Evidence of Superposition between Grooving Abrasion and Rolling Abrasion

In ball-cratering wear tests, two abrasive wear modes are commonly observed, grooving abrasion and rolling abrasion, which act in distinct areas. Observing this tendency, the aim of this article is to discuss the characterization of an intermediate condition, in which the superposition of the grooving and the rolling abrasive wear modes is observed. This phenomenon is referred to as microrolling abrasion due to the following particular characteristic: the rolling abrasion was found to act on the grooving abrasion. Additionally, in a defined sliding distance range and normal force range, microrolling abrasion is qualitatively observed to be proportional to the sliding distance and inversely proportional to the normal force.     

Friction and Wear Behavior of Steels under Different Reciprocating Sliding Conditions

The friction and wear behavior of ISO 100Cr6 steel ball sliding against conventionally hardened carbon and low-alloy steels was studied. The effect of hardness, hardening capacity, normal load, and sliding speed on the coefficient of friction and friction energy was investigated. Friction tests were carried out, without lubrication and under ambient conditions, on a reciprocating friction tester in which a ball-on-flat contact configuration was adopted. The results showed that there is a relative tendency for the friction properties to decrease with increased hardening capacity and decreased hardness. The results showed that increasing normal load decreases the coefficient of friction for the two steel nuances. However, increasing sliding speed increases the coefficient of friction of low-alloy steel and decreases the coefficient of friction of carbon steel. The oxidation of wear debris influences the wear mechanisms and friction behavior.     

On the Abrasion of Ultrafine WC–Co Hardmetals by Small SiC Abrasive

Abrasive wear of a series of WC-(5–14 wt.%)Co hardmetals was investigated employing P800 and P120 SiC abrasive papers. It was found that if fine abradant was utilized, submicron grades demonstrated substantially higher wear rates than the coarse grades. Such a behaviour was associated to different wear mechanisms operating for fine and coarse grades and correlated to the ratio of the abrasive size to size of the hard WC phase.     

磨料水喷嘴的优化设计

为提高磨料水射流加工设备中磨料水喷嘴加工性能,通过实验研究了磨料水喷嘴几何形状对喷嘴磨损的影响,并研究了磨料水喷嘴机械结构和加工性能,最终确定优化加工条件.     

Effect of Rub-Groove Wall Angle on the Leakage of Abradable Stepped Labyrinth Seals

Rub grooves are generally formed in gas-turbine labyrinth seals of the abradable type during various transients. The rub-groove shape, often the slope angle of the groove downstream wall, varies and largely depends on the rotordynamics and the thermal expansion rates of the rotor and the stator. The effect of rub-groove shape on stepped labyrinth seal leakage was studied by varying the slope angle of the groove downstream wall, using various tooth axial positions and various prerub radial clearances. The investigation was done for compressible flow, with air as the working fluid. A finite volume method was used to solve the two-dimensional axisymmetric, Reynolds-averaged Navier-Stokes equation system. The high-Reynolds-number k-? turbulence model was used along with wall functions. It was found that the wall angle of rub groove has a significant effect on the leakage as well as on the flow pattern. For the cases considered here, when the seal operates with the tooth positioned axially within the rub-groove axial width, the leakage decreases with an increase of the rub-groove downstream wall slope angle. However, for operation when the tooth lies axially just downstream of the groove, the leakage is slightly increased with an increase of the rub-groove wall angle. For cases with a certain tooth axial position and prerub radial clearance, a small change of groove sloping wall angle results in a large change in flow pattern.     

Wear and corrosion resistance of alumina dies for isothermal semi-solid processing of steel

The tool wear of high-purity alumina (Al₂O₃) dies applied in semi-solid extrusion of steel X210CrW12 under near-isothermal conditions at 1250–1350 °C is investigated. Results show excellent wear resistance of the Al₂O₃ dies against semi-solid steel and scale under experimental conditions. Minor chemical interaction was observed at the die inlet which, in contrast to the die land, is in contact with scale formed on the billet during pre-heating. This effect is attributed to the appointed billet pre-heating procedure. A tribochemical interaction mechanism between alumina dies and semi-solid steel is presented. This paper contributes to the evaluation of a self-heating ceramic tool concept for steel thixoextrusion introduced previously. Results lead to the conclusion that the targeted benefit of applying corrosion resistant but thermal shock-sensitive ceramics as die materials for the semi-solid processing of steel is achieved.     

