Claims
- 1. A method of making a composition having permanent magnet properties at room temperature comprising
- preparing a melt of a composition comprising, on an atomic percentage basis of the total composition, 0.5 to 10 percent boron, 10 to 50 percent of one or more rare earth elements where neodymium or praseodymium or a mixture thereof constitutes at least 60 percent of the total rare earth element content, and one or more transition metal elements taken from the group consisting of iron and mixtures of iron and cobalt where iron constitutes at least 60 percent of the total transition metal, such molten composition being susceptible to being rapidly cooled to solidification over a determinable and controllable range of cooling rates within which range a series of fine grained crystalline products are formed that respectively display (a) values of magnetic coercivity that continually increase toward a maximum value and decrease from such value as the cooling rate is increased, and (b) values of magnetic remanence that increase over at least a part of such range as the cooling rate is increased, and
- continually rapidly cooling portions of the melt by ejecting them onto a moving quench surface to form a fine grained crystalline product while controlling the cooling rate within said cooling range by a method comprising controlling the rate of movement of such surface such that the product has a desired combination of magnetic coercivity and remanence.
- 2. A method for making a composition having permanent magnet properties at room temperature in accordance with claim 1 where the melt is rapidly cooled by continually expressing a portion of the melt through an orifice onto a quench surface of a spinning wheel and the cooling rate is controlled by a method comprising controlling the velocity of the quench surface of the spinning wheel to form a fine grained product having an average crystal size in the range of 20 to 400 nm.
- 3. A method for making a composition having permanent magnet properties at room temperature in accordance with claim 1 where the melt composition comprises 10 to 20 atomic percent of one or more rare earth elements taken from the group consisting of neodymium and praseodymium.
- 4. A method for making a composition having permanent magnet properties at room temperature in accordance with claim 1 where the melt composition consists essentially of 0.5 to 7 atomic percent boron, 10 to 20 atomic percent of one or more rare earth elements taken from the group consisting of neodymium and/or praseodymium, and one or more transition metal elements taken from the group consisting of iron and mixtures of iron and cobalt where iron constitutes at least about 60 atomic percent of the total transition metal.
- 5. A method for making a composition having permanent magnet properties in accordance with any one of claims 1, 3 or 4 where the cooling rate is controlled within said cooling range to form a product having a fine grained crystalline microstructure of average grain size less than about 50 nanometers, said product being suitable for annealing to increase its magnetic remanence and coercivity.
- 6. A method of making a composition having permanent magnet properties at room temperature comprising
- preparing a melt of a composition comprising, on an atomic percentage basis of the total composition, 0.5 to 10 percent boron, 10 to 50 percent of one or more rare earth elements where neodymium or praseodymium or a mixture thereof constitutes at least 60 percent of the total rare earth element content, and one or more transition metal elements taken from the group consisting of iron and mixtures of iron and cobalt where iron constitutes at least 60 percent of the total transition metal, such molten composition being susceptible to being rapidly cooled to solidification over a determinable and controllable range of cooling rates within which range a series of fine grained crystalline products are formed that respectively display (a) values of magnetic coercivity that continually increase toward a maximum value and decrease from such value as the cooling rate is increased, and (b) values of magnetic remanence that increase over at least a part of such range as the cooling rate is increased, and
- continually rapidly cooling portions of the melt by ejecting them onto a moving quench surface to form a fine grained crystalline product while controlling the cooling rate within said cooling range by a method comprising controlling the rate of movement of such surface to form a product having a fine grained crystalline microstructure of average grain size less than about 50 nanometers, said product being suitable for annealing to increase its magnetic remanence and coercivity, and thereafter
- heating the product at a temperature to cause crystal growth for a period of no more than 30 minutes to form a product having an average grain size no greater than about 400 nanometers in largest dimension and thereafter rapidly cooling the product.
BACKGROUND
This is a division of application Ser. No. 508,266 filed on June 24, 1983, now abandoned, which is a continuation-in-part of U.S. Ser. No. 414,936, filed in the Unites States on Sept. 3, 1982.
