添加稀土元素对粉末冶金Ti合金显微组织和力学性能的影响

Effect of rare earth element on microstructure and mechanical properties of powder metallurgy Ti alloy

利用光学显微镜、扫描电镜(SEM)和透射电镜(TEM)等手段研究了在粉末Ti合金中添加稀土元素对烧结坯的显微组织和力学性能的影响。结果表明,添加稀土元素可以有效提高烧结坯的致密度、室温抗拉强度和延伸率,其中含1.0%Nd(质量分数)的材料致密度达99%,抗拉强度1080MPa,延伸率6%,接近锻造Ti 6Al 4V合金的性能水平,而且制备成本明显降低。稀土元素对致密度的贡献主要归因于在烧结过程中产生瞬时液相,同时稀土元素能够夺取粉末颗粒表面的氧,净化原始颗粒界面,提高粉末颗粒的烧结活性。致密度的提高,Ti合金基体氧含量的降低以及第二相Nd氧化物的存在都有助于材料力学性能的提高。然而含Nd合金的烧结温度应控制在一个合适的范围内,过高的烧结温度将导致瞬时富Nd液相的聚集和元素的偏扩散,以及由于扩散条件改善后的晶粒过度长大,反而不利于材料力学性能的提高。

The microstructure and mechanical properties of powder metallurgy(PM) Ti alloy doped with rare earth element Nd were investigated by using optical microscopy, scanning electron microscopy and transmission electron microscopy. The results show that addition of rare earth element can improve the density, tensile strength and elongation of PM Ti alloy. The alloy containing 1.0% Nd(mass fraction) has a relative density of 99%, tensile strength of 1080 MPa and elongation of 6%. The above mechanical properties are almost the same as those of Ti-6Al-4V. The contribution of rare earth element to the density lies in that transient liquid phase occurs during sintering, and the rare earth element can scavenge oxygen from the powder surface, purify the particle interface and activate the sintering process. The increase of density, the decrease of the oxygen content of Ti substrate along with the existence of Nd oxides improve the mechanical properties of PM Ti alloy. However, the sintering temperature for Nd-containing alloy should be controlled properly. An excessively high sintering temperature can lead to agglomeration of Nd-rich liquids and coarsening of grains, hence deteriorates the mechanical properties of PM Ti alloy.