Studies of high temperature sliding wear of metallic dissimilar interfaces III: Incoloy MA956 versus Incoloy 800HT

Wear variations of Incoloy MA956 slid against Incoloy 800HT between room temperature and 750 °C, and sliding speeds of 0.314, 0.654 and 0.905 m s⁻¹ were investigated using a ‘reciprocating block-on-cylinder’ (low debris retention) configuration.Three forms of wear depending largely on sliding temperature were observed: ‘severe wear’ with high transfer between room temperature and 270 °C, ‘severe wear’ with low transfer between 390 and 570 °C and ‘glaze formation’ (retarded by increased sliding speed) at 630 °C and above. The differences in wear behaviour are discussed, with wear behaviour mapped and wear surfaces at 750 °C (0.314 and 0.905 m s⁻¹) cross-sectioned and profiled.     

Studies of high temperature sliding wear of metallic dissimilar interfaces II: Incoloy MA956 versus Stellite 6

The development of wear surfaces formed during limited debris retention sliding wear of Incoloy MA956 against Stellite 6 between room temperature and 750 °C, and sliding speeds of 0.314 and 0.905 m s⁻¹ (7 N applied load, 4522 m sliding distance) were investigated. At 0.314 m s⁻¹, mild oxidational wear was observed at all temperatures, due to oxidation of Stellite 6-sourced debris and transfer to the Incoloy MA956; this debris separated the Incoloy MA956 and Stellite 6 wear surfaces. Between room temperature and 450 °C, the debris mainly took the form of loose particles with limited compaction, whilst between 510 °C and 750 °C the debris were compacted and sintered together to form a Co–Cr-based, wear protective ‘glaze’ layer. The behaviour was identical to that previously observed on sliding Nimonic 80A versus Stellite 6 at 0.314 m s⁻¹.At 0.905 m s⁻¹, mild oxidational wear was only observed at room temperature and 270 °C and dominated by Incoloy MA956-sourced debris. At 390 and 450 °C, the absence of oxide debris allowed ‘metal-to-metal’ contact and resulted in intermediate temperature severe wear; losses in the form of ejected metallic debris were almost entirely Incoloy MA956-sourced. This severe wear regime was also observed from 510 up to 630 °C, but increasingly restricted to the early stages of wear by development of a wear protective Incoloy MA956-sourced ‘glaze’ layer. This ‘glaze’ layer formed so rapidly at 690 °C and 750 °C, that severe wear was all but eliminated and wear levels were kept low.The behaviour observed for Incoloy MA956 versus Stellite 6 at 0.905 m s⁻¹ contrasts sharply with that previously observed for Nimonic 80A versus Stellite 6, in that the Incoloy MA956-sourced high Fe–Cr debris formed a protective oxide ‘glaze’, whilst the Nimonic 80A-sourced Ni and Cr oxides formed an abrasive oxide that at high sliding speeds assisted wear. The data indicates that the tendency of oxide to form a ‘glaze’ is readily influenced by the chemistry of the oxides generated.     

Investigation into the wear behaviour of Stellite 6 during rotation as an unlubricated bearing at 600 °C

The wear behaviour of Stellite 6 was studied during rotational sliding in a bespoke bearing rig at 600 °C for times between 2 min and 12 h. Six stages of wear were identified: (i) formation of a mixed oxide ‘glaze’, (ii) cobalt and chromium elemental diffusion to the ‘glaze’ surface forming chromium- and cobalt-dominated oxide layers, (iii) oxygen diffusion into the ‘glaze’ leading to a chromium-dominated oxide layer at the ‘glaze’/substrate interface, (iv) spallation of the ‘glaze’ through chemical failure, (v) re-formation of the ‘glaze’ and (vi) elemental diffusion within the ‘glaze’, again resulting in discrete oxide layer formation.     

