Ti-Ti_2AlNb功能梯度材料的激光立体成形研究

RESEARCH ON LASER SOLID FORMING OF A FUNCTIONALLY GRADIENT Ti-Ti_2AlNb ALLOY

采用激光立体成形技术制备了从Ti到Ti2AlNb成分连续渐变、外形规则、高度为17 mm的梯度材料.分析了梯度材料的组织及相结构演变规律和硬度变化规律.随着Al和Nb成分的提高,Ti—Ti_2AlNb功能梯度材料的相呈现α′→α+β→α+α′→α′→α+β→α+β/B2+α_2→β/B2+α_2→β/B2→B2+α_2+O→B2的演变过程,实现了由α型钛合金经过α+β型及β型钛合金向Ti_2AlNb基合金的转变.硬度值HV从底部纯Ti的170连续渐变到顶端Ti_2AlNb的470.基于钛合金富Ti区非平衡相图,并结合Al和Nb元素在钛合金中对α,β和α_2稳定性的影响分析,对梯度材料在激光立体成形过程中的相演化过程进行了解释.

A functionally gradient Ti-Ti2A1Nb alloy, which has continuous compositional gradient and regular outline with a length about 17 mm, was fabricated by laser solid forming. Phase morphological evolution and microstructure evolution, and microhardness along the compositional gradient direction were analyzed. With the increase of aluminum and niobium contents, a series of phase evolutions along the compositional gradient occurred：α′→α-β→α＋α′→α′→α→β→α＋β/B2＋α2→β/B2＋α2→β/B2＋α2＋O→B2 , and the compositionally gradient material accomplished a transition of αtitanium alloy, α＋β titanium alloy, β titanium alloy, finally Ti2AlNb based alloy. In the transition layers, the microhardness HV increased from 170 of Ti at the bottom to 470 of Ti2AlNb at the top. Based on the non equilibrium phase diagram of the Ti-rich corner, the phase morphological evolution during forming were explained with the analysis of the influences of the Al and Nb on the stabilities of α,β and α2 phases in titanium alloys.