Abrasive and Adhesive Wear Behavior of Arc-Evaporated Al<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>N Hard Coatings

During the last decade, the usage of difficult-to-machine materials such as austenitic stainless steels has increased continuously in various industrial applications. Tools such as blind hole taps, punches, or deep drawing molds are often exposed to severe wear while machining/forming these materials, mainly due to excessive adhesion and material transfer. On combination with abrasive wear due to work-hardened wear debris, tool lifetime in these applications is often limited. In this study, ball-on-disc experiments were carried out with arc-evaporated AlCrN coatings with different Al/(Al + Cr) ratios against Al₂O₃ and austenitic stainless steel balls in ambient atmosphere. Test temperatures of 25, 500, and 700°C were chosen for the hard Al₂O₃ balls simulating severe abrasive loads, whereas 25, 150, and 250°C were used for the softer stainless steel material to evaluate the adhesive wear behavior. Characterization of the wear tracks was done by scanning electron microscopy in combination with energy-dispersive X-ray analysis and optical profilometry. The best abrasive wear resistance during testing against Al₂O₃ was observed for the coating with the highest Al content. In the case of the austenitic stainless steel balls, sticking of the ball material to the coating surface was the dominating wear mechanism. The influence of test temperature, chemical composition, and surface roughness was studied in detail.     

Dry sliding wear behaviour of cast high strength aluminium alloy (Al–Zn–Mg) and hard particle composites

This paper describes the results of dry sliding wear tests of aluminium alloy (Al–Zn–Mg) and aluminium (Al–Zn–Mg)–10, 15 and 25 wt.% SiCp composite was examined under varying applied pressure (0.2 to 2.0 MPa) at a fixed sliding speed of 3.35 m/s. The sliding wear behaviour was studied using pin-on-disc apparatus against EN32 steel counter surface, giving emphasis on the parameters such as coefficient of friction, rise in temperature, wear and seizure resistance as a function of sliding distance and applied pressure. It was observed that the wear rate of the alloy was noted to be significantly higher than that of the composite and is suppressed further due to addition of silicon carbide particles. The temperature rise near the contacting surfaces and the coefficient of friction followed reversed trend. Detailed studies of wear surfaces and subsurface deformation have been carried out. The wear mechanism was studied through worn surfaces and microscopic examination of the developed wear tracks. The wear mechanism strongly dictated by the formation and stability of oxide layer, mechanically mixed layer (MML) and subsurface deformation and cracking. The overall results indicate that the aluminium alloy–silicon carbide particle composite could be considered as an excellent material where high strength and wear resistance are of prime importance.     

Dry wear and friction behaviour of plasma nitrided Ti–6AL–4 V alloy after explosive shock treatment

The unlubricated wear behaviour of explosive shock treated and, subsequently plasma nitrided Ti–6Al–4 V alloy was studied using a ball-on-disc wear tester. Plasma nitriding was carried out at three different temperatures (700, 800 and 900 °C) for 3, 6, 9 and 12 h. Plasma nitriding after explosive shock treatment enabled a reduction in the wear rate of two orders of magnitude. Detailed investigations of this improved wear performance dependent on the nitriding temperature and time were carried out. The friction and wear data showed a clear breakthrough transition from the nitrided layer to the core of the Ti–6Al–4 V alloy matrix. The lowest wear volume was obtained for the sample, nitrided at 900 °C for 12 h, especially at loads of 2.5, 5 and 7.5 N. Obviously, the hard nitride layers were intimately associated with low wear rate, providing a smooth low friction surface. The coefficient of friction reduced from 0.46 to 0.2 due to a thick and hard compound layer resulting from a high nitrogen diffusion rate caused by explosive shock treatment that expected to increase point defects in the alloy. Detailed examination of the wear tracks showed that plasma nitriding changes the mechanism of wear from one of adhesion for untreated Ti–6Al–4 V to both delamination and mild abrasive.     

Effect of intermetallic particles on wear behaviour of stainless steel matrix composites

Metal matrix composites were manufactured using 316L austenitic stainless steel as matrix and TiAl intermetallic as reinforcement. Three levels of reinforcement were used: 3, 6 and 9 % (vol.). Composites were made by P/M: mixing, uniaxial pressing and sintering. The sintering was carried out in vacuum, at three temperatures (1120, 1200 and 1250 °C). The influence of the addition of the intermetallic on the microstructure of the stainless steel was assessed by a complete metallographic study using optical and scanning electron microscopy, coupled with a semi-quantitative microanalysis. Wear behaviour was evaluated by a ‘pin on disk’ test. Materials were tested against tool steel, and the main test conditions were as follows: 5 N load, <30% moisture, 0.1 m/s speed, and 377 m sliding distance. X-ray diffraction of powder debris was also studied and wear tracks were observed by SEM.     

