Precipitation behavior of second phases and mechanical property of Fe–Cr–Al–Mo–Nb/Ta/Zr alloy during aging at 1073 K

Abstract

The precipitation behavior of second phases and mechanical property of Fe–13.5Cr–4.7Al–2.1Mo–0.5Nb–0.8Ta–0.2Zr (wt.%) alloy was investigated in the present study. Alloy ingots were fabricated by vacuum arc melting and multi-pass hot rolling, then solid-solutionized at 1473 K for 2 h and aged at 1073 K for 0–24 h. In the initial aging process, the precipitated phase were mainly composed of spherical Laves Fe2M (M = Nb, Ta, Zr) and Fe23Zr6 particles. With increasing the aging time, the morphology of Laves phase particles changed gradually from the spherical shape to short-rod shape, and then to granular shape. While the Fe23Zr6 particles still remain spherical during the whole aging process. It is closely related to the lattice misfit between precipitated phase and the BCC matrix, in which the lattice misfit of ε = 1.3% between Fe2M and BCC is remarkably larger than that (ε = 0.2%) between Fe23Zr6 and BCC, leading to a significant change in Fe2M particles. Moreover, the morphology of Fe2M particles in solutionized-aged state is also different from that in rolled-aged state. Consequently, the yield strength (σYS = 410 MPa) of the solutionized-aged alloy is much lower than that (σYS = 560 MPa) of the rolled-aged alloy, which is ascribed to that the strengthening contribution (σor = 48 MPa) induced by short-rod particles is less than that (σor = 153 MPa) of spherical particles.

Keywords

• Fe–Cr–Al-based alloy
• Microstructural evolution
• Precipitation kinetics
• Strengthening mechanisms