Erosion of an aligned alumina-stainless steel composite

Steady-state erosion of a fully aligned composite consisting of a regular array of alumina rods embedded into a 304 stainless steel matrix has been investigated at room temperature using alumina erodents whose mean diameters varied from 37 to 390 μm. Impact angles varied between 15° and 90° with velocities in the range of 60–100 m s⁻¹. All experiments were performed with the axis of the alumina rods perpendicular to the erosion surface. Experiments under identical conditions were performed on bulk samples of 304 stainless steel and on the same type of alumina. The composite results can be described, to a reasonable approximation, using a model whose basis is that constrained steady-state erosion occurs such that the bulk stainless steel erosion rate determines the form of a stationary erosion-surface profile. The physical basis of the constraints are discussed in terms of the erosion mechanisms.     

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.     

Particle erosion of cemented carbides with low Co content

Cemented carbides are well known for their high erosion resistance and are therefore used in many demanding applications involving erosion, such as grit blasting nozzles. A number of investigations on the erosive wear resistance of conventional cemented carbides have been published. The present paper is aimed at investigating the erosion resistance of a series of modern cemented carbides containing no or very small amounts of Co, so-called binderless carbides, and relating their performance to conventional sorts.

A series of binderless carbides with varying grain size (0.6, 2 and 5 μm) and binder content (0.25 and 1 wt.%) has been tested. The materials were eroded by SiC particles of three sizes (80, 200 and 600 μm) from four angles (90, 70, 50 and 30°) with a velocity of 70 m/s. Three conventional WC-Co grades of corresponding grain sizes were also tested, under identical test conditions.

The materials are ranked with respect to their erosion rate and scanning electron microscopy is used to analyse the worn surfaces. The influence of carbide grain size and binder amount on the wear behaviour is discussed.     

Dry sliding wear of fly ash particle reinforced A356 Al composites

In the present study aluminium alloy (A356) composites containing 6 and 12 vol. % of fly ash particles have been fabricated. The dry sliding wear behaviour of unreinforced alloy and composites are studied using Pin-On-Disc machine at a load of 10, 20, 50, 65 and 80 N at a constant sliding velocity of 1 m/s. Results show that the dry sliding wear resistance of Al-fly ash composite is almost similar to that of Al₂O₃ and SiC reinforced Al-alloy. Composites exhibit better wear resistance compared to unreinforced alloy up to a load of 80 N. Fly ash particle size and its volume fraction significantly affect the wear and friction properties of composites. Microscopic examination of the worn surfaces, subsurfaces and debris has been done. At high loads (>50 N), where fly ash particles act as load bearing constituents, the wear resistance of A356 Al alloy reinforced with narrow size range (53–106 μm) fly ash particles were superior to that of the composite having the same volume fraction of particles in the wide size range (0.5–400 μm).     

Tribological behavior of select MAX phases against Al2O3 at elevated temperatures

The layered M_n+1AC_n ternary carbides – MAX phases – Ta₂AlC, Ti₂AlC, Cr₂AlC and Ti₃SiC₂ were tested under dry sliding conditions against alumina at 550 °C and 3 N load (for a stress of ≈0.08 MPa) using a pin-on-disk tribometer. Ta₂AlC and Ti₂AlC exhibited low specific wear rates, SWRs, (≤1 × 10⁻⁶ mm³/N m), while the coefficients of friction, μ, were 0.9 and 0.6, respectively. At 0.4, μ of Ti₃SiC₂ was the lowest measured, but the SWR, at ≈2 × 10⁻⁴ mm³/N m, was high. With a μ of 0.44 and a SWR of 6 × 10⁻⁵ mm³/N m the Cr₂AlC sample was in between. No visible wear of Al₂O₃ counterparts was observed in all the tribocouples. Tribofilms, which were mainly comprised of X-ray amorphous oxides of the M and A elements and, in some cases, unoxidized grains of the corresponding MAX phases, were formed on the contact surfaces. The correlations between observed tribological properties and tribofilm characteristics are discussed.     

Assessment of the erosion resistance of steels used for slurry handling and transport in mineral processing applications

The wear environment of steels used for containing, transporting and processing erosive mineral slurries is often such that fluid borne particles form a layer moving at high speed across the wearing surface. Information on the performance ranking of such materials is limited, particularly with respect to the influence of steel hardness and microstructure on the resistance to erosion. This is particularly important for the oil sands industry of Northern Alberta where handling and processing of essentially silica-based solids results in extremely severe wear conditions. This paper presents slurry erosion data obtained on 11 commercially available wear resistant plate and pipeline steels with hardness values up to 750 HV. These data were obtained using a Coriolis erosion tester operated at 5000 rpm with an aqueous slurry containing 10 wt.% of 200–300 μm silica sand particles.

