CA1224091A - Chemical vapor deposition of metal compound coatings utilizing metal sub-halide - Google Patents

Abstract

ABSTRACT

A process for the chemical vapor deposition on sub-strates of coatings comprising compounds of a titanium sub-group of metals, the vanadium sub-group of metals and the chromium sub-group of metals at temperatures in the range of 250°C. to 850°C. is disclosed. Sub-halides, such as TiCl3, are reacted with N2 and H2 and thermodynamic and kinetic parameters are manipulated by flow rates and partial pressures of the reactants to achieve the deposition reac-tion in the temperature range of 250°C. to 850°C. An apparatus for performing the process is also disclosed.

Description

FIELD OF ~HE ~NVE~T~ON
This inventton relates to chemica~ vapor deposition of compounds of the titanium sub-group of elements and applies in addition to the vanadium sub-group and chromium sub-group o~ elements as coatin~s on a chosen substrate at low temper-atures~ It also relates to a metal compound coated article.
Such coatings can have various uses when applied to a substrate. For example, coatings of the titanium sub-groups are desirable on metalworking tools to increase the useful life of the tool. Others, such as niobium nitride coatings are useful as a super conductive material.

B~CKGROUND ART
Depending upon the use to which the coating is to be put or the substrate on which -the coating is put, the temperature at which a coating can be deposited may be important. Critical temperatures are often involved above which the properties of the substrate are al-tered.
For coating drills and machine tools with compounds of the titanium sub-group of elements to lengthen the useful life of the tool, ni-trides, carbides and carbonitrides of titanium metal are desirable coatings. Compounds such as titanium nitrlde can be deposited as coatings by chemical vapor deposition (CVD) at temperatures of about 1000C or higher.
However, most tool steels are hardened and tempered;
and if temperatures exceeding the tempering temperatures are used, the tools lose their temper and must be re-heat s, treated. When re-heat treated, distortion becomes a problem and tool tolerances are affected. Thus, it is preferable to carry out any coating deposition at temperatures below the softening point of the tool metal in order to avoid affect-ing the temper of the tool steel.
The coating of metalworking tools with titanium ni-tride, is a typical example of a coating situation in which low temperature deposition of the coating is desirable.
Present processes depocit titanium nitride by chemical vapor deposition by passing titanium tetrachloride, nitrogen and hydrogen over the substrate at temperatures of about 1000C.
or higher. Other existing processes, also operating in the range of 1000C. add a hydrocarbon gas, such as methane, to include titanium carbide in the coating deposit. These temperatures have detrimental effects on tool steel temper.
Re-heat treating to re-establish temper detrimentally affects tolerances. For example, tempered steel will lose q hardness above 500 to 600 C., stainless steel will sensitize ~ above 550 C. and nickel based super alloys ~ above 600 C.
It has been found that low deposition temperatures below the temper temperatures of such metals can be used to deposit metal compound coatings of the type discussed above by utilizing sub-halide compounds of the metal in question in the deposition reaction. The phrase metal sub-halides refers to metal halides in which the metal exhibits a valency state (oxidation state) lower than the maximum valency state known for that metal. For example, the maximum valency for titanium is ~, i.e., TiCl~. Therefore, the halide compounds of TiCl3 and TiCl2 where titanium exhibits a valency of 3 and 2, respectively, are titanium sub-halides and, in particular, titanium sub-chlorides.
Similarly, where the maximum valency state of the metal is 5, any halide compound of that metal wherein the metal exhibits a valency state lower -than 5, would be a sub-halide of that metal.
In Canadian Pa~ent NoO 1,087,OAl, -the deposition of hafnium carbide and hafnium nitride coatings by chemical vapor deposition is discussed. At that time, -temperatures typically in the neighbourhood of 1,300C. were required to produce hafnium coatings by chemical vapor deposi~ion. That patent discloses the use of the sub-'nalides of hafnium in the deposition process, and thereby achieve temperatures as low as 900C. in the deposition reaction. However, as discussed above, 900C. is still above the temper loss point for many alloys that it is desirable to coat.
SUMMARY OF THE INVENTION
-It has been found that good coatings with very favourable adhesion, structure and purity characteristics at good deposition rates using deposition temperatures less than 900C., for example, 890C., can be accomplished using metal sub-halides and properly controlling the flow rates and partial pressures of the reactants so as to promote favorable kinetic and thermodynamic conditions to promote acceptable reaction rates at the desired low temperatures. The metal coating of the present invention has shown superior adhesion to a substrate and high cohesive strength compared to known coated articles. Without being limited to any particular theory for this discovery, these improvements may result from uslng low temperatures in my coating process which permits avoiding changes in a substrate material, that adversely will effect properties and performance of the coating, ir~cluding avoiding formation of a weak interlayer between the coating and the substrate and avoiding decarborization of the substrate.
In a preferred embodiment, -titanium nitride coatings have been produced on a substrate by passing a controlled flow at about 40 volumes of hydrogen and about 10 volumes of hydrogen chloride over a bed of titanium metal particles heated to about 500C., mixing 100 volumes of hydrogen and 150 volumes of nitrogen with the resulting hydrogen and titanium chlorides an passing the gaseous mixture over a substrate hea-ted to about 600C.
