METHOD OF MANUFACTURING SINTERED COMPOSITIONS Ivor Jenkins, Pinner, England, assignor to The General Electric Company Limited, London, England Claims priority, application Great Britain October 30, 1952 7 Claims. (Cl. 75-401) This invention relates to compositions mainly comprising a metal or metals and containing also a minor proportion of one or more non-metallic elements: such compositions are hereinafter referred to as metallic compositions. The invention also relates to methods of manufacturing such metallic compositions.
It is Well known that the mechanical properties of many metals and alloys show a progressive deterioration with increasing temperature. For example, when the metals or alloys, of which machine parts are usually constructed, such as alloy steels, are subjected to high temperatures for prolonged periods of use, they usually show a progressive deterioration in mechanical properties, in particular, they suffer a decrease in resistance to deformation, which is gradual at lower temperatures and usually becomes more rapid as the operating temperature increases. This undesirable change in properties is apparently to be ascribed to changes in the structure of the metal, for example, grain growth which takes place at high temperatures.
It is an object of the present invention to provide metallic compositions having increased resistance to deformation and improved stability under the application of stress and at elevated temperatures. It is a further object of the invention to provide a method of manufacturing such metallic compositions of improved structural stability.
According to one aspect of the invention, a metallic composition is provided which consists of a major constituent composed of a basis metal or an alloy of two or more basis metals, and a minor constituent composed of an association of the atoms of a metal and a non-metal which are capable of forming a compound which is substantially insoluble in the major constituent, or of two or more such associations, the zones in which said association or associations occurs or occur being uniformly distributed throughout the major constituent.
The associations of atoms referred to in the preceding paragraph will hereinafter, for the sake of convenience, be referred to as complexes.
The atoms of the complex or complexes forming the 'minor constituent must be so incorporated in the basis metal or alloy forming the major constituent as to distort the crystal lattice of the latter. Compounds whose elements may be used to form the minor constituent in the metallic compositions of the present invention are the silicides, borides, nitrides, carbides and oxides of the metals titanium, Zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten and tellurium.
According to another aspect of the invention a method of manufacturing a metallic composition consisting of a basis metal and one or more complexes of a metal with a non-metal comprises mixing together in powder form the basis metal, at least one compound or alloy of said basis metal with one of the non-metallic elements silicon, boron, nitrogen, carbon and oxygen, and at least one alloy of said basis metal and one of the metals titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten and tellurium, which latter metal is capable of forming with the non-metallic element employed a com- 2,852,366 Patented Sept. 16, 1953 2 pound which is substantially insoluble in the basis metal, the basis metal forming the major consituent of the mixture, and pressing and sintering the mixed powders to form a coherent body.
According to a further aspect of the invention a method of manufacturing a metallic composition consisting of two or more oasis metals capable of forming an alloy, and one' or more complexes of a metal with a non-metal comprises mixing together in powder form one or more of said basis metals, at least one compound or alloy of one of the said basis metals with one of the non-metallic elements silicon, boron, nitrogen, carbon and oxygen, and at least one alloy of one of the said basis metals with one of the metals titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, and tellurium, which latter metal is capable of forming with the non-metallic element employed a compound which is substantially insoluble in the basis metal or metals, the basis metal or metals forming a major constituent of the mixture, and pressing and sintering the mixed powders to form a coherent body.
Suitable basis metals for use in manufacturing metallic compositions in accordance with the invention are, for example, iron, aluminum, chromium, cobalt, copper, magnesium, molybdenum, nickel, tantalum, titanium, tungsten and Zirconium.
The silicides, borides, nitrides, carbides and oxides, which are incorporated in the metallic compositions in accordance with the invention, have a stabilising effect on the basis metals, that is to say, they prevent or reduce the occurrence of grain growth and creep at high temperatures and under stress, and therefore prevent or considerably reduce the rate of deterioration of the me chanical properties, in particular, the reduction in resistance to deformation of the metallic compositions during use at high temperatures or under conditions of stress. The proportion of such stabilising complex or complexes employed is preferably not more than 10% by weight of the metallic composition, the optimum proportion usually being less than 2% by weight.
