Papers by Author: Richard Wuhrer

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Authors: K. Short, Richard Wuhrer, G. Collins, Wing Yiu Yeung
Authors: R. Roest, A.W. Eberhardt, Bruno A. Latella, Richard Wuhrer, Besim Ben-Nissan
Authors: Richard Wuhrer, A. Ray
Authors: Jonathon Mak, Richard Wuhrer, Norman Booth, Paul Fanos, Greg Heness, Wing Yiu Yeung
Abstract: Equal channel angular extrusion (ECAE) was employed in an attempt to develop nanostructural metal matrix composites with homogenized distribution of reinforcing particles. Zn- Al metal matrix composites reinforced with 5 μm SiC particulates were produced by casting method. A non-uniform distribution of the reinforcing particles was evident in the metal matrix. With repetitive shear deformation imposed via the ECAE process, substantial structural improvement was achieved and the reinforcing particulates were de-clustered into a finely dispersed distribution throughout the metal matrix. The homogeneity of the particle distribution was studied by the Quadrat method and the skew factors were determined. It was found that the skew factors were substantially reduced after 8 extrusion passes, showing the homogeneity of the particle distribution was greatly improved in the composites.
Authors: Malik Lee, Richard Wuhrer, Wing Yiu Yeung
Abstract: Metal laminates have experienced rapid development in many engineering applications and generally possess enhanced properties with improved service performance. Roll bonding is a major technique used in manufacture of metal laminates. This paper is to investigate the effects of atomic diffusion on the interface development of roll bonded metal laminates in the sintering heat treatment process. Copper/aluminium bi-metal laminates were prepared by roll bonding at 430oC with a 40% rolling reduction in a single pass. Sintering was then applied at 450oC for various periods. It was found that multi-phase interfacial layers developed in the sintering process and shifted towards the aluminium metal with increasing sintering time. Composition profiles of the metallic elements were carefully determined across the interfacial area of the bonded material. Interdiffusion coefficients of the metallic elements were determined using Boltzmann-Matano analysis. The results were correlated with the multi-phase development in the interfacial area.
Authors: Richard Wuhrer, Wing Yiu Yeung
Abstract: Ternary chromium aluminium nitride (Cr,Al)N coatings were produced by reactive magnetron co-sputtering technique at different nitrogen deposition pressures. Densified nanostructured coatings with grain size below 100 nm were obtained under critically controlled deposition conditions at low nitrogen partial pressures. The nanostructured coatings were generally of improved surface roughness and properties. Microhardness measurements showed that the coatings had much higher hardness than those of coarser grain sizes. It is believed that the refinement of the coating structure at low nitrogen pressures is associated with a larger number of atoms/molecules depositing on the substrate with higher energies, thus enhancing the adatom mobility and nucleated cluster formation in the coatings. The relationship between the grain size reduction and the deposition rate of the coatings was analysed.
Authors: Sam R. Humphries, Richard Wuhrer, N.G. Booth, Wing Yiu Yeung, Qiu Bao Ouyang, J. Qin, D. Zhang
Abstract: An enhanced nucleation heat treatment process was employed to refine the grain structure of 7075Al/ 7wt.% SiCp metal matrix composite material. The grain structure of the metal matrix composite was investigated. The resulting microstructures were compared. It was found that a fine grained microstructure developed after the rapid heat treatment process. An increase in hardness was achieved, with hardness increasing from 129 HV in the cold extruded state to 137 – 153 HV after the heat treatment process.
Authors: Jonathon Mak, Richard Wuhrer, Greg Heness, J. Qin, W. Lu, D. Zhang, Wing Yiu Yeung
Abstract: Particulate reinforced Ti based metal matrix composites (MMCs) were made by in-situ synthesis using vacuum arc re-melting process. The microstructure of the Ti-6Al-4V base alloy and 10 vol.% (TiB+TiC)/Ti-6Al-4V metal matrix composites was examined. The particulate reinforcements were analysed and identified TiB and TiC particles. The particle distribution was analysed using the quadrat method over 1620 quadrats. A homogeneous particle distribution was found to establish in the composites. The experimental distribution of the reinforcements agreed well with the theoretical Poisson distribution. A skew factor, which characterizes the degree of asymmetry of a statistical distribution, of 1.108 was determined for the particle distribution in the material.
Authors: Richard Wuhrer, Wing Yiu Yeung
Abstract: Development of complex ternary nitride coatings has attracted significant industrial interest in recent years. In deposition of complex ternary nitride coatings, the nitrogen deposition pressure plays an important role in structural evolution of the coatings leading to development of different mechanical properties. This paper summaries some successful analyses by the authors on the relationships amongst the deposition rate, grain size and hardness of the coatings against the nitrogen deposition pressure. It has been established that as the nitrogen pressure decreases, the deposition rate of the coatings increases and the grain size decreases. Hardness of the coatings increases due to the development of a refined and densified coating structure. Taking into account of the reaction kinetics at the targets, the interactions of the sputtered atoms occurred in their transfer to the substrate, the reaction kinetics at the substrate, the target material characteristics and the geometric arrangement of the sputter magnetron configuration, modelling to the relationships of deposition rate with nitrogen deposition pressure, grain size with deposition rate and hardness with grain size have been successfully established in this study. A limiting grain size of the coatings has also been identified in the grain refinement process.
Authors: Richard Wuhrer, G. McCredie, Wing Yiu Yeung
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