Further improvements and modifications in the process include mixing the nitrogen with the hydrogen before passing .l the mixture over the titanium metal particles and ammonia gas with the hydrogen and nitrogen mixture prior to intro-ducing it to the substrate but continuing the addition of ammonia gas for a limited period of time. Further improve-ment and modification are obtained by varying the pressureof the gaseous mixture passed over the substrate and main-taining the pressure of the mixed gas around the substrate at a pressure not more than about ~ millimeters of mercury.
The selection of pressure is such as to produce Knudsen flow of the gas.
A thermodynamic analysis indicates that the lower halides (or sub-halides) of titanium, and in particular, titanium bichloride (TiC12), and titanium trichloride (TiC13) (subchlorides of titanium) facilitate a larger reaction negative-free energy value and accordingly a greater potential for reaction involving the deposition of TiN by CVD at low temperatures. Indeed, the potential of titanium bichloride and titanium trichloride to react with nitrogen and hydrogen in a gaseous environment to deposit titanium nitride continues to increase right down to 0 K.
Nonetheless, reaction kinetics can inhibit the deposition of titanium nitride at low temperatures. However, it has been found that the potential for the reaction of TiC12 and TiC13 to form titanium nitride can be tapped in a vapor environ-ment containing nitrogen and hydrogen using reaction temper-atures in the range of 250C. to 850C. Although even lower coating temperatures are possible depending on deposition conditions used to overcome unfavorable kinetics, the temperatures used are intended to take full advantage of the favorable coating rates at a temperature which does not result in loss of temper or hardness in the tool substrates or item being coated. It is essential to keep the free energy of the reaction at or about a predetermined negative value in order that the temperature at which the reaction and the deposition of titanium nitride, in the case of titanium, takes place will be maintained in this temperature range.
In particular, the higher the equilibrium constant (Kp) of the reaction, the lower the reaction-free energy value will be, and accordingly, the partial pressure of the reactants and their flow rates are maintained at carefully controlled levels to permit the reaction to be carried out in the desired temperature range. In addition, the use of ammonia in the chemical vapor deposition stage assists in maintaining a higher equilibrium constant value and in enhancing the coating rates and quality.
Accordingly, titanium nitride is deposited by chemical vapor deposition by reacting titanium bichloride and/or titanium trichloride with hydrogen and nitrogen, and option-ally some ammonia, at a suitable temperature that will not detrimentally affect substrate properties and using flow rates which maintain partial pressures of the reactants, TiC12 and TiC13, at relatively high levels. The favorable thermodynamics and kinetic factors are thereby utilized for the deposition of titanium nitride at the desirable tempera-ture.
Titanium bichloride and titanium trichloride, because of their thermodynamic characteristics in reaction, are important ingredients in the reaction for the deposition of titanium nitride. Titanium bichloride and titanium tri-chloride can be produced by the reduction of titanium tetrachloride, but such reduction yields quantities of both that are smaller than are required to conduct the deposition of TiN at suitably high rates.
Titanium bichloride and titanium trichloride can, of course, be obtained from other sources and simply be fed to a chemical vapor deposition chamber for the production of titanium nitride. Alternatively, a second embodiment of the invention involves a preliminary in situ step for the production of titanium sub-chlorides by passing hydrogen chloride over titanium metal. Such reaction will produce titanium bichloride, titanium trichloride, and titanium tetrachloride and their relative proportions in the gas reaction mixture can be varied by manipulating the titanium metal chlorination conditions such as temperature or the partial pressures of hydrogen and the chlorinating agents such as hydrogen chloride.
To increase the concentration of TiC12 and TiC13, which are less volatile than TiCl~, in the gas reaction mixture, the in situ chlorination of titanium metal and the deposi-tion of TiN in the two stage process can also be conductedat low pressures. ~eduction of pressure in the chlorina-tion process facilitates vaporization of the sub-chlorides which have a higher vapori~ation temperature than TiC14. This, in turn, permits chlorination to be performed at a lower temperature which, in turn, promotes production of the sub-chlorides. The use of low pressures in the vicinity of ~ millimeters of mercury pressure in the second stage of the process, that is the deposition of titanium nitride, also enhance the operation by improving the kinetic factors which favor deposition of titanium nitride on the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood with reference to examples which follow and with reference to the following figures, in which:
Figure 1 shows the standard free energy versus tempera-ture plots for the reactions of titanium tetrachloride, TiC14, titanium trichloride, TiC13, and titanium bichloride, TiC12, with nitro~en and hydrogen to deposit titanium nitride, and;
Figure 2 shows the two-stage process to carry out the chemical vapor deposition of titanium nitride at low temper-atu.res utilizing the sub-chlorides of titanium metal such as TiC12 and TiC13.

