Novel reactive, liquid phase processes and the development of advanced materials

高温金属间化合物和金属-陶瓷复合材料由于熔化温度高、硬度高、延展性有限，使用传统的铸造、成形和机械加工工艺难以加工且成本高昂。通过粉末压制和烧结来制备这些材料具有制造近净形状零件的优点，减少了成形和机械加工的需要。对于反应烧结(RS)的特殊情况，使用成本相对较低的纯粉末混合物，在烧结过程中进行反应，形成所需的化合物或复合材料，具有更低的加工温度和经济生产的额外好处。然而，RS生产的多孔、不均匀的成品限制了这项技术的商业应用。我们最近对NiTi形状记忆合金(SMA)的RS的研究表明，低密度的烧结是由于形成了分布不均匀的液相，并将其孤立成不连续的“口袋”。

High temperature intermetallic compounds and metal-ceramic composites are difficult and costly to process using conventional casting, forming and machining routes due to their high melting temperature, high hardness and limited ductility. The fabrication of these materials through pressing and sintering of powders has the advantage of the fabrication of near net shape parts, reducing the need for forming and machining. For the specific case of reactive sintering (RS), the use of a mixture of relatively low cost pure powders, which react during sintering to form the desired compounds or composites, has the added benefits of lower processing temperatures and economic production. However RS suffers for the production of a porous, inhomogeneous finished product which has limited the commercial application of this technology. Our recent studies on RS of NiTi shape memory alloy (SMA) has revealed that low sintered densities result from the development of a poorly distributed liquid phase which becomes isolated into discontinuous "pockets".