Kou Shengzhong

Effect of Casting Temperature on Mechanical Properties and Microstructure of Zr53.9Cu29.4Ni4.9Al9.8Fe2 Bulk Metallic Glass

Abstract Zr 53.9 Cu 29.4 Ni 4.9 Al 9.8 Fe 2 alloy sample with the diameter of 3 mm was prepared by Cu mold suction casting at different temperatures. The effect of casting temperature on mechanical properties and microstructure of the as-cast alloy was investigated. It is found that there is a critical casting temperature for the fully amorphous structure, below which the crystallization phase might be precipitated. Experiment results show that the compressive strength increases and the compressive plasticity slightly decreases when the casting temperature increases to certain extent. However, the compressive strength and the compressive plasticity simultaneously increase when the casting voltage increases to 9 kV, and the compressive plasticity is 2.62%. Mechanical properties of BMG can be tailored to certain extent by controlling the casting temperature, which is correlated with free volume and residual stresses.

Influence of Addition of Gd on Glass Forming Ability, Thermal Stability and Compression Performance of Cu-Based Bulk Metallic Glass

Abstract In order to research the plasticity of the Cu-based bulk amorphous and the influence of rare earth element on the mechanical properties of the amorphous, the Cu50-xZr42Al8Gdx (x=0, 2, 4) alloy rods with 3.0 mm in diameter were prepared by the suspend melting-copper mold suction casting. The structure and glass forming ability of the alloys were analyzed by X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. Subsequently, through the compression performance testing and the fracture morphology observation, the effect of rare earth element Gd on the mechanical performance and the fracture behavior of the samples were investigated. The results show that the structure of the rods is composed of amorphous phase. The samples possess larger thermal stability and good glass formation ability. With the increase of Gd content, the brittleness of the samples is enhanced gradually. Fracture mode presents brittle fracture.

Effects of Pre-deformation Annealing on Mechanical Properties of Ti-Based Amorphous Alloys

Abstract Ti40Ni40Cu20 amorphous matrix composite plate specimens were fabricated by the levitation suspend melting-water cooled Cu mold process. The specimens were pre-compressed at different degrees with a universal testing machine and then annealed at 150 °C for 30 min. The effects of pre-deformation annealing processes on the microstructure and mechanical properties of Ti40Ni40Cu20 alloy system were studied by a metallographic microscope, X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show the martensitic phase transformation that of the austenite phase under external force occurs. The phase transition induced by the deformation coupled with the annealing release of residual thermal stress plays a role in enhancing both strength and toughness of the amorphous matrix composite. Both martensite phases and austenite phases are increased with the increase with the degrees of pre-deformation increasing, and martensite phases are increased faster. Thus, the yield strength of the composite increases, while the ductility declines. Therefore the controllable yield strength in the pre-compression stage for shaping can be realized.

Effects of Cu Content on Microstructures and Mechanical Properties of Ti-Ni-Based Amorphous Composites

Abstract Ti-Ni-based amorphous composite samples (Ti0.5Ni0.5)100-xCux with different Cu contents but the same diameter which has been prepared by the copper mold suction casting. The effect of the Cu contents (x=0, 10, 15, 20, 25, 30, 35, 40, at%) on the microstructures and mechanical properties of the amorphous composites was studied. Results show that both fracture strength and plastic strain of the alloy are very high when the copper content is x=20. Meanwhile the alloy exhibits the best comprehensive properties. As the x value increases, the glass forming ability of (Ti0.5Ni0.5)100-xCux alloy shows a waveform change from increasing to decreasing and then to increasing, but following an overall trend towards decreasing. The plasticity of Ti-Ni-based amorphous materials can be improved by adding Cu element in modest quantities (x≈25) to the Ti-Ni-based composites; however, adding more Cu (i.e., x>30) neither can improve the amorphous forming ability nor can enhance its strength. When x=15, the alloy has the highest breaking strength of 2440 MPa while gets the higher yield strength of 1471 MPa causing 17.15% plastic strain. The data are pretty high with respect to other amorphous systems or other alloy systems with memory of their shapes. When x=25, there is a certain increase in the alloy plastic strain with 21.35% plastic deformation.

Glass Forming Ability and Mechanical Properties of Cu-Zr-Al-Nb Amorphous Alloy

Abstract Cu46Zr44Al5Nb5 amorphous alloys were fabricated by suspend melting under an argon atmosphere using water-cooled Cu mould suction casting. Glass forming ability and mechanical properties of the alloys were studied. The analyses of DSC curves, X-ray diffraction (XRD) patterns and electron diffraction taken from the rods of Cu46Zr44Al5Nb5 with different diameters (3, 4, 6 mm) indicate that the critical diameter can be up to 6 mm at least. And the best glass former exhibits an undercooled liquid region ΔT of 52 K, and reduced glass transition temperature Trg of 0.60. The critical cooling rate (Rc) calculated from TTT (Time-Temperature-Transformation) curves of Cu46Zr44Al5Nb5 forming glassy alloy is 3.985 K/s. The intensity of broad peaks from X-ray diffraction patterns, the crystallization enthalpy and the fracture strength of the amorphous rods with different diameters, exhibit obvious difference, which is related to the variation of the cooling rate of solidification for the rods with different size.

Effect of Rectangle Wave Pulse Current on Solidification Structure of ZA27 Alloy

The effect of rectangle wave pulse current on solidification structure of ZA27 alloy was studied. The results show that the wave pattern relies on the frequency range of harmonic wave and the energy of pulse current within the frequency range of pulse current. Imposed pulse current could induce the solidification system to oscillate. The frequency range and the relevant energy distribution of pulse current exert an influence on the amount of atoms involved for forming critical nucleus, the surface states of clusters in melt, the oscillating state of melt on the surface of clusters, the active energy of atom diffusion, the frequnce response of the resonance of bulk melt and the absorbability of the solidification system to the external work. Rectangle wave pulse current involves rich harmonic waves; the amplitudes of high order of harmonic waves are higher and reduce slowly, so it has a better effect on inoculation and modification.

Effect of high-energy ball milling on synthetic reaction in Al−TiO2−C system

High-energy ball milling has a great influence on the temperature characters of synthetic reaction in Al−TiO2−C system by changing the size, distribution state and wet ability of reactants. Reaction temperature characters (reaction ignition time, ignition temperature time, the maximum temperature and temperature rising rate) were changed by different milling time. The longer the milling time, the earlier the reaction, the quicker the temperature rise and the higher the maximum temperature. When the milling time exceeded10 hours, the reactivity of reactants was so high that the synthetic reaction could take place at 850°C directly without a long time pretreatment at 670°C. The microstructure of synthetic composites became uniform and the reinforced particles (TiC and α-Al2O3) became fine with milling time increasing.