Decrease In Wear Resistance Research Articles

The influence of the composition of cobalt phase of hard alloys on tool wear upon laser hardening

The effect of laser pulsed treatment (LT) on the composition of the cobalt phase of the hard W-C alloys and operational characteristics of the cutting tool fabricated based on them are investigated. The determining role of binding cobalt in the formation of the mechanism of hardening the alloys is shown. It is shown that the LT in optimal models leads to the additional dissolution of WC in the Co binder and enrichment of the surface layer with cobalt in the laser treatment zone. The mentioned effects provide a decrease in wear resistance of the tool under the conditions of its adhesive-fatigue wear. The joint effect of the LT modes and cutting on the durability of the hardened instrument is analyzed, and the conditions are determined, at which its largest increase is provided.

Investigations on hygrothermal aging of thermoplastic polyurethane material

In this investigation, the absorption and diffusion of water in thermoplastic polyurethane (TPU) was studied. Water-sorption experiments, physical and mechanical property tests were performed after immersion in water at a set temperature of 70 °C for up to 6 months. Emphasis was given to the effect of immersion aging on thermal, mechanical and tribological properties. Fickian diffusion behaviour was found during the initial immersion time followed by saturation stage as time progressed. The use of differential scanning calorimetry (DSC) analysis showed that the glass transition temperature (Tg) was sensitive to the effect of hygrothermal aging and it decreased with increasing water uptake. More significantly, the mechanical properties in bulk material, obtained from tensile test, were affected by aging. Elastic modulus and stress at 200% of strain of the studied TPU were decreased after sufficient exposure to moisture. On the other hand, the mechanical properties of the material surface were equally investigated with the help of an abrasive wear test. A decrease in wear resistance of the aged TPU was discerned. The reversibility of mechanical and physical properties after moisture exposure was also assessed in this study. The polymer degradation was found as irreversible phenomenon. Finally, the evolution of the mechanical properties seems to be well correlated to structural modifications obtained from Fourier transform infrared spectroscopy (FTIR) characterization.

UHMWPE for arthroplasty: past or future?

Wear debris related osteolysis is recognised as being the main cause of failure in joint replacements based on UHMWPE inserts. However, many solutions and “new” polyethylenes have been suggested in order to address this issue. This review discusses “historical” issues associated with UHMWPE, such as oxidation, sterilization method and storage, as well as “new” topics, such as crosslinking and stabilization. The final aim is to aid orthopaedic surgeons in their selection of polyethylene inserts and in the information given to the patients. The main problem for the polymer is degradative oxidation, which is caused by the combination of the irradiation used for sterilization and oxygen, and which leads to a decrease in wear resistance and mechanical properties. Irradiation and packaging in the absence of oxygen can only reduce the oxidation, while sterilization with gas (EtO or gas plasma) is the only method that effectively eliminates it. Manufacturing processes are of great relevance to the clinical duration and must be considered by surgeons. Crosslinked polyethylene has been developed for joint inserts due to its superior wear resistance compared to conventional UHMWPE; to prevent the oxidation, crosslinked polyethylene requires post-irradiation thermal treatment, which reduces its mechanical properties and which depends on the producer. Several good clinical results from the use of crosslinked acetabular cups have reported at mid-term, while early results for knee replacements are also encouraging. Recently, the use of the antioxidant vitamin E (alpha-tocopherol) has been introduced for joint prostheses in order to prevent the oxidation of both crosslinked and noncrosslinked UHMWPE.

Oxidation and Wear of 100-Mrad Cross-linked Polyethylene Shelf-aged for 30 Years

Some previous studies suggest that aging influences wear and oxidatively degraded nonsterilized ultra-high-molecular-weight polyethylene (UHMWPE) exhibits decreased wear resistance. We therefore asked whether shelf-aging storage conditions influenced degradation and wear resistance of gamma-irradiated UHMWPE. We examined oxidation and wear of 100-Mrad gamma-irradiated UHMWPE (100-Mrad polyethylene) cups shelf-aged for 30 years without (n=2) or with (n=2) packages. The oxidation index of the unpackaged 100-Mrad polyethylene surface (4) was higher than that of the packaged one (2.7). The packaged 100-Mrad polyethylene cup exhibited a high wear resistance with a steady wear rate of 0.5 mg/10(6) cycles. In contrast, the unpackaged 100-Mrad polyethylene exhibited an extremely high initial wear rate of 187.9 mg/10(6) cycles over the first 0.25 x 10(6) cycles with a subsequently reduced wear rate of 5 mg/10(6) cycles after 5 x 10(6) cycles. Packaging over long periods inhibits surface oxidation and maintains the wear resistance of gamma-irradiated UHMWPE cups.

