马氏体钢干摩擦表层磨损裂纹形成的力学条件和微观机制

钢铁材料干摩擦接触表层在较高的法向载荷和滑动速度条件下将产生严重的塑性变形,其内部结构将发生演变。结构演变过程包括晶粒被拉长、细化和纳米化,这些变化将直接影响磨损裂纹的萌生与扩展行为。对干摩擦过程中的应力应变进行计算分析,采用聚焦粒子束定位切割制样(FIB)和高分辨透射表征(HRTEM)技术研究马氏体钢干摩擦过程中的结构演变力学条件和微观机制。结果表明:在干摩擦过程中产生的累积应力应变条件下,严重塑性变形层形成了纳米层片结构,裂纹将首先萌生于这些结构内部。该研究为评估干摩擦接触表层的应力应变条件、分析板条马氏体在塑性变形层的结构演变规律和揭示磨损裂纹形成机制提供了理论基础。     

氟金云母微晶玻璃／轴承钢摩擦磨损的试验研究

在盘销式摩擦磨损试验机上考察了氟金云母玻璃陶瓷与轴承钢的摩擦磨损性能,在不同载荷条件下,测试了摩擦系数和玻璃陶瓷的磨损率,用金相显微镜观察和分析磨损表面形貌,并探讨了玻璃陶瓷材料的磨损机理。结果表明：氟金云母玻璃陶瓷与轴承钢的平均摩擦系数为0．095。在较低载荷下,玻璃陶瓷的磨损失效主要源于疲劳点蚀与疲劳剥落;在较高载荷下,其磨损失效主要源于表层塑性变形与疲劳脆性断裂。     

内燃机车车轴断裂原因分析

通过对断口花样的综合分析，查明了内燃机车车轴断裂的原因，于由轴与轴套接触不当而产生相对运动，致使匹配两表面微振磨损，形成划痕和磨损坑并发展成大量微裂纹，而随后在循环载荷作用下，由微振磨损产生的裂纹处开始发生疲劳裂纹扩展，并导致了最终疲劳断裂。     

基于动载荷谱的齿轮弯曲疲劳寿命预测

为了探讨齿轮弯曲疲劳寿命计算问题,将齿轮疲劳总寿命分为两个阶段,即疲劳裂纹萌生寿命和裂纹扩展寿命.通过ADAMS软件仿真实验齿轮的工作情况,使其接近真实状况,得到齿轮载荷谱.根据齿轮载荷谱,利用有限元ANSYS软件分析在齿轮齿根危险截面处的最大应力.采用断裂力学、雨流法和Miner疲劳损伤累积模型,对考虑动载荷情况下的齿轮弯曲疲劳寿命进行预测,推导了齿根裂纹萌生期和扩展期的疲劳寿命计算公式.在高频疲劳试验机上对算例齿轮进行了双齿脉动加载齿根弯曲疲劳寿命实验研究,理论计算结果与实验结果基本吻合,验证了本文理论分析的正确性.      

15Cr14Co12Mo5Ni2齿轮钢的扭转疲劳特性及裂纹扩展行为

 通过扭转疲劳试验,研究了15Cr14Co12Mo5Ni2钢的扭转疲劳断裂的裂纹扩展行为和夹杂物尺寸与扭转疲劳寿命之间的关系。得到了钢的扭转疲劳极限强度和[τ-N]曲线,15Cr14Co12Mo5Ni2钢的扭转疲劳极限强度为350 MPa,扭转疲劳寿命分散度较大。通过断口观察,发现15Cr14Co12Mo5Ni2钢的疲劳破坏模式以表面破坏和近表面破坏为主,主要由氧化物夹杂引起。通过计算应力强度因子[ΔK]和裂纹扩展门槛值[ΔKth]分析15Cr14Co12Mo5Ni2钢的疲劳裂纹扩展的断裂力学条件,试验钢在断裂过程中受载荷情况为,II型载荷—I型载荷—II型载荷—I＋II型载荷,分别对应起裂源区、纤维区、疲劳裂纹扩展区和瞬断区;当有大裂纹产生时,则不会产生纤维区,受载荷情况则为：II型载荷—I＋II型载荷。通过公式推导和数据拟合得到夹杂物尺寸和15Cr14Co12Mo5Ni2钢扭转疲劳寿命的关系,发现随着夹杂物尺寸减小,钢的[τ-N]曲线向高寿命区移动。当引起裂纹萌生的夹杂物尺寸小于5 μm时,在350 MPa应力下,15Cr14Co12Mo5Ni2钢的扭转疲劳寿命超过107循环周次。     