Fretting Wear Study on Micro-Arc Oxidation TiO<Subscript>2</Subscript> Coating on TC4 Titanium Alloys in Simulated Body Fluid

Tribological properties of TiO₂ coatings synthesized by micro-arc oxidation (MAO) on the surface of TC4 titanium alloys were investigated at the fretting contact against 440C stainless steel in simulated body fluid (SBF). Fretting experiments were carried out by ball-on-flat contact at various loads for 1 h, with an amplitude of 100 μm and a frequency of 5 Hz. Results show that MAO TiO₂ coatings presented good tribological properties with lower friction coefficient in SBF. Less wear volume was observed for MAO TiO₂ coatings compared with that for TC4 alloy. At lower load, the wear mechanism of MAO TiO₂ coatings was dominated to abrasive wear. With an increase of normal load, however, fretting corrosion increased due to chemical reactions with SBF, and therefore, fretting fatigue coexisting with abrasive wear became the predominant mode.     

Friction and wear behaviour of stainless steel rubbing against copper-impregnated metallized carbon

A series of experimental tests were carried out using stainless steel rubbing against copper-impregnated metallized carbon under electrical current on a pin-on-disc test rig. The test parameters include the sliding speed of 60-100 km/h, normal force of 40-80 N and electrical current of 0-50 A. During testing, the friction coefficient and wear volume were recorded. The topography of worn surfaces was also observed with SEM. The cross sectional profiles of worn surfaces of stainless steel were measured with Ambios profiler. The result displays that electrical current, normal load and sliding speed have a distinct effect on the friction and wear behaviour of stainless steel rubbing against copper-impregnated metallized carbon. Without electric current, the friction coefficient is largest but the wear volume of copper-impregnated metallized carbon is lowest. With increasing electric current, the friction coefficient decreases while the wear volume of copper-impregnated metallized carbon increases. Through the whole test, it is found that the wear loss of stainless steel was light. The wear of copper-impregnated metallized carbon becomes severe when electrical current or sliding speed is high. When the electrical current or sliding speed is high, arc ablation is a dominant wear mechanism of copper-impregnated metallized carbon.     

Process performance of micro-EDM drilling of stainless steel

An experimental campaign based on the execution of through micro-holes on stainless steel plates was carried out using a micro-EDM machine Sarix SX-200. The experimental campaign was carried out by varying several process parameters, namely peak current, voltage and frequency. Tubular electrodes made of two different materials (tungsten carbide and brass) were used. A study of the in progress material removal rate (MRR) and tool wear ratio (TWR) during the drilling process was performed. Some mathematical laws governing the relation between process parameters and performance indexes were defined. Two technological windows representing TWR and MRR as a function of the hole depth, for different electrode materials, were obtained.     

Adhesive and abrasive wear behaviour of TiC alloyed,sintered, austenitic stainless steels

Abstract

This study examines abrasive and adhesive wear behaviour of austenitic stainless steel and its TiC alloyed composite produced through powder metallurgy technique. Abrasive wear tests have been carried out using a pin on disc wear tester under loads of 10, 20 and 30 N. For adhesive wear tests, a block on ring wear tester has been used under loads of 20, 40, 60 and 80 N. A possible correlation between the hardness, microstructure and wear behaviour of the samples has been investigated. The abrasive wear tests have revealed that the highest rate of mass loss occurred in the austenitic matrix stainless steel sample; also, mass losses decreased with an increased rate of reinforcing material in the composite. In adhesive wear tests, interparticle spacing developed from severe wear and extreme plastic deformation under heavy loads; however, at low loads, oxidation type wear was shown to be dominant.     

Microstructural aspects determining the adhesive wear of tool steels

In many machining applications, adhesion of the workpiece to the tool is a major problem. Adhesion may be reduced by changing the microstructure of the tool steel, e.g. by increasing the carbide content. The present work deals with the influence of some microstructural parameters in the adhesive wear of tool steels. The investigations were conducted using six model alloys based on the powder metallurgy high speed steel AISI M4, all of which had the same martensitic matrix composition after heat treatment. The alloys had MC carbide contents which varied between 0 and 25 mol% in 5 mol% increments. Ball-on-disc experiments were carried out in ambient air at room temperature using austenitic stainless steel and aluminum balls as counterfaces. Wear tracks on the disks were characterized using both a scanning electron microscope and an optical profiler. The results show that two main parameters determine the adhesive wear behavior: the carbide content and the distance between carbides.     

