Patent Description:
Cutting tools having single- or multi-layered hard coatings of TiAlN, TiC, TiN, Ti(CN), Al<NUM>O<NUM>, etc. are conventionally used to cut heat-resistant alloy steel, stainless steel, etc. With increasingly severer use conditions of such hard-coated tools, cutting tools undergo extremely high cutting edge temperatures during, for example, high-speed cutting of soft steel. At cutting edges subjected to high temperatures, the crystal structures of the hard coatings are changed to lower hardness, suffering crater wear on rake faces and thus shorter lives. To overcome such problems, cutting tools having hard coatings with better wear resistance and oxidation resistance at high temperatures are desired.

<CIT> discloses a cutting tool having a hard titanium aluminum nitride coating containing <NUM>-<NUM>% by mass of chlorine and having an fcc structure, the coating being formed on a WC-based cemented carbide substrate by a thermal CVD method at <NUM>-<NUM>, using a titanium halide gas, an aluminum halide gas and an NH<NUM> gas as starting material gases. It has been found, however, that because the hard titanium aluminum nitride coating of <CIT> has a fine granular crystal structure, it exhibits low oxidation resistance when used at high temperatures, resulting in a short life.

<CIT> discloses a hard-coated tool having a hard titanium aluminum nitride coating having an fcc structure with a lattice constant of <NUM>-<NUM>, which has a composition represented by Ti<NUM>-xAlxN (<NUM> < x ≤ <NUM>) and is formed by a thermal CVD method on a substrate, or a multi-phase coating comprising a main phase of titanium aluminum nitride and other phases. It has been found, however, that because the hard titanium aluminum nitride coating of <CIT> also has a granular crystal structure, it exhibits low oxidation resistance when used at high temperatures, resulting in a short life.

<CIT> discloses a tool covered with a hard titanium aluminum nitride coating having a multi-layer structure by a CVD apparatus <NUM> shown in <FIG>. The CVD apparatus <NUM> comprises pluralities of shelves <NUM>, on which pluralities of substrates <NUM> are set, a reaction vessel <NUM> covering the shelves <NUM>, a temperature-controlling cover <NUM> surrounding the reaction vessel <NUM>, a supply pipe <NUM> having two inlets <NUM>, <NUM>, and a discharge pipe <NUM>. The hard titanium aluminum nitride coating has a structure in which first and second unit layers having hard grains of TiAlN, AlN or TiN are alternately laminated on a WC-based cemented carbide substrate. This is because (<NUM>) first and second starting material gases (mixture gases) are ejected into the furnace through nozzles positioned at equal distance from a center of the supply pipe <NUM> in just opposite directions (<NUM>°); and because (<NUM>) different starting material gases from those in the present invention are used. It has been found that the hard titanium aluminum nitride coating having a laminate structure suffers interlayer delamination at high temperatures because of thermal expansion coefficient difference between the layers due to composition difference; and that it exhibits largely decreased oxidation resistance because of a fine crystal grain structure when used at high temperatures, resulting in a short life. <CIT> relates to a wear protection coating that has at least one Ti<NUM>-xAlxCyNz layer with stoichiometric coefficients <NUM>≤x<<NUM>, <NUM>≤y<<NUM> and <NUM>≤z<<NUM> and a thickness from <NUM> to <NUM>. The Ti<NUM>-xAlxCyNz layer has a lamellar structure with lamellae with thickness of no more than <NUM>, preferably no more than <NUM>, particularly preferably no more than <NUM>. Lamellae are made of periodically alternating regions of the Ti<NUM>-xAlxCyNz layer with alternatingly different stoichiometric proportions of Ti and Al, having the same crystal structure (crystallographic phase), and the Ti<NUM>-xAlxCyNz layer has at least <NUM>% vol. % of face centered cubic (fcc) crystal structure.

<CIT> discloses a TiAlN coating deposited via a CVD process using a first precursor gas mixture comprising TiCl<NUM>, AlCl<NUM> and H<NUM> and a second precursor gas mixture comprising NH<NUM> and H<NUM> and also discloses first and second nozzles rotating together around a common rotation axis.

