Not long ago, from the Beijing University of Technology, we learned that for the ultra-fine, nano-carbide field of international development trends, China's development status and bottlenecks, with the support of a number of scientific research projects in the country and Beijing, the National Outstanding Young Scientists Fund The recipient, Beijing High-level Innovation and Entrepreneurship Program 100 million engineering leader Professor Song Xiaoyan, responsible for the Beijing Institute of Technology hard alloy team, after more than 10 years of basic research and technological development work, established ultra-fine, nano-carbide The series of new technologies for large-scale preparation and engineering applications have developed high-value-added hard alloy materials and products, which are being promoted and applied.
Opportunities and Challenges of Nano-Carbide Materials
After more than 60 years of development, China's cemented carbide industry has become the largest country in the world for cemented carbide. According to statistics of Cemented Carbide Branch of China Tungsten Industry Association, the annual production of domestic hard alloys in the past three years (2012-2014) is between 22,000 and 25,000 tons, accounting for more than 40% of the world's total output. China's cemented carbide production and consumption accounted for the world's first, but not the strong country of the cemented carbide industry. Compared with internationally renowned cemented carbide enterprises such as Sandvik of Sweden, Kennametal of the US, Inframat of the United States, KF of Germany, Plansee of Austria, Forecreu of France, and Toshibatungaloy of Japan, the gap in the cemented carbide industry in China is reflected in the lack of high-end products and the lack of breakthroughs in key technologies. In recent years, the field of ultra-fine and nano-hard alloys has rapidly developed internationally.
In view of the international development trend in the ultra-fine and nano-carbide fields and the status quo and bottlenecks in China's development, with the support of a number of scientific research projects in the country and Beijing, the winners of the National Outstanding Youth Science Fund and high-level innovation and entrepreneurship in Beijing Planning for the 100 million engineering leader Professor Xiaoyan Song, who is responsible for the hard alloy team of Beijing University of Technology, after more than 10 years of basic research and technological development work, established a series of large-scale preparation and engineering application of ultra-fine, nano-size hard alloys. Technology, in close cooperation with domestic cemented carbide companies, has developed high value-added carbide alloy materials and products and pushed them into high-end industrial applications.
With the rapid development of modern manufacturing and the advent of various new types of difficult-to-machine materials, increasingly stringent requirements have been placed on the quality and performance of hard alloy tooling products. For WC-based cemented carbides, ultrafine grain (average grain size 200-500 nm) and nanocrystalline grain (average grain size) are compared with conventional coarse grain (usually referred to as average grain size 13 μm) cemented carbide. Dimensions below 200 nanometers. Carbide has significantly improved hardness, wear resistance and fracture strength. It is an advanced material with high efficiency and high precision in drilling, cutting, milling and other high-end processing technology.
From the late 1990s to the beginning of this century, nano-hard alloy materials have emerged a variety of new methods of preparation, followed by years of development of nano-structure, fine-characterization and comparative analysis of mechanical properties, and then to the scale of nano-carbide in recent years Chemical preparation and industrial applications have become the focus of research and development that has been highly valued and embodying cutting-edge competitiveness in the world. During this period, it has experienced the survival of the fittest among many methods for the preparation of nano-size hard alloys. For example, sol-gel/coprecipitation method, plasma method, etc. are limited to the laboratory micro-synthesis of nano-WC powders; discharge plasma sintering, ultra-high pressure consolidation, etc. are limited to the preparation of nano-polycrystalline materials with simple shapes and small three-dimensional dimensions; The spray conversion method can batch synthesize nano-WC powders; low-pressure sintering can achieve large-scale production of high-performance carbides. However, the complicated operation procedures, high process costs, and harsh control precision of the spray conversion method have greatly limited the promotion and application of nano-WC powders prepared in China. In terms of low-pressure sintering of hard alloys, domestic ultra-fine crystals are hard. The toughness, strength, and other performance indicators of the bulk alloy block/bar stock are significantly lower than those of ultra-fine grained carbide high-end products of the same composition in the world.
Breakthrough series of key technologies
The cemented carbide team of Beijing Polytechnic University broke through a series of key technologies in the development and application of new high-performance carbide materials:
Nano-scale WC-Co composite powders with controllable phase and adjustable particle size: This technology was originally developed to use tungsten cobalt oxide as a raw material to synthesize ultra-fine or nano-sized nanocrystals using solid-state in-situ reaction. New Way of 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 has a pure phase and low oxygen content. The Co content can be accurately adjusted within a wide range of 6-20 wt%, and the particle size can be accurately controlled at various sizes in the ultra-fine (200-500 nm) and nano (70-200 nm) scales. The current international quality control standards for ultra-fine and nano-WC powders have been achieved, while production costs have been greatly reduced. The composite powder can meet the requirements for the use of various hard alloy sintered materials and protective coatings with high hardness, high strength and toughness, wear resistance, and corrosion resistance.
