US3650846A - Process for reconstituting the grain structure of metal surfaces - Google Patents

Process for reconstituting the grain structure of metal surfaces Download PDF

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US3650846A
US3650846A US773135A US3650846DA US3650846A US 3650846 A US3650846 A US 3650846A US 773135 A US773135 A US 773135A US 3650846D A US3650846D A US 3650846DA US 3650846 A US3650846 A US 3650846A
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temperature
metal
electron beam
target
energy
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William P Holland
Robert E Hueschen
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General Electric Co
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General Electric Co
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F3/00—Changing the physical structure of non-ferrous metals or alloys by special physical methods, e.g. treatment with neutrons
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S148/00—Metal treatment
    • Y10S148/902—Metal treatment having portions of differing metallurgical properties or characteristics
    • Y10S148/903—Directly treated with high energy electromagnetic waves or particles, e.g. laser, electron beam

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  • ABSTRACT Surface brittle fracture of metals is inhibited by impinging on the surface of the metal an intense pulsed beam of charged particles, neutral particles or radiation while the metal is maintained at a temperature at least above its nil ductility temperature. Energy from the pulsed beam creates high thermal gradients and concomitant high stresses which in turn effect high plastic strain in the surface region and produce a unique fine subgrain structure on and immediately underneath the surface.
  • the treatment enhances the resistance of the metal surface to brittle fracture and results in decreased cracking, delaminating and grain lifting.
  • Missile shield materials, aircraft turbine blades, metal molds, electric switch contacts andX-ray tube targets are but a few of the many examples in which functional degradation results from surface fracturing.
  • the X-ray tube target is a case of unusual severity and serves as a good example.
  • Electron beam power densities at the target surface are typically from 10 to watts per square centimeter.
  • Thermal gradients at the surface may be in the range of 50,000to 100,000 Kelvin per millimeter. The high mechanical stresses created by the high thermal gradients may exceed the strength of the target material and ultimately cause plastic flow and/or brittle fracture at or near the target surface.
  • Distortion of the target surface caused by the fracturing results in a marked decrease of X-radiation output intensity, since the probability of an X-ray photon escaping from the target is markedly less for a rough target surface than for a smooth surface.
  • the power density in the electron beam must be increased to maintain the necessary X-ray output intensity.
  • the higher power densities yield higher thermal gradients which create greater mechanical stresses which in turn cause more fractures to initiate and propagate in the target surface. This cyclic process leads to rapid failure of the X-ray tube.
  • the inhibition of brittle fracture which leads to surface disruption is greatly to be desired in a high power X-ray tube target.
  • brittle fractures can propagate into the subsurface regions of the target and eventually cause the separation of the target into two or more pieces. Prevention of this catastrophic type of failure of an X-ray tube is also greatly to be desired, especially in those targets which are rotating at speeds up to 11,000 r.p.m.
  • FIG. 8 of the drawings shows a typical plot of ductility versus temperature of a metal.
  • the metal is quite brittle; this temperature region is called the brittle range.
  • the metal is quite ductile; this temperature region is called the ductile range.
  • the transition range is also called the ductile-to-brittle transition range in the literature and sometimes the temperature that corresponds with fifty percent ductility on the linear part of the curve is arbitrarily taken as the ductile-to-brittle transition temperature (DBTT).
  • DBTT ductile-to-brittle transition temperature
  • Nil ductility temperature can be defined as that temperature at which a linear extrapolation of the linear, high slope portion of the ductility temperature curve intersects the temperature axis at a point which is marked B.
  • the position of the curve with respect to the temperature axis and the slope of the linear portion depends on several factors such as the type of metal, its degree of cold work, its impurity content, the rate at which stress is applied during testing and others.
  • Ductility may be expressed in several ways. In the curve shown, ductility may be considered as being expressed in terms of percent reduction in cross-sectional area at the fracture interface when fracture occurs. Greater ductility is then indicated by greater reduction of area. Ductility may be expressed in terms of bending angle if a bending test is used.
  • the NDT or point B would shift along the temperature axis, but would, nevertheless, be a rather definite temperature regardless of the magnitude of the curve.
  • Metallurgists have attempted to solve the surface fracturing problem in high temperature applications of metals by increasing the purity of the metal, decreasing the grain size, redistributing impurities, controlling grain orientation, cold working and alloying. All of these techniques tend to lower the nil ductility temperature (NDT), above which metals are increasingly ductile and below which they are brittle.
  • NDT nil ductility temperature
  • the tendency for brittle fracture is reduced by lowering the NDT of a metal because the metal exists in a brittle state for a shorter period during a given heating cycle.
