Beijing Institute of Technology has made new progress in the development of high-performance cemented carbide

Not long ago, I learned from Beijing University of Technology that for the international development trend in the field of ultra-fine and nano-hard alloys, the status quo of China's development and bottlenecks, with the support of many research projects in the country and Beijing, the National Outstanding Youth Science Fund Winner, Beijing High-level Innovation and Entrepreneurship Program, 100 million engineering leader, Professor Song Xiaoyan is the responsible person of the Beijing University of Technology cemented carbide team, after more than 10 years of basic research and technology development work, the establishment of ultra-fine, nano-hard alloy The large-scale production and engineering application series of new technologies, the development of high value-added cemented carbide materials and products, is being promoted and applied.

Opportunities and challenges of nano-hard alloy materials
After more than 60 years of development, China's cemented carbide industry has become the world's largest producer of hard alloys. According to the statistics of the China Tungsten Industry Association's cemented carbide branch, the annual production of domestic cemented carbide in the past three years (2012-2014) is 2.2-25,000 tons, accounting for more than 40% of the global total. China's cemented carbide production and consumption are the world's first, but not a strong country in the cemented carbide industry. Compared with internationally renowned cemented carbide companies such as Sweden's Sandvik, American Kennametal, Inframat, Germany's KF, Austria's Plansee, France's Forecreu, and Japan's Toshibatungaloy, the gap in China's cemented carbide industry is reflected in the lack of high-end products and the lack of key technologies, especially In the field of ultra-fine and nano-hard alloys which have been rapidly developed in recent years in the world.
In view of the international development trend in the field of ultra-fine and nano-hard alloys, as well as the status quo and bottlenecks of China's development, with the support of many scientific research projects in the country and Beijing, the winners of the National Outstanding Youth Science Fund and Beijing's high-level innovation and entrepreneurship Planned 100 million engineering leader talent Professor Song Xiaoyan as the responsible person of the Beijing University of Technology cemented carbide team, after more than 10 years of basic research and technology development work, established a series of ultra-fine, nano-hard alloys for large-scale preparation and engineering applications Technology, working closely with domestic cemented carbide companies to develop high value-added carbide materials and products for high-end industrial applications.
With the rapid development of modern manufacturing industry and the advent of various new difficult-to-machine materials, more and more stringent requirements have been placed on the quality and performance of cemented carbide tooling products. For WC-based cemented carbides, ultrafine (average grain size 200-500 nm) and nanocrystalline (average grain) compared to conventional coarse-grain (usually referred to as average grain size 13 μm) cemented carbide With a hardness of 200 nm or less, cemented carbide has significantly improved hardness, wear resistance and breaking strength. It is an advanced material that is unmatched in high-end machining technology such as drilling, cutting and milling with high efficiency and high precision.
Nano-hard alloy materials emerged from the late 1990s to the beginning of this century. Various kinds of methods for preparing new methods emerged. In the following years, the development of nanostructures, fine characterization and comparative analysis of mechanical properties, and the scale of nano-hard alloys in recent years Chemical preparation and industrial application have become the focus of research and development in the world, which has attached great importance to the frontier competitiveness. During this period, it has experienced the survival of the fittest of many preparation methods of nano-hard alloys. For example, sol-gel/coprecipitation method, plasma method, etc. are limited to laboratory micro-synthesis of nano-WC powder; discharge plasma sintering, ultra-high pressure consolidation, etc. are limited to laboratory preparation of nano-polycrystalline materials with simple shape and small three-dimensional size; The spray conversion method can mass-produce nano-WC powders; low-pressure sintering can realize large-scale production of high-performance cemented carbide. However, the complicated operation steps of the spray conversion method, high process cost, and strict control precision greatly limit the popularization and application of this technology in the preparation of nano-WC powders in China; in the low-pressure sintering of hard alloys, domestic ultra-fine crystal hard The toughness and strength of the quality alloy block/bar material are significantly lower than those of the ultrafine grained carbide high-end products of the same composition in the world.

