冰箱压缩机阀片断裂失效分析

压缩机是冰箱的心脏,压缩机阀片的断裂失效可引起制冷系统严重故障。本文利用表面应力分析、金相组织和显微硬度分析、成分分析等方法,以及三维视频光学显微镜、扫描电子显微镜等,研究了阀片断裂的特征和机制。断口和裂纹分析表明,阀片失效是疲劳断裂机制,断口具有明显的疲劳扩展区和多处裂纹源。阀片的材质和组织正常。阀片表面的局部损伤容易引起断裂。塑料垫片和阀片形状设计对断裂失效有重要影响。在上述分析的基础上,提出了质量改进措施并取得了良好效果。     

某发动机Ⅱ级涡轮叶片排气边裂纹分析

对WP13F发动机Ⅱ级涡轮叶片排气边裂纹、断裂进行了汇总分析。该叶片裂纹、断裂都属于以低周疲劳为主的高、低周复合疲劳失效模式；在疲劳起始区均存在一个黑色粗糙区(月牙形多晶区)；断口上存在的大量粗大初生碳化物降低了材料的断裂韧性，加速了疲劳裂纹的扩展。     

汽轮机轴瓦辅助弹簧断裂失效分析

利用直读光谱仪、体式显微镜、金相显微镜、显微硬度仪以及带能谱的扫描电子显微镜等试验手段对断裂弹簧进行了失效试验分析。结果表明,断裂弹簧基体内存在大量尺寸较大的富钒氮化钛类夹杂物。失效弹簧断口可见明显的疲劳辉纹,可观察到清晰的疲劳起裂源、扩展区以及最后的失稳断裂区,具有典型的疲劳失效断裂特征。进一步的分析研究表明,疲劳裂纹起源于次表面的一个富钒氮化钛类夹杂物,疲劳裂纹在交变应力作用下扩展,直至最后失效断裂。     

空压机曲轴断裂失效分析

某空压机曲轴在运行约5 000h后发生断裂失效,通过宏观检验、断口分析、金相检验以及硬度测试等方法,对空压机曲轴断裂原因进行了分析。结果表明:由于曲轴中存在严重的疏松缺陷,在运行过程中于曲轴轴颈和轴拐R过渡表面疏松处萌生裂纹,在交变应力作用下,裂纹以疲劳方式扩展直至曲轴断裂失效。     

伺服机构涡轮泵转子叶片断裂失效分析

某伺服液压源涡轮泵转子在测试过程中转子叶片发生断裂,通过对失效转子的观察、测试与分析认为:转子叶片的断裂性质为疲劳断裂,断裂原因是在叶片根部存在疲劳裂纹,疲劳裂纹在动静载荷作用下失稳扩展而发生疲劳断裂.分析认为转子叶片发生疲劳破坏与其组织在锻造成型工艺过程中存在工艺缺陷,导致材料疲劳寿命下降有关.     

发动机三级涡轮叶片断裂分析

某发动机三级涡轮转子叶片在飞机赶快冰爬升时断裂，通过断口ＳＥＭ观察，ＥＤＡＸ成分分析，叶片基材金相检验和硬度测试等分析了叶片的断裂原因和机制，结果表明，共振是叶片失稳断裂的直接原因，热疲劳萌生裂纹，高温腐蚀疲劳控制裂纹稳态扩展，材料冶金缺陷对叶片断裂过程有促进作用。     

压气机转子叶片掉块断裂分析

某型发动机外场服役中多次出现压气机转子叶片叶尖掉块断裂故障,通过掉块叶片表面形貌观察、断口分析、硬度检测、金相检验、多起失效件的类比分析以及叶片振动模态分析,对叶片掉块断裂原因进行了分析。结果表明:所有压气机转子叶片掉块断裂模式相同,均属振动疲劳断裂掉块;叶片在发动机工作转速范围内存在高阶复合振动点,引起叶片共振是导致其振动疲劳断裂掉块的主要原因;叶片与机匣摩擦导致叶尖局部过烧或形成摩擦热应力裂纹促进了疲劳裂纹的萌生。最后针对叶片掉块断裂原因提出了相应的解决措施。     

