Solidification Of Peritectic Alloys Research Articles

Cellular automaton modelling to predict multi-phase solidification microstructures for Fe-C peritectic alloys

In this study, we developed a cellular automaton (CA) model to simulate the multiphase microstructural evolution of the solidification of Fe-C binary peritectic alloys. Three phases were considered in the model: δ, γ, and liquid (L). To simulate microstructures formed by the peritectic transformation, moving interfaces at δ-γ, δ-L, and γ-L transformations were introduced for diffusion-controlled growth. The coarsening growth of γ grains after solidification of peritectic alloys was modelled using the CA method. Numerical simulations of multi-phase microstructure evolution for hyper-peritectic and hypo-peritectic alloys were performed in two and three dimensions. In these simulations, the nuclei of γ phases were formed at the δ/L interface below the peritectic temperature. After nucleation of the γ phase in hyper-peritectic alloys, the δ phase in the calculation domain disappeared before γ solidification was completed. Conversely, in hypo-peritectic alloys, the L phase disappeared before the δ-γ transformation was complete. Moreover, the coarsening of γ grains occurred for both alloys after the end of the peritectic transformation. These outcomes agree with the fact that the phase transformation of alloys involves the solidification of peritectic alloys. Thus, we confirmed that the proposed model was a valid approach to simulating multi-phase microstructures formed by the solidification of peritectic alloys.

Phase and Microstructure Selection During Directional Solidification of Peritectic Alloy Under Convection Condition

A phase and microstructure selection map used for peritectic alloy directionally solidified under convection condition was presented, which is based on the nucleation, constitutional undercooling criterion (NCU criterion), and the highest interface temperature criterion. This selection map shows the relationships between the phase/microstructure, the G/V ratio (G is the temperature gradient, V is the growth velocity), and the alloy composition under different convection intensities and nucleation undercoolings. Comparing with the results from directional solidification experiments of Sn–Cd peritectic alloys, this selection map was generally in agreement with the experimental results.

Unsteady-State Directional Solidification of a Hypoperitectic Pb-9.5wt%Bi Alloy

Although considerable attention has been paid to studies on the unidirectional solidification of peritectic alloys, most of these investigations are carried out under steady-state solidification, where both the growth rate and the thermal gradient can be independently controlled and held constant in time. In this work, a hypoperitectic Pb-9.5wt%Bi alloy was directionally solidified under unsteady-state heat flow conditions and the microstructure evolution was analyzed. Continuous temperature measurements in the casting were monitored during solidification, using a data acquisition system and a bank of six type J thermocouples positioned along the casting length. Thermal parameters such as the growth rate (v) and the cooling rate () were experimentally determined by the experimental cooling curves. The solidification microstructure was characterized by a dendritic morphology along the entire casting length. The primary (l1) and secondary (l2) dendrite arm spacings were measured and experimental growth laws relating them to the solidification thermal parameters v and are proposed.

Peritectic transformation and primary α-dendrite dissolution in directionally solidified Pb–26%Bi alloy

Peritectic transformation is one of the main mechanisms during solidification of peritectic alloys, and accompanied with dissolution of primary phase. In the present work, the effect of solidification temperature on the peritectic transformation and dissolution of primary α-dendrite was investigated during directional solidification of Pb–26wt%Bi peritectic alloy. The resulting microstructures of the alloy in consideration of different solidification temperature have been investigated using optical microscopy. The volume fraction of peritectic β-phase and the average size of α-dendrite core were measured using image analyzing software SISC IAS V8.0. These results show that the increment in β-phase volume fraction and decrement in size of α-dendrite core first increase, then decrease with falling solidification temperature. These results can be explained from the viewpoint of a reduced solidification temperature leading to the rate of peritectic transformation first increases to a maximum, and then decreases.

Phase selection during solidification of peritectic alloys

Formation of stable and metastable phases under directional solidification conditions in materials showing peritectic phase equilibria is discussed. Based on interface response functions for single phase growth morphologies (dendrites and plane front) and on competitive growth arguments, a kinetic stabilisation of metastable peritectic phases with respect to stable ones is predicted for various growth conditions. This method is applied to two industrially important classes of materials such as steels and NdFeB permanent magnets, the properties of which depend closely on the phases formed.

Solidification of peritectic alloys

The solidification of peritectic alloys is reviewed, including both nucleation and growth. The introduction defines various compositions associated with binary peritectic alloys, their ‘equilibrium’ solidification, multicomponent peritectic systems, and metastable phases in peritectic systems. Nucleation studies are reviewed according to the rate of cooling and the type of specimen. Some comparisons are made with observations in eutectic alloys. At fast cooling rates metastable events can occur, as reviewed for alloys based on the Al-Ti and other systems. Growth studies in peritectic alloys have identified three stages: the ‘reaction’ (three phases in contact); the ‘transformation’ (the peritectic phase thickens by solid state diffusion); and ‘direct solidification’ of the peritectic phase. Models of the stages are outlined and compared with experiment for various binary alloys, followed by a summary of observations of peritectic solidification in multicomponent Fe-Cr-Ni and Fe-C-X alloys. Recent advances of single phase solidification are reviewed and applied to phase selection with increased velocity, in peritectic alloys such as in Fe-Cr-Ni, Co-Sm-Cu, and Fe-Nd-B alloys. Independent growth of the two solid phases also is discussed, as illustrated by superconducting Y-Ba-Cu-O alloys. Attempts to produce coupled structures in peritectic alloys are reviewed, followed by a discussion of low velocity banding. Limitations in current experimental or theoretical work are pointed out to aid future work in this important area.

Solidification of peritectic alloys

AbstractThe solidification of peritectic alloys is reviewed, including both nucleation and growth. The introduction defines various compositions associated with binary peritectic alloys, their ‘equilibrium’ solidification, multicomponent peritectic systems, and metastable phases in peritectic systems. Nucleation studies are reviewed according to the rate of cooling and the type of specimen. Some comparisons are made with observations in eutectic alloys. At fast cooling rates metastable events can occur, as reviewed for alloys based on the Al-Ti and other systems. Growth studies in peritectic alloys have identified three stages: the ‘reaction’ (three phases in contact); the ‘transformation’ (the peritectic phase thickens by solid state diffusion); and ‘direct solidification’ of the peritectic phase. Models of the stages are outlined and compared with experiment for various binary alloys, followed by a summary of observations of peritectic solidification in multicomponent Fe-Cr-Ni and Fe-C-X alloys. Recent ...

The constitution and solidification of peritectic alloys in the system Al-Ti

The system Al-Ti is important because Ti additions to Al base alloys promote grain refinement during easting, and this paper describes a further examination of the alloy constitution and the course of the peritectic reaction Al 3 Ti + liquid ⇌ Al. On a basis of optical microscopy and electron microprobe analyses it is concluded that only the stable compound occurs, but that the course of the peritectic reaction can produce a variety of thermal arrests over a small temperature range both above and below the peritectic temperature. A rational assessment of aluminium grain refinement is given for alloys in the range 0–5 wt. % Ti.

The constitution and solidification of peritectic alloys in the system AlTi

The constitution and solidification of peritectic alloys in the system AlTi