UIlItGd States Patent [19] [11] Patent Number: 4,647,386 Jamison [45] Date of Patent: Mar. 3, 1987

[54] INTERCALATED TRANSITION METAL Attorney, Agent, or Firm-—Robert E. Harris BASED SOLID LUBRICATING COMPOSITION AND METHOD OF SO [57] ABSTRACT , FORMING A solid lubricating composition and method for form ing such a composition are disclosed. The composition [76] Inventor: Warren E. Jamison, 528 Parkview Ave., Golden, Colo. 80401 is formed by intercalating a transition metal that has been chemically reacted with to form a lay [21] App]. No.: 538,137 ered structure. The transition metal is selected from [22] Filed: Oct. 3, 1983 niobium, tantalum, tungsten and/or an including one or more, and the transition metal is chemically [51] Int. Cl.4 ...... C10M 125/22 combined with chalcogen selected from , sele [52] US. Cl...... 252/25; 423/561 R nium and/or a combination which can also include [5 8] Field of Search ...... 252/25; 423/561 R tellurium to form a layered transition metal dischal [56] References Cited cogenide prior to intercalation with a metal, preferably U.S. PATENT DOCUMENTS a coinage metal. The effect of intercalation is to expand the lattice to create a composition having excel 3,573,204 3/1971 Van Wyk ...... 252/12 Thompson 252/12 lent lubricating characteristics the performance of 3,763,043 10/1973 which is not adversely effected by operation in a high 3,769,210 10/1973 Cais et a1...... 252/25 4,040,917 8/1977 Whittingham . .. 204/36 temperature environment. 4,094,893 6/ 1978 Dines ...... 252/25 Primary Examiner——.lacqueline V. Howard 16 Claims, 5 Drawing Figures US. Patent Mar. 3, 1987 Sheet 1 of2 4,647,386

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I I I l I I I00 I50 200 250 300 350 TEMPERATURE,(°C) Fig. i 3

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PZHQFEMOU202.21“ S6l2. .______O la.069 l5.0 I4. l6. l7. 15 I9. mnm‘mmmmmwm X in AX NbSez Fig. 4

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Flg' 5 FRICTKSN COEFFICQIENT 4,647,386 1 2 gears. Therefore, these powders are normally used in INTERCALATED TRANSITION METAL BASED combination with binders which bond them to surfaces SOLID LUBRICATING COMPOSITION AND or are used in combination with a structural material to METHOD OF SO FORMING form self-lubricating solids. While solid lubricants have heretofore been sug Government Rights gested and/or utilized, particularly where liquid lubri The Government has rights in this invention pursuant cants could not be satisfactorily utilized, such solid to Contract No. F336l5-78C-5l96 awarded by the De lubricants have nevertheless not been found to be satis partment of Air Force. factory, at least for some applications, and better solid lubricating compositions have therefore still been FIELD OF THE INVENTION needed. This invention relates to a solid lubricating composi tion and method for forming such a composition, and, SUMMARY OF THE ‘INVENTION more particularly, relates to an intercalated transition This invention provides an improved solid lubricat metal based solid lubricating composition and method ing composition that is particuarly useful in hostile envi for so forming. ronments such as is presented under high temperature BACKGROUND OF THE INVENTION conditions. The lubricating composition is formed from a transition metal that has been chemically combined Liquid lubricants are well known and such lubricants with a chalcogen to form a layered transition metal have been, and are now, successfully used for many dichalcogenide (LTMD), and then intercalated with a diverse purposes. Liquid lubricants have not, however, metal to cause expansion of the crystal lattice. proved to be satisfactory for some uses, including, for It is therefore an object of this invention to provide example, use in high temperature environments where an improved solid lubricating composition. combustion or pyrolysis of conventional liquid lubri It is another object of this invention to provide an cants would occur, at extremely low temperatures improved solid lubricating composition useful in hostile where conventional liquid lubricants would freeze or gel, and/or in highly oxidizing environments where environments such as under high temperature condi conventional liquid lubricants would present an explo tions. It is still another object of this invention to provide an sion hazard. For such uses, the powders of crystalline solids have 30 improved solid lubricating composition that is an inter long been used as lubricants, and, more speci?cally, calated transition metal based solid lubricating