Fabrication of functionally graded Al/Al_2O_3 materials using pulse current pressure sintering process

To fabricate densified Al/Al2O3 functionally graded materials (FGM) on hardness and thermal expansion, a pulse current pressure sintering process was employed. This FGM consists of an aluminum layer, an (α–Al2O3 layer and 7 inter layers between them. As a starting material, aluminum and Al(OH)3 powders were used. Results obtained were as follows, (1) Temperature of an upper punch which directly contact with Al2O3 layer reached about 1800 K when the mold temperature reached about 870 K of holding temperature. (2) Mechanical grinding of powder mixture of Al(OH)3 and 20 mass% α–Al2O3 reduced the transformation temperature of Al(OH)3 to α–Al2O3 by 300 K. (3) The hardness of inter layers gradually increased as the volume fraction of γ–Al2O3 increased. Top layer which consists of α–Al2O3 was about 1000 HV in average and the surface of this layer reached 1500 HV.