钛合金干滑动摩擦行为与磨损机理研究进展

钛合金因具有高的比强度、比刚度,良好的耐蚀性和耐热性等优点,在航空航天、化工、能源等领域广泛应用,但钛合金存在表面硬度低、抗塑性剪切能力较差、不易加工硬化以及表面氧化物保护作用较差等缺陷,使其耐磨性较差,阻碍了其在耐磨损领域的发展。为了提高钛合金自身的耐磨性潜力和扩大其应用领域,本文主要概述了近年来国内外有关钛合金干滑动摩擦磨损领域的研究现状,讨论了影响钛合金摩擦磨损性能的主要因素以及在不同条件下的磨损机理,并对钛合金干滑动摩擦磨损行为的研究进行了展望。     

Auftraglöten zum Verschleißschutz von Titanwerkstoffen

Wear Protection of Titanium using Surface Brazing Titanium and titanium alloys possess high specific strengths up to a temperature of about 600 °C in addition to an extraordinary corrosion resistance [1]. The low wear resistance constitutes a crucial impediment for a much broader use. Titanium materials are especially susceptible to friction fatigue and erosion. Coating techniques have to be developed in order to counteract this technical constraint. Surface brazing presents a promising approach. Hard metals mixed with brazing filler metals on a silver and titanium basis were brazed in a vacuum furnace and subsequently characterized. Wear resistance was quantified and optimized using ball on disc measurements.     

Tribologische Kennwerte für Reibwerkstoffe

Tribology parameters for friction materials The tribology parameters of the friction materials are currently the coefficient of friction and the wear coefficient. They are determined depending on the material, the surface pressure and the frictional speed. These two parameters are not sufficient for an evaluation of the friction materials on the basis of a wear theory. Their validity is therefore limited. It is proposed to evaluate the friction materials on the basis of the energetic wear theory. The parameters are then the wear energy density, the shear stress of friction and the linear wear intensity. These values can be shown in a diagram and allow for the direct comparison of widely varying friction materials. The reference coefficient of friction is being introduced as a new wear parameter. The determination of the proposed parameters is made on a flywheel test rig, combined with the laser‐optical online measurement of the wear particles. It was possible to demonstrate that the parameters correctly describe the practice‐relevant requirements using two proven friction materials.     

Dry forming of aluminum alloys – Wear mechanisms and influencing factors

Tribological contacts in sheet metal forming are accompanied by several wear phenomena. One of which is the transfer of material from the softer sheet material to the harder tool surface, namely adhesive wear. Forming of aluminum alloys makes high demands on forming processes. Aluminum alloys show a strong tendency of adhesion on common tool materials. Adhesions on tools reduce the surface quality, the dimensional accuracy of the parts and the process stability. In order to avoid adhesive wear during forming, nowadays a high amount of lubricant is applied to the aluminum sheets. Though economically and ecologically attractive, dry forming processes with aluminum sheets seem not to be possible. In order to develop advantageous tribological systems a comprehensive understanding of the acting mechanisms is necessary. This paper discusses the influence of the alloy composition and the influence of oxide layers on the adhesive wear in aluminum forming.     

Thermisches Spritzen vanadiumkarbidverstärkter Eisenbasisschichten

Thermal spraying of vanadium carbide reinforced iron based HVOF sprayed cermet coatings for wear protection like WC‐Co(Cr) and Cr₃C₂‐NiCr have found a broad range of applications in the past. By using chromium containing matrices, they exhibit good corrosion resistance along with outstanding wear resistance. In present research in the area of powder metallurgy and PTA welding iron based alloys with high content of chromium and vanadium have been developed, revealing similar properties and therefore being a cost efficient alternative to established cermet coatings. HVOF sprayed coatings of these iron based alloys are investigated regarding their economic applicability and their corrosion and wear properties.     

Untersuchungen zum Erosionsverschleiß an schweißtechnisch hergestellten Beschichtungen

Erosion resistance of hard‐facing deposits Erosive wear is inflicted by flying, bumping and furrowing particles inside the gaseous medium. Especially air vents – fan blades are the principal victims ‐ and conveying systems are attacked by solid particle impingement if fly ash, raw‐meal, cement or clinker are involved. High load of particles in combination with high circular velocities cause enormous loss of material on exposed components. Hard‐facing deposits as produced by flux‐cored arc and plasma trans‐arc welding in form of wear plates or local overlays at pertinent places are able to diminish this effect. Secure dimensioning of above mentioned systems during project engineering status only is hardly possible. So far solutions for wear protection are mainly based on time‐ and cost‐intensive field tests on the part of the manufacturer or user of affected plants and equipment. Within the framework of presented investigations experiences in laboratory testing of hard‐facing materials for attacked components are discussed. Wear tests on platings by practically relevant media give information about influencing factors as well as wear‐ and damage‐mechanism.     

