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

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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.