US3547713A - Methods of making structural materials having a low temperature coefficient of the modulus of elasticity - Google Patents

Description

1970 s. STEINEMANN ETAL 3,547,713

METHODS OF MAKING STRUCTURAL MATERIALS HAVING A LOW TEMPERATURE COEFFICIENT 0F THE MODULUS OF ELASTICITY 1 3 Sheets-Sheet 1 Filed April 1s. i967 Fig. 10

1y I fi Per/0o m VENTORS MAP/7N 1 672 1? A TTOR'N 5 Y5 SAMOH SITM/[MA/V/V A/V/l 1970 s. STEINEMANN ETAL 3,547,713

METHODS OF MAKING STRUCTURAL MATERIALS HAVING A LOW TEMPERATURE COEFFICIENT OF THE MODULUS OF ELASTICITY Filed April 18. L967 3 Sheets-Sheet 6 Fig. 4

Elements:

Group 118 I115 IVB vs VIB VIIB ,vnl

Period 1v Ca Sc Ti v Cr Mn V Sr y Zr Nb Mo Tc Ru' Rh Pd VI Bu Lo Hf Tu W Re Os Ir Pt lanrhanons ad'inides I Q E] cubic {-aLe cenlcrcd Structures of crystal and approximate pogih'an of H1: {5 cubic cenl-c ed phase'limiks inrhc alloqs hflqsoniu l r K complex high mmm O E] W W H room l' mfemhu O O E] El 0 O E] E] SAMUEL STE/NfMA/V/V AND MART/N PETE/Z MWMMM H TTORNEIS United States Patent O 3,547,713 METHODS OF MAKING STRUCTURAL MATE- RIALS HAVING A LOW TEMPERATURE COEF- FICIENT OF THE MODULUS F ELASTICITY Samuel Steinemann, Waldenhurg, and Martin Peter, Petit- Lancy, Switzerland, assignors to Institut Dr. lug. Reinhard Straumann A.G., Waldenburg, Switzerland, :1 jointstock company of Switzerland Filed Apr. 18, 1967, Ser. No. 631,686 Claims priority, application Switzerland, Apr. 22, 1966, 5,878/66 Int. Cl. (122E 1/00 US. Cl. 148-115 20 Claims ABSTRACT OF THE DISCLOSURE Method of producing a metallic, paramagnetic crystallized structural material of a temperature coetficient of the modulus of elasticity between per degree and +10 per degree centigrade. The components of the material are selected in type and quantity such that the material exhibits an atomic, paramagnetic susceptibility x 50-10- emE/g.-atom at room temperature and a negative temperature coefficient of the susceptibility d /a'T. The components are melted together, and a preferred orientation of the crystals by at least a mechanical or a thermal treatment of the material is produced.

The present invention relates to methods of making structural materials and elements having a low temperature coeflicient of the modulus of elasticity and more particularly having such coeflicient varying only slightly around zero.

In mechanical oscillatory systems, such as clocks and electromechanical filters, but also in spring systems such as balances, levelling apparatus, electric measuring devices and so on, structural elements, e.g. elastic bodies are employed, whose modulus of elasticity is required to be independent of temperature as far as possible. Cases can however occur wherein the elastic body should have a temperature coefficient of the E-modulus which is somewhat ditferent from Zero in order that all temperaturedependent influences of an oscillatory system shall be compensated simultaneously, an example being the increase in the moment of inertia caused by the thermal expansion of a balance wheel. Moreover this compensation, under various stress conditions, affects quite different moduli, namely the modulus of elasticity (for example in the bending of tuning forks, spiral springs etc), the shear modulus (under torsion, for example, in spirally wound tension springs) or the compression modulus, as well as combinations of all of these moduli.

