材料期刊网

采用激光立体成形技术制备了沿沉积方向成分渐变的立墙式Ti60--Ti₂AlNb梯度材料, 研究了沉积态Ti60--Ti₂AlNb梯度材料的相 与显微组织的演变规律. 随Al和Nb含量的增加, 梯度材料中呈现α+β→α+α' →α' →α+β→α+β/B2+α₂ →β/B2+α₂→β/B2+α₂+O →B2+O → B2的相演变趋势, α相在Ti60到Ti60--60%Ti₂AlNb (质量分数) 的成分范围内一直存在. 梯度材料的硬度同样随着Al和Nb含量的增加而增加, 并随着B2+O相的形成达到极大值, 不过随着在Ti₂AlNb端部全B2相的获得, 硬度急剧降低. 基于钛合金富Ti区非平衡相图, 结合Al和Nb元素对α, α₂,β/B2和O相稳定性的影响分析, 及考虑激光立体成形所具有的反复回火/退火和热积累效应, 对梯度材料在激光立体成形过程中呈现的相演化规律进行了解释.

Ti60 titanium alloy and Ti₂AlNb alloy have been developed to serve at 600 and 650---850℃, respectively. Because only some regions of hot--end components encounter extreme high temperature environments, it is appropriate to use functionally gradient materials (FGMs) according to the distribution of the working temperature. In this paper, a thin--wall Ti60--Ti₂AlNb alloy with composition gradient was fabricated by laser solid forming (LSF). The phase morphological evolution and microstructure evolution along the gradient direction were investigated. With the increase of Al and Nb contents, a series of phase evolutions along the compositional gradient occurred: α+β→α+α' →α' →α+β→α+β/B2+α₂ →β/B2+α₂→β/B2+α₂+O →B2+O → B2. α--phase can exist in a wide composition range from Ti60 to Ti60--60%Ti₂AlNb (mass fraction). The hardness of the material increases with the increase of Al and Nb contents, and reaches the maximum when B2+O phases appear, and then decreases sharply as obtaining the whole B2 phase at the top position of Ti₂AlNb part. Based on the non--equilibrium phase diagram of the Ti--rich corner, the phase morphological evolution during forming of the gradient materials was explained on combining with the analysis of the influence of the Al and  Nb on the stabilities of α, α₂, β/B2 and O phases in titanium alloys and the effects of recurrent tempering/annealing and heat accumulation in laser solid forming.