Exploratory investigations on the structure dependence of the wear resistance of polyethylene

A relatively simple hemisphere-on-flat sliding wear tester was devised for screening samples of polyethylene prior to their trial in total joint simulators and ultimately in implanted total joint replacements. Testing was done in bovine serum and wear debris was recovered quantitatively by a method previously devised. The debris, wear surfaces and wear rates were all consistent with previous work, including simulators and clinical materials. It was found that the wear rate increases by a factor of more than 30 when the molecular weight is decreased from 2 × 10⁶ to 5 × 10⁵, that irradiation in doses typical of sterilization procedures improves wear resistance, as does reduction in fusion defect size in ultrahigh molecular weight material, and that chemical cross-linking improves wear resistance in high density polyethylene but still not to the level of the ultrahigh molecular weight material. In material with a molecular weight typical of total joint replacements, an exponential dependence of wear rate on load was found.     

Mechanical behavior and numerical analysis of corrugated wire mesh laminates

The objective is to show a possibility of corrugated wire mesh laminate (CWML) structure for bone application. CWML is a part of open-cell structures with low density and high strength built with bonded mesh layers. Specimens of CWML made of 316 stainless steel woven meshes with 0.22 mm wire diameter and 0.95 mm mesh aperture, bonded by transit liquid phase (TLP) at low temperatures, were fabricated and tested under quasi-static conditions to determine their compressive behavior with varying numbers of layers of the sample. The finite element software was used to model the CWML and studied their response to mechanical loading. Then, the numerical model was confirmed by the tested sample. Consequently, CWML specimens were reasonably matched with the human tibia bone ranged over apparent density from 0.05 to 0.08 g/cm³ in Young’s modulus and from 0.05 to 0.11 g/cm³ in compressive yield strength. The CWML model can have the potential for bone application.     

Tribological behavior of CrCoNiAlTiY coating synthesized by double-glow plasma surface alloying technique

A dense CrCoNiAlTiY coating was deposited onto the γ-TiAl alloy by double-glow plasma surface alloying technique to improve its wear resistance. Microstructure analysis showed that the coating consisted of AlCr₂, σ-NiCoCr, γ-TiAl and γ׳-Ni₃Al phase, and was well diffusion bonded to the substrate. In terms of the H/E and H³/E² ratios, the CrCoNiAlTiY coating was nearly 3.5 times better than the γ-TiAl substrate. Dry wear test results indicated that the specific wear rate of γ-TiAl substrate was 3.8×10⁻⁴ mm³N⁻¹ m⁻¹, which was about 4 times greater than that of the CrCoNiAlTiY coating. The improvement in wear resistance of the CrCoNiAlTiY coating may be attributed to the increased H/E and H³/E² ratios and to good adhesion strength between CrCoNiAlTiY coating and γ-TiAl substrate.     

An Investigation of Seal Materials for High-Temperature Application

Novel rotating seal materials were developed by powder metallurgy techniques for potential aircraft applications at high speeds and high temperatures.

A systematic wear study without lubrication included several commercially available materials and the following types of experimental materials: (a) pure refractory hard metals, (b) binary alloys of refractory hard metals bonded with nickel and, (c) ternary alloys of refractory hard metals bonded with nickel and infiltrated with silver.

Two ternary alloys, containing nickel bonded WB or CrN and infiltrated with silver, showed superior wear qualities against either tool steel or a nickel—chromium—iron alloy at a sliding speed of 29,000 ft/min under a 14 lb/in² load and at ambient temperatures as high as 1300 F. A commercial titanium carbide composition showed excellent wear characteristics in contact with an identical composition at a sliding speed of 14,000 ft/min under a 16 lb/in² load and at an ambient temperature of 1050 F.     

An adhesive wear model based on variations in strength values

It is postulated that adhesive wear particles are formed when the interface at a junction between two sliding metals is strong while some path within one of the metals but near the interface is weak. Plausible assumptions about the strength values and their statistical variation are made, and it is shown that in good agreement with experimental findings wear coefficient values are obtained varying from 5.7 × 10^?3 for clean identical metals to 4 × 10^?7 for metals lubricated so as to produce a friction coefficient of 0.10. The model makes no explicit assumptions about the causes of adhesive wear but emphasizes the importance of adhesion at the interface and fluctuations in strength in the contacting materials.     

