Effect of Zr addition on the stability of precipitated Laves phase and mechanical properties of Fe–Cr–Al-based alloys at high temperatures
Ben Niu, Zhenhua Wang, Qing Wang, Sen Ge, Chuang Dong, Ruiqian Zhang, Huiqun Liu, Peter K. Liaw
Abstract
The effect of a small amount of Zr addition on the temperature-dependent stability of Laves phase particles and mechanical properties of Fe-13.5Cr-4.73Al-2.07Mo-(0.34–0.5)Nb-(0.65–0.98)Ta-(0–0.33)Zr (wt. %) ferritic alloys was investigated in the present study. The designed alloy ingots were hot-rolled, aged at 1073 K for 24 h, and then re-treated at 1273 K, 1323 K, 1373 K, and 1473 K for 1 h, respectively. It was found that the Zr addition could not only stabilize the Fe2M Laves phase (M = Mo,Nb,Ta,Zr) to a much higher temperature, but also induce the formation of stable Fe23Zr6 phase. The high-temperature (HT) microstructural stability of the alloys significantly was improved, as evidenced by the fact that a certain amount (0.66–1.19%) of precipitates (Fe2M, Fe23Zr6, and core(Fe23Zr6)-shell(Fe2M)-structured particles) with an appropriate size (∼1.0 μm) uniformly distributed in the ferritic matrix even after being re-treated at 1473 K. Particularly, the formation of core-shell-structured particles at HTs was studied from the viewpoint of both solid solubility and diffusion coefficient of M in the matrix. All these aged alloys exhibited prominent mechanical properties at both room and elevated temperatures, showing high yield strength with σYS = 490–560 MPa at room-temperature and σYS = 80–85 MPa at 1073 K. The strengthening effect was further discussed in light of various strengthening mechanisms, and the calculated strength are in good agreement with the experimental results.