The effect of microstructure and wear conditions on the wear resistance of steel metal matrix composites fabricated with PTA alloying technique

The concept of hard particles in a softer metal matrix has long appealed to number of industries dealing among others with drilling and mining. For these facilities, the PTA (Plasma Transferred Arc) alloying technique is advisable and advantageous for several reasons; the equipment may be portable and moved near the working site, the treatment may be applied strictly to the area where the wear problem is situated and after the treatment little machining is required. Four different coatings are tested against three different modes of wear occurring either alone or less frequently combined in this kind of applications, i.e. adhesion, low stress abrasion and two-body abrasion. Two of the coatings examined belong to the category of tool steels with very hard carbides in their microstructure, namely TiC, M₂C and M₆C. The other two are boride coatings belonging to the Fe–B and Fe–Cr–B system respectively. A heat treated AISI D2 tool steel commonly used in this type of applications is also examined for comparison. Fe–Cr–B coating performance is at least 2 times better in low stress and two-body abrasion and four orders of magnitude better in adhesion wear than the AISI D2 tool steel. Fe–B coating can be used in pure adhesion or abrasion situations, but their brittleness forbids their use in situations involving impact loading. AISI M2 coating presents similar wear performance with AISI D2 tool steel in abrasion, whereas in adhesion wear it performs at least two orders of magnitude better. MMC–TiC coating has good performance in pure two-body abrasion situations due to the presence of the very hard TiC particles in its microstructure.     

Some observations on two-body abrasive wear

Pin-on-disc-type two-body abrasion tests were carried out on five metals with seven particle sizes over a range of loads, lengths of travel and sliding speeds. The familiar results that two-body abrasive wear is proportional to load and to distance travelled were confirmed. The “size effect”, in which particles below about 100 μm produce progressively less wear, was shown to be independent of load, sliding speed and prior cold working. Increasing the sliding speed from 1 to about 100 mm s^?1 produced an increase in wear resistance of about 50% for AISI 1020 steel. An increase in velocity above 100 mm s^?1 had little effect on the wear resistance. Plots of the wear resistance against the hardness of the annealed metal showed significant deviations from the linear relationship reported in the literature. The result is influenced by both sliding velocity and particle size.     

硬质颗粒复合合金的组织和耐磨性

本文强调基体合金组织对硬质颗粒复合合金耐磨性的决定作用,设计并通过“真空吸附铸件表面合金化工艺”,在灰铁铸件表层稳定地制得了以不同粒度的铸造碳化钨颗粒均匀分布于高合金铬钨白口铸铁中的复合合金。磨料磨损试验表明：基体合金组织对复合合金二体尤其是三体高应力磨损耐磨性有决定性的作用;以马氏体合金白口铁为基体合金的复合合金,在二体及三体磨损条件下均具有极高的耐磨性,铸造碳化钨颗粒愈粗,复合合金耐磨性愈高,当颗粒尺寸由140～200目增大到18～28目时,其在二体和三体磨损条件下的耐磨性分别是马氏体白口铁15Cr2Mo1Cu的9～31倍和2.8～6.7倍。     

Correlations between two-body and three-body abrasion and erosion of metals

The effects of various variables on the wear resistance of different pure metals are compared for two-body abrasion, three-body abrasion and erosion. The variables studied are the annealed hardness of the worn metal, the increase in hardness of the worn metal before the wear process due to work hardening and heat treatment, the applied load, the distance travelled, the abrasive particle size and the abrasive hardness. It was found that the effects of most of these variables are similar for the three different wear processes.     

Wear behaviour of AISI D3 and AISI M3:2 tool steels in a mass production shearing operation

The wear of two tool steels (AISI D3 and AISI M3:2) was compared in a normal production shearing operation by scanning electron microscopy at fixed production intervals.After the wear-in period, in which plastic deformation was observed, abrasive wear occurred by the action of small carbides. Wear was more uniform with AISI M3:2 tool steel than with AISI D3 tool steel and the AISI M3:2 tool produced a better finish of the sheared sheet lips.     

