Mechanical performance of the Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CoCrCuFeNi high-entropy alloy system with multiprincipal elements

The Al _x CoCrCuFeNi alloys with multiprincipal elements (x=the aluminum content in molar ratio, from 0 to 3.0) were synthesized using a well-developed arc-melting and casting method, and their mechanical properties were investigated. These alloys exhibited promising mechanical properties, including excellent elevated-temperature strength and good wear resistance. With the addition of aluminum from x=0 to 3.0, the hardness of the alloys increased from HV 133 to 655, mainly attributed to the increased portion of strong bcc phase to ductile fcc phase, both of which were strengthened by the solid solution of aluminum atoms and the precipitation of nanophases. The alloys exhibited superior high-temperature strengths up to 800 °C, among which the Al_0.5CoCrCuFeNi alloy, especially, had enhanced plasticity and a large strain-hardening capacity. Moreover, the wear resistance of these alloys was similar to that of ferrous alloys at the same hardness level, while the alloys with lower hardness exhibited relatively higher resistance because of their large strain-hardening capacity.     

Effect of Oxide Content on the Tribological and Physicomechanical Properties of Filled Polytetrafluoroethylene

The effect of the nature and the amount of oxide fillers on antifriction properties of polytetrafluoroethylene under dry friction conditions with different loads and slow sliding rates is studied. It is established that oxides with a high hardness increase the friction coefficient and reduce the wear resistance of filled polytetrafluoroethylene, but oxides with a low hardness do not give rise to an increase in friction coefficient for polytetrafluoroethylene with a marked increase in its wear resistance, and this is connected with formation of a separating layer at the surface of the friction pair.     

Wear Behavior of a Novel Aluminum-Based Hybrid Composite

In the current research, the dry sliding wear behaviors of 6351 Al alloy and its composite with hybrid reinforcement (ex situ SiC and in situ Al₄SiC₄) were investigated at low sliding speed (1 m s^?1) against a hardened EN 31 disk at different loads. The wear mechanism involved adhesion and microcutting-abrasion at lower load. On the other hand, at higher load, abrasive wear involving microcutting and microplowing along with adherent oxide formation was observed. Initially, under higher load, the abrasive wear mechanism caused rapid wear loss up to a certain sliding distance. Afterward, by virtue of frictional heat generation and associated temperature rise, an adherent oxide layer was developed at the pin surface which drastically reduced the wear loss. The overall wear rate increased with load in alloy as well as in composite. Moreover, the overall wear rate of the composite was found lower than that of the 6351 Al alloy at all applied loads. The ex situ SiC particles were found to resist abrasive wear, while, in situ Al₄SiC₄ particles offered resistance to adhesive wear. Accordingly, the 6351 Al (SiC + Al₄SiC₄) hybrid composite exhibited superior wear resistance relative to the 6351 Al alloy.     

NM400/NM500级矿山机械用钢的高温磨损性能及机理

将直径为5 mm的混合烧结Al₂O₃陶瓷球安装在高温滑动摩擦试验机夹持工具上与耐磨钢组成摩擦副, 研究了耐磨钢与氧化铝陶瓷球在200~300 N、100~400 r·min-1不同载荷下的滑动摩擦行为.结合X射线衍射分析技术和扫描电镜等分析手段研究了NM400和NM500两种耐磨钢在室温~300℃下摩擦界面处材料的氧化物形成、磨损表面形貌和显微组织等行为.随温度升高, NM400和NM500的摩擦系数仍然处于0.27~0.40的范围内, 但两者的平均摩擦系数分别从0.337、0.323逐步降低至了0.296和0.288.在300℃时, 氧化物的产生是摩擦系数略有下降的主要原因.随着温度的升高, 摩擦行为首先以磨粒磨损为主, 随后逐渐发生氧化物的压入-剥离-氧化现象, 使磨损速率略有降低.通过高温摩擦磨损行为与微量氧化模型的分析发现, NM400和NM500钢在室温至300℃的磨损机制是磨粒磨损、挤压变形磨损以及微量氧化物磨损的共同作用.NM500钢表现出更加良好的耐磨性能主要原因是其硬度强度高于NM400钢.在高强微合金马氏体耐磨钢中添加少量合金元素, 使其在高温摩擦过程中产生一定量稳定附着的氧化物, 在一定程度上能够起到降低磨损率的作用.      

