The effect of EBM process parameters on porosity and microstructure of Ti-5Al-5Mo-5V-1Cr-1Fe alloy

Abstract

In this article, the authors discuss the results of studies into the processing of Ti-5Al-5Mo-5V-1Cr-1Fe near-β titanium alloy (Ti-55511) by electron beam melting (EBM), an additive manufacturing technique. Due to its high flexibility in shaping mechanical properties, Ti-55511 alloy is commonly used in aircraft components such as landing gear or airframes. In this study, Ti-55511 powder was used and its properties were described as regards chemical composition and particle size distribution in order to assess its suitability for EBM processing and repeatability of results. 20 sets of processing parameters were tested in the energy input range between 10 J/mm3 and 50 J/mm3 (cathode current, 4.5 mA-19.5 mA; scanning speed, 1080 mm/s-23400 mm/s). Four types of top surfaces were obtained, namely, flat, orange peel, with single pores, and with swelling. Best results were obtained for the energy of 30 J/mm3: flat top surface and relative density in excess of 99.9%. Analysis of chemical composition showed that aluminum loss was below the specification minimum for the analyzed parameter sets. Scanning speed most significantly affected aluminum content: the lower the scanning speed, the higher the aluminum loss. Analysis of microstructures showed the dependence of lamellar α-phase volume fraction on the process parameters used. For low scanning speed, the determined α-phase volume accounted for about 78%. Higher scanning speed resulted in a decrease of the α-phase content to 61%. The dimensions of the lamellas and the amount of the α-phase strongly effected hardness results (360 HV to 430 HV).