添加Nd元素对钛合金析出行为的影响规律

Precipitated Phase of Titanium Alloy with Adding Nd Elements

通过粉末冶金方法(冷等静压—真空烧结)制备钛合金Ti-6Al-4V-2Cr-1Nd,经过固溶-时效热处理后,利用光学显微镜(OM)、X射线衍射仪(XRD)和透射电镜(TEM)分析合金的微观组织、物相的组成及析出相的形核特点,研究添加稀土元素Nd对析出相的影响。实验结果表明,在添加1%Nd(质量分数)元素后,钛合金组织得到了明显细化;通过合金细化成核理论分析发现,添加稀土元素Nd后,固溶时效中Nd_2O_3可以作为形核的基础,促进形核,所以稀土Nd元素可以有效促进非均匀形核,主要析出相Nd_2O_3有利于晶粒的细化,是有效的形核剂;在高分辨透射电镜下对离子减薄后的试样进行观察,通过对合金的形貌和析出物进行傅里叶变换(FFT)和反傅里叶变换(IFFT)分析,得到清晰的原子排列图,发现析出相Nd_2O_3与基体α-Ti之间存在平行相界面,经分析为半共格界面。

Titanium alloy Ti-6Al-4V-2Cr-1Nd prepared by powder metallurgy method（ cold isostatic pressing and vacuum sintering）was researched. The microstructure,phase composition and precipitated phase nucleation process were analyzed by optical microscope（ OM）,X-ray diffraction（ XRD） and transmission electron microscope（ TEM） after solution and aging treatment. The effect of adding rare earth element Nd to the titanium alloy on its precipitated phase was studied. The experimental results showed that the microstructure refinement effect was obvious after adding rare earth element 1% Nd（ mass fraction）; based on the analysis of alloy refining nucleation theory,it was found that after adding Nd,Nd_2O_3 could serve as the basis of nucleation because of its high energy,promoting nucleation,there fore Nd could promote the heterogeneous nucleation effectively,the main precipitation phase Nd_2O_3 was beneficial to refining crystalline grains and it was effective nucleating agents. Through high resolution observation of ion thinning sample,and the morphology of the alloy precipitates were analyzed by fast Fourier transform（ FFT） and inverse fast Fourier transformation（ IFFT）. It was found that there was parallel interface between precipitated phase Nd_2O_3 and matrix α-Ti,and it was semi-coherent interface shown by analysis.