Erosive wear by silica sand on AISI H13 and 4140 steels

The erosive wear behaviour of AISI H13 tool steel and AISI 4140 steel has been investigated in this work using a sand blast-type rig. Samples of six different hardness levels (from annealed to 595 HV) were produced and subsequently tested using silica sand as the erodent material at impact angles ranging from 10° to 90°, air drag pressures of 0.689 and 1.38 bar (10 and 20 psi respectively), impact speeds ranging from 70 to 107 m s⁻¹ and various particle sizes. Results of erosion versus impact angle at different hardness levels showed three distinctive wear regions: (i) for impact angles of 10° and 20°, the amount of wear was higher at lower hardness values; (ii) for impact angles of 30° and 40° no significant changes were found in the amount of wear despite the increase in hardness; (iii) for impact angles of 60°, 75° and 90° the amount of wear was higher for higher hardness levels in the eroded material. Single curves showed typical ductile behaviour of these alloys, a transition towards brittle behaviour for the hardest specimens was also observed due to the formation of adiabatic shear bands. SEM analysis was conducted to identify the erosion mechanisms for each type of behaviour.     

Development and characterization of a wear resistant bainite/martensite ductile iron by combination of alloying and a controlled cooling heat-treatment

In this paper, a bainite/martensite (B/M) dual-phase ductile iron was fabricated by combining alloying and a controlled cooling heat-treatment. The microstructure, the mechanical properties and the wear performance were investigated and discussed. The ductile iron containing 3.2–3.8 wt.% carbon was alloyed with 2.5–3.0 wt.% manganese and 2.5–3.0 wt.% silicon. In general, manganese is no more than 0.7 wt.% and silicon <2.5 wt.% in commercial grade lower-bainite ductile irons. So, manganese contained in the ductile iron in this work is several times higher, and silicon slightly higher. In order to control the phase transition in the ductile iron during the heat-treatment, its continuous cooling transformation (CCT) curve was determined. The controlled cooling heat-treatment process was determined according to the CCT curve, which included three stages. The first stage was water quenching of the sample rapidly from the austenization temperature to a temperature below 350°C in a few minutes. The second stage was heat preservation of the sample from the spraying end temperature to 200°C in 2 h. The last stage was air cooling of the sample from 200°C to RT. According to the analysis using the scanning electron microscope (SEM) and the X-ray diffraction (XRD), the matrix of the ductile iron had a microstructure of bainite, martensite and a little retained austenite. The hardness and impact toughness of the heat-treated ductile iron were HRC 51.5 and 21.7 J/cm², respectively. The high values of the hardness and toughness were attributed to (1) the refined structure, (2) the presence of B/M dual-phase and (3) the presence of retained austenite. The impact abrasive wear resistance of the B/M ductile iron was observed to be comparable with that of a high chrome cast iron, and twice that of Mn13 steel.     

Solid particle erosion of diamond coatings under non-normal impact angles

This paper describes an erosion study, which examines the effect of impact angle on the erosion behaviour of diamond coatings deposited on tungsten substrates by chemical vapour deposition (CVD). The coatings were 37–60 μm in thickness and were erosion tested using angular silica sand with a mean diameter of 194 μm at a particle velocity of 268 m s⁻¹. The impact angles used were 30, 45, 60 and 90°. The results show that the damage features, termed “pin-holes” are generated at all angles, though the number of impacts required for pin-hole initiation is significantly increased at lower angles. This work provides useful information in attempting to explain the mechanism by which damage is generated during the high velocity sand erosion of CVD diamond.     

Einfluss der korngrösse auf das strahlverschleissverhalten von metall und nichtmetallischen hartstoffen

Abrasion of materials, steel St 37, C60H and sintercorund in the form of plates at different angles in a sand blasting apparatus with corund particles of 1000, 100 and 10 μm size at a velocity of 130 m/s shows that with diminishing grain size, maximum wear occurs at lower angles. With artificial basalt under similar conditions, maximum wear always occurs at an angle of 90°. The results are explained by an increase of elastic and plastic absorption of energy with decrease of fracture energy. At low strain, the materials probably absorb energy by microplastic deformation. The results show that the transformed energy at the impact of a single particle is of importance.     