Studies of high temperature sliding wear of metallic dissimilar interfaces IV: Nimonic 80A versus Incoloy 800HT

Wear variations of Nimonic 80A slid against Incoloy 800HT between room temperature (RT) and 750 °C, and sliding speeds of 0.314 and 0.905 m s⁻¹ were investigated using a ‘reciprocating-block-on-cylinder’, low debris retention configuration. These were considered alongside previous observations at 0.654 m s⁻¹.Different wear types occurring were mapped, including high transfer ‘severe wear’ (RT and 270 °C, also 0.905 m s⁻¹ at ≤570°C), low transfer ‘severe wear’ (0.314 m s⁻¹ at 390 °C to 510 °C oxide abrasion assisted at 510 °C), and ‘mild wear’ (0.314 m s⁻¹ at ≥570 °C; 0.905 m s⁻¹ at ≥630 °C). Wear surfaces at 750 °C were cross-sectioned and profiled.     

Several plasma diffusion processes for improving wear properties of Ti6Al4V alloy

Different kinds of diffusion processes, plasma nitriding, oxidizing and oxynitriding as of a combination of other two, have been applied to Ti6Al4V alloy to evaluate the effect of treatment times (1 and 4 h) and temperatures (650 and 750 °C) on wear properties of the alloy. It was observed that a hard modified layer was produced on the surface of the alloy after each diffusion process. While TiN and Ti₂N phases form in the modified layer with plasma nitriding, mainly TiO₂ phase forms after plasma oxidizing treatment. The wear tests performed at different normal loads showed that all treated samples, except for nitrided and oxidized at 650 °C for 1 h, exhibited higher wear resistance than untreated Ti6Al4V alloy. The plasma nitrided samples showed adhesive wear. On the other hand, while the plasma oxidizing samples displayed adhesive wear at lower loads, wear mechanism changed to abrasive wear as the load increased because the oxide film which covers the surface was broken during the sliding at higher loads.     

A study on wear mechanism and wear reduction strategies in grinding wheels used for ELID grinding

Metal-bonded superabrasive diamond grinding wheels have superior qualities such as high bond strength, high stability and high grindability. The major problems encountered are wheel loading and glazing, which impedes the effectiveness of the grinding wheel. Electrolytic in-process dressing (ELID) is an effective method to dress the grinding wheel during grinding. The wear mechanism of metal-bonded grinding wheels dressed using ELID is different form the conventional grinding methods because the bond strength of the wheel-working surface is reduced by electrolysis. The reduction of bond strength reduces the grit-depth-of-cut and hence the surface finish is improved. The oxide layer formed on the surface of the grinding wheel experiences macrofracture at the end of wheel life while machining hard and brittle workpieces. When the wheel wear is dominated by macrofracture, the wheel-working surface is free from loaded chips and worn diamond grits. When the oxide layer is removed from the wheel surface, the electrical conductivity of the grinding wheel increases, and that stimulates electrolytic dressing. The conditions applied to the pulse current influence the amount of layer oxidizing from the grinding wheel surface. Longer pulse ‘on’ time increases the wheel wear. Shorter pulse ‘on’ time can be selected for a courser grit size wheel since that type of wheel needs high grinding efficiency. Equal pulse ‘on’ and ‘off’ time is desired for finer grit size wheels to obtain stable and ultraprecision surface finish.     

The influence of phase transformations and oxidation on the galling resistance and low friction behaviour of a laser processed Co-based alloy

The effect of oxide formation on the tribological properties of a CO₂-laser processed Co-based material (Stellite 21) was investigated under high-load sliding conditions in air and in an oxygen free environment. The tests were carried out by sliding two identical specimens against each other in a load-scanning test. A friction coefficient at a level of about 0.20 was observed for both test environments. However, the wear of the Co base material is accelerated when the sliding is performed in an oxygen free environment. The friction level appears to be controlled by the shearing of hcp {0 0 0 1} planes rather than by the presence of an oxide layer.     

A study of the wear of explanted metal-on-metal resurfacing hip prostheses

Due to their recent introduction there are few studies of retrieved resurfacing hip prostheses. Nine such components associated with groin pain in patients, and five associated with early fracture of the femur, were obtained and analysed using a roundness measuring machine. While the ‘fracture’ components showed no more than 3 μm out of roundness, components associated with groin pain showed between 15 and 92 μm out of roundness values. These latter results indicate wear and correlated with high metal ion levels in these patients, therefore the groin pain was likely associated with an adverse reaction to excessive metal wear debris.     

