随钻仪器钻铤的断裂失效分析

利用光学显微镜、扫描电镜进行组织观察,通过力学性能测试、微动磨损测试等试验方法,对一种随钻仪器无磁钻铤的断裂失效原因进行了分析。结果表明,该随钻仪器钻铤在使用过程中发生了微动磨损,在工件过渡锥角根部形成了环形磨损凹槽。环形磨损不仅使钻铤有效直径减小,而且在带有弯曲的复杂载荷下,易在环形磨损处造成很强的应力集中,最终导致工件的断裂。环形磨损的产生是由于工件装配结构所致,但钻铤取材于原材料锻件半径的1/2位置偏内,此处晶粒较为粗大,硬度低,在同等工况下磨损相对严重。     

工件疲劳强度试验裂纹分析

为研究微动疲劳产生机阻,太原重工轨道交通设备有限公司使用全尺寸疲劳测试的方式,再现了微动磨损裂纹,并通过宏观观察、扫描电镜分析、显微组织检查、低倍分析、拉伸试验,对工件疲劳强度试验后出现的轮座部位的裂纹的性质和形成原因进行了分析。结果表明,工件断裂为疲劳断裂。断裂原因是工件表面由于微动磨损,导致微动疲劳产生接触疲劳裂纹。以接触疲劳裂纹为源,引发严重应力集中型疲劳断裂。     

高氮不锈轴承钢的微动磨损性能

为了探究应力和滑动速度对高氮不锈轴承钢微动磨损性能的影响,采用SRV-Ⅳ微动磨损试验机进行了不同应力和不同滑动速度下的微动磨损试验,对摩擦因数和磨损率进行分析,并对磨斑形貌进行观察.结果表明:试验钢的摩擦因数随应力和滑动速度的增加而减小;磨损率随应力和滑动速度的增加而增加.随着pv值(表示轴承工况的严重程度)的增大,高氮不锈轴承钢的磨损机理由黏着磨损逐渐转变为磨粒磨损和塑性挤出磨损.     

钛合金微动磨损的研究进展

钛合金耐磨性能较差,对微动磨损十分敏感,使其应用和发展受到了一定的限制。为此,总结了钛合金微动磨损性能的影响因素,综述了钛合金抗微动损伤方法的研究进展。目前,关于钛合金微动磨损的研究主要存在两方面的局限性：(1)对于钛合金微动磨损的研究大多是在单一影响因素及稳定参数下进行的;(2)缺乏关于钛合金在特殊工况下微动磨损的研究。因此,未来对于钛合金微动磨损的研究应多结合工业应用中微动磨损的失效实例,加强多因素、变参数以及特殊工况下的微动磨损研究;在掌握微动磨损失效机理的基础上,根据钛合金的特性,探索新型表面处理技术,进一步改善钛合金微动磨损失效问题。     

铜铝聚苯酯涂层性能研究

采用大气等离子喷涂技术制备了铜铝聚苯酯 (CuAl/PHB) 涂层, 对涂层进行了组织、 硬度、 结合强度、 高 温抗氧化、 抗热震、 高温硬度以及微动磨损和可磨耗性能测试和分析研究。 结果表明, CuAl/PHB 涂层孔隙和聚 苯酯占比为 17.5%, 硬度平均值 90.4 HR15Y, 结合强度 ≥25.4 MPa, 在 620 ℃下涂层具备良好的高温抗氧化性能, 700 ℃下水淬抗热震性能达到 135 次, 在 450 ℃ ~700 ℃温度范围内涂层高温硬度由 HR15Y 76.6 降低到 66.8。 在 高载荷 100 N、 高频率 100 Hz, 高温 700 ℃条件下的微动磨损结果表明, 涂层在 620℃下摩擦系数小于 0.5, 具 有良好且稳定的耐微动磨损特性; 涂层在 400 ℃ ~600 ℃模拟工况条件下具有良好的可磨耗性, 叶片进给磨损比 IDR 值小于 14.02%, 且随温度增加可磨耗性提高; 制备的铜铝聚苯酯涂层可实现耐微动磨损和可磨耗的良好结合。     

S45C-A电机转轴疲劳试验断裂原因分析及其应对措施

某S45C-A电机转轴在进行疲劳试验的过程中发生断裂。通过宏观形貌分析、金相显微组织分析、化学成分分析及扫描电镜微观形貌分析等方法,对发生断裂的转轴试样进行了失效原因分析。分析结果表明:转轴断裂是由表面擦伤引起的疲劳断裂,表面擦伤属于零件表面微动磨损的一种。预防零件表面微动磨损,首先要对零件连接部位加强紧配合,使之不出现微振,其次是在零件连接部位填充润滑油等隔离接触表面。     

