The present invention provides a Cu--Be based amorphous alloy comprising an amorphous phase of 50% or more by volume fraction. This alloy has a composition represented by the following formula: Cu.sub.100-a-bBe.sub.a(Zr.sub.1-x-yHf.sub.xTi.sub.y).sub.b. In the formula, "a" and "b" represent atomic percentages which are 0<a.ltoreq.20 and 20.ltoreq.b.ltoreq.40, and "x" and "y" represent atomic fractions which are 0.ltoreq.x.ltoreq.1 and 0.ltoreq.y.ltoreq.0.8. The alloy may contain a small amount of one or more elements selected from the group consisting of Fe, Cr, Mn, Ni, Co, Nb, Mo, W, Sn, Al, Ta and rare-earth elements and/or the group consisting of Ag, Pd, Pt and Au. The alloy has a wide supercooled-liquid temperature range and a large reduced glass transition temperature (Tg/Tm) to achieve a high thermal stability against crystallization or a high glass-forming ability.
To provide a Cu-based amorphous alloy having a glass-forming ability higher than that of a Cu--Zr--Ti amorphous alloy and a Cu--Hf--Ti amorphous alloy, as well as excellent workability and excellent mechanical properties without containing large amounts of Ti.A Cu-based amorphous alloy characterized by containing 90 percent by volume or more of amorphous phase having a composition represented by Formula: Cu.sub.100-a-b(Zr,Hf).sub.a(Al,Ga).sub.b [in Formula, a and b are on an atomic percent basis and satisfy 35 atomic percent.ltoreq.a.ltoreq.50 atomic percent and 2 atomic percent.ltoreq.b.ltoreq.10 atomic percent], wherein the temperature interval .DELTA.Tx of supercooled liquid region is 45 K or more, the temperature interval being represented by Formula .DELTA.Tx=Tx-Tg (where Tx represents a crystallization initiation temperature and Tg represents a glass transition temperature.), a rod or a sheet having a diameter or thickness of 1 mm or more and a volume fraction of amorphous phase of 90% or more can be produced by a metal mold casting method, the compressive strength is 1,900 MPa or more, the Young's modulus is 100 GPa or more, and the Vickers hardness is 500 Hv or more.