The known structural materials which exhibit suitably small and adaptable temperature coefficients are based upon ferromagnetic processes. In these materials under the influence of external load, there is a change in the local direction of the spontaneous magnetization in such a manner that the magnetostrictive distortion caused by the change in magnetization increases the shape changing effect of the load on the body (this is known as magnetostrictive extension under tension and conversely, according to the direction of stress). Thus, in a ferromagnetic body, in addition to the purely elastic extension as the result of a stress there is to be added also a magnetostrictive extension, and as contrasted with the perfectly elastic Hooke relationship the elasticity modulus therefore decreases. This elevation is known as the AE effect. The A E effect is particularly strong in the pure metals Ni, Co, Fe and is brought about essentially by the linear magnetostriction effect and is practically suppressed by external magnetic fields or cold working (both of which disturb the free inception of the spontaneous magnetization in the domains). If, on the other hand, the volume magnetostriction effect is preponderant, as for example for certain Fe-Ni, Fe-Ni-Co and Fe-Co-Cr alloys and others, then the anomalous behaviour in the ferromagnetic temperature region does not completely vanish even under conditions of magnetic saturation or intense cold working. As the magnetostriction like the spontaneous magnetization falls ofl with increasing temperature, these effects can produce the known behaviour of the E modulus if there is suitable choice of the alloy, so that in many alloys the volume effect is made use of. These theories are described in the text books by R. Becker and W. Doring: Ferromagnetismus, Springer Verlag, Berlin, (1939), pp. 336-357; R. M. Bozorth: Ferromagnetism, D. Van Nostrand Company, New York, (1951), pp. 684-699.

Nevertheless the elastic behaviour of these alloys does always exhibit a more or less strong dependence upon magnetic field. For example, the vibration frequency of a tuning fork changes directly in a magnetic field as does also its temperature coeflicient. On the other hand, the technological processes necessary for the precise adjustment of a temperature compensation are quite diflicult. An accurate cold working and heat treatment is necessary in order to make the compensation range as large as possible and to obtain small temperature coeflicients. These cold working treatments and final heat treatments in fact change the inner microscopic and sub-microscopic state of stress in the metal (on account of dislocations, precipitations, etc., but the chemical change of the phase composition involved by the precipitation hardening is not substantial) and thus have a sensitive influence upon the temperature behaviour and the elasticity modulus. On the other hand, especially when the anomalous behaviour is based upon a predominating volume magnetostriction etfect, the texture influence is less apparent.

The present invention relates to a method of producing structural materials, of the elinvar type having a small temperature coefficient of the elastic moduli, which are sensibly temperature independent. The method uses a paramagnetic material with an atomic susceptibility x 50-10 emE/g.-atom at room temperature and a negative temperature-coeflicient of this susceptibility, e.g. d /dT, and wherein a texture is produced by mechanical or heat processing. This texture is related to the type and orientation of the stress in the structural element.

It is advantageous that the overall composition, or that of principal phase of the material, has an electron concentration e/ a comprised in e/ a equal to 2.5-3.7 or 4.1-5.7 or 6.1-7.8 or

The electron concentration e/a is the ratio of the mean number of electrons situated externally of closed shells, that is to say the electrons determining bonding, to the number of atoms. Thus in an alloy consisting of n elements with the percentages by weight g,, the atomic weights A, and the number 1/, of electrons outside the closed shells (valencies) the atomic percentages are calculated by and the electron concentrations are given by e 1 11 run The product-sum 1 is given by the expression i =1 m +l n +m n in the case of cubic materials and is given by for hexagonal materials wherein l, m and n are respectively the direction-cosine of the measurement or stress direction with respect to the main axes of the cubic crystallite, and, in the case of hexagonal materials, 0, is the direction-cosine of the measurement or stress direction with respect to the hexagonal axis.

The mechanical or heat processing used to produce the texture may be drawing, or rolling or recrystallization annealing. The texture is characterised by the product-sum I of the direction-cosine between the crystal-orientation and the stress direction in the structural element, taken as the mean over all crystallite orientations in the material. The product-sum i is given by the expression in the case of cubic materials. Advantageously, for cubic materials I 0.2 for the elasticity modulus, and I 0.2 for the shear modulus (stress axis=torsion axis). In the case of hexagonal materials I O.25 for the elasticity modulus and I O.25 for the shear modulus.

