Papers by Author: Greg Heness

Abstract: There have been growing demands of high performance metal matrix composites in advanced engineering applications in virtue of their high specific strengths. This paper is to report an assessment of the mechanical properties of LC4/SiCp metal matrix composites using an innovative testing technique, small punch test. The composite materials of this study were produced by stir casting method with particulate reinforcements of 7wt.% and 14wt.% of SiC respectively. Small punch testing was performed on the LC4 base alloy and the two composites materials. The small punch test is a relatively new mechanical testing technique capable of utilizing small disk-shaped samples to determine the mechanical properties of the test materials. In this study, the equivalent fracture strain, εqf of the LC4/SiCp MMCs was characterised and compared with the base alloy. The fracture mechanism of the test samples was examined using scanning electron microscopy.

Abstract: Particulate reinforced 10 vol.% (TiB+TiC)/Ti-6Al-4V metal matrix composites (MMCs) were produced by in-situ synthesis using vacuum arc re-melting process, and the mechanical properties of the metal matrix composites were assessed by the small punch testing (SPT). Mechanical properties of the in-situ synthesized Ti MMCs were studied and compared with the Ti base alloy. From the test data, the fracture properties and equivalent fracture strain of the test materials were characterised. The fracture mechanism of the test samples was examined using scanning electron microscopy.

Abstract: This study investigates the effect of specimen volume on the compressive strength of open cell brittle ceramics. A series of unconfined compression tests were carried out on specimens ranging in volume. The crushing strength and apparent stiffness were measured and these results are correlated with the volume of material stressed. It was found that as the volume of material tested decreased the strength decreased.

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.

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.

Abstract: In the biomedical field, the surface modification of titanium aims to inhibit wear, reduce corrosion and ion release, and promote biocompatibility. Sol-gel-derived ceramic nanoscale coatings show promise due to their relative ease of production, ability to form a physically and chemically uniform coating over complex geometric shapes, and their potential to deliver exceptional mechanical properties due to their nanocrystalline structure. In this study hydroxyapatite coatings on titanium were investigated for their fracture toughness.

Abstract: SiCp/Zn-22 wt% Al metal matrix composites of different particulate sizes have been prepared and tensile tested at 250°C at various strain rates. Scheduled thermomechanical treatment of structural refinement was employed to enhance the ductility of the composites. Substantial ductility of over 500% elongation bas been achieved within the strain rates investigated. The highest elongations are generally obtained by the samples reinforced with large particulates. Microstructural examination of the tested samples shows significant material cavitation and particulate separation in the material after tensile deformation. It was found that the particles had a de-strengthening effect.