U.S. Ser. No. 274,070, entitled "High Coercivity Rare Earth-Iron Magnets", assigned to the assignee hereof, discloses novel magnetically hard compositions and the method of making them. More specifically, it relates to alloying mixtures of one or more transition metals and one or more rare earth elements. The alloys are quenched from a molten state at a carefully controlled rate such that they solidify with extremely fine grained crystalline microstructures as determinable by X-ray diffraction of powdered samples. The alloys have room temperature intrinsic magnetic coercivities after saturation magnetization of at least about 1,000 Oersteds. The preferred transition metal for the magnet alloys is iron, and the preferred rare earth elements are praseodymium and neodymium. Among the reasons why these constituents are preferred are their relative abundance in nature, low cost and inherently higher magnetic moments.
I have now discovered a new family of magnets that have markedly improved properties compared with my earlier discovery. It is an object of the subject invention to provide novel magnetically hard compositions based on rare earth elements and iron with extremely fine grained crystal structures having very high magnetic remanence and energy products and Curie temperatures well above room temperature. Another object is to create a stable, finely crystalline, magnetically hard, rare earth element and iron containing phase in melted and rapidly quenched alloys so that strong permanent magnets can be reliably and economically produced.
A more specific object is to make magnetically hard alloys by melting and rapidly quenching mixtures of one or more rare earth elements, one or more transition metal elements and the element boron. Such alloys exhibit higher intrinsic coercivities and energy products than boron-free alloys. A more specific object is to make such high strength magnet alloys from iron, boron and lower atomic weight rare earth elements, particularly neodymium and praseodymium. Another object is to make these magnetically hard alloys by melt spinning or a comparable rapid solidification process.
Yet another object of the invention is to provide a novel, stable, rare earth-iron-boron, intermetallic, very finely crystalline, magnetic phase. A more particular object is to control the formation of such phase so that the crystallite size appears to be commensurate with optimum single magnetic domain size either by a direct quench or overquench and subsequent heat treatment. Another particular object is to either directly or indirectly create such optimum domain size crystallites in a melt spun or otherwise rapidly quenched RE-Fe-B alloy, particularly a neodymium or praseodymium-iron-boron alloy.
It is a further object to provide a suitable amount of boron in a mixture of low atomic weight rare earth elements and iron to promote the formation of a stable, very finely crystalline, intermetallic phase having high magnetic remanence and energy product. Another particular object is to provide the constituent metallic elements in suitable proportions to form these new intermetallic phases and then process the alloys to optimize the resultant hard magnetic properties.
In accordance with a preferred practice of the invention, an alloy with hard magnetic properties is formed having the basic formula RE.sub.1-x (TM.sub.1-y B.sub.y).sub.x.
In this formula, RE represents one or more rare earth elements. The rare earth elements include scandium and yttrium in Group IIIA of the periodic table and the elements from atomic number 57 (lanthanum) through 71 (lutetium). The preferred rare earth elements are the lower atomic weight members of the lanthanide series, particularly neodymium and praseodymium. However, substantial amounts of certain other rare earth elements may be mixed with these preferred rare earth elements without destroying or substantially degrading the permanent magnetic properties.
TM herein is used to symbolize a transition metal taken from the group consisting of iron or iron mixed with cobalt, or iron and small amounts of such other metals as nickel, chromium or manganese. Iron is preferred for its relatively high magnetic remanence and low cost. A substantial amount may be mixed with iron without adverse effect on the magnetic properties. Nickel, chromium and manganese are also a transition metals. However, their inclusion in amounts greater than 10 percent have generally been found to have a deleterious effect on permanent magnetic properties of Nd-Fe-B alloys.