For an understanding of the invention relative to the above mentioned materials, which are essentially different from materials previously proposed for the problem, the characteristic principles of these materials will now be explained.

The cohesion energy of a metal is comprised additively of various contributions. Essentially there are three components of the energy to be considered, which originate from the interaction between the ions of the crystal lattice, between the ions and free electrons and between the free or itinerant electrons themselves. The first two components are responsible for definite uniform characteristics of the elastic behaviour of the single crystal; on the other hand the last component is decisive for certain metals and alloys, in particular in respect of the temperature relationship of the elasticity (usually this component due to the electron gas is small or independent of temperature). Upon these effects depends a group of materials of this invention, principally metals and alloys but under certain circumstances also semiconductors. These materials are not ferromagnetic and satisfy also the further requirements of resistance against corrosion, easy workability, small mechanical losses, mechanical strength and so on.

If the electrons make a decisive contribution to the cohesion characteristics, then their energy as a whole must be large, for which the effective density of states at the Fermi level N(E is determinative. If, in fact, under such conditions the crystal lattice is elastically distorted by mechanical stress, then this results also in a distortion of the Brillouin body and the kinetic energy of the free electrons exercises marked influence upon the elastic behaviour of the crystal. The mechanism is naturally effective with any stress upon the solid body; thus in the case of a dilatation for the compression modulus K (electrons in the nearly empty band and holes in the nearly filled band act in an equivalent manner), and in the case of pure shear (without dilation) and a corresponding distion of the Brillouin body, there will take place an increase of the kinetic energy in some directions and a reduction of these energies in other directions, which then results in an electron transfer (figuratively electron evaporation); this has been theoretically investigated in the special case of aluminimum by RS. Leigh (Philosophical Magazine, vol. 42, pages 139 et. seq. 1951).

If the electronic contribution to the elastic energy is high, then also temperature influences upon the kinetic energy of the electrons (or holes respectively) or indirectly upon fi(E which can be expressed as the temperature coefiicient 011V E dT will predominate in the elastic behavior of the crystal (the derivative 011V E1. d '1 is introduced in a formal manner). If the value of dN(EF) dT is negative, the temperature coefiicient of the elastic moduli becomes a positive contribution.

The high density of states fi(E is characterised by high paramagnetic susceptibility high specific heat of the electrons, and frequently also by a high superconductivity transition temperature. The temperature relationship with KLE is most clearly seen from the temperature behaviour of )4 namely d /dT.

The foregoing discussion has shown how itinerant electrons can decisively influence the elastic behavior. The relationships may be seen from FIGS. la-lc, in which there are represented, for the transition element of the third, fourth and fifth periods, and their alloys, the paramagnetic susceptibility (FIG. 1a), the temperature coefficient thereof ld dT (FIG. 1b) and the temperature coefficient of the elasticity modulus (FIG. 10), plotted in each case With respect to the electron concentration e/a.

Materials which are applicable to the purpose of the invention come out with a high value of X and a negative value of d /dT. The curves show also that the applicable ranges of the electron concentration e/ a are:

2.53.7 4.1-5.7 6.1-7.8 and 9.3l0.5

The electron concentration e/a embraces completely all alloys with two or more components between the elements of different groups and periods of the period system.

With structural materials fulfilling the requirements of the invention, the contribution of the free electrons to the elastic energy results in an anomalous temperature relationship with the elasticity. These effects are however contrasted with the conventional anomalous behaviour. The temperature independence of the previously known thermocompensating alloys is always limited at an upper temperature, in fact at that point where the required homomorphous transformations vanish; the reversible transformation of ferromagnetism to paramagnetism is the most well-known example; this anomaly extends up to the Curie temperature.