Abrasive wear resistance of some commercial abrasion resistant steels evaluated by laboratory test methods

The aim of the present study is to evaluate the abrasive wear resistance of some potential abrasion resistant steels exposed to different types of abrasive wear contact conditions typical of mining and transportation applications. The steels investigated, include a ferritic stainless steel, a medium alloyed ferritic carbon steel and a medium alloyed martensitic carbon steel.The abrasive wear resistance of the steels was evaluated using two different laboratory test methods, i.e. pin-on-disc testing and paddle wear testing that expose the materials to sliding abrasion and impact abrasion, respectively. All tests were performed under dry conditions in air at room temperature. In order to evaluate the tribological response of the different steels post-test characterization of the worn surfaces were performed using optical surface profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. Besides, characterization of the wear induced sub-surface microstructure was performed using optical microscopy.The results show that depending on the abrasive conditions a combination of high hardness and toughness (fracture strain) is of importance in order to obtain a high wear resistance. In the pin-on-disc test (i.e. in sliding abrasion) these properties seem to be controlled by the as-rolled microstructure of the steels although a thin triboinduced sub-surface layer (5–10 μm in thickness) may influence the results. In contrast, in the paddle wear test (i.e. in impact abrasion), resulting in higher forces acting perpendicular to the surface by impacting stones, these properties are definitely controlled by the properties of the active sub-surface layer which also contains small imbedded stone fragments.     

Abrasive wear and its application to digger teeth

Abrasive wear is receiving increased attention particularly as its economic importance is appreciated. Low alloy carbon steels are widely used in the heat treated condition to resist abrasion and, in particular, are used for digger teeth. Little information is available in the literature on field or service wear studies and it was necessary, therefore, to carry out field studies in parallel with a laboratory wear investigation.A particular feature of the field study is the realization that significant wear occurs by rubbing to produce smooth surfaces and surface transformation, as well as wear by cutting and micro-chipping.A laboratory investigation based upon two-body pin-on-disc testing has been used to investigate the wear of a wide range of experimental steels, a manganese steel and a commercial digger tooth steel for comparison. Wear is directly proportional to the load and inversely related to hardness, but not to sliding distance because of the degradation of the abrasive paper. Abrasion increases with harder abrasives and increased abrasive particle size.The analysis of these results, although important from a wear mechanism point of view, shows that there is currently a lack of direct correlation between the field and laboratory studies because of the different surface features developed. Further investigations are proceeding to improve this correlation.     

Wear mechanisms in ball-cratering tests with large abrasive particles

Three-body abrasive wear resistance of mild steel and 27%Cr white cast iron was investigated using a ball-cratering test. Glass beads, silica sand, quartz and alumina abrasive particles with sizes larger than 200 μm were used to make slurries. It was found that the wear rates of mild steel increased with sliding time for all abrasive particles tested, while the wear rates of 27%Cr white cast iron were almost constant with sliding time. This increase in the wear rates of mild steel was mainly due to the gradual increase in ball surface roughness with testing time. Abrasive particles with higher angularity caused higher ball surface roughness. Soft mild steel was more affected by this ball surface roughness changes than the hard white cast iron. Generally, three-body rolling wear dominated. The contribution of two-body grooving wear increased when the ball roughness was significant. The morphological features of the wear scars depended on the shape of the abrasive particles and also on the hardness and microstructure of the wear material. Angular particles generated rough surfaces similar to those usually observed in high angle erosion tests. Rounded particles generated smoother surfaces with the middle area of the wear craters having similar morphology to those observed in low angle erosion.     

Erosion of metals using angular silicon carbide particles

ABSTRACT

In this work, erosion tests conducted to evaluate the resistance of two materials, Metal Babbitt Grade 7 and AISI T1 against SiC particles. The erosion rates of these two metals compared with those obtained using AISI D2 steel in a previous work with similar testing conditions. Metal Babbitt and AISI T1 steel selected due to their high ductility and strength, respectively. A test rig similar to that shown in ASTM G76-95 standard used to perform the tests. Silicon carbide particles had a particle size between 350–450 µm. Tests carried out using different impact angles, 30°, 45°, 60° and 90° with a particle velocity of 24 ± 2 m/s and the abrasive flow rate was 0.7 ± 0.5 g/min. SEM photographs used to identify the wear mechanisms on the Babbitt and T1 steel and also obtained cross-section images of the wear scars on metal Babbitt to measure their depth.     

