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.
14.00 Normal 0 false false false EN-US X-NONE X-NONE In this project, we have made transformative advancements in synthesizing large quantity, low cost, uniform nanostructured WC/Co powders and identifying an approach to convert this nano-powder to sintered WC/Co bodies. In converting the nano-powder to sintered bodies, we allow nano-WC particles to grow in a controlled manner. As a result, thin WC platelets are formed which provide significant improvements in hardness and toughness simultaneously. We have demonstrated that dense WC-18wt.% Co with a WC platelet microstructure can exhibit simultaneous improvements in hardness and toughness over all of the WC/Co materials available today (see Materials Science and Engineering, 537 (2012) 39-48, and Figure 1). We have further demonstrated that WC platelets are not thermodynamically equilibrium shape and thus must be formed under non-equilibrium conditions (see Acta Materialia, 59 (2011) 3748-3757). Therefore, controlled growth during sintering is very important; otherwise, bulky, equiaxed WC grains are formed. Figure 2 shows that as sintering temperature increases, WC grains change their morphology from platelets to bulky and equiaxed structure, indicating that controlling the sintering temperature is critical in forming thin WC platelets. We have further demonstrated that coarse-grained WC/Co powder cannot result in the formation of thin WC platelets (see Ceramics International, 37 (2011) 3591-3597). Therefore, nano-WC/Co powder is the key to form thin WC platelets and thus to offer simultaneous enhancement in hardness and toughness. We have also found that the density of sintered WC/Co bodies plays an important role in hardness and toughness. The presence of porosity results in a large variation in the hardness and toughness of sintered WC/Co bodies with a WC platelet microstructure. WC-10wt% Co is an example of such a situation. As shown in Figure 1, WC-18wt% Co (nano) has a small variation in hardness and toughness because it has a density near the theoretical (> 99%). In contrast, WC-10wt% Co (nano) has a very large variation in hardness and toughness because its density is lower than 97.5% of the theoretical. Further work is required in the future to achieve the full density and the WC platelet microstructure at the same time for WC/Co materials with low Co concentrations (such as 10 wt% and 6 wt% Co). We have actively disseminated the research results of this project by publishing a total of 4 archival refereed journal articles and 2 conference proceedings, and making 6 technical presentations including 2 invited talks in several national and international conferences. This project has supported one PhD student and one REU undergraduate student. The PhD student has now worked at Saint-Gobain Corporation as a staff scientist, while the REU student has become a graduate student at Colorado School of Mines. The graduate student working on this project has received the Graduate Excellence in Materials Science (GEMS) Award. We have also been very active in outreach to general public, promoting science and engineering and encouraging middle and high school students to pursue careers involving science, engineering and technology. The processing and testing equipment as well as materials characterization facilities of this project in the PI’s lab have been utilized to provide hands-on experiments for middle and high school students during the ASM Materials Camps and the Engineering-2000 Project as well as tours for high school students and their families during University Open Houses and for local industries during the annual meeting of the University of Connecticut Institute of Materials Science Associate Program. Furthermore, we also participated in "Family Science Event" which was organized in support of NOVA’s Making Stuff and Nanodays.