The wear of ultrafine WC–Co hard metals

The wear performance of ultrafine-grained tungsten carbide–cobalt (WC–Co) hard metals during three-body abrasion and particle erosion has been evaluated and compared to that of similar conventional coarser grained hard metals. The tungsten carbide grain size varied between 0.5 and 3 μm with cobalt contents ranging from 6 to 15%. Silica particles were used in both forms of testing. Erosion was carried out at 60 ms⁻¹ at an impact angle of 75° and abrasion at a velocity of 0.5 ms⁻¹ and a load of 50 N.

The wear resistance of the ultrafine grades was found to be at least double that of the closest conventional fine grained hard metals. These increases in wear performance are considerably higher than any corresponding increase in hardness which is, at most, 25% and is not achieved at the expense of fracture toughness which is maintained at a similar level to that of conventional fine grained hard metals. The increase in wear resistance coincides with a change in the mechanism of material removal. Sub-micron materials experience ductile deformation and bulk removal of material whilst coarser grades display more localised response with extensive fragmentation of the WC grains.     

The mean dynamic yield strength of copper and low carbon steel at elevated temperatures from measurements of the “mushrooming” of flat-ended projectiles

Mean dynamic yield strengths for copper and mild steel are deduced from strain measurements on the “mushroomed” ends of flat-ended projectiles, after impact on a flat, nominally rigid anvil. The kinetic energy at impact is equated with plastic work, to give a mean dynamic yield strength averaged over the deformed specimen. Experiments are carried out over the temperature range 20–700°C, with impact velocities in the region of 600 ft/sec, giving a mean strain rate estimated at 5 × 10³/sec. The yield stress-temperature results obtained show an abrupt increase in dynamic/static mean yield stress ratio at homologous temperatures, T/T_M, of 0·4 for steel and 0·5 for copper. These results agree generally with the findings from other investigations into high-speed blanking⁵ and indentation.⁷

Existing theories for the mushrooming of flat-ended projectiles^{1, 3} do not predict the profiles actually obtained in the present experiments.     

Erosive wear of hardfaced Fe–Cr–C alloys at elevated temperature

Many engineering components are subjected to erosive wear at elevated temperature. As erosive wear at elevated temperature is governed by the synergistic effect of erosive wear and oxidation, it is possible to modify surfaces of the components in order to achieve improved performances. In view of the above, two different types of hardfacing alloys of Fe–Cr–C were designed incorporating Nb, Mo and B to ensure improved performances at elevated temperature. In order to achieve the above objective, mild steel was hardfaced with these alloys under optimised gas metal arc welding (GMAW) condition. The microstructures of the hardfaced coating was characterised with the help of optical microscopy (OM) and scanning electron microscopy (SEM). The mechanical properties of these coatings were obtained by means of micro indenter. Erosive wear of these coatings was evaluated for four different temperatures, for two different impact angles and at one impact velocity. The morphologies and the transverse sections of the worn surfaces are examined with SEM. The erosive wear of these coatings were compared with conventional M2 tool steel. Results indicate that erosion rate of these coatings increases with increase of test temperature and impact angles. Among various coatings, Fe–Cr–C coating containing higher amount of Nb, Mo and B exhibits best erosion resistance particularly at elevated temperature.     

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 aluminium-based claddings on steel by sand in water

This paper describes the slurry erosion of a range of HVOF deposited aluminium-based claddings on steel by sand in water. Coatings, approximately 300 μm thick, of commercially pure aluminium, eutectic aluminium/silicon alloy (12%) and of a novel composite incorporating alumina in this alloy have been tested, both as sprayed and as ground to remove surface roughness as far as possible. Angular silica sand of mean diameter 235 μm was used at a concentration of 2.5% in tapwater at impingement angles of 90° and 30° and a jet velocity of 27 m/s. Mass loss data and surface structure, as shown by electron microscopy and profilometry, are related to the test conditions, initial surface topography, material hardness and microstructure, especially porosity. They are discussed in terms of the mechanisms of erosion that occur in the different materials, with reference to microcutting and plastic deformation of the surface and to the effects of the alumina inclusions. The consequences of poor flow-out, leading to significant residual porosity of the composite cladding are discussed.     