高应力冲击磨损的白层剥落机制

研究了贝氏体钢经高应力冲击磨损后，试样表层内的组织变化及裂纹形成与扩展特征。实验发现，高应力冲击磨损后，磨损试样表层形成高硬度的白层与变形层。在白层与变形层内均产生不同程度的损伤裂纹。受力后损伤裂纹将向基体内和白层内扩展。裂纹在白层内的快速扩展造成表面白层的脆性剥落。在实验的基础上，作提出了高应力冲击磨损的白层剥落机制模型。     

20CrNi2Mo钢干摩擦磨损行为及次表层马氏体形变

 利用MMU-10试验机,在0.13 m/s的速度下,分组对20CrNi2Mo盘环对摩试样进行100、120、150 N接触载荷下的干滑动摩擦磨损试验。采用SEM、EDS、EBSD表征摩擦磨损后环试样表面和截面的形貌及元素。结果表明,接触载荷为150 N时摩擦因数最低、磨损量最大。摩擦热导致磨损表面出现严重的氧化和脱落材料焊结现象,磨损机制由氧化磨损、磨粒磨损和黏着磨损构成。磨损导致了次表层组织变化,出现严重塑性形变层和马氏体形变层。截面EBSD分析结果反映了表层至次表层的应变,EBSD菊池花样质量从表面朝深度方向逐渐提升,采用EBSD图像分割处理及Band Contrast平均值求解可准确找出磨损导致的形变层终止区域。     

交变振动载荷下Al2O3陶瓷钢摩擦副的摩擦磨损性能

在Al2O3陶瓷/45号钢摩擦副的工作过程中,摩擦副上的载荷不是单一的静载荷加载,而是复杂的振动载荷加载.在新型振动摩擦磨损试验机上采用环一块接触摩擦方式,研究Al2O3陶瓷与45号钢在交变振动载荷条件下的摩擦磨损性能,并与静载荷下的磨损性能进行对比;对陶瓷磨损表面进行扫描电镜观察与能谱分析.结果表明:在于摩擦条件下,交变振动载荷下的磨损量比正常载荷条件下的磨损量要大;交变振动载荷下氧化铝磨损表面产生微裂纹,氧化铝陶瓷的磨损机理是脆性断裂、磨粒磨损和犁沟磨损.在加载交变振动载荷与加载载荷条件下,氧化铝陶瓷磨损表面均覆盖一层金属转移膜,其主要成分为铁的氧化物.     

WC-Co硬质合金疲劳断裂机制研究

疲劳和断裂是硬质合金失效的主要原因之一.主要对WC-Co硬质合金的高周疲劳性能和裂纹扩展行为进行了较为系统的研究.结果表明,WC-Co硬质合金材料表现出明显的疲劳效应,即应力水平的降低伴随着疲劳寿命的上升.在高应力区域,合金的疲劳寿命与强度有关;合金的强度越高,其疲劳寿命越长.随着应力幅值的降低,这种强度与疲劳寿命的联系越来越不明显,特别是进入高周疲劳区域后,高粘结剂含量的合金反而表现出更高的疲劳抗性.疲劳裂纹主要沿晶界和在粘结相中扩展;材料在承受疲劳载荷后,粘结相与WC硬质颗粒之间发生了剥离,这种脱粘造成WC颗粒之间相互错动形成孔隙和微裂纹,这些孔隙和微裂纹相互连接加速了裂纹的扩展并最终导致材料的断裂.粘结相在疲劳过程中产生了大量堆垛层错并发生相变,同时有析出物产生.     

