US3436802A

US3436802A - Powder metallurgy

Info

Publication number: US3436802A
Application number: US683008A
Authority: US
Inventors: Philip Cohen
Original assignee: Magnetics Inc
Current assignee: Spang and Co; Magnetics Inc
Priority date: 1967-11-14
Filing date: 1967-11-14
Publication date: 1969-04-08
Anticipated expiration: 1986-04-08

Description

United States Patent Ser. No. 683,008

Int. Cl. 1322f 7/00 US. Cl. 29-420.5 23 Claims ABSTRACT OF THE DISCLOSURE Powder metallurgy steps which provide uniformity and reproducibility in the production of alloys are disclosed. Process steps include a powder purification step above about 300 C. but below a temperature where significant agglomeration occurs, low pressure compacting of powder to form a compacted shape of sufficient green strength to permit process handling while maintaining internal porosity and a pervious exterior, internal cleaning of the compacted shape at temperatures which avoid significant sealing of the pervious exterior, and sintering of the compacted shape after internal cleaning. The sintered shape is hot worked, e.g. by rolling or drawing at an elevated temperature. Hot working can be followed by a cold reduction. Processing of reactive metal alloys include steps to inhibit or substantially eliminate contamination of the final alloy by substantially preventing combination of impurities removed from the non-reactive ingredients with the reactive metals. Representative alloy compositions are set forth.

The present application is a continuation-in-part of application Ser. No. 382,398, filed July 13, 1964, of Philip Cohen for Powder Metallurgy and now abandoned.

This invention is concerned with novel powder metallurgy processes and novel powdered metal products.

One field of application for the invention is magnetic alloys. Magnetic alloy quality has to a large extent been dependent on the shortcomings of melt practice-requiring special additives, vacuum treatment, and other laborious provisions to remove or relieve the effect of impurities. While melt practice has been successful in improving magnetic alloy products, results from melt to melt have not been as readily reproducible as good commercial practice requires. Separate melts have to be treated individually, most often with empirical determination of annealing conditions and other requirements,

before proceeding with the fabrication of product from a particular melt.

This invention teaches novel powder metallurgy steps for manufacture of magnetic alloy products which overcome these difficulties of melt practices providing uniformity and reproducibility in magnetic alloys which simplifies core fabrication and yields cores having magnetic properties not formerly attainable by any powder metallurgical process. General teachings of the invention and novel process steps broadly applicable to most magnetic powdered metal alloys will be presented before considering specific alloys.

One prerequisite for a high degree of uniformity and reproducibilty in magnetic materials has been extreme purity in the powdered metal ingredients. P-urity approching 100%, for example 99.95% pure nickel and 99.95% pure iron, is available but the economics involved seriously limits commercial use.

The invention teaches use of certain lower purity powders for producing improved magnetic properties. Commercial powders, around 98.5% purity level, can be used and with the purification pretreatment described hereinafter enhanced magnetic properties result.

The teachings of the present invention also permit use of lower-cost powders, including powdered metal oxides, While still maintaining uniformity and reproducibility using predetermined and standardized processing, e.g. in anneal.

Another important factor for uniformity and reproducibility is particle size. In general, the finer the powder, and the more effective the blending, the better the uniformity will be. Particles permitting passage by a 325 mesh screen, and finer particle sizes produce satisfactory results.

A purification pretreatment of the relatively low purity metallic powders is performed after blending. The powders are treated in hydrogen at 300" C. to 1000" C. or higher, with the temperature and the time being selected to avoid significant welding of the particles. An average pretreatment is 450 C. for several hours. High temperatures can be used in a vertical drop furnace Without excessive agglomeration, generally permitting an increase in heat treatment temperature of 500 C. for a particular metal powder or alloy.

The preblend and purification pretreatment steps permit the use of metal oxide powder since the oxide is reduced to metal in the prepurification step. Metal oxide powders have economic and other advantages. For example, iron oxide powder is available commercially at less than one micron size while iron powder is normally not available below four to five microns. The small oxide particles when blended with other powders provide much better distribution of the various metals to be alloyed.

