Influence Of Sintering Temperature On Decohesion Mechanism Of Al-(Al2O3)p Composite
Anita Olszówka-Myalska Politechnika Śląska, Wydział Inżynierii Materiałowej, Metalurgii i Transportu, ul. Krasińskiego 8, 40-019 Katowice
Annals 1 No. 1, 2001 pages 64-67
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abstract A composite of an aluminum matrix reinforced with alumina particles of 500 mesh granulation was obtained by powder metallurgy methods. A mixture of aluminum powder (Fig. 1) and alumina powder (Fig. 2) was axially pressed in Degussa press in vacuum. Two stages of pressing were applied. At the first one, pressure of 15 MPa, temperature of 400ºC and time 30 minutes were applied and at the second, pressure was applied of 150 MPa, temperatures of 500, 550, 600 and 640ºC and time of 50 minutes. The composites density determined by Archimedes method and the hardness determined by Brinell method were changing with the pressing temperature (Table 1). Structure examinations of the obtained composites were performed on polished samples and fractures by means of a scanning electron microscope FE Hitachi 4200 with EDX Noran System 3500. The results are presented in Table 2 and Figures 3-6. At temperature of 500 and 550ºC between the aluminum powder particles a bonding was formed containing micropores and decohesion occurred on grain boundaries. The matrix ductile fracture throughout the volume was observed in the sintered material at a temperature of 600ºC and higher. Differences were found in the bonding structure: aluminium oxide particle-aluminium matrix. In composites sintered at 500oC a typical mechanical bonding occurs, which undergoes changes with a growing temperature and at 640oC has a diffusive character. Three basic decohesion mechanisms of the sintered composite Al-(Al2O3)p were identified: - intergranular, in matrix and along the boundaries matrix - alumina particle; - transcrystalline ductile in the matrix and along the boundries: matrix - particle; - transcrystalline ductile in the matrix and transcrystalline brittle in particles. The results obtained allowed to define initial conditions of sintering the Al-(Al2O3)p composite which contains intermetallic phases.