淬火温度对86CrMoV7钢抗接触疲劳性能的影响

冷轧辊接触疲劳剥落是在接触负荷下表层疲劳裂纹萌生扩展的断裂过程,与组织结构和内应力状态有关,是主要失效方式之一。本文研究淬火温度对86CrMoV7钢抗接触疲劳性能的影响。选择840、870、910和950℃四个淬火温度。测定了试样的接触疲劳寿命、硬度、残余应力和残余奥氏体量。并对金相组织、裂纹形貌及剥落断口进行了观察。研究发现,840℃淬火有最高的接触疲劳寿命;硬度和疲劳寿命有一定的对应关系,硬度为62～63HRC时接触疲劳寿命最高,更高的硬度反而使之下降。残余应力与疲劳寿命的关系较为复杂。金相组织对钢的接触疲劳寿命有重要作用:板条马氏体组织比片状马氏体组织抗接触疲劳性能好,适量的残余奥氏体可改善钢的抗接触疲劳性能。不同的裂纹及断口形貌对应不同的接触疲劳寿命。     

Properties of 3Cr2W8V Die Steel With Striations Processed by Laser

 The striations on the surface of 3Cr2W8V die steel were processed by laser. The microstructure, hardness, wear resistance and thermal fatigue behavior of the specimens processed by laser were measured. The appearance and mechanism of thermal fatigue crack propagation in the zone processed by laser were observed and discussed. The results show that the wear resistance and thermal fatigue resistance of materials processed by laser are all better than those of the unprocessed material. The processed zone by laser plays a role in baffling wearing process and crack propagation. The pile nail effect of processed zone is the main factor for improving the wear resistance and thermal fatigue resistance of material.     

稀土对钢轨钢接触疲劳的影响

利用接触疲劳磨损试验机械钢轨／车轮接触疲劳作用,了钢轨钢接触疲劳表面区剖面的形貌,显微结构和硬度。结果表明,稀土可延缓钢表面疲劳裂纹的萌生和扩展,推迟表面剥离,减小裂纹贯穿角和裂纹稳定贯穿,缩小塑性化形范围和改善表面加工硬化效果。     

Effect of Hot Deformation on Formation and Growth of Thermal Fatigue Crack in Chromium Wear Resistant Cast Iron

Chromium wear resistant cast iron is widelyusedin engineering, mining and power industry forits high strength,hardness and wear resistance .Inproduction process , some wear-resistant parts ser-ving in alternative stress due to rapid heating andcooling rate ofteninduces thermal fatigue andresultsinfailure .The badthermal fatigue property of chro-mium wear resistant cast iron is due to eutectic car-bides which distribute as continuous net in matrix.Recent researches showthat hot deformation can …     

Observation of fatigue damage process in SiC fiber-reinforced Ti-15-3 composite at high temperature

Unnotched SiC (SCS-6) fiber-reinforced Ti-15-3 alloy composite is subjected to a tension-tension fatigue test in a vacuum of 2×10⁻³ Pa at 293 and 823 K with a frequency of 2 Hz and R=0.1. Direct observation of the damage evolution process during the test is carried out by scanning electron microscopy (SEM). Test temperature dependent and independent fatigue damage behaviors are observed. The early stage fiber fractures observed at the polished surface are not influenced by the test temperature; however, matrix crack initiation and propagation behaviors differ greatly with temperature. The evolution of interface wear damage also differs with temperature, becoming more severe at 823 K, and the interface wear damage zone increases with the increase of the number of fatigue cycles. The macroscopic fatigue damage appears as a modulus reduction associated with interface sliding, matrix crack propagation, and plastic deformation of the matrix. The deformation zone of the composite tested at 823 K spreads more than that at 293 K. The fatigue life of the composite tested at 823 K is longer than that at 293 K. This behavior is related to the difference in spread of the damage zone in the matrix.     

