Improvement of Ductility of DO_3 Type Intermetallics

6.5质量%硅钢（DO_3型金属间化合物）具有良好的软磁性能。然而，这种材料是脆的，而这种脆性阻碍了它的实际应用。本研究旨在研究脆性产生的原因，提高其成形性能。研究结果总结如下：1。韧脆转变：(1)在600K以下（B区）发生脆性断裂，在600K以上（D区）材料具有韧性。然而，在韧性温度区域，在较低的应变速率下，断口表面包含脆性断裂面（B/D区）。(2)随着应变速率的增加，B区和D区之间的边界向较低的温度移动，这表明即使在较低的温度下，材料也可以在较高的应变速率下塑性成形。(1)活动滑动系统：D区和b区均存在{110}<111>和{112}<111>滑动系统。材料中存在塑性变形所必需的5个独立的滑动系统。这表明材料本质上是延展性的。(2)在B区，晶界处和晶内形成了大量裂纹。而在D区，只在特殊位置观察到裂缝。这种差异导致了这两个地区。轧制：以不同的轧制速度轧制材料。在较低的轧制速度下，材料是脆的，但在较高的轧制速度下，它变得有韧性。这证实了1(2)的期望。该材料可以在473K的高轧制速度下轧制。

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.