Improvement of Ductility of DO_3 Type Intermetallics

6.5mass%硅钢（DO_3型金属间化合物）具有良好的软磁性能。然而，该材料是脆性的，并且脆性阻碍了其实际应用。本研究旨在探讨其脆性产生的原因，并改善其成形性。主要研究结果如下：1.韧脆转变：（1）脆性断裂发生在低于600 K的温度（区域B），并且材料在高于该温度（区域D）是延性的。在韧性温度区，在较低应变速率下，断裂面包含脆性断裂面（区域B/D）。（2）区域B和D之间的边界随着应变速率的增加向低温方向移动，表明即使在较低温度下，材料也可以在较高应变速率下塑性成形。显微构造观察：（1）活动滑移系：D区和B区均存在{110}<111>和{112}<111>滑移系。材料中存在塑性变形所需的五个独立滑移系。这表明材料基本上是可延展的。(2)在区域B中，在晶界处以及晶粒内形成许多裂纹。然而，在区域D中，仅在特殊位置观察到裂纹。这种差异导致两个地区。轧制：以各种轧制速度轧制材料。在较低的轧制速度下，材料是脆性的，但在较高的轧制速度下，它变得具有韧性。这证实了1（2）的期望。该材料可以在473 K和较高的轧制速度下轧制。

6.5mass% silicon steel (DO_3 type intermetallics) has good soft magnetic properties. The material, however, is brittle, and the brittleness prevents its practical use. This research aims at studying the cause of the brittleness and improving its formability. The results are summarized as follows:1. Ductile-brittle transition: (1) Brittle fracture takes place at temperatures below 600K (region B), and the material is ductile above the temperature (region D). In the ductile temperature region, however, fracture surfaces contain brittle fracture facets at lower strain rates (region B/D), (2) The boundary between regions B and D moves toward lower temperature as strain rate increases, suggesting that the material can plastically be formed at higher strain rates even at lower temperatures.2. Microstructural observation: (1) Active slip system: {110}<111> and {112}<111> slip systems are operative both in regions D and B. Five independent slip systems necessary for plastic deformation are available in the material. This indicates that the material is essentially ductile. (2) In region B, a number of cracks are formed at grain boundaries as well as within grains. In region D, however, cracks are observed only in special locations. This difference causes the two regions.3. Rolling: The material was rolled at various rolling speeds. At lower rolling speeds the material is brittle, but at higher rolling speeds it becomes ductile. This confirms the expectation of 1(2). The material could be rolled at 473K at high rolling speeds.