Role of the strengthening phases in abrasive wear resistance of laser-clad NiCrBSi coatings

The influence of the strengthening phases on the tribological characteristics (wear intensity, specific work of wear, coefficient of friction) and the wear mechanisms in two-body abrasion tests with abrasives of different hardnesses (corundum Al₂O₃, ~2000 HV and silicon carbide SiC, ~3000 HV) has been investigated for PG-SR2 (Cr₂₃C₆, 1000–1150 HV), PG-10N-01 (Cr₇C₃, 1650–1800 HV; CrB, 1950–2400 HV), and 75% PG-SR2 + 25% TiC (TiC, 2500–2900 HV; (Cr,Ni)₂₃(C,B)₆ and (Ti,Cr)(C,B), ~2000 HV) coatings. The dominant role of the strengthening phases (compared with the role of the metal matrix) in the abrasive wear resistance of laser-clad NiCrBSi coatings has been estimated. Different wear mechanisms have been identified and, accordingly, different levels of coatings wear resistance have been achieved depending on the ratio between the hardness of the strengthening phases (carbides, borides, carboborides) and abrasive particles.     

Two-body abrasive wear of electroless nickel composite coatings

The two-body abrasive wear of electroless nickel (EN), EN-silicon carbide, and EN-alumina composite coatings have been investigated using a scratch test with a diamond indenter. The coatings were heat treated at temperatures of 100–500° C. The hardness of the coatings increased with heat treatment temperature from 500 HV100 for the as-deposited condition to 1008 HV100 when fully hardened. Scratch testing showed that the as-deposited coating had scratch tracks with a high degree of plasticity, signs of microploughing and tensile cracking and was characterised as a ductile failure. On the other hand, the heat-treated coatings showed chipping and cracking on the edge of the scratch tracks, failing in a brittle manner. The heat-treated EN-silicon carbide coatings, however, exhibited no cracking nor chipping, believed to be due to its higher fracture toughness than the other heat-treated coatings, attributable to its lower phosphorus content. The volume of material removed from the silicon carbide scratch track was 1/3 of the volume removed from the steel substrate at a 20 N load, and showed the best wear/ scratch resistance of any of the coatings tested.     

Sliding and abrasive wear behaviour of boride coatings

Polyphase boride coatings constituted by an inner layer of Fe₂B and an outer layer of FeB were thermochemically grown on iron and medium carbon steel by a pack cementation process. The tribological behaviour of borided samples was investigated under both sliding and abrasion testing conditions. Considerably different values of wear rate were found in different regions of the coatings. The differences were explained on the basis of the crystallographic order of iron borides. The resistance to both types of wear was initially poor due to the presence on the coatings of a thin, friable layer constituted by disordered crystals. Then the resistance increased to a maximum value in regions constituted by compact, highly ordered crystals of Fe₂B. The resistance to dry sliding of borided samples was better than that displayed by samples submitted to alternative surface treatments (e.g. gas nitriding) and lower that that measured for a WC-Co hard metal coating.     

Dry wear of NiAl3-reinforced mechanically alloyed aluminium with different microstructure

The tribological behaviour of mechanically alloyed (MA) aluminium-base materials reinforced by 2 vol.% NiAl₃, either as large lamellae (MA Al–Ni S) or as homogeneously dispersed rounded particles (MA Al–Ni S2) has been studied. The results are compared with that of nickel-free MA aluminium (MA Al S), taken as reference. All materials were prepared by mechanical milling of Al powder, eventually with the addition of 1 wt% Ni powder, followed by consolidation techniques of cold compaction and sintering. Tribological tests were carried out using the pin-on-disc configuration under variable normal load and temperature. MA Al–Ni S2 shows the highest wear reduction with respect to MA Al–Ni S at the highest load studied. At low load and high temperature, MA Al–Ni S2 shows the highest wear rate, probably due to severe abrasion of the steel counterpart. Friction values and wear mechanisms are discussed from SEM observations and EDS analysis of wear tracks, wear debris morphology and transfer tribolayers.     

Investigation of abrasive wear resistance and wear mechanism of composite alloys

The abrasive wear resistance of composite alloys comprising hard tungsten carbide and soft CuNiMn matrix under different wear conditions has been investigated and compared with CrMo cast iron. It was found that Yz-composite alloy with hard cast angular tungsten carbide has greater wear resistance than CrMo cast iron under two-body wear conditions, but lower resistance than Cr-Mo cast iron under three-body wear conditions. It was found that under three-body wear conditions selective wear of the matrix and digging or fragmentation of tungsten carbide particles dominate in Yz-composite alloy, and microcutting and deformed ploughing is dominant under two-body wear conditions. The abrasive wear resistance of composite alloys under two-body wear condition is independent of bulk hardness, but is closely related to the microhardness of tungsten carbide.     