In the drawings FIGS. 1a to 10 depict isotropic structures. FIGS. 2a to 2] illustrates the dependence of orientation with temperature. FIG. 3 depicts a pole figure for the cubic case. FIG. 4 illustrates the crystal structures of the elements and the approximate phase structure of the binary alloy series of the transition elements.

The FIGS. la to 10, in particular 10, refer to isotropic structures, e.g., all crystal orientations are equally prohable. The behaviour of these materials however is an anisotropic property of the crystal which has to be taken in account for the technical use in two ways; it can either be provided a texture by suitable mechanical or heat processing, or the preferred orientation in the material as obtained with customary processing is examined (for example with X-ray methods) and oriented against the stress direction in the structural element. These orientations are fully described by the product-sum 5. Structural materials according to this invention should not only retain their rigidity with varying temperature, its technical application needs also sufficient mechanical strength which can be obtained through different forms of hardening processes. In materials in accordance with this invention, such hardening processes are possible, but nevertheless, on account of the condition concerning the density of state or susceptibility, the particular influence of the alloying elements, or of the other means for hardening, have to be taken into account. The high density of state of the itinerant electrons, as advanced in this invention, has furthermore the consequence that lattice faults (e.g. vacancies, dislocations, interstitial atoms, stacking faults, etc.), as such are produced by quenching or cold-working, and impurities which occupy not the regular lattice places, but the so-called interstitial places (among these being for example gases and elements with small atom radii, as C, O, H, B, etc.) can behave in different manner than in a normal metal (as copper, aluminum, etc.). In what follows, these three groups of phenomena will be examined in relation to the technical realisation of the invention.

Polycrystalline solid bodies may have, as is known, numerous anisotropic characteristics which originate from the texture (see the textbook by G. Wassermann and Johanna Grewen Texturen metallischer Werkstoffe, Springer Verlag, Berlin, Gottingen, Heidelberg, 1962). It is however less frequently investigated how the temperature coefficients of the elasticity modulus can depend upon a texture. The AE effect of nickel, for example, is strongly anisotropic because the shape magnetostriction is strongly anisotropic; in the classical alloys having a small temperature coeflicient of the E modulus, which are known under the marks Nivarox, Ni-Span C, etc., where the volume magnetostriction predominates, the direction dependence is, on the contrary, small and in practice is not considered or controlled. On the other hand the materials in accordance with the invention depend clearly upon single crystal properties, whose anisoptropic properties cannot be ignored or neglected.

The elasticity theory describes the strains in the me chanically stressed single crystal by means of elastic constants. For the cubic crystal, which in the following will be taken as an example, it will suffice to consider three quantities, c and e (0 corresponds to ex tension along a main axis in which also the force is effective, C is an extension normal to this main axis and to the direction of the force, C44 is a shear in planes of two main axes). For the elastic energy and in particular the contribution of electrons, the following quantities are of importance:

wherein C and C correspond to two shears and K is the compression modulus. For the single crystal, there will then apply the conventionally used modulus E (elasticity modulus), G (shear modulus); see for example C. S. Barrett Structure of Metals, McGraw-Hill Book Company, New York, 1952:

are the already mentioned direction-cosines between the stress axis and the main axes of the crystal.

6 For the temperature coefficients of these moduli the following then apply:

l 1. 5mi 19 2) 1%)] K dT 3K[ c dT c dT 1 01E 1 l 1 11C 1 *'EW lT W[(E WX5 J 1 1 d6 elon 1 dG l 1 d0 1 1 d0" -eEr- {e[(mr) n WWW} The temperature coefiicients of the conventionally used moduli K, G, E depend on the temperature coefficients of the single crystal quantities C, C and K and the relative orientation of the stressing or measuring direction (also for the direction of propagation of sound waves); for the latter the values of some particular orientations in the cubic crystal are I=:0 for l00 The special, fixed value of I /s is to be inserted in the above formula for the ideal isotropic polycrystalline material where general relations between the common moduli exist (see for example W. Koester and H. Franz, Metallurgical Reviews, vol. 6, No. 2, 1961):