Abrasive wear behaviour of hardened high strength boron steel

Abstract

Abrasive wear in industrial applications such as mining, materials handling and agricultural machinery constitutes a large part of the total wear. Hardened high strength boron steels are known for their good wear resistance and mechanical properties, but available results in the open literature are scarce. This work aims at investigating how different quenching techniques affect the two-body abrasive wear resistance of hardened high strength boron steels. Furthermore, the wear as a function of depth in thicker hardened high strength boron steel plates has also been studied. The material characterisation has been carried out using microhardness, SEM/energy dispersive spectroscopy and three-dimensional optical surface profilometry. The results have shown that water quenched and tool quenched high strength boron steel had similar wear resistance. The main wear mechanisms appear to be microcutting combined with microfatigue. Workhardening during the abrasion process has been found to affect the abrasive wear.     

Influence of hardness of the counterbody in three-body abrasive wear — an overlooked hardness effect

The resistance to three-body abrasion of some common metals, mainly a tool steel and an aluminum alloy, both heat treated to different hardnesses, has been evaluated in two different tribosystems. The different materials have been tested against each other in different combinations to study the influence of the relative hardness of the two bodies on the wear rate in three-body abrasion. In all tests the abrasives have been much harder than the metals. It was observed that the wear rate of asolid body in three-body abrasion strongly depends on the hardness of the counterbody. In three-body abrasion a material may, under some circumstances, be most strongly worn if the counterbody is softer than the metal to be worn. This is because the abrasive particles can be embedded in the softer surface and groove the harder one. However, many parameters of the tribosystem influence the embedding of particles and the wear rate in three-body abrasion. It is shown that the size of the area in which the abrasives are embedded compared to the size of the wear scar in the counterbody as well as the smoothness of the surfaces are of importance.     

Correlation between abrasive wear resistance and changes in structure and residual stresses of steels

The connection between the structure and abrasive wear resistance of steels was studied. Samples of AISI 1020, 1040 and 1080 steels were tested. The initial hardness of the samples ranged from HV221 – for annealed steel AISI 1020, to HV868 – for water quenched and tempered at 180°C steel AISI 1080. Two‐body abrasive tests on silicon carbide abrasive paper of grit size 1200–240 were carried out on a friction machine under identical conditions for all specimens. X‐ray studies of the specimens were conducted before and after these tests. It was shown that characteristics such as the integral width of diffraction lines could be used as a universal indicator of abrasive wear resistance for steels, independently of their heat treatment. The compressive residual stresses in the surface layers of the steels were observed. The results showed that there is a correlation between abrasive wear resistance and the sign and magnitude of residual stresses in the surface layers of steels, as well as between abrasive wear resistance and the structural changes in these layers. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sliding wear behaviour of ZrN and (Zr, 12 wt% Hf)N coatings

In the present study, the sliding wear resistances of ZrN and (Zr, 12 wt% Hf)N coatings deposited on a hardened AISI D2 tool steel by arc-physical vapor deposition (PVD) technique were examined by a ball-on-disc wear tester. Alloying of ZrN coating with 12 wt% Hf did not change the hardness significantly, but achieved an improvement on adhesion strength and dry sliding wear resistance against steel (AISI 52100-55HRC) and Al₂O₃ balls.     

Tempering temperature effects on abrasive wear of mottled cast iron

The effects of different tempering temperatures (300–600 °C) on abrasive wear resistance of mottled cast iron were studied. Abrasive wear tests were carried out using the rubber-wheel test on quartz sand and the pin test on Al₂O₃ abrasive cloths. The retained austenite content of the matrix was determined by X-ray diffraction. The wear surface of the specimens was examined by scanning electron microscopy for identifying the wear micromechanism. Bulk hardness and matrix hardness before and after the tests were measured. The results showed that in the two-body (pin-on-disc test) system, the main wear mechanism was microcutting and high matrix hardening was presented. The wear rates presented higher correlation with the retained austenite than with the bulk and matrix hardness. In the three-body system (sand–rubber wheel), the wear surfaces presented indentations due to abrasive rolling. The wear rates had better correlation with both the bulk and matrix hardness (before and after the wear test) than with the retained austenite content. There are two groups of results, high and low wear rates corresponding to each tribosystem, two-body abrasive wear and three-body abrasive wear, respectively.     