  • the ideal condition is to have the NDT of the metal below any temperature in its operating range.
  • the surfaces of X-ray tube targets are usually made of high atomic weight refractory metals such as molybdenum and tungsten. These metals are particularly susceptible to brittle fracture because they have relatively high NDTs as conventionally processed. Moreover, in the course of normal usage the grain structure of a tungsten X-ray tube target is subject to grain growth, thereby increasing the NDT even further. For this reason, surface recrystallization by a technique such as that suggested in US. Pat. No. 3,158,513 does little to diminish the tendency of the target surface to undergo brittle fracture.
  • X-ray tube targets are used herein for exemplifying the problem of brittle fracture of metals and as a basis for describing the solution achieved by the present invention.
  • a primary object of the present invention is to provide a method for treating metal surfaces that results in inhibition of brittle fracture when the metal is subjected to high thermal stress and that imparts other desirable properties to the metal surface.
  • an object of the invention is to increase the number of subgrains on and near the surface, to reduce impurities, to redistribute residual impurities and to impart a prestressed condition in the surface region.
  • a smaller grain size is shown in the literature to result in a lower NDT, perhaps by as much as 200C. for each tenfold reduction in grain size.
  • the increased number of subgrains may afford a greater surface area and intergranular volume for distributing those impurities that remain after the surface treatment is carried out.
  • the prestressed condition which is believed to result from the increased number of subgrains, is compressive in nature and produces a shear force between the surface layer and the base metal. Upon heating the surface, much of the thermally inducted stress is used up in overcoming the prestressed condition so that the total shear stress is lower than that which occurs in the absence of prestressing. The lesser net final stress means a reduction in the forces that tend to delaminate, lift and fracture the surface grains.
  • the new method is characterized by slowly raising the temperature of a metal object to be treated to its NDT or higher and preferably to a temperature in its ductile range. This is usually done while the metal is in a vacuum ambient although the metal may be in a gas in some cases. Then,
  • the energy may be radiant or particulate as long as it is or converts to thermal energy in reacting with the surface.
  • the energy may be derived from a laser although it is preferable to employ a concentrated electron beam. It is important that the metal be at least above its NDT and preferably in its ductile range before thermal pulses are initiated in order to be sure that brittle fracture will be avoided.
  • the electron beam method there is a cathode spaced from the work piece in the vacuum and the work piece is at a positive potential to accelerate the electrons.
  • the electron beam may be deflected over the surface if desired or the work piece can be moved in the beam or a very powerful beam may cover the whole area to be treated at one time.
  • Beam current intensity may be controlled by modulating the cathode temperature or by use ofa control grid.
  • a pulse or a short series of concentrated electron pulses are impinged on the metal surface.
  • the pulses are followed by an interpulse period after which pulsing is repeated.
  • These alternate periods of high concentrated heating and cooling may be repeated for different lengths of time, depending on the nature of the metal, and generally run from 15 minutes to about 2 hours, as an illustration, although shorter or longer treatment periods are dictated in some cases.
  • the metal is used in its normally expected way and it has the desirable properties which are discussed above.
  • FIG. 1 is a schematic diagram of one type of apparatus that may be used to practice the new metal surface treatment method
  • FIG. 2 is an alternative type of apparatus, with parts omitted, for practicing the new method
  • FIG. 3 is a photomicrograph of a cross section ofa tungsten object which shows the grain and subgrain structure magnified 100 times and has been treated according to the invention
  • FIG. 4 is a photomicrograph of a cross section ofa tungsten X-ray tube target showing its structure at and immediately under its surface after having been treated according to the invention, the structure being magnified 500 times;
  • FIG. 5 is a photomicrograph of a cross section ofa tungsten target magnified 500 times and illustrating the appearance of the structure of the object shown in FIG. 4 before the new surface treatment and as it exists at a depth in the object which is beyond the penetration range of the surface treatment;
  • FIG. 6 is a photomicrograph at a magnification of 500 times, of a surface region cross section of molybdenum object that has been treated according to the invention
  • FIG. 7 is a photomicrograph, at a magnification of 500 times illustrating the structure of the molybdenum object of the preceding figure as it appears at a depth beyond the penetration range of the surface treatment;
  • FIG. 8 is a plot of ductility versus temperature for a representative metal.
  • FIG. 1 shows apparatus set up for treating the upper surface of an X-ray tube target 1.
  • the treatment is intended in this case to cover at least the circular focal track region of the tapered surface on which an electron beam impinges to produce X-rays when the target is installed in a rotary target X-ray tube.
  • the metal target 1 is adapted for being rotated while its surface is being subjected to pulses of electrons in connection with the new treatment.