Accordingly, the object of the present invention is to provide a method for producing a hard-coated tool having a hard titanium aluminum nitride coating.

The method of the present invention for producing a hard-coated tool having a hard titanium aluminum nitride coating by chemical vapor deposition, comprises.

With the total amount of the mixture gases A and B as <NUM>% by volume, the composition of the mixture gas A comprises <NUM>-<NUM>% by volume of a TiCl<NUM> gas, <NUM>-<NUM>% by volume of an AlCl<NUM> gas, and the composition of the mixture gas B comprises <NUM>-<NUM>% by volume of an NH<NUM> gas. With the total amount of the mixture gases A and B as <NUM>% by volume, the composition of the mixture gas A comprises <NUM>-<NUM>% by volume of a TiCl<NUM> gas, <NUM>-<NUM>% by volume of an AlCl<NUM> gas, and <NUM>-<NUM>% by volume of an N<NUM> gas, the balance being an H<NUM> gas, and the composition of the mixture gas B comprises <NUM>-<NUM>% by volume of an NH<NUM> gas, and <NUM>-<NUM>% by volume of an N<NUM> gas, the balance being an H<NUM> gas; and that a volume ratio H<NUM>(A)/H<NUM>(B) of the H<NUM> gas in the mixture gas A to the H<NUM> gas in the mixture gas B is <NUM>-<NUM>.

With the distance H<NUM> from an opening of the first nozzle to the rotation axis longer than the distance H<NUM> from an opening of the second nozzle to the rotation axis, the mixture gas A may be ejected from the first nozzle, and the mixture gas B may be ejected from the second nozzle, or the mixture gas B may be ejected from the first nozzle, and the mixture gas A may be ejected from the second nozzle.

A ratio H<NUM>/H<NUM> of the distance H<NUM> from an opening of the first nozzle to the rotation axis to the distance H<NUM> from an opening of the second nozzle to the rotation axis is preferably in a range of <NUM>-<NUM>.

In the production method of the present invention, the reaction pressure is preferably <NUM>-<NUM> kPa, and the reaction temperature is preferably <NUM>-<NUM>.

Because the hard titanium aluminum nitride coating has a columnar crystal structure, and comprises high-Al TiAlN having an fcc structure and network-like, high-Ti TiAlN having an fcc structure, with a microstructure in which the high-Al TiAlN is surrounded by the network-like, high-Ti TiAlN, a cutting tool having such hard titanium aluminum nitride coating suffers suppressed phase transformation of the fcc structure to an hcp structure even when its cutting edge is subjected to high temperatures during a cutting operation, thereby exhibiting remarkably high wear resistance and oxidation resistance.

The hard-coated tool obtainable in the present invention has a hard titanium aluminum nitride coating having a columnar crystal structure, which is formed on a tool substrate by chemical vapor deposition, the hard titanium aluminum nitride coating having a structure comprising high-Al TiAlN having an fcc structure, which has a composition represented by (Tix<NUM>, Aly<NUM>)N, wherein x<NUM> and y<NUM> are numbers meeting x<NUM> = <NUM>-<NUM>, and y<NUM> = <NUM>-<NUM> by atomic ratio, and network-like, high-Ti TiAlN having an fcc structure, which has a composition represented by (Tix<NUM>, Aly<NUM>)N, wherein x<NUM> and y<NUM> are numbers meeting x<NUM> = <NUM>-<NUM>, and y<NUM> = <NUM>-<NUM> by atomic ratio; the high-Al TiAlN being surrounded by the network-like, high-Ti TiAlN.

The substrate should be a material having high heat resistance, to which chemical vapor deposition can be applied, for example, WC-based cemented carbide, cermet, high-speed steel, tool steel, ceramics such as cubic-boron-nitride-based sintered boron nitride (cBN) and sialon, etc. From the aspect of strength, hardness, wear resistance, toughness and thermal stability, WC-based cemented carbide, cermet and ceramics are preferable. In the case of WC-based cemented carbide, for example, the hard titanium aluminum nitride coating in the present invention may be formed on its as-sintered surfaces, but preferably on its worked surfaces (ground surface, cutting edge surface, etc.) to increase dimension precision.