Friction of PM ferritic stainless steels at temperatures up to 300 °C

Two ferritic stainless steels (409Nb and 434L) manufactured through powder metallurgical techniques were wear tested at different temperature conditions (up to 300 °C). Two sliding speeds were used, and tests were carried out against a wrought austenitic stainless steel. Materials’ wear performance was characterized through friction coefficients and analysis of wear tracks was carried out through scanning electron microscopy. Results have shown an adhesive wear mechanism. Oxidized ferrite particles have also been found on wear tracks.     

High-temperature sliding wear of metals

Temperature can have a considerable effect on the extent of wear damage to metallic components. During reciprocating sliding, under conditions where frictional heating has little impact on surface temperatures, there is generally a transition from severe wear to mild wear after a time of sliding that decreases with increase in ambient temperature. This is due to the generation and retention of oxide and partially-oxidized metal debris particles on the contacting load-bearing surfaces; these are compacted and agglomerated by the sliding action, giving protective layers on such surfaces. At low temperatures, from 20 to 200°C, the layers generally consist of loosely-compacted particles; at higher temperatures, there is an increase in the rates of generation and retention of particles while compaction, sintering and oxidation of the particles in the layers are facilitated, leading to development of hard, very protective oxide ‘glaze’ surfaces. This paper reviews some of the main findings of extensive research programmes into the development of such wear-protective layers, including a model that accounts closely for the observed effects of temperature on wear rates during like-on-like sliding.     

Experimental observation of the improvement in MTF from backthinning a CMOS direct electron detector

The advantages of backthinning monolithic active pixel sensors (MAPS) based on complementary metal oxide semiconductor (CMOS) direct electron detectors for electron microscopy have been discussed previously; they include better spatial resolution (modulation transfer function or MTF) and efficiency at all spatial frequencies (detective quantum efficiency or DQE). It was suggested that a ‘thin’ CMOS detector would have the most outstanding properties [1], [2] and [3] because of a reduction in the proportion of backscattered electrons. In this paper we show, theoretically (using Monte Carlo simulations of electron trajectories) and experimentally that this is indeed the case.     

Wear and friction behavior of sand cast brake rotor made of A359-20 vol% SiC particle composites sliding against automobile friction material

The effect of load range of 30-100 N and speed range of 3-12 m/s on the wear and friction behavior of sand cast brake rotor made of A359-20 vol% SiC particle composites sliding against automobile friction material was investigated. Dry sliding frictional and wear behavior were investigated in a pin-on-disc type apparatus. Automobile friction material was used as pin, while the A359-20 vol% SiC particle composites formed the rotating disc. For comparison, the wear and friction behavior of commercially used cast iron brake rotor were studied. The results showed that the wear rate of the composite disc decreased with increasing the applied load from 30 to 50 N and increased with increasing the load from 50 to100 N. However, the wear rate of the composite disc decreased with increasing the sliding speed at all levels of load applied in the present work. For all sliding speeds, the friction coefficient of the composite disc decreased with applied load. The worn surfaces as well as wear debris were studied using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analyzer and X-ray diffraction (XRD) technique. At load of 50 N and speed range of 3-12 m/s, the worn surface of the composite disc showed a dark adherent layer, which mostly consisted of constituents of the friction material. This layer acted as a protective coating and lubricant, resulting in an improvement in the wear resistance of the composite.     

Tribological performance evaluation of (1 1 1) preferred oriented TiN duplex coatings

The duplex surface coating of hot work tool steel, which comprises nitriding of a substrate and coating of a TiN layer, has been the subject of a series of studies as a potential surface modification for tools and machine parts. Through sliding experiment against an aluminum alloy without lubrication, it was shown on a wear map that there are two domains depending on sliding conditions: the wear domain and the transfer domain. In this study, focusing on the improvement in the tribological properties of the duplex coating in terms of the wear domain, the effects of film characteristics on film resistance to erosion wear and film life were investigated. Two kinds of duplex coatings with different film characteristics were prepared by hollow cathode discharge ion plating: a newly developed TiN film with a strong (1 1 1) orientation and an ordinary TiN film with (1 1 1) and (2 0 0) orientations. The erosion wear rate of duplex coating was evaluated by a micro slurry jet erosion test. Film life was evaluated by a sliding test against an aluminum alloy as in previous experiments. It was revealed that the duplex coating with the newly developed TiN film (N-coating) shows higher erosion resistance than previously reported duplex coating (C-coating). From the sliding test, it was also revealed that the N-coating whose XRD intensity ratio of (1 1 1) to (2 0 0) is over 100 shows a wear mode with only chipping, with no scratching, which shortens film life. The film life of N-coating increases about twice as long as C-coating, which has shown higher performance than a conventional duplex coating. Possible mechanisms of the improvement in the tribological properties with N-coating are discussed.     

