Melting and precision casting of Ti-6Al-4V alloy by use of electron beam furnace

Abstract

For melting and casting of Ti-6Al-4V alloy by use of an electron beam furnace, key technologies have been developed: measurement and control of temperature, amount, and chemical composition of molten pool. Temperature in the molten pool was measurred by applying three devices; a thermocouple, a two color pyrometer and the rate of vaporization from the molten pool. Temperature measured by an optical pyrometer without influence of plasma by shifting the wave lengths of the light for the optical pyrometry from those of plasma evolved above the molten pool was in a good accordance with that estimated from the vaporization rate. By combining temperatures measured by three methods, the temperature gradient in the molten pool was estimated to be a level of 100 K/cm. In order to derive an empirical equation for the depth of molten pool of various metals, the depth of the molten pool was determined for Ti, Ti-6Al-4V alloy, solar grade Si, low carbon steel, and stainless steel by chemical etching of vertical cross section of an ingot melted and solidified in a skull crucible. Chemical compositions of Ti-6Al-4V alloy melt before casting was adjusted by adding an aluminum block into the pool before pouring, which compensated vaporization loss of Al from the pool surface under high vacuum. Since, a key to settle Al content in the specified range is the yield and distribution of Al in every castparts, influences of operating variables on the yield have been studied by paying attention to rapid temperature change observed immediately after addition of aluminum.