Greater Wear Research Articles

Investigation of the structure, composition, and properties of the carboplasic contact surface in tribotests

The processes evolving on carboplastic surfaces during contact interaction with a steel counterbody are discussed. The structure, composition, and tribological properties of the film of secondary structures appearing during friction are investigated. The dependences of the friction coefficient and wear on pressure and sliding velocity are established. The results of comparative tests allow us to identify FUT B83 as the carboplastic with the lowest friction coefficient and UGET as the carboplastic with the greatest wear resistance.

Studies on wear behavior of nano-intermetallic reinforced Al-base amorphous/nanocrystalline matrix in situ composite

Resistance to wear is an important factor in design and selection of structural components in relative motion against a mating surface. The present work deals with studies on fretting wear behavior of in situ nano-Al 3Ti reinforced Al–Ti–Si amorphous/nanocrystalline matrix composite, processed by high pressure (8 GPa) sintering at room temperature, 350, 400 or 450 °C. The wear experiments were carried out in gross slip fretting regime to investigate the performance of this composite against Al 2O 3 at ambient temperature (22–25 °C) and humidity (50–55%). The highest resistance to fretting wear has been observed in the composites sintered at 400 °C. The fretting wear involves oxidation of Al 3Ti particles in the composite. A continuous, smooth and protective tribolayer is formed on the worn surface of the composite sintered at 400 °C, while fragmentation and spallation leads to a rougher surface and greater wear in the composite sintered at 450 °C.

Generation of Wear Protective Layer in High Speed Turning of Gray Cast Iron Containing Aluminium and Magnesium

This paper focuses on the influence of difference of tool materials on generation of wear protective layer when turning gray cast iron containing Al and Mg. In this experiment, the gray cast iron to which small quantities of Al and Mg was added were cut with cermet, P grade carbide (P10), silicon nitride ceramics (Si3N4), titanium nitride (TiN) coated carbide and K grade carbide (K10) at high speed. In turning gray cast iron containing Al and Mg with cermet, the tool wear was significantly reduced compared to that resulting from the cutting of conventional gray cast iron. Further, the protective layer consisting of nonmetallic inclusions in the work material was formed on the tool surface. In addition to cermet, this layer was formed on tool surface of Si3N4 and TiN coated carbide. The elements of Al and Mg added to the work materials were detected in the layers formed on these tool surfaces as well as cermet. The inhibiting effect on tool wear was also caused when turning with P10. However, P10 had much greater wear than cermet. On the other hand, in the case of turning with K10, the effect reducing wear with the addition of Al and Mg was not caused. The wear increased as cutting speed increased regardless of work materials.

Generation of Wear Protective Layer in High Speed Turning of Gray Cast Iron Containing Aluminium and Magnesium

This paper focuses on the influence of difference of tool materials on generation of wear protective layer when turning gray cast iron containing Al and Mg. In this experiment, the gray cast iron to which small quantities of Al and Mg was added were cut with cermet, P grade carbide (P10), silicon nitride ceramics (Si3N4), titanium nitride (TiN) coated carbide and K grade carbide (K10) at high speed. In turning gray cast iron containing Al and Mg with cermet, the tool wear was significantly reduced compared to that resulting from the cutting of conventional gray cast iron. Further, the protective layer consisting of nonmetallic inclusions in the work material was formed on the tool surface. In addition to cermet, this layer was formed on tool surface of Si3N4 and TiN coated carbide. The elements of Al and Mg added to the work materials were detected in the layers formed on these tool surfaces as well as cermet. The inhibiting effect on tool wear was also caused when turning with P10. However, P10 had much greater wear than cermet. On the other hand, in the case of turning with K10, the effect reducing wear with the addition of Al and Mg was not caused. The wear increased as cutting speed increased regardless of work materials.

Tibial Post Wear in Posterior-stabilized Knee Replacements is Design-dependent

Polyethylene tibial post wear in posterior-stabilized knee designs is a major problem. The Insall-Burstein II (IB PS II) reportedly has severe anterior wear of the post in retrieved implants. We hypothesized the more anterior placement in the IB PS II would be reflected in greater wear at the anterior face than the IB PS I. We examined 234 retrieved inserts using subjective scales to grade post damage and wear. Of the IB PS II inserts, 38% demonstrated severe wear compared with only 25% of IB PS I inserts. The most prevalent damage location for the IB PS II was the anterior face, whereas the IB PS I sustained wear mainly on the medial face. While the IB PS post was not designed to constrain posterior femoral displacement, our observations confirm contact in hyperextension or other paradoxic anterior tibial translation is common and design-dependent. Minimizing wear and damage through proper post placement and changes in implant design to anticipate contact on the anterior post should be considered for future posterior stabilized knee replacements. These changes cannot occur in isolation, however, because changes in post placement and design also depend on their relation to the shape and location of the tibial bearing surfaces.