composi powdered graphite has long been used in industry as a tion. lubricant for use in hostile environments in which oils It is still another object of this invention to provide an and greases are forbidden. improved solid lubricating composition formed by In its natural state, graphite absorbs moisture from 35 chemically reacting a transition based metal with a the atmosphere and this moisture is essential to the chalcogen to form a layered transition metal dichal graphite functioning as a lubricant. If graphite is ex cogenide, and then intercalating the layered transition posed to a vacuum for extended periods however, the metal dichalcogenide with a metal to cause expansion of moisture is lost and the graphite becomes abrasive. To the crystal lattice. overcome this problem, graphite lubricating composi It is still another object of this invention to provide an tions, including iodine and other moisture substitutes, improved method for forming a solid lubricating com have heretofore been developed for speci?c applica position. tions. It is yet another object of this invention to provide an disul?de (M052), a natural material, has improved method for forming a solid lubricating com properties similar to those of graphite but does not 45 position by reacting a transition metal with chalcogen require moisture for good lubricating performance. For to form a dichalcogenide and then intercalating the this reason, molybdenum disul?de has more recently dichalcogenide. been used in the aerospace industry as a lubricant for With these and other objects in view, which will satellites and space vehicles and in other areas where become apparent to one skilled in the art as the descrip oils and greases are forbidden or dif?cult to employ, 50 tion proceeds, this invention resides in the novel con such as, for example, in self-lubricating bearings and struction, combination, arrangement of parts and food processing machinery. In addition, molybdenum method substantially as hereinafter described and more disul?de has also been utilized as an additive to oils and particularly de?ned by the appended claims, it being greases to improve their performance at extremely high understood that changes in the precise embodiment of loads. 55 In attempting to improve the lubricating effectiveness the herein disclosed invention are meant to be included of solid lubricants for space applications, it was empiri as come within the scope of the claims. » cally found that mixtures of silver, antimony oxide and BRIEF DESCRIPTION OF THE DRAWINGS molybdenum disul?de exhibited superior lubricating performance to molybdenum disul?de alone. Subse The accompanying drawings, together with the spec quently, it was found that other metal disul?des and i?cation, illustrate a complete embodiment of the inven diselenides, including tungsten disul?de (W52), molyb tion according to the best mode so far devised for the denum diselenide (M0862), and tungsten diselenide practical application of the principles thereof, and in_ (W Seg) are good solid lubricants. _ which: These materials are usually found in the form of pow 65 FIG. 1 is a representation of a stacked layered con ders, however, which are dif?cult to use as lubricants struction of graphite; for at least some applications, including, for example, FIG. 2 is a representation of a stacked layered con rolling bearings and mechanical components such as struction of molybdenum sul?de; 4,647,386 3 4 FIG. 3 is a graph showing friction coef?cient versus tent should not exceed ?fty atomic percent of the total temperature for selected solid lubricants; chalcogen content. FIG. 4 is a plot of friction coef?cients versus silver The transition metals (T) and (X) are concentration in AXNbSeZ; and chemically reacted to produce a dichalcogenide (TXZ) FIG. 5 is a bar graph showing room temperature with a layered structure similar to that shown in FIG. 2 friction coef?cients for AgXNbSySeZ.y and related mate for molybdenum disul?de. This is effected by mixing rials. powders of the elements and sealing them in evacuated DESCRIPTION OF THE INVENTION vials, which are heated to temperatures above 850° C. for at least 24 hours and then slowly cooled to room Graphite is composed exclusively of carbon atoms temperature. Alternate preparation procedures include which are bonded together in two dimensional hexago passing hydrogen disul?de gas over powders of the nal arrays. Layers consisting of planar arrays of carbon metals at high temperatures and other procedures atoms are stacked, as shown in FIG. 1. The