Microstructure, microhardness and dry friction behavior of cold-sprayed tin bronze coatings

In this paper, two types of tin bronze coatings (Cu–6 wt.% Sn and Cu–8 wt.% Sn) were prepared by cold spray process. The as-sprayed coatings were subjected to a vacuum heat treatment at 600 °C for 3 h. The coating microstructure, microhardness and tribological performance were characterized. The effects of the tin content and the vacuum heat treatment on the microstructure, microhardness and tribological behavior of the coatings were investigated. It is found that the as-sprayed CuSn6 (As6) and CuSn8 (As8) coatings exhibit practically an identical porosity. Meanwhile, As8 presents a higher microhardness than As6. In addition, the increase of the tin content in the powder feedstock leads to a lower wear rate. After a heat treatment, coating porosities are significantly reduced. However, the coating hardness is significantly decreased and the coating presents a much decreased wear resistance. For the as-sprayed coatings, such factors as ploughing and particle delamination could determine the sliding process. The heat treatment results in a distinct modification of the tribological behavior. For the annealed coatings, the adhesion, between the coating and the counterpart, could play a dominant role in the sliding process.

Influence of microstructure on the abrasive edge wear of WC–Co hardmetals

Abrasive wear of the tool edge is a damage observed in various industrial applications. Although, the abrasive wear of flat specimens has been investigated thoroughly, still there are some challenges in the understanding of edge wear micromechanisms. In the present research, edge wear of coarse WC–6,9,14 wt.%Co and ultrafine/nano WC–5,6,9 wt.%Co hardmetals was examined using edge-on-disc abrasion test using P800 SiC abrasive paper. The specimens had an edge angle of 90° and were abraded in a direction perpendicular to the edge line. Experimental results demonstrated that Co content and WC grain size influenced wear resistance of the edge remarkably. Increase in Co content resulted in decrease of wear resistance in the coarse and in the ultrafine grades. Comparing to the ultrafine grades of the same Co content, the coarse grades demonstrated higher wear rates at the beginning of sliding, but lower wear rates at the final stages. This behaviour was associated with a transition of pullout of WC grains at the beginning to a binder removal followed by WC grains detachment at final stages. The ultrafine grades showed ploughing wear over all the sliding distances.

Influence of the anodizing temperature on the porosity and the mechanical properties of the porous anodic oxide film

The microhardness and fretting wear resistance of anodic oxide layers, produced on commercially pure aluminium by potentiostatic anodizing in sulphuric acid under conditions of controlled convection and heat transfer in a reactor with a wall-jet configuration, were evaluated as a function of the electrolyte temperatures in a wide range from 5 °C up to 55 °C. Additionally, information on the microstructure of the anodic films was acquired by FE-SEM analyses whereas image analysis of high-resolution surface images yielded quantitative information on the evolution of the surface porosity as a function of the electrolyte temperature. Hence measured mechanical properties were directly related to the corresponding microstructure. The microhardness of the anodic films progressively decreased with increasing electrolyte temperatures whereas the wear resistance remained constant for the lower considered temperatures from 5 °C to 25 °C, followed by a decreasing wear resistance with increasing electrolyte temperature from 25 °C onwards. Both mechanical properties displayed an important decrease when the electrolyte temperature was raised from 45 °C to 55 °C. FE-SEM analyses indicated the formation of porous oxides with initially equal pore diameters at the metal-oxide interface, though pore widening due to chemical dissolution of the oxide by the electrolyte led to films with cone-shaped pores. This phenomenon became more pronounced with increasing electrolyte temperature and towards the surface of the anodic layer. The deterioration of the microhardness with increasing electrolyte temperatures could mainly be attributed to the increase of the porosity in the outer region of the oxides since the rate of microhardness reduction is almost synchronous with the rate of porosity increase. In contrast, the variation of the wear resistance with increasing anodizing temperature indicates that the degradation of the wear resistance does not only depend on the oxide porosity and is also affected by other characteristics of the oxide.