The pretreatment of the metal powders contributes to uniformity of the material throughout a process billet and throughout a process batch. It is believed that impurities, if any, remaining in the material after pretreatment are uniformly distributed by the process and this contributes to the unusual results. In addition to enhanced magnetic properties, the green strength of process shapes is increased by the pretreatment making them more suitable for the process handling required before sintering.

After the blending and purification pretreatment the metallic powders are formed into the desired shape by pressure compacting. Billet thicknesses of one to four inches are practical. One suitable method is to pour the blended powders into a rubber bag designed for hydrostatic pressing. The bag is filled with metal powder and can be gas-evacuated and purged with hydrogen. Pressure compacting can be carried out at pressures up to about twenty-five tons per square inch but a low pressure compacting, around ten to fifteen tons per square inch is specifically taught by the present invention. The pretreatment of the powders, as described above, helps increase the green strength of these low pressure compacts making them suitable for process handling while maintaining internal porosity and a pervious exterior permitting internal cleaning. At significantly greater pressures than this, porosity is decreased and, in turn, the opportunity for internal cleaning of the compacted shape, an important concept of this invention, is reduced.

After compacting, the shape is cleaned by heat treatment in a controlled environment of hydrogen or other suitable reducing atmosphere, such as cracked ammonia or, in some cases, in a vacuum such as 10- mm. of mercury, at temperatures about 600 C. to 750 C. Heat treatment at significantly higher temperature tends to close off pores at the surface of the shape and prevent or inhibit internal cleaning. The low temperature heat treatment of the invention is continued until it is evident that most impurities have been removed from the compacted shape. This may be determined by measuring the dew point of the exit gas from the heating furnace since the water formed by the hydrogen combining with oxygen is a convenient measure of impurities removed or being removed. Ordinarily, a dew point temperature about C. or lower is desired. Gas analysis, e.g. mass spectrometry, may also be used to determine impurity removal. The length of the heat treatment depends on size of the compacted shape, furnace load, impurity removal tests, and other factors.

Separating the cleaning step from the sintering step, as taught above, provides a high degree of internal cleaning which would not otherwise be available.

The compacted shape, after cleaning, can be sintered in the same furnace by increasing the temperature at any convenient rate to a temperature in the range of 1150 C. to 1450 C. with 1200 C. to 1375 C. being preferred, and holding at the desired temperature for periods up to twenty-four hours as required. Sintering time for most magnetic alloys will fall between ten and sixteen hours and, if a single time is desired which is suitable for most alloys, it should be set at about twelve hours. Having separated the cleaning step, the chief purpose of the sintering is compacting of the metal powders. The combination of sintering with hot working as taught by this invention results in densities equivalent to those obtained in melt practice.

The sintered shape may be removed from the sintering furnace at a high temperature or cooled at any convenient rate within the furnace.

Hot reducing plays an important part in producing the improved product of the present invention. Hot rolling reductions of up to 95% per pass can be employed, dependent on mill, to reduce the thickness of the billet to hot rolled strip gages around .2 inch to .05 inch, most commonly around .1 inch. The hot rolling can be carried out in air with a starting temperature about 1175 C. to 1325 C. The temperature during hot rolling should not drop below roughly 875 C.; this last temperature can guide starting and intermediate temperatures and rolling procedures. It has been found that hot rolling drastically reduces porosity by the closing over and welding together of pores. Hot rolling has other advantages which show up in the improved magnetic properties available when hot rolling is combined with other steps in the invention, but definite reasons for some of these advantages are not fully known at the present time.

The hot rolling can be carried out in a planetary hot mill, or suitable two-high mill. A simple planishing pass may be employed after hot roll reductions in the planetary mill or the strip may be reduced further in a two-high mill following the planetary mill. Heating of the shape in a reducing atmosphere is preferred when the end product is to be .001" or less in order to avoid pitting of the surface. In turn, this avoids breaking of the strip when cold rolling to thin gages.

After cooling, the strip is cleaned of oxides by grit blasting, pickling, heating in a reducing atmosphere or a combination of these before cold rolling. The cleaned, hot rolled strip is usually cold rolled to a gage between .03 inch and .0001 inch with suitable intermediate heat treatment, depending on final application and alloy if required. The cold rolled strip is then formed into parts and a final anneal is applied to the parts to attain desired magnetic properties. The final anneal should be carried out in a protective atmosphere, i.e. either a reducing or inert atmosphere.