The influence of wear paths produced by hip replacement patients during normal walking on wear rates

Variation in wear paths is known to greatly affect wear rates in vitro, with multidirectional paths producing much greater wear than unidirectional paths. This study investigated the relationship between multidirectional motion at the hip joint, as measured by aspect ratio, sliding distance, and wear rate for 164 hip replacements. Kinematic input from three-dimensional gait analysis was used to determine the wear paths. Activity cycles were determined for a subgroup of 100 patients using a pedometer study, and the relationship between annual sliding distance and wear rate was analyzed. Poor correlations were found between both aspect ratio and sliding distance and wear rate for the larger group and between annual sliding distance and wear rate for the subgroup. However, patients who experienced a wear rate <0.08 mm/year showed a strong positive correlation between the combination of sliding distance, activity levels, and aspect ratio and wear rate (adjusted r(2) = 55.4%). This group may represent those patients who experience conditions that most closely match those that prevail in simulator and laboratory tests. Although the shape of wear paths, their sliding distance, and the number of articulation cycles at the hip joint affect wear rates in simulator studies, this relationship was not seen in this clinical study. Other factors such as lubrication, loading conditions and roughness of the femoral head may influence the wear rate.

Wool peptide derivatives for hand care

Hands experience much greater wear and tear during normal daily routines compared with most other parts of the body, and thereby demand specific needs from cosmetics targeted at hand care. Keratin proteins are the major structural component of the outer layers of the skin. In this work a novel keratin fraction from wool, which has high cystine content present in the S-sulphonated form, has been developed to target hand care applications. In vivo long-term studies were performed to evaluate the water-holding capacity and elasticity of hand skin following topical application of keratins. Moreover, protection of healthy skin against detergent-induced dermatitis was evaluated after topical application of the keratin-active formulation. Significant results in the measured biophysical parameters were found, which indicated an improvement in the skin's water-holding capacity, hydration, and elasticity for volunteers with dry skin as a result of the keratin peptide treatment. Results also indicated that the keratin peptide treatment can prevent some of the damaging effects associated with surfactant exposure.

Orientation and wear of the acetabular component in third generation alumina-on-alumina ceramic bearings

We studied 33 third generation, alumina ceramic-on-ceramic bearings retrieved from cementless total hip replacements after more than six months in situ. Wear volume was measured with a Roundtest machine, and acetabular orientation from the anteroposterior pelvic radiograph. The overall median early wear rate was 0.1 mm3/yr for the femoral heads, and 0.04 mm3/yr for the acetabular liners. We then excluded hips where the components had migrated. In this stable subgroup of 22 bearings, those with an acetabular anteversion of &lt; 15° (seven femoral heads) had a median femoral head wear rate of 1.2 mm3/yr, compared with 0 mm3/yr for those with an anteversion of ≥15° (15 femoral heads, p &lt; 0.001). Even under edge loading, wear volumes with ceramic-on-ceramic bearings are small in comparison to other bearing materials. Low acetabular anteversion is associated with greater wear.

Plasma coatings of (TiCrC)-(FeCr) composite powder alloys: Structure and properties

The coatings of the (TiCrC)-(FeCr) composite are deposited on steel and titanium alloy by plasma method. The composition, structure, and tribotechnical properties of these coatings are studied in comparison with traditional materials based on the Ni-Cr alloy. The effect of preliminary surface treatment methods, i.e., sandblasting treatment and electrospark alloying, on coating properties is examined. The fretting corrosion of coatings is investigated. It is established that coatings based on double titanium-chromium carbide have considerably greater wear resistance than that of Ni-Cr alloys at almost equal friction coefficients. It is established that electrospark alloying is competitive with traditional sandblasting treatment in environmental effect and coating-to-based adhesion.