Influence of aging treatment on microstructure, wear and corrosion behavior of a nickel base hardfaced coating

In this work nickel based hardfacing alloy (Colmonoy 5) was deposited on 316 L (N) stainless steel substrate to study the effects of aging treatment on coating microstructure, wear and corrosion properties. Coatings, deposited through plasma transferred arc (PTA) welding process, were aged at 923 K for 5000 h. Microstructural characterization studies carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the coarsening of dendrites and precipitation of Cr₂₃C₆ particles in the aged coating. The wear behavior of the as deposited and aged coatings was compared in room temperature (RT) and high temperature (823 K) under dry sliding wear condition (pin-on-disc configuration). At RT, aged coating experienced more wear loss when compared to as-deposited. At high temperature, the wear loss was almost same with similar operating wear mechanisms (tribo-oxidation) for both as-deposited and aged coating. From pitting corrosion studies, it was found that aged coatings are more prone to pitting when compared to the as-deposited coatings.     

低温微量润滑高速铣削PH13—8Mo刀具磨损试验研究

针对高强度不锈钢材料加工性能差、刀具耐用度低的问题,进行了硬质合金刀具在低温微量润滑条件下高速铣削高强度不锈钢PH13—8Mo的刀具磨损试验,结果表明：WSP45刀片比WXM35适合加工PH13—8Mo,低温微量润滑（cMQL）能有效地抑制刀具磨损,提高刀具耐用度;两种刀具在铣削过程中前、后刀面同时发生磨损,最终因刃口严重崩刃而失效。     

Adhesive wear of stir cast hypereutectic Al–Si–Mg alloy under reciprocating sliding conditions

This paper describes an attempt to enhance the wear properties of hypereutectic cast aluminium–silicon alloys produced by semi-solid metal (SSM) processing technique. The rheological experiments on SSM slurries were performed under continuous cooling condition from liquidus temperature. Wear characteristics of alloy under investigation were studied using pin on flat wear system over a range of normal load (10–40 N) at constant average sliding speed (0.2 m/s) against cast iron and stainless steel counter surface. Stir cast alloy showed lesser weight loss compared to conventional cast alloy. Stir cast and conventional cast alloys showed higher weight loss against the stainless steel as compared to that against cast iron counter surface. Optical microscopy of the conventional cast and stir cast hypereutectic alloy has shown that stir casting causes refinement of primary silicon particles and modification of eutectic silicon compared to conventional cast alloy. The scanning electron microscopy of wear surfaces was carried out to investigate the mode of wear.     

Tribological behaviour of DLC coatings compared to different materials used in hip joint prostheses

The goal of the study carried out in the laboratory was to quantify the wear and the friction of two materials used for the manufacturing of hip prostheses. Tests used had to obtain in a short time the tribological behaviour laws of the materials. Tests on a hip simulator have been excluded because their cost and their duration were too high for a program of preliminary development of new materials.

To amplify wear phenomena, dry friction tests were carried out for two configurations: ball-on-disc and pin-on-disc. The influence of the contact pressure at constant sliding velocity on the wear of materials has been clearly shown.

Results obtained with several different tested materials (stainless steel/UHMWPE, stainless steel+DLC coating/UHMWPE, stainless steel+DLC coating/stainless steel+DLC coating, titanium alloy+DLC coating/UHMWPE, titanium alloy+DLC coating/titanium alloy+DLC coating, zirconium dioxide/UHMWPE, alumina/UHMWPE, alumina/alumina) have shown the superiority of DLC coatings. Promising results obtained during this study are in the validation stage on a hip simulator.     

Measurements of plastic strain in copper due to sliding wear

Wear experiments have been conducted to determine the plastic strains that are introduced in surface material near sliding wear tracks. Both oillubricated and dry-sliding experiments have been carried out at different sliding distances on surfaces of copper. The strain values were determined from selected-area electron channelling patterns obtained from regions as small as 10 μm in size and 0.05 μm deep around the wear track using a scanning electron microscope. A deformed calibration specimen was used to relate the electron channelling band contrast to the deformation strain. Strain maps were obtained on the wear surface lateral to the wear track and also below the surface using electropolishing metal removal techniques. Particular attention was given to the near-surface strain values. In all cases the maximum strain was found at the wear surface located at the track center and the strains decreased uniformly with depth. Significant large strains were also found outside the wear tracks. The results are compared with those previously reported for iron and with other relevant studies.     

