High Power Electron Beam Technology
This year’s conference was held at Harrah’s in Reno, Nev., on the very site where the conference was born in 1983. Participants came from Bulgaria, Canada, France, Germany, England, Estonia, Japan, Kazakhstan, Russia, the Ukraine and the United States.
History of Electron Beam TechnologyMathias Neumann of von Ardenne Anlagentechnik, the leading supplier of EB-powered systems, started with a presentation that reviewed 50 years of electron-gun and melting-furnace progress. Early electron guns arrived in late 1950s. The first electron beam melting furnace for reactive and refractory metals, 45 KW, was built in 1959. A milestone EB melting furnace of 1.2 megawatts of power was built in 1964-66. Their underlying principles still govern today’s prevailing technology. Von Ardenne’s guns are the most powerful EB guns available today, and they are used in a wide range of operations, including melting, coating and heat treating. Fig. 1 shows the EH800/50, which is capable of delivering 800 KW of power. This gun is the workhorse of all the most recent large EB melting installations.
PresentationsLen Korzon of TIMET, Morgantown, Pa., the largest EB melting installation in the world, with a total capacity of 20 megawatts of power delivered by five furnaces, reported on the design of the two newest furnaces, each powered by six 825-KW guns, comparing the design to existing furnaces. These two chamber furnaces can cast slabs as large as 26x65x165 inches, up to 50,000 pounds. Fig. 2 shows a schematic of the newest furnaces.
J.P. Bellot from the University of Nancy next presented results of studies including modifying and simulation of the thermal behavior of Ti6Al4V electrode in the electron beam remelting process. The work conducted in a 100-KW ALD Vacuum Technologies-built furnace focused on studying losses of alloy elements. Lower melting rates reduce Al losses.
Elena Koleva from the Institute of Electronics, Bulgarian Academy of Science in Sofia followed with a presentation on the analysis of inclusion removal. She began with the theoretical aspects of the process. The influence of beam power density and its distribution on the molten pool was investigated with optimization of the EBM regime. Simulation application based on a statistical approach in addition to results of experimental measurements provide the possibility to predict impurity content in the refined ingot with changes in process conditions. Some inclusions change concentration while others do not. The changes depend on power, flow rate and time.
EB Safety PanelNext, a panel chaired by Douglas Hughes of Reading Alloys with N. Dagle of Zak, R. Dorvel from H.C. Starck and L. Heinz of Heinz Engineering discussed EB Melting Safety. Preventative maintenance, OSHA hazards, communication standards, job-safety behavior, job-safety analysis and risk assessment were discussed. Though EB melting is a very dangerous process with high voltage, high temperature, X-rays and vacuum involved, there have been virtually no accidents in the industry.
S. Ladokhin of the Physico Technical Institute of Metals and Alloys of the National Academy of Science of Ukraine was the next presenter. He had results of studies of EB melting Ti-Al and TiNi Alloys. The technology proposed includes introduction of Al and Ni, while electromagnetically stirring, in the finishing stages of melting alloys with Al concentration from 14-17% and 32-34% and TiNi alloys with Ni concentration of 55%. The investigation of the structure and hardness show the possibility of regulation of these characteristics by modifying the EB heating regime without changing the chemical composition. Properties of the alloys investigated indicate that the alloy permits casting of shaped parts.
Only highlights of a paper by A. Gladkov and V. Chemiavsky were given, as the speakers could not obtain visas to attend the conference. The paper was devoted to Zr and Nb production in an EB furnace with electromagnetic stirring (EMS). Zr ingots of 290 mm diameter and Nb ingots of 200 mm diameter were cast. EB melting with EMS made possible reduced grain-size ingots while in Nb EB melted with EMS reduced oxygen content to 0.16% and nonmetallic inclusions from 0.5 down to 0.19%.
V. Arzhakova of the AA Bochvar All Russian Institute of Inorganic Material followed with a paper titled “Features of Melting and Molding Ingots of Hafnium.” Physical and foundry properties of Hf and the areas of its use were discussed. The metal is produced by both calcium reduction and the Van Arkel process method. In the EB melting furnace, Fe, Si, Mg, Ni and to a lesser degree O and C are removed while vacuum-arc melting does not significantly affect its composition. Comparing analysis and hardness of ingots after EB and vacuum-arc melting show that EB melting of Hf with installations of intermediate capacity is the optimum process for production of metal of high quality.
The presentation by I. Grosse of Perryman described the company’s new 2.4-megawatt EB Cold Hearth Refining (EBCHR) installation (Fig. 4), which is powered by three 800-KW von Ardenne guns for processing Ti to be converted to large bar and hot-rolled products and will start with 30-inch-diameter ingot, 180 inches long. He also discussed the pioneering utilization of dry-compression screw-type vacuum pumps (Oerlikon Leybold’s ScrewLine SP630) in the EBCHR furnace. These pumps replaced conventional piston pumps with similar capacities. Although more expensive, they offer many advantages (Table 2).
