J. D. Gates

Two-body and three-body abrasion: A critical discussion

Abstract It is argued that the common classification of abrasive wear into ‘two-body abrasion’ and ‘three-body abrasion’ is seriously flawed. No definitions have been agreed upon for these terms, and indeed there are two quite different interpretations, the implications of which are mutually inconsistent. In the dominant interpretation, the primary thrust of the two-body/three-body concept is to describe whether the abrasive particles are constrained (two-body) or free to roll (three-body). In this view, two-body abrasion is generally much more severe than three-body. The alternative interpretation emphasises the presence (three-body) or absence (two-body) of a rigid counterface backing the abrasive. In this view, three-body abrasion is equated to high-stress (or grinding) abrasion and is generally more severe than two-body (low-stress) abrasion. This paper recommends that the ‘two-body/three-body’ terminology be abandoned, to be replaced by an alternative classification scheme based directly upon the manifest severity of wear.

Effect of hardness on three very different forms of wear

Abstract Different abrasive wear tests have been applied to materials with hardnesses ranging from 80 HV (aluminium) to 1700 HV (tungsten carbide). The test were: dry sand rubber wheel (DSRbrW); a similar test using a steel wheel (DDDdW); a new combined impact-abrasion test (FIA). The DSRbrW results were as expected, giving generally decreasing wear with increasing hardness. White cast irons and tool steels containing coarse, hard carbide particles performed better than more homogeneous materials of comparable hardness. When normalized to load and distance, the DSStlW results for the homogeneous materials were similar to the DSRbrW results. The multi-phase materials performed poorly in the DSStlW test, with volume loss for high-speed steel (880 HV) higher than that of aluminium. Within this group, wear increased with increasing hardness. These unexpected results are explained in terms of (a) differential friction coefficients of wheel and specimen, (b) increased fracture of sand, and (c) introduction of microfracture wear mechanisms. The FIA combined impact-abrasion results lacked clear correlations with hardness. The span relative wear rates was similar to that reported for materials in ball mills. White cast irons at maximum hardness performed fairly poorly and showed evidence of microfracture.

Determination of retained austenite using an X-ray texture goniometer

A new X-ray technique has been developed for determining the amount of retained austenite in steels with preferred orientation, such as white cast irons and deformed steels. The technique uses an X-ray texture goniometer. The X-ray goniometer was run as ifa texture was being determined, but the raw data were collected via a special program. From analysis of the raw data for several austenite and martensite reflections, a very accurate value for the retained austenite content was obtained. The technique has been evaluated using a textured specimen with a known amount of retained austenite, and by carrying out the determination at different orientations of a single specimen. Compared with other methods, this technique can produce retained austenite values to an accuracy of +/-1.5%. As an application of this technique, the relationship between the amount of retained austenite and heat-treatment parameters in a white cast iron has been studied

The effect of heat treatment on the toughness, hardness and microstructure of low carbon white cast irons

The effect of destabilisation and subcritical heat treatment on the impact toughness, hardness, and the amount and mechanical stability of retained austenite in a low carbon white cast iron have been investigated. The experimental results show that the impact energy constantly increases when the destabilisation temperature is raised from 950°C to 1200°C. Although the hardness decreases, the heat-treated hardness is still greater than the as-cast state. After destabilisation treatment at 1130°C, tempering at 200 to 250°C for 3 hours leads to the highest impact toughness, and secondary hardening was observed when tempering over 400°C. The amount of retained austenite increased with the increase in the destabilisation temperature, and the treatment significantly improves the mechanical stability of the retained austenite compared with the as-cast state. Tempering below 400°C does not affect the amount of retained austenite and its mechanical stability. But the amount of retained austenite is dramatically reduced when tempered above 400°C. The relationship between the mechanical properties and the microstructure changes was discussed.

A model of stress induced martensitic transformation in Fe-Ni-C alloy

A model for the stress induced martensitic transformation in an Fe-Ni-C alloy [1] was further studied. Because the stress induced transformation occurs preferentially in the grains, which are orientated such that the stress axis is close to , a texture in the untransformed austenite was effectively generated when the martensite amount is less than 32%. This texture has been experimentally confirmed by X-ray diffraction. According to the model, the first formed martensite variant in a given grain will be the one with the largest stress assistance. As a result of the additional stress field caused by the formation of this first variant, the variant with the second largest stress assistance will form next to the first, which leads to a formation of coupled growth martensite pair. The model predicts that the stress induced coupled growth martensite does not change the overall strain energy. This agrees with the experimental results.

The effect of the reduction of carbon content on the toughness of high chromium white irons in the as-cast state

Three high chromium white cast irons were examined in the as-cast state to determine the effect of the carbon content on the fracture toughness. The plane strain fracture toughness KIc and the fracture strength were measured for each alloy. X-ray mapping was used to identify the phases on the fracture surfaces. Scanning electron fractography and optical microscopy were used to determine the volume fraction of each phase on the fracture surfaces. It was found that most fracture occurred in the eutectic carbides, but that for the alloys with a reduced volume fraction of eutectic carbides, a small amount of crack propagation occurred in the austenitic dendrites. This change in crack path correlated with an increase in fracture toughness. The Ritchie-Knott-Rice model of brittle fracture was applied. It was found to sensibly predict the critical length for fracture for each alloy. Deep etching was employed to examine the distribution of eutectic carbides. It was found that the eutectic carbides formed a continuous network in each case.

Determination of habit planes using trace widths in TEM

A simple and accurate method of determining the habit planes from the determination of beam and habit plane trace directions using Kikuchi line diffraction patterns and the measurement of the thickness of the thin foil has been developed. The thickness of the thin foil can be calculated from the measurements of the widths of the habit plane trace at two different positions. The first orientation is with the foil normal to the electron beam (zero tilt) and the second one is where the foil has been tilted by a known amount about an axis parallel to the original trace at zero tilt. From the beam and the trace directions and thickness of the thin foil, the indices of the habit plane normal may be calculated. The technique has been tested using {111} annealing twin interfaces in stainless steel and shown to be capable of determining habit planes to within a degree or two. Extension of this method to the measurement of martensite habit planes is described.

Transmission electron microscopy of a transformation toughened white cast iron

Transmission electron microscopy has been used to study the microstructure of an experimental white cast iron, in which a combination of modified alloy composition and unconventional heat treatment has resulted in a fracture toughness of 40 MPa m-1/2. Microstructural features of the alloy that contribute to the toughness improvement and hence distinguish it from conventional white irons have been investigated. In the as-cast condition the dendrites are fully austenitic and the eutectic consists of M7C3 carbides and martensite. During heat treatment at 1130 °C the austenite is partially destabilized by precipitation of chromium-rich M7C3 carbides. This results in a dendritic microconstituent consisting of bulk retained austenite and secondary carbides which are sheathed with martensite. The martensite sheaths, which contain interlath films of retained austenite, are irregular in shape with some laths extending into the bulk retained austenite. Emphasis has been placed on the morphology, distribution, and stability of the retained austenite and its transformation products in the dendrites. The implications of these findings on the transformation toughening mechanism in this alloy are discussed.

Synergistic corrosion-abrasion of cast wear-resistant materials in HN03

Synergistic corrosion—abrasion may be a serious contributor to wear in minerals processing operations, even when pure corrosion rates do not appear to be significant. In this work, a simple laborat...