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DEVELOPEMENT OF MICROSTRUCTURE-CONTROLLED B2-ORDERED HIGH TEMPERATURE INTERMETALLICS

微观结构控制的B2有序高温金属间化合物的开发

基本信息

批准号：
07555503
负责人：
NEMOTO Minoru
金额：
$ 0.45万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

A wide variation of microstructures can be obtained in B2-ordered intermetallicsdepending 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. The lattice misfits at interphase interfaces in NiAl (B2)-Ni_2AlTi (L2_1) and NiTi (B2)-Ni_2AlTi (L2_1) pseudobinary systems have been estimated by transmission electron microscopy (TEM). When the size of Ni_2AlTi precipitates is smaller than a critical value, the precipitates keep their lattice coherency with the NiAl and NiTi matrices. After longer periods of aging the Ni_2AlTi precipitates lose their coherency by introducing interface dislocations surrounding them. The coherency loss occurs catastrophically and the shape of the precipitates changes to a globular one after the loss of coherency, while keeping the cubic-cubic orientation relationship. The morphology of dislocations intr … More oduced by the deformation of B2-ordered NiTi containing fine precipitation of L2_1-ordered Ni_2AlTi is correlated with the yield strength variations during aging and deformation temperatures. The Burgers vectors of 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. With increasing the deformation temperature dislocations start to move as wavy single dislocations. In NiAl contaning 2 and 5 mol% of Hf, fine plate-like L2_1-type Ni_2AlHf precipitates are formed on the {111} planes of the NiAl matrix keeping the lattice coherency with the matrix lattice at the beginning of aging. By longer periods of aging Ni_2AlHf precipitates lose their coherency and change their morphology to the spherical ones surrounded by misfit dislocations. 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 obsernvations suggested 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. Less

根据化学成分和时效温度，B2 有序金属间化合物中可以获得各种各样的微观结构。晶体各向异性和化学计量成分的偏差在时效过程中的微观结构和强度变化中起着重要作用。通过透射电子显微镜（TEM）估计了NiAl（B2）-Ni_2AlTi（L2_1）和NiTi（B2）-Ni_2AlTi（L2_1）伪二元系统中相界面处的晶格失配。当Ni_2AlTi析出物的尺寸小于临界值时，析出物与NiAl和NiTi基体保持晶格共格。经过较长时间的老化后，Ni_2AlTi 沉淀物会通过在其周围引入界面位错而失去其共格性。相干性损失会灾难性地发生，并且在失去相干性后，沉淀物的形状变为球状，同时保持立方体-立方体的取向关系。由含有L2_1有序Ni_2AlTi细粒析出的B2有序NiTi变形引起的位错形态与时效和变形温度期间的屈服强度变化相关。滑移位错的伯格斯矢量为<100>型，并且在欠时效状态下剪切H相，但在过时效状态下绕过。在未老化状态下，超位错对是通过室温变形形成的。随着变形温度的增加，位错开始以波状单位错的形式移动。在含2mol％和5mol％Hf的NiAl中，在NiAl基体的{111}面上形成细小的板状L2_1型Ni_2AlHf析出物，并在时效开始时保持与基体晶格的晶格共格性。经过较长时间的老化，Ni_2AlHf 沉淀物失去了相干性，并将其形态改变为被错配位错包围的球形。 Ni_2AlHf析出物与NiAl基体之间的晶格失配大约是NiAl-Ni_2AlTi体系的四倍。细小的Ni_2AlHf相的析出显着提高了高温强度和蠕变强度。 TEM 观察表明，颗粒/基体界面处位错的吸引力相互作用对于提高 NiAl 基合金的高温强度起着重要作用。较少的