Fabrication of functionally graded Al/Al₂O₃ 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.