Comparative study of the wear behavior of composites for posterior restorations

This investigation sought to compare the abrasive wear rates of resin composites designed for posterior applications. Seventy-five specimens were fabricated with conventional hybrid (Charisma and Filtek Z250) or packable composites (Filtek P60, Solitaire II and Tetric Ceram HB), according to a randomized complete block design (n = 15). Specimens were finished and polished metallographically and subjected to abrasive wear which was performed under a normal load of 13N at a frequency of 2 Hz using a pneumatic device (MSM/Elquip) in the presence of a mucin-containing artificial saliva. Wear was quantified profilometrically in five different locations of each specimen after 1,000, 5,000, 10,000, 50,000 and after every each 50,000 through 250,000 cycles. A split-plot ANOVA showed a significant difference between the wear resistance of composites (alpha = 0.05). Tukey's test ascertained that while the composites Filtek Z250 and Charisma wore significantly less than any other of the materials tested, Tetric Ceram HB experienced the greatest wear rates. Filtek P60 and Solitaire II showed intermediate rates of material removal. The wear pattern of composites proved to be biphasic with the primary phase having the faster wear rate. In conclusion, packable resin composites may not have superior wear compared to conventional hybrid composites.

Comparison of the wear exerted on engine valves and seat inserts under various speeds and mileages

Under actual engine driving conditions, there is a possibility of engine valve and seat insert wear occurring as a result of various speed changes and accumulation of mileage. It is therefore necessary to examine the wear-related problems of engine valves and seat inserts and to determine by comparison whether speed or mileage inflicts the greater wear. This work focuses on the various degrees of wear produced at three different singular test speeds (10 Hz, 25 Hz, and multi-Hz) and two different cycle numbers (2.1 — 106 and 6.0 — 106). Throughout all tests performed in this study, the temperature of the outer surface of the seat insert was controlled at 350°C and the test load was 1960 N. Wear depths were measured using a confocal laser microscope, and wear mechanisms were observed using a scanning electron microscope. The extent of wear produced at higher speeds (25 Hz) was found to be greater than that produced at lower speeds (10 Hz) under identical test conditions (temperature, valve displacement, cycle number, and test load). Although test cycle numbers were increased by a factor of 3, for example from 2.1 — 106 to 6.0 — 106, the wear depths were not proportionally increased. Wear occurred rapidly during the initial stages of the test and wear depths increased less significantly with each cycle number. Wear depth of the 2.1 — 106 cycle number test at 25 Hz was much larger than that of the 6.0 — 106 cycle number test at 10 Hz in both the valve and the seat insert. Therefore, this result indicates that speed (Hz) might have a greater effect than mileage (cycle number) on the valve and seat insert while the engine is running. As the cycle number was increased, the wear depth at multi-Hz showed a tendency to near the wear depth at 25 Hz (high speed) rather than that at 10 Hz (low speed). Adhesive wear and shear strain were observed in the wear mechanisms of the valves. Furthermore, adhesive wear and surface fatigue wear were observed in the wear mechanisms of the seat inserts.

Effect on composite tribological properties of different fillers and methods for introduction into polytetrafluoroethylene

The effect of methods for introducing different fillers on the structure and tribological properties of composites based on fluoroplastic is studied. It is established that the maximum distribution uniformity for finely-dispersed fillers of different nature in composites is provided by use of a fluoroplastic base in the form of a suspension. The effect of counterbody material on wear resistance and friction coefficient of pure and filled fluoroplastic is studied. It is established that the greatest wear resistance is exhibited by fluoroplastic filled with carbon fibers in a friction pair with counterbodies made of titanium and stainless steel. It is shown that with friction for aluminium and its alloy D16T in a pair with pure fluoroplastic there is catastrophic wear for both the polymer and the metal counterbody. A considerable improvement in the wear resistance of this pair is achieved by introducing finely-dispersed graphite into the fluoroplastic matrix.

Wear Characteristics of Particulate Reinforced Metal Matrix Composites Fabricated by a Pressureless Metal Infiltration Process

The effect of size and volume fraction of ceramic particles with sliding speed on the wear properties were investigated for metal matrix composites fabricated by a pressureless metal infiltration process. The particulate metal matrix composites exhibited about 5.5 - 6 times greater wear resistance compared with AC8A alloys at high sliding speed, and by increasing the particle size and decreasing the volume fraction the wear resistance improved. The wear resistance of the metal matrix composites and AC8A alloy represented different aspects: the wear loss of the AC8A alloy increased with sliding speed linearly, whereas, the metal matrix composites displayed more wear loss than the AC8A alloy in the slow-speed region. However, a transition point of wear loss was found in the middle-speed region, which shows the minimum wear loss. Furthermore, wear loss in the high-speed region exhibited almost the same value as the slow-speed region. In terms of wear mechanism, the metal matrix composites showed abrasive wear at a slow to high sliding speed generally. However, the AC8A alloy showed abrasive wear at low sliding speed and adhesive and melt wear at a high sliding speed.

