L. Ceschini

Mechanical and impact behaviour of (Al2O3)p/2014 and (Al2O3)p/6061 Al metal matrix composites in the 25–200°C range

The present work is aimed at studying the impact behaviour of commercially available Aluminium matrix composites, in a temperature interval ranging from 25°C to 200°C. The results of instrumented impact tests and of microstructural and fractographic observations are correlated with the tensile properties of these materials. A description of the phenomena involved (particles cracking, interfacial failure associated to matrix-reinforcement reaction layers, ductile behaviour of the matrix) is given. The effect of testing temperature as well as that of the matrix characteristics are presented and discussed.

Sliding behaviour of nanophased AISI M2 tool steel obtained by mechanomaking and hot isostatic pressing

Abstract The friction and wear behaviour of a nanophased AISI grade M2 tool steel was studied under dry sliding conditions and compared with that of a conventional AISI M2 steel. The nanocrystalline steel was produced by mechanosynthesis followed by cold and hot isostatic pressing. Slider-on-cylinder tests were performed against a ceramic coated countermaterial under loads of 10, 20, and 30 N and sliding speeds of 0.3 and 1.2 m s-1 up to 10 km sliding distance. The nanocrystalline material underwent mild wear with low coefficient of friction under all testing conditions. The commercial M2 steel displayed distance dependent transitions from a regime of mild wear with low coefficient of friction, to a regime of severe wear with high coefficient of friction. The first tribological regime was due to the formation of a layer of iron oxides on the worn surfaces. In this regime, the wear resistance of both steels is mainly dominated by the mechanical properties of the carbides which have high load carrying capability. The second tribological regime, observed in the commercial steel, was due to the formation of cracks both on the mechanically mixed layer and at a depth beneath this layer, which also led to the detachment of carbides from the matrix. This abrasive ‘third body’ produced high wear damage of the commercial steel under high applied loads.

High strain rate superplasticity in aluminium matrix composites

Abstract Recently, several studies have demonstrated that a variety of metallic materials, including aluminium-based composites, can exhibit superplasticity at relatively high strain rates (≤10−2s−1). High strain rate superplasticity (HSRS) is very attractive for commercial applications, mainly for materials difficult to shape or machine with conventional techniques, such as metal matrix composites. In this work, the possibility of achieving HSRS in a recently developed composite with an AA6013 matrix reinforced with about 20 vol % of SiC particles (AA6013/20/SiCp) was studied. Uniaxial tensile tests were carried out at high strain rates (1 × 10−1s−1 and 1 × 10−2s−1) and in a temperature range between 520 and 590°C. A maximum elongation-to-failure of 370 per cent was obtained at 560°C with a strain rate of 1 × 10−1s−1. This temperature is very close to the temperature at which melting of the composite starts. Scanning electron microscopy (SEM) analyses of fracture surfaces in the optimum superplastic condition showed the presence of filaments, the formation of which generally related to the presence of a liquid phase at the grain boundaries and/or at the interfaces.