Correlation of microstructure and mechanical properties of Ti2AlNb manufactured by SLM and heat treatment

Abstract

Ti2AlNb intermetallic has a promising application in aeronautics and aerospace industries due to its high strength-to-weight ratio and high creep resistance at an elevated temperature. Selective laser melting (SLM) of this material has been emerging recently. The correlation of its microstructure and mechanical properties after the SLM and heat treatment determines the application of this material. In this paper, the process window of SLM for Ti2AlNb was determined. Characteristics of lath, acicular and grain boundary (GB) precipitates were studied after different heat treatments. The relation of solution heat treatment (SHT) temperature on the size and volume fraction of precipitates before and after aging treatment (AT) were established. High-temperature tensile test of the SLMed and heat-treated intermetallic were conducted. A relation between microstructure and mechanical properties was proposed. The change of the tensile strength and elongation at elevated temperature were rationalized. The results show that for the SLMed sample the dominating B2 phase led to a good room temperature ductility, but at 650 °C the continuous precipitation along the GB deteriorated the tensile strength and ductility. After SHT (920 °C) + AT, the maximum elongation (El) at 650 °C was significantly increased due to the precipitation of large-sized lath O+α2 phase. After SHT (1000 °C) + AT, the maximum ultimate tensile strength (UTS) of the tensile test at 650 °C increased to 820 MPa due to the precipitated acicular O phase.