The hard titanium aluminum nitride coating formed by chemical vapor deposition has a columnar crystal structure, and comprises Ti, Al and N as indispensable components. The composition of indispensable components in the hard titanium aluminum nitride coating preferably comprises <NUM>-<NUM> atomic % of Ti, <NUM>-<NUM> atomic % of Al, and <NUM>-<NUM> atomic % of N, with the total amount of Ti, Al and N as <NUM> atomic %. Outside the above composition range, the desired microstructure cannot be obtained. The composition of indispensable components more preferably comprises <NUM>-<NUM> atomic % of Ti, <NUM>-<NUM> atomic % of Al, and <NUM>-<NUM> atomic % of N. <NUM> atomic % or less of N may be substituted by C or B. Though the hard titanium aluminum nitride coating may contain Cl as an inevitable impurity, the Cl content is preferably <NUM> atomic % or less, more preferably <NUM> atomic % or less. The composition of the hard titanium aluminum nitride coating can be measured by EPMA.

The high-Al TiAlN has a composition represented by the general formula of (Tix<NUM>, Aly<NUM>)N, wherein x<NUM> and y<NUM> are numbers meeting x<NUM> = <NUM>-<NUM>, and y<NUM> = <NUM>-<NUM> by atomic ratio. The percentage x<NUM> of Ti of less than <NUM> leading to too much Al causes the precipitation of an hcp structure, resulting in low hardness, and poor wear resistance at high temperatures. When x<NUM> is more than <NUM>, the hard titanium aluminum nitride coating has a fine granular crystal structure, having reduced oxidation resistance. For higher performance, the atomic ratio of (Tix<NUM>, Aly<NUM>) to N is preferably <NUM>/<NUM> to <NUM>/<NUM>, more preferably <NUM>/<NUM> to <NUM>/<NUM>.

The high-Ti TiAlN has a composition represented by the general formula of (Tix<NUM>, Aly<NUM>)N, wherein x<NUM> and y<NUM> are numbers meeting x<NUM> = <NUM>-<NUM>, and y<NUM> = <NUM>-<NUM> by atomic ratio. The percentage x<NUM> of Ti of less than <NUM> leading to too much Al causes the precipitation of an hcp structure, resulting in low hardness and wear resistance. The x<NUM> of more than <NUM> leads to too little Al, resulting in drastically reduced oxidation resistance. For higher performance, the atomic ratio of (Tix<NUM>, Aly<NUM>) to N is preferably <NUM>/<NUM> to <NUM>/<NUM>, more preferably <NUM>/<NUM> to <NUM>/<NUM>.

The compositions of high-Al TiAlN and high-Ti TiAlN can be determined by the measurement results of EDS described later.

As is clear from <FIG>, the high-Al TiAlN (pale gray portion) having an fcc structure is surrounded by the network-like, high-Ti TiAlN (dark gray or black portion) having an fcc structure. Though portions having small concentration differences between high-Al TiAlN and high-Ti TiAlN are partially observed in <FIG>, the effects of the present invention can be obtained as long as at least <NUM>% of high-Al TiAlN is in contact with surrounding high-Ti TiAlN. Accordingly, "high-Al TiAlN surrounded by network-like, high-Ti TiAlN" means that at least <NUM>% of the high-Al TiAlN is in contact with the surrounding network-like, high-Ti TiAlN. At least <NUM>% of the high-Al TiAlN is preferably in contact with the surrounding network-like, high-Ti TiAlN. The "network-like" means that high-Ti TiAlN is distributed in a network form in a photomicrograph.

