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Experimental and numerical studies of hot tearing formation in steel are reported. On the one hand, an ingot punching test is presented. It consists in the application of a deformation at the surface of a solidifying 450 kg steel ingot. The experimental parameters are the displacement of the pressing tool, together with its velocity, leading to variations of a global strain rate. On the other hand, three-dimensional finite element thermomechanical modeling of the test is used. The time evolution of the strain tensor serves to compute an index to evaluate the susceptibility to create hot tears. It is based on the integration of a hot tearing criterion (HTC) that compares the local accumulation of strain with the expression of a critical value proposed in the literature. The main variable of the criterion is the brittleness temperature range (BTR) that refers to the solidification interval during which strain accumulates and creates hot cracks or tears. Detailed comparison of the simulation results with the measurements reveals the importance of the BTR for the prediction as well as excellent capabilities of the HTC to predict the formation of hot tears. [ABSTRACT FROM AUTHOR]

he purpose of this study is to clarify the relationship between ionic conductivity and phase transformation of zirconia system codoped with scandium oxide Sc2O3 and ytterbium oxide Yb2O3. Aiming to achieve high ionic conductivity as well as high mechanical strength, the authors have also investigated the relationship between phase transformation and mechanical strength. The results have been discussed with respect to both the conductivity and the mechanical strength. The Sc- and Yb-codoped zirconia (ZrO2) used as samples in this study were prepared by a standard solid-state reaction. X-ray powder diffraction (XRD) method was used to determine the crystal structures of the sintered samples. To detect any phase change between room temperature and 1273 K, thermal mechanical analysis (TMA) was conducted. To determine oxygen-ion conductivity in a temperature range from 873 to 1273 K in air impedance measurements were performed with alternating current (ac). Single-cell performance was confirmed under the condition of 26.2 Pa partial hydrogen pressure. Finally, to measure bending strength, three-point bending tests were performed with a universal testing machine. The results of XRD and TMA showed that codoping of Sc2O3 and Yb2O3 into ZrO2 successfully stabilized the cubic phase when the average radius ratio of these two dopants in total was close to the ideal one for the eight-coordinate. The ac impedance measurement demonstrated that the cubic-phase stabilization achieved a high conductivity. Adequate amounts of dopants produced oxygen vacancies for high conductivity without complex defects: ZrO2 system doped with 1 mol % of Yb2O3 and 8 mol % of Sc2O3 showed the highest conductivity at 1273 K and 0.30 S/cm. The bending strength decreased with increasing the content of doped Sc2O3 from 7 mol % to 11 mol %, depending on the amount of the tetragonal phase, which contributes to strengthen materials. In the performance test, the ZrO2 system stabilized with doping 1 mol % Yb2O3 and 8 mol % Sc203 with thickness of 2.16mm showed maximum power density at 1273 K, that is, 210 mW/cm2. From all the above tests, we recommend that, based on electrical and mechanical considerations, 1Yb8ScSZ is the present best option for an electrolyte material for a solid oxide fuel cell. [ABSTRACT FROM AUTHOR]

Fundamental design considerations of the write head for a hard disk drive with a higher data transfer rate are described. With a shorter yoke, the eddy current damping can be suppressed effectively. The head inductance is also reduced by yoke length reduction so that the rise time of write current can be reduced. To reduce yoke length, we adopted a double layer coil, which enabled us to increase coil winding turns. With half yoke length and the coil turns increase, we successfully reduced the NLTS by about half. The FIB pole trimming at wafer level can make an appropriate pole shape for generating a highly efficient writing field. [ABSTRACT FROM PUBLISHER]