Key Engineering Materials Vol. 871

Abstract: The effect of riser necking ratio and taper on solidification process of 96T steel ingot have been studied numerically using the software package ProCAST. The results show that the solidification time decrease with the increase of riser necking ratio, and the position of shrinkage porosity moves up and the secondary porosity presents a tendency of increase, and the inclusions on the shoulder of body ingot decreases. The riser taper has little effect on the solidification process of heavy ingots.

Abstract: In the process of metal parts fabricated by Laser Melting Deposition (LMD), a high temperature gradient will generate due to the instantaneous high laser energy input, which will cause residual stress in the formed part of metal parts, the residual stress will result in defects like warping deformation or even cracking. In this paper, a finite element method based on inherent strain method is proposed to predict the deformation of metal parts fabricated by LMD. Firstly, combing with the birth and death element technology, a local model is established to simulate the layer-by-layer deposition in the LMD forming process, and the values of inherent strain is obtained. Secondly, the obtained inherent strain values is applied to large-sized part layer by layer, and the final deformation of large-sized part is calculated. Based on the proposed method, the efficiency of deformation prediction of large-sized metal parts fabricated by LMD could be effectively improved.

Abstract: In this study, the effect of forming temperature, blank holder force, die entrance radius, die corner radius and blank local thickening on the springback of square cups were studied, by conducting finite element simulations of the hot stamping of 2024 aluminum alloy sheet blanks. Within the range of process parameters investigated in this study, increasing the forming temperature, blank holder force and die corner radius or decreasing the die entrance radius all lead to lower values of springback in hot stamped square cups after unloading. Compared to uniform blank, local-thickened sheet blank can significantly reduce the springback in hot stamped square cup. When the side length of the square-ring-shaped convex rib of the thickened blank is equal to the punch width and the convex rib faces downward, significant reductions in the springback, of at least 55.9%, can be achieved.

Abstract: Electrohydraulic forming (EHF) is a kind of high speed forming process, which deforms the metal by shock wave through instantaneous discharge of high voltage in water. Compared with the traditional forming methods, this high speed forming process can greatly improve the formability of the materials. There are many processing factors that affect the forming efficiency and performance of the electrohydraulic forming process, one of which is the discharge voltage between the electrodes. In this paper, three electrohydraulic forming experiments with various die shapes were carried out under various discharge voltage conditions. And the bulge height and axial length of the aluminum alloy A6061 tubes under different conditions were compared. Besides, finite element numerical simulation was also performed to quantitatively investigate the deformation history of the tube.

Abstract: The annealing process of an improved Q420 cold drawn tube was studied by using different annealing temperatures (430°C, 450°C, 470°C, 490°C and 510°C) with a same annealing holding time (3h). The effect of different annealing temperatures on the mechanical properties, microstructure and fracture features of the cold drawn tube was studied by means of tensile test, microstructure observation and scanning electron microscopy analysis. The results show that, annealing temperature has great influence on the strength and plasticity of the cold drawn tube. When the annealing temperature increased to 450°C, banded microstructure was mitigated and the pearlite is relatively dispersed. The tensile fracture morphology under the annealing temperature of 450°C has more dimples and deeper bremsstrahlung than other annealing temperatures. The best annealing process of the cold drawn tube was 450°C×3h. Under this annealing process, the cold drawn tube with good strength and toughness can be obtained.

Abstract: IASCC of stainless steel has been the most important issue for internals BFBs. The inspection data analysis indicates that there is a closed relation between irradiation fluence and cracked BFBs distribution. Then the nanoindentation and 3DAP tests were carried out to study the hardening and radiation induced segregation (RIS) behaviors of the reactor internals stainless steel specimens irradiated with 6 MeV Xe ions at room temperature. It is indicated that higher irradiation damage will cause more significant hardening and RIS and consequently increase the IASCC susceptibility.

Abstract: In this paper, aiming at the mechanics of tube hydroforming, the plasticity method was adopted in analyzing the stress yield behavior of the process. The stress character and yield behavior during the different stage of tube hydroforming was given and discussed. And then, basing on the discussing result, the yield behavior calculating formula was given and derived. At the same time, combining with the formula, figure of yield behavior was given. Base on the yield behavior character the process analysis was discussed in the end.

Abstract: Compared with the atmosphere plasma spraying (APS), low pressure plasma spraying (LPPS) has been widely used due to deposit a specific and unique coating. A new low pressure thermal spraying plasma torch was designed according to the plasma spray characteristic in the low pressure environment. The plasma jet characteristic and the coatings microstructure were analyzed. In this study, Kundsen number has a great effect on the heat transfer of feedstock powder. With the increase of current, the plasma torch efficiency will decrease. A equiaxed microstructure of 316L coatings were deposited.

Abstract: In this study, one novel WC/Ni flexible cloth coatings were prepared to enhance the abrasion and erosion resistances and meanwhile to accommodate the complicated component surfaces. Neither precipitation of WC particle nor pores or cracks were detected in the coating. The scarification extent of WC particle decreased with the increase in the WC content. With the abrasion mechanism of three body abrasive wear, the WC/Ni coating with 59.8 wt.% WC (WC/Ni-59.8 wt.%) showed the best abrasion resistance with the wear rate of 0.3% of 304 stainless steel. At 30° of impact angle, the WC/Ni-59.8 wt. % exhibited a superior erosion resistance to that of WC coating developed by high velocity oxygen fuel (HVOF). The application potential of WC/Ni flexible cloth coating for the commercial components was testified by developing the coating on a ball valve disc.

Abstract: Metal materials are very important engineering materials, which are irreplaceable in the history of mankind. Infiltrating theoretical basis described in the paper comprehensively introduces the super hydrophobic of metal surface which has important theoretical significance and broad application prospects in many fields of basic research and industrial application including self-cleaning, fluid drag reduction, water miniature conveyer, condensation, ice prevention, resistant corrosion and protection, liquid transmission, oil-water separation, biological fouling and Marine fouling and control, etc. It also puts forward the corrosion mechanism of super hydrophobic surface to extend the bionic super hydrophobic metal materials in the field of industrial and civilian sectors.