Fabrication of Zr- and Cu-base bulk metallic glass/Cu surface composites by high-energy electron-beam irradiation

Zr- and Cu-base bulk metallic glass (BMG)/Cu surface composites were fabricated by high-energy electron-beam irradiation in this study. The mixture of Zr- or Cu-base amorphous powders and LiF + MgF2 flux was deposited on a pure Cu substrate, and then electron beam was irradiated on this powder mixture to fabricate an one-layered surface composite. A two-layered surface composite was also fabricated by irradiating electron beam again onto the powder mixture deposited on the one-layered surface composite. The microstructural analysis results indicated that a number of soft, coarse, and Cu-rich crystalline phase particles were formed in the one-layered Zr-base BMG surface composite layer, whereas a small amount of hard and fine crystalline particles were homogeneously distributed in the amorphous matrix of the two-layered Zr-base BMG surface composite layer. On the other hand, the two-layered Cu-base BMG surface composite layer consisted of Cu-rich crystalline phases without amorphous phases because the cooling rate was not fast enough to form amorphous phases during the electron-beam irradiation, thereby indicating that amorphous forming ability was the most important factor in successfully fabricating BMG surface composites. The two-layered Zr-base BMG/Cu surface composite which fully took advantages of BMG alloys was successfully fabricated by the use of flux to shield protect oxidation environments, the second electron-beam irradiation to melt already-formed crystalline particles, and the fast heating and cooling rates to improve amorphous forming ability.