Unlubricated sliding and rolling wear of thermoplastic dynamic vulcanizates (Santoprene) against steel

The friction, sliding and rolling wear characteristics of thermoplastic dynamic vulcanizates (TPV; Santoprene^® grades), composed of polypropylene (PP), ethylene/propylene/diene rubber (EPDM) and extender oil, were studied against steel counterparts in dry condition. The composition and basic mechanical properties of the TPV of various hardness (Shore A = 60°, 70° and 80°) were evaluated. The wear performance of the TPVs was investigated in different tribotests, viz. pin-on-plate (POP), cylinder-on-plate (fretting) and rolling ball-on-plate (RBOP), whereby “plate” was always the rubber. From the above tests the coefficient of friction (COF) and specific wear rate were determined. It was established that with increasing hardness usually both COF and the specific wear rate were reduced. Values of the COF and wear rate depended strongly on the configuration and testing parameters of the related tribotests. The wear mechanisms were concluded by inspecting the worn surfaces by white light profilometry and scanning electron microscopy (SEM), respectively, and discussed.     

The effects of load and substrate hardness on the development and maintenance of wear-protective layers during sliding at elevated temperatures

Transitions to low wear rates often occur during sliding between contacting metal surfaces, due to the establishment of high-resistance load-bearing layers. Such layers are developed from compaction of wear debris particles, with adhesion between the particles being an important factor in determining whether the layers are maintained, leading to wear protection, or break down, leading to abrasive wear. They are formed more easily and retained more effectively at higher temperatures, due to increased sintering and adhesion between the debris particles and to enhanced oxidation of these particles. This paper presents the results of a study of the reciprocating sliding wear and friction of dissimilar combinations of pin and disc steel specimens (high-speed steel and high-chrome steel pins and carbon steel discs) at temperatures of 500–600°C, with emphasis on the influence of load and substrate hardness on the development and maintenance of such wear-protective particulate layers. Complex relationships occur between the effects of increased load in producing larger debris particles, in decreasing the critical particle size for establishing the layers and in decreasing the separation between the sliding surfaces, and the effects of hardness of the substrates on the sizes and amounts of wear particles and on the topographies of the wear scars. The relationships are complicated further by oxidation and sintering of debris particles, leading to development of oxide or oxide-containing ‘glaze’ surfaces, and subsequent breakdown of the layers during sliding.     

Mechanical properties and features of erosion of cermets

The erosive wear resistance of cermets with different composition, structure and properties has been investigated. It has been shown that cermets erosive wear resistance cannot be estimated only by hardness, characterised by resistance to penetration. The differences in wear resistance between cermet materials with equal hardness level can be attributed to differences in their resistance to fracture. The present paper discusses some features of the material removal process during the particle–wall collision. Solid particle erosion tests on eight materials have been performed using silicon carbide and silica abrasive particles within a range of erodent size of 0.1–0.3 mm, impact angles from 30 to 90° and particle velocity from 30 to 80 m s⁻¹. In order to clarify the details of the impact, the process of interaction of solid particles with cermet targets was studied using a laser Doppler anemometer (LDA) measuring technique. Systematic studies of the influence of the impact variables on the collision process have been carried out.     

Sliding speed-temperature wear transition maps for Si3N4/iron alloy couples

The superior high temperature resistance of silicon nitride (Si₃N₄) based ceramics makes them suitable for tribological applications above room temperature or in high speed unlubricated sliding. There are some published works on the wear behaviour of Si₃N₄/metal alloys. However, experimental data are shown in a form that is not of direct use for engineers involved in materials selection. In the present work, Si₃N₄ pins were tested against tool steel and grey cast iron on a pin-on-disc tribometer. Ceramics were produced by hot-pressing and tested without lubrication at variable temperature and sliding speed. SEM/EDS and XRD analysis were used for chemical and microstructural characterisation of worn surfaces and wear debris. At low speeds (0.05–0.5 m s⁻¹) and room temperature, Si₃N₄ surfaces are polished-like due to a combination of humidity-assisted tribo-oxidation and abrasive action of very fine wear debris. At high sliding speeds (2–3.5 m s⁻¹), as well as for temperatures in the range 400–600°C, an extensive coherent tribolayer mainly composed by iron oxides spreads over the ceramic surfaces. Polishing and protection by adherent tribolayers are the mechanisms responsible for observed severe and mild wear regimes, respectively. Wear maps are constructed showing the transition of wear regimes in Si₃N₄/iron alloys contacts determined by constant flash temperature curves. Equations for calculation of bulk and flash contact temperatures in tribocontacts between dissimilar materials are deduced.     