As an example of the use of the method of the invention for stabilising a single basis metal, nickel has been stabilised by means of a titanium-silicon complex, forming a titanium-nickel-silicon composition. This composition is manufactured in accordance with the invention, by pressing and sintering a mixture of powdered nickel, powdered nickel-titanium alloy and powered nickel-silicon alloy. Similarly, nickel may be stabilised by means of a titanium-boron complex, the composition being manufactured by pressing and sintering a mixture of nickel, nickel-titanium alloy and nickel-boron alloy, all in powder form.
During the sintering operation, the stabilising complex or complexes is or are formed in the metallic composition by a reaction between the alloys containing the constituents of said complex or complexesthe complex or complexes thus being in a state of dispersion throughout the mass of the basis metal or basis alloy. The mechanism of the reaction which takes place is not precisely known, but it is believed that there is at least incipient precipitation of the silicide, boride, nitride, carbide or oxide, the incipient precipitate being dispersed throughout the basis metal or alloy-each of the compounds just mentioned being one having a relatively high energy of formation. For example, referring to the formation of the nickel-titanium-silicon composition mentioned above, titanium and silicon are both soluble in nickel,
and it appears that when a mixture of nickel-titanium alloy and nickel-silicon alloy is heated the titanium and silicon atoms become preferentially disposed relatively to one another within the crystal lattice of the basis metal (nickel) preparatory to precipitation as a distinct phase,
-as;.titanium silicide or titanium boride.
- 3 and some (or even complete) actual precipitation may occur. This reaction .is due to .the fact that titanium silicide has a high energy of formation: the silicon will combine with that element, among those elements present,,with which 'itforms a compound of the lowest free -energy, which compound is also the least soluble and therefore, tends to be precipitated.
When two or more basis metals are present the two xronstituents .of the stabilising complex may be added 'in the formcf alloys, either with the same basis metal :or with different basis metals.
In the manufacture of metallic compositions in accord- :ance with the invention, the pressure to which the mixture of powders is subjected must be sufiicient to form a compact body which can be sintered and is usually at least 20 tons/sq. in. The sintering may be carried out :in pure hydrogen, that is to say, hydrogen which is substantially free from nitrogen and oxygen, or in vacuo; the sintering temperature will vary according to the basis metal-or metals present in each case.
Some specific methods of manufacturing metallic compositions in accordance with the invention will now be "described by way of example.
Example 1 Forthe manufacture of a nickel-titanium-silicon composition'in'which the titanium-silicon complex performs 'thc function of stabilising the nickel, small proportions of a nickel-titanium alloy and a nickel-silicon alloy are added to nickel powder. The nickel-titanium and nickelsili'con alloys are prepared bymelting mixtures of nickel and titanium powders, and nickel and silicon powders respectively, in purified hydrogen in an induction fur- .nace, allowing the: alloy thus formed to freeze in the crucible, and crushing the resulting solid alloy in a tungsten carbide mill to form a powder sufficiently fine to pass through a 200 mesh sieve. The compositions of the alloys thus prepared are 81% nickel,'19% titanium in the case of the nickel-titanium alloy, and 71.9% nickel to 281.1% silicon in the case of the nickel-silicon alloy.
The nickel-titanium and nickel-silicon alloys prepared as described above are mixed with nickel powder in such proportions that the mixture contains approximately 1% of titanium and 1% of silicon by. weight. The mixed powders are pressed at 35 tons/sq. in. and the pressed bodies thus formed are sintered at 1250 C. in anatmosphere of pure hydrogen.
Example 2 .A, nickel-titanium-boron composition, in which the staubilising complex is composed of titanium and boron, is
prepared in a manner similar-to that described in Exam- .ple 1 with referenceto a nickel-titanium-silicon composi- 'tion, the nickel-silicon alloy being replaced in this case by a nickel-boron alloy of composition 90.9% nickel and 9.1% boron by weight. The nickel-boron 'alloy is prepared-in-asimilar manner to the nickel-silicon alloy described in Example 1.
