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MICROSTRUCTURE AND PHASE EVOLUTION IN Ti60--Ti2AlNb GRADIENT MATERIAL PREPARED BY LASER SOLID FORMING |
YANG Mocong; LIN Xin; XU Xiaojing; CHEN Jing; HUANG Weidong |
State Key Laboratory of Solidification Processing; Northwestern Polytechnical University; Xi'an 710072 |
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Cite this article:
YANG Mocong LIN Xin XU Xiaojing CHEN Jing HUANG Weidong. MICROSTRUCTURE AND PHASE EVOLUTION IN Ti60--Ti2AlNb GRADIENT MATERIAL PREPARED BY LASER SOLID FORMING. Acta Metall Sin, 2009, 45(6): 729-736.
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Abstract 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.
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Received: 08 December 2008
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Fund: Supported by Program for New Century Excellent Talents in University of China (No. 06--0879), National High Technology Research and Development Program of China (No. 2006AA03Z0449) and National Basic Research Program\par of China (No. 2007CB613805) |
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