超音速等离子喷涂NiCr-Cr_3C_2涂层的组织结构与微动磨损性能

采用超音速等离子喷涂法在1045钢表面制备NiCr-Cr_3C_2涂层,分析涂层的微观结构及化学成分以及涂层的晶粒结构,利用MICROMET-6030显微硬度仪和Nano-test 600纳米压痕仪测定涂层的显微硬度与弹性模量,通过油润滑微动摩擦磨损试验测试涂层的微动磨损性能。结果表明,NiCr-Cr_3C_2涂层为明显的层状结构,具有单晶、纳米多晶与过渡区共存的复杂晶体学结构,显微硬度HV0.3高达998,约为基体材料硬度的3倍,弹性模量为224.6GPa;涂层的微动摩擦因数随载荷增大而减小,随温度升高而增大。喷涂层的抗微动摩擦磨损性能较基体优异,摩擦因数及体积磨损量分别比基体降低36.7%和55.6%。涂层的磨损机理以磨粒磨损和疲劳剥落为主。     

NC30Fe合金在氯化钠溶液中的微动腐蚀特性

在PLINT微动磨损试验机上附加电化学测试系统,采用十字交叉接触方式,位移幅值为100μm,法向载荷20、50和80 N条件下,研究NC30Fe合金传热管在氯化钠溶液中的微动腐蚀行为.使用电化学工作站记录微动腐蚀过程中开路电位变化,运用电位扫描法测量微动过程的极化曲线;采用扫描电子显微镜观察磨痕的表面形貌,光学轮廓仪测定磨痕的三维形貌及磨损量.微动磨损使损伤区域金属原子活性增大,腐蚀倾向增大,加速了NC30Fe合金的腐蚀.在氯化钠溶液中,NC30Fe合金由于微动磨损过程产生腐蚀产物膜起到润滑减摩作用,摩擦系数较纯水中降低;但因腐蚀与磨损的交互作用,在氯化钠溶液中的磨损量比纯水中高.氯化钠溶液中的磨损机制主要表现为磨粒磨损和剥层的共同作用.      

冲击微动磨损条件下304不锈钢管道的变薄现象

 为了探究高温高压下不锈钢管变薄的原因,采用高温冲击微动试验机,对核电站压水反应堆所使用的304不锈钢管进行微动磨损试验。结果表明,冲击微动磨损受机械和化学作用及其交互作用的影响,磨损量大于单纯的微动与冲击之和,并且磨损更易受到化学作用的影响。随着水温升高,磨损量和磨损深度增加。当温度超过90 ℃时,磨损量趋于稳定。随着振动频率的增加,磨损量和磨损深度减小。     

位移幅值对Inconel600合金微动磨损性能和机制的影响

采用高精度微动磨损试验机SRV Ⅳ研究蒸汽发生器传热管材料Inconel600合金在不同位移幅值下的微动磨损行为,分析了位移幅值对摩擦因数和磨损体积的影响.采用光学显微镜和扫描电子显微镜观察磨损表面和截面的形貌,并用透射电子显微镜对摩擦学转变组织进行观察.结果表明:随位移幅值的增加,摩擦因数和磨损体积逐渐增大,材料的微动行为先后经历以黏着为主的部分滑移区以及滑动为主的完全滑移区;磨损机制也由黏着磨损逐步转变为氧化磨损和剥层磨损的共同作用;微裂纹出现在黏着区域和滑动区域的交界处以及滑动区域内;黏着区氧分布密度和磨痕外基体的相一致,氧化主要发生滑动区域;磨痕亚表层的组织发生了严重的塑性变形,产生纳米化现象,摩擦学转变组织的晶粒尺寸约100 nm,远小于原始组织的15~30μm.      

Machining Characteristics of Ce-ZrO2/CePO4 Ceramics

Two-phase mixtures of Ce-ZrO2 and monazite-type CePO4 were fabricated. Drilling and grinding experiments were carried out to investigate the machining characteristics of Ce-ZrO2/CePO4 ceramics. The machined surfaces of ceramics and wear surfaces of drill bits were observed with scanning electron microscope. Material removals and grinding forces were measured. The transgranular fracture of CePO4 grains, intergranular fracture between ZrO2 and CePO4 grains, and ductile deformation of ceramics were observed on Ce-ZrO2/CePO4 machined surfaces. With the increase of CePO4 proportion to composites, drilling material removal rates increases and specific normal grinding forces decreases.There existed rapid wear of conventional metal cutting tool is caused by abrasive wear. The experimental results indicate that the weak interfaces and properties of Ce-ZrO2/CePO4 ceramics have influences on material removal and machinability.     