Specific alloys and novel products forming part of the present invention will be described in subsequent paragraphs.

In describing specific alloys and core characteristics, standard measurements and definitions as covered in AIEE Standards Paper No. 432 will be used. Simplified definitions of some frequently used terms in discussing particular materials follows:

Saturation flux density (B )-the practical maximum fiux density,

Residual flux density (B )-the flux density remaining in a core after the core has been saturated and magnetizing force is reduced to zero,

Squareness ratio or rectangularitythe ratio of B to B H an indication of hysteresis loop width, AHan indication of the slope of the linear portion of the dynamic hysteresis loop.

Oriented nominal 50% Ni-50% Fe powdered metal alloy In melt practice squareness ratio in the range of 96% to 98% is considered very good. Powdered metal processes have not been known to produce a squareness ratio product over in combination with other acceptable properties. In accordance with the present invention, a squareness ratio of 97% to 99% is consistently obtained while maintaining other commercial acceptable magnetic properties using powdered metals as follows:

Nickel 47% to 49.5%, particle size- 400 mesh and preferably finer. Iron 50% to 52.5%, particle size- 400 mesh and preferably finer. Metal additive Up to 35%, particle size-400 mesh and preferably finer, selected from aluminum, manganese, molybdenum, tin or titanium.

The magnetic properties discussed earlier can be influenced by selection of metal additives, e.g. tin can substantially reduce the H parameter of the alloy, but also lowers the squareness ratio.

After hot rolling, this alloy is cleaned of oxides and can be heat soaked at 1000 C. or higher for periods up to twenty-four hours in order to increase squareness, raise initial permeability, and lower H in the final prodact.

The alloy is then cold rolled. The cold rolling reduction should be around 98% or higher. 97% will produce acceptable product but, at cold reductions of 96% and less, the B,.:B ratio starts to fall off rapidly. No intermediate heat treatment is necessary in the cold rolling except as may be required by particular rolling mill limitations.

The final cold rolled gage can be as thin as .0001 inch. One of the advantages of this product is that the final anneal can be preselected without the requirement for empirical anneal testing and without danger of harming the consistently good magnetic properties of the product.

Annealing ranges coverTemperature: about 1100 C. to about 1250 C. Minimum time: about 15 minutes.

This process yields product with outstanding magnetic characteristics, typically:

B kilogauss 15.6 (B,:B X 100 H percent 98 1 oersteds .20 AH do .020

Cores produced from this alloy meet requirements of very high squareness and high gain and are used in computers, saturable reactors, magnetic amplifiers, switching devices, control circuitry, etc.

Square loop nominal 80% Ni powdered metal alloy This product is consistently reproducible using the following composition:

Nickel 80% to 80.5%, particle size 400 mesh and preferably finer.

and preferably finer.

5 After sintering and cooling, the shape is then reheated near 1200 C. to 1300 C. and hot rolled to about .1 inch to .07 inch.

After hot rolling, the strip is cooled, conditioned, e.g. pickled, and then cold reduced by rolling to .03 inch to .015 inch, with .025 inch preferred. At about .025 inch, the strip is heated in a hydrogen or other reducing atmosphere to 1200 C. to 1300" C., preferably 1250 0, held at this temperature for four to twentyfour hours, preferably about twelve hours, and then cooled. The strip is then cold rolled to final gage ranging from .0001 inch to .006 inch.

After cold rolling to final gage, the strip is slit longitudinally, formed into cores, and given a final anneal. Typical properties for .002 inch material which can be readily reproduced with the composition and process described, are:

B 7.2 kilogauss.

(B :Bm) 100 At least 84%.

H .025 to .036 oersteds.

AH .003 to 006 oersteds, depending on final product anneal conditions.

Typically, the product anneal can range from 1050 C. to 12 C. and from one to four hours without detriment to the above magnetic properties. Slow cooling after final anneal is preferred, for example 1 C. per minute.

Round loop-nominal 80% Ni powdered metal alloy An alloy which will product parts such as cores having much higher initial permeability but lower squareness ratio and core again than the last described alloy can be produced with the following composition:

Nickel 79.1% to 83.5%, particle sizeat least 400 mesh or preferably finer.

