Correlation between abrasive wear resistance and changes in structure and residual stresses of steels

The connection between the structure and abrasive wear resistance of steels was studied. Samples of AISI 1020, 1040 and 1080 steels were tested. The initial hardness of the samples ranged from HV221 – for annealed steel AISI 1020, to HV868 – for water quenched and tempered at 180°C steel AISI 1080. Two‐body abrasive tests on silicon carbide abrasive paper of grit size 1200–240 were carried out on a friction machine under identical conditions for all specimens. X‐ray studies of the specimens were conducted before and after these tests. It was shown that characteristics such as the integral width of diffraction lines could be used as a universal indicator of abrasive wear resistance for steels, independently of their heat treatment. The compressive residual stresses in the surface layers of the steels were observed. The results showed that there is a correlation between abrasive wear resistance and the sign and magnitude of residual stresses in the surface layers of steels, as well as between abrasive wear resistance and the structural changes in these layers. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comments on the sliding wear of metals

The author reviews selected experimental results which have contributed to improved understanding of sliding wear processes. The emphasis is on the chemical and structural changes which occur at and near the surface of metallic materials during sliding in different environments. The importance of plastic deformation, fracture, transfer, mechanical mixing, phase transformations and oxidation is discussed. Examples of transitions are described, and interesting correlations noted. In selecting the content of this paper, the author includes controversial results and conclusions and raises questions about the development of wear equations, interpretations of the wear coefficient, the importance of adhesion, the roles of hardness, the causes of transitions and the location of debris-producing cracks.     

Investigations on the influence of graphite filler on dry sliding wear and abrasive wear behaviour of carbon fabric reinforced epoxy composites

In this experimental study, the dry sliding wear and two-body abrasive wear behaviour of graphite filled carbon fabric reinforced epoxy composites were investigated. Carbon fabric reinforced epoxy composite was used as a reference material. Sliding wear experiments were conducted using a pin-on-disc wear tester under dry contact condition. Mass loss was determined as a function of sliding velocity for loads of 25, 50, 75, and 100 N at a constant sliding distance of 6000 m. Two-body abrasive wear experiments were performed under multi-pass condition using silicon carbide (SiC) of 150 and 320 grit abrasive papers. The effects of abrading distance and different loads have been studied. Abrasive wear volume and specific wear rate as a function of applied normal load and abrading distance were also determined.The results show that in dry sliding wear situations, for increased load and sliding velocity, higher wear loss was recorded. The excellent wear characteristics were obtained with carbon-epoxy containing graphite as filler. Especially, 10 wt.% of graphite in carbon-epoxy gave a low wear rate. A graphite surface film formed on the counterface was confirmed to be effective in improving the wear characteristics of graphite filled carbon-epoxy composites. In case of two-body abrasive wear, the wear volume increases with increasing load/abrading distance. Experimental results showed the type of counterface (hardened steel disc and SiC paper) material greatly influences the wear behaviour of the composites. Wear mechanisms of the composites were investigated using scanning electron microscopy. Wear of carbon-epoxy composite was found to be mainly due to a microcracking and fiber fracture mechanisms. It was found that the microcracking mechanism had been caused by progressive surface damage. Further, it was also noticed that carbon-epoxy composite wear is reduced to a greater extent by addition of the graphite filler, in which wear was dominated by microplowing/microcutting mechanisms instead of microcracking.     

The formation mechanism and the influence factor of residual stress in machining

Residual stresses generated in cutting process have important influences on workpiece performance. The paper presents a method of theoretical analysis in order to explicate the formation mechanism of residual stresses in cutting. An important conclusion is drawn that the accumulated plastic strain is the main factor which determines the nature and the magnitude of surface residual stresses in the workpiece. On the basis of the analytical model for residual stress, a series of simulations for residual stress prediction during cutting AISI 1045 steel are implemented in order to obtain the influences of cutting speed, depth of cut and tool edge radius on surface residual stress in the workpiece. And these influences are explained from the perspective of formation mechanism of residual stress in cutting. The conclusions have good applicability and can be used to guide the parameters selection in actual production.     