Experimental composite brackets: Influence of filler level on the mechanical properties

Despite their popularity in satisfying esthetic demands, plastic brackets still have some disadvantages because of decreased wear resistance and hardness. Our aim in this study was to investigate the mechanical properties of an alternative bracket-polymer urethane-dimethacrylate (UDMA) reinforced by silicon dioxide fillers with several filler levels. Three bracket groups were created: (1) unfilled UDMA, (2) UDMA with a filler content of 40% by volume, and (3) UDMA with a filler content of 70% by volume. Flexural strength, fracture force, and Vickers hardness of the bracket groups were tested. In addition, a 3-medium wear test was performed. The filler-reinforced brackets showed increased hardness, greater stiffness, and improved wear resistance compared with unfilled brackets. Higher filler concentrations in a polymer matrix result in greater stiffness of the polymer. Despite this, the filled composite brackets were not statistically more susceptible to fractures than the unfilled plastic brackets. Experimental UDMA brackets reinforced with silicon dioxide fillers showed an obvious trend for improved mechanical properties compared with unfilled UDMA brackets.

Cu CMP에서 Citric Acid가 재료 제거에 미치는 영향

Chemical mechanical polishing (CMP) achieves surface planrity through combined mechanical and chemical means. The role of slurry is very important in metal CMP. Slurry used in metal CMP normally consists of oxidizers, complexing agents, corrosion inhibitors and abrasives. This paper investigates the effects of citric acid as a complexing agent for Cu CMP with . In order to study chemical effects of citric acid, X-ray photoelectron spectroscopy (XPS) was peformed on Cu sample after etching test. XPS results reveal that CuO, layer decrease but layer increase on Cu sample surface. To investigate nanomechanical properties of Cu sample surface, nanoindentation was performed on Cu sample. Results of nanoindentation indicate wear resistance of Cu surface decrease. According to decrease of wear resistance on Cu surface removal rate increases from in Cu CMP.

Wear characteristics of functionally designed cellular cemented carbides produced by coextrusion

Abstract A series of cemented carbide materials were prepared using a coextrusion process, followed by rapid omnidirectional compaction for complete consolidation. The coextrusion process allows the carbide and metal binder phases to be reengineered into specific locations at a mesoscale level (10’s to 100’s of microns), resulting in a functionally designed cellular (FDC) architecture. Results of the study showed that the wear performance of FDC carbide materials was not dependent on the orientation of the composite architecture, despite the anisotropic nature of the material. It was determined that the wear characteristics of the FDC materials were controlled by the formation of Co 2+ x W 4− x C, which led to increased material loss due to fracture causing as much as a 330% decrease in wear resistance of the FDC materials as compared to monolithic ROC materials with equivalent cobalt content.

Mechanical properties of interference thin films on colored stainless steel evaluated by depth-sensing nanoindentation

Aiming to evaluate the influence of morphology on mechanical properties of interference films, electrodeposited using alternating pulse current on AISI 304 stainless steel, depth-sensing nanoindentation was employed. Film porosity was measured in field emission scanning electron microscopy images. Surface roughness of the films was evaluated by atomic force microscopy. Dry wear resistance under a load of 30 N against a strip of CrO3 0.5 μm abrasive paper was also measured. Load–displacement response of a Berkovich indenter reveals that the interference films analyzed are softer than the uncoated substrate. Nanoscratching and wear resistance decrease as the porosity of the interference films increases. A linear relation between film hardness and its porosity was obtained. By correlating film properties with process parameters, it was found that the mechanical resistance of the interference film is controlled by the pulse size employed in the electrochemical reaction.

Dry sliding wear behaviour of Fe–0.4C–25Cr– XNi cast steels

The effect of composition and heat treatment (solutionizing at 1200 °C and aging at 750 °C) on the room temperature mechanical properties (hardness and impact toughness) and dry sliding wear resistance of Fe–0.4C–25Cr– XNi steels (where nominal Ni contents were 4, 12 and 20 wt.%) have been investigated. The steel containing 4 wt.% Ni had ferritic and others (12 and 20 wt.% Ni) had austenitic matrixes along with M 23C 6 type chromium carbides. The applied heat treatment resulted in precipitation of sigma phase in austenitic matrix, which was accompanied by an improvement in hardness and a decrease in impact toughness. Ferritic matrix steel exhibited higher hardness and lower impact toughness than austenitic matrix steels. The results of the wear tests conducted on an unlubricated M2 quality tool steel disc revealed that at test pressures lower than 2.2 N/mm 2, the dominant wear mechanism was mild wear. However, at high test pressures (>2.2 N/mm 2) severe wear mechanism was operative. Increase of hardness and decrease of toughness resulted in a decrease in wear resistance under mild wear conditions. However, these mechanical properties were not effective on wear resistance under severe wear testing conditions.