Friction and wear of diamond-containing polyimide composites in water and air

Polyimide-based composites containing fine diamond powder were fabricated using spark plasma sintering. The based material was polyimide (PI) containing a small amount of polytetrafluoroethylene (PTFE). Two types of diamond powder were used: one synthesized by statically high pressure, i.e., high-pressure diamond (HD), and the other synthesized by shock compression, i.e., shock-compression diamond (SD). We evaluated their tribological properties using a reciprocating friction tester in water and air using an Al₂O₃ mating ball. Adding HD to the polyimide-PTFE-based material decreased the composite's friction in water, but the effect of this addition in air was negligible. The specific wear rate of composites with different HD content was similar to that of the based material alone in water, while the wear of composites decreased with the addition of diamond in air. The effect of diamond powder size on friction and wear of composites was generally low in both water and air. The addition of SD decreased the friction coefficient of composites, but SD content only negligibly affected the friction in water and air. The specific wear rate was minimal at SD content of 5 vol.%, when diamond content was varied. Wear was almost independent of diamond powder size. SD reduced composite friction and wear better than HD; regardless of environment, its friction coefficient was less than 0.1 and the specific wear rate was in the level of 10⁻⁷ mm³/N m in both water and air.     

Calculation of wear (f.i. wear modulus) in the plastic cup of a hip joint prosthesis

The wear equation is applied to the wear process in a hip joint prosthesis and a wear modulus is defined. The sliding distance, wear modulus, wear volume, wear area, contact angle and the maximum normal stress were calculated and the theoretical calculations applied to test results.During the wear process the increase of the wear modulus is about 100 Nmm^?2 per mm sliding distance in the Charnley and the Charnley-Muller hip joint prosthesis. From the wear volume point of view the Charnley prosthesis is probably superior to the Charnley-Muller prosthesis if run-in before implantation.     

Modelling of Tool Wear Based on Component Forces

Polynomial and exponential wear models of the joint effect of different combinations of component forces or ratios were fitted to determine the wear model that would give the best approximation of actual tool wear rates. Statistical analysis revealed the combination of force ratios: F ₁=F _f/F _t, F ₂=F _r/F _t and F ₄ = to have the highest statistical significance with tool wear rate based on F _cal and r ² statistics for both polynomial and exponential models, with the latter giving the best approximation of the actual tool wear rates. A wear map was established using the exponential wear model of the force ratios for the machining of a nimonic C-263 nickel-base alloy with PVD TiN/TiCN/TiN-coated carbide insert grade.     

The Lubricating Performance of an “in Situ” Process MoS2 Film in Air and in Liquids

The performance of a synthetic MoS₂ film, produced by electrodeposition of molybdic oxide followed by a temperature-pressure H₂S conversion to a molybdenum sulfide compound, is examined under extreme pressure conditions immersed in various fluids. Friction wear and EP characteristics, measured on various test machines, are compared to those of the fluids alone and also to conventional bonded films.

The fluids examined include: mineral oil, jet fuel, hydraulic fluid, silicone fluid.

The dry films include: burnished MoS₂ powder, MIL-L-8937 resin bonded film, MIL-L-8129 silicate bonded film and the synthetic “in situ” MoS₂ film.

The performance of the synthetic MoS₂ film on titanium and stainless steel is also examined.     

Influence of fiber orientation on abrasive wear of unidirectionally reinforced carbon fiber–polyetherimide composites

A composite with continuous carbon fibers (CF) (80% by vol.) and high performance thermoplastic polyetherimide (PEI) matrix was developed and evaluated for various mechanical properties as a function of fiber orientation angle (0°, 30°, 45°, 60° and 90°). It was observed that Young's modulus, Poisson's ratio, toughness and % strain decreased with the increase of fiber orientation angle with respect to loading direction. In-plane shear modulus was highest for fibers with 45°. Overall, unidirectional (UD) CF reinforcement enhanced all strength properties of PEI significantly. Composites with fibers in 0° (parallel to loading direction) proved best in almost all the properties. Tribological evaluation in abrasive wear mode under different loads and fiber orientations indicated that coefficient of friction (μ) and specific wear rate (K₀) decreased with load, in general. Comparatively low specific wear rate (K₀), (in the order of 0.7 1×10^?9 m³/Nm) was observed for 0° fiber orientation, while fibers in 90° showed almost three times higher wear rate. Overall fiber reinforcement in 0° orientations proved beneficial from both strength and tribological performance point of view. SEM proved useful to correlate wear rate with surface topography.     