Molybdenum 4.0% to 6.5%, particle size400 mesh or preferably finer.

Manganese Up to .6%, preferably about .25 particle size400 mesh or preferably finer.

Iron Balance, particle size-400 mesh or preferably finer.

After the mixing, compacting, cleaning and sintering steps, the compacted shape is hot rolled to a gage of .2 inch to .05 inch.

After conditioning, the hot rolled strip can be heat soaked at 1000" C. or higher for periods up to twentyfour hours in order to improve the permeability of the final product. The strip is cold rolled to final gages ranging from .06 to .0001 inch. Parts formed from this material can be annealed as follows:

Temperature 10001350 C. Minimum time 15 minutes. Cooling rate For selected values of molybdenum and nickel within the above range, there is a cooling rate which maximizes permeability. Typical data are set forth in the following table.

MO-Ni PERCENTAGES FOR MAXIMUM PERMEABILIIY AT RATES OF C. PER MINUTE AND 20 0. PER

Cooling rate (percent Ni) Mo, percent 5 CJmin. 20 CJmin.

The novel steps described above are applicable in the production of other powered metal alloys to enhance magnetic, expansion, or other properties. For example, enhanced magnetic properties also .result when following the steps of the present invention with the following alloys: (nominal percentages shown) 65-68% Ni, 1-3% Mo, balance Fe, and oriented 47-50% Ni, 13% Mo, balance Fe Advantages stemming from the novel steps described above, which are of special value to production of thermal expansion alloys, include close chemistry control throughout the material, low impurity control, and minimum inclusion. Examples of thermal expansion alloys include: (nominal percentages shown) nickel, balance iron nickel, balance iron nickel, balance iron nickel, 17% cobalt, balance iron nickel, 26% cobalt, balance iron 33% nickel, 12% cobalt, balance iron 54% cobalt, 36.5% iron, 9.5% chrominum Other examples of alloys showing improved results with the present powder metallurgy process include: (nominal percentages shown) 1% silver, balance copper 10% copper, balance nickel, and 620% chromium, balance nickel When working with alloys which include vanadium, titanium, zirconium, beryllium, niobium, aluminum, and magnesium, that is alloys which include a reactive metal as an alloying ingredient, the process taught must be car- .ried out in a special way. More specifically, when a reactive metal is present as an alloying ingredient (as distinguished from a small percentage additive as in the high squareness alloy described earlier), the powders require more than just blending and pretreating together. Otherwise, the purification stages can be ineffectual and the resulting alloy can be as contaminated as the original powders.

As previously covered, pretreatment of powders has two purposes, removing powder impurities and softening the metals thereby improving green strength of compacted shapes. Reactive metal powders are selected so as to have the desired state of purity since, because of their reactive nature, they ordinarily cannot be refined at the process temperatures taught. Therefore, for impurity removal purposes, it is the non-reactive metal powders which are refined by the present process. For example in the case of 98.5% purity carbonyl iron powder, it is possible to reach 99.96% iron purity levels by removing carbon, oxygen and nitrogen.

However, it has been found that difficulties with contaminates remain notwithstanding use of pure reactive metals and heat treatment at temperatures which should remove carbon or other undesired impurities from the non-reactive metals. One explanation of this problem is that impurities removed from the non-reactive metals combine with the reactive metals and contaminate the final alloy being prepared. The invention teaches several methods for dealing with reactive metal alloys which inhibit or substantially prevent impurities removed from non-reactive ingredients from combining with reactive metals present.

In one method taught by the present invention the non-reactive and reactive metal powders are preblended and given a purification pretreatment together. However, to avoid contamination of the final alloy in this method, the powder clean-up is exercised under what is termed dynamic conditions, that is under conditions such that impurities from refining of the non-reactive metals, which are in gaseous form, are removed before they can combine to any substantial degree wtih the reactive metals. One procedure is to rapidly flush the heat treatment furnace, i.e. the powder itself, with hydrogen to remove impurities before an opportunity exists for combination with the reactive metals. Another is to apply the purification heat treatment under vacuum conditions, e.g. 10- mm. of mercury.