Though not necessarily clear, a reason why the hard titanium aluminum nitride coating has higher performance than those of conventional hard titanium aluminum nitride coatings is considered as follows: Hard titanium aluminum nitride coatings formed by conventional chemical vapor deposition methods have structures in which TiAlN having different Al contents or TiN and AlN are alternately laminated. Because each layer in the laminate has fine granular crystal grains, there are a high percentage of crystal grain boundaries. When cutting is conducted by a tool having such hard titanium aluminum nitride coating, crystal grain boundaries act as paths for oxygen intrusion at cutting edges of the tool at elevated temperatures, so that oxidation is accelerated to drastically reduce wear resistance and oxidation resistance at high temperatures. Also, the fcc structure of high-Al TiAlN layers in the laminate is transformed to an hcp structure at high temperatures, causing interlayer delamination and thus resulting in a shorter life.

On the other hand, in the hard titanium aluminum nitride coating, high-Al TiAlN is surrounded by network-like, high-Ti TiAlN. Because the high-Al TiAlN surrounded by the network-like, high-Ti TiAlN acts as starting portions of coating growth, titanium aluminum nitride crystal grains grow predominantly in one direction, resulting in columnar crystals. Accordingly, even when the high-Al TiAlN having an fcc structure shrinks by transformation to an hcp structure at a temperature elevated by cutting, the breakage of the coating is suppressed by the surrounding network-like, high-Ti TiAlN having an fcc structure. Such characteristic microstructure is not owned by conventional hard titanium aluminum nitride coatings. Thus, the hard titanium aluminum nitride coating has much higher high-temperature hardness than those of conventional hard titanium aluminum nitride coatings, resulting in excellent wear resistance. Also, because the hard titanium aluminum nitride coating has a large Al content, and a columnar crystal structure having fewer crystal grain boundaries than a granular crystal structure, it is less oxidized (having excellent oxidation resistance). The microstructure having high-Al TiAlN surrounded by network-like, high-Ti TiAlN can be identified by the measurement results of nanobeam diffraction (see <FIG>).

The "average of maximum diameters" is an average of the maximum diameters of high-Al TiAlN portions in columnar crystal grains of the hard titanium aluminum nitride coating, in a TEM photograph of a cross section perpendicular to a substrate surface. The "average of maximum lengths" is an average of the maximum lengths of the high-Al TiAlN portions in directions perpendicular to the maximum diameters, in a TEM photograph of a cross section perpendicular to the substrate surface. Specifically, the "average of maximum diameters" of high-Al TiAlN is determined by arbitrarily selecting five high-Al TiAlN portions surrounded by network-like, high-Ti TiAlN in the TEM photograph (magnification: <NUM>,<NUM> times) of <FIG>, measuring the maximum diameter in each selected portion, and arithmetically averaging five measured values. The "average of maximum lengths" of high-Al TiAlN is determined by measuring the maximum lengths of five selected portions in directions perpendicular to the maximum diameters in the TEM photograph of <FIG>, and arithmetically averaging five measured values.

The high-Al TiAlN generally has a flat shape (see <FIG>), with a larger average of maximum diameters than an average of maximum lenghts. Specifically, the average of maximum lengths of high-Al TiAlN is preferably <NUM>-<NUM>, more preferably <NUM>-<NUM>. When the average of maximum lengths is less than <NUM>, the hard titanium aluminum nitride coating has too small an Al content, resulting in poor oxidation resistance. On the other hand, when the average of maximum lengths exceeds <NUM>, the hard titanium aluminum nitride coating has too large an Al content, resulting in an increased percentage of an hcp structure, and thus lower hardness. The average of maximum diameters of high-Al TiAlN is preferably <NUM>-<NUM>, more preferably <NUM>-<NUM>. When the average of maximum diameters is less than <NUM>, the hard titanium aluminum nitride coating has low oxidation resistance. On the other hand, when the average of maximum diameters exceeds <NUM>, the hard titanium aluminum nitride coating has a finer granular crystal structure, suffering the phase transformation of an fcc structure to an hcp structure, and thus poor wear resistance at high temperatures.