The; metallic compositions in which the major constituent is 'nickeL manufactured as described in Examples 11; and 2,."may'v be worked and drawn into the form of wire rwhichis then annealedat temperatures up to 1100 C. .Themechanical.properties of wire manufactured in this way and annealed at various temperatures have been :determined at room temperature and compared with thosepfnickelcontaining no stabilising complexes such It has been found that whereas nickel containing no stabilising complexes, annealed at temperatures above 700 C., showed a projgrcssive deterioration in tensile strength up to an annealing temperature of 900 C., followed by a further sharp :decline-wvhich may be associated with excessive grain :gr'owth:.at higher annealing temperatures, both the nickel .compositions containing titanium silicide and titanium boiidexrespectively showed little deterioration in tensile elongation when annealed at the higher temperatures within this range.
X-ray examination of samples of the nickel-titaniumsilicon and nickel-titanium-boron compositions which had been annealed at 600 C. and 1000 C. showed that in both these alloys there was an appreciable expansion i and distortion'of the nickel, these features being brought about by the early stages of precipitation of the titanium silicide and titanium boride respectively.
I claim:
1. A method of manufacturing a metallic composition composed of a major constituent comprising atleast one i metal selected from the group consisting of iron, aluminum, chromium, cobalt, copper, magnesium, molybdenum, nickel, tantalum, titanium, tungsten, and zirconium, and a minor constituent comprising at least one complex of a metal with a non-metal, said majorconstituent forming at least 90% of the metallic composition and said minor constituent forming not more than 10% of the metallic composition: which method comprises, mixing together in powder form themajor constituent,-at least one compound of said major constituent with the complexing non-metallic element which non-metallic element is selected from the group consisting of silicon, ,boron,.nitrogen, carbon and oxygen, and at least one alloy of said major constituent with the complexing metal which is difierent'from the metal selected as the-major j constituent and is selected from-the group consisting of titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten and tellurium, which latof formation than any compound which the non-metallic element could form with the major constituent in the conditions employed, and pressing and sintering the mixed powders to form a coherent body in whichsaid complex, consisting of groupings of :atomscorresponding empirically to said substantially insoluble compound, is uniformly distributed throughout the major constituent in a stable state of incipient precipitation.
2. A method of manufacturing a metallic composition composed of a major constituent comprising at least two metals selected from the group consisting of iron, aluminum, chromium, cobalt, copper, magnesium, molybdenum, nickel, tantalum, titanium,'tungsten, and zirconium and capable of forming an alloy, and a minor constituent including at, least one complex of a metal with a non-metal, said major constituent forming at least 90% of the metallic composition and said minor constituent forming not more than 10% .of the metallic composition: which method comprises mixing togetherin powder form at least one of the metalsv of said major constituent, at least one compound of one of the metals of said major constituent with the complexing non-metallic element which non-metallic element is selected from the group consisting of silicon, boron, nitrogen, carbon and oxygen, and at least one alloy of one of the metals of said major constituent with the complexing metal which is different fromany of the metals selected to form the major constituent and is selected from the. group consisting of titanium, zirconium, vanadium, niobiumftanj talum, chromium, molybdenum, tungsten and tellurium, which latter metal is capable of forming with thevnonmetallic element employed a compound which is substantially insoluble in the major constituent and has a higher energy of formation than any compound which the non-metallic element couldformwith any one of the -metals of the major constituent in the conditions employed, and pressing and .sintering the mixed powders to forma coherent body in which said complex, consisting of groupingsof ,atoms corresponding.-.empirically. to
said substantially insoluble compound, is uniformly distributed throughout the major constituent in a stable state of incipient precipitation.
3. A method according to claim 1, wherein the proportion of the minor constituent is less than 2% by weight of the metallic composition.
4. A method according to claim 1, wherein the basis metal is nickel and the minor constituent is composed of titanium and silicon, and wherein the nickel-titaniumsilicon composition is manufactured by pressing and sintering a mixture of powdered nickel, powdered nickeltitanium alloy and powdered nickel-silicon alloy.
5. A method according to claim 1, wherein the basis metal is nickel and the minor constituent is composed of titanium and boron, and wherein the nickel-titaniumboron composition is manufactured by pressing and sintering a mixture of powdered nickel, powdered nickeltitanium alloy and powdered nickel-boron alloy.
6. A method according to claim 1 wherein the pressing is carried out at at least twenty tons per square inch.
7. A method according to claim 2, wherein the proportion of the minor constituent is less than 2% by weight of the metallic composition.
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