Abstract: This paper utilized self-made high-frequency micro-forging machine to treat NiCrBSi alloy cladded by laser, Optical Microscopy(OM) to study geometric characteristic of plastic deformation, OM and SEM to observe influence on surface microstructure and cracking behavior of the laser cladding layer under micro-forging. The results have shown that: Regularly dendrite microstructure, which is peculiar of laser cladding layer, was broken into pieces. Cracking behavior of laser cladding layer improved greatly.
Abstract: Based on welding heat transfer theory, heat elastoplasticity theory and phase transformation theory, welding residual stress in multi-layer welded joint of 9% Ni steel for liquefied natural gas (LNG) storage tanks was simulated using SYSWELD finite element analysis software. Taking into account nonlinear relationships between temperature and mechanical properties, together with influence of transformation latent heat on temperature field, double ellipsoid heat source model was applied in the simulation of the three fields (temperature field, microstructure field and stress-strain field). Distribution pattern of welding residual stress in 9%Ni steel welded joint was obtained through numerical simulation. Results showed that heat affected zone (HAZ) showing high-level residual stress was the main stress concentrated part of the welded joint. Longitudinal residual stress appeared to be tensile in the weld and HAZ, and compressive in regions remote from the weld. A match of low heat input and high interpass temperature should be employed to lower residual stress level in HAZ. Simulation results were well consistent with theoretical analysis.
Abstract: Fe-Co single-phase alloy melts with different Co contents were undercooled using fluxing method. The maximum undercooling DT = 457K (relative undercooling DT/Tm=0.259) was achieved in this work. At low undercooling (DT), single-phased microstructure was observed, but metastable bcc phase emerged in the as-solidified microstructure once DT exceeded a critical value, DTcrit. In the presence of classical nucleation theory, phase selection in the undercooled Fe-Co melt was investigated, and the theoretical calculation was coincided with the experimental result.
Abstract: The contact shape, size and stress of thrust ball bearings are simulated with taking 1/13 part of bearing as finite element model, neglecting the influence of cage and lubrication, imitating the boundary curve with high order element, meshing the top and bottom raceways with sweep and the ball with free meshed by finite element software ANSYS in the contact area for the effective and exact designing of thrust ball bearing. The simulation results are corresponded to the results of Hertz’s contact theory. There are less margins for error between main dimensions except the shortest axis of an ellipse. More important will be obtained from the simulation on finite element software which cannot be derived from the traditional theory. It could improve the designing efficiency of thrust ball bearing.
Abstract: The mechanism of prolonging service life of tap in low frequency vibration tapping was studied from two aspects of the reduction of wear and the insensitivity of the passivation of tap. Repeated cutting and separate type boundary lubrication improved the contact and lubrication status on rear face of tap. On the one hand, it greatly reduced the wear of rear face the tap, on the other hand, it markedly decreased the passivation sensitivity of tap to blunt radius and flank wear. With the interaction of two factors mentioned above, the service of life was prolonged greatly by low frequency vibration tapping.
Abstract: TiAlN coatings have been deposited by reactive magnetron sputtering from TiAl alloy target using a direct current (DC) power source. The crystal structure, chemical composition, surface morphology and hardness of TiAlN coatings which were prepared at various N2 flow rates have been systemically investigated. The results show a strong effect of N2 flow rates on the orientation, grain size and densification in TiAlN coatings. The TiAlN coating shows the highest hardness at a certain N2 flow rate when it has the most compact structure.
Abstract: This article presents an approach which first combines grey relational grade and weighted quality loss function to convert the values of multiple responses obtained from each of the Taguchi orthogonal designed experiments into a single performance evaluation value. Then the analysis of variance (ANOVA) and the SN ratio based Taguchi analysis are conducted to find out respectively the relative importance of the process parameters and a set of near optimal parameter settings. A validation experiment is then conducted to confirm the finding. A case of multi-response turning process optimization is used to illustrate the proposed approach. Two sets of weights for the total quality loss were applied and the results were compared. The effectiveness of this approach was demonstrated by the improvement of turning performance in the both weight settings.
Abstract: In order to fabricate high-quality microchannels in a fused silica, the fundamental frequency laser with the wavelength of 1064nm of a Q-switched Nd:YAG laser and the mixing laser composed of 70 percent second harmonic laser and 30 percent fundamental frequency laser are used to irradiate a fused silica substrate respectively to induce the plasma, by which microchannels in a fused silica substrate were fabricated.The result show that the interior wall of the microchannels processed by mixing laser are smoother and the drilling rate is faster than ones processed by fundamental frequency. Furthermore, the depth of the microchannels processed by the mixing laser is up to 8mm, longer than the depth of 4mm reported at present. The reasons of causing to the differences between two kinds of processing are analyzed.
Abstract: The influence of working pressure on microstructure and mechanical properties of magnetron sputtered ZrN coatings were systemically investigated. The results reveal that a decreased working pressure results in preferred orientation evolution from (111) to (200) and cross-sectional morphologies transition from columnar structure to equiaxed grains. These microstructural changes are considered responsible for an increase in hardness and modulus with decreasing working pressure. Chip spallation and plastic deformation failure modes are observed during scratch testing, and the increased critical loads are attributed to higher hardness and elastic modulus, as well as moderate compressive stress at lower working pressure.
Abstract: The effect of deposition temperature on microstructure and mechanical properties of ZrN coatings fabricated by DC magnetron sputtering was investigated. X-ray diffraction, scanning electron microscope, nanoindentation and scratch test were applied to characterize the ZrN coatings. The results show that with the increasing of substrate temperature the preferred orientation of the coating changed from (111) to (200), the ZrN crystalline phase almost disappeared at 600 resulting from nitrogen loss and the formation of ZrO2 phase. From 50 to 450 , the coatings showed columnar structure, and at 600 the columnar disappeared, presenting equiaxed structure instead. The hardness of coatings showed few significant variations under 450 , and at 600 the coating hardness dropped for the low crystallinity and ZrO2 phase softening. The substrate-coating adhesion decreased with the increasing of temperature before 450 , and then followed by an elevation at 600 .