Composition Design, Fabrication And Properties Of Cu-Rich Bulk Amorphous Alloys

Cu-based bulk amorphous alloys have attracted extensive attention from science to engineering community, due to their good mechanical properties, physical and chemical functions etc, and also have been considered as one hot topic of advanced metallic materials. Up to date, investigations still fail to fully understand bulk amorphous alloys, especially to clarity glass-forming ability of glass formers. On the other hand, the poor plasticity and corrosion resistance of bulk amorphous alloys is still an urgent puzzle for the application of bulk amorphous alloy as structural materials. For these, the thesis aims to develop a simple composition design method with the aid of computational thermodynamics, to predict the solidification of multiple components of Cu-based alloys. In addition, microalloying technique was used to construct Cu-based bulk amorphous alloy composites for the improvement of plasticity of these alloys. Using X-ray diffraction, differential scanning calorimetry and microstructure analysis characterized the amorphous nature of alloys. Furthermore, the effects of microalloying elements and ultraviolet light on the corrosion of as-cast Cu-based bulk amorphous alloys and composites were studied.Through correlating the linear relationship between T_m and T_g, the parameter ), characterizing the glass-forming ability, was rationally derived to i, which indicates that solidus temperature （T_m） and liquidus temperature （Ti） are two important parameters for the characterization of glass-forming ability. On the other hand, the derived equation transforms Trg from a posteriori parameter, only utilizing for characterizing the glass-forming ability, to a transcendental parameter which is suitable for prediction of composition of glass-forming alloys. Importantly, this parameter reveals that solidification temperature range can intrinsically affect the glass-forming ability of glass-forming alloys. With this score, a series of Cu-Zr-Ti and Cu-Zr-Al bulk amorphous alloys were designed and fabricated.By the mechanical tests, the thesis explores that ternary Cu-Zr-Ti bulk amorphous alloys with 7.5-8.5 at.% of Ti element are of large plasticity. With computational thermodynamics and prediction of solidification of compositions, Cu-Zr-Ti-（Al, Ni, Si） bulk amorphous alloys and composites were fabricated, in which Cu_54.5Zr₃₇Ti₈Ni_0.5 （in Cu-Zr-Ti-Ni alloy system）, Cu_54.5Zr₃₇Ti₈Si_0.5 and Cu_53.5Zr₃₇Ti₈Si_1.5 （in Cu-Zr-Ti-Si alloy system） display excellent plastic deformation behavior. By analyzing the binary phase diagram among alloying elements （Mo, Nb, Hf elements） and components （Cu, Zr and Ti elements）, Ti elements in Cu_50.2Zr_40.8Ti₉ was partly substituted by alloying elements with the quantity of 0.5-2 at.%. Cu_50.2Zr_40.8Ti₈Mo_1.0, Cu_50.2Zr_40.8Ti₈Nb_1.0 and Cu_50.2Zr_40.8Ti₈Hf_1.0 bulk amorphous alloy composites shows the best fracture strength and plasticity in own alloy system. And also, the plasticity of Cu_50.2Zr_40.8Ti₈Nb_1.0 and Cu_50.2Zr_40.8Ti₇Nb_2.0 alloys is better than that of alloys with Mo and Hf elements with any quantity. In all designed and fabricated bulk amorphous alloys and composites, some of them indicate good comprehensive mechanical performances. Specifically, the plasticity and fracture strength of Cu₅₀Zr_42.5Ti_7.5, Cu_51.7Zr_40.8Ti_7.5, Cu_54.5Zr₃₇Ti₈Ni_0.5, Cu_50.2Zr_40.8Ti₈Nb_1.0 and Cu_50.2Zr_40.8Ti₇Nb_2.0 exceed 10% and 2000 MPa, respectively. The results of indentation creep of two bulk amorphous alloy composites with remarkable difference in plasticity disclose that their plasticity strongly correlates with relaxation of amorphous matrix.The added alloying elements, including Al, Si, Ni, Mo, Nb and Hf elements, into ternary Cu-Zr-Ti bulk amorphous alloys can enhance the corrosion potential of alloys. The corrosion current density of Gu_54.5Zr₃₇Ti₈Si_0.5 shows a dramatical decrease to Cu₅₅Zr₃₇Ti₈. Potentiodynamic polarization curves and electrochemical impedance spectra, corroded morphologies indicate that pitting potential increases, the number of pitting sites decreases and corroded area reduces, revealing the ultraviolet light can improve the pitting potential of Cu-based bulk amorphous alloys.