The frictional coefficients and associated wear resistance of novel low-shrink resin-based composites

Frictional forces play a major role in the oral wear process of dental resin-based composites (RBCs) and it would be of interest to consider how the energy from friction is dissipated at the material surface. Consequently, the micromechanical wear properties of conventional methacrylate compared with novel oxirane RBCs were assessed. The frictional coefficient (mu), volume loss and Vickers hardness number (VHN) of oxirane (EXL596 and H1) and methacrylate RBCs (Z100 and Filtek Z250) were evaluated. Archard's wear equation was implemented to obtain the wear coefficient (K) and expressed as a 'fraction of friction' (K/micro) to indicate the dissipation of frictional energy that resulted in wear. Scanning electron microscopy (SEM) was used to qualitatively asses the wear facets of each RBC following 50000-cycles. The mean frictional coefficients observed between the oxirane and methacrylate RBCs were not significantly different (P > 0.05). However, the volume loss of EXL596 and H1 (5.9 +/- 0.4 and 4.7 +/- 0.3 x 10(-2) mm(3)) was significantly increased compared with Z100 and Filtek Z250 (1.7 +/- 0.2 and 2.3 +/- 0.3 x 10(-2) mm(3)). The VHN of EXL596 and H1 was either significantly greater (P = 0.021) or similar (P = 0.089) to Filtek Z250, respectively. An increase in K/micro was reported for EXL596 and H1 (34.7 +/- 4.1 and 22.8+ /- 2.4 x 10(-4)) compared with Z100 and Filtek Z250 (8.50 +/- 0.7 x 10(-4) and 8.62 +/- 1.0 x 10(-4)) (P < 0.05). SEM images of the oxirane RBCs exhibited increased surface fatigue and delamination of the surface layers compared with the methacrylate RBC specimens following 50,000-cycles. The significant decrease in wear resistance of the oxirane compared with methacrylate RBCs was unexpected since frictional coefficients and/or surface hardness were statistically similar. The decreased wear resistance of EXL596 and H1 compared with Z100 and Filtek Z250 was further explained by the increase in K/micro from wear theory and the associated increase in surface fatigue identified from SEM. The simplistic testing procedure combined with SEM utilized in the current investigation provided a greater insight into the wear mechanism by considering the effect of frictional energy at the specimen surface which may benefit the development of improved wear resistance for experimental RBC materials.

Improvement of Wear Resistance of Plasma-Sprayed Molybdenum Blend Coatings

The wear resistance of plasma sprayed molybdenum blend coatings applicable to synchronizer rings or piston rings was investigated in this study. Four spray powders, one of which was pure molybdenum and the others blended powders of bronze and aluminum-silicon alloy powders mixed with molybdenum powders, were sprayed on a low-carbon steel substrate by atmospheric plasma spraying. Microstructural analysis of the coatings showed that the phases formed during spraying were relatively homogeneously distributed in the molybdenum matrix. The wear test results revealed that the wear rate of all the coatings increased with increasing wear load and that the blended coatings exhibited better wear resistance than the pure molybdenum coating, although the hardness was lower. In the pure molybdenum coatings, splats were readily fractured, or cracks were initiated between splats under high wear loads, thereby leading to the decrease in wear resistance. On the other hand, the molybdenum coating blended with bronze and aluminum-silicon alloy powders exhibited excellent wear resistance because hard phases such as CuAl2 and Cu9Al4 formed inside the coating.

Microstructure, wear and high-temperature oxidation resistance of laser clad Ti5Si3/γ/TiSi composite coatings on γ-TiAl intermetallic alloy

Mixed NiCr–Si precursor powders on γ-TiAl intermetallic alloy (Ti–48Al–2Cr–2Nb) have been investigated for laser cladding treatment to modify the tribology and high-temperature oxidation properties of the material simultaneously. The alloy samples are pre-placed with NiCr–50% and NiCr–40%Si (wt.%), respectively, and laser treated at the same parameters, i.e., laser output power 2.8 kW, beam scanning speed 2.0 mm/s, beam dimension 1×18 mm. The treated samples underwent tests of microhardness, full dry sliding wear and high-temperature oxidation. The results showed that laser cladding with different constitution of mixed precursor NiCr–Si powders improve the surface hardness in all cases. Laser cladding with NiCr–40% Si precursor mixed powders results in the better modification of tribology and high-temperature oxidation behavior. However, with NiCr–50%Si precursor powders shows decreased wear resistance compared to the original TiAl alloy due to the existence of a large amount of hard and brittle Ti5Si3 and TiSi compounds. Optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive spectrometer (EDS) analyses indicated that the formation of the reinforced primary Ti5Si3, γ/TiSi eutectics and the refinement of the microstructure and both the continuous and dense Al2O3, SiO2 hybrid oxide scales are supposed to be responsible for the modification of the relevant properties. Laser cladding with NiCr–Si mixed powders is anticipated to be a promising wear- and oxidation-resisting surface modification technique for TiAl intermetallic alloy.