Break through the key technologies of the series
The cemented carbide team of Beijing University of Technology has broken through a series of key technologies in the development and application of new high-performance cemented carbide materials:
Large-scale preparation technology of nano-WC-Co composite powder with controllable phase and adjustable particle size: The technology originally developed a tungsten-cobalt oxide with carbon as raw material, and synthesizes ultrafine or nano in one step by solid phase in situ reaction. A new approach to WC-Co composite powders. It has the technical advantages of significantly simplified preparation route, short process flow, low equipment and process cost, energy saving and environmental protection. The composite powder phase is pure, the oxygen content is low, the Co content is accurately adjustable within a range of 6-20wt%, and the particle size is accurately controllable at various size levels of ultra-fine (200-500nm) and nano-(70-200nm) scales. It has reached the international quality control standards for ultra-fine and nano-WC powders, and the production cost has been greatly reduced. The composite powder can meet the requirements of various hard alloy sintered materials and protective coatings such as high hardness, high toughness, abrasion resistance and corrosion resistance.
Large-scale preparation technology of high-flow, nanostructured WC-based spray powder: This technology invents a granulation process of spray drying combined with heat treatment to prepare a thermal spray powder that maintains both nanostructures and high fluidity, and fundamentally solves The international technical problem that nano-powder is prone to decomposition and decarburization in the hot spray high-temperature flame flow. Developed a series of nanostructured thermal spray powders such as WC-Co, WC-Co-Cr, WC-, sphericity >95%, bulk density 4.0-5.0g/cm3, flow rate <18s/50g, performance under the same composition conditions The index exceeds the performance of international famous brand spray materials such as Praxair, Inframat and Starck in Germany.
Preparation technology of high-density, high surface quality cemented carbide wear-resistant and corrosion-resistant coating: this technology synergistically adjusts the initial powder composition, agglomeration granulation and thermal spray process, through carbon content design, unique heat treatment process, particle size reorganization, High-performance nanostructured carbide coatings were prepared by thermal spray process parameter combination optimization. The coating has a high density of porosity <0.5%; has a significantly improved surface quality than conventional micro-structured coatings, surface roughness Ra < 0.5m; has high hardness, wear resistance, corrosion resistance and excellent strength Resilience fit. Compared with the micro-structure coating prepared by the Praxair and Inframat spray powders of the United States under the same composition and process conditions, the toughness is improved by 44%, the wear resistance is improved by 28%, and the cavitation resistance is increased by 53%.
Preparation technology of ultra-fine size nanocrystalline cemented carbide block: This technology develops a unique field effect sintering process with slower temperature rise rate, lower pressure in low temperature zone, rapid heating in sections in high temperature zone, higher pressure and no heat preservation. The average grain size is 60-100 nm, a dense nanocrystalline cemented carbide bulk material. The dense nanocrystalline cemented carbide with an average grain size of 60 nm is a cemented carbide sintered material which has been reported to the international minimum to achieve the minimum grain size, and has high hardness and high fracture toughness performance indexes, reaching nanocrystalline hard The international frontier level of alloyed sintered materials.
Preparation technology of high-strength and tough ultra-fine grained cemented carbide sintered material: Based on the low-pressure sintering equipment used by domestic enterprises, the low-pressure sintering process for in-situ synthesis of ultra-fine and nano-composite powders is established. The structure-effect relationship between the microscopic parameters of the nanocrystalline composite phase and the transverse rupture strength breaks through the technical bottleneck of the reverse change of hardness and toughness. Under the premise of maintaining high hardness of the ultrafine grained cemented carbide material, high toughness is obtained. And ultra high breaking strength. Taking WC-12Co as an example, the hardness of the sintered block/bar material is HRA 90-93.0, the fracture toughness is 13.0 18.0 MPa·m 1/2, and the transverse rupture strength is 4800-5200 MPa, compared with the sintered cemented carbide of the same composition. The comprehensive mechanical properties have reached the international advanced level.

Successfully developed high performance cemented carbide products
At present, the cemented carbide team of Beijing University of Technology has undertaken more than 10 cemented carbide research and development projects such as the National 973, 863, Science and Technology Support Program, the National Natural Science Foundation, the Beijing Natural Science Foundation Key Project, and the Beijing New Materials Industry Key Technology Project. Question. He has obtained more than 30 national invention patents in the field of cemented carbide materials and technology, published more than 100 academic papers in well-known journals at home and abroad, and made more than 20 invited reports at international and domestic academic conferences.
The developed high-performance cemented carbide has been tested and certified by internationally renowned hard alloy R&D institutions such as the United States and Germany and the domestic authoritative qualification department. Based on batch stabilization of ultra-fine and nano-hard alloy materials, a series of high value-added cemented carbide coatings and sintered products, such as hydraulic piston coating, induced draft fan blade coating, and acid rolling unit clamping, have been developed. Roll coating, micro-drilling, end mill, high-temperature alloy cutting inserts and other products, used in aerospace, coal mining, oil drilling, thermoelectric energy, steel rolling, precision manufacturing and other important engineering fields.
The ultra-fine and nano-WC-Co composite powder prepared by the team's low-cost, short-flow solid-phase in-situ reaction synthesis technology is used to prepare thermal spray materials, wear-resistant and corrosion-resistant hard alloy protective coatings, high strength and toughness. Key initial materials such as alloy sintered blocks/bars have superior market competitiveness and application prospects in terms of cost performance. The new series of technologies adapt to the current equipment and operation level of the domestic powder metallurgy industry, which is conducive to the transformation of results and popularization and application. It is expected to improve the national productivity of high-performance cemented carbide products and replace expensive imported products, thus promoting the high-end tungsten resources in China. Additional value utilization. The system-based technology chain develops composite manufacturing technology, which can be transplanted and applied in the manufacture and remanufacturing of key components of mechanical equipment involving superhard, tough, wear-resistant and corrosion-resistant conditions, which can extend the use of large-scale equipment. Life expectancy can effectively reduce equipment manufacturing costs and maintenance costs, save resources and energy, and have broad development space.

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