Early results of combined treatment in Hodgkin''s disease with nitrogen mustard, vincristine, Natulan and prednisone (MOPP treatment)]

High frequency cinematographic films were made of the mode of operation of common oto-surgical drilling instruments on bone and cartilage. Rose bits and surgical fraises of different sizes were used at 5,000-80,000 R.P.M. The evaluation of the slow motion pictures was performed on the running films and by review of single frames. In detail: The preparation of the drilling head on the bone without simultaneous flushing leads to a filling of the cutting channel and decreased cutting. Drop flushing only prevents the increasing soiling of the drilling head if the drop sequence is rapid and which must be markedly increased with increasing R.P.M. of the drilling instrument. Flushing with a stream of water, which definitely prevents soiling, is preferable. Both drop flushing as well as the water stream must continuously wet the drilling head, i.e. must be absolutely centric in every case. Safest is the automatic spray flusing which is mounted on the handpiece, but which has so far not been used in oto-surgery. During the preparation, the air space of the working area is always filled with drilling dust or haze. Cutting is always performed tangenitally. The cutting speed lies between 2,9 m/s to 16 m/s. It depends on the R.P.M. of the drilling instrument. A drill head running out of true, even with a gently percussing shaft, touches the bone only with a part of its cutting surface which strikes more vigorously than desired and easily gets soiled, despite flushing. Cutting is therefore less and uncontrolled. An increased feeding energy (pressure on the support) in order to speed up cutting leads to heavy wear of the drilling instrument and unsafety in handling due to jumping of the drilling head. During each contact of a cutter with the bone, coarse fraises with low R.P.M. (5,000 R.P.M. = 83 R/s) show a short stopping of the rotation which results in a jerk and vibration of the whole preparation and can thus lead to a damage of the inner ear.     

包覆机主轴腐蚀疲劳断裂分析

40CrNiMo包覆机主轴使用中出现异常断裂。为了弄清断裂原因,通过宏观观察、扫描电镜及能谱仪分析、光学显微观察对断轴进行了深入探讨,结果表明：主轴断裂为腐蚀疲劳失效,由于主轴钢质较差,在环境介质浸蚀下,主轴表面形成一些腐蚀坑,并在应力集中作用下,发展成微裂纹;微裂纹在循环工作应力作用下不断扩展,最终导致主轴疲劳断裂失效。可通过提高钢材质量,降低环境腐蚀性以及改善热处理工艺等措施加以解决。     

Fretting Fatigue Behavior of 304 Austenitic Stainless Steel Considering the Effect of Mean Stress and Tensile Overload

Effect of mean stress on fretting fatigue behavior of 304 austenitic stainless steel has been investigated by conducting fretting fatigue tests at a constant contact pressure of 100 MPa under three different mean stresses i.e., 0, 350 and 450 MPa. For comparisons, plain fatigue tests were also carried out. The influence of tensile overload on fretting fatigue life was also investigated. The results showed that with an increase in mean stress, the reduction in fatigue strength due to fretting increased drastically from 51% at 0 MPa mean stress to 71% at 450 MPa mean stress. The application of tensile overload during fretting fatigue had significant influence on the fretting fatigue lives when the tensile overload was above yield strength. The fretting variables, i.e., tangential stress and relative slip amplitude were measured during fretting fatigue tests. Fracture surfaces were examined using scanning electron microscope. The results have been discussed based on the tangential stress measurement, relative slip amplitude evaluation during fretting fatigue and fracture surface examinations.     

WEAR MECHANISMS DUE TO DIFFERENT ROCK DRILLING CONDITIONS

Abstract

Depending on the type of rock and on the drilling procedure used in rock drilling, cemented carbide is exposed to greatly differing mechanical and thermal conditions. These influence the properties of the cemented carbide required. By means of metallographical examination of rock drill inserts used under different conditions, it has been possible to determine what type of wear mechanism is critical in each case. Two kinds of mechanisms in particular were found to have a great influence on performance. When a drill is run under conditions of high mechanical stress and high temperature, which is the condition present when drilling in highly abrasive rocks, a major factor influencing performance is the creep resistance of the cemented carbide. One way of improving this property appears to be to increase the grain size. Percussive drilling in low-abrasive rock, where the mechanical stress is moderate, gives rise to another wear mechanism. In this, high thermal stresses are induced which lead to the formation of cracks and sometimes to rupture. Thus for this kind of application good thermal-crack resistance is important. During percussive drilling in rocks, with intermediate abrasivity, both mechanisms are active, making the choice of cemented carbide for this application more difficult.     

CQ-160高气压环形潜孔钻车液压制动系统设计

CQ-160高气压环形潜孔钻车是井下新型潜孔凿岩设备,主要用于非煤地下矿山及隧道、水利等岩土工程中进行全方位大直径深孔凿岩。本文详细阐述其制动液压系统工作原理及主要元件的参数计算方法。     

钛合金榫头微动疲劳试验研究现状与发展

综述了涡轮发动机钛合金叶片榫头微动疲劳失效的两种试验方法(轴向微动疲劳试验和榫型微动疲劳试验)的研究现状。轴向微动疲劳试验技术适用于微动疲劳失效机理的研究,应用于抗微动疲劳防护层试验验证的研究也较多;而榫型微动疲劳试验技术则多用于力学分析和模型建立等方面。榫头微动疲劳问题的研究还远未完善,应综合运用微动磨损、轴向微动疲劳和榫型微动疲劳等技术,并配合有限元分析手段,开展微动疲劳机理、多因素影响及防护层作用等方面的系统研究。