The Influence Of Fabrication Process On Microstructure And Properties Of Cu-Zr-Al-Y Bulk Metallic Composites

Amorphous alloys have received much attention because of their unique good properties such as high strength, but the low plasticity in room temperature restrained their applications as engineering materials. Currently, the way to improve the plasticity of amorphous alloys is to fabricate metallic glass composites. In addition, copper mold casting, annealing crystallization process and pre-plastic deformation have been regarded as main methods to fabricate metallic glass composites. Endogenous B2-CuZr/CuZr-based amorphous composite has been a research hotspot for the improvement on the plasticity and ductility of amorphous matrix by the ?transformation-induced plasticity? resulted from B2-Cu Zr. Hence, we chose Cu-Zr-Al-Y system as the master alloy for its high glass forming ability and low cost to prepare amorphous alloy whose nominal compositions is(Cu_47.5Zr_47.5Al₅)₉₆Y₄. Then, the characterization was took by XRD, DSC, SEM and EDS to analyze the microstructure, micro vickers hardness and room-temperature compressive tests were took to test compression properties, respectively. We learned how cooling rate, annealing and cold rolling influence on the micro-structure and mechanical properties. The study is expected as an experimental basis for high-performance Cu Zr-based alloys.The master alloy was spray cast into three different cylindrical BMGCs rods with diameters of 2mm, 4mm, 5mm by vacuum quenching furnace to control the cooling rate. The results showed that the decrease of cooling rate?the increase of diameter? had no obvious influence on the glass formation ability, but it could accelerate the eutectoid reaction of metastable B2-Cu Zr. And the distribution of crystal became more and more uneven, the morphology transformed into dendrite from small sphere B2 phase, and B2-Cu Zr evolved into big irregular polygon eutectoid decomposition phase. There was a precipitation of Al2 Zr and a transformation of ?B2?Austenite??B19'?Martensite??in the alloy with a diameter of 5mm. The effect of the improvement on the plasticity by the ?blocking effect? and ?transformation-induced plasticity? resulted from precipitates and B2-Cu Zr all reduced with the decrease of cooling rate. Furthermore, the strength and compressive plasticity had similar regularity. The result of EDS shows that a center segregation of Y appeared, and that is in favour of the precipitation of Cu Zr because of its coherent relationship with CuY. In this experiment, a single B2-Cu Zr has been obtained from the alloy with a diameter of 2mm, it also showed up excellent mechanical properties, for example, 1.5% compressive plastic deformation.Sub-Tg annealing on as-cast rods of 2mm in 593 k and 643 k for different time, the results showed that the increasement of annealing temperature or time could improve Tg, reduce thermostability, accelerate the decomposition of B2-Cu Zr into eutectoid phase of Cu10Zr7+CuZr2, weaken the reinforcement on the matrix caused by the phase transition of B2-CuZr. Theoretically, alloy structural relaxation caused by annealing leads to excess annihilation of free-volume. And so traditional annealing treatment declined the mechanical properties of as-cast(Cu_47.5Zr_47.5Al₅)₉₆Y₄ distinctly.Nominal compositions of(Cu_47.5Zr_47.5Al₅)₉₆Y₄ was fabricated into 10.1mm×1.6mm plate samples by vacuum spraying cast, and samples were cold rolled with micro-deformation. As following: precipitation of B2-CuZr and Cu10Zr7 was promoted by cold rolling, transformation of ?B2-Cu Zr?Austensite??B19'?Martensite?? also occured. Also, stress gradients induced by cold rolling would facilitate nucleation/interaction of shear bands. In addition, the amount of B2-Cu Zr would increase and then reinforce alloys, which would finally increase the compressive plasticity of alloys. After pre-deformation of 0.992%, the compressive plasticity of(Cu_47.5Zr_47.5Al₅)₉₆Y₄ amorphous composites increased by 1.3% and the compressive strength also increased.Overall, strict controlling on the cooling rate can obtain Cu Zr-based alloys with good comprehensive properties for a single B2-CuZr enhancement; annealing crystallization process decrease the mechanical properties of(Cu_47.5Zr_47.5Al₅)₉₆Y₄ amorphous composites obviously. Micro-pre-deformation can improve the compressive plasticity and strengthen the intensity and toughness.