Effect of Hydrogen Pressure on Moisture-Based Fabrication of Lotus-Type Porous Nickel

Lotus-type porous nickel, which has long straight pores aligned in one direction, was fabricated by utilizing moisture during unidirectional solidification in argon atmosphere. We studied the effect of the quantity of hydrogen in the atmosphere on the fabrication of lotus-type porous nickel. Adding hydrogen in the atmosphere, it was expected that the porosity of the lotus-type porous nickel with a smaller pore diameter became larger because not only the moisture but also hydrogen gas in the atmosphere were the supply source of hydrogen bubble. However, in fact, the pore diameter and the porosity of lotus-type porous nickel gradually decreased as the hydrogen partial pressure increased up to a point. When hydrogen was further added to the atmosphere, the pore diameter and porosity increased while the number of pores decreased dramatically. As a result of the fabrication under various pressures, the partial pressure of hydrogen at the border was 0.05MPa. No moisture can be dissociated when a large amount of hydrogen is dissolved in the molten nickel. [doi:10.2320/matertrans.47.2120

Effects of CaO Addition and Strain Rate on the Texture Evolution of AZ31 Alloy

The controlling alloying elements and deformation parameters are significant factors of the plastic deformation of Mg alloys due to their low formability and difficult-to-control texture. In this study, we investigated the effect of both CaO addition and the strain rate on the texture evolution and flow behavior of AZ31 alloys by carrying out hot torsion. The dislocation components of the deformed AZ31 alloys were evaluated using X-ray line profile analysis (XLPA). The XLPA results showed that the strain rate variation significantly affected the dislocation components and dislocation density of the alloys while CaO addition has only dislocation density effect. According to the results, weaken texture evolution by CaO addition is based on not variation of slip modes but grain boundary mobility. Also, it was determined that high strain rate deformation affect texture evolution by fortifying -type slip mode

Preventing Evaporation Products for High-Quality Metal Film in Directed Energy Deposition: A Review

Directed energy deposition (DED), a type of additive manufacturing (AM) is a process that enables high-speed deposition using laser technology. The application of DED extends not only to 3D printing, but also to the 2D surface modification by direct laser-deposition dissimilar materials with a sub-millimeter thickness. One of the reasons why DED has not been widely applied in the industry is the low velocity with a few m/min, but thin-DED has been developed to the extent that it can be over 100 m/min in roller deposition. The remaining task is to improve quality by reducing defects. Thus far, defect studies on AM, including DED, have focused mostly on preventing pores and crack defects that reduce fatigue strength. However, evaporation products, fumes, and spatters, were often neglected despite being one of the main causes of porosity and defects. In high-quality metal deposition, the problems caused by evaporation products are difficult to solve, but they have not yet caught the attention of metallurgists and physicists. This review examines the effect of the laser, material, and process parameters on the evaporation products to help obtain a high-quality metal film layer in thin-DED

Hot Deformation Behavior of AA6005 Modified with CaO-added Mg at High Strains

Hot torsion tests were carried out on an AA6005 modified with CaO-added Mg to study its hot deformation behavior. The flow curves indicated that the failure strain of the modified alloy was greater than that of the conventional alloy at low temperature and all strain rates employed in this study. The constitutive analysis was conducted on the effective stress–effective strain data, and the derived activation energy for hot deformation of the modified alloy was lower than that of the conventional alloy. The processing maps were established at various strains, and the power dissipation efficiency increased as the strain increased. The gap between contour lines decreased as the strain increased, indicating that the power dissipation efficiency became more sensitive to the strain. The optimum deformation conditions were determined by comparing the power dissipation efficiency in the processing maps. However, the power dissipation efficiency of the modified alloy was greater than that of the conventional alloy. The observed microstructure demonstrated that the lower activation energy, greater failure strain, and higher power dissipation efficiency were primarily attributed to the different states in the distribution of second phase particles caused by the use of CaO-added Mg

Microstructure and Density of Sintered ZnO Ceramics Prepared by Magnetic Pulsed Compaction

Three different sintered ZnO ceramics were prepared by magnetic pulsed compaction (MPC) and other conventional methods. The microstructures of the sintered ZnO ceramics prepared by MPC at sintering temperatures ranging from 900 to 1300°C showed a homogeneous grain growth compared to those of the samples prepared using other methods under the same sintering conditions. This implies that interpowders and/or intergrains can induce the minimization of wall friction effect because of the application of a high compaction pressure for a short process time in the MPC method. In addition, the microstructure of the sample obtained using the cold isostatic pressing method showed the presence of heterogeneous regions, indicating its low quality even though the densities of the three different samples were almost similar in the range of 97–99% at sintering temperatures of 900, 1100, and 1300°C. Therefore, different methods used for the compaction of ZnO ceramics may result in different microstructural and physical properties of the product