The Influence of Molecular Oxygen on Wear Protection by Surface-Active Compounds

Four-ball wear experiments were performed with zinc di-n-oc-tyldithiophosphate (ZDP), bis [N,N′-dihexyl(dithiocarbamato-s,s′)] nickel (II) (NiDTC) and tetraoctylthioperoxydiphosphate (TPDP) dissolved in a synthetic hydrocarbon base stock. The experiments were conducted both under air and under nitrogen atmospheres. The reactivities of these compounds towards peroxy radicals were evaluated by measuring the uptake of oxygen during peroxy radical titration experiments.

Atmospheric oxygen profoundly influenced metal wear protection by ZDP. This was reflected in the wear rate, wear asymmetry, production of soluble iron, and in the composition of the surface layers produced on the metal. Oxygen had little effect on results with TPDP. The NiDTC exhibited oxygen sensitivity intermediate to tile other additives. The influence of oxygen on the wear behavior of these compounds was paralleled by their relative reactivities toward peroxy radicals.

Ancillary experiments showed that the activation of ZDP as a highly effective antiwear agent cannot be unambiguously ascribed to peroxy radical reactions. An initial electron transfer step is suggested as an alternate working hypothesis to account for the experimental results.     

TiN、CrN的环境摩擦磨损对比研究

采用直流叠加脉冲偏压电弧离子镀技术在45钢表面沉积了TiN、CrN薄膜。用显微硬度计测试了薄膜的硬度,用划痕仪测量了薄膜的膜基结合力,用球-盘式摩擦磨损试验机评价了不同介质条件下（干摩擦、水润滑、油润滑）TiN、CrN薄膜的摩擦学特性,用表面轮廓仪测试了薄膜磨痕处的磨损轮廓,用扫描电镜（SEM）观察了薄膜磨痕形貌。结果表明,相对于干摩擦条件下,在水润滑和油润滑条件下TiN和CrN薄膜的摩擦因数和磨痕深度都有所降低。在相同的介质条件下,CrN薄膜的摩擦因数和磨痕深度始终小于TiN薄膜。     

三体磨损过程理论研究

建立了三体磨损过程中摩擦副表面粗糙度的预测模型。算例表明 ,定载荷作用下 ,(1 )经受三体磨粒磨损之摩擦表面的粗糙度随着磨程的进行逐渐趋于某一平衡值 ,之后不随磨程而改变 ;(2 )平衡粗糙度的大小与磨粒粒度分布参数有关 ,对应于粒度的某均方根值 ,摩擦面的平衡粗糙度最大     

Evaluation of the Reciprocating-Wear Behavior of Unlubricated Hypereutectic Al-Si Alloys

The reduction of abrasive and scuffing wear between aluminum and cast-iron wear-pairs is an important goal for the automotive industry given the implications for improved engine performance and reliability. Hypereutectic aluminum-silicon alloys such as B390 may help lead the way towards this goal because of their potential for wear resistance and durability. Yet, despite this potential, B390 has not been evaluated under the severe reciprocating conditions typical of automotive applications. Moreover, the influence of various manufacturing and processing steps on the resulting wear resistance of the alloy has not been studied at all. To help fill this void, a series of unlubricated tests were conducted using cast, spray-formed, spray-formed then extruded, and semi-solid formed variations of B390 reciprocated against gray cast-iron under a constant contact-stress. Originally, the weight-loss per reciprocating distance was measured and converted to volume-loss to determine the steady-state wear rates for each alloy variation. However, it was determined that debris from the mating cast-iron surface was adhering to the B390 and obscuring the actual material lost to wear. To compensate for the trapped iron debris, the volume-loss was directly calculated from the changing contact area or “flat” originally measured for the loading adjustments. After this correction, the data indicated that the spray-formed, spray-formed then extruded, and semi-solid formed all experienced measurable, albeit modest decreases in their wear rates relative to the cast B390. However, there were not any significant disparities in the observed wear rates between the spray-formed, spray-formed then extruded, and semi-solid formed hypereutectic alloy despite their processing and microstructural differences.     

