Novel Processing of WC/Co Hardmetals with Simultaneous Improvements in Hardness and Toughness Derived From Nanocrystalline Powder

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The research objective of this award is to develop innovative manufacturing methods that can produce novel materials derived from nanocrystalline powder with low costs and superior mechanical properties simultaneously. Specifically, a novel manufacturing process, termed as the Integrated Mechanical and Thermal Activation (IMTA) process, will be utilized to make low cost nanostructured WC/Co powder which will subsequently be densified using the innovative sintering strategy to allow the conversion of nano-WC particles to submicrometer-sized WC platelets. The dense WC/Co cermets with submicrometer-sized WC platelets are expected to offer unprecedented simultaneous improvements in hardness and toughness. To achieve the best improvements, WC platelets will be fabricated to have both high aspect ratio and thin thickness. The thin thickness will limit the slip distance of dislocations and thus provide high hardness, while the high aspect ratio of platelets will offer effective crack deflection and thus result in high toughness. Thin and high aspect ratio WC platelets will be produced via detailed and comprehensive studies of the effects of sintering conditions, the size of the starting WC particles, the Co concentration, the free carbon concentration, and addition of a small amount of dopants. The microstructure of WC/Co with and without doping sintered under various conditions will be characterized in detail to elucidate the formation mechanism of WC platelets and the effect of various dopants and processing conditions. Deliverables include mechanistic understanding of the effects of sintering conditions, the size of the starting WC particles, the Co concentration, the free carbon concentration, and a small amount of dopants on the formation of WC platelets, dense WC/Co cermets with simultaneous improvements in hardness and toughness, engineering students education, and research experience for middle/high school underrepresented minority students.If successful, the results of this research will produce a new generation of low cost and high performance WC/Co cermets with superior hardness and toughness for advanced structural applications by many industries. These novel WC/Co cermets could also open up new opportunities in areas outside their current application windows. The understanding developed from this research will lay a scientific foundation for enhancing anisotropic growth of crystals and can be applied directly to other hardmetals such as WC-Ni, WC-NiCo, and WC-CoCr. The scientific principles discovered can also shed light on the processing and microstructure design of advanced ceramics with the anisotropic grain growth property (e.g., Ti3SiC2, Ti3AlC2, and liquid-phase-sintered Si3N4, SiC and Al2O3). Graduate and undergraduate engineering students will benefit from this project through classroom instruction and involvement in the research. Through specially designed summer programs, middle/high school underrepresented minority students will participate in the research. These summer programs will nurture underrepresented minorities towards positive thinking, increase their interest in science and technology, and motivate them to pursue higher education and become future leaders of the society.