Papers by Author: Yu Feng Zheng

Abstract: The effect of Y addition on the average grain size and mechanical properties of Ni-Mn-Ga magnetic shape memory alloys is researched by means of optical microscope, compressive test and scanning electron microscope (SEM) in the paper. The results show that Y addition refines the grains of Ni-Mn-Ga alloy significantly and significantly enhances the compressive strength and maximum compressive strain. In addition, the fracture type changes from typical intergranular crack to transgranular crack gradually with Y addition.

Abstract: The spring steel strip 50CrVA which is cold rolled was applied to manufacture the diaphragm of the automotive horn by means of sheet metal forming. The combination of the experiments with back-propagation artificial neural network (BPANN) is used to solve the springback problem of the diaphragm. Experiments have shown that a 4-8-1 BPANN is able to predict the springback of the diaphragm successfully, and the network is able to model the relationship between the springback of the diaphragm and the process parameters rationally. BPANN simulation results and experimental ones have shown that the springback of the diaphragm is particularly influenced by such parameters as blank thickness, Young’s modulus, punch radius and yield ratio. Furthermore, the springback of the diaphragm decreases with the increase of blank thickness and Young’s modulus, but increases with the increase of punch radius and yield ratio.

Abstract: Backward ball spinning is applied to manufacturing thin-walled tubular part with longitudinal inner ribs. Rigid-plastic finite element method (FEM) is used to simulate and analyze backward ball spinning of thin-walled tubular part with longitudinal inner ribs. The fields of stress and strain in the deformation zone of the spun part are obtained by means of FEM. Finite element simulation results show that the deformation zone of the spun part is caused to be in a three-dimensional compressive stress state. The deformation zone in the inner rib is under the tensile strain in the radial and axial direction, and the compressive strain in the tangential direction. The wall deformation zone beside the inner rib is under the compressive strain in the radial direction, and the tensile strain in the axial and tangential direction. The three spinning force components all increase with the increase of the stroke of the ball. Furthermore, of all the three spinning force components, the radial force component is greater than the other two force components, and the tangential force component is minimum.

Abstract: In this paper, the TaCx coating with thickness around 1.2 μm was prepared by radio frequency magnetron sputtering technique on the 316L stainless steel substrate to improve its hemocompatibility. The structure and morphology of the coating were characterized by XRD and SEM. The XRD results indicated that TaCx, as a new species, appeared on the surface of the 316L stainless steel substrate. SEM images showed that the surface morphology of the TaCx coating was uniform and dense. The mechanical characteristics of the coating were measured by nanoindentation, giving a nanohardness of 13 GPa and a Young’s modulus of 210 GPa. The adhesion strength of the TaCx coating to 316L stainless steel depended on the sputtering bias voltages and increased for a higher bias voltage. The hemocompatibility of the TaCx coating, as evaluated by platelet adhesion tests, was compared to that of the bare 316L stainless steel. The results indicated that the hemocompatibility of 316L stainless steel with TaCx coating was significantly improved as compared to the original one.

Abstract: The advanced manufacturing technology of TiNiNb wide hysteresis shape memory alloy fastener ring was performed by using the tungsten inert gas (TIG) welding technique. It was found that transformation temperatures of the joint were about 20 °C higher than these of the base alloy, which should be ascribed to the heat treatment in the joint caused by welding. The strain recovery behavior of the ring after the diameter expanding process was studied. For the ring with the diameter expansion of 16% and without the heat treatment after welding, the strain recovery began at 55°C and ended at 75°C. It is concluded that, by appropriate expanding diameter process, TIG welding technique is suitable for the production of TiNiNb wide hysteresis shape memory fastener ring.

Abstract: Nickel-titanium alloy are extensively used in engineering and biomedical fields for their excellent properties of shape-memory, super-elasticity and biocompatibility. Their fatigue performance has been attracted increasingly attention, because they are often used under cyclic conditions. In this paper, the ultrasonic fatigue behavior of nickel-titanium endodontic files under unconstrained condition has been studied using the self-designed ultrasonic fatigue testing equipment. The vibration and harmonious response properties of nickel-titanium endodontic files are also analyzed using finite element method. Experimental results show that the average ultrasonic fatigue life of nickel-titanium endodontic files under unconstrained conditions is more than 108. Fracture of the files always occurred at the position about 2 -3 mm near the file tip. Results of finite element analysis show that the maximum stress of the nickel-titanium endodontic files located at the position about 2 -3 mm near the file tip, where is prone to generate fatigue cracks. The results of finite element analysis are consistent with the experimental results. The scanning electronic microscope (SEM) results show that the ultrasonic fatigue cracks always initiated at the surfaces of the files, where the secondary phases or impurities existed and induced fatigue cracks under repeated stress.