The hard titanium aluminum nitride coating has a columnar crystal structure. The "average lateral cross section diameter" of columnar crystals is an average diameter of cross sections of columnar crystal grains in a plane perpendicular to the substrate surface. To have high hardness and excellent wear resistance, the average lateral cross section diameter of columnar crystals is preferably <NUM>-<NUM>, more preferably <NUM>-<NUM>. At the average lateral cross section diameter of less than <NUM>, a percentage of crystal grain boundaries to titanium aluminum nitride crystal grains is high, resulting in drastically reduced oxidation resistance at high temperatures. On the other hand, when the average lateral cross section diameter is more than <NUM>, cracking occurs in crystal grains, resulting in the breakage of the coating. Specifically, the average lateral cross section diameter is determined by measuring the lateral cross section diameters of <NUM> arbitrary columnar crystal grains in a thickness-direction immediate portion of the hard titanium aluminum nitride coating on the SEM photograph of <FIG>, and arithmetically averaging the measured values.

To prevent peeling from the substrate while exhibiting excellent wear resistance and oxidation resistance, the thickness of the hard titanium aluminum nitride coating is preferably <NUM>-<NUM>, more preferably <NUM>-<NUM>. The thickness of less than <NUM> does not provide sufficient coating effects, and the thickness of more than <NUM> likely causes cracking in the coating because of too much thickness. The thickness of the hard titanium aluminum nitride coating can be properly controlled by coating time. Because the hard coating and each layer constituting it are not completely flat, what is simply called "thickness" means an "average thickness.

The hardness of the hard titanium aluminum nitride coating measured by a nanoindentation method is preferably <NUM> GPa or more. When the hardness is less than <NUM> GPa, the hard titanium aluminum nitride coating has insufficient wear resistance. By industrial production, the hardness of <NUM>-<NUM> GPa can be achieved.

Though not particularly restrictive, a Ti(CN) coating, a TiN coating or a TiZr(CN) coating is preferably formed by chemical vapor deposition as an underlayer for the hard titanium aluminum nitride coating. A Ti(CN) coating has poor heat resistance at high temperatures despite excellent wear resistance, but its disadvantage of heat resistance can be overcome by forming the hard titanium aluminum nitride coatingthereon.

The temperature of forming a Ti(CN) coating by chemical vapor deposition is <NUM>-<NUM>, substantially equal to the preferred coating temperature (<NUM>-<NUM>) of the hard titanium aluminum nitride coating, resulting in high industrial productivity. In the hard-coated tool, an adhesion-increasing intermediate layer may be formed between the hard titanium aluminum nitride coating and the Ti(CN) coating. The intermediate layer is preferably a TiN coating or a TiAl(CN) coating.

Though not particularly restrictive, a single- or multi-layer hard coating indispensably comprising at least one element selected from the group consisting of Ti, Al, Cr, B and Zr, and at least one element selected from the group consisting of C, N and O may be formed by chemical vapor deposition, as an upper layer on the hard titanium aluminum nitride coating. The upper layer is a single- or multi-layer coating of, for example, TiC, CrC, SiC, VC, ZrC, TiN, AlN, CrN, Si<NUM>N<NUM>, VN, ZrN, Ti(CN), (TiSi) N, (TiB)N, TiZrN, TiAl(CN), TiSi(CN), TiCr(CN), TiZr(CN), Ti(CNO), TiAl(CNO), Ti(CO), TiB<NUM>, etc..