DESCRIPTION OF THE INVENTION
Figure 1 includes a thermodynamic evaluation of the potential reactions available in a CVD coating process using titanium chlorides and indicates what reactant is preferable for reaction in any desired temperature range. In particu-lar, Figure 1 shows the standard free energy versus tempera-ture plots for reactions 1, 2 and 3 below:
4(g) / 2(g) 2(g) (s) (g) TiC13(g) 1/ N2(g) 3/2H2(g)~~ T (s) C (g) ( )

2(g) / 2(g) 2(g) ~ (s) (g) Figure 1 indicates the standard free energy values ( ~G) for these reactions at reaction temperatures ranging from -273~C. (0K.) to 1627C. (1900K.) As indicated, the lower the free energy value the greater is the potential for reaction, although there is a point beyond which it is difficult to tap this potential due to unfavorable kinetics.
The plois in Figure 1 disclose that whereas ~14 can be effective in depositing TiN at temperatures ofw~ QC.
(1000K.) and greater, TiC13 and TiC12 have potential for participating in the above reactions and depositing TiN at reactions temperatures down to -273C. (0K.). The poten-tial for reaction of the latter compounds is due to the large negative free energy change accompanying reactions (2) and (3). The formation of TiN from TiC12 or TiC13 becomes -8- ~2~

more favorable as the temperature is decreased. Nonethe-lessl at -273C. (absolute 0K.) any reaction would be very limited because of unfavorable kinetics. In addition, to trigger the reaction at any temperature requires manipula-tion of the physical process variables (i.e., kineticvariables), such as pressures and flow rates, and the thermodynamic values, such as the equilibrium constants (~p~, a key constituent in the free energy value of the reaction. Varying ~inetic factors and thermodynamic values ~0 will result in the reaction occurring at different tempera-tures. This will be be~ter understood in part b~7 reference to the factors which control the free energy value and in parlicular the relation beiween the free energy value and in the equilibrium value (K~). Table I lists the equilibrium constants (Kp) for the reactions (1), (2) and (3) at temper-atures in the range of 27C. to 1627C.