Micro-scale abrasive wear testing of PVD coatings on curved substrates

A method is presented which enables a micro-scale abrasion test to be used to measure the wear performance of a coating over a small region, typically of millimetre dimensions, on a curved surface. The method is also applicable to studies of the wear resistance of any bulk material with a surface having complex curvature. The technique is illustrated by measurement of the intrinsic abrasion resistance of thin PVD coatings of TiZrN, ZrNbN and TiNbN on both flat and cylindrical tool steel and flat stainless steel substrates. The ability to measure the wear resistance of both a coating and its substrate, independently of each other and by a single test, is confirmed by experiment.     

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.     

Microstructure and abrasive wear resistance of cast Ni-Cr-C alloys

The abrasive wear behaviour of directionally solidified Ni-Cr-C alloys was investigated using a pin-type test. M₇C₃ carbide volume fractions (CVF) were varied from 0 to 40%. Two sets of alloys with different carbide and dendrite spacings were abraded with bonded SiC and corundum particles, varying the grit size and applied load. M₇C₃ carbides greatly improved the abrasive wear resistance against fine-grained SiC particles within the whole range of compositions. By refining the primary carbide structure in hypereutectic alloys, the wear resistance against coarse-grained SiC particles was also improved with increasing CVF although SiC is known to be much harder than M₇C₃. Coarse SiC abrasive particles had a detrimental effect on the wear resistance of all hypoeutectic alloys and, even more, of hypereutectic alloys if the primary carbides were coarse. In testing with corundum, the wear resistance always improved with increasing carbide volume fraction.Wear damage was arranged in three classes. First, SiC and corundum abrasives were partially broken from the substrate at the entrance edge of the specimen. The edges of SiC grains stayed sharp during the wear process whereas the edges of corundum particles were rounded or the corundum was crushed by M₇C₃ carbides. Secondly, damage in the wear surface occurred by fracturing of the edges of carbides facing the wear surface. In addition, SiC abrasives were able to groove carbides. Thirdly, coarse SiC grains transmitted shear stresses causing severe subsurface damage leading to microstructure disintegration and spalling of primary carbides. SiC transmitted larger shear stresses than corundum because the latter was separated by a thin layer of wear debris from the unworn material.The microstructural parameters influencing wear were CVF, size, morphology and distribution of carbides. Optimum wear resistance depended on the abrasive mineral. Alloys with high CVF and coarse primary carbides were best suited for wear with corundum whereas fine primary carbides were required to resist wear by SiC.     

Diamond coatings for increased wear resistance

Use of small particle sizes in wear coatings is discussed and the control that can be maintained of the size and shape of the particles is described. The physical properties of the diamond coating used and the effect of particle shape, particle concentration and operating temperature on its performance under test conditions are investigated and the results obtained for a range of applications are presented     

On the comparison of the abrasive wear behavior of aluminum alloyed and standard Hadfield steels

The abrasive wear behaviors of aluminum alloyed Hadfield steel at the high and low stress wear conditions were studied and compared with non-Al alloyed Hadfield steel. The wear tests were done with the pin on disc method using the abrasive wheel. The main parameters such as alloy compositions, normal load, sliding speed and sliding distance were evaluated. It is shown that at the low stress condition, the aluminum alloyed Hadfield steel has higher wear resistance than the non-Al alloyed Hadfield steel. But at the high stress wear conditions, the non-Al alloyed Hadfield steel is more resistant than the Al alloyed.     

Study of wear resistance of thermal-diffusion boron nitride coatings on titanium

The wear resistance of commercially pure titanium VT1-0 covered with boron nitride coatings in pair with steel U8 is studied. It is found that the boron nitride coatings deposited from amorphous boron by thermal-diffusion saturation in molecular nitrogen at temperatures of 800?C850°C using the noncontact method improve the wear resistance of titanium during boundary sliding friction. Their characteristics are compared with those of boride coatings on titanium deposited by the same method. It is shown that the high-gradient strengthened layers formed during contact thermal-diffusion boronitriding within the 900?C950°C temperature range affect adversely the tribological performance of the boron nitride coating-steel pair.     

Performance of abrasive wear of WC-12Co coatings sprayed by HVOF

The performance of multimodal and conventional materials in the form of coatings deposited by high velocity oxy-fuel (HVOF) thermal spraying has been studied. WC-12Co coatings were deposited under same conditions using multimodal and conventional WC-12Co powder feedstocks. The phase composition of the feedstock powders and the coatings were analyzed by XRD. Abrasive wear resistances of coatings were carried out on wet sand rubber wheel abrasion tester. The characterizations of spraying feedstock powders, microstructure and surface micrographs of the prophase and anaphase attrition surfaces were performed by SEM. The results indicated the multimodal coating shows slight higher microhardness and better abrasive wear resistance than the conventional counterpart. Also, the thermally sprayed carbide-based coatings have excellent wear resistance with respect to the hard chrome coatings.     