chemical known to persons skilled in the art. bonds within the layers are strong, while the bonds The transition metal dichalcogenides (TX2) are fur which hold the layers together are weak, allowing one ther reacted with a metal which can intercalate the layer to easily slide over another and this enables graph structure of the TX; compound to cause an expansion of ite to be effectively used as a lubricant. the crystal lattice. Metals that can be utilized are cop Molybdenum disul?de has a similar layered structure, per, silver, , germanium, bismuth, lead, and as shown in FIG. 2, in which hexagonal arrays of mo with the coinage metals copper, silver and gold lybdenum atoms are sandwiched between hexagonal being preferred. Germanium is known to produce good arrays of sulfur atoms. The intra-layer chemical bonds lubrication when intercalated into tantalum diselenide, are strong, while the inter-layer bonding is weak, and although the lubricating properties do not appear to be lubrication with molybdenum disul?de is effected by slip or shearing actions between the layers. as good as with coinage metal intercalates. The other listed metals are known to intercalate the transition The group IV metals (Ti), zirconium (Zr) metal dichalcogenides and produce crystal lattic expan and hafnium (Hf), the group V metals (V), sions. niobium (Nb) and tantalum (Ta), and the group VI _; .metals (Cr), molybdenum (Mo) and tungsten The metal intercalate species (M) may comprise from (W) all form layered structures similar to that of molyb about ?ve atomic percent to one hundred atomic per denum disul?de when combined with chalcogen (sul cent of the transition metal (T) content (M005 TX; to fur, and tellurium) atom, and molybdenum and M100 TX2). With the coinage metals, intercalate con tungsten form good lubricating compositions when tents of one-third of the transition metal content are combined with sulfur or selenium. preferred (M033 TXZ). The layered structure of niobium and tantalum disul The intercalate metal may be combined with the TXZ ?des and diselenides are quite similar to those of the 35 compound by mixing powders of the two materials in good lubricating materials, but heretofore such struc the desired proportion, and reacting the mixtures in tures have not exhibited good lubricating properties. In evacuated vials at temperatures above 850° C. for 48 this invention by using intercalation reactions, coinage hours. Other preparation techniques may also be uti metal atoms are inserted between the layers in the crys~ lized, including electrochemical methods, for the inter * tal structures. The effect of these atoms is to cause an calation reactions. With the coinage metals, powders of increase in the separation of the layers and a shift in the the elements (the transition metals, the chalcogens and registry of one layer over another, to thereby effect the intercalate metals) may be mixed and reacted to good lubrication performance in these structures which gether in evacuated-vials as described hereinabove. previously exhibited poor lubricating qualities. In addi Lubrication performance evaluations were made tion, the material thus formed by these intercalation with a reciprocating tester and with a Faville-Levalley reactions have superior structural properties to their Flat Washer Tester. The reciprocating tester was oper molybdenum and tungsten disul?de counterparts, and ated in two modes. In the ?rst mode, a cylindrical pellet have better high temperature lubricating performance. of compacted solid lubricant was held with its axis ver As brought out more fully hereinafter, an improved tical and its end loaded against a flat metal test coupon. lubricating composition preferably includes the transi A load of 1500 g produced a contact stress of 120 psi on tion metals niobium, tantalum and tungsten, chemically the end of a 3/16 inch diameter pellet. The pellet was combined with the chalcogens sulfur, selenium and then moved slowly back and forth over a one inch track tellurium in the approximate ratio of one molecular and the friction force measured. Also, visual observa weight of the metal to two molecular weights of the tions were made on the wear and transfer of lubricant to chalcogen. the metal. In the second mode, a I inch diameter steel The metal may be pure niobium, tantalum or tung ball was reciprocated under the same conditions over a sten, or an alloy of two or more in any ratio, or an alloy solid lubricated substance. of any with another transition metal, or an alloy of any The Faville~Levalley tester