镀铬层在固定磨料挤压作用下的磨损行为

通过在调质、淬火和氮化基体上镀硬铬，分析了镀层在法向载荷作用下的磨损及镀层结合强度等。指出调质基体镀硬铬的耐磨性和镀层结合强度最好，其中载荷与磨料粒度对耐磨性均有影响，以磨粒度的影响更大。其磨损机制包括滑动靡损、压痕磨损、疲劳剥落等。具体的机制与基体强度、磨料度、载和试样形状有关。３５ＣｒＭｏ钢镀铬后基体力学性能在试验镀层厚度范围里未发生变化。     

准贝氏体钢渗碳特性及磨损性能研究

研究了准贝工体钢渗碳特性及渗层磨损性能。结果表明，准贝氏体钢渗碳后空冷，渗碳最外层为高碳马氏体和残留奥氏体组织，无碳化物及石相析出；心部为准贝氏体组织，渗层碳浓度及浓度梯度平缓，显示出准贝氏体渗碳特性。磨损试验表明，渗碳后不同温度回火，准贝氏体钢渗层耐磨性接近和超过１８Ｃｒ２Ｎｉ４ＷＡ渗碳钢水平，二体磨料磨损朵制以微切削机制为主，三体产磨损以应变疲劳为主，准贝氏体钢可作为渗碳钢代替含 高Ｃｒ、Ｎｉ     

WC_p/高锰钢基复合材料及复合结构的冲击磨损性能

采用挤压铸造法制备出WC_p/高锰钢基复合材料和复合材料-钢复合结构,研究复合材料和复合结构的冲击磨料磨损性能。在复合结构的WC预制体中及周围添加还原Fe粉,以控制复合结构中复合材料-钢的界面结构。结果表明:复合结构中复合材料-钢的界面在还原Fe粉吸热熔化的作用下,并没有出现复合材料中WC的熔解和形成过渡层的现象。复合材料磨损表面发生材料的崩落,耐磨性低于高锰钢,而复合结构耐磨性比高锰钢提高了1.34倍。通过对磨损形貌及组织的分析,讨论了复合材料崩落的原因及复合结构对冲击磨料磨损改善的机理。     

贝氏体和马氏体耐磨钢的高温磨损性能对比研究

目前,对贝氏体和马氏体耐磨钢在高温环境下的磨损性能研究较少。利用销盘磨损试验机,对400 HB级低合金贝氏体耐磨钢NR400和马氏体耐磨钢NM400的高温(400℃)耐磨性能进行了对比研究,利用扫描电镜及台阶仪等对其组织及磨损表面进行分析,并对磨损机理进行了探讨。结果表明:由于NR400钢具有高硬度、较好的回火稳定性和韧性,其磨损率小于NM400钢的,高温耐磨性较好;NM400钢的磨损机理主要为磨粒磨损、氧化磨损和疲劳磨损,NR400钢的磨损机理主要为磨粒磨损和氧化磨损。     

耐磨材料中残余奥氏体在磨损中的结构变化及其影响

通过x衍射分析、薄膜透射电镜分析和亚表层硬度分析,研究了GCr15和高铬铸铁两类耐磨材料中残余奥氏体在磨料磨损中的结构变化及其影响。试验结果表明,磨损中相当数量的残余奥氏体发生马氏体转变,形成密排六方ε型马氏体,提高表面硬化程度,改善一定磨损条件下材料的耐磨性。     

粗晶TM52钢结硬质合金的冲击磨料磨损性能研究

系统对比研究了粗晶粒TM52钢结硬质合金与分别采用真空烧结和低压烧结制备的细晶粒TM52钢结硬质合金在不同冲击功工况下的抗磨料磨损性能与行为,并在对磨损面形貌进行电镜观察分析的基础上探讨了粗晶粒TM52钢结硬质合金的磨损机理。研究发现,粗晶TM52合金的抗磨料磨损性能随着冲击功的逐步提高呈现先下降后增强的变化规律,这与其高锰钢基体在高冲击功条件下的高硬化速率及硬化效果更快、更充分有关。相对于细晶粒钢结硬质合金,粗晶粒TM52钢结硬质合金在抗冲击磨料磨损方面具有明显的性能优势,尤其在高冲击功(3~4J/cm~2)条件下,耐磨性能可提高40%~80%。在此工况下磨损机制主要为碾碎性磨料磨损、擦伤式磨料磨损和疲劳磨损,凿削式磨料磨损不明显。     

