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两相或多相合金的组织控制。需要更高的操作温度，这样的化合物由于具有复杂有序的晶体结构和因此具有高熔点而受到青睐。由于这种金属间化合物本质上是脆性的，因此用于微结构控制的策略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，在先前的工作中开发的一类新的耐热材料，表现出比商业镍基高温合金的上级的性能，凝固缺陷，如宏观孔隙和微裂纹已频繁地导致在凝固过程中。这应该是由脆性金属间化合物金属相之间的热膨胀系数差异引起的，金属间化合物金属相通常以初生固相出现。 关于我们 从液体中析出，并通过不变反应形成韧性相。为了获得良好的铸锭，必须通过控制凝固过程来避免这些缺陷，以便准确地评价力学性能，从而设计适当的组织控制。和Nb，其硅化物如MoSi_2为主要成分，各元素与硅形成一定量的韧性原生固溶体。并与电弧熔炼法和光学浮区法进行了比较。并尝试设计了一类以Fe_3AlC为主要成分的新型铁基合金。结果表明，通过适当选择OFZ法的凝固速度，可以用定向的两相混合物制造出具有良好高温强度和一定延展性的优质铸锭。

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