  • the target 1 is held with a nut on a metal stem 2 which extends from an induction rotor 3.
  • the rotor 3 has internal bearings 4 which journal it to a stationary shaft 5.
  • Target 1, stem 2 and rotor 3 rotate together.
  • the rotor is encircled in a vacuum-tight casing that includes a nonmagnetic cylinder 6 which is sealed at its lower end by a cap 7 and at its upper end by a thin ring 8. The latter is grazed in the bore of a heavy ring 9 which is gasketed and bolted to base plate 10.
  • the base plate has a bell-jar-like enclosure 11 bearing on it with a vacuum-tight gasket 12 intervening. Since X-rays are emitted from the target during the surface treatment, it is desirable to preclude radiation by making enclosure 11 of sufficiently thick metal. Ifenclosure 11 is made of an X- ray transmissive material such as glass, an additional X-ray shield, not shown, should be installed around the apparatus. Refractory metal radiation shield 42 may also be used to surround the target to prevent vacuum gasket 12, and other system components from overheating.
  • the enclosure 11 may also be equipped with devices such as 13 for admitting a sensor, not shown, that measures the temperature of target 1 during treatment and that permits viewing of the target, if desired, when no X-rays are being produced.
  • An X-ray absorbing lead glass window may also be installed in device 13 for making observations during the treatment.
  • the interiors of cylindrical enclosure 11 and the casing around the rotor 3 are evacuable through a pipe 14 which leads to a conventional vacuum system, not shown.
  • the rotor 3 and target are rotated by induction with a stator assembly 15 which is analogous to that used in connection with rotating target X-ray tubes.
  • stator assembly 15 which is analogous to that used in connection with rotating target X-ray tubes.
  • the rotor 3 With 60 Hz. to Hz. applied to the stator, the rotor 3 is generally rotated at about 3,000 to l0,000 r.p.m., accounting for slip during treatment. Other rotational speeds may be used depending on the choice of some other parameters as will appear later.
  • an electron beam is used to preheat and induce high thermally caused stresses in the target surface.
  • the electron beam 16 emanates from a heated filament 17 which is supported from an insulating disk 18 that is mounted on a beam focusing cup 19.
  • This type of electron gun is functionally the same as those that are commonly used in X- ray tubes.
  • Metal focusing cup 19 is supported on metal rods 20 which attach to a support bracket 21. The bracket is held with a nut on an insulator feed-through 22 which is sealed in the base 10 of the apparatus.
  • a bare nickel wire 23 for one side of filament 17 extends through insulator 24 in base 10. The other side of the filament 17 is connected at a point marked 40 to support bracket 21.
  • One side of the filament 17 is connected to the secondary of the stepdown transformer 25 by the use of wire 26 from the atmospheric end of feed-through insulator 24.
  • the other side of filament 17 is connected to the secondary of transformer 25 by use of wire 41 through feed-through insulator 22.
  • the electron beam current 16 is set by the temperature and emissivity of the filament l7 and this is controlled in this example by adjusting a variable resistor 27 in the primary of filament transformer 25.
  • the primary is supplied from an autotransformer 28 which may be energized from a 60Hz. power line through a disconnect switch 29.
  • a relatively high full wave rectified electron accelerating voltage is applied between focusing cup 19 and lower cap 7, and hence, target 1 through the agency of a pair of conductors 30 and 31 extending from the DC output terminals of a rectifier bridge 32.
  • the bridge is supplied with AC from the secondary winding of a step-up transformer 33.
  • the secondary is split at the center to include a milliameter 34 which effectively reads the electron beam current 16.
  • the primary of transformer 33 is supplied from autotransformer 28 through a fastacting relay switch 35.
  • Accelerating voltage may be set by adjusting a tap 36 on autotransformer 28.
  • Switch 35 may be a semiconductor type, such as a silicon-controlled rectifier, which is gated on and off to produce electron pulses for the surface treatment which are of any desired pulse duration and repetition rate.
  • Applied voltage may be read on a voltmeter 37 which is scaled in terms of peak voltage that appears across the secondary of transformer 33.
  • Relay switch 35 is symbolized as being operable by a solenoid coil 38 which is energized intermittently in accordance with the setting of an interval timer 39. Knobs and scales on the interval timer 39 are intended to symbolize that the timer can be set to produce pulses of any desired duration and repetition rate.
  • the interval timer is a type that is well-known to those who are involved in manufacturing X-ray exposure interval timers and need not be explained further.