残余应力测试技术的进展与动向

针对几种常见的残余应力测试方法的研究进展与应用现状,指出了较为成熟的残余应力测试方法是盲孔法和X射线法,但盲孔法受限于对测试对象有损伤,X射线法受限于测试条件的苛刻,其它的残余应力测试方法在有效性、准确性和操作简便性等方面还不能很好地满足工业需求.而利用压痕法测量残余应力是一个值得关注的研究动向,在局部压载作用下,材料...     

The influence of surface oxidation on the wear resistance of cast iron

This paper reports a study of the influence of surface oxidation on the wear resistance of ductile iron, grey iron and vermicular iron during dry sliding friction. The mechanisms of wear are also reported. This study shows that the effect of surface oxidation (formed under normal atmospheric conditions) on the wear rate depends on the complex functions of graphite morphology and matrix structure. Generally the presence of surface oxidation decreases the wear rate of grey iron but increases the wear rate of ductile iron and vermicular iron when the cast iron has high hardness. This trend is reversed for low hardness cast iron.     

A study on wear resistance of the white layer

The white layer has received some consideration, but there are two different opinions on its wear characteristics. It is considered to be of tribological advantage in some instances. However, the microcracks and voids formed by adiabatic shearing are precursors to fracture and should decrease the wear resistance. As to the white layer previously generated by impact wear, the wear characteristic of the white layer is studied by a pin on disc machine in the present paper. It is found that the white layer causes delamination of material, which increases the wear loss significantly. The delamination of the white layer, being prior to the cutting wear, is the primary wear mechanism for materials with the white layer.     

Dry sliding of plasma-sintered iron—The influence of nitriding on wear resistance

Samples of unalloyed iron were sintered in the presence of an abnormal glow discharge using the confined anode–cathode configuration in order to allow surface enrichment of the sample with atoms from the cathode. AISI 430 and AISI 1020 cathodes were used to sinter the iron with and without Cr enrichment, respectively. The chromium favors the formation of a hard compound layer after nitriding (with a microhardness up to 1300 HV) due to the presence of chromium nitrides. In order to evaluate the wear resistance and surface damage to the samples, dry sliding wear tests were carried out using a block-on-ring system with applied normal loads of 25–150 N. A large scatter in the experimental results was observed for the unnitrided samples. This effect was attributed to the capacity of the materials to undergo a severe-to-mild wear transition during sliding. Nitriding was found to reduce the wear rate by at least one order of magnitude. In particular, the nitrided samples enriched with chromium (540 °C) did not display any damage at 25 N, the lowest normal load used in the present investigation.     

透明BOPP薄膜耐磨性能与材料成分关系的实验方法

提出了一种分析薄膜耐磨性能与材料成分关系的实验方法。该方法使用薄膜划痕图像的灰度共生矩阵特征参数表征薄膜的耐磨性能,建立了薄膜的耐磨性能与材料成分之间的关系。采用Retinex图像增强方法消除图像中的薄雾,并对比了该方法与灰度变换法和同态滤波法的图像增强效果;使用灰度共生矩阵分析薄膜划痕的纹理信息,获得共生矩阵的多个特征参数;用多个特征参数表征的薄膜耐磨性作为多元回归的解释变量,以薄膜材料成分作为被解释变量,建立回归模型;分析回归模型得到解释变量和被解释变量之间关系的定量描述。实验中使用以二元共聚KS359为原料的双向拉伸聚丙烯(biaxially oriented polypropylene,BOPP)薄膜加ABS04S弹性体的比例作为被解释变量,分析得到用特征参数表征的薄膜耐磨性能与该被解释变量之间的复相关系数为0.992,表明该方法具有可行性。     

