Mechanical-Alloying-Assisted Syntheses of Cobalt-Containing Multi-Component Systems and MAX Phases

机械合金化(MA)是一种材料加工方法，通常在高能球磨机中对混合粉末颗粒进行重复焊接、破碎和再焊接，以产生可控的、非常精细的组织，从而获得高性能的最终材料。MA辅助合成的特点是将混合粉末机械合金化成非常细小的结构，然后烧结。在本研究中，将利用MA技术合成两类材料。第一种是基于钴基高温合金和高熵合金相结合的概念而设计的含钴多元体系(MCS)。前者也被称为钨铬钴合金，由于其独特的化学成分，具有优异的高温强度、腐蚀、氧化、磨损和耐磨性。后者由至少5个等原子或近等原子组成的元素组成，通过引入额外的熵来稳定结构，表现出高硬度、良好的延展性和高温稳定性等各种优良性能。与传统的HEA不同的是，所提出的含钴MCS合金仍以Co为主，并加入了Cr、W、Mo、Ni、Mn等元素，但与Stellite合金相比，Co的含量将降低，从而降低了合金的成本。MAX相是层状的三元碳化物和氮化物，使金属和陶瓷材料的性能结合在一起，在极端环境中被广泛使用。在这项研究中，MAX相，包括Cr2AlC，Ti3SiC2，Ti3AlC2，Ti2AlC和Ti2AlN，可能用于核应用，也将用MA合成，以通过创造非常细晶的微观结构来提高它们的性能。MA混合粉末将通过放电等离子烧结和激光熔覆等特殊烧结工艺进行凝固，由于快速加热和冷却，这些工艺能够产生非常细小的微观组织。预计通过先进工艺合成的这些新型材料具有优于传统方法合成的现有材料的性能，成为各种工业应用的新兴先进材料。

Mechanical alloying (MA) is a materials-processing method that involves the repeated welding, fracturing, and rewelding of a mixture of powder particles, generally in a high energy ball mill, to produce a controlled, very fine microstructure, which results in high performance of the final material. MA-assisted-synthesis is characterized by a combination of mechanical alloying the mixed powder to very fine structure and then sintering. In this research two categories of material will be synthesized utilizing the MA technique. The first is cobalt-containing multi-component system (MCS), which is designed based on the combined concept of cobalt-based superalloy and high-entropy alloy (HEA). The former is also known as Stellite alloy, displaying exceptional properties such as high temperature strength, corrosion, oxidation, wear and erosion resistance, due to the unique chemical composition. The latter is composed of at least five elements in equiatomic or near equiatomic composition, exhibiting various excellent properties such as high hardness, good ductility and high temperature stability, by introduction of extra entropy to stabilize the structure. Different from traditional HEAs, the proposed cobalt-containing MCS alloys still have Co as the major element alloying with Cr, W, Mo, Ni, Mn, etc., but Co content will be reduced compared to Stellite alloys, thus lowering the cost of the alloys. MAX phases are layered ternary carbides and nitrides, making property combination of metallic and ceramic materials, which are popularly employed in extreme environments. In this research, MAX phases, including Cr2AlC, Ti3SiC2, Ti3AlC2, Ti2AlC, and Ti2AlN, potentially for nuclear applications, will also be synthesized with MA to improve their performance by creating very fine grained microstructures. The MA mixed powders will be solidified via special sintering processes such as spark plasma sintering and laser cladding, which enable to produce very fine grained microstructures due to rapid heating and cooling. It is expected that these novel materials synthesized by the advanced process possess superior performance to the existing materials from conventional methods, becoming emerging advanced materials for various industrial applications.