TECHNOLOGIES & APPLICATIONS
EQUIPMENT & TECHNIQUES FOR PULSED ELECTRON-BEAM
TREATMENT OF METALLIC MATERIALS AND ARTICLES
Fig.1. Source of low-energy
high-current electron beams
The proposed equipment and techniques are intended for surface treatment of materials and articles with the purpose to improve their strength, electrochemical, and electrophysical characteristics.
Outline and technical and economic characteristics
The essence of the techniques is that the working surfaces of materials and articles are irradiated many (5-50) with a low-energy, high-current electron beam (LEHCEB) of microsecond duration in modes of surface melting and/or initial evaporation.
To produce the LEHCEB, an unique, having no analog by the combination of parameters, electron source based on an explosive-emission-cathode plasma-filled diode is used. The electron source parameters are as follows:
|Electron energy (max)||50 keV|
|Pulse duration||24 ms|
|Maximum e-beam current||50 kA|
|E-beam diameter||up to 8 cm|
|Pulse repetition rate||0.10.2 Hz|
|Efficiency of electrical energy-to-beam energy conversion||40 %|
|Input power||5 kW|
|Area taken by the system||3 m2|
As a result of fast quenching from melt, metastable structure-phase states are formed in the near-surface layer that are capable of improving the performance of materials and articles. The realization of the techniques proposed is exemplified below.
Lengthening the life of hard-alloy cutting tools. E-beam irradiation of cutting plates made of type BK8, T15K6, and T5K10 type hard alloys increases their life in high-speed cutting 2-5 times (Fig. 2).
Fig. 2. Height of the wear track area at the rear surface of cutting plates made of T5K10 alloy as a function of length of cut before (1) and after LEHCEB treatment (2-4) at a varied energy density. Treated material: Steel 40X.. Cutting conditions: S = 0.14 mm/rev, d = 1.5 mm, v = 300 m/min.
Structure analyses have shown that in contact melting of the carbide phases and the binding phase the grain size of the cobalt binder in the surface layer becomes smaller and the binder becomes additionally doped with tungsten, titanium, and carbon. This suppresses the diffusion of treated material into the cobalt binder under treatment and, hence, increases the life of the tool.
Estimates show that with the productivity of the electron-beam system, the cost of commercially produced tools, investments, operating costs, and the expected profit, the total cost of the equipment will be warranted in one or two years.
of the fatigue characteristics of compressor vanes of gas turbine engines (GTEs). Experiments performed with specimens made of titanium alloys of BT6, BT8M, and other types which simulated the operation of GTE compressor vanes have demonstrated that pulsed melting of the surface of such vanes will give ~20% gain in endurance limit and increase the useful life by about an order of magnitude (Fig. 3). The improvement of fatigue characteristics is related to the smoothing and cleaning of the surface due to its melting and an increase in aluminum content in the near-surface layer.
Fig. 3. Fatigue curves for BT8M alloy specimens in the original state (a) and after irradiation followed by annealing (b).
Smoothing of heat-resistant protective coatings. Nickel-based (e.g, Ni-Cr-Al-Y) heat-resistant protective coatings show a rather high original roughness of the surface. Experiments have demonstrated that pulsed melting of such a coating, owing to a substantial reduction of the surface roughness, may upgrade the coating heat resistance by ~20% (at 1050°C).
Removal of heat-resistant protective coatings. LEHCEB irradiation can be used as an alternative to the routine environmentally hazardous technology for removal of worked-out coatings. Experiments have shown that such coatings can be removed efficiently (~1 mm per pulse) with an electron beam of energy density ~30 J/cm2. On doing this, the structure of the substrate (a heat-resistant nickel alloy) changes not substantially.
Surface alloying. When the beam energy density is 10-20 J/cm2, this offers the possibility of pulsed deposition of a coating and melting the latter together with the substrate. Experiments with Cu-Fe, Al-Fe, Ti-Fe, and other systems have shown that the concentration of the alloying component in the near-surface layer is substantially over its equilibrium concentration. The thickness of the alloyed layers produced is several micrometers, which is an order of magnitude grater than that of alloyed layers produced by ion implantation.
The unique electric-arc evaporator placed in the working chamber makes it possible to deposit various coatings of thickness some tens of microme-ters on the surface of articles and melt the deposited coating together with the substrate material in a unified vacuum cycle, i.e., to accomplish highly efficient surface alloying.
Upgrading corrosion resistance and wear resistance of structural alloys. Experiments with specimens of type D16 and type AD33 aluminum alloys have shown that pulsed melting of the surface layer enhances substantially corrosion resistance. This is related to the fact that the second phase particles originally present in the surface layer are resolved and an oxide film homogeneous in thickness is formed on the surface.
A substantial rise in corrosion resistance due to dissolving of second phase particles is observed as well on pulsed melting of austenitic stainless steels (type 12X18H10T and the like). E-beam irradiation also leads to surface hardening of this type of alloys and to enhancement of their wear resistance.
Upgrading of the electric strength of vacuum insulation. Pulsed melting results in smoothing of the surface of and electrode and in cleaning it of impurities and dissolved gases. When combined with subsequent conditioning of the gap by low-current pulsed discharges, this treatment decreases substantially the prebreakdown current and increases the electric strength of the vacuum insulation.
As compared to the high-power pulsed lasers used for surface thermal treatment, the LEHCEB source features a higher efficiency of conversion of the stored electric energy to the e-beam energy, a higher reliability, and a lower cost. Moreover, an electron beam, as distinct from a laser one, is absorbed by a target almost completely. The sources of high-power ion beams (HPIBs), which are also applied for surface treatment, use high (up to ~1 MeV) accelerating voltages. This, first, makes the high-voltage equipment more complicate and less reliable and, second, poses the problem of radiation protection. (The elevated intensity of X-radiation in HPIB sources is due to the presence of a stray electron load.)
The most similar alternatives to the technique proposed are methods based on the use of pulsed lasers and high-power electron and ion beam sources. The above comparison suggests that the proposed equipment and techniques have a number essential advantages over the alternative ones.
The method for production of LEHCEBs have secured three Russian patents. There are Russian patents and affirmative decisions for patenting the methods for hardening stainless steels, the method for strengthening hard-alloy tools, and the method for surface alloying.
R & D groundwork on the technology for strengthening hard-alloy cutting tools is completed. The technology for upgrading operational characteristics of GTE vanes is being developed. Work on improving the e-beam stability and on making the e-beam source more reliable is under way.
Suggestions for collaboration
Collaboration is suggested to commercialize the developments, to patent them, and to organize joint production and marketing the e-beam system and products to be treated by the techniques proposed. Other forms of collaboration are also possible.
For further information please contacts:
Dmitry I. Proskurovsky,
Professor, Dr. Sci. (Phys. & Math.), Laboratory Head
Phone: (3822) 49-27-09
Fax: (3822) 49-24-10
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