂。     

一种7075铝合金液压油缸的失效分析

采用扫描电镜和透射电镜对7075铝合金缸体出现的断裂现象进行了显微组织观察和失效分析.结果表明,7075铝合金缸体疲劳裂纹的萌生与阳极氧化膜有关,其表面的微孔洞在循环应力作用下容易产生应力集中,从而成为疲劳裂纹形核的场所.防止措施:建议将过渡圆弧半径加大以降低应力集中,减少疲劳裂纹萌生的可能性.     

某活塞销的断裂失效分析

某活塞销在远低于设计寿命的状态下提前发生断裂失效,通过磁粉探伤、断口宏观、微观分析、金相组织检测和表面渗碳层检验等手段对其失效性质及裂纹萌生原因进行了分析。结果表明:该活塞销的断裂性质为疲劳断裂,裂纹起源于销轴内孔孔壁。销轴内孔有高温进入,造成其金相组织转变,弱化了内孔渗层硬度和强度,降低了活塞销心部的抗冲击性能,是其断裂的主要原因;该活塞销基体的非金属夹杂含量较多,酸洗后留下的腐蚀坑易造成应力集中,同时带状组织明显,降低了基体的横向力学性能,二者对裂纹的起源和扩展均有促进作用。     

汽车焊接桥壳失效原因分析

汽车焊接桥壳在台架试验中发生早期断裂。对桥壳的开裂位置、断口的宏微观特征进行观察分析,对桥壳材料的化学成分、硬度和金相组织进行了测试和分析,结合有限元模拟方法,分析桥壳受力。结果表明:断裂发生在下板托焊缝端部,断口呈现明显的疲劳特征;造成断裂的主要原因是板托焊缝端部的应力水平较高,以及焊缝存在未焊透缺陷加剧应力集中,名义应力较大,诱发了疲劳疲劳裂纹源的萌生,提出了提升焊接质量、优化桥壳附件设计等措施,对延长桥壳的疲劳寿命具有指导意义。     

制氢装置水分离器入口法兰及三通失效分析

应用光学显微镜,扫描电镜、光电子谱,显微硬度仪,铁素体测量仪等对开裂失效试样进行分析,结果表明,三通和法兰开裂效是由于氢致开裂所致;同时也具有明显的氯化应力腐蚀破裂敏感性。     

马氏体轴承钢碳氮共渗滚动接触疲劳失效机理EI北大核心CSCD

碳氮共渗工艺应用广泛,但对碳氮共渗后零部件的滚动接触疲劳失效机理研究较少。采用气体碳氮共渗对马氏体轴承钢进行表面改性处理,对碳氮共渗试样进行滚动接触疲劳试验,研究碳氮共渗对轴承钢滚动接触疲劳性能的影响及其失效机理。研究结果表明:碳氮共渗试样表面硬度、残余应力和残余奥氏体含量显著提高,使得其接触疲劳寿命明显高于常规试样。疲劳裂纹萌生于表面和亚表面,其中大量表面平行裂纹主要由表面白色蚀刻层硬度梯度变化而导致,表面材料受到严重微观塑性变形产生晶粒细化;亚表面裂纹萌生位置受最大应力的分布和渗层厚度的影响。表面和亚表面疲劳裂纹的扩展和连接最终导致碳氮共渗试样出现浅层剥落和分层剥落的失效形貌。     

TRANSFORMATION OF RETAINED AUSTENITE IN CARBURIZED CASE DURING FATIGUE CRACK GROWTH

The morphology of the retained austenite in the carburized case of 20CrNiMo steel and itstransformation during fatigue crack propagation through the case were investigated by usingX-ray and TEM analysis.In the carburized case both film and block shaped retainedaustenite were found.Due to the crystallographic orientation relationship at the interface,thefatigue crack is inclined to pass through the block shaped retained austenite and thereby stim-ulates its strain-induced martensitie transformation.During the process of the fatigue frac-ture,most of the retained austenite structures on the crack path are transformed into themartensite,and the untranaformed parts on the fracture surface remain less than 6%.Thetransformation of the retained austenite,which is restrieted mainly within the plastic zone,oc-curs only during the proeess of fracture,and is independent of the magnitudes of the externalstress,stress ratio and cyclic number.The volume expansion accompanying the transforma-tion creates an additional residual displacement of about 0.44μm on fracture surfaces,whichis equivalent to the magnitude of the plasticity-induced residual displacement.The phasetransformation induced fatigue crack closure is believed to be an important factor affectingthe fatigue crack behaviors in the high carbon laver of the carburized case.     

