Nickel-molybdenum bonded titanium nitride-titanium carbide

BACKGROUND OF THE INVENTION

There is considerable art available on metal-bonded nitride-carbide cutting tools such as U.S. Pats. No. 1,895,959 and 1,996,220 and more recently No. 3,409,416 and No. 3,409,419. However, none of these references disclose titanium nitride and titanium carbide bonded with the nickel-molybdenum mixture of this invention.

I have discovered that titanium nitride and titanium carbide bonded with the above described nickel molybdenum mixtures when not pressed as described herein form dense fine-grained bodies of outstanding strength which are also quite hard and resistant to wear, scratching, oxidation and corrosion.

SUMMARY

In summary this invention is directed to refractory compositions consisting essentially of from 49.5 to 94 volume percent titanium nitride, from 5 to 49.5 volume percent titanium carbide and from 1 to 15 volume percent of metal consisting essentially of 20 to 50 volume percent nickel and 50 to 80 volume percent molybdenum, said composition having a density in excess of 99 percent of theoretical and an average grain size of less than 2 microns, and to the method of preparing such solid solutions by heating homogeneous mixtures of titanium carbide and titanium nitride powders having a particle size of less than one micron and nickel and molybdenum powders having a particle size of less than 10 microns to a temperature between 1650° and 1900° C., preferably between 1750° and 1850° C. and immediately pressing at a pressure between 1000 and 5000 pounds per square inch and then rapidly cooling the resultant compact.

The resulting dense compositions are useful in making wear resistant and corrosion-resistant parts of exceptional strength and hardness and can be fabricated into attractive articles of jewelry.

DESCRIPTION OF THE INVENTION

This invention is directed to refractory compositions consisting essentially of 49.5 to 94 volume percent titanium nitride, 5 to 49.5 volume percent titanium carbide and from 1 to 15 volume percent metal consisting essentially of from 20 to 50 volume percent nickel and from 50 to 80 volume percent molybdenum, said composition having a density in excess of 99 percent of theoretical and an average grain size of less than 2 microns; and to the method of preparing such solid solutions by heating homogeneous mixtures of finely divided titanium nitride, titanium carbide, nickel and molybdenum powders to a temperature of between 1650° and 1900° C. and immediately pressing at a pressure between 1000 and 5000 pounds per square inch and then rapidly cooling the resultant compact.

Components

The titanium nitride and titanium carbide suitable for use in preparing the solid solutions of this invention should have an average particle size of less than one micron and preferably less than 0.5 micron.

Suitable titanium nitride can be obtained commercially as —325 mesh powder from Materials for Industry, Inc., Ambler, Pa. or Consolidated Astronautics Inc., Long Island City, N.Y. or can be prepared by conventional methods as disclosed in U.S. Pat. No. 3,409,416, in U.S. Pat. No. 3,409,419 or in the “Nitrides” Chapter VIII in the book “High Temperature Technology” by J. M. Blocher Jr., John Wiley & Sons, N.Y., 1956.

Suitable titanium carbide can be obtained commercially as —325 mesh powder from Materials for Industry Inc., Ambler, Pa. or Cerac Inc., Butler, Wis., or can be prepared by conventional methods well known to the art.

If the titanium nitride or titanium carbide obtained has too large a particle size, it can be reduced by simply milling the titanium nitride until the desired comminution is achieved.

The metal powders suitable for use in this invention should have an average particle size of less than 10 microns and preferably less than 2 microns.

Suitable nickel powder can be obtained commercially as Mond standard grade fine nickel powder from International Nickel Co., or can be prepared by conventional methods well known to the art.

Suitable molybdenum powder can be obtained commercially as standard grade molybdenum powder —325 mesh from Sylvania Electric Products Inc., or can be prepared by conventional methods well known to the art.

The four components are preferably quite pure and it is particularly important that they be substantially free of impurities such as oxygen which have deleterious effects on the solid solutions. Minor amounts of impurities normally picked up in milling or mixing the components have little or no deleterious effect on the refractory compositions. Thus small amounts of low melting metals such as cobalt or iron, or higher melting metals such as tungsten, which are ordinarily encountered in milling equipment or media, can be tolerated as can small amounts of refractory materials such as other carbides, nitrides or oxides which are encountered in the handling described above.

As pointed out above, the titanium nitride is ordinarily used in compositions of this invention in amounts of from 49.5 to 94 volume percent. It is preferably used in amounts ranging from 60 volume percent to 85 volume percent as such amounts result in a refractory composition having a very desirable combination of properties and appearance. When amounts of titanium nitride range between 60 and 85 volume percent, it is preferred to use from 12 to 30 volume percent of titanium carbide and from 3 to 10 volume percent of metal.