Laser composite surfacing of AISI 304 stainless steel with titanium boride for improved wear resistance

The present study concerns development of a hard in situ boride-dispersed composite layer on the surface of AISI 304 stainless steel substrate to improve the wear resistance property. Laser processing was carried out by melting the surface of sand-blasted AISI 304 stainless steel substrate using a continuous wave CO₂ laser and simultaneous deposition of a mixture of K₂TiF₆ (potassium titanium hexafluoride) and KBF₆ (potassium hexafloroborate) (in the weight ratio of 2:1) using Ar as shrouding environment. Powder feed rate was maintained constant at 4 g/min. Irradiation results in dissociation of a pre-deposited mixture along with a part of the stainless steel substrate, intermixing and rapid solidification to form the composite layer on the surface. The micro-structure of composite layer consists of dispersion of titanium boride particles in AISI 304 stainless steel matrix. Volume fraction of particles is found to be uniform throughout the composite layer, though varied with laser parameters. The micro-hardness of the surface was improved 250–350 VHN as compared to 220 VHN of the AISI 304 stainless steel substrate with a significant improvement in wear resistance property. The mechanism of wear was found to be a combination of adhesive and abrasive in as-received stainless steel. However, it was predominantly abrasive for laser composite surfaced stainless steel.     

Wear and frictional mechanisms of copper-based bearing alloys

The present study investigated the role of alloy microstructure and surface roughness on wear and friction behavior of leaded and unleaded tin bronzes. Ball-on-disk experiments were carried out under dry conditions with steel balls sliding against bronze disks. Scanning electron microscopy (SEM), energy dispersive electron microscopy (EDX), x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy were performed to analyze the sliding tracks and the ball scars. The wear reducing effect of lead was associated to the formation of an oxidized lead rich layer. When no such film formed on the leaded bronze wear was more severe than in case of unleaded bronze. Nevertheless, the presence of lead in the alloy was a necessary but not sufficient condition to obtain a smeared layer and thus a lubricating effect of the leaded alloy. Two mechanistic hypotheses were formulated to explain the formation of the smeared layer.     

Erosion wear and mechanical properties of plasma-sprayed nickel- and iron-based coatings subjected to service conditions in boilers

The erosion wear and mechanical properties after exposure to simulated industrial service conditions in boilers of nickel-based, iron-based and chromium–nickel plasma-sprayed coatings on carbon steel and stainless steel have been obtained. These types of coatings are used as heat transfer and structural elements in boilers. Different tests simulating boiler service conditions under standard and extreme situations were carried out at 400, 600 and 800°C in a laboratory combustion unit. The influence of high temperature oxidation processes on the adherence, microhardness, microstructure, and wear erosion behaviour of both base materials and coatings have been evaluated.     

Improving the wear life of a cocoa spray‐drying unit

In the chocolate production process, the moisture content of ground cocoa is removed in a spray‐drying unit, in which wet cocoa is pumped through a high‐pressure pump. Wear occurs in this high‐pressure pump, which can cause problems in the system. Originally, valves and beds were made of AISI 316 Ti austenitic stainless steel, and their average wear life was less than 280 h, obviously too short for use in industrial production. The aim of the research reported in this paper was to investigate ways to increase the wear life of these parts. In this respect six different materials were tested. Valves and beds were produced from four different steels and two powder metals. The steel parts were hardened by heat treatment. All the parts were electroplated with CrN or TiN. Wear life tests were carried out, and it was shown that AISI M2 high‐speed steel valves and beds gave the longest wear lives.     

Three-body abrasive wear of TiC–NiMo cermets

The mechanism of three-body abrasive wear of TiC-base cermets was studied. The wear rate of a series of cermets with different percentage of NiMo binder phase (20–60 wt%) was studied. Silica sand was used as an abrasive. The wear rate of the cermets decreases with the increase of TiC and Mo content, which corresponds to the increase in the bulk hardness. The post-run wear tracks of the worn blocks were analyzed with SEM. The material is removed by several processes such as extrusion and removal of the binder and also fractures of the carbide grains and the carbide network.     

Dry Sliding Wear of Active Screen Plasma Carburised Austenitic Stainless Steel

Low temperature diffusion treatments with nitrogen and carbon have been widely used to increase the tribological performance of austenitic stainless steels. These processes produce a layer of supersaturated austenite, usually called expanded austenite or S-phase, which exhibits good corrosion and wear resistance. The novel active screen technology is said to provide benefits over the conventional DC plasma technology. The improvements result from the reduction in the electric potential applied to the treated components, and the elimination of such defects and processing instabilities as edge effects, hollow cathode effects and arcing. In this study, AISI 316 coupon samples were plasma carburised in DC and active screen plasma furnaces. The respective layers of carbon expanded austenite were characterised and their tribological performance was studied and compared. Detailed post-test examinations included SEM observations of the wear tracks and of the wear debris, EDX mapping of the wear track, EBSD crystal orientation mapping of the cross sections of the wear tracks, and cross-sectional TEM. Based on the results of wear tests and post-test examinations, the wear mechanisms involved are discussed.