碳化硅陶瓷新型反应连接技术研究

在碳化硅陶瓷反应连接工艺的基础上研究了一种新型的反应连接工艺,利用该工艺连接了自制的反应烧结碳化硅（RB-SiC）陶瓷。连接的RB-SiC陶瓷样品表面经过初步抛光后,测试了焊缝宽度、焊缝处的显微组织结构、连接层的力学性能和高低温实验后连接层对表面面形的影响。测试结果表明：利用新型反应连接工艺连接的RB-SiC陶瓷的焊缝宽度分布在54-77μm之间;焊缝处的显微组织结构非常均匀,接近基体材料;测试了十个样品的室温抗弯强度,平均值为307MPa,而且断裂都产生在母材上,说明焊缝处力学性能优异;高低温实验后,整块碳化硅陶瓷表面面形无变化,说明连接层的热学性能与母材一致,无残余应力。     

Drilling of hybrid Al-5%SiCp-5%B4Cp metal matrix composites

Hybrid metal matrix composites consist of at least three constituents—a metal or an alloy matrix and two reinforcements in various forms, bonded together at the atomic level in the composite. Despite their higher specific properties (properties/unit weight) of strength and stiffness, the nonhomogeneous and anisotropic nature combined with the abrasive reinforcements render their machining difficult. The work piece may get damaged and the cutting tools experience high wear rates, which may lead to an uneconomical production process or even make the process impossible. This work reports on the drilling of Al-5%SiC_p-5%B₄C_p hybrid composite with high-speed steel (HSS), not expensive PCD, or carbide drills in an attempt to explore the viability of the process. Drilling of Al-5%SiC-5%B₄C composites with HSS drills is possible with lower speed and feed combination. The cutting conditions for minimized tool wear and improved surface finish are identified. Characterization of tool wear and surface integrity are also carried out.     

Carbon fabric reinforced polyetherimide composites: Optimization of fabric content for best combination of strength and adhesive wear performance

Polyacrylonitrile (PAN) based high strength carbon fabric (plain weave) reinforced polyetherimide (PEI) composites were fabricated using impregnation technique by selecting five different contents of carbon fabric, viz. 85, 75, 65, 55 and 40 vol.%. These bidirectional (BD) composites were evaluated for their mechanical strength as well as tribological behavior in adhesive wear mode. Dry adhesive wear studies were conducted on a custom designed wear tester in which high PV conditions can be simulated. Tests were conducted at various operating parameters such as load, temperature and orientation of fabric with respect to the sliding plane. Two important results were observed; firstly the moderate CF contents (75, 65 and 55 vol.%) proved to be the most effective in manifold increase in mechanical strength of PEI and secondly, the composites with fabric in the direction normal to sliding plane led to very high coefficient of friction (μ). When fabric was parallel to the sliding plane, significant improvement in the tribo-properties of PEI in terms of very high tribo-utility (up to 600 N), appreciably low μ and enhanced wear resistance (W_R) (in the range of 10⁻¹⁶ m³/N m) was achieved. The extent of improvement, however, strongly depended on the operating parameters and fabric content. A fairly good correlation was obtained between W_R and combination of mechanical properties such as ultimate tensile strength (S), and interlaminar shear strength (ILSS). Wear mechanism studies by SEM supported the observed wear performance of composites.     

Effects of Co content and WC grain size on wear of WC cemented carbide

WC cemented carbides are used extensively to improve abrasion resistance. Co content and WC grain size influence the mechanical properties of the cemented carbides. In this study, the effects of Co content and WC grain size of cemented carbide on wear were examined. We prepared 13 different cemented carbides with different Co content and WC grain size. Wear tests were carried out against 0.45% carbon steel under dry condition at 98 N and 232 mm/s. From the results, we found that wear increased with both Co content and WC grain size. Specific wear rate of the cemented carbides tested was in the range of 10⁻⁷ mm³/(N m). We discussed the wear properties with hardness and the mean free path of the cemented carbide. These two parameters alone cannot explain the wear property.     

