Exceptional phase-transformation strengthening of ferrous medium-entropy alloys at cryogenic temperatures

Abnormal austenite–ferrite transformation behaviour in substitutional Fe-based alloys

Results on high-resolution synchrotron X-ray diffraction, optical microscopy and scanning electron microscopy are presented for a Ti–46Al–1.9Cr–3Nb (at.%) alloy at room temperature and at elevated temperature. The phase equilibria for the composition of the alloy have been calculated and have been found to correspond perfectly well to the molar phase fractions for γ, α2 and B2 phases, which were for the first time derived from the fitting procedure of the diffraction patterns at elevated temperatures. Thermal expansion coefficients and relative volume change for the major γ and α2 phases have been independently determined. X-ray diffraction and microscopy data prove the presence of oxidation at temperatures above about 1100 °C, with formation of Ti2O and Al2O3 oxides.

High-temperature synchrotron X-ray diffraction study of phases in a gamma TiAl alloy

Neutron-diffraction study and modeling of the lattice parameters of a NiAl-precipitate-strengthened Fe-based alloy

The nonlinear lattice expansion of iron alloys in the range 100-1600K

The ferrite and austenite lattice parameters of Fe–Co and Fe–Cu binary alloys as a function of temperature

A general three-dimensional model for the development of microstructure in metals by diffusion-controlled processes has been constructed. The model has been applied to the austenite (γ-Fe) to ferrite (α-Fe) phase transformation in plain-carbon steels. Starting from a Voronoi construction for the austenite grains, the ferrite is assumed to nucleate at the corners of the original austenite grains. Subsequently, the growth of the ferrite grains is assumed to be radial and to fulfil the conditions of local equilibrium at the ferrite–austenite interface. The development of the ferrite fraction, the ferrite grain size, and the number of active nucleation sites have been evaluated as a function of time during continuous cooling. The influence of the nucleation rate, the growth rate, the nucleus density, the cooling rate, and the carbon concentration on the development of the microstructure is discussed.

A three-dimensional model for the development of the microstructure in steel during slow cooling

Field-dependent neutron depolarization study of the ferrite formation in medium-carbon steels

Three-dimensional neutron depolarization experiments have been performed in order to study the phase transformations from austenite (γ-Fe) into ferrite (α-Fe) and cementite (Fe 3 C) in two medium-carbon steel samples with different carbon concentrations. The rotation of the neutron polarization vector during transmission through the sample is a direct measure for the ferromagnetic ferrite fraction. The degree of depolarization is related to the magnetic correlation length, which gives an indication of the characteristic length scales of the microstructure.

Neutron depolarization study of phase transformations in steel

Neutron depolarisation experiments on ferrite phase transformations in an unalloyed steel during continuous cooling and heating are presented. In the experiments the mean magnetisation and the magnetic correlation length are determined simultaneously as functions of time and temperature. From these parameters the ferrite fraction and the mean ferrite particle size, respectively, are determined. The potential of the technique is illustrated on a C60 steel. IS/1188

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S.G.E. te Velthuis

Papers

The ferrite and austenite lattice parameters of Fe–Co and Fe–Cu binary alloys as a function of temperature

A three-dimensional model for the development of the microstructure in steel during slow cooling

Field-dependent neutron depolarization study of the ferrite formation in medium-carbon steels

Neutron depolarization study of phase transformations in steel

Neutron depolarisation: A novel technique for studying phase transformation kinetics in steels