Large size polysynthetically twinned crystals of Ti-46 Al-8 Nb alloy with a parallel lamellar microstructure were successfully prepared using a Ti-43 Al-3 Si seed by our new operation.A large amount of columnar B2 pha...Large size polysynthetically twinned crystals of Ti-46 Al-8 Nb alloy with a parallel lamellar microstructure were successfully prepared using a Ti-43 Al-3 Si seed by our new operation.A large amount of columnar B2 phase paralleling to the growth direction was found in the final lamellar microstructure.Higher growth rate(>30 mm/h)led to the failure of seeding process.Based on these results,a new mechanism is proposed to describe the seeding process of the hypo-peritectic Ti Al alloys.The peritecticαphase is suggested to directly nucleate from the melt,and then act as nucleus for transformedαphase in the subsequentβtoαtransformation.At the higher growth rate,the appearance ofβphase secondary dendrites and homogeneous nucleation lead to the failure of seeding process.High Nb addition leads to a large amount of residualβphase,and theseβdendrites finally evolve into B2 phase.The room temperature tensile elongation was measured to be 11.9-18.5%for Ti-46 Al-8 Nb PST crystals,which is the highest ever reported value for Ti Al based alloys.展开更多
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 o...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%.展开更多
基于全片层 γ- Ti Al基合金的微结构 ,通过细观力学的方法和位错发射机理建立了临界屈服载荷与片层夹角的定量关系。同时还从连续细观力学的角度给出了横向同性片层复合材料计算基体Mises等效应力的一种解析方法 ,并用于分析全片层γ- ...基于全片层 γ- Ti Al基合金的微结构 ,通过细观力学的方法和位错发射机理建立了临界屈服载荷与片层夹角的定量关系。同时还从连续细观力学的角度给出了横向同性片层复合材料计算基体Mises等效应力的一种解析方法 ,并用于分析全片层γ- Ti Al基合金材料的屈服。两种分析结果表明基于位错发射机理的方法与实验结果相吻合 ,这说明全片层γ- Ti Al基合金的屈服载荷与片层夹角的变化关系是由展开更多
基金National Natural Science Foundation of China(No.51701209)National Key Research and Development Program of China(Nos.2016YFB0701304)。
文摘Large size polysynthetically twinned crystals of Ti-46 Al-8 Nb alloy with a parallel lamellar microstructure were successfully prepared using a Ti-43 Al-3 Si seed by our new operation.A large amount of columnar B2 phase paralleling to the growth direction was found in the final lamellar microstructure.Higher growth rate(>30 mm/h)led to the failure of seeding process.Based on these results,a new mechanism is proposed to describe the seeding process of the hypo-peritectic Ti Al alloys.The peritecticαphase is suggested to directly nucleate from the melt,and then act as nucleus for transformedαphase in the subsequentβtoαtransformation.At the higher growth rate,the appearance ofβphase secondary dendrites and homogeneous nucleation lead to the failure of seeding process.High Nb addition leads to a large amount of residualβphase,and theseβdendrites finally evolve into B2 phase.The room temperature tensile elongation was measured to be 11.9-18.5%for Ti-46 Al-8 Nb PST crystals,which is the highest ever reported value for Ti Al based alloys.
基金Project (2011CB605500) supported by the National Basic Research Program of ChinaProject (FRF-MP-10-005B) supported by the Fundamental Research Funds for the Central Universities,China
文摘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%.
文摘基于全片层 γ- Ti Al基合金的微结构 ,通过细观力学的方法和位错发射机理建立了临界屈服载荷与片层夹角的定量关系。同时还从连续细观力学的角度给出了横向同性片层复合材料计算基体Mises等效应力的一种解析方法 ,并用于分析全片层γ- Ti Al基合金材料的屈服。两种分析结果表明基于位错发射机理的方法与实验结果相吻合 ,这说明全片层γ- Ti Al基合金的屈服载荷与片层夹角的变化关系是由
基金financially supported by the National Science Foundation of China(52322101,92163215,51731006,51771093,52174364,52101143,52305379)the National Key R&D Program of China(2021YFA1200201)the Fundamental Research Funds for the Central Universities(30922010202)。
