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Lei Y.-W.,Tianjin Polytechnic University | Lei Y.-W.,Tianjin Key Laboratory of Advanced Mechatronics Equipment Technology | Wu E.-X.,Central South University
Cailiao Kexue yu Gongyi/Material Science and Technology

In order to inhibit the grain growth of WC during the sintering process and obtain ultrafine WC-12Co alloys with high strength and hardness, the influence of VC/Cr3C2 inhibitors and sintering temperature on the microstructure and mechanical properties of ultrafine WC-12Co was investigated using JSM-5600LV scanning electron microscope, LJ-3000 stretcher and Rockwell HR-150 sclerometer. The mechanism of grain growth inhibition was also analyzed. The results show that alloys with homogeneous microstructure and excellent properties are obtained when the optimal proportion of additions is added. Sintered at 1450 °C, the transverse rupture strength and hardness reach 3710 MPa and 91.5 HRA for the ultrafine WC-12Co alloy with 0.2%VC/0.5% Cr3C2 (wt%). The mechanism of VC/Cr3C2 inhibitors is that the reaction between WC and VC leads to the presence of small (V, W)C precipitates on WC/Co interfaces, which decreases the interfacial energy; on the other hand, Cr3C2 mainly dissolved in the binder phase reduces the solubility of WC in the binder phase. The driving force for WC grain growth from reprecipitation process is decreased and WC grain growth is retarded. Source

Liu D.-H.,Tianjin Polytechnic University | Xing J.-Z.,Tianjin Polytechnic University | Xing J.-Z.,Tianjin Key Laboratory of Advanced Mechatronics Equipment Technology | Chen X.-X.,Tianjin Polytechnic University
Jisuanji Jicheng Zhizao Xitong/Computer Integrated Manufacturing Systems, CIMS

Aiming at the different neutral curves in cross sections perpendicular to the axis made by the taper deformation under flexspline of harmonic drive produced by cam wave generator, a spatial tooth profile of circular spline was designed to improve meshing performance. The spatial tooth profile was constructed with a series plane tooth profiles in the cross sections by spatial deformation of flexspline. A design method for spatial tooth profile of circular spline which spatial engaged with deformed flexspline and a calculation method of backlash between engaged teeth surface were established. Based on the conjugated tooth profiles in planes, the spatial tooth profile was generated by using lofting algorithm, and the interference and backlash results were checked. The research found that the spatial tooth profile could increase the meshing domains and contact area. There was a little difference between the loft method of two sections with straight guide line and a series section loft spatial tooth profiles, which could meet the design requirement of normal precision of harmonic transmission device. ©, 2015, CIMS. All right reserved. Source

Xing J.,Tianjin Polytechnic University | Geng P.,Tianjin Polytechnic University | Yang T.,Tianjin Polytechnic University | Yang T.,Tianjin Key Laboratory of Advanced Mechatronics Equipment Technology
Composite Structures

Multiple winding angle filament-wound (FW) structures may lead to more uniform strength for all filament layers, while there is no analysis method for deformation and stresses calculation of FW cylinder with variation wound angle. Deformation and stresses of a thick cylinder with multi-angle winding hybrid filament under axial loading and internal and external pressure were investigated. The deformation and stresses of each orthotropic unit of fiber layers, as well as longitudinal stress along the fiber direction, transverse stresses perpendicular to the fiber direction and shear stress in fiber layer were obtained analytically. The degenerated case of the model includes single winding angle FW cylinder, FW vessel with a liner, and sandwich pipe with one or multiple core layers. Numeric results of finite element models are present, which are very close to the theoretical results. The research shows that material utilization and working pressure can be increased by multi-angle FW procedure. © 2015 Elsevier Ltd. Source

Sun R.-L.,Tianjin Polytechnic University | Sun R.-L.,Tianjin Key Laboratory of Advanced Mechatronics Equipment Technology | Niu W.,Tianjin Polytechnic University | Lei Y.-W.,Tianjin Polytechnic University | Tang Y.,Tianjin Polytechnic University
Cailiao Rechuli Xuebao/Transactions of Materials and Heat Treatment

Laser cladding was carried out on the surface of TC4 titanium alloy by Nd: YAG laser using Ni60+Ni/MoS2 powder mixture as cladding material. The microstructure of the coating was examined by XRD, EDS, SEM and OM. Microhardness and tribological properties of the coating were measured. The results show that MoS2 decomposes during laser cladding process. The selective chemical reaction between S and Cr occurs and non-stoichiometric CrxSy forms. TiC phase forms due to the fact that C reacts with Ti. C and Ti come from the Ni60 alloy and substrate, respectively. The nearly spherical CrxSy particle and dendritic TiC uniformly distribute in the cladding coating. Due to the reinforcement of TiC and anti-friction of CrxSy, laser cladding coating not only has high wear resistance, but also has a low and smooth friction coefficient. Source

Lei Y.,Tianjin Polytechnic University | Lei Y.,Tianjin Key Laboratory of Advanced Mechatronics Equipment Technology | Sun R.,Tianjin Polytechnic University | Tang Y.,Tianjin Polytechnic University | Niu W.,Tianjin Polytechnic University
Optics and Laser Technology

A three dimensional model was proposed to simulate high power laser clad TiC/NiCrBSiC composite coatings on Ti6Al4V alloys. The temperature distribution, temperature curves on different nodes, three dimensional shape and size of TiC melting region, molten pool and heat affected zone (HAZ) of the substrate were obtained. To have a clear physical insight into the phase transformation and microstructure evolution in the coatings during laser cladding process, a theoretical kinetic analysis was performed to elucidate the nucleation, growth velocity, and size of TiC particles on the basis of simulated temperature curves of the molten pool. A good quality TiC/NiCrBSiC composite coating with low dilution rate and excellent metallurgical bond was fabricated under optimal processing parameters using powder mixture of TiC and NiCrBSiC as clad material and cuboid of Ti6Al4V alloys as substrate. To validate the reliability of the proposed model, the theoretical results were compared with the microstructure of the coatings. It shows that these theoretical results are in excellent agreement with the experiment cases. © 2011 Elsevier Ltd. All rights reserved. Source

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