BEHAVIOR OF LATTICE DEFECTS IN MICROSTRUCTURE-CONTROLLED INTERMETALLICS

用透射电镜（TEM）研究了L1_2基、B2基和T1_0基金属间化合物的相分解特征和位错与沉淀相的相互作用。用分析电子显微镜测量了Ni_3Al和NiAl中的晶格占位和扩散系数。根据化学成分和时效温度的不同，可以得到多种不同的微观结构，包括失稳分解、区带形成、相干和非相干沉淀。晶体各向异性和偏离化学计量比的成分对时效过程中的显微组织和强度变化起着重要作用。金属间化合物中沉淀的最典型特征之一是无序相在有序基体中的沉淀。L1_2有序Ni_3Al和Co_3Ti在淬火后时效时由共格fcc无序γ相的细小析出物略微硬化。 关于我们 ng从固溶退火温度。在这些合金中，超位错被有效地吸引到无序颗粒并在沉淀物中扩展其宽度。这些合金的蠕变强度明显增加。在含有细小弥散碳化物的Ni_3Al和TiAl中观察到位错绕过硬沉淀物而留下环的典型例子。透射电子显微镜观察了NiAl（B2）-Ni_2AlTi（L2_1）和NiTi（B2）-Ni_2AlTi（L2_1）赝二元系中的相分解和形变诱发位错，发现滑移位错是一种<100>类型，在欠时效时剪切H相，而在过时效时绕过H相。在未时效状态下，室温变形形成超位错对。Ni_2AlHf相与NiAl基体的晶格失配度约为NiAl-Ni_2AlTi相的4倍。细小Ni_2AlHf相的析出使合金的高温强度和蠕变强度都有明显的提高。TEM观察表明，颗粒/基体界面处位错的吸引相互作用对提高NiAl基合金的高温强度起着重要作用。当金属间化合物在金属间化合物中析出时，强化取决于析出物的晶体结构、滑移位错的Burgers矢量和变形过程中形成的反相晶界能。少

Transmission electron microscope (TEM) investigations have been performed to investigate the characteristic features of phase decomposition and of interaction between dislocations and precipitates in L1_2-based, B2-based and T1_0-based intermetallics. Lattice site occupation and diffusivity in Ni_3Al and NiAl are measured by using an analytical electron microscope. A wide variation of microstructures including spinodal decomposition, zone formation, coherent and incoherent precipitation can be obtained depending on the chemical compositions and aging temperatures. The crystal anisotropy and the deviation from the stoichiometric composition play important roles in the microstructure and the strength variation during aging. One of the most typical features of the precipitation in intermetallics is the precipitation of disordered phases in the ordered matrices. L1_2-ordered Ni_3Al and Co_3 Ti harden appreciably by fine precipitates of coherent fcc disordered gamma upon aging after quenchi … More ng from solution annealing temperature. In these alloys superdislocations are effectively attracted to the disordered particles and extend their widths in the precipitates. The creep strengths of these alloys increase appreciably. A typical example of dislocation bypassing leaving loops surrounding hard precipitates has been observed in Ni_3Al and TiAl containing fine dispersion of carbides. TEM examination of phase decomposition and deformation induced dislocations in NiAl (B2)-Ni_2AlTi (L2_1) and NiTi (B2)-Ni_2AlTi (L2_1) pseudobinary systems have revealed that the glide dislocations are of a <100> type and shear the H-phase at the underaged state but by pass at the overaged state. In the underaged superdislocation pairs are formed by the deformation at room temperature. The lattice misfit between the Ni_2AlHf precipitate and the NiAl matrix is about four times as large as that of NiAl-Ni_2AlTi system. The high temperature strength as well as creep strength increase appreciably by the precipitation of fine Ni_2AlHf phase. TEM observations suggest that the attractive interactions for dislocations at the particle/matrix interfaces plays an important role to increase the high temperature strength of NiAl-based alloys. When intermetallic compounds precipitate in intermetallics, strengthening is dependent on the crystal structures of precipitates, Burgers vectors of glide dislocations and antiphase boundary energies formed during deformation. Less