全片层BT18Y钛合金在α+β相区固溶时的显微组织演化

EVOLUTION OF MICROSTRUCTURE OF FULL LAMELLAR TITANIUM ALLOY BT18Y SOLUTIONIZED AT α +β PHASE FIELD

对BT18Y(Ti-6.9Al-3.6Zr-2.7Sn-0.7Mo-0.6Nb-0.21si)钛合金进行了一系列的固溶处理,利用OM,SEM 和TEM观察了在α+β两相区固溶后的显微组织形貌,发现连续的晶界α相发生了球化,一部分晶内初生α片端部具有“叉形”结构.分析了球化的原因和“叉形”结构的形成机理:晶界α相表面曲率不同造成的溶质浓度差异而引起的扩散是晶界相球化的根本原因,不同晶界α片的交接对球化有一定的贡献;晶内初生α片的各个部位与β相之间的相界面结构和界面能的不同是造成α+β相区固溶时α片端“叉形”形貌的主要原因,α片端面与β相之间为高界面能易移动的非共格界面,在固溶时β相容易在该处向α片内生长形成β片,与之对应的α片便出现了“叉形”结构.

BT18Y titanium alloy was treated with several groups of heat treatment. After solutionized frectment at α + β phase field, metalloscopy, transmission electron Microscope (TEM) and scanning electron microscopy (SEM) were employed to observe the microstructures. It was found that the continuous grain boundary (GB) α phase is spheroidizes and the edges of some intragranular primary α laths show forked morphology. The ultimate reason of the spheroidization of GB α is the diffusion of solute atoms due to the difference of solute concentration, which results from the different interfacial curvatures at different sites. The joint of two GB α lamellas also gives some contribution to the spheroidization of GB α. The forked morphology at the edge of primary α lath results from different interfacial structures and energies between β phase and different parts of α lath. The incoherent interface between β phase and the edge of α lath has high interfacial energy and moves easily. When the alloy is solutionized at α + β phase field, β phase trends to grow into α lath and forms β lath, which results the forked morphology of primary α lath.