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，涉及粉末颗粒混合物的重复焊接，破碎和粉碎，通常在高能球磨机中，以产生受控的，非常精细的微观结构，从而导致最终材料的高性能。MA辅助合成的特征在于将混合粉末机械合金化至非常精细的结构然后烧结的组合。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设计的含钴多元合金体系（MCS）。前者也被称为钨铬钴合金，由于其独特的化学成分，显示出优异的性能，如高温强度，耐腐蚀性，抗氧化性，耐磨性和耐侵蚀性。后者由至少五种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异性能。与传统的HEAs不同，所提出的含钴MCS合金仍然具有Co作为与Cr、W、Mo、Ni、Mn等合金化的主要元素，但与司太立合金相比，Co含量将减少，从而降低合金的成本。MAX相是层状三元碳化物和氮化物，是金属和陶瓷材料性能的结合体，广泛应用于极端环境中。在这项研究中，MAX相，包括Cr2AlC，Ti3SiC2，Ti3AlC2，Ti2AlC和Ti2AlN，潜在的核应用，也将与MA合成，以提高其性能，通过创建非常细的晶粒显微组织。MA混合粉末将通过特殊的烧结工艺（例如放电等离子烧结和激光熔覆）固化，这使得能够由于快速加热和冷却而产生非常细的晶粒显微组织。预计这些新材料的合成工艺将使其具有比传统方法合成的现有材料更优越的上级性能，成为新兴的先进材料，应用于各种工业领域。

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.