Control of the floating zone stability during electron beam melting process of Ni-25%Si alloy

In this study, the Ni-25at%Si alloy was fabricated by electron beam floating zone (EBFZ) method. The finite element method was used to calculate the temperature field of electron beam refining process. The electron beam refining process was controlled based on the temperature distribution which was varied with the process parameters. The electron beam refining process of Ni-25at%Si can be divided into 2 stages. The first stage featured the forming of a stable floating zone and the second stage featured the moving of the stable floating zone. The experimental results showed that it was difficult to balance the surface tension and gravity during the melting process due to the low surface tension of Ni-25at% Si alloy. The heat capacity of Ni-25at%Si alloy bar was limited, which easily led to the heat accumulation inside the melting zone during the refining process, resulting in the dynamically changing of surface tension and decreasing the stability of the refining process. Based on the inherent relationship among temperature, surface tension and the stability of the melt zone, the temperature field of the floating zone was quantitatively analyzed by numerical simulation and the process parameters for maintaining the stability of the floating zone were obtained. Then the “beam attenuation” technique was put forward to eliminate the heat accumulation during the refining process and a stable refining process was finally obtained.