was ?tted with a pellet two with another transition metal, or an alloy of all holder and three 3/16 inch pellets on a 1.49 inch diame 'three with another transition metal. The alloying transi ter circle were rubbed against a 52100 steel flat washer tion metals may be chromium, vanadium, molybdenum, at a speed of 100 rpm (390 feet/min. sliding speed). A tungsten, or any other similar metal. These alloying maximum load of 40 pounds was applied which pro transition metals should not exceed thirty atomic per duced a contact stress of 483 psi. cent of the total transition metal content. The reciprocating tester proved to be suitable for The chalcogens may be sulfur and selenium alone or screening bad lubricants from marginal-to-good lubri in any combination, or a combination of sulfur and cants, but was not suf?ciently sensitive to rank the latter tellurium or selenium and tellurium, or sulfur, selenium group. The bad lubricants generally fell into two clas and tellurium. Inany combination, the tellurium con~ ses—those that transferred a non-lubricating ?lm to the 4,647,386 5 6 . substrate, and those that were abrasive. The results are intercalate contents in FIG. 4. Intercalation of only 0.1 summarized in Table l as follows: silver atoms per niobium atom changed the transformed See Table l at end of Speci?cation. NbSez from a poor to a good lubricant, reducing the The non-lubricating ?lm formers included TiSZ, friction coef?cient from 0.238 to 0.070, lower than that T2152 and their intercalated structures as listed in Table of M08; or WSe; under the same conditions. This is l. Abrasive materials that would not form burnished attributed more to the change in structure from 2H ?lms and could not be pressed into pellets included NbSg to 2H MoSz then to any change in interlayer spac PbTaSg, PbTiSg, GeTiSZ, CuTiSz, and AgTiSZ. Gener ing. Addition of more silver increased the friction coef ally, the intercalated structures of the niobium dichal ?cient. This effect is probably due to the greater quan cogenides formed metallic-looking transfer ?lms and tity of silver in the van der Waals gap inhibiting the ran smoothly with reasonable friction coef?cients. interlayer slippage. The lubrication performance tests on the Faville Only the Ag0_33NbSe2 materials were tested at ele Levalley tester were conducted on the niobium sul?des vated temperatures. These samples generally showed a and selenides, tungsten selenides, a single intercalated monotonic increase in friction with increasing tempera tantalum selenide and molybdenum disul?de as a base ture, rather than a minimum friction at temperatures in line material. Results of the tests made on the Faville the 200° C. to 250° C. range, the cause of which is un Levalley Tester as shown in Table 2 as follows: known. See Table 2 at end of Speci?cation. Copper was intercalated into the NbSez structure at % Pellets made from commercial molybdenum disul?de 20 Cu atom per Nb atom. The structural changes are felt to were tested three times during the course of the experi be parallel to those of the Ag intercalated NbSeg. This mental program, and the results were used as a basis for material also exhibited excellent lubricating potential, comparison of other experimental solid lubricants. The with a friction coef?cient which rose steadily from _ molybdenum disul?de (M052) ran smoothly with low 0.070 as temperature was increased. friction at temperatures up to 320° C. (608° F.), even 25 Whereas NbSg is a poor lubricant, intercalation of though the high temperature lubricating properties silver at 0.33 atoms per Nb atom transformed it into a were reported to be poor. A minimum in friction coef? good lubricant as shown in Table 2, just as it trans cient was observed at 225° C. As shown in FIG. 3, formed NbSe; into a good lubricant. Mixed sul?des and minimum in friction coef?cients were observed at this selenides show better lubrication performance than 30 temperature for a variety of materials. ' either of the pure sul?des or selenides. For this reason, Tungsten diselenide also is a known good lubricant, a series of samples were made at a constant silver con and exhibited only slightly inferior properties in these - tent with various sulfur and selenium contents. FIG. 5 tests to MoS2. Pellets of WSez were much softer than shows the friction coef?cient of these and related ‘mate pellets of M052, built a metallic looking transfer ?lm 35 rials. Basically, all compositions containing intercalated and wore at a more rapid rate than M082. Silver interca silver proved to be good