Reciprocating sliding wear of 9% Cr steel in carbon dioxide at elevated temperatures

Experiments were conducted on the initial stages of reciprocating sliding wear of a 9% chromium steel in an environment of carbon dioxide at temperatures in the range 200 to 550°C. At ambient temperatures of 290°C and above, an initial severe wear mode was followed by a transition to mild oxidational wear. At any given ambient temperature above 290°C, the distance of sliding required to reach such a transition was found to depend on load and mean sliding speed, although the dependency on speed was not simple. When a transition occurred, most of the surfaces were covered with a stable oxide film which consisted of an agglomerate layer of wear debris being mainly of oxide at the surface and mainly at the metal boundary. This film was supported by a work hardened layer extending for about 30 μm into the bulk of the metal. A surface model is proposed to explain the mechanism of formation of the supportive oxide layer; predictions of volume of material removed and final oxide coverage at the transition are in close agreement with experimental values     

Wear behavior of Al-Mg-Cu-based composites containing SiC particles

The friction and wear behavior of Al-Mg-Cu alloys and Al-Mg-Cu-based composites containing SiC particles were investigated at room conditions at a pressure of 3.18 MPa and a sliding speed of 0.393 m/s using a pin-on-disk wear testing machine. This study is an attempt to investigate the effects of adding copper as alloying element and silicon carbide as reinforcement particles to Al-4 wt% Mg metal matrix. The wear loss of the copper containing alloys was less than that for the copper free alloys. It was observed that the volume losses in wear test of Al-Mg-Cu alloy decrease continuously up to 5%. Also it was found that the silicon carbide particles play a significant role in improving wear resistance of the Al-Mg-Cu alloying system. The formation of mechanically mixed layer (MML) due to the transfer of Fe from counterface disk to the pin was observed in both Al-Mg-Cu alloys and Al-Mg-Cu/SiC composites.     

Study of tribological performance of ECR-CVD diamond-like carbon coatings on steel substrates: Part 2. The analysis of wear mechanism

This paper describes the tribological performance of diamond-like carbon (DLC) coatings deposited on AISI 440C steel substrates by electron cyclotron resonance chemical vapor deposition (ECR-CVD) process. A variety of analytic techniques were used to characterize the coatings, such as Raman spectroscopy, atomic force microscopy (AFM) and nano-indentation. The sliding wear and friction experiments were carried out by the conventional ball-on-disk tribometry against 100Cr6 steel counterbody at various normal loads (1-10 N) and sliding speeds (2-15 cm/s). All the wear tests were conducted under dry sliding condition in ambient air for a total rotation cycle of 1 × 10⁵ (sliding distance ∼2.2 km). Surfaces of the coatings and the steel balls were examined before and after the sliding wear tests. The DLC coatings that had been tested all showed relatively low values of friction coefficient, in the range of 0.1-0.2 at a steady-state stage, and low specific wear rates (on the order of 10⁻⁸ mm³/Nm). It was found that higher normal loads or sliding speeds reduced the wear rates of the coatings. Plastic deformation became more evident on the coating surface during the sliding wear test at higher contact stresses. The friction-induced transformation of the coating surface into a graphite-like phase was revealed by micro-Raman analysis, and the flash temperature of the contact asperities was estimated. It was suggested that the structural transformation taking place within the wear tracks was mainly due to the formation of compact wear debris layer rather than the frictional heating effect. On the other hand, an adherent transfer layer (tribolayer) was formed on the counterface, which was closely related to the steady-state friction during sliding and the wear mechanisms. Fundamental knowledge combined with the present tribological study led to the conclusion that adhesive wear along with abrasion was probably the dominant wear mechanism for the DLC/steel sliding systems. Additionally, fatigue processes might also be involved in the wear of the coatings.     

