Mechanical and high temperature oxidation response of Nb-18.7Si–5Ti–5Zr alloy

Abstract

In the present work, the influence of addition of Ti and Zr elements (5 at.% each) on the microstructure, room temperature mechanical behavior and cyclic oxidation response (800–1400 °C) of the cast Nb-18.7Si alloy has been studied. The cyclic oxidation behavior of the alloy in both the uncoated and Fe,Cr modified silicide slurry coating conditions have been investigated at the pest oxidation temperature of 800 °C and at high temperatures of 1200 °C, 1400 °C. The microstructure of the Nb-18.7Si–5Ti–5Zr alloy exhibited the desirable α-Nb5Si3, Nbss phases in the cast alloy, which is otherwise needs high temperature heat treatment for longer duration. Further, a minor fraction of γ–Nb5Si3 phase is also present which resulted from the segregation of Ti, Zr elements during the solidification of the alloy. The alloy is measured with significantly high compressive strength (2236 ± 81 MPa) and fracture toughness (10.59 ± 0.35 MPa m1/2). The addition of Ti and Zr has not improved the oxidation resistance and the alloy is dimensionally degraded within 15min/1cycle of oxidation at all the test temperatures. Whereas, the Fe–Cr modified silicide coating provided the oxidation life of 350–425 min (23–28 cycles) during the oxidation test in the temperature range of 800–1400 °C. The formation of multi-layer oxide sale on the surface is attributed to the improvement in the oxidation life of the alloy.