Abstract: Dental diamond bur is now a regular rotary tool, with its head made of diamond particles embedded into nickel coating, and its shank made of stainless steel. There are strong demands from the dentist on prolongation of usage life and avoiding of breakage. To solve this problem, on the one hand, since diamond is hard to be wetted under the condition of normal temperature and pressure due to the high interfacial energy between diamond and general metals and alloys. Diamond particles coated with titanium layer was used for the preparation of composite electroplating with the intention of improving the interfacial adhesion between diamond and metal matrix; on the other hand, superelastic biomedical NiTi alloy was used as the substrate to improve the flexibility and prevent the breakage. In this study, the optimal preparation parameters of Ni/surface-modified diamond electroplating were determined by orthogonal test, and the bonding conditions between the diamond particles and the NiTi alloy substrate were studied by scanning electron microscope. Further performance comparison of Ni/modified and Ni/un-modified diamond composite electroplating was conducted on a pin-on-disc wear machine under the dry sliding condition, and the material removal volume was used as the evaluating criterion of wear resistance. The results showed that the binding strength between diamond particles and NiTi alloy substrate could be enhanced, as well as the wear resistance, which may give direction on the future design of dental bur.

Abstract: Zr-ZrC-ZrC/DLC gradient nano-composite films have been prepared on the NiTi substrates by the technique of plasma immersion ion implantation and deposition (PIIID) combining with plasma-enhanced chemical vapor deposition (PECVD). The influence of C2H2 flow rate ranging from 30 sccm to 50 sccm on the chemical structure, microstructure, mechanical properties and corrosion resistance of resulting thin films are investigated by Raman spectrum, XPS, XRD, friction coefficient test, nano-indentation, electrochemical corrosion test and atomic absorption spectrometry. XPS and XRD results indicate that on the outmost layer, the Zr ions are mixed with the DLC film and form ZrC phase, the binding energy of C 1s and the composition concentration of ZrC depend heavily on the C2H2 flow rate. With the increase of C2H2 flow rate, the content of ZrC and the ratio of carbon sp3/sp2 decreases. The nano-indentation and friction experiments indicate that the gradient composite film at 30 sccm has a higher hardness and lower friction coefficient compared with that of the bare TiNi alloy. The microscratch curve tests indicate that Zr-ZrC-ZrC/DLC gradient composite films have an excellent bonding property with the substrate. Based on the electrochemical measurement and ion releasing tests, we have found that the Zr-ZrC-ZrC/DLC gradient composite films exhibit better corrosion resistance property and higher depression ability for the Ni ion releasing from the NiTi substrate in the Hank’s solution at 37°C.

Abstract: The phase constitution, mechanical properties, and corrosion behavior of TiMoSn alloys were investigated by means of XRD, tensile test, electrochemical measurement and XPS techniques. The XRD analysis results showed that at room temperature TiMoSn alloys are mainly composed of β phase, with minor content of α" phase, in as-cast and solid solution treated conditions. The tensile test results indicate that the elastic moduli of the Ti-Mo-Sn alloys are in the range of 52~74GPa. The electrochemical measurement results indicate that TiMoSn alloys have excellent corrosion resistance in simulated body fluid. The XPS analysis results reveal that the passive films of TiMoSn alloys after polarization consist of TiO2, SnO2 and Mo2O5.

Abstract: Near-equiatomic Ni-Ti alloys are known to exhibit shape memory effect associated with a B2↔B19’ martensitic transformation. These alloys are often used in various cyclic modes in application, typically as actuators and sensors. The B2↔B19’ martensitic transformation in Ni-Ti is accompanied with a large lattice distortion. Cycling through this transformation, induced thermally, mechanically or by the combination of the two, is found to cause structural damage to the alloys, hence changes their functional properties. This study investigates the effect of transformation cycling and heat treatment on the property stability of near-equiatomic Ti-Ni. It was found that in the case of thermally induced transformation cycling, incomplete transformation cycles caused less structural damage to the matrix than full transformation cycles whereas in the case of mechanically induced transformation cycling via pseudoelasticity in tension, partial or full transformation cycling caused similar property changes. The indifference of the case of pseudoelastic cycling is attributed to the localisation of the deformation, commonly known as the Lüders-type deformation.