Microstructure and fatigue properties of plasma transferred arc alloying TiC-W-Cr on gray cast iron

In this paper, TiC-W-Cr powders were alloyed on grey cast iron by plasma transferred arc (PTA). The alloying samples were characterized the microstructure, microhardness, fatigue life and fatigue crack growth. From the results, it is indicated that two distinguishing region: alloying zone, heat affected zone are formed on the surface after PTA alloying. The alloying zone mainly consists of primary austenite, martensite, a eutectic of (Fe,Cr)₇C₃ carbide and austenite as well as the uniformly distributed un-melted TiC particles. PTA alloying TiC-W-Cr eliminates the stress concentration at the edge of graphite and produced hard carbide, resulting in frequent crack deflection. As a result, the Weibull distribution of fatigue life demonstrates that PTA alloying TiC-W-Cr exhibits longer lives compared to matrix and PTA hardening without reinforcement, but more scattered. In addition, on the basis of the careful observation of fatigue crack growth, it is shown that the fatigue crack growth rate could be retarded by PTA alloying TiC-W-Cr at low stress intensity.     

Duplex stainless steel fracture surface analysis using x-ray fractography

The fatigue fracture surface of a duplex stainless steel was analyzed using x- ray fractography. A lower than average austenite content was observed at the fracture surface due to the transformation of austenite into deformation- induced martensite. The influence of fatigue cycling on the transformation was confined to a depth of about 30 μm below the fracture surface. X- ray analyses of both the ferrite- martensite and the austenite phases indicated residual stresses (σ_r) increasing with depth from the fracture surface and reaching a maximum some tens of microns below the fracture surface. The lower σ_r observed at the fracture surface has been attributed to the stress relaxation effects caused by the new fracture surfaces created in the crack growth process. The observed decrease in full width at half maximum (FWHM) in the ferrite- martensite phase was presumed to be due to the dynamic recovery effect that was likely to occur within the material close to the crack tip as a consequence of fatigue cycling.     

航空发动机风扇叶片裂纹失效分析

航空发动机风扇叶片产生了裂纹故障。通过对故障叶片进行外观检查、断口分析、叶尖端面检查、化学成分分析、硬度检测及金相组织分析,确定了风扇叶片裂纹的性质和产生原因。结果表明:风扇叶片裂纹为高周疲劳裂纹;钛合金风扇叶片与镍包石墨涂层摩擦相容性差,叶片与机匣镍包石墨涂层发生严重摩擦是导致叶片产生早期疲劳开裂的主要原因;同时,结构的应力集中以及振动应力也会引起疲劳裂纹的萌生及扩展;并提出了相应的改进建议,避免类似故障的发生。     

铌微合金化重载齿轮钢的疲劳性能

利用旋转弯曲疲劳试验方法研究了三种重载齿轮钢渗碳后的疲劳性能。结果表明,添加铌能够细化重载齿轮钢组织,提高渗碳层硬度,从而提高其疲劳强度。同时,疲劳裂纹在渗碳层沿原奥氏体晶界扩展,铌微合金化重载齿轮钢的晶粒细化,从而可以阻碍疲劳裂纹的扩展。此外,扫描电镜观察疲劳断口发现,重载齿轮钢渗碳后疲劳裂纹起源于基体或夹杂物,夹杂物尺寸越小,疲劳性能越好。     

Influence of retained austenite on short fatigue crack growth and wear resistance of case carburized steel

The influence of the amount of retained austenite on short fatigue crack growth and wear resistance in carburized SAE 8620 steel was studied in this article. Different amounts of retained austenite in the microstructure of the carburized case were obtained through different heat treatment routes applied after the carburizing process. The wear tests were carried out using pin on disk equipment. After every 200 turns the weight loss was registered. Four point bend fatigue tests were carried out at room temperature, using three different levels of stress and R=0.1. Crack length versus number of cycles and crack growth rate versus mean crack length curves were analyzed. In both tests the results showed that the test pieces with higher levels of retained austenite in the carburized case exhibited longer fatigue life and better wear resistance.     

不同热处理条件下贝氏体钢的微观组织和疲劳裂纹扩展

以贝氏体钢为研究对象,设计了4种热处理工艺,研究了不同热处理工艺下试验钢的显微组织及疲劳裂纹扩展速率。结果表明,热轧态试验钢的微观组织以粒状贝氏体为主,其上分布有少量的板条贝氏体、马氏体和粗大块状M/A岛,残留奥氏体的体积分数为16.2%,但稳定性较差,裂纹能够直接穿过粗大的块状M/A岛继续扩展,疲劳裂纹扩展速率最快。经900 ℃奥氏体化+空冷后,显微组织以板条贝氏体和马氏体为主,M/A岛仍为粗大的块状,残留奥氏体含量减少至12.3%,疲劳裂纹扩展速率略有降低。经900 ℃奥氏体化+380 ℃盐浴等温30 min +空冷后,显微组织以细密、有序的板条贝氏体为主,残留奥氏体含量减少至10.2%,以薄膜状伴生在板条贝氏体间,板条状贝氏体及板条间的残留奥氏体薄膜会使裂纹端钝化、分叉、偏折,阻碍裂纹扩展的能力增强;经350 ℃回火240 min后,显微组织以马氏体和板条贝氏体为主,残留奥氏体含量比热轧态略微降低,为14.9%;而经450 ℃回火240 min后,显微组织以板条状贝氏体为主,其上分布有少量的马氏体,残留奥氏体体积分数减少至8.6%,也以薄膜状伴生在贝氏体板条间,同时有大量的碳化物析出,裂纹扩展速率最慢。