It is believed that molybdenum penetrates the titanium carbide lattice and it is preferred that a large excess of metal over that which it is believed can be taken up in the titanium carbide lattice not be present. This is so because a large excess of metal reduces corrosion resistance, scratch resistance and hardness of the refractory compositions. It is therefore preferred that there be

3,671,201 present in the compositions of this invention no more than 1 part by volume of metal per part by volume of titanium carbide.

Preparation

The mixture of component powders are prepared much in the manner described in U.S. Pat. No. 3,451,791. Suitable titanium nitride, titanium carbide, nickel and molybdenum, as described above, are homogeneously intermixed, such as by ball-milling, for up to 120 hours or more. The mixed powders are then hot-pressed at temperatures of from 1650° to 1900° C. and preferably between 1750° to 1850° C. and pressures of from 1000 to 5000 pounds per square inch followed by rapid cooling of the compact in the manner described in U.S. Pat. No. 3,451,791.

Refractory compacts

The hot-pressed refractory compacts are characterized by a porosity of less than one percent which translates into a density of at least 99 percent of theoretical, and an average grain size of less than 2 microns. As mentioned above, the preferred compositions of this invention contain from 60 to 85 volume percent titanium nitride, from 12 to 30 volume percent titanium carbide, from 3 to 10 volume percent metal, and have an average grain size of less than one micron. The chemical content as well as the physical properties of the compositions of this invention can be determined by methods well known in the art and described in detail in the U.S. Pats. Nos. 3,409,416; 3,409,419; 3,413,392, and 3,451,791 referred to above.

The solid solutions of this invention demonstrate a hardness of from 92 to about 94 on the Rockwell A scale and a transverse rupture strength of from about 200,000 to almost 325,000 pounds per square inch. This combination of strength and hardness along with their low porosity, fine grain size and refractory nature make the compositions of this invention useful in applications requiring corrosion resistance, oxidation resistance, scratch resistance and wear resistance. They are particularly useful in cutting and turning metal. In addition their distinctive color combined with their resistance to scratching and marring make them desirable for use in articles of jewelry such as watch cases.

This invention is further illustrated by the following illustrative examples wherein parts and percentages are by weight unless otherwise noted.

EXAMPLE 1

This is an example of a composition containing 65 volume percent of titanium nitride, 30 volume percent of titanium carbide, 2.5 volume percent of molybdenum metal, and 2.5 volume percent of nickel metal.

The titanium nitride used is of grade —325 mesh available from Materials for Industry, Inc., and has a specific surface area of 1.1 square meters per gram as determined by nitrogen adsorption. An electron micrograph shows dense particles of irregular shapes with sizes between 1 and about 10 microns, the bulk being between 1 and 2 microns. The carbon content is 0.33 percent and the oxygen content is 0.87 percent. Chemical analysis reveals 76.19 percent of titanium and 18.71 percent of nitrogen.

The titanium carbide powder used has a nominal average particle size of 0.6 micron as measured by the Fisher Sub-Sieve Sizer and a specific surface area of about 10 square meters per gram as determined by nitrogen absorption. This titanium carbide powder “milled to 0.6 micron” grade is commercially available from the Adamas Carbide Corp., Kennilworth, N.J. An electron micrograph of a dry mount preparation shows that the titanium carbide grains are between 0.2 and 3 microns in diameter and sometimes are clustered in the form of loose aggregates. The titanium content is about 77.8 percent, the total carbon content is about 18.8 percent, the free carbon is around 0.07 percent, and the oxygen analyses indicate the oxygen content may vary between about 0.8 to 1.6 percent. Analysis by emission spectroscopy shows that titanium is the major component and also shows 0.5 to 2 percent molybdenum, 0.5 to 2 percent tungsten, 0.5 to 2 percent nickel, 500 to 2500 p.p.m. of aluminum, 200 to 1000 p.p.m. of cobalt, 300 to 1500 p.p.m. of iron, 300 to 1500 p.p.m. of niobium, 200 to 1000 p.p.m. of chromium, 200 to 1000 p.p.m. of silicon, 100 to 500 p.p.m. of zirconium, 50 to 250 p.p.m. of calcium, 50 to 250 p.p.m. of manganese and 5 to 25 p.p.m. of magnesium.