The most preferred alloys contain the rare earth elements Nd and/or Pr and the transition metal element, Fe. The superior properties of these light rare earth-iron combinations are due, at least in part, to ferromagnetic coupling between the light rare earth elements and Fe. That is, in optimum alloys the orbital magnetic moments (L) of the rare earths align in the same parallel direction as the spin moments of the iron (S) so that the total moment (J) equals L+S. For the heavy rare earth elements such as Er, Tb and Ho, the magnetic coupling is antiferromagnetic and the orbital magnetic moments of the rare earths are antiparallel to the iron spin moment so that the total moment J=L-S. The total magnetic moment of the ferromagnetically coupled light rare earth-iron alloys is, therefore, greater than that of antiferromagnetically coupled heavy rare earth-iron alloys. The rare earth element, samarium, may couple ferro or antiferromagnetically with iron, behaving therefore as both a light and a heavy rare earth element within the context of this invention.
B is the atomic symbol for the element boron. X is the combined atomic fraction of transition metal and boron present in a said composition and generally 0.5.ltorsim..times..ltorsim.0.9, and preferably 0.8.ltorsim..times..ltorsim.0.9. Y is the atomic fraction boron present in the composition based on the amount of boron and transition metal present. An acceptable range for y is 0.005.ltorsim.y.ltorsim.0.10, the preferred range being 0.5.ltorsim.y.ltorsim.0.7. B should not be present as more than about 10 atomic percent of the total composition, and preferably less than 7 percent. The incorporation of only a small amount of boron in alloys having suitable finely crystalline microstructures was found to substantially increase the coercivity of RE-Fe alloys at temperatures up to 200.degree. C. or greater, particularly those alloys having high iron concentrations. In fact, the alloy Nd.sub.0.2 (Fe.sub.0.95 B.sub.0.05).sub.0.8 exhibited an intrinsic magnetic room temperature coercivity exceeding about 20 kiloOersteds, substantially comparable to the hard magnetic characteristics of much more expensive SmCo.sub.5 magnets. The boron inclusion also substantially improved the energy product of the alloy and increased its Curie temperature.
Permanent magnet alloys in accordance with the invention were made by mixing suitable weight portions of elemental forms of the rare earths, transition metals and boron. The mixtures were arc melted to form alloy ingots. The alloy was in turn remelted in a quartz crucible and expressed through a small nozzle onto a rotating chill surface. This produced thin ribbons of alloy. The process is generally referred to in the art as "melt spinning" and is also described in U.S. Ser. No. 274,040. In melt spinning, the quench rate of the melt spun material can be varied by changing the linear speed of the quench surface. By selection of suitable speed ranges I obtained products that exhibited high intrinsic magnetic coercivities and remanence. Furthermore, I found that products with such properties could be produced either as directly quenched from the melt, or as overquenched and annealed as will be described hereinafter. In each case where good magnetic properties were obtained, the magnetic material comprised very small crystallites (about 20 to 400 nanometers average diameter) apparently sized near the optimum single magnetic domain size or smaller. The fairly uniform shape of the crystallites as exhibited by scanning electron microscopy suggests a crystal structure that is fairly uniform in all directions such as a tetragonal or cubic structure. Alloys of such structure constitute a heretofore unknown magnetic phase.
The inclusion of boron in suitable amounts to mixtures of rare earth elements and iron was found to promote the formation of a stable, hard magnetic phase over a fairly broad range of quench rates. The magnetic remanence and energy product of all melt-spun, magnetically hard, boron-containing, RE-iron alloys were improved. The Curie temperatures of the alloys were substantially elevated. My invention will be better understood in view of the following detailed description.
FIG. 1 is a plot of room temperature intrinsic coercivity for magnetized melt spun Nd.sub.0.4 (Fe.sub.1-y B.sub.y).sub.0.6 alloys as a function of the linear speed (V.sub.s) of the quench surface.
FIG. 2 is a plot of room temperature intrinsic coercivity for magnetized melt spun Nd.sub.0.25 (Fe.sub.1-y B.sub.y).sub.0.75 alloys versus the linear speed of the quench surface.
FIG. 3 is a plot of room temperature intrinsic coercivity for magnetized melt spun Nd.sub.0 15 (Fe.sub.1-y B.sub.y).sub.0.85 alloys as a function of the linear speed (V.sub.s) of the quench surface.
