钛合金激光沉积热行为及组织演变

Thermal Behavior and Microstructure Evolution of Titanium Alloy by Laser Deposition

为了考察激光沉积过程热行为对其微观组织的影响,采用了有限元方法对激光沉积过程进行建模,分析了多层多道激光沉积TA15钛合金试样的温度分布及内部节点的热循环特性变化,并对试样的组织进行了考察。模拟结果显示基材和沉积层上任一节点均要经历循环加热和冷却的过程,由于热量累积效应使冷却速度下降,且温度的谷值有上升的趋势。沉积试样的组织由基材的双态组织,经由热影响区,过渡到宏观组织为粗大的初生β晶粒的激光沉积区。因各沉积层经历的热循环和热历史的不同,晶内α相分别呈现针状、片层状和板条状。因冷却速度较快,α相同时在晶界处和β晶内析出,呈现网篮状魏氏体和网篮状混合集束状魏氏体形貌。主要合金元素Al、Zr、Mo、V由基体到激光沉积区均匀分布,无宏观偏析,表明沉积层组织形貌的变化跟成分偏析无关。

In order to analyze the effect of thermal behavior on microstructural evolution of laser deposition manufacturing process, a finite element model was constructed to simulate the temperature field distribution and thermal cycle characteristics. The simulation results showed that any node in substrate and deposition layer experienced heating or cooling cyclically. And the macro and microstructure of laser deposition manufacturing specimen were investigated to determine the evolution of microstructural features in multi-pass deposition layers. The macro and microstructures exhibited epitaxial coarse columnar prior β grains with basketweave or colony α lamella. The width of α lamella changed gradiently, and α lamella had basketweave Widmanstatten or colonies Widmanstatten morphology. The line scanning results by energy dispersive spectrometer （EDS） showed that major alloy elements, Ti, Al, Zr, Mo and V, were distributed uniformly from the substrate to deposited layer without fluctuation and segregation, which showed that evolution of microstructure was not a result of segregation but heat history.