The molybdenum powder used in current standard grade available from Sylvania Electric Products, Inc., Philadelphia, Pa. and has a grain size of less than 325 mesh, a specific surface area as determined by nitrogen adsorption of 0.29 square meter per gram and an average crystallite size of 354 millimicrons as determined by X-ray diffraction line broadening. An electron micrograph shows the molybdenum powder consists of grains Vi to 3 microns in diameter clustered together in open aggregates. Chemical analysis of the powder reveals 0.2 percent oxygen and no other impurities over 500 p.p.m.

The nickel used is a fine powder, available from International Nickel Co., containing 0.15 percent carbon, 0.07 percent oxygen, and less than 300 p.p.m. iron. The specific surface area of the nickel powder is 0.48 square meters per gram and its X-ray diffraction pattern shows only nickel, which from the line broadening has a crystallite size of 150 millimicrons. Under electron microscope, the powder appears as aggregate grains 1 to 5 microns in diameter.

The powders are milled by loading 6000 parts of preconditioned cylindrical cobalt-bonded tungsten carbide inserts, Va, inch long and ¹/4 inch in diameter, into a 1.3 liter steel rolling mill about 6 inches in diameter, also charged with 290 parts of “Soltrol” 130 saturated paraffinic hydrocarbon, boiling range 165-210° C. The mill is then charged with 105.9 parts of titanium nitride, 44.50 parts of titanium carbide, 7.6 parts of molybdenum powder, and 6.6 parts of nickel powder, all of them as above described.

The mill is then sealed and rotated at 90 revolutions per minute for 5 days. The mill is then opened and the contents emptied while keeping the milling inserts inside. The mill is then rinsed out with “Soltrol” 130 several times until all of the milled solids are removed.

The milled powder is transferred to a vacuum evaporator, and the excess hydrocarbon is decanted off after the suspended material has settled. The wet residual cake is then dried under vacuum with the application of heat until the temperature within the evaporator is between 200° and 300° C., and the pressure is less than about 0.1 millimeter of mercury. Thereafter the powder is handled entirely in the absence of air.

The dry powder is passed through a 70 mesh screen in a nitrogen atmosphere, and then stored under nitrogen in sealed plastic containers.

A consolidated billet is prepared from the powder by hot pressing the powder in a cylindrical graphite mold having a cavity with a square cross-section l-'/io inches x l%e inches and fitted with opposing close-fitting pistons. One piston is held in place in one end of the mold cavity while 31 parts of the powder are charged to the cavity under nitrogen and evenly distributed by rotating the mold and tapping it lightly on the side. The upper piston is then put in place under hand pressure. The assembled mold and contents are then placed in a vacuum chamber of a vacuum hot press, the mold is held in a vertical position, and the pistons extending above and below are engaged between opposing graphite rams of the press under pressure of about 600 pounds per square inch. Within a period of a minute the mold is raised into the hot zone of the furnace at 1175° C. and at once the furnace temperature is increased io 1800° C. in 10 minutes, and the temperature of the mold is held at 1800° C. for another 2 minutes to ensure uniform heating of the sample. A pres

3,671,201 sure of 4000 pounds per square inch is then applied through the pistons for four minutes. Immediately after pressing, the mold and contents, still being held between the opposing rams, is moved out of the furnace into a cool zone where the mold and contents are cooled to dull red heat in about 5 minutes.

The mold and contents are then removed from the vacuum furnace and the billet is removed from the mold and blasted with abrasive grit to remove any adhering carbon.

Density of the finished piece as determined by accurate weighing and measurement of the dimensions is 5.48 grams per cubic centimeter, which corresponds to the theoretical density.

The hot pressed composition is essentially nonporous when examined under ΙΟΟΟχ magnification. This property is important since nonporous materials are more corrosion resistant than porous materials of the same chemical composition. Structurally the composition consists of an extremely fine network. The porosity based on optical micrographs is A1/X2 on the ASTM scale of porosity.

Electron micrographs indicate a very fine grain structure, few grains exceeding 1 or 2 microns in size. Electron micrographs show an inter-granular or matrix phase. The micrograph gives the appearance that the metal phase has completely wet the titanium carbide-titanium nitride phase or phases.

The specimen is very tough and does not break or chip when dropped freely to a hardwood floor from a height of 7 feet.

The sample is polished by pressing its faces firmly against rotating diamond impregnated cloth discs. A Beuhler polishing machine is employed for this operation. A 400 grit diamond wheel is used at 1175 revolutions per minute in the first polishing step and a 1000 grit diamond at 550 revolutions per minute is used in a second, finishing step.

The sample polished in this manner has an attractive ornamental appearance with a golden color.