涂层疲劳损伤声发射特征参数及损伤机理

使用超音速等离子喷涂设备在1045钢基体上制备了铁基合金涂层。以球盘式接触疲劳试验机为平台,研究了涂层接触疲劳损伤过程中声发射特征参数的变化规律,并分析了涂层的接触疲劳损伤机理。结果表明,在转速为2500r/min和应力水平为1.58GPa实验条件下,点蚀是涂层的主要失效形式,表现为在涂层磨痕轨迹范围内出现大量的点蚀坑,点蚀坑深度为20～30μm。涂层表面粗糙的微凸体与轴承球滚压接触产生黏着磨损,以及涂层、磨粒、滚动轴承三者形成三体磨料磨损是点蚀失效产生的主要原因。声发射幅值、有效值(Root Mean Square,RMS)、能量、计数和平均频率对涂层表面粗糙微凸体去除、弹塑性变形、裂纹萌生、裂纹稳定扩展和失稳扩展过程比较敏感,并且在不同的疲劳损伤阶段具有不同的信号反馈特点。     

新型高强韧性高耐磨性奥氏体—贝氏体钢

以新的合金设计思想,研究了一种由奥氏体和贝氏铁素体组成的普通低合金高碳钢——奥氏体-贝氏体钢。实验结果表明,这种材料具有有很高的屈服强度、韧性与加工硬化能力,在高应力尤其是强烈冲击磨料磨损条件下耐磨性十分优异,是抗高应力、强烈冲击磨料磨损的理想材料。     

介稳奥氏体锰钢磨粒磨损与拉伸变形行为及其组织变化

通过拉伸变形和冲击磨粒磨损试验,结合X射线衍射、SEM、TEM、热图、电子探针和Mossbauer谱等分析手段以及经验价电子理论和热力学计算,研究了(4～13)Mn-1C和6Mn-(1～3)Cr-1C钢的耐磨性、合金元素与碳在基体中的分布、应变诱发马氏体相变和加工硬化机制。结果表明,在低冲击功下以6Mn-2.5Cr钢耐磨性最佳。随着冲击功的增大,介稳奥氏体锰钢的耐磨性降低,而高锰钢的增强。低温时效可提高介稳奥氏体锰钢在较高冲击功下的耐磨性。碳与合金元素原子在水韧处理状态奥氏体锰钢中以C-Me形式,在低温时效状态者中以-C-Me-C-Me-形式呈短程有序偏聚分布,并存在着合金元素原子优先处于碳的第一近邻倾向。在磨损和变形过程中,水韧处理状态介稳奥氏体锰钢诱发得到无碳马氏体和合金马氏体,无碳马氏体首先形成,合金马氏体在变形量较大的条件下产生。时效处理状态介稳奥氏体锰钢只诱发得到无碳马氏体。马氏体相变受固相奥氏体中原子间共用电子对数目控制,其值越大相变阻力越大。热力学计算表明,对于介稳奥氏体锰钢,KPC模型与实际最接近,规则溶液模型次之,LFG模型相差最大。 介稳奥氏体锰钢的加工硬化机制是应变诱发马氏体相变和剩余奥氏作的动态应变时效。其耐磨机制是磨面高度加工硬化、诱发相变提高了基体的抗疲劳性能,以     

Ti6Al4V基体及其改性试样的冲击磨损行为分析

在Ti6Al4V合金基表面制备了N+注入与氮化层、TiN膜及DLC膜,进行小载荷反复冲击,分析不同冲击周次下磨痕形貌及磨坑深度,比较磨损性能。结果表明疲劳磨损是反复冲击条件下实验试样的共同失效机制,主要表现为疲劳剥落。改性后试样的抗冲击磨损能力较基体材料均有提高,其中N+注入与氮化的"长程强化效应"使试样在较高冲击周次保持良好的抗磨性能;晶态结构TiN膜层由于较高的表层硬度,提高了试样的耐磨性,尤其是较低的冲击周次下;DLC膜的特殊非晶态结构,使其在整个冲击过程中具有小的磨损深度,高的失效周次。     

Matrix microstructure effect on the abrasion wear resistance of high-chromium white cast iron

The two-body abrasion resistance of high-chromium white cast iron was investigated as a function of cast iron microstructure. Different microstructures were obtained by means of heat treatment. The chromium and carbon content were chosen in order to have different matrix microstructures (austenitic, martensitic and ferritic) with the same amount of eutectic carbide (M₇C₃). The results show that the cast iron with an austenitic matrix has the best wear resistance. The good wear resistance of this material is due to strong work hardening of the austenitic matrix resulting in a hardness which exceeds that of other structures. The effect of abrasive paper deterioration on abrasion has also been investigated.     

