| Zirconium and zirconium alloys have excellent properties such as low elastic modulus,good biocompatibility,excellent corrosion resistance and low magnetic susceptibility.They have broad application prospects in the field of biological implant materials.It has been found that Zr-Nb binary alloys and Zr-Nb-Ti ternary alloys have large miscibility gap,which makes it possible to design Zr-Nb and Zr-Nb-Ti alloys with spinodal decomposition.So,in this paper,the spinodal decomposition mechanism and the evolution of microstructure of Zr-Nb and Zr-Nb-Ti alloy system are studied by phase-field method.Firstly,the phase field model of spinodal decomposition of Zr-Nb binary alloy and Zr-Nb-Ti ternary alloy is constructed,and the thermodynamic analysis of the phase field model is carried out.Then,the simple spinodal decomposition(ignoring elastic strain energy)and spinodal decomposition of Zr-Nb alloy were simulated by phase field method.And the effects of alloy composition,aging temperature and applied strain on the spinodal decomposition process were studied.On this basis,the phase field simulation of the spinodal decomposition process of Zr-Nb-Ti ternary alloy was carried out,and the effects of alloy composition and aging temperature on the spinodal decomposition process were studied.The main researches and results are as follows:(1)Phase field models of spinodal decomposition of Zr-Nb and Zr-Nb-Ti alloys were constructed.Through the thermodynamic analysis of the phase field model,it can be found that the thermodynamic curve of the model was a double-well shape,which accords with the thermodynamic conditions of phase transformation(2)Simple spinodal decomposition(ignoring elastic strain energy)and spinodal decomposition of Zr-Nb alloy were simulated by phase field method.Then,the effects of aging temperature,alloy composition and external strain on the morphology,amplitude,wavelength and volume fraction of amplitude modulation structure were studied.In the absent of elastic strain energy,the morphology of ? phase in Zr-30 at.%Nb and Zr-40 at.%Nb alloy is discrete droplets,Zr-50 at.%Nb alloy is coherent non-oriented maze-like and plane-like shapes,Zr-60 at.%Nb alloy is aggregated clusters;With the contribution of elastic strain energy,in the aging process,the orientation of ? phase in Zn-Nb alloy system is obvious,along the direction of <110>.When the applied strain is,the ? phase in Zr-50 at.% Nb alloy orientates along <010>direction,while when the applied strain is the ? phase orientates along <110>direction.(3)Spinodal decomposition of Zr-Nb-Ti alloy was simulated by phase field method.Then,the effects of aging temperature(800K-925K)and alloy composition on the morphology,amplitude and wavelength of spinodal structure were studied.The morphology of rich-Ti phase in Zr-40Nb-20Ti(at.%)alloy is coherent non-oriented maze-like and plane-like shapes,Zr-40Nb-25Ti(at.%)alloy is discrete droplet,and Zr-33Nb-29Ti(at.%)alloy is aggregated clusters.With the increase of aging temperature,the morphology of rich-Zr and rich-Ti phases in Zr-40Nb-25Ti(at.%)alloys change from continuous non-oriented maze-like structure to discrete droplet-like structure,while the size of enriched phase increases first and then stabilizes,and there is no spinodal decomposition at 925K. |
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