The Coriolis erosion tester was selected because it provides a low-angle scouring action that simulates the erosive conditions encountered in oil sands and tailings pipeline transport and in some related processing operations. Results show that this test method is able to discriminate clearly between the erosion resistance of these steels, expressed in terms of specific energy (the energy necessary to remove unit volume of test material), with the most erosion resistant steel being more than five times superior to the least resistant. A graphical relation between steel hardness and erosion resistance is given. A comparison is also made between slurry erosion data and the performance of the materials in the ASTM G65 dry sand rubber wheel (DSRW) sliding abrasion test. Comments on the influence of the macro- and microstructures of the steels on their wear behaviour are included.     

Erosive wear behaviour of weld hardfacing high chromium cast irons: effect of erodent particles

Five commercial hardfacing high chromium cast iron alloys were deposited by flux cored arc-welding method. The solid particle erosion studies were carried out using air blast type erosion test rig with 125–150 μm cement clinker, 125–150 μm blast furnace sinter, 100–150 μm silica sand and 125–150 μm alumina particles at a velocity of 50 m s⁻¹ and at impingement angles of 15–90°. The observed erosion rates were rationalised in terms of relative hardness of erodent particles and ability of erodent particle to cause gross fracture of the carbides. The dependence of erosion rate on impingement angle was found to be quite weak for hardfacing high chromium cast iron alloys. However, significant differences were observed in the ranking of the alloys when eroded with different erodent particles. The presence of large volume fraction of carbides proved to be beneficial to the erosion resistance when the erodent particle were softer than the carbides. With silica sand particles at normal impact and with alumina particles large volume fraction of carbides proved detrimental to the erosion resistance. The operating erosion mechanisms involved small-scale chipping, edge effect, indentation and fracture and fatigue.     

A comparison of the erosion rate of casing steels by sand-oil suspensions

The erosion rates (expressed as grams per square millimeter per minute) of three casing steels (P110, N80 and K55) and hot-rolled 1020 steel in quartz sand-oil suspensions, GFN 140, solids loading 0.5–4 wt.%, at speeds from 9.35 to 18.7 m s⁻¹ have been measured in a slurry pot tester. The velocity exponent was determined as 2.4 and the relationship of erosion rate to solids loading and particle size (for the particle size range 53–180 μm) determined. The erosion rates for all the steels were found to lie within a scatter band of ±15% and could not be related predictively with the measured tensile properties. Results are discussed in terms of the rate of particle impact on the eroding target and the need to control flow conditions through appropriate design to minimize erosion.     

Friction and wear properties of Ni–Cr–W–Al–Ti–MoS2 at elevated temperatures and self-consumption phenomena

The composites of Ni–Cr–W–Al–Ti–MoS₂ with different adding amount of molybdenum disulfide (6–20 wt.%) were prepared by powder metallurgy (P/M) method. Their mechanical properties and tribological properties from room temperature to 600 °C were tested by a pin-on-disk tribometer. The effects of amounts of molybdenum disulfide, temperature, load, and speed on the friction and wear properties of composite were discussed. Besides, the tribological properties against different counterface materials, such as alumina, silicon nitride and nickel-iron-sulfide alloys were also investigated. Results indicated that the molybdenum disulfide was decomposed during the hot-press process and the eutectic sulfides of chromium were formed. The hardness and anti-bending strength can be improved by adding 6 wt.% molybdenum disulfide due to reinforcement of molybdenum. The friction coefficients and wear rates of composites decrease with the increase of adding amount of molybdenum disulfide until a critical value of 12 wt.%. The composite with 12% MoS₂ shows the optimum friction and wear properties over the temperature range of RT 600 °C. The friction coefficients of composite with 12% MoS₂ decrease with the increase of temperature, load, and sliding speed, while the wear rates increase with the increasing temperature and are insensitive to the sliding speed and load. The friction coefficients of less than 0.20 at 600 °C and mean wear rates of 10⁻⁵ mm³/N m are obtained when rubbing against alumina due to the lubrication of sulfide films and glaze layer formed on the friction surface at high temperature, while a relatively low wear rate of around 10⁻⁶ mm³/N m presents when rubbing against nickel-iron-sulfide alloys. At high temperature, wear rates of composite containing sulfide are inversely proportional to friction coefficients approximately.     

Effect of carbide fraction and matrix microstructure on the wear of cast iron balls tested in a laboratory ball mill

The effect of carbide volume fraction from 13 to 41% on the wear resistance of high chromium cast irons was evaluated by means of ball mill testing. Martensitic, pearlitic and austenitic matrices were evaluated.