  • the whole apparatus is analogous in function to an X-ray tube and its power supply which suggests that the new method of surface treating X-ray targets may be carried on in the X-ray tube itself as an adjunct to the usual degassing and seasoning process. It is probably more desirable, however, to perform the surface treating method in the vacuum chamber 11 of FIG. 1 to avoid reduction of tube filament life and to avoid condensation of filament vapors and extracted nongaseous target impurities on the glass X-ray tube envelope,
  • a tungsten surface, prior to treatment in accordance with the new method, will usually have an NDT around 200C. to 500C.
  • Most grades of tungsten are extremely brittle at room temperature which accounts for the bad surface fracture that occurs in use when untreated targets are subjected to rapid heating and cooling cycles which produce damaging high thermal stresses ordinarily.
  • Pure, single crystals of tungsten may have an NDT near room temperature.
  • Molybdenum, which has a body centered cubic crystalline structure like tungsten, has an NDT usually between room temperature and about 150C.
  • Beryllium, a close-packed hexagonal metal usually has an NDT between 300C. and 500C. The NDT and, more commonly, the DBTT of various metals are given in the literature.
  • Target 1 may be raised to above its NDT and preferably in its ductile range with the apparatus in FIG. 1 by heating the target with a low energy electron beam.
  • the accelerating voltage may be set at about 100 kilovolts peak and the current in beam 16 may be set at about milliamperes while target 1 is rotating at 3,000 to 10,000 r.m.p. This relatively small power input will heat rather massive tungsten targets to as much as 500C. in five minutes. Gradual heating in this phase of the process with low beam current avoids producing high thermal gradients and concomitant stresses in the target and avoids surface melting in the focal region of the electron beam.
  • the electron beam current and voltage for preheating will depend in practice on several variables such as the metallurgical characteristics of the object being prepared for treatment and on its mass and elemental constituency. Other methods of preheating may occur to anyone desiring to perform the new method with other types of apparatus.
  • proper beam energy for carrying out the surface treatment can be determined by adjusting the beam current and voltage until a throwaway sample piece exhibits slight surface melting and then reducing the beam energy to about percent of that energy so melting of the pieces in a production run will be avoided. After the pulsing procedure is underway, the target or other object is maintained adequately ductile by the electron pulses.
  • the method involves heating intensely for a very short time and then discontinuing application of the energy that creates the heat for a short time. It is the short heating intervals which create the high thermal gradients and the high stress and plastic strain which effect the change in structure progressively in small volume increments near the surface. Despite the fact that temperature gradients are extremely high, the temperature of the bulk of the metal near the surface does not reach the point where melting occurs.
  • either the electron current density or the duration of the pulses or both may be reduced. External cooling may also be applied. Other alternatives are to defocus the beam or to increase the rate of relative movement between the beam and the object being treated.
  • the crystal reconstitution mechanism is not susceptible to positive proof, one hypothesis is that the unique structure is produced in the following manner.
  • the radiation beam is converted at the surface to thermal energy having a power density approximately 10 watts per cubic centimeter or a power flux of 10 watts per square centimeter.
  • Resulting high temperatures concentrated in small regions of the surface produce huge thermal gradients in the surface. Under these conditions, vacant atom sites are created and there is a prolific production, motion and annihilation of dislocations in the crystals.
  • C concentration of vacant atom sites in a crystal increases with increasing temperature by the relation C A exp (E,/kT) where A is an entropy factor, E, the formation energy of a vacancy, (approximately equal to l ev.), and k is Boltzmans constant 1.38054 X10 ergs/deg. Kelvin.
  • the number of dislocations N that can be produced by the cyclic input of electrons in the metal are directly related to the shear stress developed in the metal.
  • the plastic strain 2 is proportional to the shear stress and depends on thermal gradients and the thermal expansion of the metal:
  • the dislocations are free to move, subject to local stress, and aggregate at elevated temperatures to create pronounced new boundaries within an existing grain or crystal.
  • new vacancies are created which can again diffuse to dislocations, or to the surface or fall into new dislocation loops or other defects.
  • the metal were not held at least above its NDT, the crystals would not deform plastically or ductilely to any significant degree under the rapidly applied high thermal stresses and they would undergo brittle fracture. Brittle fracture delaminates the grains in the surface of an X-ray tube target during treatment just as it does when an untreated target is subjected to cyclic exposure.
  • An important aspect of the new method is to obtain sufficiently high power density and high thermal gradients between the surface and substrate layers.
  • depth of penetration is inversely proportional to the atomic number of the metal and directly proportional to the accelerating voltage. Greater penetration means lesser power density, but one cannot compensate in most cases by increasing beam current or intensity because the correspondingly higher power that results may melt the metal.
