In order to increase oxidation resistance at elevated temperatures for Ni-Al alloy, the feasibility of Pt coating on Ni-Al alloy has been investigated. In the preliminary study, Ni-Al alloy was heated on a Pt plate and quenched just after melting the alloy. Then the cross section was metallographically observed using a scanning electron microscopy. Pt could be melted in the molten Ni-Al alloy but the concentration in the liquid phase was limited because the reaction time was short. Furthermore, the solute content was not uniform in the liquid phase. After the power for the heater was switched off, solidification started from both solid sides. Due to the small difference between liquidus and solidus temperatures, the primary Ni phase solidified with the cellular interface rejecting Al and Pt during solidification. Since the crystallographic structures of the base and weld metals are all fcc and microsegregation during solidification is very small, the weldability of this system is judged to be very good.

  In sand molds made by additive manufacturing, the outer-shape slope is formed by stacking layers composed of micro horizontal surfaces and micro edge slopes. In this study, additive manufacturing experiments were carried out under the combined conditions of outer-shape slope angles θ (5, 10, 15, 20, 25, 30, 45°), binder contents C_B (1.6, 2.0, 2.5mass%), and placements of sand molds (normal/opposite). Then, the visibility characteristic in which stair-steps cannot be visually recognized over 30° of θ was reconfirmed, and the edge angles φ and maximum height roughness Rz, were measured from the side-view images of the slopes.

  The findings of a 3-ways ANOVA test confirmed an important characteristic whereby φ is constant and does not depend on θ, C_B, and placement. Furthermore, the visibility characteristic was explained based on the mean φ value of 36° (SD ＝ 8.6°, N ＝ 240). The mean value of Rz was found to coincide with the larger of the Rz due to stair-steps forming at the mean φ value of 36° and the Rz of the horizontal plane. In addition, for the condition of θ ≦ 20°, at which the stair-steps were visible, most of the measured Rz values fell within the range defined by the 95% prediction interval of φ.

  Porosities in a diecasting are generally classified into gas porosity and shrinkage porosity. It is recommended that molten metal should be injected as atomized flow during the injection process, though the reason is not obvious. In this study, theoretical equations are first derived from a quite simple assumption that molten metal includes multiple pores during solidification. These theoretical equations simultaneously describe the formation of both gas porosities and shrinkage porosities. The equations are then quantitatively verified by comparisons with experimental data. Lastly, it is shown from the equations that finer atomized flow suppresses the expansion of shrinkage porosities in a diecasting.