Papers by Author: Kai Feng Zhang

Abstract: The deep drawing of SiC/2024Al composites using pulse current heating were designed and established in this works. The whole process system mainly include pulse current heating system, electrode lifting system, temperature control system and deep drawing forming system. In addition, the feasibility of thermal deep drawing using pulse current heating was experimentally investigated and the optimal process parameters were explored to ensure defect-free products. The temperature of specimen is up to around 673K at a rate of 13.5K/s under the current density of 21.7A/mm². The stainless steel inserts make temperature difference reducing by 73.3%. Moreover, the workpiece was successfully deep drawn and exhibited good surface quality. The dimensional accuracy achieved within ±0.2mm.

Abstract: As a new effort, combined reactive sintering with hot pressing technique, the Ti-22Al-25Nb alloy was successful prepared with element mixed powders. Meanwhile, the reactive sintering was divided into two temperature ranges, which were at 873 K and 1373 K, respectively. The starting sintering kept 1h at 873K, and then the temperature was increased to 1373K, keeping 2h. The orthorhombic (Ti2AlNb) phase was observed in this sintered alloy. Moreover, the homogenization treat was conducted at 1473 K for 2h after the final sintering was accomplished, and the fraction of the orthorhombic phase increased significantly. The microstructures and the phases were analyzed. And the generation mechanism of the orthorhombic phase was also analyzed.

Abstract: Pulse current effects during hot tensile process and superplastic forming process of AZ31 magnesium alloy and TA15 titanium alloy were investigated in this paper. The experimental results indicate that the current can produce polarity effect to coarse grain AZ31 magnesium alloy, but to fine grained TA15 titanium alloy, the polarity effect is not obvious. The impact of electron wind force can change the strength of material during tensile process and affect final shape of part, making the dome of AZ31 hemisphere part deviated from the axis to the side of positive pole during superplastic forming process. In addition, the impact of current depends on current density and dislocation density.

Abstract: Nb-16Si-2Fe alloy were processed by mechanical alloying (MA) and hot pressing sintering (HPS). Microstructure analysis revealed the presence of four phases: Nb solid solution (Nbss), three kinds of intermetallics Nb3Si, Nb5Si3 and Nb4Fe3Si5. The maximum elongation over 500% was obtained at 1450°C and strain rate of 2.31×10-4s-1. TiAl powder pre-alloyed was carried out on pulse current sintering equipment (PCS) with high heating rate. The effect of heating rate on microstructures and high temperature ductility was investigated. The results show that relatively high heating rate is beneficial for obtaining fine grained microstructures. And the resultant intermetallic alloy with equiaxed near gamma structures exhibits superplasticity at relatively low temperature.

Abstract: Superplasticity of nanocrystalline materials is a hot spot in the field of scientific research. In this paper, Ni-Co alloy was produced through pulse electrodeposition. Tensile tests were carried out to study the room temperature strength, high temperature plasticity. The superplastic formability under complex stress was evaluated through the superplastic bulging tests. The tests were studied through the methods of resistance heating and furnace temperature heating. The maximum ratios of height and diameter with different heating method were compared. Fracture behavior and microstructure were observed by the method of SEM.

Abstract: Using ring compression tests, the interfacial friction and flow stress of 3Y-TZP/Al₂O₃ composite at elevated temperatures were investigated. Theoretical calibration curves of the friction factor and the relative average pressure curves for the ring compression tests of 6:3:2 standard rings were drawn based on a velocity field capable of describing the bulge phenomena. The lubricant was the boron nitride (hexagonal). The tests were adopted at temperature range of 1400°C-1600°C. Results indicate that the interfacial friction factor has the value in the range of 0.34-0.49, so that boron nitride lubricant can be used effectively in present temperatures. As two extremely important parameters, the temperature and strain rate have no significant effect on the fraction factor. It is proved reliable that the ring-compression test at 1400°C and even higher is used to evaluate the performance of boron nitride lubricant.

Abstract: Float polishing is one of the advanced ultra-smooth surface polishing techniques. Mechanical structure and polishing principle of float polishing are introduced. Polishing experiment about polishing ultra-smooth surface of GCr15 rectangular workpiece is performed by the CJY500 ultra-precision polishing machine, experimental results show that float polishing should be achieved metal nanometer level surface without degenerating layer. The application scope of float polishing is extended, the application has significant reference value for polishing ultra-smooth surface of metal workpiece.

Abstract: Tape casting and hot-press sintering were used to fabricate an Al2O3/3Y-TZP laminated composite. In order to investigate the deformation properties, the as-prepared material was deep drawn at high temperatures. It was found that the microstructure of the material sintered at 1550°C was fine and no significant pores were detected from SEM observations at the interfaces between the two types of layers. The superplastic forming experiment shown that, when the strain rate was constant, temperature had a great influence on the superplasticity of the Al2O3/3Y-TZP laminated composite. A hat-like part with the largest deformation height was obtained at 1500°C.

Abstract: The Si3N4- Si2N2O composites were fabricated with amorphous nano-sized silicon nitride powders by the liquid phase sintering(LPS) method. The sintering temperatures ranged from 1500°C to 1700°C. Microstructure and component of the composites were performed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results show that sintered body consists of Si2N2O and β-Si3N4, with an average grain size about 1μm. The maximum value of flexural strength of the material is 680MPa when sintered at 1700°C. Transcrystalline cracking is the main fracture mechanism of the composites.

Abstract: The deformation behavior of gas pressure forming of amorphous Fe78Si9B13 alloy was investigated under equibiaxial tension. The gas pressure forming was carried out in the temperature range of 430°C~530°C below the crystallization temperature Tx and die apertures of 5mm~10mm. The dome height and amorphous ribbon thickness of deformed specimens at the pole was measured. It was found that amorphous Fe78Si9B13 alloy had exhibited good plasticity in the experimental temperature range. The near-semisphere specimens of the radius 5mm and the height 4.5mm were obtained from the gas-pressure forming at 450°C and 530°C for 30min, which is similar to the superplastic forming.