New device for analysis of metal particles in oil

A portable graphite furnace atomic absorption (AA) spectrometer, developed under a contract for this laboratory, has been evaluated using powdered metal particles suspended in oil. The portable wear metal analyzer (PWMA) was designed to support the deployed aircraft requirement for spectrometric oil analysis. The PWMA is a microprocessor-controlled automatic sequential multielement AA spectrometer packaged in two cases having a total weight of 49 kg. The PWMA will analyze for nine elements (nickel, iron, copper, chromium, silver, magnesium, silicon, titanium and aluminum) at a rate of 4 min per sample. The graphite tube and modified sample introduction system increase the detection of particles in oil when compared with the currently used techniques of flame AA or spark atomic emission spectroscopy and represent the major reason for this work — the qualification and calibration of the PWMA with known “wear metal” samples in turbine engine oil. Five (nickel, iron, copper, chromium and silver) of the nine elements analyzed by the PWMA are reported here owing to space limitations. These five elements represent the minimum and maximum concentration ranges of all nine elements. The PWMA shows good-to-excellent response for particles in the size ranges 0–5 and 5–10 μm and fair response to particles of 10–20 and 20–30 μm. All trends in the statistical variations are easily explained by system considerations. Correction factors to the calibration curves are necessary to correlate the analytical capability of the PWMA to the performance of existing spectrometric oil analysis instruments.     

Erosion of 304 stainless steel

Erosion rate measurements and scanning electron microscopy observations were made for the steady state erosion of 304 stainless steel eroded by sharp alumina particles. Both the velocity and the particle size dependence of the erosion rates were similar at all angles of impact between 10° and 90°. Micrographic observations of the steady state erosion surfaces disclosed similar overall features at low and high angles of impact. Results reported in the literature for aluminum tend to confirm these observations. It was concluded that a single erosion mechanism can be operative at all impact angles 7in ductile metals such as stainless steel, rather than a superposition of different mechanisms for the low angle and high angle range. The physical basis for a single mechanism of erosion by sharp particles was discussed.     

Sliding wear of graphite crystallized chromium white cast iron

The effects of sliding velocity, heat-treatment and graphite shape on sliding wear of graphite crystallized chromium white cast iron were studied. Two types of graphite crystallized chromium white cast irons having flaky or spheroidal and another type of 2.6C–15Cr white cast iron were prepared for this study. The effect of sliding velocity on wear resistance was studied by the Okoshi type and pin-on-disk type wear tests on materials which have experienced “as cast” and “heat-treated” conditions. The Okoshi type wear test results are divided into two relationships depending on sliding velocity or distance. Two regimes, initial wear and steady-state wear, existed for wear loss and sliding distance. A characteristic form of wear curve with a peak and a minimum was obtained when correlating wear loss and sliding velocity. The wear resistance of graphite crystallized chromium white cast irons were superior to that of 2.6C–15Cr white cast iron. In the results of pin-on-disk tests, there was no clear difference in the reported wear loss and friction coefficient among the alloys. However, an opposite tendency has appeared in the wear loss and friction coefficient: the wear loss value reached a peak in the wear curve at 0.52 m/s, while the friction coefficient reached a minimum at 0.52 m/s.     

An investigation of the properties and wear behaviour of plasma-nitrided hot-working steel (H13)

The microstructural properties and wear behaviour of AISI H13 steel which had been plasma nitrided at 530 and 550 °C for times between 4 and 100 h have been investigated. The effect of treatment temperature and time on the microstructure have been examined. The wear behaviour of material treated for 4 and 100 h has also been observed. It was seen that a total case depth of 0.55 mm with a hardness of 1000 HV can be achieved in 100 h. However, the white layer thickness is increased to 17 μm while the core hardness is reduced to 480 HV at 550 °C. The wear rate of the sample treated at 550 °C for 100 h is higher than that of the sample treated at 550 °C for 4 h.     