The hard titanium aluminum nitride coating is formed by chemical vapor deposition, using a thermal or plasma-enhanced chemical vapor deposition apparatus (CVD furnace). As shown in <FIG>, the CVD furnace <NUM> comprises a chamber <NUM>, a heater <NUM> arranged inside a wall of the chamber <NUM>, pluralities of shelves (jigs) <NUM>, <NUM> rotating in the chamber <NUM>, a reaction vessel <NUM> covering the shelves <NUM>, <NUM> and having pluralities of vents 5a, first and second pipes <NUM>, <NUM> vertically penetrating center openings 4a of the shelves <NUM>, <NUM>, and pluralities of nozzles 11a, 12a, 12b attached to each pipe <NUM>, <NUM>. The shelves <NUM>, <NUM>, on which large numbers of insert substrates <NUM> are set, are rotated in the chamber <NUM>. The first and second pipes <NUM>, <NUM> constitute a pipe assembly with both end portions integrally fixed by holding members (not shown), and penetrate a bottom of the chamber <NUM> such that they are integrally rotated. The first and second pipes <NUM>, <NUM> are rotatably connected to outside pipes (not shown). A bottom of the chamber <NUM> is provided with a pipe <NUM> for discharging a carrier gas and unreacted gases.

The production method of the hard titanium aluminum nitride coating will be explained in detail below, taking a case of using a thermal vapor deposition method for example, but it should be noted that the present invention is not restricted thereto, and that other chemical vapor deposition methods can be used.

An H<NUM> gas, an N<NUM> gas, and/or an Ar gas are introduced into a CVD furnace in which substrates are set, and after heated to the coating temperature, a starting material gas comprising a TiCl<NUM> gas, an N<NUM> gas, a CH<NUM>CN gas (or a CH<NUM>CN gas and a C<NUM>H<NUM> gas), and an H<NUM> gas are introduced into the CVD furnace to form a titanium carbonitride underlayer.

The composition of a starting material gas for forming an l-Ti(CN) coating having a columnar crystal structure as an example of the underlayers preferably comprises <NUM>-<NUM>% by volume of a TiCl<NUM> gas, <NUM>-<NUM>% by volume of an N<NUM> gas, and <NUM>-<NUM>% by volume of a CH<NUM>CN gas, the balance being an H<NUM> gas, their total amount being <NUM>% by volume. With the amounts of a TiCl<NUM> gas, an N<NUM> gas, a CH<NUM>CN gas and an H<NUM> gas outside the above ranges, the resultant titanium carbonitride coating has too high a carbon concentration, or contains too large columnar crystal grains, resulting in low adhesion to an upper hard titanium aluminum nitride layer.

As starting material gases for forming the hard titanium aluminum nitride coating, a mixture gas A comprising a TiCl<NUM> gas, an AlCl<NUM> gas, an N<NUM> gas, and an H<NUM> gas, and a mixture gas B comprising an NH<NUM> gas, an N<NUM> gas, and an H<NUM> gas are used. It is preferable that with the total amount of a TiCl<NUM> gas, an AlCl<NUM> gas, an NH<NUM> gas, an N<NUM> gas, and an H<NUM> gas as <NUM>% by volume, the composition of the mixture gas A comprises <NUM>-<NUM>% by volume of a TiCl<NUM> gas, <NUM>-<NUM>% by volume of an AlCl<NUM> gas, and <NUM>-<NUM>% by volume of an N<NUM> gas, the balance being an H<NUM> gas, and the composition of the mixture gas B comprises <NUM>-<NUM>% by volume of an NH<NUM> gas, and <NUM>-<NUM>% by volume of an N<NUM> gas, the balance being an H<NUM> gas, a volume ratio H<NUM>(A)/H<NUM>(B) of the H<NUM> gas in the mixture gas A to the H<NUM> gas in the mixture gas B being <NUM>-<NUM>. At any volume ratio H<NUM>(A)/H<NUM>(B) of less than <NUM> or more than <NUM>, the reaction speed of the starting material gas is uneven, providing hard titanium aluminum nitride coatings formed on substrates set in the CVD furnace with poor thickness distributions. In the mixture gases A, B, part of the H<NUM> gas as a carrier gas may be substituted by an Ar gas. More preferably, the composition of the mixture gas A comprises <NUM>-<NUM>% by volume of a TiCl<NUM> gas, <NUM>-<NUM>% by volume of an AlCl<NUM> gas, and <NUM>-<NUM>% by volume of an N<NUM> gas, the balance being an H<NUM> gas, and the composition of the mixture gas B comprises <NUM>-<NUM>% by volume of an NH<NUM> gas, and <NUM>-<NUM>% by volume of an N<NUM> gas, the balance being an H<NUM> gas. Further preferably, the composition of the mixture gas A comprises <NUM>-<NUM>% by volume of a TiCl<NUM> gas, <NUM>-<NUM>% by volume of an AlCl<NUM> gas, and <NUM>-<NUM>% by volume of an N<NUM> gas, the balance being an H<NUM> gas, and the composition of the mixture gas B comprises <NUM>-<NUM>% by volume of an NH<NUM> gas, and <NUM>-<NUM>% by volume of an N<NUM> gas, the balance being an H<NUM> gas. The volume ratio H<NUM>(A)/H<NUM>(B) is more preferably <NUM>-<NUM>.