某压缩机45钢转轴断裂原因分析

某压缩机转轴在正常工作中突然发生断裂,通过对失效转轴的化学成分、力学性能、显微组织、裂纹及断口形貌进行分析和检验,查明了其断裂原因。结果表明:该转轴断裂为旋转弯曲疲劳断裂;断裂起源于转轴补焊热影响区的沿晶微裂纹,转轴加工过程中表面进行补焊并且补焊工艺控制不当是导致其断裂失效的主要原因。     

某超临界电站锅炉送风机叶片的断裂原因分析

某火电厂超临界锅炉在运行中发生送风机叶片断裂事故。运用宏观检验、金相检验、硬度测试、断口微区分析的方法,对断裂的送风机叶片进行了综合检测分析。结果表明:由于送风机叶片表面及内部存在大量的铸造缺陷,尤其是从铸造缩孔延伸出来的裂纹,极大地降低了叶片的抗疲劳性能;在叶片长期旋转的循环载荷作用下,铸造缺陷处形成的裂纹成为疲劳源,并逐渐扩展直至叶片最终断裂。     

汽轮机叶片断裂原因分析

某热电厂汽轮机组扩容检修时发现末级叶片出现早期断裂的质量问题。采用断口分析、金相检验、化学成分分析、表面硬化层工艺分析等方法,对汽轮机叶片的断裂原因进行了分析。结果表明:该汽轮机叶片的失效机理为疲劳断裂,叶片表面硬化层存在裂纹、气孔、局部未硬化等缺陷,降低了叶片的耐冲蚀能力,是叶片发生早期疲劳断裂的主要原因。     

动叶可调轴流式送风机叶片断裂分析

某电厂一锅炉送风机在投入运行较短时间内即发生叶片断裂事故,严重影响了电厂的安全经济运行。通过化学成分分析、金相检验、力学性能测试、断口分析和能谱微区成分分析等方法对叶片断裂的原因进行了分析。结果表明:导致叶片断裂的主要原因是叶片质量不合格,叶片上存在着十分严重的裂纹类原始缺陷;另叶片材料化学成分不合格,存在较多的铸造疏松缺陷,塑性和韧性较差等也是导致其早期断裂的原因。     

Investigation of the failure of the L-0 blades

A last stage (L-0) turbine blades failure was experienced at the 110 MW geothermal unit after 1 year of operation period. This unit has two tandem-compound intermediate/low-pressure turbines (turbine A and turbine B) with 23 in./3600 rpm last-stage blades. There were flexible blades continuously coupled 360 degrees around the row by loose cover segment at the tip and loose sleeve and lug at the mid-span (pre-twist design). The failed blades were in the L-0 row of the LP turbine B connected to the generator. The visual examination indicated that the group of 12 L-0 blades of rotor B on the generator side was bent and another group of 5 blades at 140 degrees from the first damaged group was also bent. The cover segments were spread out from the damaged blades and had cracks. Laboratory evaluation of the cracking in the cover segments indicates the failure mechanism to be high cycle fatigue (HCF), initiating at the cover segment holes outer fillet radius. The L-0 blades failure investigation was carried out. The investigation included a metallographic analysis of the cracked cover segments and bent blades, Finite Element Method (FEM) stress and natural frequency analysis (of blades/cover segments), fracture mechanics and crack propagation analysis. This paper provides an overview of the L-0 blades failure investigation, which led to the identification of the blades vibrations within the range 250–588 Hz induced due to unstable flow excitation (stall flutter) as the primary contribution to the observed failure.     

Identification of failure mechanisms in nickel base superalloy turbine blades through microstructural study

Failures in gas turbine blades can occur by various mechanisms that are operative at high temperatures. Most frequent ones are the creep and stress rupture. These mechanisms are strongly dependent on the microstructure of the blades and often, they are facilitated due to microstructural degradation that occurs during service exploitation. The study of these failures, therefore, requires detailed microstructural examination. This paper reports the basic microstructural features in cast nickel base superalloys that control the failure mechanisms in gas turbine blades followed by analysis of two service failures. A methodology has been suggested for effective microstructural analysis of turbine blades after service exposure. It has been shown how systematic microstructural study on the turbine blades can be helpful in establishing engine operating conditions.     