Tribological performance of microwave sintered copper-TiC-graphite hybrid composites

Copper matrix composites are finding many applications due to their inherent properties such as good electrical and thermal conductivity and corrosion resistance. New series of copper-TiC (5-15 vol%)-graphite (5-10 vol%) hybrid composites are fabricated through a novel microwave processing technique. Pin-on-disc is used to evaluate their tribological properties under testing parameters of normal loads 12-48 N and sliding speed of 1.25-2.51 m/s. The formation of mixed smooth layer with higher graphite hybrid composites improves the wear resistance and reduces the friction coefficient. Morphology of worn out surfaces and wear debris were analyzed to understand the wear mechanisms.     

The influence of current load on fretting of electrical contacts

The fretting corrosion behavior of tin coated brass contacts is studied at various current loads (1, 2 and 3 A). The typical characteristics of the change in contact resistance with fretting cycles are explained. The fretted surface is examined using scanning electron microscope, laser scanning electron microscope and energy dispersive analysis of X-rays to assess the surface morphology, extent of fretting damage, extent of oxidation, surface profile and elemental distribution across the contact zone. The degradation of contacts at high and low values of current is explained with reference to the thermal and electrical phenomena occurring at the contact interface. The results showed that irrespective of the current loads under study, the contact resistance is maintained at 1.0±0.02 Ω where the oxide debris formation and the electrical breakdown of oxide particles competed with each other maintaining the equilibrium. The number of cycles to failure of the contacts is delayed at lower current. The fretting corrosion degradation of tin coated contacts occurs much faster at higher currents as it generates more accumulation of oxide wear debris at the contact zone. The observed surface morphology and the tin profile of the fretted surface are in agreement with the experimental results.     

Studies of high temperature sliding wear of metallic dissimilar interfaces

The evolution of microstructures in the glaze layer formed during limited debris retention sliding wear of Nimonic 80A against Stellite 6 at 750 °C and a sliding speed of 0.314 m s⁻¹ (7 N applied load, 4522 m sliding distance) was investigated using scanning electron microscopy (SEM), energy dispersive analysis by X-ray (EDX), X-ray diffraction (XRD), scanning tunnelling microscopy (STM) and transmission electron microscopy (TEM). The collected data indicate the development of a wear resistant nano-structured glaze layer. The process of ‘fragmentation’ involving deformation, generation of dislocations, formation of sub-grains and their increasing refinement causing increasing misorientation was responsible for the formation of nano-structured grains. The rapid formation of this glaze layer from primarily cobalt–chromium debris transferred from (and also back to) the surface of the Stellite 6, kept wear of both the Nimonic 80A and Stellite 6 to very low levels.However, increasing the sliding speed to 0.905 m s⁻¹ (750 °C) suppressed glaze formation with only a patchy, unstable glaze forming on the Stellite 6 counterface and an absence of glaze development on the Nimonic 80A sample (the Nimonic 80A surface was covered with at most, a very thinly smeared layer of oxide). The high levels of oxide debris generated at 0.905 m s⁻¹ instead acted as a loose abrasive assisting wear of especially the Nimonic 80A. This behaviour was attributed to a change in oxide chemistry (due to the dominance of nickel and chromium oxides generated from the Nimonic 80A) resulting in poor oxide sintering characteristics, in combination with increased mobility and reduced residency of the oxide debris at 0.905 m s⁻¹.     

Transition of elevated-temperature wear mechanisms and the oxidative delamination wear in hot-working die steels

Dry sliding wear tests of H13 and H21 steels were performed at 400 °C. The wear mechanisms and their transitions were studied, and an oxidative delamination wear was suggested. A mild oxidative wear prevailed with oxide fatigue delamination under less than 3.54 MPa. Under 3.54-5.31 MPa, the oxidative wear prevailed with oxide fatigue delamination and the oxidative delamination wear. As the pressure surpassed 5.31 MPa, a severe wear prevailed with the oxidative delamination wear and the plastic extrusion. The oxidative delamination wear meant that the delamination occurred inside the matrix underneath tribo-oxides with long-ditch delamination and belt-like wear debris.