Experimental investigation of oil pockets effect on abrasive wear resistance

The experiments were carried out using a block-on-ring tester. The stationary blocks were modified by a burnishing technique in order to obtain surfaces with oil pockets of spherical shape. The area density of oil pockets varied in order to explore their effect on wear resistance and wear intensity. Specimen surfaces had dimples with depths 45-60 μm and diameters 1-1.2 mm. The area density of oil pockets S_p was in the range 4-20%. The block samples were made from bronze B101 (CuSn10P) of 138 HB hardness. The rotated rings were made from 42CrMo4 steel, hardness of 40 HRC obtained after heat treatment. The tested assembly was lubricated by mineral oil L-AN 46. The experiment was carried out under artificially increased dustiness conditions. The dust added to oil consists mainly of SiO₂ (74%) and Al₂O₃ (15%) particles. During the test friction force and temperature of block sample were registered. The tendencies of block surface topography changes during wear were analysed. It was found that sliding pairs with textured specimens were not superior to a system with a turned block with regard to abrasive wear resistance.     

Influence of precipitation and solution strengthening on abrasive wear resistance

The influence of precipitation and solution strengthening on gouging abrasion resistance has been studied using a 6061 aluminium alloy heat treated to obtain four different microstructures. Single-event abrasive grooves were generated using a modified Charpy impact tester and the specific energy consumption in grooving was recorded and used as a measure of wear resistance. In addition, the mechanisms of chip formation and material removal were studied by metallographic analysis of “quick-stop” specimens.The results of the grooving tests show that for small grooves precipitation strengthening yields higher energy values than solution strengthening, the wear resistance increasing with decreasing precipitate size. The ranking of the different heat treatments with respect to specific grooving energy depends, however, on the considered damage depth and the opposite order of ranking is found at the largest groove depths. On the basis of the results of the grooving tests, a discussion on the influence of groove depth and microstructure on chip formation and specific grooving energy is presented. In particular, the inhomogeneous nature of the plastic deformation involved in chip formation is discussed, and the resulting importance of the thermal stability of the material in determining wear resistance is emphasized.     

42CrMo钢振动磨料磨损研究

为研究振动对材料磨损的影响,对经过低温、中温、高温回火的42CrMo钢在自制的振动磨料磨损试验机上进行了振动磨损实验.结果表明,试样的塑性、硬度及磨料的振动参数综合影响其耐磨性,磨损量并不与磨料的振动频率成正比,磨粒的振动影响材料的磨损形貌.     

Principles of abrasive wear

The mechanisms of abrasive wear are reviewed and laboratory test methods assessed. The results of abrasive wear tests on technically pure metals, heat treated steels, cold work hardened materials, hard wear resistant materials and minerals against fixed abrasive grains are discussed. The correlation between abrasive wear resistance and the physical properties of materials is established; the effect of the relative hardness of the abrasive and impact loading is considered. The basic principles of abrasive wear derived are outlined.     

Structure and wear resistance of electron-beam nitrous coatings

The paper deals with the study of the tribological properties of nitrogen-containing austenite coatings deposited by electron-beam facing during abrasive wear and the sliding friction of a VK6 hard alloy indentor. The abrasive wear resistance of the nitrous coatings deposited by the electron-beam facing of steel 60Kh24AG16 powder in quartz sand is lower than that of the steel 65G coatings after hardening; it increases with increasing mass share of the filler. At contents of nitrided ferrovanadium of 10?C30 wt % the abrasive wear rate increases by 30?C50%, respectively. It is found that under a certain load applied to the VK6 ball indentor the friction coefficient and the shear resistance of the surface layer diminish. It is shown that under heavy specific loads applied to the ball indentor the nitrous coating faced from steel 60Kh24AG16 powder and composite nitrous coatings have wear resistance exceeding that of steels 110G13 and Kh18N10 by more than two and seven times, respectively. Based on the results of structural studies an explanation of the observed behavior of the nitrous coatings is proposed.     

Ductility and the abrasive wear resistance of hot work die steels

Two-body abrasive resistance has been determined as a function of tempering temperature for a conventional hot work die steel and two experimental hot work die steels. After tempering in the secondary hardening range both experimental steels exhibit abrasive wear resistance comparable with or superior to that of the conventional die steel. In addition, the abrasive wear behavior of the three steels has been assessed using an approach suggested by one of the authors which emphasizes the role of ductility in determining abrasive wear resistance. As suggested by that approach, the product of the wear ratio and the bulk hardness tends to decrease with increasing tensile strain to fracture.     

Influence of abrasive hardness on the wear resistance of high chromium irons

The resistance to abrasive wear was determined for a series of alloyed white cast irons in a high stress abrasion test which utilizes a specimen in sliding contact with bonded abrasives. These were conducted on silicon carbide, alumina and two sizes of garnet abrasive.The results indicate that the hardness, or type, of abrasive used in the test significantly influenced the wear rate of white irons, i.e. the rate of wear increased with increasing hardness of the abrasive. Also, the results indicate that the type of abrasive used in the test was a significant factor in ranking white irons for resistance to high stress abrasion. When tested on silicon carbide or alumina abrasive, as-cast austenitic irons exhibited lower rates of wear than heat treated martensitic irons; when tested on garnet, an abrasive of lower hardness, those irons with martensitic matrix microstructures exhibited the same or less wear than irons with austenitic matrix microstructures. It was also evident that heat treated irons with martensitic matrix microstructures exhibited varying degrees of resistance to abrasive wear depending on cooling rates and alloy content.