Metallurgical investigation into the failure of a chopper blade used for cutting of hot-rolled steel coils

In the present work, failure investigation of a chopper blade received from an integrated steel plant has been presented. Chopper blades are used in chopping machines for cutting trimmed edges of hot-rolled coils into pieces to convert them into scrap. These blades are manufactured from hot forged or rolled billets or flats of high carbon high chromium cold work tool steel. The investigation consists of visual examination, chemical analysis, microstructural analysis through optical and scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and hardness measurement. The chemical analysis confirmed the steel as equivalent to D2 grade in AISI notation. Carbide volume fraction of the broken blade was in the normal range of 10–15% as commonly observed in D2 tool steel. Microstructural examination under light and scanning electron microscopy showed non-uniform distribution of large eutectic primary carbides of irregular morphology forming strings or bands in tempered martensite matrix preferentially aligned in a specific direction. The uneven carbide arrangement in the matrix made the structure highly anisotropic and susceptible to localized stress concentration. The carbides were identified mainly as M₂₃C₆ type. Cracks were observed to initiate at the edges of the blade and propagate to the interior through clustered zones of carbides. SEM study suggests that the crack initiation was associated with decohesion of carbide particles in the cluster which culminated into final fracture by the mechanism of void coalescence and subsequent crack growth.     

GCr15钢旋片式助力泵泵体磨损失效分析

某GCr15钢旋片式助力泵泵体内环面在安装使用后短期内出现较多的断续磨痕,发生磨损失效;采用化学成分分析、金相检验和扫描电镜及能谱分析等方法,对泵体的磨损失效原因进行了分析。结果表明:由于该助力泵叶片在装配工序中装配精度不足,直接影响到叶片与泵体的配合精度,使叶片在高速旋转过程中,与泵体表面发生严重的塑性变形,产生粘着磨损。     

Recrystallization and fatigue failure of DS alloy blades

This paper analyzed cracks and fractures of DS alloy blades. The failure modes and causes were studied on the basis of fracture surfaces and metallographical examination, and prevention measures were given. The results showed that the cracks and fractures failed in the same mode—fatigue failure caused by surface recrystallization of the blades. The surface recrystallization formed during the solution heat treatment because the blades deformed plastically.     

Failure Prevention of Gas Turbine Blades Through Pack Aluminization

Pack aluminization of low-pressure turbine blade of an aero gas turbine engine has been carried out following a well-defined systematic procedure. The process parameters are first optimized on dummy blades, and optimized process is followed for the actual blades for evaluation and testing. Visual and binocular examination followed by metallurgical evaluation has been carried out to validate the process and to establish the adequacy and correctness of the coating. The coated blades are then evaluated through component-level test and engine-level test followed by field evaluation trials for performance and durability. The results of engine-level tests and inspection post-accelerated mission test cycles ensure that the blades with aluminide coating can withstand severe engine operating cycles without any damage or failure which otherwise would have experienced. The failure-free operation for an equivalent TBO life and post-AMT condition of blades are an indication of enhanced life of aluminide blades and prevention of failure of the turbine blades through pack aluminization.     

Failure analysis of the final stage blade in steam turbine

A failure case of the low pressure blades of steam turbine is presented in this paper. The suction side of blades has been quenched to improve the erosion resistance. Cracks with different lengths were found in the quenched region of final stage blades after about 13,200 h service. The failure analysis of blades was performed in terms of composition analysis, microstructure and mechanical tests, etc. The yield strength and tensile strength conform to the corresponding standard, whereas the elongation, area reduction and impact toughness are lower than the criteria. From the crack morphology, fractography and composition analysis on the fracture surface, it was found that the failure mechanism of blades is the environment-assisted fatigue fracture. The location of fatigue crack initiation is related with the salient of blades due to the stress concentration. In order to decrease the blade cracking susceptibility, the increment of tempered temperature in both modified treatment and high-frequency hardening was recommended.     

Thermo-mechanical Fatigue Failure of a Low-Pressure Turbine Blade in a Turbofan Engine

This paper concerns a failure analysis case study of low-pressure turbine blades in an aero-engine. The operational condition of the engine was studied, and metallurgical investigations were carried out on two fractured blades. The failure in one blade originated at the leading edge, while in another it originated at the trailing edge then propagated in the forward direction. The crack propagation region showed mixed mode fractographic characteristics before the final failure. The mixed mode region was considered indicative of a thermo-mechanical fatigue propagation mode. Surface analysis of the blades indicated oxidation of variant thicknesses including oxide-filled intergranular cracks and grain boundary thickening beneath the oxide layer. It is considered more probable that the mechanism was more oxidation and fatigue dominated as opposed to creep-related.