DOE OSTI2012
High-temperature treatment processes (such as nitriding, carburizing, and boronizing) are well-established and used widely by numerous industrial sectors to achieve superior mechanical and tribological properties on all kinds of engineering components made out of ferrous materials. Unfortunately, these traditional processes are very slow and energy intensive, and they produce large amounts of CO 2 emissions and liquid/solid wastes to deal with during and after each process run. From economic and environmental points of views, it is highly desirable to develop and implement novel surface treatment technologies that are quick, cheap, clean, and energy efficient. The main objective of this project was to develop an industrial-scale ultra-fast boriding process that realizes all of these desirable attributes. The other objectives of the project were to demonstrate the superior performance, properties, and durability of borided surfaces under relevant test conditions and to transfer optimized technology to industry for large-scale practice. Major research activities included process design, modeling, product optimization, and scale-up. This project has achieved all of its stated objectives, and the industrial-scale boriding process has been successfully transferred to industry. Specifically, all of the original tasks have been completed, and the milestones have been met by scaling up from a small proof-of-concept system (which could only handle about 0.25 kg melt) to a commercial-scale boriding unit that can handle up to 4,000 kg melt. Mechanical and tribological testing of borided test samples and industrial parts has also been carried out, and their superior performance over a broad range of test conditions has been validated. With the large-scale, ultra-fast boriding process, we could achieve thick, hard, and uniform boride layers on all kinds of steel components, even after only 5 min of treatment time. We could also attain excellent uniformity in thickness over the entire exposed surfaces — even in the very sharp corners or interior sections of odd-shaped workpieces. Boriding of numerous nonferrous materials was also demonstrated, and thick boride layers (up to 300 µm in thickness) were achieved on their outer surfaces. With the use of a large-scale boriding unit at Argonne National Laboratory, our research team has successfully treated large numbers of industrial components in a batch-to-batch operation without creating any in-house gaseous emissions or producing solid and/or liquid wastes. With the use of this large unit, our team achieved surface hardness values of 15 to 45 GPa, depending on the type of metal or alloy being treated. The thick boride layers attained on steel components consisted of FeB, Fe 2 B, and Fe 3 B phases, and their hardness values ranged from 16 to 22 GPa. Layers consisting of Fe 2 B phase alone are also possible with this process, and in the case of nonferrous materials. Overall, because of the much superior property and performance improvements in treated products, much lower energy consumption, and nearly zero environmental waste and emissions, the demonstrated boriding technology may find broad applications in many cross-cutting industries. Mechanical wear, abrasion, erosion, corrosion, and scuffing are often life-limiting factors in mechanical systems that are used in manufacturing, transportation, aerospace, agricultural, earth-moving, and mining equipment; but the machine components treated by ultra-fast boriding can effectively prevent such degradations. In this project, the ultra-fast boriding was proven to be most ideal for the treatment of iron and many other ferrous alloys, like stainless steel. We have shown through our experimental studies that our method can also be used for the treatment of many nonferrous metals and alloys. In the case of superalloys and Ni 3 Al intermetallic materials, more than a 300-µm thick boride layer can be achieved with our boriding furnace within 15 to 30 min (which results in five times the hardness of the base materials). Pre-carburized steels and nonferrous alloys can also be treated by the new boriding technique. Overall, very thick (more than a quarter millimeter) and hard surface layers produced by ultra-fast boriding are expected to have a positive impact on the performance and durability of all types of machine components that are subject to corrosive, erosive, abrasive, and adhesive wear. Since the focus of our project was primarily on the large-scale boriding of ferrous materials, in this report, we will broadly cover the results from various ferrous materials that were used in our experiments. Another transformational feature of ultra-fast boriding is that it does not create any greenhouse gas emissions or solid and/or liquid wastes to deal with during or after the treatment; hence, it is an ultra-green technology (no need for expensive waste disposal and/or treatment facilities). It may eliminate the use of natural gas and other carbon-based fuels as the primary energy source in the heat treatment industry (which is the most common practice at present), thus, minimizing the CO 2 , NO x , CO, and SO x emissions that are generated in large quantities by current heat treatment practices. The main ingredient used during boriding is borax, which is a natural mineral. Our demonstrated and scaled-up technology can now be used in a wide range of manufacturing and transportation applications. It can deliver thick and uniform boride layers of more than 200 µm in steels, if needed, over the entire exposed surfaces — even in the very sharp corners or interior sections of workpieces (which are typical of gears, tools, pipes, and other components). Beneath the distinct boride layers is an equally-thick boron diffusion layer or zone, which is comparable to the diffusion zones achieved by carburizing and nitriding processes. In the cases of traditional boriding, nitriding, and/or carburizing methods, achieving such layer thickness and case depths would have taken several hours, and these surfaces would not have achieved the same levels of hardness and other desirable properties as they do with ultra-fast boriding. Some of the key stakeholders of ultra-fast boriding technology include companies that are active in heat-treatment, thermal-diffusion, and hard-coating processes; metal-forming, machining, and other manufacturing processes; and technologies related to transportation (including original equipment manufacturers for autos), mining and oil exploration, agricultural and heavy equipment. Bodycote Thermal Processing was the cost-sharing industrial partner and licensee in this project. They also provided test components and technical and commercial information pertaining to industrial components that are most suitable for ultra-fast boriding. Bodycote also coordinated some of the field tests and metallurgical examinations. Overall, ultra-fast boriding is a transformational technology that can complement, if not replace, many of the energy- and carbon-intensive surface treatment processes that are in use today, such as conventional boriding, carburizing, nitriding, carbo-nitriding, and physical and chemical vapor deposition. In our project, the developed technology was scaled-up and proven to be an ultra-green, ultra-efficient process that can drastically reduce costs, increase productivity, and improve the performance and reliability of machine components used in cross-cutting industrial applications.