Optimisation of electron-beam surface hardening of cast iron for high wear resistance using the Taguchi method

The paper presents the application of the Taguchi method to develop an optimised electron-beam surface hardening of cast iron for high wear resistance. The experiments were conducted on both the ductile and grey cast iron. The factors investigated during the surface-hardened process included the material matrix, the accelerating voltage, the electrical current, the travel velocity, the melted width, the beam oscillation, and the post-heat treatment temperature. In this study, the L18 and L9 orthogonal arrays were introduced through the two-stage experimental designs and trials. Smaller-is-better was used as a quality characteristic to evaluate the experimental results by computing their signal-to-noise (S/N) ratios of the wear volume after wear tests.It was found that using the Taguchi method coupled with a two-round experimental design strategy is simple, effective and efficient in developing an optimised EB surface hardening process. The experimental results show that the most important process parameters identified are the accelerating voltage, the travel speed, the electrical current and post-heat treatment, respectively. The best wear resistance result obtained through the best combination of process parameters is 8.845×10⁸ kg-mm/mm³.     

Investigation on overlap joining of AZ61 magnesium alloy: laser welding, adhesive bonding, and laser weld bonding

This paper presents the research on weldability of magnesium alloy AZ61 sheets by overlap laser welding, adhesive bonding, and laser seam weld bonding processes. Microstructures and mechanical properties of the joints are investigated. In overlap laser welding, the joint fractures at the interface between the sheets and maximum shear strength can reach 85% of that of the base metal. Off-center moment during tensile shear test can lead to the strength loss, while the weld edge can also influence the strength as a cracking source. Adhesive bonded joint can offer high tensile shear failure force but low peel strength. Laser weld bonded joint offers higher tensile shear failure force than either laser welded joint or adhesive bonded joint does, and the improved failure load is due to combined contribution of the weld seam and the adhesive. The weld seam can block the adhesive crack propagation, and the adhesive improves the stress distribution, so they can offer a synergistic effect.     

Artificial lubrication of joint prostheses

The great success of total joint replacement in surgery has been disturbed mainly by the later loosening of the prostheses and wear of the plastic components. In an attempt to improve long term performance, and to eliminate the adverse effects of wear debris, the concept of artificial lubrication and encapsulation of the joint articulating parts has been proposed by a number of workers in recent years^1–3. This paper covers the selection of a lubricant candidate and a tribological study on both all-metal and metal/plastic combinations.     

The wear behavior of ultrahigh molecular weight polyethylene

The wear behaviour of ultrahigh molecular weight polyethylene has been studied using a thrust-washer testing machine. The data are examined in the light of findings of other workers and of clinical results. The wear factor exhibits a maximum at about 500 lb in^?2 surface pressure for polyethylene samples tested in water. The use of plasma in place of water does not change the wear factor and this indicates that the wear of polyethylene is not sensitive to the type of liquid environment likely to be encountered in a total joint prosthesis.     

Friction and dry sliding wear of bismaleimide filled with carbon nanotubes

Three types of bismaleimide–carbon nanotubes (CNTs) nanocomposites were fabricated using two types of original multiwalled CNTs with different diameters and one amide functionalized CNTs. The influence of diameter, content and functionalization of CNTs on the flexural and dry sliding wear behaviour were measured with universal testing machine and pin-on-disc wear apparatus. The experimental results indicated that at 1.5 wt-%, the bismaleimide-functionalized MWCNTs exhibited highest flexural strength of 156 MPa which is increased by 164% as compared to the neat matrix, and lowest specific wear rate of 1.8 × 10^?4 mm³ N^?1 m^?1 which is decreased by 90% as compared to the neat matrix. This was attributed to the dispersion of CNTs in the matrix and the filler-matrix adhesion and internal strength of the composite.     

The effect of acetabular cup position on wear of a large-diameter metal-on-metal prosthesis studied with a hip joint simulator

Clinically, malposition of the acetabular cup in large-diameter metal-on-metal prosthetic hip designs is associated with high wear, adverse reaction to metal debris and early failure. A steep angle of the cup (>60°) may lead to poor tribological performance. Large-diameter CoCr-on-CoCr prostheses were run in the HUT-4 hip joint simulator so that a steep angle was included. With a correct position, the tribological behaviour was excellent, the wear rate being 0.1 mm³/10⁶ cycles. In the steepest position, lubrication failed and the wear rate was two orders of magnitude higher. This study stresses the importance of rigorous pre-clinical testing.