Tribological Properties of PTFE and PTFE Composites at Different Temperatures

The friction and wear properties of polytetrafluoroethylene (PTFE) and its composites with fillers such as bronze, glass fiber, carbon fiber, carbon, graphite, and polymer were studied at ambient temperature and high temperature. The wear resistance and hardness were enhanced by the fillers. Results showed that the wear resistance of all composites was much higher than that of pure PTFE. Pure PTFE has the lowest friction coefficient at ambient temperature (temperature: 23 ± 2°C, humidity: 50 ± 10%) but highest friction coefficient at high temperature (above 100°C). The PTFE composite filled with bronze showed the best wear resistance at ambient temperature but the poorest wear resistance at high temperature. The carbon-graphite- or polymer-filled PTFE composite showed a lower friction coefficient and moderate wear resistance at both ambient and high temperature.     

Abrasion of cemented carbides by small grits

The abrasion properties of a series of cemented carbides with different carbide grain sizes, different amounts and types of binder phases have been investigated under varied conditions. Abrasion results from other works are also incorporated for comparison reasons. The results are interpreted in the light of a previously published model for the abrasion properties of multiphase materials, although this is the first time this model is applied to materials with very high amounts of hardphase. It is confirmed that the abrasion resistance of tungsten carbide–cobalt materials may vary considerably, also for fixed amounts of metal and hardphase. Not only the wear resistance level but also the ranking depends both on the test conditions and on the microstructure. It is further showed that some nano-crystalline materials posses a wear resistance superior to those of the pure carbide material.     

Abrasive erosive wear of powder steels and cermets

Composite materials produced by powder metallurgy provide solutions to many engineering applications that require materials with high abrasive wear resistance. The actual wear behaviour of a material is associated with many external factors (abrasive particle size, velocity and angularity) and intrinsic material properties of wear (hardness, toughness, Young modulus, etc.). Hardness and toughness properties of wear resistant materials are highly dependent on the content of the reinforcing phase, its size and on the mechanical properties of the constituent phase. This study is focused on the analysis of the (AEW) abrasive erosive wear (solid particle erosion) using different wear devices and abrasives. Powder materials (steels, cermets and hardmetals) were studied. Wear resistance of materials and wear mechanisms were studied and compared with those of commercial steels. Based on the results of wear studies, surface degradation mechanisms are proposed. The following parameters characterizing the materials were found necessary in materials creation and selection: hardness (preferably in scale comparable with impact), type of structure (preferably hardmetal type) and wear parameters characterizing material removal at plastic deformation.     

MoSi2/45#钢在油润滑状态下的摩擦学性能研究

在M - 2 0 0型磨损试验机上进行了金属间化合物MoSi2 / 4 5 # 钢的摩擦磨损试验 ,考察了载荷和润滑状态对MoSi2 材料摩擦磨损性能的影响 ,采用扫描电子显微镜 (SEM)和微探针观察了其磨损形貌 ,并分析了其磨损机理。结果表明 :油润滑明显改善了MoSi2 材料的摩擦学性能。MoSi2 材料的磨损机理在低载荷 (5 0～ 80N)下主要表现为疲劳磨损和磨粒磨损 ,高载荷 (12 0N以上 )下以氧化磨损为主。载荷为 15 0N时 ,MoSi2 材料具有较好的综合摩擦磨损性能 ,摩擦系数和磨损率分别为 0 1和 0 0 0 9g·km-1。     

Simulation of textured surface topography during a low wear process

Wear experiments were conducted on a block-on ring tester. The stationary block made from cast iron of 50 HRC hardness was ground. The rotated ground ring was made from 42CrMo4 steel of 32 HRC hardness. The rings were modified by a burnishing technique in order to obtain surfaces with oil pockets. Oil pockets of spherical and of drop shape were tested. The correlation and regression analysis of parameters of textured surface topography was carried out. Two sets of surfaces were analysed: after machining and after “zero-wear”. As the result of analysis, minimum number of parameters describing this surface kind was obtained. A simple truncation model of the ring surface change was used. Worn surface topographies, after a low wear, were also modeled in a different way. An idea of the proposed method of surface topography modeling is imposition of random surface of Gaussian ordinate distribution on the base surface (after burnishing). The modeled surfaces were correctly matched to the measured surfaces in 90% of all analysed cases. Basing on the simulation, the local wear values during a low wear process were calculated and compared with experimental ones.     