A second sample of the same size is fabricated as above indicated and cut so that 0.070 inch x 0.070 inch square bars for transverse rupture strength are separated from each side of a center piece. Portions of the sample are used for indentation hardness tests and for other product characterization. The average transverse rupture strength as measured by bending the 0.070 inch x 0.070 inch test bars on a inch span is about 300,000 pounds per square inch. The hardness is 93.0 on the Rockwell A scale.

One of the bars used for transverse rupture measurement is crushed and ground up in a carbon steel mortar and the powder thus obtained is used in X-ray diffraction analysis. The X-ray diagram obtained shows a strong face centered cubic pattern with a lattice parameter of 4.2678. This pattern corresponds to a titanium nitride-titanium carbide solid solution. The lattice parameters of face centered cubic titanium nitride and titanium carbide are about 4.24 and about 4.32, respectively. All lattice parameters are given in kX units.

The composition of this example shows excellent oxidation and corrosion resistance, resistance to thermal shock, resistance to scratching, and low reactivity with metals.

The unusual combination of high strength and high hardness added to the above mentioned characteristics makes the composition of this example an excellent material for wear parts, corrosion resistant parts and cutting tools for machining metals.

Polished specimens of this composition can also be used as articles of jewelry.

EXAMPLE 2

The procedure of Example 1 is repeated except that the components are used in amounts to give a composition containing 88.5 volume percent titanium nitride, 10 volume percent titanium carbide, 1 volume percent molybdenum metal and 0.5 volume percent nickel.

Actual amounts loaded in the 1.3 liter steel mill are 144.20 parts of titanium nitride powder, 14.81 parts of titanium carbide powder, 3.66 parts of molybdenum metal powder, and 0.89 part of nickel metal powder.

A square billet prepared as in Example 1 which has a cross-section of Ε/ίβ inches and about 0.300 inch in thickness is cut so that specimens 0.070 inch x 0.070 inch x about 1 inch are obtained from both sides of a center piece.

The bars are used for transverse rupture strength measurements and the value obtained is 275,000 pounds per square inch. The rest of the sample is used for Rockwell A hardness measurement and for other tests. Average Rockwell A value obtained is 93.2.

The density is found to be 5.45 grams per cubic centimeter, which is over 99 percent of the theoretical density.

The composition of this example shown excellent oxidation and corrosion resistance, resistance to thermal shock, resistance to scratching, and low reactivity with metals.

The unusual combination of high strength and high hardness added to the above mentioned characteristics makes the composition of this example an excellent material for wear parts, corrosion resistant parts, and cutting tools for machining metals.

Polished specimens of this composition can also be used as articles of jewelry.

EXAMPLE 3

The procedure of Example 1 is repeated except that the components are used in amounts to give a composition containing 50 volume percent titanium nitride, 36 volume percent titanium carbide, 7 volume percent molybdenum metal and 7 volume percent nickel metal.

The actual amounts loaded into the 1.3 liter steel mill are 81.43 parts of titanium nitride powder, 53.32 parts of titanium carbide powder, 21.40 parts of molybdenum metal powder and 18.67 parts of nickel metal powder.

A consolidated billet is fabricated by hot pressing, and is tested as indicated in Example 1.

The average transverse rupture strength measured is 315,000 pounds per square inch and the average Rockwell A hardness is 92.7.

The density is found to be 5.83 grams per cubic centimeter, which corresponds to the theoretical density.

The composition of this example shows excellent oxidation and corrosion resistance, resistance to thermal shock, resistance to scratching, and low reactivity with metals.

The usual combination of high strength and high hardness added to the above mentioned characteristics makes the composition of this example an excellent material for wear parts, corrosion resistant parts, and cutting tools for machining metals.

EXAMPLE 4

The procedure of Example 1 is repeated except that the components are used in amounts to give a composition containing 45 volumes percent titanium carbide, 50 volume percent titanium nitride, 3 volume percent molybdenum metal and 2 volume percent nickel metal.

The actual amounts loaded into the 1.3 liter steel mill are 66.68 parts of titanium carbide powder, 81.44 parts of titanium nitride powder, 9.17 parts of molybdenum metal powder and 5.33 parts of nickel metal powder.

A consolidated billet is fabricated by hot pressing, and is tested as indicated in Example 1.

Average transverse rupture strength measured is 260,000 pounds per square inch and average Rockwell A hardness is 93.2.

The density is found to be 5.38 grams per cubic centimeter, which is over 99 percent of the theoretical density.

The composition of this example shows excellent oxidation and corrosion resistance, resistance to thermal shock, resistance to scratching, and low reactivity with metals.

The unusual combination of high strength and high hardness added to the above mentioned characteristics

3,671,201 makes the composition of this example an excellent material for wear parts, corrosion resistant parts and cutting tools for machining metals.