Effects of TaB2 Addition on the Microstructure and Properties of Laser Melting Deposited Nb–16Si–22Ti–3Al Alloy

Abstract

The phase composition, microstructure and properties of laser melting deposited Nb–16Si–22Ti–3Al alloys with different TaB₂ (0, 0.25, 0.5, 1.0, 2.0 at%) additions were studied. The results showed that the microstructure of Nb–16Si–22Ti–3Al alloy without TaB₂ was mainly composed of Nbss phase, Nbss/Nb₃Si eutectic and a small amount of α-Nb₅Si₃ phase. With the TaB₂ addtion increased, the Nbss/Nb₃Si eutectic in the alloy gradually diminished and Nbss + (α,γ)-Nb₅Si₃ eutectic structure were found. Compared to the untreated condition, when 0.25 at% TaB₂ was added, the Nbss content in the alloy sample increased from 50.2 to 56.2 vol%, the Nb₃Si content decreased from 36.7 to 14.2 vol%, the α-Nb₅Si₃ content rose from 12.1 to 23.7 vol%, and the γ-Nb₅Si₃ phase emerged (5.2 vol%). The average fracture toughness of 0.25 at% TaB₂ alloy was the best among all samples, reaching up to 13.1 MPa·m^1/2. The reasons for this were attributed to the refinement of the microstructure and the increase in the content of the ductile phase (56.2 vol%) together with the decomposition of Nb₃Si into Nb + Nb₅Si₃. The microhardness and compressive strength of the alloy both increased continuously with the addition of TaB₂, reaching the maximum values up to 615.3 HV_0.2 and 2053 MPa, respectively for the alloy with 2.0 at% TaB₂ addtion. The reason for this were the increase in volume fraction and the growth of the silicide phase in the alloy.

Graphical Abstract