Another method taught is to purify the non-reactive metals separately from the reactive metals before blending. Temperatures are selected to secure workable purity level for desired end properties while avoiding significant agglomeration of the non-reactive particles. Then at the later presintering heat treatment cleaning step the temperatures can be raised beyond the powder treatment temperature, since some agglomeration can be accommodated, as long as the surface of the compacted shape remains pervious and pores for escape of impurities r not closed off during the cleaning step. With reactive metals present, the presintering heat treatment is carried out under dynamic conditions so that impurities from the non-reactive metals are removed before significant contamination of the alloy can occur.

In the separate pretreatment method, heat treatment of the reactive metals is generally not required. The reactive metals are preselected to have the desired purity level since they would not be refined at the temperatures taught. And, the reactive metals do not generally require a heat treatment to improve green strength properties since the relatively high percentage of non-reactive metals present will ordinarily take care of this requirement.

Another method taught for processing of alloys which include reactive metals is based on a principle of shielding or masking the reactive metal from likelihood of contamination prior to blending with remaining powders in the alloy. For example, when an alloy calls for 0.5% Mg, such reactive metal can be alloyed with a small portion of the total required nickel to form a master alloy before blending with the remaining powders of the final alloy. The master alloy may be of 50% Ni-50% Mg alloy for example. After sintering, this alloy is then pulverized and blended with remaining powders to make the desired final alloy. For example, an alloy calling for 99.5% Ni and 0.5% Mg would be blended from the following powders:

Percent Ni 99 Master alloy 50% Ni-50% Mg 1 Total of a 99.5% Ni 0.5% Mg alloy 100 Alloying of the nickel and magnesium in the master alloy provides at least partial protection of the reactive metal against contamination during process purification steps of the bulk of the final alloy.

The intermetallic compound of nickel and magnesium can be made from high purity nickel and still remain economical because of the small percentage of nickel employed in relation to the final alloy. Or the standard, rela tively lower purity nickel can be used in making the master alloy since because of the 50-50 or other selected relationship of nickel and magnesium in the master alloy, only a small portion of the Mg will become contaminated and impurity percentage level of the final alloy will be well within acceptable limits.

The reactive metal shielding method can be used with reactive metals other than Mg. For example with Al. Requirements for the master alloy are that the sintered master alloy must be brittle enough to permit grinding for subsequent blending with the remainder of the powders.

Typical reactive metal alloys treated in accordance with the present invention include:

55% nickel plus 45% titanium .05 0% zirconiumbalance nickel 2.7% titaniumbalance nickel 4549% iron, 4549% cobalt, and 2-10% vanadium 52% nickel, .15 zirconium, balance iron .05 magnesium, .03% silcon, balance nickel Various novel processes and products have been described in disclosing the invention. In the light of such disclosure, modifications will be possible for those having skill in the art, for example, the advantages resulting from the combination of steps claimed including powder purification, low pressure compacting and low temperature internal cleaning are available with other alloys and with other shapes such as strip or tubing produced by direct rolling pressure compacting, or with wire and tubing drawn from sintered shapes. Therefore, it is to be understood that the scope of the present invention is to be determined by the appended claims.

What is claimed is:

1. Powder metallurgy process for producing high squareness ratio magnetic material including the steps of:

blending finely divided metallic powders consisting essentially, by weight, of

about 47 to 49.5% nickel, up to .35 of a metal selected from the group consisting of aluminum, manganese, molybdenum, tin and titanium, and the balance substantially iron, heat treating the blended metallic powders in an atmosphere containing free hydrogen at a temperature above about 300 C. but below a temperature where significant agglomeration occurs, pressure compacting at least a portion of the heat treated metallic powders at approximately 10 to approximately 15 tons per square inch to form a desired shape having internal porosity communicating with a pervious exterior permitting internal cleaning,

cleaning the pressure compacted shape internally by heating at about 600 C. to about 750 C. in an atmospherically controlled environment selected from the group consisting of a reducing atmosphere and a vacuum, and then sintering the pressure compacted shape in an atmospherically controlled environment selected from the group consisting of a reducing atmosphere and a vacuum at temperatures up to about 1350 C.