  • molybdenum has a lower density than tungsten and is, therefore, penetrated more deeply. If the same power density were used for surface treating both, molybdenum might melt. Thus, a reduced power density must be used for treating molybdenum.
  • Both types of metals are usually treated at a level to maximize the plastic strain without causing brittle fracture and without melting.
  • FIG. 2 An alternative form of apparatus for practicing the new method is shown in FIG. 2.
  • the upper end of the belljar enclosure 11 has an electron gun 46 mounted in it.
  • the gun assembly has horizontal and vertical deflecting plates for sweeping the electron beam 16 over the stationary object 49 being surface treated in the manner that a raster is produced on a television picture tube screen.
  • the beam 16' may be a continuous DC beam because the cyclic heating and cooling of surface regions is effected by instantaneous exposure followed by movement of the sharply focused beam.
  • One may also sweep the beam in one direction and translate the object to distribute the beam spot over the surface. The beam may be swept over the object until the grain structure is converted to a depth that is satisfactory for the intended use of the object.
  • base 10' has a cavity 50 through which cooling water may be circulated by means of inlet and outlet pipes 51 and 52.
  • a connection 14' is provided for evacuating the chamber before and during the surface treatment method.
  • the beam sweeping voltage generators and the power supply are omitted from FIG. 2 because they are conventional.
  • the rates of relative motion between the beam and the treated object and the beam current voltage and current values may be adjusted in both the FIGS. 1 and 2 embodiments so that the power density and exposure intervals are equivalent to each other, in which case, the same results can be produced with each.
  • the thickness of the layer of subgrains depends on the duration of the treatment and is not limited by electron penetration. Generally, sharper rise time of surface temperature in a zone results in more rapid development of subgrains.
  • a recrystallized tungsten X-ray tube target was seasoned conventionally by heating in a vacuum ambient for several hours and then cooled to near room temperature. It was then raised to 800C, which is in its ductile range, and maintained at that temperature by an external power source. It was then exposed to kilovolts peak (KVP), 1,000 milliampere pulses of 0.0 l 2 seconds duration at a repetition rate of two exposures per minute until 7,613 exposures were accrued.
  • KVP kilovolts peak
  • 1,000 milliampere pulses 1,000 milliampere pulses of 0.0 l 2 seconds duration at a repetition rate of two exposures per minute until 7,613 exposures were accrued.
  • the target was rotating at about 3,600 r.p.m.
  • a full wave rectified, threephase, 60 Hz. power supply was used.
  • the electron beam size was about 2 millimeters by 9 millimeters in cross section.
  • a section through the electron focal track area was removed from the target and prepared for a photomicrograph. There is an average of 9,770 subgrains per square millimeter over an average depth of 0.0025 to 0.0035 inch from the surface.
  • the unconverted substrate grain size is 990 grains per square millimeter, almost 10 times as large as the converted layer.
  • the photomicrograph is shown in FIG. 3 herein.
  • a recrystallized tungsten X-ray target was seasoned in the manner of example number one. It was raised to about 800C, which is in its ductile range, and exposed to 80 KVP, 600 milliampere pulses of one-thirtieth second duration at a repetition rate of 20 exposures per minute until 3,000 exposures were accrued.
  • the target was rotating at about 3,600 r.p.m. and a full wave rectified, 60 Hz. single-phase power supply was used.
  • the electron beam was 2 millimeters by 9 millimeters in cross section. A section was taken from the target and a photomicrograph prepared.
  • the surface layer photomicrograph is shown in FIG. 4.
  • the unconverted substrate grain count averages 990 grains per square millimeter as shown in the FIG. 5 photomicrograph.
  • a molybdenum target was seasoned by heating it in a vacuum with a kilovolts peak, 4 milliampere beam for one-half hour. Being at a temperature in its ductile range it was exposed to 55 KVP, 600 milliampere pulses of one-thirtieth second duration at 20 exposures per minute for 1,000 exposures followed by 2,000 exposures at 55 KVP, 575 ma., one-thirtieth second pulses, 20 per minute. Treatment continued at 55 KVP, 550 ma., one-thirtieth second pulses, 20 per minute until 12,000 exposures had accrued. Beam spot size was 2 millimeters by 9 millimeters. A single-phase, 60 Hz., full wave rectified power supply was used.
  • the target was rotated at about 3,600 r.p.m. At an average depth from the surface of 0.007 inch and ranging from 0.0061 to 0.009 inch the count is about 7,300 subgrains per square millimeter as illustrated by the photomicrograph in FIG. 6.
  • the grain count in the unconverted substrate beneath the surface layer is about 1,260 grains per square millimeter as shown in FIG. 7.
  • a nickel sample was placed in the chamber of FIG. 2 which was then evacuated.