超声滚压工艺对TC4钛合金表面残余应力的影响

钛合金关节轴承是航空发动机的重要部件之一,但由于其润滑条件较差,极易产生磨损从而导致失效事故。采用超声滚压工艺对钛合金试件表面进行强化试验,以有效增强试件表面耐磨性能和抗疲劳特性,并着重研究静压力、滚压次数和主轴转速等超声滚压强化工艺参数对钛合金表面残余压应力与剪切应力的影响规律。试验结果与理论分析结果表明,残余压应力随着静压力、滚压次数和主轴转速的提高而增大,剪切应力随着静压力、滚压次数和主轴转速的提高而总体减小;滚压后试件表面可获得-2 000～-500 MPa的残余压应力和-600～-300 MPa的剪切应力。超声滚压技术可以有效提高钛合金材料表面的残余压应力,并有效降低表面的剪切应力。     

Quantum-chemical investigation of the effect of grain-boundary segregation on wear resistance of steel

Quantum-chemical calculations of polyatomic clusters modeling the grain boundaries in the surface layer of steel are presented. Along with iron atoms, the clusters contain atoms of doping and impurity elements yielded to the boundary due to grain-boundary segregation. The effect of the chemical composition of segregants on the bond strength between the grains and, ultimately, on the wear resistance of steel is investigated. It is shown that the bond strength of segregated atoms with iron atoms in the surface layer of a metal is a substantial factor affecting the wear resistance.     

激光处理冷轧Q235/40Cr干摩擦试验研究

采用CO2横流式激光器对Q235/40Cr材料进行表面强化处理。使用S-360型扫描电镜观察激光硬化区金相组织及成分并观察表面磨损形貌,采用CHX-1超显微硬度计测量激光强化区断面的显微硬度。通过40Cr与冷轧Q235配副进行干摩擦试验,结果表明,与淬火40Cr配副的Q235的平均磨损速率最小,而与1400 W激光功率处理40Cr配副的Q235的平均磨损速率最大,淬火的40Cr平均磨损速率是激光处理的2~3倍。40Cr磨损为磨粒磨损并有微裂纹产生,Q235以磨粒磨损为主,表面产生较深的犁沟。经激光硬化处理后40Cr的耐磨性要优于正常淬火40Cr的耐磨性。     

Formation of tangential pre-stress as a residual stress and its influence on the tribological performance of nodular cast irons

Since any state of residual stress influences the service behavior of a material, it is of particular interest for engineers and designers to know its benefits to machine parts, and where it can be utilized successfully. From this point of view, mechanical tangential pre-stress as circumferential compressive residual stress has been investigated for wear performance. For this purpose, a thick walled cylinder specimen model was established as a tribo-element, and the force, which will form the desired tangential pre-stress representing residual stress, has been calculated by the rules of elasticity theory. In order to compare the effect of residual stress on the wear performance under dry and lubricated conditions, 0.8 R_e (R_e: unidirectional yield strength) were applied to the nodular cast iron (DDK-40, DDK-60) specimens. Wear test results have been evaluated in terms of two different stress levels, 0 R_e and 0.8 R_e, formed on the specimen.     

Experimental evaluation of the stress distribution on the outer surface of the outer race of conventional and double‐decker high‐precision bearings

Experimental investigations have been carried out on the stress distribution on the outer surface of the outer race of conventional and double‐decker high‐precision bearings (DDHPBs). The investigations, in general, indicate that the overall level of stress variation on conventional bearings in various modes of loading under static conditions is greater than that of DDHPBs having an identical inner bore. The cyclic stress levels have been found to be higher for the outer race of conventional bearings compared to that of DDHPBs. Also, the frequency of stress cycles on the outer race of conventional bearings is greater than that of DDHPBs. A comparison of the stress distribution pattern indicates that, under identical loads, the ratio of deflection to indentation on the elements of DDHPBs and conventional bearings is less than unity. Also, under identical operating conditions, the ratio of stresses due to centrifugal forces on the elements of DDHPBs and conventional bearings of the same bore and outer diameter is less than unity. It is concluded that the life of DDHPBs as compared to conventional bearings should be longer under identical operating conditions.