Corrosion Resistance of Different Metallic Coatings on Press‐Hardened Steels for Automotive

The corrosion resistance of laboratory press‐hardened components in aluminized, galvanized or galvannealed boron steels was evaluated through VDA 621‐415 cyclic test for the automotive industry. 22MnB5 uncoated steel for hot stamping and standard galvanized steel for cold forming were also included as references. Corrosion resistance after painting (cosmetic corrosion) was quantified by measuring the delamination of electro‐deposited paint from scribed panels. The rusting on their edges was used for determining the cut‐edge corrosion resistance. The corrosion resistance on unpainted deformed panels (perforating corrosion) was quantified by mass losses and pit depth measurements. Zinc‐coated boron steels were found to be more resistant to cosmetic corrosion than the other materials, and slightly more resistant to cut‐edge corrosion than the aluminized one. Red rust apparition could not be avoided due to the high iron content in all these hot‐stamped coatings. The three coated boron steels showed similar performances in terms of resistance to perforation. Aluminized boron steel presents the advantage of being less sensitive to hot‐stamping process deviation. Its robustness has been proved for many years on cars.     

A Study on Influence of Aging Treatment on Sliding Wear Resistance of a Nickel Based Hardfacing Alloy

In the present study, Ni-based Colmonoy 5 was deposited on Type 316L (N) stainless steel. The deposit was aged at 580 and 650°C for 5,000 h to study the influence of aging on sliding wear resistance. The aged deposits show more wear loss due to reduced hardness. However, the reduced hardness after aging was not reflected on wear test at 550°C irrespective of sliding distance. This is due to stability of microstructure as well as the generation of oxide layer during high temperature tests. Subsequently, an empirical relation was developed based on outcome experimental data using full factorial design of experiments in terms of hardness (H), test temperature (T) and sliding distance (D). Based on the empirical relation, it was found that the test temperatures (T) play a predominant role on wear loss than hardness (H) and sliding distance (D). Further, the developed relationships were validated using analysis of variance (ANOVA).     

Heat-Resisting Aluminized Coatings Modified by Chromium Addition Produced on Nickel-Based Alloys

Aluminizing process is an important technology in which aluminum is introduced into the surface of base material. In this work, aluminized layers were produced by the pack cementation process on Inconel 600, Inconel 625 and Nimonic 90 nickel-based alloys. Powder mixture contained 80% of Al and 20% of Fe–Cr. Microstructure, hardness, chemical composition and heat resistance were investigated. The microstructure consisted of intermetallic phases near the surface, and below them, the solid solution was observed. The oxidation resistance at elevated temperature of alloys with the layer was compared with pure alloys. After 20-h annealing at 1000 °C, the phase analysis was carried out. On the Nimonic 90 with aluminized coatings, a lot of Cr₂O₃ and Al₂O₃ oxides were produced, whereas on the pure Nimonic 90, a lot of NiO oxides were observed. It was found that the best heat resistance was obtained for the layer produced on the Nimonic 90.     

Wear behaviour of Fe3 Al intermetallic particle reinforced PM based iron metal matrix composites

Abstract

The wear behaviour of unreinforced and reinforced PM based iron metal matrix composite, the latter containing 10 and 20 vol.-% nano sized Fe₃Al intermetallic particles, was studied as a function of sliding distance under two different loads and dry lubricated conditions. The intermetallic Fe₃Al nanoparticles were prepared by mechanical alloying and used as particle reinforcement with 10 and 20 vol.-% in the matrix. The processing of the composites included mixing and cold compaction followed by sintering at 1120°C. The influence of Fe₃Al additions on the dry sliding wear behaviour was studied at loads 20 and 40 N over sliding distances 2160, 3240, 4320 and 6480 m. The study showed that the composite exhibited a lower wear rate than that of the unreinforced matrix and the wear rate was influenced by the volume percentage of Fe₃Al particles. It is understood that iron aluminide reinforcement has a beneficial effect on the wear properties. Delamination and microcutting were the chief mechanisms of wear for the composites.     

Effects of Pb and Cu additives on microstructure and wear corrosion resistance behaviour of PM Al–Si alloys

Abstract

The wear and wear corrosion resistance of Al–20Si–XPb–YCu (X=0–10 wt-%, Y=0–3 wt-%) alloys fabricated using powder metallurgy technique and subsequent heat treatments were evaluated using a block on ring tribotest. The microstructures of all aluminium alloys were observed using an optical microscope, a scanning electron microscope and an X-ray energy dispersive spectroscope. The evaluation studied the effects of applied potential and environments of dry air and 3·5 wt-%NaCl aqueous solution. The microstructural analysis showed that Pb was bimodally distributed in Pb containing alloys, and Cu particles formed the intermetallic phase CuAl₂. Additionally, the hardness of both Pb and Cu containing alloys increased significantly. The wear and corrosion results showed that the addition of both lead (Pb) and copper (Cu) increased the wear resistance and the corrosion rate, while heat treatments reduced the corrosion rate of most alloys except the Al–Si alloy. Furthermore, comparison of all alloys following heat treatment shows that the wear corrosion resistance of Al–Si alloy is inferior to that of the other alloys. Therefore, addition of Pb and Cu further improved the wear corrosion resistance. Additionally, at anodic potential, the wear corrosion rate and current density of both Al–Si and Al–Si–Cu alloys containing particle Pb were significantly lower than those of alloys containing no Pb, because the layer produced by corrosion comprised Al, O and Pb elements.     

