Solidification process control of intermetallic-based multi-phase heat resistant alloys applicable at ultra-high temperature

耐热材料的设计涉及到以金属间化合物为主要成分的双相或多相合金的显微组织控制。较高的操作温度是理想的，这种化合物具有复杂的有序晶体结构，因此具有高熔点。由于这种金属间化合物本质上是脆性的，组织控制的策略一直是引入一定量的延性相，并通过例如不变反应来设计混合物的形态。然而，在开发一种性能优于商品镍基高温合金的新型耐热材料的工作中，在凝固过程中经常会产生宏观空洞和微观裂纹等凝固缺陷。这应该是由于脆性金属间化合物相之间的热膨胀系数的差异造成的，而脆性金属间化合物相最常表现为初级固相…更多的Se来自液体，通过不变反应形成延性相。研究了Mo、Ta、Nb等难熔金属元素的凝固工艺参数，其中以MoSi2等难熔金属元素为主要成分，加入一定量的韧性初生固溶体。并与电弧法和光浮区(OFZ)法进行了比较。并尝试设计了以Fe_3AlC为主要成分的新型铁基合金。结果表明，通过合理选择OFZ法的凝固速度，取向两相混合物可以获得良好的高温强度和较低的延性。

Design of heat resisting materials has involved the microstructure control on two- or multi-phase alloys in which an intermetallic compound is the major constituents. Higher the operating temperature is desired, such compounds are favored as having a complex ordered crystal structure and therefore a high melting point. Since such a intermetallic compound is brittle in nature, strategy for the microstructure control has been to introduce some amount of ductile phase and to design the morphology of the mixture via for example an invariant reaction. However in the previous work on developing a new class of heat resisting materials which exhibit a superior performance than the commercial nickel-base superalloys, solidification defects such as macro-voids and micro-cracks have been frequently resulted during solidification. It should be caused by the difference in thermal expansion coefficient between a brittle intermetallic metallic phase, which is most often appears as a primary solid pha … More se from a liquid, and a ductile phase formed through an invariant reaction. It is necessary to avoid those defects by controlling the solidification process in order to obtain a sound ingot so that the evaluation of mechanical properties should be accurate to design a proper microstructure control.In the present work, the solidification process parameters have been investigated in alloys based on such refractory metal elements as Mo, Ta, and Nb in which their silicides such as MoSi_2 are the major constituent with some amount of ductile primary solid solution of each element with silicon. Comparison has been made with the processes of arc melting and optical floating zone (OFZ) methods. Also the design of a new class of iron-base alloys in which Fe_3AlC is a major constituent has been attempted. It has been shown that by proper choice of solidification rate upon OFZ method, a sound ingot can be fabricated with aligned two-phase mixture to exhibit an excellent combination of high temperature strength and some ductility Less