These laws may be demonstrated, for example, for pure palladium, which is one of the metals in the class of structural materials in accordance with the invention. In FIG. 2 there are indicated the measured data for 0:0 CIZIAZ (cu-C12), and therefore K, E100, E110, E111 are derived according to the above formulae. The marked orientation dependence of the temperature curve is obvious from this figure. The question can now be posed for what direction, that is to say what value of 1 the behaviour required of the material in accordance with the invention will be available and g and e are approximately equal to zero. With the above mentioned formulae and with the temperature coefficient of a single crystal obtained from the curves it is found that of 300 K.

g=0 at $20.09 and e=0 at @2032.

g is negative for i 0.09 and e is negative for I 0.32. It appears to be quite certain therefore that, as regards the technical utilisation of the materials in accordance with the invention, this direction dependence is to be taken into account, and in fact for obtaining uniform results a definite texture, that is to say a more or less rigidly determined value of I is to be imposed upon the structural element of sensibly constant elasticity. A definite I is therefore necessary and is also a means in accordance with the invention for adjusting the temperature coefilcients of the elastic moduli. An isotropic polycrystalline structure (whose I would be 0.2) can frequently not be obtained through processing and it is a better procedure to produce a texture with suitable processing steps; according to this invention, this texture is then to orient with regard to the appearing stress in the structural element, e.g. the texture is produced with regard to the given type and direction of stress or the structural element is cut in suitable orientation from the textured material. The decisive quantity for the texture relationship is in any case the quantity I taken as the mean over the polycrystalline material; P can be represented in a so-called pole figure,

which is done in FIG. 3 (for the cubic case). The product-sum I must have a value u2 for the elastic modulus and 02 for the shear modulus in cubic materials. Similar relations as above hold for the temperature coefiicients of hexagonal materials when expressed in terms of single crystal-properties (however more complicated) in this case however I O.25 for the elastic modulus and I 0.25 for the shear modulus. Such texture relationships can be determined and controlled by wellknown techniques of X-ray crystallography.

A texture can be achieved by drawing and/or rolling at room or elevated temperatures; recristallization annealing is also a process to create or sharpen a texture. In this connection, the conditions are frequently such that, for example, in cubic body-centered materials (pure metals, alloys behave frequently otherwise) the 110 direction lies parallel to the drawing or rolling direction I against this working direction), and for cubic facecentered materials a portion of the crystallites adjusts its 100 direction and another part its 111 direction parallel to the drawing or rolling direction (against the working direction, 1 has then values between near 0 and 0.33).

In FIG. 4 there are set out the crystal structures of the elements and the approximate phase structure of the binary alloy series of the transition metals. The comparison with FIG. 1 now shows the previously stated fact that the materials in accordance with the invention are not restricted to a fixed crystal structure. On the contrary such materials in accordance with the invention are consistent also with complex structures if the condition is fulfilled that I\ (E is large and that TABLE 1 40 atom percent Ir 60 atom percent- Nb 67 atom percent. Re 33 atom percent. W 67 atom percent- R11 33 atom percent Ca 1-phaso. }Of structural type wMn. }Of structural type 015 (Laves phase).

According to this invention, given ranges of the electron concentration e/a (which are in fact a consequence of physical requirements concerning the susceptibility) and processing steps which must impose minimum respectively maximum values of (which is a description of the texture) are necessary to obtain structural materials whose rigidity is essentially temperature-independent. Useful materials have furthermore to satisfy the conditions of high strength and hardness and small mechanical losses (for example in oscillators for time-keeping devices and electromechanical filters) and hardening processes are adopted such as cold Working, dispersion hardening, precipitation hardening, polyphase structure, addition of alloying elements for chemical hardening, phase transformation, either individually or combined with each other.

