Precipitation in a Ni–Al–Mo Directionally Solidified Eutectic Composite
The most recently developed high temperature materials are known as in-situ composites or directionally solidified eutectics. Since the composites are formed during solidification, they have excellent morphological stabilities up to near their melting temperatures. The Ni-Al-Mo system has received the greatest attention for recent several years(1)~(3) since the alloy is expected to form a structure consisting of ductile α-Mo fibers aligned in aductile γ+γ' matrix†. However variations in microstructures and the resultant strength by thermal treatments have not been investigated in earlier papers(1)~(3). In a separate paper(4) the present authors have reported the detailed microstructural analysis of as-grown composite and the microstructural and strength variations of the composite due to quenching from high annealing temperatures. The present paper describes the microstructural changes occurring during ageing of a Ni-12.7at%Al-21.6at%Mo alloy composite after quenching from 1533K studied by transmission electron microscopy
Precipitates in Nickel-rich Ni–Al–Mo Ternary Alloys
Etude par microscopie electronique a transmission, par mesure de durete, par diffraction d'electrons de la precipitation de phases stables ou metastables entre 873 et 1373 K dans des alliages Ni-7% a 30% poids Mo-2% a 11% poids Al. Durant le vieillissement on observe la formation des phases γ', NiMo(δ), Ni 2 Mo, Ni 3 Mo et Ni 4 MO dependante de la composition de l'alliage et de la temperature de vieillissement
Theory of domain walls in ordered structures—II: Pair approximation for nonzero temperatures
Abstract The surface free energy of antiphase boundaries in the body centered cubic AB -type alloy and related structures is discussed for nonzero temperatures using the pair approximation and the Bragg-Williams approximation. Two kinds of walls are discussed: the P -wall and the W -wall. In b.c.c. structures the {110} wall is the former and the {100} wall is the latter. For each wall direction, the atomic-plane-center case and the interstitial-plane-center case are differentiated. For the P -wall, the interstitial-center case is shown to be more stable, for which the surface entropy vanishes at absolute zero. For the W -wall, the atomic-center case and the interstitial case are shown to have nearly the same surface free energy, but the surface entropy does not vanish at absolute zero. For the stable cases, the surface free energies resulting from use of the Bragg-Williams and the pair approximations are shown to agree well when plotted against T / T c .