High-flow, nano-structured WC-based spray powder preparation technology: This technology invented a spray drying and heat treatment granulation process to prepare a thermal spray powder that maintains both nanostructure and high flowability, fundamentally solving the problem. Nano-powders are prone to decomposition and decarburization in thermal spray flames at high temperature. Developed WC-Co, WC-Co-Cr, WC-series nanostructured thermal spray powders with sphericity> 95%, bulk density 4.0-5.0g/cm3, flow rate <18s/50g, performance under the same composition The indicators exceeded the performance of international branded spray materials such as Praxair, Inframat and Germany Starck.
Preparation of high-density, high-surface-quality carbide wear-resistant corrosion-resistant coatings: This technology is coordinated with the initial powder composition, agglomeration granulation, and thermal spraying processes, through the design of carbon allocation, unique heat treatment process, and particle size recombination. The combination of thermal spray process parameters optimization, etc., to prepare a high-performance nanostructured hard alloy coating. The coating has a high density of porosity <0.5%; a significantly higher surface quality than the conventional micro-structured coating, surface roughness Ra <0.5m; with high hardness, wear resistance, corrosion resistance and excellent strength Toughness fits. Compared with the micro-structured coating prepared under the same composition and process conditions using the United States Praxair, Inframat spray powder, the toughness increased by 44%, the wear resistance increased by 28%, and the cavitation resistance increased by 53%.
Preparation technology of ultrafine size nanocrystalline hard alloy bulk material: This technology develops a unique field effect sintering process in which the temperature rising rate in the low temperature zone is relatively low, the pressure is high, the high temperature zone is rapidly heated in sections, the pressure is large, and the heat is not kept. The average grain size is 60-100 nm, dense nanocrystalline carbide bulk material. The dense nanocrystalline carbide with an average grain size of 60 nm is the hard alloy sintered material with the smallest grain size reported so far in the world, and it also has a high hardness and high fracture toughness performance index, achieving nanocrystalline hardness. Quality alloy sintered materials at the international frontier level.
Preparation technology of high-strength ultra-fine grained tungsten carbide sintered materials: This technology is based on the low-pressure sintering equipment currently used by domestic companies, and establishes a low-pressure sintering process for the in-situ synthesis of ultra-fine, nano-composite powder heat shrinkage characteristics, and proposes ultra-fine grain The structure-activity relationship between the microstructure parameters and the transverse rupture strength of the nanocrystalline composite structure breaks the technical bottleneck of the reverse change of hardness and toughness, and obtains high toughness on the premise that the ultra-fine crystal carbide material maintains high hardness. And ultra-high breaking strength. Take WC-12Co as an example, the hardness of the sintered block/bar stock is HRA 90-93.0, the fracture toughness is 13.0 18.0MPa·m1/2, and the transverse rupture strength is 4800-5200MPa, compared with the same composition sintered cemented carbide, The comprehensive mechanical properties have reached the international advanced level.
Successfully developed high-performance carbide products
At present, the Beijing University of Technology hard alloy team has undertaken more than 10 projects such as National 973, 863, Science and Technology Support Program, National Natural Science Foundation, Beijing Municipal Natural Science Foundation Project, Beijing Key Technology Research Project for New Materials Industry, etc. Question. He has obtained more than 30 national invention patents in the field of hard alloy materials and technology, and has published more than 100 academic papers in well-known domestic and foreign journals, and has made more than 20 invited lectures at international and domestic academic conferences.
The developed high-performance cemented carbide has been recognized by the United States, Germany and other internationally recognized hard alloy research and development institutions and domestic authoritative qualification departments. Based on the batch stabilization of ultra-fine and nano-carbide materials, a series of high-value-added hard alloy coatings and sintered products have been developed, such as hydraulic piston coating, induced draft fan blade coating, and acid mill clamping. Roller coatings, micro drills, end mills, high temperature alloy cutting inserts and other products are used in aerospace, coal mining, oil drilling, thermoelectric energy, steel rolling, precision manufacturing and other important engineering areas.
The ultra-fine and nano-WC-Co composite powders prepared by a team-developed low-cost, short-flow solid-phase in-situ reaction synthesis technology are used to prepare thermal spray materials, wear-resistant and corrosion-resistant hard alloy protective coatings, and high-strength hard tough materials. Key initial materials such as alloy sintered blocks/bars have superior market competitiveness and application prospects in terms of their cost performance. The new series of technologies adapts to the current equipment conditions and operating levels of the domestic powder metallurgy industry, which is conducive to the transformation of results and popularization and application. It is expected to increase the national production rate of high-performance carbide products and replace expensive imported products, thus promoting the high-end tungsten resources in China. Added value use. The development of composite manufacturing technology based on the technology chain of the system can be applied in the manufacture and remanufacturing of key components of mechanical equipment involving super-hard, tough, wear-resistant, corrosion-resistant and other working conditions, which can extend the use of large-scale equipment. The longevity can effectively reduce equipment manufacturing costs and maintenance costs, save resources and energy, and has broad space for development. (â–¡ Wang Bin)
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