The effect of sulphuric anodisation of aluminium alloys on contact problems

Damage of aluminium alloys is a major problem in industrial applications. Especially under contact loadings, aluminium alloys show surface degradation independently of contact configurations and operating conditions such as fretting in bearing holder for gear box and abrasion in buckets of trucks. To improve wear resistance, some surface treatments have been performed, particularly sulphuric anodisation (SA) which is often used. The present work deals with the effect of such treatment in two different contact problems. The first concerns abrasion of the 5xxx alloy, whereas the second treats fretting of the A357 alloy. It was found that SA treatment effect depends on the contact configurations. It has been shown that SA treatment decreases wear resistance and provides a transition wear mechanism from ploughing to cutting under scratch. However, in fretting mode, SA treatment eliminates wear kinetics transition and maintains a low wear regime.

The Electrocrystallization of Nanonickel

We investigated the micro-and nanostructure, microhardness and wear resistance of d.c.-plated Ni electrodeposits prepared from high-and low-concentrate electrolysing Watts-type baths, also with KCl instead of NiCl 2 , withor without organic compounds, on a Cu substrate, which was subsequently removed from the deposits. Increasing current density and temperature increased grain dimensions and decreased wear resistance. When the type of bath was changed, particularly when organic compounds were added, the deposit grain size was found to decrease markedly, until deposits with an average grain size of about 20 and 50 mn were obtained. In discussing the factors controlling deposit grain size, it is concluded that the presence of organic compounds in the bath may play a decisive role.

Anomalous relationship between hardness and wear properties of a superelastic nickel–titanium alloy

We have studied the behavior of microwear and hardness of a superelastic nickel–titanium alloy using a triboindenter at various temperatures. Wear resistance was found to anomalously decrease with an increase in hardness. The observations are analyzed based on simple contact theory which suggests that the increase of hardness with the temperature is mainly due to an increase in phase transition stress, while the decrease of wear resistance with the temperature is due to an increase of the austenite elastic modulus and a decrease of the amount of phase transition that can be recovered.

Structure and properties of electrodeposited silver–bismuth alloys

The elemental and phase compositions, the deposition rate, the structure, and some physico-mechanical properties, such as hardness, wear resistance, roughness and internal stress of electrodeposited coatings of silver–bismuth alloy have been studied. The possibility of deposition of alloy coatings of desired composition depending on the electrolysis conditions and on the composition of the electrolyte used has been demonstrated. With increase in the Bi content in the coatings, hardness and wear resistance decrease, and at Bi contents higher than 50 wt.% the wear resistance remains unchanged. The roughness of the coatings is independent of their Bi content. The alloy coatings reveal a negative (compressive) internal stress. They consist of two phases and are heterogeneous both in the bulk and in the surface layer. A clearly expressed columnar structure is observed, the columns being of different phase composition. This structure is sometimes accompanied by a lamellar structure. The simultaneous deposition of phases with different Bi content leads to self-organization phenomena and formation of wave, spiral and target structures on the electrode surface.

Synthesis of Ti(C, N, O) coatings by unbalanced magnetron sputtering

Several TiCNO coatings were deposited using an unbalanced magnetron sputtering system. The composition of C, N, O was first studied using GDOS (glow discharge optical spectrometer). The coating properties as a function of oxygen/nitrogen flow ratio were then studied by using SEM, scratch testing and nano-indentation measurement. The tribological properties of the coatings were then investigated using a ball-on-disk setup with alumina balls. The sliding speeds were set at 10, 20, and 30cm/min. The results show that coating properties and performance are greatly affected by the flow rate of oxygen. With oxygen flow rate set at 4sccm during deposition, the TiCNO coating shows the lowest wear rate and friction coefficient among all. Further increase in oxygen flow rate caused a decrease of wear resistance with the increase of friction coefficient. The wear debris were analyzed using Raman spectroscopy. The tribological behavior of the selected TiCNO coating was also compared with other Ti-based hard coatings.