  • the DC electron beam was adjusted to 35 KV and 65 ma.
  • the circular beam cross section was 0.020 inches in diameter.
  • the sample was moved at a speed of 0.33 inch per second as the beam was swept over it at 109 Hz. and blanked out on the back sweep.
  • the relative motion between the beam and sample was such that the beam spot exposed any point on the sample about seven times as the object passed under the beam one time.
  • the sample was passed 100 times, thus exposing each point on the sample 700 times.
  • Nickel has a DBTl below room temperature and, therefore, required no preheating.
  • the bottom of the sample was water-cooled to preclude melting and enhance the thermal gradient.
  • a photomicrograph showed that the fine structure was produced in a layer 0.002 inch thick measured from the surface.
  • Another nickel sample was treated in the manner of preceding example No. 4 except that it was passed through the region swept by the beam 50 instead of 100 times. A photomicrograph showed that the time converted structure was produced to a depth of 0.0017 inch measured from the surface.
  • ' may also be varied in dependence on the choice of other parameters. If volume power density is so great as to melt the metal in the beam spot, the accelerating voltage may be reduced to compensate.
  • the power densities are great enough to melt the metal being treated were it not for relative movement between the beam and the sample.
  • the power densities are great enough to melt the metal being treated were it not for relative movement between the beam and the sample.
  • the beam or sample is moved at speeds ranging from 1,000 to 21,000 inches per minute. Electron pulses having short rise and decay times and higher repetition rates seem to be most effective.
  • the photomicrograph designated FIG. 3 typifies tungsten that has been surface treated by the new method.
  • This is a vertical section taken through an X-ray tube target that has been treated in the circular focal track region.
  • the many fine subgrains and additional boundaries occupy a little more lateral space than the fewer original grains which is believed to cause a compressive stress or negative prestressed condition in the surface when the target is cool. When heated, this prestress is first relieved before shear stress is developed between the surface and substrate grains in which case the net final shear is less and there is less tendency for the surface grains to uplift.
  • the new grain structure survives multiple heating and cooling cycles under normal X-ray tube exposure factors.
  • FIG. 4 shows just the surface layer of a treated tungsten target with the subgrains magnified 500 times.
  • the large number of subgrains that are formed from the coarser original grains are evident and one may also see that additional subgrains are beginning to form as revealed by discontinuous dark lines within larger grains near the bottom of the photomicrograph. Grain reconstitution at this greater depth could be completed with additional exposures or pulses under the original conditions.
  • FIG. 5 shows the large substrate grains, at the same magnification of 500, which underlie the surface subgrains of the preceding figure.
  • FIG. 6 is a photomicrograph of the surface layer of a molybdenum target which has been treated by the new method.
  • FIG. 6 is a photomicrograph of a substrate layer in the same target and at the same magnification of 500 times. Additional subgrains may be formed by continuing the treatment as evidenced by the new discontinuous subgrain boundary lines which are just beginning to appear.
  • the ratio of the number of apparent grains in the surface layer to the number in the substrate ranges between about 6 or 10 to l it should be recognized that if the new surface treatment is only carried on until a 2 to 1 ratio is achieved, the benefits of the treatment will be realized to some degree. Moreover, the method can be continued until the ratio is much greater such as 25 or more to l, to obtain even greater benefits in most cases. There are, of course, economic disadvantages to going beyond what is necessary to mitigate brittle fracture to the desired degree in a particular case.
  • FIGS. 4 and 6 indicate that the small grains are formed from larger original grains.
  • Polygonization is the metallurigical term used for the production of subgrains of this nature. As is known in the art, sometimes when a cold-worked metal is heated under suitable conditions, a subgrain structure of this type forms. It is generally characterized by many regions of perfect lattice which are slightly misoriented and at low angles with each other. Polygonization has also been observed during creep testing, which is a low stress method of testing metals at high temperature. Insofar as is known, polygonization has not been produced with thermal pulses heretofore.
  • apparent grain size and subgrain used herein may require further definition in relation to the present invention.
  • Photomicrographs of cross sections of metal objects which have been surface treated according to the new method exhibit what appear to be small grains near the surface and large grains underlying the surface.
  • the term apparent grain size is adopted for both situations.
  • the new surface treatment also reduces the impurities in the surface layer. Intense thermal energy in the beam spot liberates more of the gaseous impurities such as hydrogen and oxygen which may cause poor ductility in metals. Carbon and oxygen, both especially harmful to ductility, are removed by diffusion to the surface and are desorbed. Other impurities are more effectively diffused to the subgrain boundaries by the high thermal energy and they are distributed over a greater volume which results in higher purity grain boundaries, more toughness, greater ductility and a higher melting point in the surface layer.