2. The process of claim 1 further including the steps of hot rolling the sintered billet with a starting temperature about 1200 C. to about 1325 C. to form hot rolled strips,

cleaning the hot rolled strip of oxide, and then cold reducing the hot rolled strip by cold rolling to a thickness gage between approximately .006 inch and approximately .0001 inch.

3. Powder metallurgy process for producing magnetic material including blending finely divided metallic powders consisting essentially, by weight, of

about to 80.5% nickel, about 4.2% molybdenum, up to .50% manganese, and the balance substantially iron,

heat treating the blended metallic powders in an atmosphere containing free hydrogen at a temperature above about 300 C. but below a temperature where significant agglomeration occurs,

pressure compacting at least a portion of the metallic powders at 10 to 15 tons per square inch to form a desired shape having internal porosity communicating with a pervious exterior permitting internal cleaning,

9 cleaning the pressure compacted shape internally by heat treatment at about 600 C. to about 750 C. in an atmospherically controlled environment selected from the group consisting of a reducing atmosphere and a vacuum, and then sintering the shape in an atmospherically controlled environment selected from the group consisting of a reducing atmosphere and a vacuum at about 1200 C. to about 1375 C. 4. The process of claim 3 further including the steps of hot rolling the sintered shape to form strip having a thickness gage near .1 inch to .07 inch, the hot rolling temperature being above 875 C., then cleaning the hot rolled strip of oxides, cold rolling the strip to a thickness gage about .030

inch to about .015 inch, then reheating the strip in an atmosphere containing free hydrogen at about 1200 C. to about 1300" C., and then cold rolling the strip to a final thickness gage in the range of .03 inch to .0001 inch. 5. Powder metallurgy process for manufacturing magnetic material including the steps of blending finely divided metallic powders consisting essentially, by weight, of

79.1% to 83.5% nickel, about 4% to 6.5% molybdenum, up to .6% manganese, and the balance substantially iron, heat treating the blended metallic powders in an atmosphere containing free hydrogen at a temperature above about 300 C. but below a temperature where significant agglomeration occurs, pressure compacting at least a portion of the heat treated powdered metals at approximately 10 to approximately 15 tons per square inch to form a desired shape having internal porosity communicating with a pervious exterior permitting internal cleaning, then cleaning the pressure compacted shape internally by heating in an atmospherically controlled environment selected from the group consistign of a reducing atmosphere and a vacuum at about 600 C. to about 750 C., and then sintering the pressure compacted shape in an atmospherically controlled environment selected from the group consisting of a reducing atmosphere and a vacuum at temperatures up to 1350 C. 6. The process of claim 5 further including the steps of reducing the sintered product by hot rolling to form strip with a thickness gage of .2 inch to .05 inch, then cold rolling the hot rolled strip to a thickness gage in the range of .06 inch to .0001 inch. 7. Powder metallurgy process comprising the steps of blending an alloy composition from finely divided particles, the particles being selected from the group consisting of chromium, cobalt, copper, gold, iron, manganese, molybdenum, nickel, selenium, silicon, silver, tungsten, and alloys and compounds thereof, heat treating the blended particles in an atmosphere containing free hydrogen at a temperature above about 300 C. but below a temperature where significant agglomeration of the alloy composition occurs, compacting the heat treated alloy composition under pressure to form a desired shape of suitable green strength for process handling while maintaining internal porosity communicating with a pervious exterior permitting internal cleaning, then cleaning the compacted shape internally by heating in an atmospherically controlled environment selected from the group consisting of a reducing atmosphere and a vacuum at a temperature which permits removal of impurities from within the compacted shape without significant sintering of the compacted shape, and following such internal cleaning,

heating the compacted shape to the minimum sintering temperature for the selected alloy composition in an atmospherically controlled environment selected from the group consisting of a reducing atmosphere and a vacuum.

8. The process of claim 7 in which the blended powders are heat treated at a temperature between about 300 C. and about 1000 C.

9. The process of claim 7 in which the purified powders are compacted at a pressure of approximately 10 to approximately 15 tons per square inch.

