Crystallization behavior of Zr₅₅Al₁₀Ni₅Cu₃₀ amorphous alloys with different morphologies and thermal history conditions

This work investigated the crystallization behavior of Zr₅₅Al₁₀Ni₅Cu₃₀ amorphous alloy (bulk and powder with different morphologies) under different heating and cooling rate conditions, and has found that the crystallization behavior of Zr55Al₁₀Ni₅Cu₃₀ under different thermal history conditions was quite different. Under conventional heat treatment condition, the heating and cooling rates of the alloy were lower, the Zr₅₅Al₁₀Ni₅Cu₃₀ bulk amorphous alloy began to crystallization above the outset crystallization temperature T_x, the CuZr₂ nanocrystalline was formed. With increasing temperature, its grain size became bigger, when exceeding the melting point, the thick CuZr₂ lath+eutectic organizations of lath (CuZr₂)+(Zr, Cu, Al, Ni) were formed under furnace cooling condition; under laser melting condition, however, the heating and cooling rates of alloy were higher, with increasing number of pulse frequency, the crystallization effect of Zr₅₅Al₁₀Ni₅Cu₃₀ bulk amorphous alloy accumulated gradually, in heat affected zone spherulites were precipitated and grew up, subsequently became unstable and finally a belt of equiax crystals were formed along the weld pool boundary. For amorphous alloy powder, due to its poorer the cooling performance than bulk amorphous, the cooling rate was lower, causing the powder particles crystallized into equiaxed dendrite during laser melting process, and with increasing laser energy, the equiaxed dendrite size increased.