  • a process for treating a refractory metal surface to make it more ductile and thereby enhance its resistance to brittle fracture comprising:
  • a process for treating a refractory metal surface to make it more ductile and thereby enhance its resistance to brittle fracture comprising:
  • a process for treating a refractory metal surface of a metal object to make the surface more ductile and to thereby enhance resistance of the surface to brittle fracture comprismg:
  • a process for treating a surface of a refractory metal object to make the surface more ductile and thereby enhance resistance of at least a part of the surface to brittle fracture comprising:
  • a process for treating a refractory metal target surface which is intended for production of X-rays in an X-ray tube for increased ductility in the surface so as to increase its resistance to brittle fracture comprising the steps of:

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  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Particle Accelerators (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)
US773135A 1968-11-04 1968-11-04 Process for reconstituting the grain structure of metal surfaces Expired - Lifetime US3650846A (en)

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Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2354518A1 (de) * 1972-11-02 1974-05-16 Gen Electric Target aus einer molybdaenlegierung fuer roentgenroehren zur mammographischen verwendung
US4047984A (en) * 1975-11-17 1977-09-13 Caterpillar Tractor Co. Corpuscular energy beam produced microasperities
DE2823108A1 (de) * 1977-05-31 1978-12-14 Western Electric Co Verfahren zur waermebehandlung von nichteisenmetall
US4159686A (en) * 1975-12-01 1979-07-03 Manufacture Belge D'aiguilles S.A. Process for smoothing the eye of a needle and needle made thereby
US4289544A (en) * 1978-10-16 1981-09-15 United Kingdom Atomic Energy Authority Inhibition of fretting corrosion of metals
US4303137A (en) * 1979-09-21 1981-12-01 Smith International, Inc. Method for making a cone for a rock bit and product
WO1982001016A1 (en) * 1980-09-11 1982-04-01 Sciaky Bros Method and apparatus for surface hardening cams
US4323401A (en) * 1975-11-17 1982-04-06 Caterpillar Tractor Co. Bearing having an array of microasperities
US5306360A (en) * 1991-07-02 1994-04-26 Arvind Bharti Process for improving the fatigue crack growth resistance by laser beam
US5813265A (en) * 1997-12-12 1998-09-29 General Electric Company Balanced electromagnetic peening
RU2164547C1 (ru) * 2000-01-26 2001-03-27 Омский государственный университет Способ поверхностной модификации титановых сплавов
US6436553B1 (en) * 1997-10-14 2002-08-20 Berndorf Band Gesmbh Continuous steel strip for twin presses and method for producing the same
US20060102597A1 (en) * 2004-11-16 2006-05-18 Exponent, Inc. Electron beam welding method and apparatus using controlled volumetric heating
US20070017608A1 (en) * 2005-07-22 2007-01-25 Gkn Sinter Metals, Inc. Laser rounding and flattening of cylindrical parts
US20110232573A1 (en) * 2008-12-09 2011-09-29 Ulvac, Inc. Catalytic Chemical Vapor Deposition Apparatus
US20110272134A1 (en) * 2010-05-06 2011-11-10 Schlumberger Technology Corporation High frequency surface treatment methods and apparatus to extend downhole tool survivability
CN102576668A (zh) * 2009-10-02 2012-07-11 三洋电机株式会社 催化cvd装置、膜的形成方法和太阳能电池的制造方法
CN105442034A (zh) * 2016-01-14 2016-03-30 重庆理工大学 一种改变锆合金表面织构的方法
US20210371323A1 (en) * 2020-05-28 2021-12-02 Fato Automation Technology Co., Ltd Cutting method and equipment of auxiliary packaging containers for testing

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GB2411662A (en) * 2004-03-02 2005-09-07 Rolls Royce Plc A method of creating residual compressive stresses
CN111239154A (zh) * 2020-01-18 2020-06-05 哈尔滨工业大学 一种横向差动暗场共焦显微测量装置及其方法
CN111239155B (zh) * 2020-01-18 2023-06-23 哈尔滨工业大学 一种轴向差动暗场共焦显微测量装置及其方法
CN111239153B (zh) * 2020-01-18 2023-09-15 哈尔滨工业大学 一种轴向差动暗场共焦显微测量装置及其方法
CN111220625B (zh) * 2020-01-18 2023-04-07 哈尔滨工业大学 表面及亚表面一体化共焦显微测量装置和方法
CN113209351A (zh) 2020-02-03 2021-08-06 广州迪克医疗器械有限公司 带加热装置的空气消毒装置

