变形量对锻造Ti-6Al-4V组织、织构和力学性能的影响

常用锻造Ti-6Al-4V的微观结构主要有等轴、层状和双峰结构,这些结构与对应的晶粒尺寸分布等微观组织特征对Ti-6Al-4V的拉伸和疲劳等力学性能有着主要影响。然而在实际加工条件(如非等温条件,非恒定应变率)下,对微观组织与力学性能之间关联性的研究较少。基于此,本文研究了在锻造实验中,理论变形量对Ti-6Al-4V的显微结构、拉伸和疲劳性能的影响。起始材料由等轴和层状α相组成。在进一步的变形和退火中,随理论变形量从10%增加到50%,球状初生α相的体积分数增加了约20%,抗拉强度和屈服强度增加了约50 MPa,伸长率保持不变。这归因于球状α相体积分数的增加和α相基面取向与外加拉伸载荷方向之间夹角的角度减小。疲劳强度也随理论变形量的增加而增加。根据Ti-6Al-4V锻造和退火后球状初生α的体积分数增加对双峰显微组织的影响,讨论了这些观察结果的重要性。

Morphology transformation of primary strip α phase in hot working of two-phase titanium alloy

Microstructural development in hot working of TA15titanium alloy with primary stripαstructure was investigated withthe aim to globularizeαstrips.Results show that the mechanisms of morphology transformation are the same to the spheroidizationmechanisms of lamellar structure.Boundary splitting and termination migration are more important than coarsening due to the largesize of stripα.Theαstrips are stable in annealing due to the unfavorable geometrical orientation of intra-αboundaries,the largethickness of strip and the geometrical stability ofαparticles.Predeformation and low speed deformation accelerate globularization ofαstrips in the following ways:direct changing of particle shape,promotion of boundary splitting and termination migration byincreasing high angle grain boundaries and interfacial area,promotion of coarsening by forming dislocation structures.Largepredeformation combined with high temperature annealing is a feasible way to globularize stripα.

MAMT法制备半固态浆料中初生相的形核机理

研究了熔体分散混合法制备的半固态浆料初生相形成过程。通过对浆料组织EPMA和金相组织层剥离等试验、熔体分散混合工艺处理熔体的过冷度测定,描述了球状初生相的形成机制。结果表明,熔体在制浆室内均匀过冷,大量的晶核在过冷熔体中以非自发形核的机制形成,均匀分布在熔体中,并且在过冷熔体中被保留下来,成为有效晶核,继而生长成为球状初生相。