轧辊材料疲劳裂纹扩展理论计算与分析

辊面剥落是轧辊失效的主要形式之一。依据疲劳裂纹扩展理论,计算了轧辊材料裂纹扩展过程中裂纹扩展速率与应力强度因子幅的关系即da/d N—ΔK,分析了各因素对裂纹扩展速率的影响以及不同轧辊的裂纹扩展特征。结果表明,弹性模量、应力比、残余应力、晶粒度、断裂塑性、工作应力、断裂强度等对轧辊裂纹扩展速率的影响越来越不明显,弹性模量影响最大,而屈强比几乎没有影响;轧辊材料较高的弹性模量、较低的残余应力、较粗大的晶粒、较高的断裂塑性可以有效抑制轧辊裂纹的疲劳扩展;轧辊工作层比心部、支承辊比工作辊、锻钢辊比铸铁辊具有更高的耐裂纹扩展断裂能力。结果有助于分析轧辊失效机理并采取有效措施,防止轧辊剥落。     

冲击载荷对10Mn钢磨损性能的影响及耐磨机制分析

通过水韧处理配合450℃时效热处理工艺,研究10Mn钢在2和5 J冲击载荷下耐磨性能.结果表明,10Mni钢在5J冲击载荷下失重量更少,加工硬化的速率更快,并且在不同冲击载荷下磨损失重量都出现了周期性变化.磨损表面SEM结果表明,表面存在犁削磨损、凿削磨损、裂纹.通过XRD数据对亚表面奥氏体和马氏体体积分数进行定量计算...     

煤矿刮板运输机16Mn钢中部槽的磨损失效分析

研究了煤矿用刮板运输机热轧16Mn钢中部槽磨损表面层磨损形貌特征、显徽组织和硬度分布。试验结果表明，中部槽存在磨料磨损、疲劳磨损、粘着磨损和腐蚀磨损等综合磨损，16Mn钢不能满足中部槽耐磨性要求。改用40Mn2冷轧板中部槽后，耐磨性显著提高，应用表明能满足该部件的耐磨性要求。     

Wear characteristics of TiNi shape memory alloys

The wear characteristics of TiNi shape memory alloys against Cr-steel have been studied. Experimental results indicate that the Ti₄₉Ni₅₁ alloy can exhibit a better wear resistance than Ti₅₀Ni₅₀ alloy due to their higher hardness and pseudoelastic behaviors. Four main mechanisms, adhesion, abrasion, surface fatigue, and brinelling, are found to have important contributions to the wear characteristics of TiNi alloys. The weight loss increases with increasing wear load and sliding distance but decreases with increasing sliding speed. The contact area during sliding wear will be increased due to the variant accommodation and/or pseudoelasticity and, hence, will reduce the average compressive stress and wear damage. Variant accommodation and/or pseudoelasticity can also stabilize the crack tips and hinder crack propagation, hence improving the wear characteristics of TiNi alloys.     

Ultrasonic Fatigue Damage Behavior of 304L Austenitic Stainless Steel Based on Micro-plasticity and Heat Dissipation

Very high cycle fatigue behavior(107-109 cycles)of 304 Laustenitic stainless steel was studied with ultrasonic fatigue testing system(20kHz).The characteristics of fatigue crack initiation and propagation were discussed based on the observation of surface plastic deformation and heat dissipation.It was found that micro-plasticity(slip markings)could be observed on the specimen surface even at very low stress amplitudes.The persistent slip markings increased clearly along with a remarkable process of heat dissipation just before the fatigue failure.By detailed investigation using a scanning electron microscope and an infrared camera,slip markings appeared at the large grains where the fatigue crack initiation site was located.The surface temperature around the fatigue crack tip and the slip markings close to the fracture surface increased prominently with the propagation of fatigue crack.Finally,the coupling relationship among the fatigue crack propagation,appearance of surface slip markings and heat dissipation was analyzed for a better understanding of ultrasonic fatigue damage behavior.