lubricants, with marginally lated WSeZ exhibited a 2.6% increase in c/na ratio and better performance as the sulfur content was increased. was much softer than even the WSeZ. The material was Intercalation of copper into NbSSe produced the so soft that the pellets wore away rapidly and smeared expected level of lattice expansion, but did not improve material over the test ?xture. The slightly higher fric 40 lubrication performance over that of copper interca tion is attributed to a larger contract area from the lated NbSe2. smeared material. Although the Ag intercalated W562 Intercalation of silver into TaSeg provided a structure did not perform well as a solid lubricant in these tests with poor performance as a solid lubricant as shown in because of excessive softness, the softness may not be Table 2. detrimental in applications where the lubricant is inte 45 In summary, the experimental work conducted shows grated into a supporting stucture, and it is expected that that material with good lubricating potential (at least to the intercalated W862 will exhibit superior lubrication 600° F.) can be prepared by intercalating niobium disul performance to non-intercalated WSeZ, particularly at ?des and diselendies with copper and silver. The chemi high temperatures. cal and physical theory of intercalation with these met Contrary to WSeZ, the AggWSeg did not exhibit sig 50 als suggests that the same properties can be imbued in ni?cantly increased friction at high temperatures. An comparable tantalum compounds. insuf?cient amount of the Cu0_33 W862 was available for The experimental work also showed that the ‘best a thorough evaluation, although preliminary results lubricating performance (under the conditions of test showed it to be harder than the silver intercalated mate ing) was achieved at the lower concentrations of inter 55 rial. calate atoms, although performance was not signi? NbSz and NbSez were con?rmed to be poor lubri cantly impaired at higher concentrations. It is suggested cants by their inability to provide low friction sliding as however, that better high temperature lubrication can shown in Table 2. Both of these compounds exhibited be achieved with higher intercalate concentrations, such high friction that the pellets disintegrated under 60 wherein excess intercalate can inhibit intra-crystalline the conditions of the test. shear and can promote stability through sacri?cial oxi Intercalation of silver into the NbSeg structure was dation. accomplished at ?ve different silver concentrations, As can be appreciated from the foregoing, this inven ranging from 0.1 to 1.0 times the atomic niobium con tion provides an‘ improved solid lubricating composi centrations. With even less than a 3% lattice expansion 65 tion utilizing a transition metal based solid lubricant that the effects on lubrication performance are shown .to be has been reacted with a chalcogen and then intercalated quite remarkable. The room temperature friction coef? by a metal, as well as an improved method for forming cients from Table 2 have been plotted against silver such a composition. 4,647,386 7 8 TABLE 1 Test Friction Temp. No. Con?g. Lubricant Substrate Coeff. (°F.) Observations Rla Pellet M052 Steel 0.179 room Rlb Pellet MoSZ Copper 0.156 room R2a Ball MoSZ Steel 0.074 room R3a Pellet T152 Steel 0.190 room R3b Pellet T182 Copper 0.200 room R3c Pellet TiSZ Brass 0.193 room R3d Pellet TiSZ Alum. 0.163 room R3e Pellet TiSZ Steel - 0.210 300 R31 Pellet T152 - Steel 0.190 500 R3g Pellet T152 Steel 0.177 750 R3h Pellet TiSg Steel -— 1000 Stick-slip R4a Pellet GeTaSg Copper 0.150 room High freq stick-slip RSa Ball GeTaSZ Copper 0.183 room Dull grey burnished ?lm R6A Pellet Cu0_67TaS2 Copper 0.213 room R7a Ball Cu0_67TaS2 Copper 0.348 room Film broke down R8a Pellet TaSz Copper 0.154 room Violent stick-slip R9a Ball TaSz Copper 0.348 room Film broke down. Sample 105-1, previous program RlOa Pellet NbSZ Copper 0.146 room Leaves transfer ?lm R1 la Pellet MoSZ Copper 0.140 room R'12a Ball M052 Copper 0.100 room Rl3a Ball Cu1_0NbSe2 Copper 0.181 room Sample 125-1 from previous program R14A Ball AgOI67NbSeZ Copper 0.109 room Sample 124-3 from previous program RlSa Ball Cu0‘67NbS2 Copper 0.116 room Sample 124-2 from previous program R16a Ball AgQ67NbS2 Copper 0.090 room Sample 124-1 from previous program R 17a Ball M052 . Copper 0.069 room R 1 8a Pellet AgQ_33NbS0_5Se L5 Brass 0.110 room R18b Pellet Ag()_ 33NbSQ_ 5Se145 Steel 0.110 room R 19a Pellet Ago_33NbSSe Steel 0.218 room R 19b Pellet Ag0,33NbSSe Brass 0.311 room R20A Pellet Ag0_33NbS1_5Se0_5 Brass 0.127 room R20b Pellet Ag0_33NbS1_5Se0_5 Steel 0.127 room