TABLE I
Temperature Reaction (1) Reaction (2) Reaction (3) DK(C) Kp Kp Kp 300 (27) 1.1 X 10 8 1.7 X 10162 1.4 X 10244 500 (227) 3.0 X 10_13 7~3 X 104 1.2 X 1015 700 (427) 2.6 X 10 3.9 X 10 8.2 X 1013 800 (527) 2.1 7.6 X 12 1.9 X 109 1,000 (727) 1.57 6.7 X 10 4.0 X 104 2 1,50~ (1227) 10. 3.3 X 10 5.1 X 12 1,900 (1627) 24.8 8.8 5.0 X 10 Kp and GT relate as follows - (using reaction 3 for illustration purposes):

(K )T = (P-HCl) x (P-TiN) (4) P P-TiC12 x (P-~2) 1 2 x P-H2

3~

9 ~2~

wherein P-HCl denotes the partial pressure of HCl at the reaction temperature T.
~ GT = -RT ln (Kp)T (5) where R is the universal gas constant, T is the reaction temperature ln (Kp)T is the log to the base e of (Kp)T.
As can be seen from equation (5) the free energy change (~ GT) is proportional to the negative of the equilibrium constant. AccGrdingly, the larger the equilibrium constant, the greater the negative value of free energy change and the greater the potential for reaction.
Therefore, from Figure 1, using TiC13, it will be seen that for TiC13 to participate in reaction (2) at a tempera-ture of about 5G0C., the free energy value needs to be in the range of -14Kcal/per mole of TiN. With these free energy and temperature values, equation (5) then determines a fixed value for Kp at that temperature and from this series of partial pressure combinations for the reactants of the reaction are available. In addition, as discussed further below, it has been found beneficial to introduce ammonia into the reaction of TiC12 and TiC13 in reactions (2) and (3) to enhance the rate of deposition of TiN.
Process apparatus for carrying out TiN deposition will now be described and will be followed by examples of deposi-tion of TiN coatings on substrates at the desired reaction temperatures by varying and manipulating the process vari-ables.
Figure 2 shows a process apparatus which comprises two basic reaction cha~bers, a first chlorination chamber 1 upstream of and connected integrally with a coating chamber 2. The chlorination chamber is heated by a conventional resistively heated furnace 4. The tool substrate 3 is mounted within the coating chamber 2 and the chamber 2 is heated using conventional resistive heating means 5. In 3~

addition and alterna-tively the substrate 3 is independently heated in the coating chamber utllizing a conventional resistively heated cartridge heater 6.
In chamber l -the resistance heated furnace 4 heats titanium Ti metal chips from 150C. to 1100C. and HCl and ~2 are fed through flow meters 7 passed over the heated titanium 8 -to produce TiCl2 and TiCl3 and hydrogen in accordance with the following resultant reactions:

X HCl(g) ~ Ti(s)--? TiCl(X) ~ X H (X = 2 or 3) (6) This reaction may also produce quantities of TiCl4.
However the parameters of this reaction are controlled by 1 using suitable combinations of reaction temperatures and relative flow rates of H2 and HCl to provide lower partial pressures of HCl to steer the reaction towards predominant production of TiCl3 and TiCl2.
The TiCl2 and TiCl3 gases are carried by a carrier gas such as hydrogen or helium from chlorination chamber 1 to coating chamber 2 to which hydrogen and nitrogen are fed through flowmeters to foster reactions (2) and (3). Before reaching chamber 2 the hydrogen and nitrogen are preheated by passing through the furnace 4 in an annular chamber about 2~ reaction chamber 1. As discussed above for the desired reactions (2) and (3) at a temperature in the range of 250 C. to 850C. the value of Kp is fixed thermodynamically by formula (5) and a range of flow rates and partial pres-sure values can be determined. As will be appreciated the flow rates chosen will affect the kinetics of the reaction.
All the following examples are carried out on equipment o~
the type generally illustrated in Figure 2 and produced Tir~
coatings and except where indicated other~ise the equipment is operated at 1 atm. pressure.
_ ~;~2~