Improving High‐Temperature Wear Resistance of Fe–Cr13–C Hardfacing Alloy by Nitrogen Alloying

Nitrogen alloying of Fe–Cr13–C hardfacing alloy produces marked precipitation strengthening to achieve an improvement in high‐temperature wear resistance. Two hardfacing alloys of Fe–Cr13–C (with and without nitrogen) are slid on carbon steel at high‐temperature of 600°C and high load of 600 N, and wear behaviors are studied systematically. It is found that abrasive wear occurrs on the surface of the hardfacing alloy due to abrasive action of crushed oxide particles coming from the surface of carbon steel on the high temperature. The wear resistance is determined by the size and distribution of precipitates. The results show that the hardfacing alloy can obtain a great increase in hardness and a marked decrease in wear depth of grooving due to the effect of carbonitirde precipitates. The high‐temperature wear resistance of the Fe–Cr13–C hardfacing alloy is improved by nitrogen alloying, and the wear mechanism is mainly plastic deformation with minimum depth of grooving caused by the oxide particles.     

Selection of Heat Treatment Process and Wear Mechanism of High Wear Resistant Cast Hot-Forging Die Steel

 Dry sliding wear tests of a Cr-Mo-V cast hot-forging die steel was carried out within a load range of 50-300 N at 400 ℃ by a pin-on-disc high-temperature wear machine. The effect of heat treatment process on wear resistance was systematically studied in order to select heat treatment processes of the steel with high wear resistance. The morphology, structure and composition were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS); wear mechanism was also discussed. Tribo-oxide layer was found to form on worn surfaces to reduce wear under low loads, but appear inside the matrix to increase wear under high loads. The tribo-oxides were mainly consisted of Fe3O4 and Fe2O3, FeO only appeared under a high load. Oxidative mild wear, transition of mild-severe wear in oxidative wear and extrusive wear took turns to operate with increasing the load. The wear resistance strongly depended on the selection of heat treatment processes or microstructures. It was found that bainite presented a better wear resistance than martensite plus bainite duplex structure, martensite structure was of the poorest wear resistance. The wear resistance increased with increasing austenizing temperature in the range of 920 to 1120 ℃, then decreased at up to 1220 ℃. As for tempering temperature and microstructure, the wear resistance increased in following order: 700 ℃ (tempered sorbite), 200 ℃ (tempered martensite), 440 to 650 ℃ (tempered troostite). An appropriate combination of hardness, toughness, microstructural thermal stability was required for a good wear resistance in high-temperature wear. The optimized heat treatment process was suggested for the cast hot-forging steel to be austenized at 1020 to 1120 ℃, quenched in oil, then tempered at 440 to 650 ℃ for 2 h.     

Study of Wear Stabilisation in Cryoprocessed Cobalt-Based High Speed Steel

Cryogenic treatment is employed for high speed tool steels in order to enhance their wear resistance. The improvement in wear resistance is associated with a decrease in retained austenite and or by formation of eta-carbide/nano-scale carbides. In the present work, a complex alloyed high speed tool steel (M35) specimens were hardened at 1,200?°C, triple tempered at 400?°C, cryosoaked at ?185?°C for 4?C48?h and soft tempered (100?°C). The microstructure of the samples were characterised for hardness, carbide density, impact energy, wear loss and residual stress. Influence of these measured parameters on wear behaviour was studied to understand underlying wear mechanism. The cryotreated specimens exhibited mild to stable wear transition at 16?h and then subsequent wear stabilisation for all higher cryosoaking intervals.     