Fretting wear behaviors of steel wires under friction-increasing grease conditions

Fretting wear tests were performed on the self-made fretting wear rig to investigate fretting wear behaviors of steel wires under friction-increasing grease conditions. The results demonstrated that the fretting regimes were dependent on displacement amplitudes and normal loads. The friction coefficient exhibited different variation trends in different fretting regimes. Friction-increasing grease changed the fretting running behavior and had a very good wear resistance for steel wires. Wear was slight in partial slip regime. Mixed regime was characterized by plastic deformation, fatigue cracks and abrasive wear. Slip regime presented main damage mechanisms of abrasive wear, fatigue wear and oxidation.     

The Slow-Speed Wear Behavior of Case-Carburized Gears Lubricated with NLGI 00 Grease under Boundary Lubrication Conditions

NLGI 00 greases are often used to lubricate gears running at low pitch line velocities, such as, for example, in large open gear drives. At low pitch line velocities, sliding wear, which under these operating conditions is referred to as slow speed wear, is often the limiting factor to gear lifetime. A thorough knowledge of the effect of different grease components on the wear behavior is therefore important when selecting a grease to effectively reduce gear wear in a given gear drive. In order to systematically investigate and analyze the influence of different grease components on the slow-speed wear behavior of case-carburized gears, systematic gear tests using the Gear Research Center's (FZG) back-to-back gear test rig were conducted. Primarily, the focus of the experimental investigations is on the influence of the base oil viscosity and type, the additive type, and also the type of soap thickener on the gear wear behavior at low pitch line velocities. To experimentally determine the influence of these different grease components on the wear behavior of case-carburized gears, a modified, more stringent wear test, based on the standard DGMK slow-speed wear test for gear oils, was developed. Different NLGI 00 greases with base oil viscosities between ν₄₀ = 70 and 1,200 mm²/s were investigated.

Base oil type and base oil viscosity were shown to have only a minor effect on the wear behavior under boundary lubrication conditions. On the other hand, the thickener type and especially the additive type play an important role in determining the wear behavior.     

The effect of nitrogen on the scratch resistance of austenitic stainless steels

High nitrogen stainless steels (HNSS) are being considered a new promising class of engineering materials. When nitrogen is added to austenitic steels it can simultaneously improve fatigue life, strength and wear and localized corrosion resistance. In this work, a single pass pendulum scratch test was used to study the effect of nitrogen on the scratch resistance of an UNS S30403 austenitic stainless steel. Samples with increasing nitrogen contents at the surface were obtained through high temperature gas nitriding. The thermochemical treatments were performed at 1473 K in (N₂+Ar) gas atmospheres for 36.0 ks, obtaining fully austenitic cases (surface nitrogen contents up to 0.5 wt%) ca. 1.5 mm in depth. The scratch tests were performed in a single-pass pendulum, equipped with strain gages to measure normal and tangential forces during scratching. The specific absorbed energy was calculated as the ratio between the measured absorbed energy and the amount of mass removed from the specimen. An increase of the specific absorbed energy with increasing nitrogen content was observed. The results of the scratch tests were analyzed taking into account the stress–strain behavior during depth sensing indentation tests and the energy absorbed during Charpy impact tests. The improvement in scratch resistance due to nitrogen alloying was attributed to the strong hardening effect of nitrogen in solid solution, which does not affect significantly work hardening and toughness. A comparison between the scratch resistance and the cavitation-erosion resistance, measured in previous work, was made too.     

Friction and Wear Characteristics Due to Stick-Slip under Fretting Conditions

Friction and wear characteristics between two steel surfaces under fretting conditions are investigated experimentally. The fretting damage caused by low-amplitude oscillatory sliding can be classified into three regimes of gross-slip, mixed-slip, and partial-slip due to the stick-slip phenomenon. One of the most important characteristics of fretting wear is the transition from gross-slip to mixed-slip. Several criteria have been introduced for a quantitative determination of the transition between mixed-slip and gross-slip. However, the transition criteria have some problems in determining the regimes because parameters are difficult to calculate or depend on the system. To introduce new transition criteria in this study, the phase difference between friction force and relative displacement is used to determine the transition and predict the fretting wear. It is found that the phase difference with a range of 0° to 90° can predict the onset of fretting conditions.