钛合金激光熔覆的研究现状与发展趋势

钛合金具有高比强、良好的耐蚀性能等优点,但其耐磨性差,限制了它在摩擦机构的应用.激光熔覆技术是近年来发展起来的一种新型表面改性工艺.在钛合金表面进行激光熔覆,可提高钛合金的表面性能,获得高硬度、耐磨性能好、低摩擦系数的熔覆层.简要阐述了钛合金表面激光熔覆的研究现状,包括激光熔覆工艺、熔覆层的组织与性能,指出了存在的问题,并展望了钛合金激光熔覆的发展方向.     

Untersuchungen zum Verschleißverhalten von Metall/Metall – Gleitpaarungen aus CoCrMo‐Legierungen

Investigation of the Wear Behaviour of Metal/Metal Bearings of Co Cr Mo – Alloys CoCrMo‐alloys are successfully used for long‐term implants, because of their corrosion and wear resistance as well as their mechanical properties. In order to improve CoCrMo‐alloys for metal‐on‐metal bearings the influence of carbon content on wear behaviour is investigated. Casted or forged CoCrMo‐alloys with a carbon content from 0.008 to 0.48 wt % were studied in ring on disc oscillating tests. Friction torque, weight loss and surface roughness, as well as light and scanning electron microscopic investigations of the sample surface were used to characterize the wear behaviour. – All alloys show similar friction torque and weight loss. But the surface roughness and the wear mechanisms are depended on the carbon content.     

Gefüge und magnetische Eigenschaften von Chromgusseisen für Mahlkugeln

Microstructure and magnetic properties of white cast irons for grinding balls Many types of cast ferrous alloys are used for applications in the grinding, crushing, mineral‐handling and earthmoving industries. The finish grinding process for cement materials uses ball mills with differently sized grinding balls. This work deals with grinding balls of high chromium white cast irons with various chemical composition. Using certains thermal treatments, the influence of parameters of microstructure on abrasive and impact wear resistance has been studied. A special test system has been adapted for the assessment of the impact properties of these alloys. Examination of the carbides were performed using a transmission electron microscope. Additional microstructural examinations were made using the Scanning electron microscope. For a nondestructive inspection of the grinding balls, the possibilities of using the magnetic characteristics for determining the structural state and mechanical properties of white cast irons are analyzed. The results showed that the hardness and the dynamic fracture toughness are important for the combined impact‐abrasion resistance. It has been established that the microstructure has a decisive influence on the magnetical properties of white cast irons.     

Herstellung HVOF gespritzter,feinststrukturierter Cermetschichten unter Verwendung von feinen WC‐12Co Pulvern

Manufacturing of HVOF sprayed, finest structured cermet coatings using fine WC‐12Co powders The continuous increase in productivity and performance of modern sheet metal forming processes combined with the employment of novel, high strength materials cause high wear on tool systems. Coating technologies like thermal spraying provide a high potential to functionalize and to protect the surface of forming tools. However, it has to be ensured that the high shape and dimensional accuracy of the tool contour is preserved after the application of a wear protective coating. This aim cannot be achieved using currently applied, thermally sprayed coating systems with conventional, coarse grained microstructure. To solve this problem, novel finest structured coatings have been developed in this study by thermal spraying of fine WC‐12Co powders using the HVOF technique. For this purpose the influence of varying HVOF combustion gas compositions on the spray process as well as on the corresponding coating properties has been investigated. Next to a high surface quality the focus was placed on achieving coatings with high hardness and corresponding high wear resistance, low porosity as well as a good adhesive strength on the substrate material.     