Microstructure and wear properties of TiC–VC reinforced iron based hardfacing layers

TiC–VC reinforced Fe based hardfacing layers were obtained by shielded manual arc welding (SMAW) of which H08A rare electrodes were coated by different amounts of ferrotitanium (FeTi), ferrovanadium (FeV) and graphite. The microstructure of the hardfacing layers was investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA). The thermodynamics and effect of elements on the carbides were also discussed. It was shown that TiC–VC carbides could be formed during arc welding. The composition and amount of flux evidently affect the microstructure and properties of the coatings. Good crack resistance and higher hardness of the harfacing layer could be obtained, while the amounts of graphite, FeTi and FeV were controlled within a range of 8–10%, 15–18% and 8–12% respectively. TiC–VC reinforced Fe based hardfacing layers possess much greater wear resistance and a smaller friction coefficient than 1045 steel substrate.

Profilometric and Microradiographic Studies on the Effects of Toothpaste and Acidic Gel Abrasivity on Sound and Demineralized Bovine Dental Enamel

The objective of this study was to assess the abrasive effects of toothpastes and acidic F gels on sound and demineralized enamel. Pairs of enamel specimens were cut from bovine incisors, embedded in epoxy resin and polished. An artificial subsurface lesion of 80–90 µm depth was created in one specimen from each pair. The samples were covered with adhesive tape, thereby exposing the enamel for abrasivity testing. All samples were divided into six groups of 15 and brushed with a slurry (1:3) of F gel or toothpaste and human saliva. Brushing with water (control) or with slurry was carried out (16,000 strokes) using a medium toothbrush (load 275 g) mounted in a brushing machine. Abrasion was evaluated using laser profilometry, and was about 50% less on sound than on demineralized enamel (p < 0.001). In the latter, brushing with water (0.09 ± 0.03 µm) or with fluoride-free gel (0.08 ± 0.03 µm) resulted in negligible wear. With a medium-abrasive paste (1.76 ± 0.85 µm) and an acidic F gel (2.48 ± 0.72 µm), brushing abrasion was significantly greater (p < 0.001) than with a low-abrasive paste (0.84 ± 0.38 µm). The greatest wear (16.6 ± 10.8 µm) was observed with high-abrasive paste (p < 0.001), and here transversal microradiography revealed a complete loss of the pseudointact surface after brushing. In vitro formed caries-like lesions can be abraded (by toothbrushing) more easily than sound enamel; hence, initial white spot lesions should preferably be brushed with oral hygiene products of low abrasivity.

Sliding wear of calcium α-sialon ceramics

The sliding wear behaviour of calcium α-sialon ceramics having two distinct microstructures, large elongated-grained and fine equiaxed-grained was revealed by observing the evolution of wear rate, wear track and debris as a function of apparent contact pressure and sliding speed, using a ball-on-disc type wear tester. The thresholds for the transition from mild to severe wear in terms of apparent contact pressure and the controlling material removal mechanisms were identified for both microstructures. The large elongated-grained microstructure had a higher wear transition threshold and exhibited a reduced wear rate in the severe wear regime, compared to the fine equiaxed-grained microstructure. This behaviour is attributed to a greater resistance to crack extension arising from the large elongated-grained microstructure. As the apparent contact pressure decreased, mild wear occurred at pressures below the thresholds for each of the microstructures. The material removal for the large elongated-grained microstructure was controlled by transgranular fracture, whereas grain pull-out prevailed in the fine equiaxed-grained microstructure. Consequently, a greater wear rate results for the fine equiaxed-grained microstructure in mild wear regime. An increase in sliding speed caused a slight increase in wear rate for both microstructures, more evidently in the mild wear regime. Models were developed to clarify the effect of microstructure on severe and mild wear of Ca α-sialon. They revealed that grain aspect ratio plays a more important role than grain diameter in the control of wear behaviour.

