Hongxiang Jiang

Solidification of Immiscible Alloys: A Review

Immiscible alloys gained a considerable interest in last decades due to their valuable properties and potential applications. Many experimental and theoretical researches were carried out worldwide to investigate the solidification of immiscible alloys under the normal gravity and microgravity condition. The objective of this article is to review the research work in this field during the last few decades.

EFFECT OF MICRO-ALLOYING ELEMENT Bi ON SOLIDIFICATION AND MICROSTRUCTURE OF Al-Pb ALLOY

Monotectic alloys are characterized by a miscibility gap in the liquid state. Many of them have great potentials to be used in industry. For example, alloys based on Cu-Pb and Al-Pb are good candidates to be used as advanced bearing materials if the soft Pb phase is dispersed in the Al or Cu matrix. Cu-Cr alloy is a highstrength, high conductivity material and Cu-Co alloy is an excellent magneto-resistive material, etc.. However, when a homogeneous monotectic alloy melt is cooled into the miscibility gap, it will transform into two liquids. The liquid-liquid decomposition generally causes the formation of a phase segregated microstructure. In recent years, considerable efforts have been made to investigate the solidification behavior of monotectic alloys. A lot of experiments have been carried out under microgravity conditions in space as well as under the gravitational conditions on the earth. The solidification behaviors of monotectic alloys under the conventional and rapid solidification conditions as well as the effect of external fields, such as electric current, magnetic field etc., are investigated. Models describing the solidification process have been built and the microstructure formations under different conditions have been calculated. It has been demonstrated that the microstructure evolution during cooling an alloy in the mis*国家自然科学基金项目51271185和51471173,以及中国载人航天工程项目TGJZ800-2-RW024资助 收到初稿日期: 2015-06-26,收到修改稿日期: 2015-12-23 作者简介:孙倩,女, 1990年生,博士生 DOI: 10.11900/0412.1961.2015.00331 第497-504页 pp.497-504

Solidification of Pb–Al Alloys Under the Influence of Electric Current Pulses

Continuous solidification experiments are carried out with Pb–Al alloys under the influence of the electric current pulses (ECPs). The results demonstrate that the ECPs mainly affect the microstructure formation through changing the energy barrier for the nucleation of the minority phase droplets (MPDs) and minority phase particles (MPPs) during cooling Pb–Al alloys in the liquid–liquid and liquid–solid phase transformation temperature ranges in advance of the solidification of the matrix liquid. For Pb–Al alloys with Al-rich droplets/particles as the minority phase, the ECPs lower the energy barriers for the nucleation of the MPDs/MPPs and cause a significant increase in the nucleation rate of the MPDs/MPPs and, thus, promote the formation of Pb–Al alloys with a well-dispersed or even nanoparticles dispersed microstructure. The ECPs parameters show an important influence on the microstructure formation of Pb–Al alloys. The refinement extent of the MPDs/MPPs increases with the increase in the peak current density. For a given peak current density, the refinement extent of the MPDs/MPPs increases with the increases in the pulse frequency and pulse width first, and then level off and become asymptotic.

Microstructure Evolution of a Ternary Monotectic Alloy During Directional Solidification

A model was developed to describe the microstructure evolution in a directionally solidified ternary monotectic alloy. The directional solidification experiments were carried out on Al–3Pb–1Sn (wt%) alloys by using a Bridgman apparatus. The microstructure evolution in the directionally solidified sample was calculated. The numerical results agree well with the experimental ones. It is demonstrated that the nucleation of the minority phase droplets occur at two different positions. One corresponds to the liquid–liquid decomposition, which occurs in front of the solidification interface. The other is at the liquid/solid interface. The nucleation rate of the minority phase droplets at the liquid/solid interface is significantly higher than at the position in front of the solidification interface. The characteristic of the nucleation process leads to a bimodal size distribution of the minority particles in the directionally solidified sample.

Solidification of Immiscible Alloys Under the Effect of Electric and Magnetic Fields

Immiscible alloys have aroused considerable interests in the last decades on account of their special physical and mechanical properties and potential applications. A considerable number of researches have been implemented to investigate the solidification behaviors of immiscible alloys in electric and magnetic fields. It has been indicated that the magnetic field and electric current can remarkably affect the solidification process and microstructures of immiscible alloys. The solidification techniques under the effects of electric and magnetic fields have great potentials for the fabrication of immiscible alloys. This paper reviews the research work in this field in recent years.