10. The process of claim 7 in which the compacted shape is cleaned internally in an atmosphere containing free hydrogen.

11. The process of claim 7 in which sintering temperature range for the compacted shape extends to about 1450 C.

12. The process of claim 7 in which sintering is carried out in an atmosphere containing free hydrogen.

13. Powder metallurgy process comprising providing an alloy composition from finely divided powders including at least one high purity reactive metal powder selected from the group consisting of vanadium, titanium, zirconium, beryllium, niobium, hafnium, aluminum, and magnesium, and at least one non-reactive-metal powder selected from the group consisting of iron, nickel, cobalt, molybdenum, copper, chromium, manganese, silver, gold, selenium, silicon, and alloys and compounds thereof, the nonreactive-metal powder being heat treated in an atmosphere containing free hydrogen to at least partially purify such powder, with such heat treatment being carried out so as to substantially prevent impurities removed from the non-reactive-metal powder from combining with the reactive-metal powder, the heat treatment temperature being above about 300 C. but below agglomeration temperature for the alloy composition,

compacting the alloy composition under pressure to form a desired shape of suitable green strength for process handling while maintaining internal porosity communicating with a pervious exterior permitting internal cleaning, then cleaning the compacted shape internally by heating in an atmospherically controlled environment selected from the group consisting of a reducing atmosphere and a vacuum of at least 10 mm. of mercury at a temperature which removes impurities from within the compacted shape without significant sintering of the compacted shape and simultaneous removing impurities from the vicinity of the compacted shape to substantially prevent combination of such impurities with reactive metal present, and following such internal cleaning heating the compacted shape to the minimum sintering temperature for the alloy composition in an atmospherically controlled environment selected from the group consisting of a reducing atmosphere and a vacuum of at least 10- mm. of mercury.

14. The process of claim 13 in which the nonreactive metallic powder is heat treated before combining with reactive metal powder to provide the alloy composition.

15. The process of claim 13 in which the reactive metal powder and the non-reactive-metal powder are blended and the heat treatment to at least partially purify the nonreactive metal powder is carried out with an atmosphere containing free hydrogen being flushed over the alloy composition.

16. The process of claim 13 in which the reactive metal powder and the non-reactive-metal powder are blended and the heat treatment to at least partially purify the nonreactive-metal powder is carried out in a vacuum of about 10 mm. of mercury.

17. The process of claim 13 in which the impurities are removed from the non-reactive-metal powder so as to prevent such impurities from combining with the reactive metal powder by shielding the reactive metal powder from a major portion of the non-reactive-metal powder in a master alloy comprising the steps of preparing a master alloy by blending substantially all of the reactive metal powder with a minor portion of the total non-reactive-metal powder,

sintering such master alloy,

pulverizing the sintered master alloy, and

blending the pulverized master alloy with the remainder of the non-reactive-metal powder prior to heat treatment of the alloy composition powders.

18. The process of claim 13 in which the finely divided alloy composition powders are heat treated at a temperature between about 300 C. and about 1000 C.

19. The process of claim 13 in which the finely divided alloy composition powders are compacted at a pressure of approximately 10 to approximately 15 tons per square inch.

20. The process of claim 13 in which an atmosphere containing free hydrogen is flushed over the compacted shape during internal cleaning.

21. The process of claim 13 in which the internal cleaning of the compacted shape is carried out in a vacuum of about 10- mm. of mercury.

22. The process of claim 13 in which the sintering temperature for the powdered metal product extends to about 1450 C.

23. The process of claim 13 in which sintering is carried out in an atmosphere containing free hydrogen.

References Cited UNITED STATES PATENTS 2,776,887 1/1957 Kelley 75224 XR 2,793,116 5/ 1957 Cuthbert 75224 2,806,786 9/1957 F. C. Kelley 75224 XR 2,928,733 3/1960 Wagner 75224 3,081,529 3/1963 Schwyn 75211 XR 3,144,330 8/ 1964 Storchheim 75226 3,216,824 11/1965 Boghen 75224 XR 3,268,368 8/1966 Mackin 75226 XR 3,293,006 12/1966 Bartz 75-214 XR 3,326,676 6/1967 Riibel 75211 XR 3,326,677 6/ 1967 Alexander 7521 FOREIGN PATENTS 345,736 3/1931 Great Britain. 789,048 1/ 1958 Great Britain.

JOHN F. CAMPBELL, Primary Examiner.

PAUL M. COHEN, Assistant Examiner.

US. Cl. X.R.