大粒径磨料作用下高铝砖气固冲蚀磨损的"粒径效应"

以平均粒径分别为0.28 mm、0.40 mm、0.52 mm、0.80 mm的棕刚玉为磨料对I等高铝砖进行常温垂直气固冲蚀磨损试验,对磨料和靶材冲后表面进行扫描电镜显微结构分析,在宽粒径范围内研究磨料粒径对靶材耐磨性与冲蚀机制的影响.借助ANSYS/LS-NYNA软件建立多粒子冲蚀模型,分析不同磨料粒径下的冲蚀行为.结果表明:I等高铝砖出现"粒径效应",临界粒径0.40 mm;靶材最大等效应力随磨料粒径的增加而增加;平均粒径≥0.40 mm时磨料发生破碎,0.28 mm、0.40 mm、0.80 mm磨料冲蚀下靶材的主要冲蚀机制分别是基质和骨料微切削、基质和骨料断裂、缺陷处断裂.     

一种考虑介质污染度的液压泵轴尾机械密封磨损的计算方法

为了准确计算液压柱塞泵机械密封的磨损,基于有限元方法提出一种考虑污染度水平和机械密封运动工况的磨损量计算方法。首先,针对单个磨粒模型建立机械密封表面的有限元模型,并基于实际工况进行仿真;然后对仿真和实验数据进行回归分析,确定单个磨粒造成的磨损量;最后研究介质中多种磨损颗粒对机械密封表面磨损的综合影响,提出一种考虑油液污染度的液压柱塞泵轴尾密封磨损的计算模型。通过对轴尾密封的表面观测结果,验证机械密封的磨损形式,并计算得出实际磨损量。通过对比基于提出的模型的解析结果与实际观测结果,证明提出的方法在计算含污染颗粒的机械密封磨损量时的有效性。     

Microstructure,mechanical and wear properties of aluminum borate whisker reinforced aluminum matrix composites

The microstructural features and the consequent mechanical properties were characterized in aluminium borate whisker (ABOw) (5, 10 and 15 wt.%) reinforced commercially-pure aluminium composites fabricated by conventional powder metallurgy technique. The aluminium powder and the whisker were effectively blended by a semi-powder metallurgy method. The blended powder mixtures were cold compacted and sintered at 600 °C. The sintered composites were characterized for microstructural features by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. Porosity in the composites with variation in ABOw contents was determined. The effect of variation in content of ABOw on mechanical properties, viz. hardness, bending strength and compressive strength of the composites was evaluated. The dry sliding wear behaviour was evaluated at varying sliding distance at constant loads. Maximum flexural strength of 172 MPa and compressive strength of 324 MPa with improved hardness around HV 40.2 are obtained in composite with 10 wt.% ABOw. Further increase in ABOw content deteriorates the properties. A substantial increase in wear resistance is also observed with 10 wt.% ABOw. The excellent combination of mechanical properties of Al−10wt.%ABOw composites is attributed to good interfacial bonds, less porosity and uniformity in the microstructure.     

WC-Ni硬质合金密封圈损伤失效研究

某核主泵采用的WC-Ni硬质合金O形密封圈在运行一段时间后,密封圈端面出现较多的裂纹。为研究密封圈端面损伤失效原因,对密封圈损伤区进行微观形貌分析、白光干涉测试分析、损伤区化学成分分析和表面残余应力测试,讨论WC-Ni硬质合金密封圈表面出现的损伤特征,并对其服役安全性进行评估。结果表明:裂纹源多在密封圈槽堰区和坝区的交界处产生,裂纹多数分布在坝区,坝区损伤程度相比槽堰区较大;裂纹区存在氧化现象,但氧化程度比较轻微,氧化产物主要为W的氧化物;裂纹的产生主要是由密封圈槽堰区和坝区之间较大的应力差导致的,但裂纹体积较小,损伤轻微,短期内不会对整体机械密封装备造成重要影响。     

耐磨合金钢的回火脆性、变质处理及组织遗传性

探讨了耐磨合金钢的回火脆性、变质处理及组织遗传性3个特征对其组织与力学性能的影响,分析了获得高性能耐磨合金钢的关键问题和方法。     

Cutting performance and wear mechanism of Sialon ceramic tools in high speed face milling GH4099

This work aims to reveal the cutting performance and wear mechanisms of Sialon ceramic tools for the high-speed face-milling of GH4099, with the goal of improving this process as well as designing more advanced ceramic cutting tools in the future. At the outset of this study, several single-factor experiments were designed with speed as a variable to gather various data on such tools. Failure patterns and tool life curves were first obtained through cutting tests. Afterwards, the tools were split at their place of wear (middle of notch and 1/2 depth of cut) to prepare for further analysis. Wear morphology and element composition distribution in the depth direction of the corresponding interface were then analyzed using a field emission scanning electron microscope (FE-SEM) and energy dispersive spectrometer (EDS) to explore potential diffusion and/or chemical wear. Finally, studies were conducted into the tools’ chemical wear under specific cutting conditions, finishing with a theoretical verification based on the thermodynamic principle of chemical reactions. This research discovered that notch wear was the main failure pattern for the high-speed face-milling of GH4099 under the suitable cutting conditions. Overall, the optimal cutting speed was 1000 m/min, with a tool life of about 3 min. Compared with cemented carbide tools, the machining efficiency for Sialon ceramic tools increased by over a factor of 16. The wear mechanisms for such tools demonstrated a mixture effect of abrasive, adhesive, diffusive and chemical wear. Diffusive wear mainly occurred in their flank faces, but did not constitute the main mechanism of notch wear; chemical wear proved to be a key reason for notch wear at higher temperatures. Based on the aforementioned research, this paper concludes with a proposed comprehensive model for notch wear.     

