稀土La对粉末冶金钛合金组织和力学性能的影响

Effects of LaH_2 and LaB_6 addition on microstructure and mechanical property of powder metallurgy Ti alloy

在Ti-Fe-Mo合金中以LaH2和LaB6两种形式引入稀土La,制备含La的粉末冶金钛合金,研究La的添加量对钛合金烧结行为以及组织与力学性能的影响,探讨合金中La的存在形式及其在烧结过程中的作用机理。结果表明,钛合金相对密度随LaH2添加量(质量分数)的增加而升高,当LaH2的添加量达到0.6%后,钛合金的相对密度不再发生明显变化;但随着LaB6添加量的增加先升高后降低,在LaB6添加量为0.15%时出现峰值。添加LaH2的钛合金中,稀土元素主要以La2O3颗粒的形式存在,随La含量增加,颗粒发生长大;而在添加LaB6的合金中,烧结反应产物主要是纤维状的TiB、具有规则外形的La2O3颗粒以及含Ti和O的富La絮状颗粒。随LaH2和LaB6的添加量增加,合金的室温抗拉强度和伸长率均先升高后降低。LaH2的添加量达到0.6%时出现强度峰值,添加量达到0.3%时出现伸长率的峰值;而LaB6的添加量达到0.15%时抗拉强度和伸长率均出现峰值。

Ti-Fe-Mo alloys with rare earth La（LaH2 and LaB6） addition were fabricated by powder metallurgy.The effect of La content on sintering behaviors,microstructures and mechanical properties of the titanium alloy was investigated.The exist form of the rare earth La and its effects on the sintering densification process of the Ti alloys were also discussed.The results show that the density of the as-sintered Ti alloy firstly increases with the content of LaH2 increasing from 0 to 0.6%（mass fraction）,and then remains unchanged when the content of LaH2 is more than 0.6 %.Whereas,the density of the as-sintered Ti alloy with LaB6 addition exhibits a peak at the LaB6 content of 0.15% followed by a decrease with the increase of the LaB6 content.The microstructure analyses show that in the as-sintered Ti alloy with LaH2 addition,La2O3 particles is the main exist form of the rare earth element La.The size of La2O3 particle increases with the increase of La content.In the as-sintered Ti alloy with LaB6 addition,fibroid TiB and uniform-geometry La2O3 particles are in situ synthesized by the reaction between Ti and LaB6,and flocculated La-rich particles containing B,O and Ti are also detected.The tensile strength and elongation of the alloy with LaH2 and LaB6 addition firstly increase and then decrease with the increase of the content of LaH2 and LaB6.The peak strengths of the alloy with LaH2 and LaB6 addition appear at the addition content of 0.6% and 0.15% respectively.It is found that the sintering density,particle strengthen mechanism and the change of oxygen contents in Ti matrix are the main factors effecting of mechanical properties.