TABLE II
COATING CONDITIONS

No. Coating Temperature Flow rates (ml/min.) ( C. ) Chamber 2 H2 N2 l 500 50 ',0 2 500 100 lOO

4 700 lOO 50 6 600 100 lOO

12'' 600 l50 100 16 600 lOO 230 17 600 lOO 350 18 600 lOO 350 l9 600 lOO 350 21 800 lOO 350 * Deposition conducted at a total pressure of 4.1 mm.

-12- ~2~
TABLE III
CHLORINATION CONDITIONS
No. Reaction O Flow Rates (ml/min.) Temperature ( C.) H2 HCl 2 500 200 8.5 12~ 600 150 5 1~ 600 1200 12 * Chlorlnation conducted at a total pressure of 4.1 mm.

-l3-It has been further found that the quality of the deposit and the rate of deposition o~ TiN in the above CVD
reactions can be improved by the addition of ammonia to the gas reaction mixture, In the examples which follow, sub-strate materials such as copper, stainless steel and nickelbased su,per alloy are independently heated in the coating chamber by mounting them on a cartridge heater. The temper-ature of the cartridge heater was controlled using a temper-ature controller. Temperatures of the copper, stainless steel and nickel based super alloy substrate materials are monitored using a separate thermocouple attached to their surfaces. The walls of the coating chamber are maintained at a constant temperature using the resistively heated furnace arrangement, as in the previous examples in Tables II
and III. It is, of course, always important -to have the coating chamber and its walls at a temperature hiyh enough to keep the metal sub-halides in the gas phase and avoid any condensing-out at the walls.
A coating period of one hour and an operating pressure of l atm. is used for all the coating runs summarized in Table IV. In all of the examples given in Table IV the same chlorination step in chamber l is conducted at 500 C. and at flow rates of lO ml~min. of HCl and 400 ml/min. of H2.
Details of the deposition conditions used are given in Table IV.
From the previous examples relating to the use of ammonia, it can be seen from the results given in Table IV
that ammonia is not only effective in enhancing the deposition of TiN thermodynamically as a comparison of the examples l with ~ shows; but also improves the kinetics of the depos-ition of Ti~N, as a comparison of the examples 3 with l, 2, and ~ illustrates.

22~

The examples shown in Table V illustrate the advan-tages of pressure reduction in the chamber where a coating is occurring and in the chlorination process. It will be seen in Table V, with a pressure in the coating chamber of 2 millimeters of mercury and flow rates as shown and the addition of ammonia, good coatings are obtained. Table V
also illustrates, in the third example, the effect of introducing the nitrogen in the first stage of the process during chlorination. Unexpectedly, the nitrogen does not result in nitrides being retained in the first reaction but permits a better control. In the third example with a flow rate of 20 millilitres of hydrogen and 6 millilitres of HCl and 20 millilitres of N2 with the chamber pressure of 1.5 millimeters of mercury a suitable coating could be obtained.
While Table V illustra~es examples of operation at reduced pressure, it has been found that introduction of nitrogen in the first stage is also practical at atmospheric pressures.
A detailed description of the procedure used in coating with particular reference to the first example of Table V
follows.
The apparatus is partially evacuated through the exhaust with all inlet gas flows shut off . The whole apparatus is flushed with a gas such as hydrogen or helium which is not reactive with other materials. Flushing is continued to rid the apparatus of water vapor and oxygen.
The temperature of the titanium is raised to 500C. by furnace 4 and the temperature of substrate 3 is raised to 600C. by heating means 5. These temperatures are measured by suitably located therrnocouples.
The pressure within the apparatus is reduced.
Hydrogen and hydrogen chloride at volume ratio of ~0/12 is now permitted to flow over the titanium and hydrogen, -15- :~2~

