Chemistry Control in Electron Beam Deposited Titanium Alloys

Abstract

Direct manufacturing of metallic materials has gained widespread interest in the past decade. Of the methods that are currently under evaluation, wire-fed electron beam deposition holds the most promise for producing large-scale titanium parts for aerospace applications [1]. This method provides the cleanest processing environment as the deposition is performed under vacuum. While this environment is beneficial in preventing contamination of the deposit, there is the potential for preferential vaporization of high vapor pressure elements during the deposition process. This can lead to detrimental chemistry variations, which can have negative impacts on physical and mechanical properties. Past experience has shown that deposition of the alloy Ti-6Al-4V using electron beam direct manufacturing can produce material with aluminum content below the specification minimum [2]. As aluminum has a high vapor pressure with respect to titanium and vanadium, it preferentially vaporizes from the molten pool. This aluminum loss scales with the size of the molten pool and thus the chemical content can vary throughout the build. Compensating for this loss is necessary in order to achieve nominal chemistry in the deposited material. This paper examines established processing conditions for direct manufacturing of titanium, quantitatively determines deposited alloy chemistry changes under various conditions, and suggests a feedstock composition that will result in deposited material with nominal Ti-6Al-4V chemistry.