Cooperative processes of the electrons characterise magnetic phenomena. On account of this cooperative aspect and therefore of the wide range of interaction, magnetic phenomena suffer strong perturbation by cold work or external fields; the classical ferromagnetic alloys with constant elastic modulus show in fact a marked decrease of the temperature coeificient when cold worked or exposed to a magnetic field. Such influences are absent in materials according to the invention. A high density of states fi(E signifies in fact that geometrical and chemical perturbations of the perfectly regular lattice, e.g. lattice faults and interstitial impurity atoms, are well screened off (substitutional atoms, either impurities or alloying additions are considered as bonding components), while at the same time the reciprocal forces between the faults diminish. The work-hardening of such materials is influenced and relaxation processes which are connected with the interaction between structural faults and impurities, may become important. In this respect the very important property for the structural materials according to the invention appears to be the fact that the elastic behaviour and its temperature coefficient are modified not at all or only slightly by cold working; this is in contrast to the classical ferromagnetic materials. Therefore this behaviour permits making full use of cold working steps for the production of a texture. It is however important in the case of the materials in accordance to this invention to supervise and control the content of dissolved substances of low atomic number, which are susceptible to occupy interstitial places; in higher concentrations these substances may embrittle the materials and a lower content may provide relaxation processes. These relaxations modify the elasticity behaviour over limited temperature ranges, and can be unwanted under certain circumstances but wanted for the benefit of adapting an elasticity-temperature curve in others.

Alloy systems of structural materials according to this inventions, and which shall be capable of polyphase hardening, precipitation hardening or dispersion hardening, have an electron concentration e/a where at least the main phase lies in the previously given ranges. These hardening mechanisms involve different phases or a phase decomposition. The properties of the whole depend then on the proportions of present phases, which themselves have different e/a-values and hence also different thermoelastic properties. Resulting from the inconsistency, there now appears a basically different behaviour of paramagnetic alloys. As is evident from FIG. 1c, very small temperature coefficients alternate with strongly negative coefficients of temperature within very closely adjacent e/a ranges. Definite relationships between these temperature coeificients now hold so that, for a given alloy which is brought into the oversaturated metastable condition, the temperature coefficient is adjustable through a different annealing heat treatment. An example of this is the hardenable alloy system 25% zirconium and 75% niobium, which when rapidly cooled down from, for example, 1000 C., can then be cold formed about by drawing (whereby a 110 drawn texture results), whereafter a heat treatment at SSW-600 for four hours brings the required properties. Before this thermal treatment the temperature coefficient is positive, but with the phase separation, the zirconium rich mixed crystal separates which has a markedly negative temperature coefficient, separates out and makes the temperature coetficient of the whole more negative and towards zero. The electron concentration e/ a of this alloy amounts to 4.75.

Processes essentially similar take place in precipitation hardening. A material in accordance with the invention of given electron concentration is heat treated above the temperature dependent solubility limit (Solvus) and quenched, and then (possibly after cold forming) heat treated below the solubility limit. Due to the displacement of e/a in the matrix and the contribution of the precipitate, the adjustment of the temperature coefiicient is achieved. Addition elements whereby the precipitation hardening can be achieved without an excessive degree of solubility usually follow definite laws, known as the Hume-Rothery Laws. An example is an alloy of Nb and 5% Cr which has an e/a value of 5.1 and which can be subjected to a similar treatment to that above described for the Nb Zr alloy. In this case the precipitated phase effecting the hardening is NbCr Such alloys are suitable for use in tuned measuring devices, for example clocks and in fact for its elastic elements in the form of spiral springs, tuning forks or other forms of vibratory element. Furthermore electromechanical filters may be made from such alloys. Spring elements which have such small thermoelastic coefficients are employed also for force measurement, for example in balances, electrical measuring instruments, levelling apparatus and similar devices. Another application of such alloys is for structural materials capable of retaining their rigidity over a wide temperature range; such needs are for example present in turbines, planes, or rockets where components are subjected to mechanical stresses and whose elasticity shall not vary with temperature or where stresses might induce oscillations which should be controllable over a wide temperature range.