When the TiCl<NUM> gas is less than <NUM>% by volume, the amount of Al is too large in the mixture gas A, so that an hcp structure is precipitated, resulting in a hard titanium aluminum nitride coating having low hardness. On the other hand, when the TiCl<NUM> gas is more than <NUM>% by volume, the resultant hard titanium aluminum nitride coating does not have the microstructure described above.

When the AlCl<NUM> gas is less than <NUM>% by volume, the hard titanium aluminum nitride coating contains too small an amount of Al, having low oxidation resistance. When the AlCl<NUM> gas is more than <NUM>% by volume, the hard titanium aluminum nitride coating contains too large an amount of Al, having an hcp structure precipitated, and thus low wear resistance.

When the N<NUM> gas is either less than <NUM>% by volume or more than <NUM>% by volume, the reaction speed of starting material gases is uneven, so that hard titanium aluminum nitride coatings having a poor thickness distribution are formed on substrates set in a CVD furnace.

When the NH<NUM> gas is either less than <NUM>% by volume or more than <NUM>% by volume in the mixture gas B, the reaction speed is uneven, failing to obtain a microstructure peculiar to the present invention.

To form a microstructure in which high-Al TiAlN having an fcc structure is surrounded by network-like, high-Ti TiAlN having an fcc structure, by mixing highly reactive mixture gases A and B to control their reaction speed, the mixture gases A and B should be introduced into a CVD furnace <NUM> without contact. For this purpose, for example, a CVD furnace <NUM> comprising a pipe assembly <NUM>, in which three pipes <NUM>, <NUM>, <NUM> in total are fixed as shown in <FIG> and <FIG>, is used.

The mixture gases A and B should be separately introduced into the CVD furnace <NUM>, without hindering the flow of the mixture gases A, B ejected from each nozzle. To this end, as exemplified in <FIG>, with one of the first and second nozzles ejecting the mixture gases A, B arranged at a center, and the other arranged on a periphery, the mixture gases A and B should be separately ejected from the first and second nozzles.

To obtain the characteristic microstructure, the nozzles 11a, 12a introducing the mixture gases A, B are preferably rotated at a speed of <NUM>-<NUM> rpm. The rotation directions of the first and second nozzles 11a, 12a are not restricted.

<FIG> show preferred examples of the arrangements of nozzles ejecting the mixture gases A, B. With respect to the rotation axis O of the pipe assembly <NUM>, the first nozzles 11a are positioned on the periphery side, while the second nozzles 12a are positioned on the center side. To form the above characteristic microstructure, the distance from an opening of a nozzle ejecting the mixture gas B to a substrate is preferably smaller than the distance from an opening of a nozzle ejecting the mixture gas A to a substrate. A TiCl<NUM> gas and an AlCl<NUM> gas in the mixture gas A are so highly reactive with an NH<NUM> gas in the mixture gas B that they are rapidly reacted after introduced into the CVD furnace. A high reaction speed likely causes reaction before reaching the substrate. Accordingly, if nozzle openings ejecting the mixture gases A and B are positioned at equal distance from the rotation axis (H<NUM> = H<NUM>) as shown in <FIG>, the reaction of the mixture gases A and B occurs remarkably until they reach the substrate, resulting in a hard titanium aluminum nitride coating having a fine granular crystal structure. Oppositely, the distance from an opening of a nozzle for the mixture gas A to a substrate may be smaller than the distance from an opening of a nozzle for the mixture gas B to a substrate.

