US3450580A - Permanent magnets - Google Patents

Description

United States Patent U.S. Cl. 14831.57 3 Claims ABSTRACT OF THE DISCLOSURE An improved anisotropic columnar crystal magnetic composition is disclosed which consists essentially of:

Balance essentially iron.

This invention relates to permanent magnets of the Fe-Al-Ni-Co-Cu alloy type, particularly to the highenergy forms based on a columnar crystal structure.

Until relatively recently it was thought that the presence of Ti, commonly made a further constituent of alloys of the type in question to impart high coercivity, was incompatible with the development of the columnar crystal structure that is so conducive to high energy. However, as shown by British Patent Nos. 987,636 and 999,523, the inclusion with Ti of S and/ or Se enables a columnar crystal structure to be produced, so that the simultaneous attainment of high energy and high coercivity is possible, without significant departure from the ordinary commercial methods of producing permanent magnets with a columnar crystal structure. Such methods include casting into exothermic moulds or heated refractory moulds, with the use of chills, zone-melting of a previously cast rod, and continuous casting.

It has now been found that Te can usefully be present together with Ti for the simultaneous attainment of high energy and high coercivity, and is particularly beneficial when, in order to encourage high energy, a content of Co in the higher part of the range usually considered suitable, or even beyond the usual upper limit of that range, is present.

According to the present invention, an anisotropic columnar crystal magnet has a composition, by weight:

The minimum content of Te is preferably greater than 0.5% and it is believed generally advantageous for the composition, by weight, of the magnet to be as follows:

Percent 6.5 to 8.5

3,450,580 Patented June 17, 1969 Ni 12.0 to 16.0 C0 33.0 to 43.0 Cu 2.0 to 4.5 Ti 6.0 to 9.0 Nb 0.8 to 3.0 Si Up to 0.5 Te 0.5 to 3.0 Fe and impurities Balance By impurities is to be understood minor amounts of constituents present as unavoidable impurities and also constituents present by deliberation for the improvement of magnetic and/or mechanical properties. Thus, S and/ or Se may be present for the amelioration of brittleness, but preferably in suflicient amount for the previously mentioned assistance in the simultaneous attainment of high energy and high coercivity. Thus, instead of Te alone, to the above-indicated amount of 0.5% to 3.0%, Te and S may be present together, in the ratio of about 3:1 by weight, in the range 0.4% to 2.4%. Again, a particularly preferred range for Te alone is 0.75% to 1.5%, but if S is present as a further constituent the correspondingly particularly preferred amounts for Te and S (in a ratio of about 3:1) together fall in the range 0.6% (0.45% Te and 0.15% S) to 1.25% (0.9% Te and 0.35% S). If Se is present in whole or partial replacement of, S together with the essential Te, the amount of Se to be used is the amount of S replaced, increased by the ratio of the atomic Weights of Se and S.

The Te is preferably added to the melt as compacts pressed from tellurium powder or as broken pieces of a moderately brittle 50:50 copper/tellurium alloy. The quantity of tellurium added is approximately double the amount required in the alloy, to compensate for melting losses which occur due to the low melting point (454 C.) and boiling point (1390 C.) of tellurium.

Nb is another addition that may be present for the encouragement of columnar structure and/or enhanced coercivity. Nb usually being available in combination with Ta, the indicated amounts of Nb can be somewhat greater when the combined constituent is used.

The magnet alloys as cast or solidified are subjected appropriately to the usual heat treatment, including the application of a magnetic field in the lengthwise direction of the columnar structure, followed by tempering. Particular examples of heat treatment and tempering are given below.

The following are examples of the application of the invention to obtain magnets, by ordinary commercial methods for producing a columnar crystal structure, which magnets have a coercivity of at least 1200 oersteds and energy of at least 6.0 10 gauss-oersteds, from Ti-containing alloys of commerce such as have either not been susceptible to combined high energy and high coercivity except by the inclusion of S and/or Se, or have not even proved so susceptible even with the inclusion of S and/or Se, it appearing that Te facilitates the attainment of particularly high values of energy (even in excess of 8.0x 10 in alloys with the high amounts of Ti necessary for the higher values of coercivity (even around 2000), and that the simultaneous presence of S and/or Se with the Te is conducive to the attainment of such highly desirable combination of magnetic properties.

Table 1 shows the compositions (by analysis, percent by weight) of the alloys (all cast in exothermic moulds, with end chills); Table 2 describes the ditferent heat treatments applied to the alloys, all including isothermal treatment in a magnetic field; and Table 3 shows the resultant magnetic properties.

Heat treatments A, B and C, including the application of a magnetic field, and tempering.

A, B, C Heat to solution temperature, 1,250 C. A Blast coiol to room temperature in magnetic field, 3,400

oerste s. B Blast cool to black in 1% to 2 minutes (no magnetic field). A l. Reheat in magnctic field, 7,000 oersteds, to 800 C. or 810 C., and hold for 20 minutes (total time in furnace 35 minutes). B Reheat in salt bath to 820 C. in magnetic field, 2,800 oersteds, and hold for 13 minutes (total time in bath 15 minutes). Quench from 1,250 0. into salt bath at 820 C. in magnetic field, 2,800 oersteds, and hold for 15 minutes. A, B, 0..-- Temper: 590 C. for 48 hours, plus 560 0., for 48 hours.

TABLE 3 Energy (BH)mux. Remanence Coercivity (guass) Treatment B, (gauss) Ha (oersteds) oersteds- 10,750 1,215 6 25x10 8,430 1,655 6 22X10 9, 020 1, 722 7. 6X10 8,950 2,010 8 43x10 8,350 1,908 6 06X10 9,120 1,628 7 69 10 8,150 1,980 7.0)( 8,700 1,880 6 x10 11,700 1, 235 7. 1X10 All the magnets were finally magnetised in a magnetic field of 7000 oersteds applied in the direction of the columnar crystal structure.

An alternative to blast cooling is oil quenching. An alternative to the salt bath (KCl-NaNO is a bath of molten aluminium. Alternative tempering is 680 C. for 4 hours plus 560 C. for hours.

While field strengths in the range 2500 to 3500 oersteds (as the 2800 oersteds and 3400 oersteds appearing above) may be used, it appears that higher field strengths (as the 7000 oersteds also appearing above), or still higher, as 10,000 oersteds or more, are conducive to improving the fullness of the demagnetisation curve. It is believed that 4 a content of Si in the alloys is helpful in making higher field strengths more effective.

What we claim is: 1. An anisotropic columnar crystal magnet consisting essentially of:

Percent Al 5 to 9 Ni 11 to 22 Co 33 or 34 to 50 Cu 1 to 6 Ti 1 to 9 Cb 0 to 4 Si Up to 1 Te 0.10 to 4 Balance essentially iron.

2. An anisotropic columnar crystal magnet consisting essentially of Percent Al 6.5 to 8.5 Ni 12.0 to 16.0 C0 33.0 to 43.0 Cu 2.0 to 4.5 Ti 6.0 to 9.0 Cb 0.8 to 3.0 Si Up to 0.5 Te 0.5 to 3.0

Balance essentially iron. 3. An anisotropic columnar crystal magnet consisting L. DEWAYNE RUTLEDGE, Primary Examiner.

PAUL WEINSTEIN, Assistant Examiner.

US. Cl. X.R.