Refinement of tempered martensite structure and its effect on wear mechanism in SAE 8620

All mechanical components that undergo sliding or rolling contact are subjected to some degree of wear. Carburising treatment is important in improving wear characteristics of AISI 8620 gear steel. An experimental investigation was conducted on carburised AISI 8620 steel. Gas carburising of the specimens was carried out in sealed quenched furnace at 1198 K for 6 h followed by hardening at 1133 K, oil quenching at 393 K and followed by tempering at 453 K. Carburised cryotreated samples were cooled in a controlled manner soaked at 88 K for 16 h in a cryoprocessor subsequently followed by soft tempering at 373 K. Specimens were characterised by microhardness test, wear test and retained austenite content by XRD. 3D wear surface response and 2D contour map showed that wear rate decreased by 32% in the case of carburised cryotreated specimens as compared to only carburised specimens. It was concluded that there was an improvement in hardness and wear resistance of carburised cryotreated steel as compared to only carburised steel. Refinement and densification in martensitic structure resulted in shift in wear transition from severe wear regime to mild wear regime.     

Sliding abrasion resistance assessment of metallic materials for elevated temperature mineral processing conditions

The multiplicity of harsh environments in mining, processing and transporting ore and related waste, cause severe wear, extremely high maintenance costs and lost production.Elevated temperature processing is one of the conditions that influence the performance of possible materials of construction. This takes the forms of reduced hardness and strength, deleterious changes in the structure and properties of materials during protracted exposure and increased oxidation and corrosion.Drag chain conveying of hot solids e.g. in smelting, typically results in three-body sliding abrasion and adhesive wear of connecting pins and hole surfaces in link assemblies and of moving paddles that impel the particulates in enclosed channels. Selected materials have been assessed for this type of service under reciprocating sliding abrasion contact conditions using an adapted Cameron-Plint TE77 wear rig at 20 °C and 350 °C. These include the current carburised low alloy steel, other steels, Cr white irons and Co-based alloys in bulk, overlay and surface treated forms.Examination of wear scars, using scanning electron microscopy, identified the main wear mechanisms affecting the highly resistant powder metallurgical (PM) tool steels and HVOF coating as micro-scratching and as indentation leading to micro-fracture. Materials with lowest resistance displayed evidence of significant material removal by micro-ploughing. The formation of oxide layers on some samples during testing appeared to be beneficial.     

On the wear of reinforced thermoplastics by different abrasive papers

Single-pass two-body abrasion tests were run on unfilled and glass-fibre-and glass-sphere-filled polyethylene terephthalate sliding dry against different abrasive papers. The abrasive grains varied in hardness and size. Wear mechanisms were studied by using scanning electron microscopy. A functional relationship was developed between the single-pass wear rate under severe abrasive conditions (dominated by microcracking events) and a term considering the hardness and macrofracture energy of the composites as well as a probability factor for microcracking. The probability factor includes parameters of the abrasive counterbody and some geometrical and frictional details of the composite investigated.     

Variations in wear loss with respect to load and sliding speed under dry sand/rubber-wheel abrasion condition: a modeling study

The dry sand/rubber-wheel abrasion tester is widely used to evaluate the low-stress abrasion resistance of materials for the mining/mineral processing industry particularly for the oil sand mining industry. Since wear loss is usually proportional to the applied load, this test is often performed under a fixed load at a fixed sliding speed to rank materials. However, inaccurate or misleading information might be generated under an inadequate load. It has been observed that D2 tool steel exhibits very different responses to variations in the applied load. Above a certain load level, further increase in the applied load may lead to a decrease in wear loss of D2 steel. In order to understand this phenomenon, computer simulation was performed to investigate wear responses of several engineering materials, including D2 tool steel, stainless steel, Al 6061 and Cu 110, to variations in applied load under the dry sand/rubber-wheel abrasion condition. It was demonstrated that the decrease in wear loss of D2 tool steel with an increase in the applied load was attributed to failure of the abrasive sand. Wear losses of the materials with respect to the sliding speed were also investigated. The prediction from the simulation was compared to experimental observations.     

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.     

Abrasive wear mechanisms of fluoropolymer based composite coatings on aluminum substrates

Experimental studies on wear performance and wear mechanisms of fluoropolymer based composite, non-stick coatings on aluminum substrates were carried out by using particular wear testing methods, i.e. the “mechanical tiger paw (MTP) Test” and the “Nord Test”. Both are supposed to simulate household abrasive operating conditions in a laboratory environment. It was found that the wear process involved in the MTP Test was an accelerated one, but that in the Nord Test was decelerated due to a transition from severe three-body abrasion to milder two-body sliding wear. In addition, both effects of the microstructure of the coatings and of the surface treatment of the substrates were discussed.