FIG. 4 is a plot of room temperature intrinsic coercivity for magnetized melt spun Nd.sub.1-x (Fe.sub.0.95 B.sub.0.05).sub.x alloys as a function of the linear speed of the quench surface.
FIG. 5 is a plot of remanent magnetization B.sub.r of melt spun Nd.sub.1-x (Fe.sub.0/95 B.sub.0.05).sub.x alloys at room temperature as a function the linear speed of the quench surface.
FIG. 6 shows demagnetization curves for melt spun Nd.sub.0.25 (Fe.sub.0.95 B.sub.0.05).sub.0.75 as a function of the linear speed of the quench surface.
FIG. 7 shows demagnetization curves for melt spun Nd.sub.0.2 (Fe.sub.0.96 B.sub.0.04).sub.0.8 alloy for initial magnetizing fields of 19 kOe and 45 kOe.
FIG. 8 shows demagnetization curves for melt spun Nd.sub.0.25 (Fe.sub.1-y B.sub.y).sub.0.75 alloys.
FIG. 9 is a plot of room temperature intrinsic coercivity for magnetized Pr.sub.0.4 Fe.sub.0.6 and Pr.sub.0.4 (Fe.sub.0.95 B.sub.0.05).sub.0.6 alloys as a function of the linear speed of the quench surface.
FIG. 10 shows demagnetization curves for melt spun Nd.sub.0.15 (Fe.sub.1-y B.sub.y).sub.0.85 alloys.
FIG. 11 s a plot of energy product, magnetic remanence and magnetic coercivity of Nd.sub.1-x (Fe.sub.0.95 B.sub.0.05).sub.x as a function of neodymium content, and FIG. 12 shows intrinsic coercivities of Nd.sub.1-x (Fe.sub.0.95 B.sub.0.05).sub.x alloy as a function of neodymium content.
FIG. 13 is a scanning electron micrograph of the fracture surface of a melt spun ribbon of Nd.sub.0.135 (Fe.sub.0.946 B.sub.0.054).sub.0.865 alloy as quenched, the micrographs being taken at the free surface, the interior and the quench surface of the ribbon.
FIG. 14 shows demagnetization curves (M versus H and B versus H) for the melt spun Nd.sub.0.135 (Fe.sub.0.946 B.sub.0.054).sub.0.865 alloy of FIG. 13.
FIG. 15 shows demagnetization curves for melt spun Nd.sub.1-x (Fe.sub.0.95 B.sub.0.05).sub.x alloys.
FIG. 16 shows demagnetization curves for melt spun Nd.sub.0.33 (Fe.sub.0.95 B.sub.0.05).sub.0.67 at several different temperatures between 295.degree. K and 450.degree. K
FIG. 17 shows demagnetization curves of melt spun Nd.sub.0.15 (Fe.sub.0.95 B.sub.0.05).sub.0.85 at several different temperatures between 295.degree. K and 450.degree. K.
FIG. 18 plots normalized log values of intrinsic coercivity for three neodymium-iron-boron alloys as a function of temperature.
FIG. 19 is a plot showing the temperature dependence of magnetic remanence for several neodymium-iron-boron alloys.
FIG. 20 plots the temperature dependence of magnetization for melt spun Nd.sub.0.25 (Fe.sub.1-y B.sub.y).sub.0.75 at several different boron additive levels.
FIG. 21 plots the magnetization of several melt spun Nd.sub.1-x (Fe.sub.0.95 B.sub.0.05).sub.x alloys as a function of temperature.
FIG. 22 shows representative X-ray spectra for melt spun Nd.sub.0.15 (Fe.sub.1-y B.sub.y).sub.0.85 alloy for values of two theta between about 20 and 65 degrees.
FIG. 23 shows X-ray spectra of melt spun Nd.sub.0.25 (Fe.sub.0.95 B.sub.0.05).sub.0.75 taken of material located on the quench surface of a ribbon of the alloy and of a sample of material from the free surface remote from the quench surface.