What we claims is:

1. A method of producing an elastically stressed body of a non-magnetic elinvar which comprises:

(a) mixing in the liquid state metallic components so as to obtain an alloy system whose atomic paramagnetic susceptibility x is larger than 5010* e.m.u./ mol at room temperature and which has a negative temperature coefficient of susceptibility d /dT,

(b) solidifying said metallic components,

(c) producing a preferred orientation of the crystallites of the system by at least a mechanical treatment, followed by at least one additional mechanical and/or thermal treatment, said preferred orientation being defined by the mean value of the product sum of the direction cosine taken overall the crystallite orientations with respect to the stress direction, said value being in cubic crystal structures greater than 0.2 for the elastic modulus and smaller than 0.2 for the shear modulus, and said value being in hexagonal crystal structures smaller than 0.25 for the elastic modulus and greater than 0.25 for the shear modulus.

2. A method as claimed in claim 1, wherein the alloy system has an electron concentration e/a within the range of 2.73.5.

3. A method as claimed in claim 1, wherein the alloy system has an electron concentration e/ a within the range of 4.45.3.

4. A method as claimed in claim 1, wherein the alloy system has an electron concentration e/a within the range of 6.2-7.4.

5. A method as claimed in claim 1, wherein the alloy system has an electron concentration e/ a within the range of 95-103.

6. A' method as claimed in claim 1, wherein the alloy system contains up to 10% by weight of a component promoting precipitation hardening.

7. A method as claimed in claim 1, wherein the alloy system contains up to 2% by Weight of a component promoting dispersion hardening.

8. A method as claimed in claim 1, wherein the elinvar is multiphase.

9. A method as claimed in claim 1, including the step of producing a preferred orientation by drawing.

10. A method as claimed in claim 1, including the step of producing a preferred orientation by rolling.

11. A method as claimed in claim 1, including the step of producing a preferred orientaiton by recrystallization annealing.

12. A method as claimed in claim 1, including the step of producing a preferred orientation by drawing or rolling, and recrystallization annealing in the temperature region of homogeneous equilibrium phase structure.

13. A method as claimed in claim 1, including the step of producing a preferred orientation by hot drawing.

14. A method as claimed in claim 1, including the step of producing a preferred orientation by hot rolling.

15. A method as claimed in claim 1, further comprising the steps of cold working and annealing for obtaining an adjutment of the temperature coefficient.

16. A method as claimed in claim 1, further comprising the steps of quenching and annealing at lower temperature for obtaining an adjustment of the temperature coefficient.

17. A method as claimed in claim 1, wherein the temperaure coefficient is adjusted, sai-d adjustment including steps of a heat treatment above the equilibrium decomposition temperature and quenching, followed by a heat treatment below the decomposition temperature.

18. A method as claimed in claim 1, wherein an alloy system consisting of 10-40% zirconium and the remainder of niobium is rapidly cooled from a high temperaure, subjected to more than 30% of cold working and then subjected to a heat treatment at 500-650 C. for a sumcient time to obtain the required temperature coefficient in the body when cooled.

19. A method as claimed in claim 6, wherein the precipitation hardening component consists of 2-10% chromium and the remainder niobium.

20. A method as claimed in claim 1, wherein the system contains oxygen, nitrogen, boron, beryllium or hydrogen in trace amounts.

References Cited UNITED STATES PATENTS 3,167,692 1/ 1965 Matthias -174X 3,215,569 11/1965 Kneip, Jr. et al 75-174X 3,253,191 5/1966 Treuting et a1. 14811.5X 3,271,200 9/1966 Zwicker 14811.5 3,275,480 9/1966 Betterton, Jr. et a1. 14811.5X 3,374,123 3/1968 Masumoto et al. 148--11.5

L. DEWAYNE RUTLEDGE, Primary Examiner G. K. WHITE, Assistant Examiner US. Cl. X.R. 148--12.7, 13, 158

Images