Effect of surface nanocrystallization on the tribological properties of 1Cr18Ni9Ti stainless steel

Surface nanocrystallization of 1Cr18Ni9Ti austenite stainless steel was conducted by the supersonic fine particles bombarding (SFPB) technique. The friction coefficients and wear losses in air and vacuum were tested to analyse the effect of surface nanocrystallization on the tribological properties of 1Cr18Ni9Ti steel. The results show that the microstructure of the surface layer was refined into nano-grains successfully by SFPB treatment; furthermore, strain-induced martensitic transformation occurred during the treatment. The tribological properties of SFPB treated samples enhanced greatly, The dominant wear mechanism of the original 1Cr18Ni9Ti stainless steel is abrasive wear and adhesive wear, while it transfers to the combined action of fatigue wear, abrasive wear and adhesive wear after surface nanocrystallization by SFPB.     

Laser surface alloying of case hardening steel with tungsten carbide and carbon

Abstract

The laser surface alloying process was used to introduce two different alloying materials, tungsten carbide (WC/Co) and carbon, into the molten surface of a case hardening steel (16MnCrS5), to improve its hardness and wear resistance. The chemical composition and the resulting microstructure in the alloyed layers were of particular interest in this investigation, because the strengthening mechanism was strongly dependent upon the type and amount of the alloy material. For laser alloying with carbon the increase in hardness and wear resistance was based on the martensitic transformation in the composition range concerned. For alloying with tungsten carbide it was necessary to consider two different strengthening mechanisms, namely, martensitic transformation and precipitation of carbides. In both cases the grain refinement in the laser affected zone had an additional effect. Resistance to dry abrasive sliding wear was measured using a conventional pin-on-disc wear testing machine. For both alloy materials the wear rate was substantially lower than that of a substrate that had been laser remelted without alloying additions.

MST/1556     

WC颗粒增强铁基复合材料的性能研究

通过离心法制备了外径290mm,内径130mm,高72mm,WCp/Fe-C复合材料工作层厚度25～30mm的厚壁环形试样.通过光镜、扫描电镜和性能试验设备研究了两种不同WCp体积分数WCp/Fe-C复合材料的力学性能、耐磨损性能和抗热疲劳性能,并与硬质合金和高铬铸铁进行比较.结果表明WCp体积分数在80%和65%左右的两种WCp/Fe-C复合材料,其抗拉强度达到了320和348MPa,冲击韧性均＞4J/cm^2,硬度为HRC63.5和HRC61.5.20和40N载荷下的耐磨性分别达到208.33、90.91和127.06、57.14,抗热疲劳性能优良.与硬质合金和高铬铸铁相比,WCp/Fe-C复合材料的冲击韧性、抗热疲劳性能以及20和40N载荷下的耐磨性均有大幅度提高.     

Fracture surfaces and the associated failure mechanisms in ductile iron with different matrices and load bearing

Ductile iron (DI) is a family of cast alloys that covers a wide range of mechanical properties, depending on its matrix microstructure. For instance, ferritic matrices used in parts, such as automotive suspension components, demand high impact properties and ductility among some of their main requirements. On the other hand, pearlitic and martensitic matrices are used when hardness, strength and wear resistance are of particular concern. When it comes to very high strength parts, ausferritic matrices, typically austempered ductile iron (ADI), are widely used.DI has been employed to replace cast and forged steels in a large number of applications and its production has shown a sustained rate of growth over the last decades.Knowing about failure modes and fracture mechanisms associated to materials with the properties mentioned above is crucial, since they can be of great value for designers of mechanical components.This paper deals with the analysis of fracture surfaces of ductile cast iron generated under different conditions of load application, temperature and environments.The studies include the examination of fracture surfaces obtained by means of tensile tests, impact tests and by samples used to determine fracture toughness properties, where the zones of fatigue pre-crack and monotonic load condition were evaluated. A special case of ductile iron fracture is also examined.The study of the different surfaces permitted to establish patterns that contributed to unveil the fracture mechanisms of ductile iron with different matrices, nodule count, etc.     