Titanium MarketThe next paper by D. Esser of ALD was a slight departure from the essentially technical vein of the conference. It instead concentrated on the following markets for Ti and its continued growth in demand.
- Aerospace, including commercial and military
- Industrial, including everyday chemical
- Secondary and emerging markets, including medical comprising devices, implants and tools
- Consumer markets, including sports and leisure
Niobium MarketThe next paper was by D. Proch and titled “Niobium Demand for Superconductor (SC) Accelerator Systems.” These types of systems have proven superior to conventional, conducting-design accelerator concepts. The pioneering applications in storage rings for high-energy physics accelerators were followed by projects at Oak Ridge and Desy. There are also several operating projects related to the acceleration of heavy ions or protons.
Superconducting RF-accelerator systems are built from niobium. High-purity Nb is required for this application, where contamination must stay at or under the level of 10 ppm. In the technical specifications, the material is defined at Residual Resistance Ratio RRR300. This is an indirect measure of the purity by measuring electrical resistance at room and cryogenic temperatures.
This high purity of Nb has implications for the vacuum quality of the melting facilities and the number of melts. The bulk of the Nb material is bought in the form of small-grain sheets. Recently, there is interest in large-grain and even single-crystal sheet. The unsolved challenge is to develop an operating cycle of the melting facility with high yield of large-grain and even single-crystal structure.
At present, the largest SC accelerator project under construction is the XFEL at Desy. Nb demand is around 30 tons over three years starting in 2009. Major upgrades of existing installations, like the CEBAF lineac at Jefferson Laboratory, Newport News, are increasing demand by 2 to 3 tons during 2009-2013. At SNS at Oak Ridge, 1.5 tons during 2010 are approved. Conceptual- and advanced-design studies are on the way for the international linear collider (ILC) – 500 tons in 2015-2022. These are truly notable increases in demand for Nb.
C. Punshon followed with a paper on equipment and applications of reduced-pressure EB technology for melting and surface modification with active gases. EB welding, melting and surface treatment has been carried out using vacuum chambers and relatively good vacuum (10 mbar). The development of high-power (100 KW), reduced-pressure (1 mbar) systems led to the possibility of using local sealing and mobile vacuum technology as well as the possibility to introduce inert or active gases employed to modify mechanical and metallurgical properties of materials.
C. Metzner of the Fraunhoffer FEP, Dresden, next discussed new applications for PVD by electron beam evaporation for photovoltaic-concentrated-solar and high-efficiency lightning. Functional layers in thin-film photovoltaic can be deposited with high productivity on large-area substrates by electron beam evaporation. Potential applications are the intrinsic layer in silicon-based solar cells, electrically insulating layers for monolithic circuitry of solar cells and metallic layers as electrode on silicon-wafer cells. Some of these layers can be up to several micrometers and dictate for coating with high rates. Plasma activation of vapor is an effective method for densification of the layer structure. Single cells must be separated from the large coated area for circuitry on the substrate, and structuring by electron beam micromachining can also be used.
EBPVD CoatingThe next two papers were also devoted to EBPVD coating. The first, by J. Singh from Penn State University’s Applied Research Laboratory, was titled “Nano Structured Component Fabrication by Electron Beam Physical Vapor Deposition (EBPVD).” It demonstrated the versatility of EBPVD in engineering materials with controlled microstructure and microchemistry. In the form of coatings, EBPVD technology is being explored in forming precision net-shaped components for many applications, including space, turbine, biomedical and automotive. Simultaneous co-evaporation of multiple ingots of different compositions in the high-energy EBPVD chamber has brought considerable interest in the architecture of functional graded coatings, nano-lamination coatings and designing new structural material that could not be produced economically by conventional methods such as various metallic and ceramic coatings, including carbides nitrides of Ti, Hf, TiBeN and oxides of zirconia. Fig. 5 shows an SEM of a fractured surface of nano-layered ceramic produced by evaporation, Fig. 6 shows recoated graphite cores produced simultaneously by EBPVD and Fig. 7 shows a graphite nozzle produced by EBPVD.
Diffusion barriers are employed between the bond coating and the thermal barrier. This is usually a thin AlO ceramic zone on top of the bond coating, and it is an ideal condition for applying thermal-barrier coatings using the EBPVD machine by oxidizing surface aluminum of either the MCrAlY or the Pt Aluminide. The thermal-barrier coatings (TBC) are the final layer that protects the turbine components from the high temperature. This paper-thin coating allows high gas temperatures – exceeding by 100-150°F the melting point of the Ni-base-superalloy component, yttrium stabilized ZrO – was proven to be the ideal material for these TBCs. The coatings serve both aircraft and stationary power engines. Fig. 8 shows a family of EBPVD systems, and Fig. 9 shows the process chamber of a PVD system. ALD has been very active in the development of this technology and today is the leading supplier of EBPVD systems for this task. High-rate electron beam has been superior to all other coating techniques. IH