nitro~en and ammonia in -the volume ratio of 20/10/3 are mixed ~ith the resulting gases ~rom the first s-tage.
The mixed gases flow into chamber 2 and a total pressure of about 2mm.Hg. is maintained. The temperatures, gas flows and pressures are main-tained for a suitable period of time, one hour for example.
At the end of the cycle the apparatus is permitted to cool down, the gas flow reverted to inert gas and the workp~ece removed. Preferably the stage l portion of the apparatus is at least partially sealed off before the chamber 2 is opened to atmosphere thus simplifying the flushing process in the next cycle.
It will be understood that the above disclosure has dealt with TiN coatings only by way of example~ The low temperature deposition principles disclosed above apply equally to the aeposit of zirconium nitride, hafnium ni-tride, carbides and carbonitrides of titanium, zirconium and hafnium nitrides and carbides and carbonitrides of vanadium, niobium and tantalum (the vanadium sub-group of metals) and of chromium molybdenum and tungsten (the chromium sub-group of metals). In fact, the invention applies to those metals of Group IVB, Group VB and Group VIB and to combinations of those metals because the metals have a ~ariable valency and it is possible to use those valencies which have the lower free energy of formation when forming metallic halides. In the case of carbide coatings the reactant gases in the depos-ition reaction are a hydrocarbon such as CH~, H2 and the metal sub-halide. In the case of carbonitride coatings the reac-tant gases in the deposition reaction are hydrocarbon such as CH~, H2 and N2 and/or NH3 and the metal sub-halide. The sub-strates mentioned in this disclosure are exemplary, not exclusive. Other known substrates can be coated using the method and apparatus of -this invention. Other known inert gas can be used.

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While I have shown and described one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to those skilled in the art, and I, therefore, do not wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

Claims (30)

I CLAIM:

1. A method of producing metal compound coatings of one of the group of metals including titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum.
and tungsten on a substrate comprising:
(a) reacting in a reaction chamber in the presence of a substrate a gaseous mixture of the metal subchlorides with one member of the groups of gaseous mixtures comprising hydrogen and nitrogen; hydrogen, nitrogen and ammonia; hydrogen and a hydrocarbon;
hydrogen, nitrogen and a hydrocarbon; and hydrogen, nitrogen, ammonia and a hydrocarbon;
(b) manipulating the free energy value for the reaction and the kinetic parameters of the reaction to facilitate a reaction temperature in the range of 250°
to 850°C.;
(c) maintaining the reaction temperature of the substrate and the reaction chamber in the said reaction temperature range;
whereby the coating being one of the group of a metal nitride, and a metal carbide and a metal carbonitride is deposited on the substrate.

2. A method of producing metal and metal compound coatings of one of the group of the metals including titani-um, zirconium and hafnium on a substrate comprising:
(a) reacting in a reaction chamber in the presence of a substrate of gaseous mixture of the metal subchlorides with one member of the groups of gaseous mixtures comprising hydrogen and nitrogen; hydrogen, nitrogen and ammonia; hydrogen and a hydrocarbon;
hydrogen, nitrogen, and a hydrocarbon; and hydrogen, nitrogen, ammonia and a hydrocarbon;

(b) manipulating the free energy value for the reaction and the kinetic parameters of the reaction to facilitate a reaction temperature in the range of 250°
to 850°C.;
(c) maintaining the reaction temperature of the substrate and the reaction chamber in the said reaction temperature range;
whereby the coating being one of the group of a metal nitride, and a metal carbide and a metal carbonitride is deposited on the substrate.

3. A method of producing coatings of nitrides of one of the group of the metals including titanium, zirconium and hafnium on substrates comprising:
(a) reacting a reaction chamber in the presence of a substrate a gaseous mixture of the metal sub-chlorides with one member of the groups of gaseous mixtures comprising hydrogen and nitrogen; and hydro-gen, nitrogen and ammonia;
(b) manipulating the free energy value for the reaction and the kinetic parameters of the reaction to facilitate a reaction temperature in the range of 250°
to 850°C.;
(c) maintaining the reaction temperature of the substrate and the reaction chamber in the said reaction temperature range;
whereby the metal nitride is deposited on the substrate.