Martensitic transformation and work hardening of metastable austenite induced by abrasion in austenitic Fe-C-Cr-Mn-B Alloy - a TEM study

Abstract

The martensite transformation and work hardening of metastable austenite induced by abrasive wear in an austenitic Fe-C-Cr-Mn-B alloy were studied by TEM. The results show that an α' martensitic transformation occurred to form an elongated and equiaxial cellular dislocation substructure and the untransformed austenite matrix produced an equiaxial cellular dislocation substructure on the abraded surface. Electron diffraction patterns of the abraded material are composed of diffraction rings with series of broken arcs resulting from a fine grain structure and the deformation texture. The work hardening zone of austenite at the subsurface reveals heavy slip bands and deformation faults, at which the dislocations pile up. Examples of ? martensite induced by abrasive wear can be detected. The α' martensite transformation and metastable austenite work hardening should bring about an increase in surface hardness and wear resistance. Additionally, the cellular dislocation substructure of α' and γ have a significant effect on increasing the hardness of the wear surface. Observation by TEM indicates that the α' martensite transformation happens more easily in the austenite matrix near the carbide (Fe, Cr)₇C₃ as a result of the depletion of carbon and chromium.     

不同类型颗粒混合增强铁基复合材料的磨损性能

采用电流直加热动态热压烧结工艺制备陶瓷颗粒增强铁基复合材料,研究高体积分数(25%,30%,35%)下,单一类型颗粒(SiC,TiC,TiN)及混合类型颗粒(TiC+TiN,SiC+TiN,SiC+TiC)作为增强相对铁基复合材料磨损性能的影响。结果表明:单一类型粒子强化时,TiNP/Fe复合材料的耐磨性最好,TiCP/Fe次之,SiCp/Fe最差。混合粒子作为增强体时,(TiC+TiN)P/Fe复合材料磨损性能显著优于其对应的单一颗粒增强材料;其中粒子含量为30%时,(TiC+TiN)P/Fe复合材料磨损性能提高最大,其磨损量比TiCP/Fe降低了51.9%,比TiNp/Fe复合材料降低了44.1%,体现出可贵的混合增强价值。(SiC+TiC)_P/Fe和(SiC+TiN)P/Fe复合材料的磨损性能分别处于对应的两个单一颗粒增强材料之间。磨损表面观察表明,耐磨性好的(TiC+TiN)P/Fe复合材料的磨损机理为磨粒磨损,而(SiC+TiC)_P/Fe和(SiC+TiN)P/Fe复合材料除磨粒磨损外还存在明显的疲劳磨损现象。     

Abrasive wear property of bainitic nodular cast iron in laser processing

The effects of the different austenitizing and isothermal transformation temperature and time on the wear resistance in bainitic ductile iron has been investigated and compared with surface hardening by laser processing, to find the best wear resistance for the bainitic ductile iron. It was found that the wear resistance of the lower bainitic ductile iron was better than upper bainitic ductile iron, and that the factor affecting hardness and wear properties the most was the isothermal transformation temperature. After surface hardening by laser processing, the hardening reached RC 55 or more, no evidence of any difference between the lower and the upper bainitic ductile iron being found.     

Austempered ductile iron: an alternative material for earth moving components

Traditionally steels have enjoyed some kind of monopoly in earth movement applications like ripper tips and grader blades. Earth movement demands that the material possesses both wear resistance and toughness. Ironically, the limitation of steels is that it is difficult to get a good combination of these properties. Recent research efforts in earth movement have focused on austempered ductile iron (ADI) as an alternative material, which exhibits both these properties. ADI is obtained when ductile cast iron is accorded a special heat treatment known as austempering. Before the usage of ADI can flourish, there is a need to thoroughly understand its mechanical and tribological behaviour. This paper details the heat treatment of ductile iron to yield ADI and also examines its mechanical and abrasive wear properties. These properties are compared with those of a proprietary quenched and tempered (Q&T) steel used in applications requiring wear resistance. Typically, when a load of 0.25 N mm⁻² is used, the relative abrasion resistance (RAR) of ADI austempered at 375 °C with an initial hardness of 315 Hv is 2.01, while that of a Q&T steel, of hardness 635 Hv is 2.02. The good wear resistance exhibited by ADI despite the low initial hardness can be attributed to the surface transformation of retained austenite to martensite during abrasion. This phenomenon has been positively confirmed by XRD.