Simulation of Fretting Wear at Orthopaedic Implant Interfaces

Osteolysis due to wear debris is a primary cause of failure of total joint replacements. Although debris produced by the joint articulating surfaces has been studied and simulated extensively, fretting wear debris, produced at nonarticulating surfaces, has not received adequate attention. We developed a three-station fretting wear simulator to reproduce in vivo motion and stresses at the interfaces of total joint replacements. The simulator is based on the beam bending theory and is capable of producing cyclic displacement from 3 to 1000 microns, under varying magnitudes of contact stresses. The simulator offers three potential advantages over previous studies: The ability to control the displacement by load, the ability to produce very small displacements, and dynamic normal loads as opposed to static. A pilot study was designed to test the functionality of the simulator, and verify that calculated displacements and loads produced the predicted differences between two commonly used porous ingrowth titanium alloy surfaces fretting against cortical bone. After 1.5 million cycles, the simulator functioned as designed, producing greater wear of bone against the rougher plasma-sprayed surface compared to the fiber-mesh surface, as predicted. A novel pin-on-disk apparatus for simulating fretting wear at orthopaedic implant interfaces due to micromotion is introduced. The test parameters measured with the fretting wear simulator were as predicted by design calculations, and were sufficient to measure differences in the height and weight of cortical bone pins rubbing against two porous ingrowth surfaces, plasma-sprayed titanium and titanium fiber mesh.

The case for bulk metallic glass

The last ten years have seen the discovery of amorphous metal alloys that are glass forming at cooling rates as slow as 1°C s−1 to 100°C s−1 in the bulk via conventional metal processing such as casting, but with the ease of molding of polymers. They are twice as strong as steel, have greater wear and corrosion resistance, are tougher than ceramics, and yet have greater elasticity. Increased plasticity in amorphous/crystalline composites now promises new structural applications.

Investigation of antiwear coatings deposited by the pvd process

AbstractThe tribological properties of various PVD‐deposited coatings (vacuum arc method) have been tested, both single‐layer coatings (TiN, CrN, Ti(C,N), and Cr(C,N)) and multilayer coatings (Cr(C,N)/CrN/Cr and CR(C,N)/(CrN+Cr2N)/CrN/Cr). An unlubricated ball‐on‐disc tribosystem was used in which an Al2O3 ball is pressed against a coated steel disc rotating in the horizontal plane. A novelty of the method is the removal of wear debris from the contact zone using a draught of dry argon. This improves the repeatability of the test results and the stability of the tribological characteristics.It is shown that CrN coatings exhibit the best antiwear properties and Ti(C,N) the worst. Multilayer coatings have better antiwear properties than single‐layer ones. The friction coefficients for CrN and Cr(C,N) coatings are much smaller than for the commonly used TiN.A correlation has also been found between the physical properties of the coatings tested (adhesion of the coating to the substrate assessed in scratch tests, and coating hardness) and their antiwear properties. An improvement in coating‐substrate adhesion results in wear reduction, while greater hardness (causing a coating embrittlement increase and a change in the wear mechanism) brings about greater wear. There is no correlation between the physical properties and the friction coefficients of the coatings tested.

Wear resistance of experimental Ti–Cu alloys

After using cast titanium prostheses in clinical dental practice, severe wear of titanium teeth has been observed. This in vitro study evaluated the wear behavior of teeth made with several cast titanium alloys containing copper (CP Ti+3.0 wt% Cu; CP Ti+5.0 wt% Cu; Ti–6Al–4 V +1.0 wt% Cu; Ti–6Al–4 V+4.0 wt% Cu) and compared the results with those for commercially pure (CP) titanium, Ti–6Al–4 V, and gold alloy. Wear testing was performed by repeatedly grinding upper and lower teeth under flowing water in an experimental testing apparatus. Wear resistance was assessed as volume loss (mm 3) at 5 kgf (grinding force) after 50,000 strokes. Greater wear was found for the six types of titanium than for the gold alloy. The wear resistance of the experimental CP Ti+Cu and Ti–6Al–4 V+Cu alloys was better than that of CP titanium and Ti–6Al–4 V, respectively. Although the gold alloy had the best wear property, the 4% Cu in Ti–6Al–4 V alloy exhibited the best results among the titanium metals. Alloying with copper, which introduced the α Ti/Ti 2Cu eutectoid, seemed to improve the wear resistance.