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

该奖项的研究目标是开发创新的制造方法，能够以低成本和优异的机械性能同时生产由纳米晶粉末衍生的新型材料。具体地说，一种新的制造工艺，称为集成机械和热激活(IMTA)工艺，将被用来制造低成本的纳米结构WC/Co粉末，随后将使用创新的烧结策略进行致密化，从而使纳米WC颗粒转化为亚微米尺寸的WC片状。致密的WC/Co金属陶瓷具有亚微米尺寸的WC片层，预计将在硬度和韧性方面提供前所未有的同步改善。为了实现最好的改进，WC小片将被制造成既具有高纵横比又具有较薄厚度。较薄的厚度将限制位错的滑移距离，从而提供高硬度，而小片的高纵横比将提供有效的裂纹偏转，从而导致高韧性。通过详细而全面地研究烧结条件、起始WC颗粒尺寸、Co浓度、游离碳浓度和少量掺杂的影响，可以制备出薄而高纵横比的WC片层。对不同烧结条件下WC/Co掺杂前后的显微组织进行了详细的表征，以阐明WC片层的形成机制以及各种掺杂和工艺条件对WC片层的影响。成果包括对烧结条件、初始WC颗粒尺寸、Co浓度、游离碳浓度和少量掺杂对WC片层形成的影响的机理了解、致密的WC/Co金属陶瓷和同时提高硬度和韧性的致密WC/Co金属陶瓷、工程学生教育以及针对初中/高中未被充分代表的少数民族学生的研究经验。如果这项研究成功，这项研究成果将生产出新一代低成本、高性能的WC/Co金属陶瓷，具有优异的硬度和韧性，适用于许多行业的高级结构应用。这些新型WC/Co金属陶瓷还可以在其当前应用窗口之外的领域开辟新的机会。本研究的认识将为促进晶体的各向异性生长奠定科学基础，并可直接应用于其他硬质合金，如WC-Ni、WC-NiCo和WC-CoCr。所发现的科学原理也可以为具有各向异性晶粒生长特性的先进陶瓷(如Ti3SiC2、Ti3AlC2和液态烧结的Si3N4、SiC和Al_2O_3)的工艺和微观结构设计提供指导。工程专业的研究生和本科生将通过课堂教学和参与研究，从这个项目中受益。通过特别设计的暑期计划，初中/高中代表不足的少数族裔学生将参与研究。这些暑期计划将培养未被充分代表的少数群体积极思考，提高他们对科学技术的兴趣，并激励他们追求高等教育，成为社会未来的领导者。

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.