Thermisch gespritzte titankarbidverstärkte Eisenbasisschichten als Alternative zu konventionellen karbidischen Werkstoffen

Thermal sprayed titanium carbide strengthened iron coatings as alternative for conventional carbide materials High velocity oxygen fuel (HVOF) sprayed carbide based materials are industrially well established as wear and corrosion protection coatings. Because of the high carbide content of typically 75 weight percent and more they are providing a very high hardness and excellent wear resistance. However, at the same time this characteristic is resulting in major difficulties during post‐processing steps. Cost‐effective machining processes such as turning and milling are usually not applicable and any sprayed oversize has to be reduced by grinding. To overcome these drawbacks a novel carbide‐based material concept, which is already in use for sintering processes, is offering promising properties. Titanium carbides at a reduced content of 33 weight percent embedded in a ferrous matrix can provide distinctly improved characteristics for optimal machinability. Depending on the carbon content the iron‐base material can additionally offer a temperable matrix for enhanced wear behaviour. Within this study spray trials have been carried out to investigate the sprayability of titanium carbide strengthened iron powders with a gaseous and a liquid fuel driven high velocity oxygen fuel spraying system. Optimised parameters were developed by implementing the statistical method of design of experiment (DoE). The resulting coatings were analysed with respect to microstructure, hardness and phase composition and compared to sintered reference materials. Furthermore thermally sprayed iron‐based coatings strengthened with titanium carbides were heat treated to proof the retained temperability of the iron matrix after thermal spray processing.     

Entwicklung hochverschleißbeständiger wolframschmelzkarbidbasierter Schichten auf Aluminiumbauteilen durch Plasma‐Pulver‐Auftragschweißen

Development of high wear‐resistant FTC‐based coatings on aluminium components using plasma transferred arc welding Nowadays, functional surfaces of components can be effectively protected from extreme wear with the help of fused tungsten carbide (FTC) coatings. The wear protection of steel components using FTC has been well known for many years. This paper presents the feasible study of improving the wear resistance of aluminium components with FTC particles using plasma powder arc welding. The FTC coatings are developed with two methods: one is the dispersion of carbide particles in aluminium and the other one is the combination of dispersing and alloying of FTC‐based composite powders. In this research, coatings within a thickness range of a few millimeters are developed with varying process parameters and compositions of the filler materials. The developed coating systems are tested with regard to their specific properties and their wear resistance. Finally, their application potential is presented.     

Investigation of wear resistance and microstructure of a newly developed chromium and vanadium containing iron‐based hardfacing alloy

Plasma transferred arc (PTA) welded Ni and Co‐based alloys have gained high acceptance in many industrial applications for the wear protection of components. Recently, the cost of nickel and cobalt is rising drastically. This paper presents the development of a cost‐effective high chromium and vanadium containing iron‐based hardfacing alloy with high hardness and wear resistance. The welding processing of the alloy is carried out by PTA welding of atomized powders. Investigations on powder production as well as on weldability are presented. The coatings are metallographically studied by optical microscopy, SEM, EDX and micro‐hardness measurements. The wear resistance properties of the coatings are examined using pin on disk, dry sand rubber wheel and Miller testing, the corrosion properties are determined by immersion corrosion tests. The newly developed iron‐based alloy has nearly the same wear resistance as Ni‐based alloys with fused tungsten carbides at a higher level of corrosion resistance and much lower cost.     

The effect of titanium addition on the microstructure,mechanical and tribological properties of Ni3Si alloys prepared by powder metallurgy method

Ni₃Si alloy with different content of titanium was fabricated by powder metallurgy method. The microstructures, hardness and tribological properties of the alloys were investigation. The results showed that pure Ni₃Si alloy was composed of β₁‐Ni₃Si phase and γ‐Ni₃₁Si₁₂ phase, and Ni₃Ti phase formed with titanium addition. The hardness of the alloy decreased with the increasing titanium content. The friction coefficient of pure Ni₃Si alloy increased with the increasing load, while the friction coefficient of the alloy with titanium addition decreased. The wear rates of the alloys were all increased with increasing load, and the alloy with 5 % titanium addition had the best wear resistance properties. The wear mechanisms of the alloys were abrasive wear at low load, and the wear mechanisms changed to oxidative wear at high load.     

Correlation of processing route and heat treatment with the abrasive wear resistance of a plastic mold steel

The processing of polymers necessitates the use of corrosion and wear resistant tool materials being in direct contact with the feedstock material. Corrosion resistant cold work tool steels, the so called plastic mold steels, are successfully applied here, offering both a good wear and corrosion resistance. The lifetime of this tool depends on the applied heat treatment but also the processing route has a distinct effect on the resulting properties. In this work, different powder metallurgical routes like hot isostatic pressing, build‐up welding (plasma transfer arc (PTA)) and thermal spraying (high velocity oxy fuel (HVOF) and atmospheric plasma spraying (APS)) were applied to produce coatings on low‐alloyed construction steel. Coatings are compared in relation to the changes in microstructure and the feasibility of an adequate heat treatment. This paper discusses strategies to maximize wear resistance in dependence of heat treatment and the microstructural changes arising from the processing.     

