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

Abstract:

Nb-Si based alloys show great promise to surpass current 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 the literature, small amount (≤ 3 at. % ) of Al have frequently examined, and 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, and the study of Nb-Si alloys with these possible Nb alumininides is lacking, so we focus our efforts on primarily whether Nb aluminide is formed or not by adding more Al in the as-cast Nb-Ti-Si alloys. This work studied the microstructures and mechanical properties of two Nb-Ti-Si-Al alloys (A2: Nb-18Ti-14Si-9Al, A4: Nb-21Ti-14Si-9Al) with higher Al content, and the A4 alloy was designed to examine the alloying effect of more Ti. The A2 alloy consists of (Nb), Nb₅Si₃ and Nb₃Al, while the A4 alloy is composed of (Nb) and Nb₅Si₃. The comparable fracture toughness of the A2 alloy and the A4 alloy is 11.1 MPa.m_1/2 and 10.9 MPa.m_1/2, respectively. Moreover, the indention experiments are employed to characterize the micro scale mechanical properties of these Nb-Ti-Si-Al alloys.

Key words:Nb-Si based alloys; Al addition; microstructure; fracture toughness; indention experiments