Bulky La–Al–TM (TM=Transition Metal) Amorphous Alloys with High Tensile Strength Produced by a High-Pressure Die Casting Method

Abstract

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 (ΔH_x) remain unchanged in the thickness range of 1 to 7 mm for the La₅₅Al₂₅Cu₁₀Ni₁₀ alloy. T_g and ΔH_x are nearly the same as those for the melt-spun ribbon. The tensile fracture strength (σ_f) and elongation (ε_f) for the La₆₅Al₂₀Cu_7.5Ni_3.75Co_3.75 cylinder with a diameter of 3 mm are 700 MPa and 1.5%. Although the ε_f value is nearly the same as that for the melt-spun ribbon, the σ_f value is about 80% as high as that for the ribbon. The decrease in σ_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 σ_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.