Strangpressen von verschleißbeständigen Fe‐Basis MMC

Hot extrusion of wear resistant Fe‐base metal matrix composites (MMC) Increasing demands on technical surfaces, i.e. thermal load, corrosion or wear, often prompt the development of tailored materials or coatings. In highly abrasive environments the progress in powder metallurgy has lead to the production of highly wear‐resistant materials based on metal‐matrix composites (MMC). Such materials are produced from a metal matrix (MM) based on Fe, Ni or Co and additional hard phases (HP), such as carbides, nitrides, borides or oxides. Moreover, powder metallurgical techniques can be used to adapt the particle size, the distribution and the content of the hard phases to the wear system on a large scale. HIP cladding is an established method of producing such MMC, but due to its near net shape capsule technique it is quite expensive. Because of this reason hot direct extrusion of capsules filled with powder blends was researched in a DFG‐Project as a method of producing long cylindrical products. Aiming at a high abrasive wear resistance, powder blends of hardenable steels with additions of fused tungsten carbide (WSC) or titanium carbides (TiC) were used. The extruded MMC were investigated with respect to their densification and microstructure, their bending strength and their wear resistance.     

The effect of aging treatments on wear behavior of aluminum matrix functionally graded material under wet and dry sliding conditions

This study investigated that the effect of aging treatments on wear behavior of functionally graded material (FGM) that was reinforced via being integrated with aluminum 2014 alloy (AlCu4SiMg) and 15 vol% SiC. The specimens were obtained via centrifugal casting technique, and then two different aging treatments were applied. Wear experiments were applied at 1.256 m/s constant sliding velocity, under two different loads and two different sliding distances for each condition via a pin‐on‐disc wear apparatus. The variations that occurred on wear behavior of cast and aged materials were analyzed. The results show that the minimum wear loss values were obtained under dry sliding conditions due to the aging processes. On the other hand, with increasing sliding distances under wet sliding conditions, the aging processes' effect was decreased on wear resistance.     

钛合金激光表面熔覆的研究与进展

钛合金具有优异的高比强,良好的抗腐蚀、蠕变、疲劳和韧性,但其表面抗磨性能差,不能作为机械零件使用,大大限制了其性能潜力的发挥.为提高钛合金的表面性能,激光熔覆技术在钛合金表面上进行了相关的研究,获得了陶瓷相增强的高硬度金属基体复合涂层,为钛合金在机械零件上的应用提供了理论基础.本文综述了近几年来钛合金激光熔覆技术的状况,存在的问题,提出进一步研究的方向.     

Eine Übergangsbedingung beim Strahlverschleiß von Gesteinen und Betonen

A transition criterion for the erosion of rocks and concrete materials Depending on loading regime and material type, mineralic materials behave either elastic or elastic‐plastic if eroded by solid particles. A simple transition number, X, that combines fracture toughness and compressive strength, can be used to distinguish between both modes. Conventionally ‘hard’ materials, namely granite and feldspars, own low X‐values and respond elastic. Conventionally ‘soft’ material, namely limestone, mortar and schist, are characterised by high X‐values and show an elastic‐plastic response.     

Influence of electron beam deflection techniques used during the cladding process on the wear and corrosion behaviour of cobalt‐based protective coatings on austenitic stainless steel

The present work aims to improve the wear resistance of the austenitic stainless steel X6CrNiMoTi17‐12‐2. In view of the potential use of this alloy, however, corrosion resistance should be maintained where possible. An electron beam surface treatment (cladding) was performed, and the cobalt‐based alloy Stellite® 12 was used as the wear‐resistant material. The presented results show the effects of several electron beam oscillation figures during the cladding process with regard to layer bonding, microstructure formation and hardness. The surface hardness achieved was 576±18 HV 0.3, almost three times higher than that of the base material (203±3 HV 0.3). The scratch energy density – which represents the resistance to abrasive wear – could be increased by a factor of 1.5. Under abrasive‐adhesive stress loading conditions, the determined wear volume decreased by a factor of almost 5. Based on the corrosion investigations carried out, it was possible to prove that in comparison to the base material, the tendency towards pitting corrosion could be almost completely suppressed.