AbstractIn the present research, a comparison of worn surface morphologies and wear mechanisms observed for worn deep drawing dies and sheets from the automotive car body manufacturing and worn surfaces obtained by a slider‐on‐flat‐surface (SOFS) tribometer has been carried out. Abrasion and adhesion were identified as the main surface damage mechanisms on the investigated dies and sheets. Comparison of the results obtained in laboratory testing using the SOFS tribometer showed that the test method properly simulates the tribological conditions occurring in actual sheet metal forming operations. Copyright © 2007 John Wiley & Sons, Ltd.
AbstractIron‐based hardfacing alloys are widely used to protect machinery equipment. A strong correlation is given between microstructure and chemical composition of welding deposit with the resulting wear behaviour. Concerning precipitation of metallurgical hard phases and synthetic added hard particles, the bonding strength of the hard phases in the metallic matrix seems to play a dominating role to obtain high wear resistance.The main objective of this study was to evaluate the wear behaviour for pure abrasion, combined impact/abrasion and high impact wear, respectively, for four different Fe‐based hardfacing alloys. Tests were performed with a standard ASTM G65 dry‐sand/rubber‐wheel tester. An impeller–tumbler apparatus enabled investigation of impact abrasion wear tests. Additional wear tests with high impact loading were performed on a drop hammer apparatus. Fracture surface analysis was carried out after drop hammer testing and results were correlated with microstructure and interfacial bonding behaviour of precipitations in metallic matrix. Copyright © 2008 John Wiley & Sons, Ltd.
Utilisation of hydrogen is expected to be one of the solutions against the problems of exhaustion of fossil fuels and reduction of carbon dioxide emissions. Evaluation of the materials for hydrogen utilisation machines is required. The objectives of this study are the characterisation of fretting fatigue strength of low-alloy steel SCM435H and heat-resistant steel SUH660, and the validation of effectiveness of nitriding in hydrogen gas environment. Fretting fatigue tests were conducted up to 3 × 107 cycles. The decrease of fretting fatigue strength in hydrogen gas environment was found at the long-life region exceeding 107 cycles. The amount of the decrease of the fretting fatigue limit at 3 × 107 cycles was 11% for SCM435H and 15% for SUH660. However, at the stress level above the fretting fatigue limit in air, the finite life in hydrogen gas increased more than that in air. The cause of extension of fatigue life was the delay of start of stable crack propagation. Fretting fatigue crack, which was smaller than 200 µm in length, consumed approximately 60% of the fatigue life in hydrogen gas environment. Fretting fatigue crack was steadily propagated after the test was started in air. Observations of the fretted surface showed that the fretting wear process in hydrogen gas environment was dominated by adhesion. Tangential force coefficient was higher in hydrogen gas environment than that in air. It is considered that the adhesion has a close relation to crack initiation in hydrogen gas environment, and as a result, the failure of specimen occurred at a lower stress level comparing the fretting fatigue limit in air. Copyright © 2008 John Wiley & Sons, Ltd.
AbstractThis paper presents an experimental study of tribological characteristics of electroless Ni‐P (EN) coatings and optimisation of coating process parameters based on Taguchi method coupled with grey relational analysis. A grey relational grade obtained from the grey relational analysis is used as performance index to study the deposition of EN coating with multiple tribological performance characteristics. Experiments are carried out by utilising the combination of process parameters based on L27 Taguchi orthogonal design with four process parameters, namely, bath temperature, concentration of nickel source solution, concentration of reducing agent and annealing temperature. It has been observed that concentrations of nickel source solution and bath temperature are the most significant parameters for controlling the friction and wear behaviour of EN coating. The surface morphology, composition and wear mechanism of coatings are also studied with the help of scanning electron microscopy, energy dispersed X‐ray analysis and X‐ray diffraction analysis. Copyright © 2008 John Wiley & Sons, Ltd.
AbstractCoefficients of friction and wear rates for polyacetal and polytetrafluoroethylene are measured on small‐scale cylinder‐on‐plate tests and large‐scale flat‐on‐flat tests. Three models for extrapolation between small‐ and large‐scale test results, which are based on experimental parameters, are presented: (i) one single mechanical parameter (normal load), (ii) the contact‐pressure–sliding‐velocity model (temperature limit), and (iii) a macroscopic geometry model. The last model is most extensively evaluated and considers thermal effects, sample geometry and contact conditions. After correction for the thermal sliding regime and viscoelastic deformation, the coefficients of friction can be extrapolated while the wear rates are more sensitive to the contact situation. High‐temperature tests on small scale are not representative for high‐load tests on large scale. Besides mechanical effects such as stress concentrations and debris mobility, variations in polymer structure under sliding (formation of rigid amorphous phase) and chemical interactions (wear debris polymerisation) also change with testing scale. The latter effects are explicitly illustrated from spectroscopic measurements on the worn surfaces. Copyright © 2008 John Wiley & Sons, Ltd.