FIG. 24 shows differential scanning calorimetry tracings for Nd.sub.0.25 (Fe.sub.1-y B.sub.y).sub.0.75 alloys taken at a heating rate of 8020 K per minute.
FIG. 25 shows differential scanning calorimetry traces for Nd.sub.0.15 (Fe.sub.0.85), Nd.sub.0.15 (Fe.sub.0.95 B.sub.0.05).sub.0.85 and Nd.sub.0.15 (Fe.sub.0.91 B.sub.0.09).sub.0.85 taken at a heating rate of 80.degree. K per minute for melt-spinning quench speeds of V.sub.s =30 and 15 m/s.
FIG. 26 shows typical demagnetization curves for several permanent magnet materials and values of maximum magnetic energy products therefor.
FIG. 27 shows the effect of adding boron to Nd.sub.1-x (Fe.sub.1-y B.sub.y).sub.x alloys on Curie temperature.
FIG. 28 is a plot showing the relative coercivities of samples of Nd.sub.0.15 (Fe.sub.0.95 B.sub.0.05).sub.0.85 melt spun at quench wheel speeds of 30 and 15 meters per second and thereafter annealed at about 850.degree. K for 30 minutes.
FIG. 29 is a demagnetization curve for Nd.sub.0.14 (Fe.sub.0.95 B.sub.0.05).sub.0.86 originally melt spun and quenched at V.sub.s =30 m/s and then taken to a maximum anneal temperature of Ta=950.degree. K at a ramp rate of 160.degree. K per minute, held for 0, 5, 10 and 30 minutes.
FIG. 30 is a comparison of the demagnetization curves for Nd.sub.0.14 (Fe.sub.0.95 B.sub.0.05).sub.0.86 alloy melt spun and quenched at wheel speeds of V.sub.s =27.5 and 30 m/s and annealed at ramp rates of 160 and 40.degree. K per minute.
FIG. 31 is a plot of maximum energy product as a function of the linear speed of the quench surface for Nd.sub.0.14 (Fe.sub.0.95 B.sub.0.05).sub.0.86 alloy. The open circles form the curve for the alloy as quenched, while the open squares, triangles and closed circles represent material melt spun at the indicated V.sub.s value and later annealed at a ramp rate of 160.degree. K per minute to maximum temperatures of 1000, 975 and 950.degree. K.
FIG. 32 is a demagnetization curve for Nd.sub.0.135 (Fe.sub.0.935 B.sub.0.065).sub.0.865 alloy at several linear quench surface speeds also indicating maximum energy product for a particular V.sub.s.
FIG. 33 shows X-ray powder diffraction patterns of Nd.sub.0.135 (Fe.sub.0.935 B.sub.0.065).sub.0.865 melt spun and quenched at several different quench surface speeds (V.sub.s).
FIG. 34 shows differential scanning calorimetry tracings for Nd.sub.0.135 (Fe.sub.0.946 B.sub.0.054).sub.0.865 alloy taken at a heating rate of 160.degree. K per minute for alloys quenched at V.sub.s =19, 20.5 and 35 m/s.
FIG. 35 is a demagnetization curve for Nd.sub.0.135 (Fe.sub.0.946 B.sub.0.054).sub.0.865 alloy originally quenched at a linear quench surface rate of V.sub.s =20.5 m/s and then annealed at heating and cooling ramp rates of 160.degree. K per minute to maximum temperatures of 950, 975 and 1000.degree. K indicating the maximum energy product for each.
FIG. 36 is a curve like that of FIG. 35 except that V.sub.s =35 m/s.
FIG. 37 is a panel of three scanning electron micrographs taken along the fracture surface of a melt spun ribbon of Nd.sub.0.14 (Fe.sub.0.95 B.sub.0.05).sub.0.86 alloy where the linear speed of the quench surface V.sub.s =30 m/s. The SEM's are representative of the microstructure near the free surface, the center and the quench surface of the ribbon.