A study on the effect of surface orientation on erosion wear of flat specimens moving in a solid-liquid suspension

Wear characteristics of a ductile material, namely, brass have been investigated by orienting the flat specimens at different orientations relative to the velocity direction in a pot tester containing a solid-liquid suspension. The erosion behavior has been studied at various orientation angles, defined as the angle between the tangent to the plane surface and its velocity. Results at different orientation angles show that the wear at any orientation angle increases with increase in velocity and particle size but decreases with increase in solid concentration. It is also seen that the wear at various operating conditions increases with increase in the orientation angle till 30° attaining the maximum value and then decreases up to 90°. It is further observed that the maximum wear is around 3-4.5 times higher than the surface wear measured at 90° orientation angle.     

Research on oxidation wear mechanism of the cast steels

The uni-directional pin-on-disk wear tests were performed in elevated-temperature air at 400 °C for the Cr–Mo–V cast steels with different compositions. Morphology, composition and structure of worn surfaces, oxidation films and matrix were examined using SEM, EDS, XRD and TEM. The relations between oxidation wear rate and matrix were studied. The mechanism of wear was clarified. Under elevated-temperature air at 400 °C, typical oxidation wear was presented in the cast steels. Oxidation of worn surface and fatigue delamination of oxide film proceed alternatively during sliding. As there are not coarse second phases in steel, oxide film is main factor in determining wear rate, which conforms to Quinn's oxidation wear theory. In this case, delamination of oxide film was found to take place inside oxide film or at interface of matrix and oxide film. This is classified as mild oxidation wear with lower wear rate. As coarse second phases exist in steel, the wear rate is strongly dependant on microstructures of matrix. In this case, oxide film delaminates from the inside of matrix under oxide film. This is classified as severe wear with high wear rate.     

Characterisation of wear debris from UHMWPE on zirconia ceramic, metal-on-metal and alumina ceramic-on-ceramic hip prostheses generated in a physiological anatomical hip joint simulator

There is currently much interest in the characterisation of wear debris from different types of artificial hip joints. There have been numerous studies on the wear of UHMWPE in hip joint simulators, but relatively few studies on the wear of alternative materials such as metal-on-metal (MOM) and ceramic-on-ceramic (COC). The aim of this study was to compare the wear volumes and wear debris generated from zirconia ceramic-on-UHMWPE, MOM and COC hip joints under identical conditions in the same hip joint simulator.

All prostheses showed an initial higher ‘bedding in’ wear rate, which was followed by a lower steady state wear rate. The zirconia ceramic-on UHMWPE prostheses showed the highest wear rates (31±4.0 mm³/million cycles), followed by the MOM (1.23±0.5 mm/million cycles), with the COC prostheses showing significantly (P<0.01) lower wear rates at 0.05±0.02 mm³/million cycles. The mode (±95% confidence limits) of the size distribution of the UHMWPE wear debris was 300±200, 30±2.25 nm for the metal particles, and 9±0.5 nm for the ceramic wear particles. The UHMWPE particles were significantly larger (P<0.05) than the metal and ceramic wear particles, and the metal particles were significantly larger (P<0.05) than the ceramic wear particles. A variety of morphologies and sizes were observed for the UHMWPE wear particles, including submicrometer granules and large flakes in excess of 50 μm. However, the wear particles generated in both the MOM and COC articulations were very uniform in size and oval or round in shape.

This investigation has demonstrated substantial differences in volumetric wear. The in vitro wear rates for the zirconia-on-UHMWPE and MOM are comparable with clinical studies and the UHMWPE and metal wear particles were similar to the wear debris isolated from retrieved tissues. However, the alumina/alumina wear rate was lower than some clinical retrieval studies, and the severe wear patterns and micrometer-sized particles described in vivo were not reproduced here.

This study revealed significant differences in the wear volumes and particle sizes from the three different prostheses. In addition, this study has shown that the alternative bearing materials such as MOM and COC may offer a considerable advantage over the more traditional articulations which utilise UHMWPE as a bearing material, both in terms of wear volume and osteolytic potential.