A secondary liquid phase with a droplet shape is separated from the primary liquid phase in Cu-Ni-Fe-Mo-Si alloy during Laser Metal Deposition process. In the subsequent quenching process, the secondary liquid phase solidifies into hard particles that are dispersed in the primary matrix phase. The increase in Ni content suppresses the coarsening of the hard particles, but the mechanism of the phenomenon has not been clarified. In this study, we investigated the effects of Ni content on the hard particle sizes, mainly focusing on Marangoni effect controlled by the temperature variation of interfacial energy. The effects of Ni content on the hard particle size were analyzed based on the change in the start temperature of the separation of two liquid phases (L1 and L2) and the temperature dependence of interfacial energy with Ni content calculated by thermodynamic calculations. The results showed that Ni content had little effect on the temperature variation of interfacial energy. On the other hand, an increase in Ni content decreases the temperature of L2 droplet formation and shortens the time to solidification, resulting in reduced moving distance of the droplet. Therefore, the collision frequency of L2 droplets caused by the Marangoni effect was reduced and coarsening of the droplets was suppressed.

In die casting, laminations are a serious problem because they cause blisters, stripping defects and zinc deposition on the mold surface. Blisters and stripping defects reduce the quality of the product, and zinc deposits on the mold surface reduce productivity. Therefore, the analytical prediction of the risk of lamination formation and the optimization of the gating system for reducing the occurrence of defects due to laminations are very important before designing a mold. To optimize the gating system, we used an evaluation criterion formulated using the shear rate of the molten metal flow in a die casting simulation. In this study, we proposed a coupling analysis method consisting of mold temperature and mold filling analyses, and applied it to the optimization of a gating system based on the evaluation criterion. Using this method, we eliminated the occurrence of blisters due to laminations after plating.

Mater. Trans. 61 (2020) 2393-2401に掲載

For reducing the frictional losses on the sliding surfaces of mounting parts and improving the wear resistance in order to extend the life of the component, diamond-like carbon (DLC) film coating has been considered, in recent years. However, reduction of the long processing time involved is desirable for mass production. For achieving this, the effect of mixing hydrocarbon gas and hydrogen gas in the deposition process is compared, and the differences in the resulting DLC films are determined in this study. DLC films are deposited on Si wafers through radio frequency plasma chemical vapor deposition (RF-PECVD), with a mixture of methane gas and hydrogen (dilution gas) as the raw material. In addition, DLC films are prepared by mixing acetylene gas with hydrogen gas for comparison, and the effect of the hydrogen gas mixture on the deposition rate, composition, and hardness of the films is confirmed. When hydrogen gas is mixed with methane gas, the deposition rate increases with the increase in the ratio of hydrogen gas in the raw material, and the percentage of sp³ bonds increases; however, the hardness and elastic modulus decrease. Furthermore, the adhesiveness deteriorates with the increase in the hydrogen gas ratio.

Mater. Trans. 63 (2022) 351-356に掲載．Fig. 1を修正．