TABLE 2 Test Sample Room Friction Coefficient No. Lubricant No Temp 100° C. 225“ C. 270° C. 320° C. F1 M082 Comml 0.114 0.111 0.084 0.094 0104 F2 M082 Comml 0.114 0.114 0.084 0.094 0.101 F3 M052 Comml 0.141 0.141 — — — F4 NbSe; Comml 0.238 0.416 (a) (a) (a) F5 NbSeg Comml 0.238 0.420 (a) (a) (a) F6 NbSZ 127-1 0.336 (a) (a) (a) (a) F7 WSez 132-3 0.128 0.097 0.097 0.141 0.201 F8 AgQ_33NbS7_ 128-1 0.094 0.138 0.064 — — F9 AgQJNbSeZ 137-3 0.070 — — — — F10 AgQZNbSEZ 138-1 0097 — — — - F11 Ag110_33NbSe2 138-2 0.101 0.104 0.114 0.181 0.299 F12 AgQ33NbSe2 134-1 0.114 0.101 0.128 — 0.315 F13 Ag0_33NbSe2 128-2 0.141 0.134 0.074 -— — F14 Ag0_5NbSe2 138-3 0.144 -- -— -- — F15 Ag1_0NbSe2 138-4 0.104 — — — — F16 AgQIIBNbSQjSCLS 135-3 0.101 0.144 0.141 0.128 0.181“ F17 Ag0_33NbSSe 133-2 0.094 0.091 0.091 0.111 0.138 F18 Ag0_33NbSSe 137-2 0.094 0.094 0.117 0.104 0.134 F19 AgQ,33NbS1‘5Se0_5 135-4 0.138 0.134 0.104 0.114 0.084 F20 Ag()_33WSe2 129-2 0.1 14 (b) (b) (b) (b) F21 Ag0_33WSe2 1324 0.121 0.148 0.144 0.104 0.107 F22 AgOI33TaSeZ 128-3 0.188 0.138 0.342 (a) (a) F23 CuQ_33WSe1 129-3 0.134 (c) (c) (c) (c) F24 Cu0‘33NbSe2 133-3 0.080 0.067 0.131 0.185 0.282 F25 CuQ_33NbSSe 137-1 0.117 0.128 0.272 0.295 0.309 (a) Pellets disintegrated from high friction. (b) Pellets crushed from insufficient structural strength, but left good transfer ?lm. (c) lnsuf?eient material to complete testing.

What is claimed is: 1. An intercalated transition metal based solid lubri- 65 cating composition, comprising: and tungsten that also includes an alloying metal a transition metal selected from one of tungsten and selected from one of chromium, vanadium, molyb an alloy including at least one of niobium, tantalum denum, tungsten and iron; 4,647,386 9 10 a chalcogen selected at least in part from one of sul 9. The composition of claim 5 wherein said layered fur, selenium, a combination of sulfur and selenium, transition metal dichalcogenide includes an alloying a combination of sulfur and tellurium, a combina metal that does not exceed thirty atomic percent of the tion of selenium and tellurium, and a combination total transition metal content. of sulfur, selenium and tellurium, said chalcogen 10. A method for forming an intercalated transition being reacted with said transition metal to form a metal based solid lubricating composition, said method layered transition metal dichalcogenide; and comprising: an intercalating metal intercalating said layered tran selecting a transition metal from one of niobium, sition metal dichalcogenide, said intercalating tantalum, tungsten, and an alloy including at least metal being selected at least in part from one of 10 one of niobium, tantalum, and tungsten; copper, silver, gold, germanium, bismuth, lead, mixing and chemically reacting a chalcogen, selected indium and gallium, and said intercalating metal at least in part from one of sulfur, selenium, a com content being equal to between about ?ve atomic bination of sulfur and selenium, a combination of percent and one hundred atomic percent of said sulfur and tellurium, a‘ combination of selenium and transition metal content. 15 tellurium, and a combination of sulfur, selenium 2. The composition of claim 1 wherein said alloying and tellurium, with said transition metal to form a metal does not exceed about thirty atomic percent of layered transition metal dichalcogenide; and the total transition metal content. intercalating by mixing and chemically reacting said 3. The composition of claim 1 wherein said tellurium layered transition metal dichalcogenide with an in any said combination does not exceed ?fty atomic intercalating metal, selected at least in part from percent of the total chalcogen content. one of copper, silver, gold, germanium, bismuth, 4. The composition of claim 1 wherein said intercalat lead, indium and gallium, with said intercalating ing metal content comprises about one-third of said metal content being equal to between about ?ve transition metal content. atomic percent to one hundred atomic percent of 5. An intercalated transition metal based solid lubri 25 said transition metal content, to form a composition cating composition, comprising a layered transition having useful lubricated properties. metal dichalcogenide that has been formed from a tran 11. The method of claim 10 wherein said step of se sition metal reacted with a chalcogen to form niobium lecting said transition metal includes selecting said al dichalcogenide NbSySeZ-y where 0

65