Microstructure control and mechanical properties of directionally solidified TiAl-Nb alloys

The double directional solidification（DS） technique was developed to control the lamellar microstructures in primary β TiAl-Nb alloys.Polysynthetically twinned（PST） crystals with lamellar boundaries parallel to or inclined 45o to the growth direction were achieved due to the complete peritectic transformation during directional solidification of the alloys with the dendritic solid/liquid interface.The PST crystals with aligned lamellar boundaries only parallel to the growth direction were produced when lamellar grains with lamellar boundaries in the same orientation were seeded by themselves under appropriate growth conditions.Low boron addition is harmful to align the lamellar orientation because of the growth of non-peritectic α phase.Due to the larger yttria particles and boride ribbons in the directionally solidified TiAl-Nb alloys,the tensile plastic elongations of the alloys are only close to 2%.

TiAl金属间化合物材料本构模型的研究进展

从宏观唯象方面和微细观方面系统地介绍了国内外对TiAl金属间化合物材料本构模型的研究进展。在宏观唯象方面,主要介绍了Arrhenius方程和Zener-Hollomon参数在描述TiAl金属间化合物高温流变行为方面的应用,以及Z-A模型在描述TiAl金属间化合物在高温、高应变速率下流变行为方面的应用;在微细观方面,主要介绍了国内外基于TiAl金属间化合物的微细观结构特征和变形机理等,以及运用晶体塑性理论和有限元分析建立的微细观预测模拟模型。