BULKY LA-AL-TM (TM = TRANSITION-METAL) AMORPHOUS-ALLOYS WITH HIGH-TENSILE STRENGTH PRODUCED BY A HIGH-PRESSURE DIE-CASTING METHOD

The application of a high-pressure die casting technique to La-Al-TM (TM=Co, Ni, Cu) alloys was found to produce bulk amorphous alloys in cylinder and sheet forms. The maximum sample diameter (d(c)) for formation of an amorphous phase is 3 mm for La55Al25(Ni or Cu)20, 7 mm for La55Al25Ni10Cu10 and above 9 mm for La55Al25Cu10Ni5Co5. There is a clear tendency for d(c) to increase with an increase in the temperature interval of a supercooled liquid region. The glass transition temperature (T(g)), the crystallization temperature (T(x)) and the heat of crystallization (DELTAH(x)) remain unchanged in the thickness range of 1 to 7 mm for the La55Al25Cu10Ni10 alloy. T(g) and DELTAH(x) are nearly the same as those for the melt-spun ribbon. The tensile fracture strength (sigma(f)) and elongation (ef) for the La65Al20Cu7.5Ni3.75Co3.75 cylinder with a diameter of 3 mm are 700 MPa and 1.5%. Although the er value is nearly the same as that for the melt-spun ribbon, the sigma(f) value is about 80% as high as that for the ribbon. The decrease in sigma(f) by 20% is presumably due to the existence of pores based on the result that the porosity of the cast samples is about 20%. The achievement of the sigma(f) for the cast alloys with 20% in porosity indicates that the bulk amorphous alloys also have a ductile nature which is comparable to that for the melt-spun ribbon.