An investigation on machinability assessment of Al-6XN and AISI 316 alloys: an assessment study of machining

This work presents machinability assessment of AL-6XN super austenitic stainless steel alloy. Cutting forces, surface roughness, work hardening tendency and tool wear were analyzed. The assessment was conducted based on a comparison between the AL-6XN alloy and the well-known alloy in the machining field AISI 316. Finite element analysis (FEA) study was also conducted and used in this assessment. Experimental results showed maximum increase of 70% and 57% in the feed and normal forces of the AL-6XN alloy, respectively. Maximum increase in the work hardening tendency of 59% was recorded for the AL-6XN alloy while only 29% was recorded for the 316 alloy. The roughness analysis recorded an increase of 186% for the AL-6XN alloy compared to the 316 alloy. Tool wear analysis revealed the build-up edge formation, severe chipping, flank and crater wear (CW) during cutting AL-6XN alloy whereas small chipping, flank and CW were noticed during cutting 316 alloy. FEA study showed when the AL-6XN alloy machined using 65 and 94?m/min cutting speeds, the increases (compared to the 316 alloy) were: 12% and 8% in plastic strain; 20% and 20% in stresses; 48% and 100% in residual tensile stresses; 22% and 92% in residual compressive stresses, respectively.     

Advanced Friction–Wear Behavior of Organic Brake Pads Using a Newly Developed System

The objective of this study was to investigate the influence of an advanced performance system on the tribological behavior of brake pad material using a specially designed brake pad tester system following standard SAE J-661. The tribological behavior and friction and wear characteristics of the organic brake pad samples were evaluated. During braking tests, the samples, in contact with a cast iron disk, were studied at different disc speeds, temperatures, and braking cycles under a constant pressure. In order to understand the friction and wear behavior, the unworn surfaces, worn surfaces, and wear debris were characterized by means of scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX). Furthermore, the surface characteristics and differences in the wear modes of the brake pad samples were examined. Wear debris was permitted to deform the brake pad surfaces, leading to friction layers and enabling the estimation of the friction behavior of the brake pads. The results showed that the best friction–wear behavior was obtained with lower braking cycles at low speeds and temperature. Thus, the newly developed brake pad tester system proved very effective in evaluating the performance of the brake pad samples.     

Microstructure and Wear Behaviors of Plasma-Sprayed FeCrNiMoCBSi Coating with Nano-Grain Dispersed Amorphous Phase in Reciprocating Sliding Contact

A novel FeCrNiMoCBSi amorphous/nanocrystalline coating was fabricated using a plasma spraying process. The coating was dense with a low porosity of approximately 0.99%. The coating consisted of a 67.8 vol% amorphous phase coupled with many nanocrystalline grains that were approximately 5?nm in diameter. The mechanical properties of the as-sprayed coating were determined by nanoindentation measurement, and the tribological behaviors were systematically investigated in a reciprocating sliding contact. The results show that FeCrNiMoCBSi coatings possess superior wear resistance compared to other typically similar Fe-based amorphous coatings. The tribological behaviors evolve with the combination of normal load and sliding velocity. Herein, the dominant wear mechanisms are delamination wear and oxidation wear. With an increase in normal load and sliding velocity, the abrasive wear is gradually weakened, the formation of oxide films on the worn surfaces is facilitated, and wear debris is ground to powder. The oxide films suffer from fatigue wear with induced cracks undergoing reciprocating sliding effects.     

Enhancing the Tribological Behavior of Lubricating Oil by Adding TiO2, Graphene,and TiO2/Graphene Nanoparticles

This article investigates the tribological behavior of nanoparticles (NPs) of titanium dioxide anatase TiO₂ (A), graphene, and TiO₂ (A) + graphene added to the pure base oil group ΙΙ (PBO-GΙΙ). The morphology of these two nanostructures of TiO₂ (A) and graphene was characterized by transmission electron microscopy (TEM). Oleic acid (OA) was blended as a surfactant into the formulation to help stabilize the NPs in the lubricant oil. A four-ball test rig was used to determine the tribological performance of six different samples, and an image acquisition system was used to examine and measure the wear scar diameter of the stationary balls. Field emission–scanning electron microscopy (FE-SEM) was used to examine the wear morphology. Energy-dispersive X-ray spectroscopy (EDX), element mapping, and Raman spectroscopy were employed to confirm the presence of (TiO₂ (A) + graphene) and the formation of a tribolayer/film on the mating surfaces. Moreover, a 3D optical surface texture analyzer was utilized to investigate the scar topography and tribological performance. The experiments proved that adding (0.4?wt% TiO₂ (A) + 0.2?wt% graphene) to the PBO-GΙΙ optimized its tribological behavior. These excellent results can be attributed to the dual additive effect and the formation of a tribofilm of NPs during sliding motion. Furthermore, the average reductions in the coefficient of friction (COF), wear scar diameter (WSD), and specific wear rate (SWR) were 38.83, 36.78, and 15.78%, respectively, for (0.4?wt% TiO₂ (A) + 0.2?wt% graphene) nanolubricant compared to plain PBO-GΙΙ lubricant.