Effect of Ti and Al interaction on microstructures and mechanical properties of the Nb-Ti-Si-Al alloys

Nb-Si based alloys show great promise to surpass currently advanced Ni-base superalloys due to their low densities and high melting points. Both Ti and Al are beneficial alloying elements for Nb-Si based alloys. In literatures, a small amount (≤3 at%) of Al can be frequently examined, while Nb aluminides are usually not formed in this case. Since Nb₃Al and Nb₂Al have good strength and creep properties, NbAl₃ is also a candidate hot-section material; however the study of Nb-Si alloys with these possible Nb aluminides is lacking, so we focus our efforts on whether Nb aluminide is formed or not by adding more Al in the as-cast Nb-Ti-Si alloys. The microstructures and the mechanical properties of two Nb-Ti-Si-Al alloys (A2: Nb-18Ti-14Si-9Al, A4: Nb-21Ti-14Si-9Al) with higher Al content were studied in the present work. A4 alloy was designed to examine the alloying effect of more Ti. Results show that A2 alloy consists of (Nb), Nb₅Si₃ and Nb₃Al, while the A4 alloy is composed of (Nb) and Nb₅Si₃. The room temperature fracture toughnesses of A2 alloy and A4 alloy are 11.1 and 10.9 MPa·m^1/2, respectively. Moreover, the microindention tests were conducted to characterize the micro scale mechanical properties of these Nb-Ti-Si-Al alloys.