发动机涡轮导向器叶片掉块分析

某发动机试车后,检查发现一片高压涡轮导向叶片排气边掉块.应用扫描电镜、光学显微镜等,对掉块叶片断口及其金相组织进行了系统地分析与检验.结果表明,该叶片掉块性质为烧蚀掉块,烧蚀掉块的原因是叶片排气边局部出现瞬时高温.     

高速铁路钢轨表面伤损分析

某路段高速铁路钢轨发生伤损,主要表现为浅层状龟裂掉块.采用金相显微镜、扫描电镜、背散射电子衍射取向成像技术、透射电镜、显微硬度计等对钢轨的正常部位和伤损部位进行了分析.结果表明:钢轨踏面龟裂掉块是由于列车启动时车轮短时打滑空转,致使钢轨表面承受巨大的摩擦力,表层金属发生剧烈塑性变形,温度瞬时升高到奥氏体化温度以上进而又...     

摩托车发动机排气阀断裂原因分析

对断裂的摩托车发动机排气阀进行宏观、金相、化学及断口分析。结果表明,排气阀氮化过程中表面未形成具有抗蚀性能的致密ε相,导致其抗氧化性能下降,在工作过程中排气阀由于受到高温及氧化气氛的作用发生氧化腐蚀疲劳,最终导致断裂。     

日立公司制造的Φ1020×4320轧辊剥离掉块失效分析

日立公司离心复合铸造的高合金Φ１０２０×４３２０轧辊在鞍钢厚板厂使用中发生低寿命剥离掉块失效。本文通过超声探伤、ＳＥＭ断口、金相及微区成分分析查明剥离掉块起源于轧辊最后凝固的热节区，由于冶金质量低劣致使该区夹渣缺陷集中、材料脆化、内外层间熔合不良，从而导致轧辊冷热疲劳抗力下降发生低寿命剥离掉块失效。     

日立公司制造的Φ1020＊4320轧辊剥离掉块失效分析

日立公司离心复合铸造的高合金Φ１０２０＊４３２０轧辊在鞍钢厚板厂使用中发生低寿命剥离掉块失效。本文通过超声探伤、ＳＥＭ断口、金相及微区成分分析查明剥离掉块起源于轧辊最后凝固的热节区，由于冶金质量低劣致使该区夹渣缺陷集中，材料脆分，内外层间熔合不良，从而导致轧辊冷热疲劳抗力下降发生低寿命剥离掉块失效。     

埋地压力管道检测方法及要点解析

随着石油、天然气工业发展迅速,我国现有集输管道达30万公里,长输管道达7.3万公里,公用管道(包括城市燃气管道和城市热力管道)达7.18万公里.由于埋地管道输送的介质大多具有易燃、易爆、有毒或腐蚀等特点,一旦发生泄漏或断裂往往引起火灾、爆炸、中毒等灾难性事故.同时,埋地管道的高     

排气阀杆早期断裂失效分析

对某批早期断裂的排气阀杆进行了成分分析和金相观察,对其断口也进行了宏观和微观观察分析。结果表明:该批排气阀杆锁槽早期断裂主要是由于阀杆组织存在表面粗晶层,在高频率冲击应力作用下,阀杆的锁槽处形成严重的能量集中和表面应力集中,从而在锁槽圆周产生多个裂纹源。同时,阀杆内部大量分散的夹杂物又形成内部应力集中源,加速排气阀杆的断裂,导致阀杆早期断裂。     

4Cr9Si2钢中富硅区引起的脆性断裂研究

针对4Cr9Si2钢排气阀锁夹槽的异常断裂问题,应用热场发射扫描电镜和能谱分析等方法分析了断裂部位的成分、微观组织和形貌.重点分析了钢中富硅区的微观组织,并与粉末包埋热扩散法获得的渗硅层的微观组织进行了对比.结果表明,4Cr9Si2钢排气阀锁夹槽处断裂属严重脆性断裂,源于钢中硅元素的局部严重偏聚引起的组织不均匀,以及富硅区的固有脆性和调幅组织引起的性能不均匀.     

提高热处理炉前金相检验速度

热处理现场生产的炉前金相检验,是保证生产工艺和提高产品质量的重要手段。例如汽车、拖拉机、机床等机械装备的齿轮及其许多零件渗碳(或碳氮共渗)均须按规定的标准进行金相检验,否则就达不到既定的性能。如碳化物多(级别高),容易在磨削中产生裂纹,使用中剥落掉块。残余奥氏体多(级别高),零件在使用中容易产生麻点、沟槽、不耐磨损。又如汽车万向节U型螺栓金相组织不符合要求,容易断裂,这要造成翻车事故,车毁人亡。生产中的炉前金相检验,力求快而准,即保证能看准金相组织的     

某发动机轴承失效原因分析

在对某发动机工作过程中轴承失效的基本特征进行综合分析的基础上,确定了轴承失效属早期发生的疲劳剥落导致的最终失效,轴承早期疲劳剥落与滚棒上沿晶断裂特征有关.对滚棒非正常的沿晶脆性断裂进行了热处理模拟和金相组织以及断口分析,结果表明,掉块主断面上典型的沿晶断裂特征与该滚棒在热处理时局部接触900℃以上的高温有关.     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.