The 50-mm diameter balls were tested simultaneously in a 40 cm diameter ball mill. Hematite, phosphate rock and quartz sand were wet ground. The tests were conducted for 200 h.

Quartz sand caused the highest wear rates, ranging from 6.5 to 8.6 μm/h for the martensitic balls, while the wear rates observed for the phosphate rock ranged from 1.4 to 2.9 μm/h.

Increasing the carbide volume fraction resulted in decreased wear rates for the softer abrasives. The almost complete protection of the matrix by carbides in eutectic microstructures caused the eutectic alloy to present the best performance against hematite or phosphate rock. The opposite effect was observed for the quartz sand. The quartz abrasive rapidly wears out the matrix, continuously exposing and breaking carbide branches. A martensitic steel presented the best performance against the quartz abrasive.

With phosphate rock, the wear rate of 30% carbide cast irons increased from 1.46 to 2.84 and to 6.39 μm/h as the matrix changed, respectively, from martensitic to austenitic and to pearlitic. Wear profiles of worn balls showed that non-martensitic balls presented deep subsurface carbide cracking, due to matrix deformation. Similar behavior was observed in the tests with the other abrasives.

In pin-on-disc tests, austenitic samples performed better than the martensitic ones. This result shows that pin tests in the presence of retained austenite can be misleading.     

Design of a low-cost nano-manipulator which utilizes a monolithic, spatial compliant mechanism

This paper presents the design of a novel, low-cost nano-manipulator which uses a six-axis compliant mechanism which is driven by electromagnetic actuators. The mechanism's monolithic, planar geometry is easily fabricated via planar manufacturing processes, enables compact packaging and incorporates a flexure mechanism for achieving small transmission ratios. The manipulator tolerates ±1 mm actuator misalignment with less than 0.1% full-scale position error. Measurements over a 100 nm × 100 nm × 100 nm work volume show resolution better than our measurement capability of 5 nm and open-loop parasitic errors less than 5 nm. Measurements over a 100 μm × 100 μm × 100 μm work volume show open loop errors less than 0.2% full-scale. The mechanism's equilateral symmetry and planar geometry make it possible to limit thermal drift in position and orientation to less than 23 nm and 4 μrad over a 30 min start up period. The nano-manipulator, built at US$ 2000 cost (excludes electronics), is used as an ultra-precision fiber optic aligner.     

Slurry wear properties of pump lining materials

In order to study the slurry wear properties of elastomeric lining materials for sand, sludge and sewage pumps, several tests were carried out under various test conditions with a slurry jet device and prototype pump. Preliminary tests were done with 13 materials including polymers, metals and ceramic coatings. Polyurethane, fluid elastomer and rubber showed good wear resistance compared with the hard metals, and were examined in detail. The test conditions were as follows: jet velocity v (8–25 m s⁻¹), impingement angle (10°−90°), mean diameter of silica sand d (42–415 μm), and sand concentration by weight c (0.1–7 wt.%). The slurry wear rates of the polyurethane and the fluid elastomer were maximum at the impingement angle of approximately 30°. The rubber showed almost the same wear rate regardless of impingement angle. The slurry were rate increased according to a power law of the jet velocity above a critical velocity and sand concentration. As the particle size increased above a critical size at the same weight concentration, the wear rate first increased but then decreased. The influence of impingement variables and particle variables observed using both test methods shows a similar tendency for each lining material, so the slurry wear loss can be described with a single empirical equation. Comparing the slurry wear resistance of three lining materials, the polyurethane showed the lowest resistance because it contained many pores which were produced during the lining process. The rubber showed the highest slurry wear resistance which is probably related to its high tear strength.     

Stylus-laser surface calibration system

A stylus-laser surface calibration system was developed to calibrate the NIST sinusoidal roughness Standard Reference Materials (SRM) 2071-2075. Step height standards are used to calibrate the stylus instrument in the vertical direction, and a laser interferometer is mounted on the traversing unit of the stylus instrument to calibrate the instrument in the horizontal direction. The calibration uncertainty (±2δ) for SRM 2075 is ±1.2% for roughness calibrations ((R_a = 1 μm), and ±0.06% for spatial wavelength calibrations (S_m = 800 μm).     

Design and performance of a high velocity air–sand jet impingement erosion facility

This paper describes the design, construction and capabilities of a high velocity air–sand erosion rig. It has been designed with the aid of computational fluid dynamics to approximately simulate the erosion conditions often experienced by subsea choke valves used in the offshore oil industry. It has also been designed to evaluate the erosion performance of CVD diamond coatings at sonic velocity. The rig is of the gas-blast design in which solid particles, typically sand 60–660 μm in size, are injected into a high velocity air stream and accelerated down a 16-mm-diameter tube, 1 m in length, before striking the sample under test. Tests can be carried out with particle velocities of up to 340 m/s under a wide range of sand fluxes, impact angles and standoff distances. The results of pressure, velocity and sand flux calibration work are described. In addition, preliminary experimental data on tests carried out on mild steel, bulk and sprayed tungsten carbide are also presented. The flexibility of the air–sand rig allows the erosion behaviour of materials to be studied under a wide range of conditions.     