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2968723A (en) * 1957-04-11 1961-01-17 Zeiss Carl Means for controlling crystal structure of materials
US3158513A (en) * 1959-02-26 1964-11-24 Philips Corp Method of manufacturing disc-shaped anodes for rotary-anode X-ray tubes
US3240639A (en) * 1957-01-12 1966-03-15 Lihl Franz Ferro-carbon alloys of improved microstructure and process for their manufacture

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3240639A (en) * 1957-01-12 1966-03-15 Lihl Franz Ferro-carbon alloys of improved microstructure and process for their manufacture
US2968723A (en) * 1957-04-11 1961-01-17 Zeiss Carl Means for controlling crystal structure of materials
US3158513A (en) * 1959-02-26 1964-11-24 Philips Corp Method of manufacturing disc-shaped anodes for rotary-anode X-ray tubes

Cited By (24)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2354518A1 (de) * 1972-11-02 1974-05-16 Gen Electric Target aus einer molybdaenlegierung fuer roentgenroehren zur mammographischen verwendung
US4047984A (en) * 1975-11-17 1977-09-13 Caterpillar Tractor Co. Corpuscular energy beam produced microasperities
US4323401A (en) * 1975-11-17 1982-04-06 Caterpillar Tractor Co. Bearing having an array of microasperities
US4159686A (en) * 1975-12-01 1979-07-03 Manufacture Belge D'aiguilles S.A. Process for smoothing the eye of a needle and needle made thereby
DE2823108A1 (de) * 1977-05-31 1978-12-14 Western Electric Co Verfahren zur waermebehandlung von nichteisenmetall
US4151014A (en) * 1977-05-31 1979-04-24 Western Electric Company, Inc. Laser annealing
US4289544A (en) * 1978-10-16 1981-09-15 United Kingdom Atomic Energy Authority Inhibition of fretting corrosion of metals
US4303137A (en) * 1979-09-21 1981-12-01 Smith International, Inc. Method for making a cone for a rock bit and product
WO1982001016A1 (en) * 1980-09-11 1982-04-01 Sciaky Bros Method and apparatus for surface hardening cams
US5306360A (en) * 1991-07-02 1994-04-26 Arvind Bharti Process for improving the fatigue crack growth resistance by laser beam
US6436553B1 (en) * 1997-10-14 2002-08-20 Berndorf Band Gesmbh Continuous steel strip for twin presses and method for producing the same
US5813265A (en) * 1997-12-12 1998-09-29 General Electric Company Balanced electromagnetic peening
RU2164547C1 (ru) * 2000-01-26 2001-03-27 Омский государственный университет Способ поверхностной модификации титановых сплавов
US20060102597A1 (en) * 2004-11-16 2006-05-18 Exponent, Inc. Electron beam welding method and apparatus using controlled volumetric heating
US20070017608A1 (en) * 2005-07-22 2007-01-25 Gkn Sinter Metals, Inc. Laser rounding and flattening of cylindrical parts
US7416621B2 (en) 2005-07-22 2008-08-26 Gkn Sinter Metals, Inc. Laser rounding and flattening of cylindrical parts
US10000850B2 (en) 2008-12-09 2018-06-19 Ulvac, Inc. Deposition method and method of manufacturing a catalyst wire for a catalytic chemical vapor deposition apparatus
US20110232573A1 (en) * 2008-12-09 2011-09-29 Ulvac, Inc. Catalytic Chemical Vapor Deposition Apparatus
CN102576668A (zh) * 2009-10-02 2012-07-11 三洋电机株式会社 催化cvd装置、膜的形成方法和太阳能电池的制造方法
US20110272134A1 (en) * 2010-05-06 2011-11-10 Schlumberger Technology Corporation High frequency surface treatment methods and apparatus to extend downhole tool survivability
US8555965B2 (en) * 2010-05-06 2013-10-15 Schlumberger Technology Corporation High frequency surface treatment methods and apparatus to extend downhole tool survivability
CN105442034A (zh) * 2016-01-14 2016-03-30 重庆理工大学 一种改变锆合金表面织构的方法
US20210371323A1 (en) * 2020-05-28 2021-12-02 Fato Automation Technology Co., Ltd Cutting method and equipment of auxiliary packaging containers for testing
US12049421B2 (en) * 2020-05-28 2024-07-30 Fato Automation Technology Co., Ltd. Cutting method and equipment of auxiliary packaging containers for testing

Also Published As

Publication number Publication date
GB1285203A (en) 1972-08-16
DE1952854A1 (de) 1970-05-06
FR2022546A1 (de) 1970-07-31
AT301291B (de) 1972-08-25

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