Dry sliding wear behavior of plasma-sprayed aluminum hybrid composite coatings

Al-SiC _p composite and Al-SiC _p -C _p hybrid composite coatings were produced by plasma spraying of premixed powders onto A356 alloy substrates. Four composite coatings, Al+20 vol pct SiC _p , Al+20 vol pct SiC _p +C _p , Al+40 vol pct SiC _p , and Al+40 vol pct SiC _p +C _p , were obtained. The dry sliding wear behavior of these coatings and pure aluminum have been studied at a sliding velocity of 1 m/s in the applied-load range of 25 to 150 N (corresponding to a normal stress of 0.5 to 3 MPa). The composite coatings had a significantly improved wear resistance over pure Al. The composite coatings with a higher SiC _p content of 40 vol pct exhibited superior wear resistance than those with a lower SiC _p content of 20 vol pct. The presence of graphite particles had different influences on the wear resistance, depending on the applied load. At lower loads, graphite improved the wear resistance considerably. At higher loads, the wear resistance of the hybrid composite coatings was similar to that of the composite coatings without graphite particles. At lower loads, an oxidative wear mechanism was dominant. At higher loads, delamination was a major wear mechanism. Graphite particles did not change their wear mechanism at the same applied loads.     

Wear behaviour of stainless steel sintered and alloyed with titanium,cobalt and molybdenum

Abstract

In this study, a powder mixture was prepared by adding 1–3 wt-% of FeMo, FeTi and Co powders to the austenitic stainless steel powders and samples were produced by the powder metallurgy method. Attempts were made to establish correlations between the microstructure, hardness, toughness, and abrasive wear values of these samples. Wear resistance of the materials was measured by a two body pin-on-disk wear tester. SiC abrasive papers of 65 μm and 177 μm sizes were used as the abrasive media. Wear tests were performed at the loads of 10, 20, and 30 N at room temperature. They showed that the softer, base austenitic stainless steel exhibited higher mass loss than the alloyed samples. Furthermore, the abrasive wear resistance of the base austenitic stainless steel composites increased with increasing FeTi, FeMo,Co content. The wear rate with the 177 μm SiC abrasive paper increased more than that with the 65 μm SiC abrasive paper.     

The effect of high temperature low cycle fatigue on the corrosion resistance of austenitic stainless steels

The effect of high temperature (650 °C) low cycle fatigue on the corrosion behavior of five austenitic stainless steels (Types 304, 316L, 321, and Incoloy Alloys 800 and 800H) has been investigated. For comparison, corrosion tests were also performed on samples of as-received material as well as material which had been solutionized and material which was sensitized at 650 °C. It was observed that cyclic loading at high temperature reduces the corrosion resistance to a much greater extent than does just the exposure of unstressed material to elevated temperatures. Formation of chrome carbides during cycling and depletion of chromium from the matrix is responsible for the decrease in corrosion resistance. Of the alloys tested, Type 304 exhibited the lowest corrosion resistance. Superior corrosion resistance of the other alloys was due to the following: (a) a lower carbon content, (b) a higher chromium content, and (c) the presence of a strong carbide forming element (stabilized material).     

Microstructural Aspects and Wear Behavior of Sinter Hardened Distaloy HP

Effect of cooling rate during sinter hardening on the microstructure and wear behavior of sintered steel grade Distaloy HP has been studied. Wear performances are closely related to macro and micro hardness of the materials. Dry sliding wear tests have been conducted using a reciprocating pin on flat wear testing machine under normal loads of 25, 35 and 45N and at a constant speed of 0.3 m/s. The samples were sinter hardened at different cooling rates 0.5–3 °C/s in order to investigate the influence of microstructure and hardness on wear behavior. It has been shown that, sintering process and cooling rate change the microstructure and hence the hardness and wear behavior of the material. The best wear resistance was detected at a cooling rate of 3 °C/s. At this cooling rate the material had an almost martensitic microstructure and the wear rate was some how independent of the applied load.     

Effect of iron (Wt.%) on adhesive wear response of Al-12Si-1Cu-0.1Mg alloy in dry sliding conditions

The presence of iron leads to different types of intermetallics in Al-Si alloys, among them needle shaped β-phase (Al₅FeSi) can lead to variations in hardness of the Al-Si alloy which ultimately can affect the wear resistance of the alloy. In this paper, the effect of iron on wear behavior of cast Al-Si alloys has been reported. Sliding wear behavior of eutectic alloy Al-12Si-1Cu-0.1Mg was investigated in dry sliding conditions by using pin-on-disk test configuration against heat treated EN31 steel counter-surface at room temperature. Sliding wear behavior has been evaluated at four normal loads of 5, 20, 50 and 70 N and two sliding speeds, 2 m/s and 4 m/s. Worn pin surfaces were examined by scanning electron microscopy (SEM) for analyzing wear mechanisms. The wear mechanism has been found to be mild oxidative type at lower sliding speed of 2m/s for entire range of loads used in the study. Transition to severe metallic wear occurs at higher sliding speed of 4 m/s at normal load of 5 N. Hardness of the alloy increased with increase in iron addition primarily due to presence of needle shaped Fe-rich intermetallics but it leads to an increased wear rate.     

