The influence of nickel covering of Al2O3 on properties of composite material with aluminium matrix
Aleksy Patejuk Wojskowa Akademia Techniczna, Instytut Materiałoznawstwa i Mechaniki Technicznej, ul. Kaliskiego 2, 00-908 Warszawa
Annals 2 No. 5, 2002 pages 328-332
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abstract In the work, the results of researches about influence sintering temperature on composite material strengthen by aluminium reinforced with Al2O3 particles, has been presented. Samples of composite materials was made by hot pressing method. Such a matrix material aluminium powder has been used. Al2O3 particles covered by nickel layer with thickness about 2 μm make reinforce material. Before sintering process ceramics particles in correct proportion into aluminium powder was added and mechanical mixed. Then mixed powder in special form into furnace was placed. This furnace was a part of special laboratory appliance. Work parameters of this appliance permitted for smoothly regulation of pressing force to 10 kN. However used furnace permitted for smoothly regulation of sintering temperature to 900°C. During sintering process form temperature close by sintered sample was controlled. Sintering process without protective atmosphere was made. For every option (Tab. 1) minimum three samples with diameter φ 8 and length 10÷15 mm have been made. To compare several aluminium samples - without Al2O3 particles have been made. Sintering time for every option was the same: 15 minutes. In first steep microscope observation and chemical composition analysis in microareas have been done. Metalographicall cross sections where made by grinding and polishing using diamond suspension 3 and 1 μm. To study SEM microscope Philips XL-30 LaB6 was used. Microscopical observation showed that composites made by sintering process have multiphase structure. Particles of reinforce phase have varied dimension - from few to several micrometers (Fig. 1). Connection between particles and matrix has diffusion-adhesive character. The results of line chemical microanalysis made across phase boundaries investigated composites confirm above statement (Fig. 1). In next steep selected mechanical test using Instron 8501 have been done. During test computer continuous registration of results has been done. The results show relatively weekly influence of pressing force used during sintering process on compression strength composite samples. Only inconsiderable tendency to increase mechanical properties with increasing pressing force has been observed. However, the biggest influence on mechanical properties have as well a volume fraction of used reinforce material and sintering temperatures (Fig. 2). It concerns specially a level of max. fracture strength. Relatively weekly influence of sintering temperature and a volume fraction of reinforce material (in range 10÷20%) on results of ductility parameters investigated composite samples has been observed (Fig. 2b, d). A tendency of increasing of composite samples ductility with increasing sintering temperature was observed. However, the influence of volume fraction of reinforce material in composite is inconsiderable and its tendencies are dependent from sintering temperature and a pressing force used during sintering process. The hardness test of composite samples by Vickers method in five points for every sample has been done. The samples sintered with force 4 kN have the highest hardness (Fig. 3). Increasing of a volume fraction of reinforced material increases hardness of samples in whole range of sintering temperatures. Moreover, higher sintering temperature causes higher difference of hardness obtained for samples made with different pressing force 2 and 4 kN. The obtained results show that to obtain relatively high hardness one should use 20% reinforce material and press force about 4 kN as well as sintering temperature should be no less than 600°C