Showing papers by "H.F. Zhang published in 2011"

Reactive composite brazing of Cf/SiC composites to Ti alloy with (Ag–6Al)+Ti+C composite filler materials

Abstract: Cf/SiC composite and Ti alloy (TC4) were successfully joined by the mixed powders of Ag, Al, Ti and short carbon fibres under vacuum condition. The Microstructure of the joints was investigated by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry. The results show that the good chemical bonding and reactive composite brazing joints are obtained by reactive composite brazing with both (Ag–6Al)+Ti and (Ag–6Al)+Ti+C filler materials. The addition of short carbon fibres contributes a lot to the shear strength by alleviating the thermal stress of the joints and to the in situ synthesised TiC which surround the uniformly distributed short carbon fibres. Ti element can improve filler metal’s wettability to Cf/SiC composite and restrain the oxidation of Al element. The max shear strength obtained is 90·8 MPa and the optimal parameter is brazing at 910°C within 10 min.

Joining of Cf/SiC composite to TC4 using Ag–Cu–Ti–SiC composite filler material

Abstract: Cf/SiC was successfully joined to TC4 with Ag–Cu–Ti–SiC mixed powders. Microstructures of the brazed joint were investigated by SEM, EDS and XRD. The mechanical properties of the brazed joints were measured by mechanical testing machine. The results showed that the performed joints have dense bonding layers reinforced by residual SiC and reaction products from reaction of SiC and Ti in the bonding layers. These composite brazing layers relaxed the thermal stress of the joint effectively. These characteristics were beneficial to the joint, of which the shear strengths were remarkably higher than the optimal shear strengths of the joint brazed with Ag–Cu–Ti.

An in situ high-energy X-ray diffraction study of micromechanical behavior of Zr-based metallic glass reinforced porous W matrix composite

Abstract: The micromechanical behavior of the Zr-based metallic glass reinforced porous W matrix composite was investigated by means of in situ high-energy synchrotron X-ray diffraction (HEXRD) during uniaxial compression. The lattice strain of the W phase during compressive deformation was quantitatively measured by fitting diffraction patterns. A self-consistent model was accordingly used to simulate the mechanical properties of the W phase. The stress and strain distributions of the Zr-based metallic glass phase were calculated using the rule of mixture. The results indicated that the W phase yielded firstly in the early stage of deformation, while the metallic glass phase remained elastic. The transfer of the load accelerated with the stress increased. The formation and propagation of shear bands contributed to the deformation of the metallic glass phase.

Effect of Strain Rate on Plastic Flow in Zr-Based Metallic- Glass-Reinforced Porous Tungsten Matrix Composites

Abstract: The rate-dependent deformation of Zr38Ti17Cu10.5Co12Be22.5 bulk metallic-glass-reinforced porous tungsten matrix composites was investigated over a wide range of strain rates. The composites were examined in two forms: the as-cast composite and the as-extruded composite by extrusion. In addition to showing greater strain hardening, the as-cast composite also shows much more obvious strain rate dependence of flow stress than the as-extruded composite. Microhardness tests were performed on the tungsten and the metallic glass phase in both composites, respectively. The results from the microhardness measurements indicate that the strain rate sensitivity of the as-extruded composite is primarily a result of strain rate sensitivity of the tungsten phase.

Magnetocaloric Effect in ErSi Compound

Abstract: The magnetic properties and magnetocaloric effects (MCEs) have been investigated in ErSi compound, which crystallizes in the orthorhombic CrB-type structure. This compound is antiferromagnetic (AFM) with a Neel temperature TN of 12.5 K. The measurements of the temperature and field dependences of the magnetization clearly show that the ErSi compound undergoes a field-induced metamagnetic transition from AFM to ferromagnetic (FM) state below TN. The isothermal magnetic entropy change (ΔSM) and refrigerant capacity (RC) of ErSi have been measured for various applied magnetic fields and their values are found to be -14.8J ·kg -1·K -1 and 210 J ·kg -1 for a field change of 0-5 T, respectively. The large MCE is attributed to the field-induced AFM to FM metamagnetism occurring in this compound.

Current enhanced wettability of eutectic SnBi melt on Cu substrate

Abstract: The effect of a direct electric current on the wetting behaviour of eutectic SnBi melt on Cu substrate at 220 degrees C was investigated in the present study. It is found that the application of current enhanced the growth rate and lateral growth of interfacial reaction layer between eutectic SnBi melt and Cu substrate. Furthermore, with the increase in the current, the spread of eutectic SnBi melt on Cu is accelerated significantly and the steady state contact angle is decreased markedly. The reason for these is also discussed in the present paper.

Combustion synthesis of SiC nanosized powders at low nitrogen pressure

Abstract: Combustion synthesis of β-silicon carbide (SiC) powders was accomplished at a nitrogen pressure lower than 2 MPa. The combination of mechanical activation and chemical stimulation was effective in enhancing the reactivity of Si powder reactants, which was responsible for the reduction in the minimum nitrogen pressure normally required for the combustion synthesis of SiC. Nanosized β-SiC powders with spherical particles were synthesised at nitrogen pressure as low as 1 MPa. The combustion synthesised SiC powders have a narrow particle size distribution in the range of 50–100 nm and could be hot pressed to 99·1% theoretical density with 10 wt-%Y2O3 and AlN as additives.

Transformation of precipitated phases in Zr50·5Cu34·5−xNi4Al11Agx alloy master ingots with adding Ag

Abstract: The transformation of precipitated phases of Zr50·5Cu34·5−xNi4Al11Agx alloy master ingots with Ag substitution of Cu was studied in detail by phase analysis. The precipitated (Zr–Cu) rich phases deteriorate the glass forming ability (GFA) of Zr50·5Cu34·5Ni4Al11. Two new (Zr–Cu) rich phases, A1 with bcc structure and a = 0·339 nm and A2 with fcc superlattice structure and a = 1·21 nm, were identified by a transmission electron microscope. When x = 2, A1 phase disappears, and A2 phase remains and is suppressed gradually with further Ag addition. When x = 13, one precipitated phase with Ag more than 13 at-% begins to deteriorate GFA. In the view of chemistry, the precipitation of (Zr–Cu) rich phases means that the interaction between Cu and Zr atoms is rather drastic. The addition of Ag weakens the interaction between Cu and Zr. The similar competition mechanism proposed by the authors plays an important role in suppressing precipitated phases and improving GFAs.

Martensitic transformation behaviour of non-equilibrium heat treated Ni50·9Ti49·1 alloys

Abstract: Ni50·9Ti49·1 specimens were heat treated using a thermal simulator. The martensitic transformation behaviours of selected areas of the thermal simulating treated specimens were studied with resistivity temperature measurements. In the thermal simulating process specimens were heated by a large electric current to a given peak temperature (400, 500, 600, 800, 900 or 1100°C respectively) and immediately water cooled to room temperature. As the two ends of a NiTi alloy specimen were fixed in copper jigs, unequal heat treatment effect areas were formed in the specimen segments near its two ends. In the unequal area of an 800°C thermal simulating treated sample, a wide transformation temperature range phenomena appeared. The experimental results indicate that non-equilibrium heat treatment proves to be an effective method to fabricate transformation temperature gradient shape memory materials.