FIG. 38 is a panel of three scanning electron micrographs taken along the fracture surface of a melt spun ribbon of Nd.sub.0.14 (Fe.sub.0.95 B.sub.0.05).sub.0.86 alloy originally quenched at a linear quench surface speed of V.sub.s =30 m/s and then annealed at a maximum temperature of 950.degree. K at a heating and cooling ramp rate of 160.degree. K per minute, the SEM's being taken near the free surface, the center, and the quench surface of the ribbon.
FIG. 39 is a demagnetization curve for Nd.sub.0.135 (Fe.sub.0.946 B.sub.0.054).sub.0.865 alloy originally quenched at linear quench surface rates of V.sub.s =29, 20.5 and 35 m/s, annealed at 950.degree. K maximum at a heating and cooling ramp rate of 160.degree. K per minute.
FIG. 40 is a demagnetization curve for Pr.sub.0.135 (Fe.sub.0.935 B.sub.0.065).sub.0.86 alloy melt spun at a linear quench surface speed of V.sub.s =30 m/s and then annealed at a ramp rate of 160.degree. K per minute to maximum temperatures of 900, 925 and 975.degree. K.
FIG. 41 is a plot of RE.sub.0.135 (Fe.sub.0.935 B.sub.0.065).sub.0.865 melt spun and quenched at a linear quench surface speed of V.sub.s =30 and then annealed to a maximum temperature of 950.degree. K at a heating and cooling ramp rate of 160.degree. K per minute where RE is praseodymium, neodymium, samarium, lanthanum, cerium, terbium and dysprosium.
FIG. 42 is a demagnetization curve for (Nd.sub.0.8 RE.sub.0.2).sub.0.135 (Fe.sub.0.935 B.sub.0.065).sub.0.865 alloy melt spun and quenched at a linear quench surface speed V.sub.s =30 m/s and then annealed at a heating and cooling ramp rate of 160.degree. K per minute to a maximum temperature of 950.degree. K.
FIG. 43 is a demagnetization curve for Nd.sub.0.135 (TM.sub.0.935 B.sub.0.065).sub.0.865 alloys originally melt spun at a quench speed of V.sub.s =30 m/s annealed at a ramp rate of 160.degree. K per minute to a maximum temperature of 950.degree. K, where TM is iron, cobalt and nickel.
FIG. 44 shows demagnetization curves for Nd.sub.0.135 (Fe.sub.0.841 TM.sub.0.094 B.sub.0.065).sub.0.865 alloy originally melt spun at a quench surface speed of V.sub.s =30 m/s annealed at a heating and cooling ramp rate of 160.degree. K per minute to a maximum temperature of 950.degree. K, where TM is cobalt, nickel, chromium, manganese and copper.
FIG. 45 is a demagnetization curve for Nd.sub.0.135 (Fe.sub.0.784 TM.sub.0.187 B.sub.0.065).sub.0.865 alloys originally melt spun at a quench surface rate of V.sub.s =30 m/s and then annealed at a heating and cooling ramp rate of 160.degree. K per minute to a maximum temperature of 950.degree. K, where TM is cobalt, nickel, chromium and manganese.
US Referenced Citations (2)
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 56-116844 |
Sep 1981 |
JPX |
Non-Patent Literature Citations (2)
| Entry |
| Croat, "Preparation And Coercive Force Of Melt-Spun Pr-Fe Alloys," Appl. Phys. Lett. 37 (12), Dec. 15, 1980, pp. 1096-1098. |
| Kabacoff et al., (Kabacoff), "Thermal And Magnetic Properties Of Amorphous Pr.sub.x (Fe.sub.0.8 B.sub.0.2).sub.1-x," J. Appl. Phys. 53(3), Mar. 1982, pp. 2255-2257. |
Divisions (1)
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Number |
Date |
Country |
| Parent |
508266 |
Jun 1983 |
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Continuation in Parts (1)
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Number |
Date |
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| Parent |
414936 |
Sep 1982 |
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Patent Grant
5056585
