Microstructure and mechanical properties of directionally solidified and heat treated Nb–14Si–24Ti–2Cr alloy

Abstract

In this work, the directional solidification of an Nb–14Si–24Ti–2Cr alloy (at-%) was performed at 1900°C with withdrawal rates of 1·2, 6 and 18 mm min−1, and the alloy was then heat treated (HT) at 1450°C for 100 h. The microstructures and mechanical properties of the directionally solidified and HT alloy were investigated. The phases present in the sample were confirmed to be NbSS dendrites, lath-like Nb3Si, eutectic NbSS+Nb3Si and Ti enriched areas. As the withdrawal rate increased, the effects of directional solidification became more evident, and the microstructure became more refined. After the heat treatment, the microstructure was characterised by NbSS dendrites, residual Nb3Si and lamellar eutectic NbSS+Nb3Si, which was decomposed from the lath-like Nb3Si. An increase in the withdrawal rate resulted in a decrease in the room temperature fracture toughness of the HT alloy. However, the room temperature compressive strength of the HT alloy increased to 1593·9 MPa with increasing withdrawal rate, which was twice the value of the compressive strength before heat treatment.