Very high cycle fatigue properties at 973 K of additively manufactured and conventionally processed intermetallic TiAl 48-2-2 alloy

Abstract

The fatigue lives of 2nd generation γ-TiAl alloy Ti–48Al–2Cr–2Nb manufactured both by additive manufacturing using electron beam powder bed fusion (EB-PBF) as well as conventional casting process by vacuum arc remelting for comparison (REF) were investigated. Both batches (EB-PBF and REF) were subject to the common treatment process, i.e. hot isostatic pressing and heat treatment to achieve a duplex microstructure. As a result, a fine- and a coarse-grained microstructure consisting of γ-grains and colonies of α2/γ lamellae have evolved for the EB-PBF and conventionally cast material, respectively. Uniaxial fatigue tests were performed in the very high cycle fatigue (VHCF) range up to 109 cycles at a load ratio of R = −1 using ultrasonic fatigue testing equipment at an elevated temperature of 973 K. The SN data of both batches were discussed with respect to the influence of microstructure and temperature on the processes of crack initiation and propagation. The additive manufactured material showed superior fatigue strength compared to the conventional material due to its smaller grain size. It was shown that the fine-grained duplex microstructure of the batch EB-PBF is particularly appropriate to decrease short crack propagation at elevated temperatures due to its microstructural characteristics.