Mechanical and tribological investigations of sol–gel derived SiO2 optical coatings

Sol–gel silica coatings were deposited on soda lime glass substrates by dip-coating. The silica films were amorphous, crack free, and smooth with an average roughness of less than 3 nm and thickness of 0.8–1.2 μm. Mechanical and tribological properties were investigated using nanoindentation, Taber abrasion and a polishing wear test. The hardness increased with increased thermal exposure from 2200 MPa for samples fired at 480 °C for 2 min to 3800 MPa for those fired at 560 °C for 14 min. In Taber abrasion, failure was due to penetration of the coatings by the abrasive particles of the Taber grinders, which caused scratches and subsequent delamination. For polishing wear experiments, hardness was inversely proportional to polishing wear rate. This suggests that hardness is a good indicator for the resistance of sol–gel silica coatings to polishing.     

Nanomechanical characterization of multilayered thin film structures for digital micromirror devices

The digital micromirror device (DMD), used for digital projection displays, comprises a surface-micromachined array of up to 2.07 million aluminum micromirrors (14 μm square and 15 μm pitch), which switch forward and backward thousands of times per second using electrostatic attraction. The nanomechanical properties of the thin-film structures used are important to the performance of the DMD. In this paper, the nanomechanical characterization of the single and multilayered thin film structures, which are of interest in DMDs, is carried out. The hardness, Young's modulus and scratch resistance of TiN/Si, SiO₂/Si, Al alloy/Si, TiN/Al alloy/Si and SiO₂/TiN/Al alloy/Si thin-film structures were measured using nanoindentation and nanoscratch techniques, respectively. The residual (internal) stresses developed during the thin film growth were estimated by measuring the radius of curvature of the sample before and after deposition. To better understand the nanomechanical properties of these thin film materials, the surface and interface analysis of the samples were conducted using X-ray photoelectron spectroscopy. The nanomechanical properties of these materials are analyzed and the impact of these properties on micromirror performance is discussed.     

Development of an air servo displacement sensor

This paper introduces a new type of displacement sensor called an “air servo displacement sensor.” The sensor’s piston automatically follows a measured object using a pneumatic servomechanism with a nozzle-flapper that acts as a detecting device. Because the piston is supported by an aerostatic bearing, it experiences almost no friction. An optical linear scale mounted on the piston is used to measure the displacement of the measured object because the gap between the nozzle and the measured object is maintained at a constant level. As a result, this new sensor can successfully perform non-contact displacement measurements over a much longer measuring range, when compared to the traditional air micrometer. The optimal parameters for the sensor structure were obtained using simulations and experiments. Performance accuracy tests with a micrometer showed a repeatability error below ±0.5 μm and a linearity error below ±2 μm, with a measuring range beyond 10 mm. It has been verified that that the sensor exhibits a sufficient level of accuracy for the operational requirements.     

A future technology for silicon wafer processing for ULSI

Two types of current surface grinder methods used in the preparation of silicon wafers are compared (creep-fed and in-fed). The creep-fed method left deeper residual damage in the waters as compared to the in-fed method. Second- and third-generation grinder developments, also discussed, indicate the possible directions for future production processes. For the second generation, electrolytic dressing was used to achieve stable grinding with the very rigid metal-bond with fine diamond. The maximum damage depth obtained was about 1 μm. In the third generation, plastic-regime grinding was used. A method of stripping silicon layers analogous to wood shaving is proposed. With this technology, it is expected that the damage depth would be about 0.2–0.3 μm and the accuracy of surface flatness to be ± 0.01 μm. It is expected that even with this accuracy, high productivity grinders for larger diameter wafers ( 200 mm) will be available in the near future.     

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.     

Design of an optical probe for testing surface roughness and micro-displacement

This paper presents a practical monitoring tool for measurements of surface roughness and micro-displacement. An optical probe of the methods based on light scattering for measuring surface roughness and optical triangulation for measuring micro-displacement is described. The proposed technique allows evaluation of surface roughness and micro-displacement of specimen by using just one device. The theoretical models of surface roughness and micro-displacement measurements have been established for the probe. The measuring principles applied in the design are described in detail and the validity of the design is demonstrated by experimental evaluations. The experimental results show that, for specimens with surface roughnesses R_a in the range from 0.005μm to 0.1 μm, micro-displacement measurements in the linear range of ± 300μm can be obtained.