两种热作模具钢的高温摩擦磨损性能

采用高温摩擦磨损试验机研究了HTCS-130和DAC55两种热作模具钢在100~700℃范围内的耐磨性差异及磨损机制, 并结合X射线衍射仪(XRD)、扫描电子显微镜(SEM)、光学轮廓仪等手段对表面相组成、磨损表面、截面形貌等进行分析. 结果表明: 两种钢的磨损率均在100~700℃范围内呈现先增后减的趋势; 其磨损机制表现为在100℃和300℃分别发生黏着磨损和黏着-轻微氧化磨损; 500℃时磨损机制转变为单一氧化磨损, 磨损表面氧化层由FeO、Fe₂O₃和Fe₃O₄组成, 亚表面发生轻微软化并出现塑性变形层; 700℃时磨损进入严重氧化磨损阶段, 氧化物数量急剧增多, 同时由于马氏体基体回复导致材料出现严重软化, 磨损表面形成连续的氧化层. HTCS-130钢优异的热稳定性能使得基体具有较高硬度和更窄的摩擦软化区, 能够更好地支撑氧化层, 从而在700℃下比DAC55钢更耐磨.      

Evaluation of Thermal and Mechanical Behavior of CuNiCoZnAl High-Entropy Alloy Fabricated Using Mechanical Alloying and Spark Plasma Sintering

Thermal behavior investigation of CuNiCoZnAl high-entropy alloy powder produced by mechanical alloying indicated that a FCC single-phase solid solution transformed into two new phases at 500 °C. Despite this phase transformation, no indication of intermetallic compounds or amorphous phases was detected. Heat treatment of the high-entropy alloy was then carried out for 2 hours, and the nanocrystalline structure of heat-treated milled powder was retained up to 1000 °C. Besides, grain growth of CuNiCoZnAl high-entropy alloy powder at high homologous temperatures (> 0.6 T_m) was studied, and sluggish grain growth of the powder was observed clearly. Consolidation of the alloy powder was performed by spark plasma sintering at 800 °C, and a sample with porosity of 6.87 pct and density of 7.32 g cm⁻³ was achieved. Elastic moduli, Vickers microhardness, and fracture toughness of the bulk sample were measured as 186 ± 17 GPa, 599 ± 31 HV, and 4.45 MPa m^0.5, respectively. The evaluation of wear behavior indicated that the dominant wear mechanism was adhesive wear. Moreover, tribochemical wear (oxidation) was found to be the minor wear mechanism. The present study revealed that CuNiCoZnAl high-entropy alloy has the potential to be used in many applications that high hardness and low elastic moduli are favorable.

     

Controlled graphitization as a potential option for improving wear resistance of unalloyed white irons

Effect of heat treatment on the microstructure and resistance to abrasive wear has been studied in an unalloyed white iron used for manufacturing cylindrical pebbles used as grinding media by the cement and other industries. Heat treatment comprised holding at 800 °C, 850 °C, 900 °C, and 950 °C for 30, 60, 90, 120, and 180 minutes followed by oil quenching. Heat treatment in general improved the wear resistance over that in the as-cast (as-received) state. The extent of maximum improvement differed with temperature and in the decreasing order occurred at (1) 180 minutes, 800 °C, OQ; (2) 30 minutes, 950 °C, OQ; (3) 90 minutes, 900 °C, OQ; and (4) 180 minutes, 850 °C, OQ. From the point of view of commercial application, the heat treatment at (2) is most favored. Microstructural changes occurring during heat treating comprised (1) changes in matrix microstructure; (2) a reduction in volume fraction of massive carbides due to its part graphitization/destabilization; and (3) changes in graphite morphology, size, and distribution. Amongst the aforesaid changes, graphitization has emerged as the key parameter in improving wear resistance. Graphite morphology in a near-nodular form of optimum size and distribution was found to be most effective. Upon increasing the heat-treating temperature, the tendency of nodules to develop spikes increased. Similarly, interlinking of graphite flakes was also observed. These features and the possible formation of free ferrite adversely affected wear resistance. The role of other beneficial changes in the microstructure, e.g., globularization of carbides, possible retention of austenite, and formation of optimum volume fraction of martensite, have been duly considered while optimizing microstructure(s). The key feature of the present study is that, despite its fundamental significance, it has a well-focused application potential.