4. A method of producing coatings of titanium nitride on a substrate, comprising:
(a) reacting in a reaction chamber in the presence of a substrate 2 gaseous mixture of titanium subchlorides with a gaseous mixture of hydrogen and nitrogen;
(b) manipulating the free energy value for the reaction and the kinetic parameters of the reaction to facilitate a reaction temperature in the range of 250°
to 850°C.;
(c) maintaining the reaction temperature of the:
substrate and the reaction chamber in the said reaction temperature range;
whereby the titanium nitride is deposited on the substrate.

5. A method of producing coatings of titanium nitride on a substrate comprising:
(a) reacting in a reaction chamber in the presence of a substrate a gaseous mixture of titanium subchlorides with a gaseous mixture of hydrogen, nitrogen and ammonia;
(b) manipulating the free energy value for the reaction and the kinetic parameters of the reaction to facilitate a reaction temperature in the range of 250°
to 850°C., (c) maintaining the reaction temperature of the substrate and the reaction chamber in the said reaction temperature range;
whereby the titanium nitride is deposited on the substrate.

6. A method of producing coatings of titanium nitride on a substrate as claimed in claim 4 wherein the manipulated reaction temperature is in the range of 380° to 800°C.

7. A method of producing coatings of titanium nitride on a substrate as claimed in claims 4 or 5 wherein the manipulated reaction temperature is in the range of 400° to 610°C

8. A method as claimed in claim 3 whereby the flow rates and partial pressures of the reactant gases are regulated to produce a reaction free energy value and reaction kinetics that facilitate said reaction temperature.

9. A method as claimed in claim 3 comprising the additional prior step of producing the metal sub-chlorides in a reaction area upstream of said deposit reaction in said reaction chamber, said prior step comprising:
(a) passing gaseous hydrogen chloride and hydrogen over the metal in said reaction area;
(b) maintaining said reaction area in the temperature range of 150° to 1100°C.;
(c) maintaining the flow rates and partial pressures of hydrogen and hydrogen chloride to provide low partial pressures of hydrogen chloride and promote the production of the metal sub-chlorides.

10. A method as claimed in claim 4 comprising the additional prior step of producing titanium sub-chlorides in a reaction area upstream of said deposit reaction in said reaction chamber, said prior step comprising:
(a) passing gaseous hydrogen chloride and hydrogen over titanium metal in said reaction area;
(b) maintaining said reaction area in the temperature range of 150° to 1100°C.;
(c) maintaining the flow rates and partial pressures of hydrogen and hydrogen chloride to provide low partial pressures of hydrogen chloride and promote the production of the titanium sub-chlorides.

11. A method as claimed in claim q in which said reaction area is maintained in the temperature range of 500°
to 850°C.

12. A method as claimed in claim 4 comprising the additional prior step of producing titanium sub-chlorides in a reaction area upstream of said deposit reaction in said reaction chamber, said prior step comprising:
(a) passing gaseous hydrogen chloride and hydrogen over titanium metal in said reaction area;
(b) maintaining said reaction area in the temperature range of 500° to 850°C.;
(c) maintaining the flow rates and partial pressures of hydrogen and hydrogen chloride to provide low partial pressures of hydrogen chloride and promote the production of the titanium sub-chlorides.

13. A method as claimed in claim 4 wherein the gas reactants flow into said reaction chamber continuously, the method comprising the additional step of including ammonia gas in the initial flow of gas reactants and terminating all flow of ammonia gas once said deposition has commenced.

14. A method of producing metal compound coatings of at least one of the metals from groups IVB, VB and VIB on a substrate comprising:
(a) reacting in a coating chamber in the presence of a substrate of gaseous mixture of metal subhalides with a gaseous mixture comprising hydrogen and nitro-gen; hydrogen, nitrogen and ammonia; hydrogen and hydrocarbon; hydrogen, nitrogen, and a hydrocarbon; and hydrogen, nitrogen, ammonia or a hydrocarbon;

(b) manipulating a free energy value for the reaction and kinetic parameters of the reaction to facilitate a reaction temperature in the range of about 250° to less than 900°C.;
(c) maintaining the reaction temperature of the substrate and the reaction chamber in said reaction temperature range;
whereby a coating of metal nitride, a metal carbide or a metal carbonitride is deposited on the substrate.

15. The method according to claim 14 wherein the metal of the metal compound is titanium, zirconium or hafnium.

16. The method according to claim 15 wherein the gaseous mixture in the coating chamber is a mixture com-prising hydrogen and nitrogen; or hydrogen, nitrogen and ammonia; whereby metal nitride is deposited on the sub-strate.

17. The method according to claim 14 wherein the metal is titanium and the gaseous mixture in the chamber is hydrogen and nitrogen; whereby titanium nitride is deposited on the substrate.

18. The method according to claim 14 wherein the temperature range is 380° to 800°C.

19. The method according to claim 14 wherein the temperature range is 400° to 610°C.

20. The method according to claim 14 further compris-ing producing the metal sub-halide by passing at least hydro-gen halide over the metal in a reaction area, maintaining the reaction area in the temperature range of 150° to 1100°C and controlling the flow of hydrogen halide over the metal to promote the production of metal sub-halide.

21. The method according to claim 20 further comprising introducing nitrogen gas into the process of the reaction area of where the metal sub-halide is being produced.

22. The method according to claim 14 wherein the substrate includes copper, stainless steel or nickel based super alloy.

23. A method of producing titanium nitride coatings on a substrate comprising:
passing a controlled flow of about 40 volumes of hydrogen and about 12 volumes of hydrogen chloride over a bed of titanium metal particles heated to about 500°C forming sub-halides;
mixing 20 volumes of hydrogen and 10 volumes of nitrogen with the resulting hydrogen and titanium chloride gases; and passing the gaseous mixture over a substrate heated to about 600°C to obtain a titanium nitride coated substrate.

24. The method according to claim 23 further comprising main-taining the gaseous mixture surrounding the substrate at a pressure of not more than about 4 millimeters of mercury.

25. The method according to claim 20 further comprising intro-ducing ammonia into the coating chamber and into the gaseous mixture for a limited period of time during the initial coating process.

26. The method according to claim 23 further comprising main-taining the gaseous mixture at a pressure such that Knudsen flow predominates.

27. The method according to claim 23 further comprising intro-ducing ammonia into the coating chamber and into the gaseous mixture for a limited period of time during the initial coating process.

28. A coated article comprising:
(a) a metal coating of metal nitride, metal carbide or metal carbonitride; the metal veing at least one of the metals from Group IVB, VB, and VIB or the Periodic Table of the Elements; and the metal coating being formed using a metal sub-halide; and (b) the metal coating being deposited on and adhered to a substrate.

29. The article according to claim 28, wherein the substrate is a copper, stainless steel and nickel based super alloy.

30. A method of producing metal compound coatings of at least one of the metals from Groups IVB, VB and VIB on a sub-strate comprising:
(a) reacting in a coating chamber in the presence of a substrate of gaseous mixture of metal sub-halides with a gaseous mixture comprising hydrogen and nitrogen; hydrogen, nitrogen and ammonia; hydrogen and hydrocarbon; hydrogen, nitrogen, and hydrocarbon; and hydrogen, nitrogen, ammonia or hydrocarbon;
(b) manipulating a free energy value for the reaction and kinetic parameters of the reaction to facilitate a reaction temperature avoiding a change in properties of the substrate being coated;
(c) maintaining the reaction temperature of the substrate and the reaction chamber at said reaction temperature;
whereby a coating of metal nitride, a metal carbide or a metal carbonitride is deposited on the substrate.