To obtain the characteristic microstructure, a ratio H<NUM>/H<NUM> of the distance H<NUM> from an opening of a first nozzle 11a to the rotation axis O to the distance H<NUM> from an opening of a second nozzle 12a to the rotation axis O is preferably in a range of <NUM>-<NUM>.

<FIG> shows an example of first pipe assemblies <NUM> for introduced the mixture gases A and B into a CVD furnace <NUM> without contact. This pipe assembly <NUM> comprises two first pipes <NUM>, <NUM>, and one second pipe <NUM>, both end portions of the first and second pipes <NUM>, <NUM>, <NUM> being integrally fixed by holding members (not shown).

The first pipe <NUM> has a radius R<NUM>, and the second pipe <NUM> has a radius R<NUM>. The center axis O<NUM> of the first pipe <NUM> is positioned on a circle C<NUM> having a first diameter D<NUM> around the rotation axis O. Accordingly, two first pipes <NUM>, <NUM> are positioned at equal distance from the rotation axis O. A center angle θ of the center axes O<NUM>, O<NUM> of the first pipes <NUM>, <NUM> to the rotation axis O is preferably <NUM>-<NUM>°. The center axis O<NUM> of the second pipe <NUM> is at the same position as that of the rotation axis O, and an outer periphery of the second pipe <NUM> is on a circle C<NUM> having a second diameter D<NUM> (= 2R<NUM>) around the rotation axis O.

The nozzles (first nozzles) 11a, 11a of the first pipes <NUM>, <NUM> are directed outward in a just opposite direction (<NUM>° direction). Though each first pipe <NUM> has a vertical line of nozzles (first nozzles) 11a in the depicted example, it is not restrictive, but the first nozzles 11a may be aligned along plural lines. The second pipe <NUM> has two vertical lines of nozzles (second nozzles) 12a, 12a arranged in a diametrical direction (<NUM>° direction). Of course, the second nozzles 12a are not restricted to two lines, but may be in one line. Because the first diameter D<NUM> is larger than the second diameter D<NUM> [D<NUM> ≥ <NUM> (R<NUM> + R<NUM>)], the first nozzles 11a, 11a are located outside, and the second nozzles 12a, 12a are located inside, when the pipe assembly <NUM> is rotated around the rotation axis O.

When the second pipe <NUM> has a line of second nozzles 12a, and the center angle θ of the center axes O<NUM>, O<NUM> of the first pipes <NUM>, <NUM> is less than <NUM>°, the second nozzles 12a are directed preferably in a distant direction (opposite to the center angle θ) from the first nozzles 11a, 11a. In this case, the ejection direction of the first nozzles 11a is preferably perpendicular to the ejection direction of the second nozzles 12a.

It is preferable that when the center axes O<NUM>, O<NUM> of the first pipes <NUM>, <NUM> and the center axis O<NUM> of the second pipe <NUM> are on the same line, and when the second pipe <NUM> has two lines of second nozzles 12a, 12a, the first nozzles 11a, 11a are directed outward oppositely (<NUM>° direction), and the second nozzles 12a are directed oppositely and perpendicularly to the first nozzles 11a, 11a (at a center angle of <NUM>°).

<FIG> shows an example of second pipe assemblies <NUM> for introducing the mixture gases A and B into a CVD furnace <NUM> without contact. This pipe assembly <NUM> comprises one first pipe <NUM> and one second pipe <NUM>, both end portions of the first and second pipes <NUM>, <NUM> being integrally fixed by holding members (not shown). The first pipe <NUM> has a line of nozzles (first nozzles) 11a, and the second pipe <NUM> has a vertical line of nozzles (second nozzles) 12a.

The center axis O<NUM> of the second pipe <NUM> is at the same position as that of the rotation axis O of the pipe assembly <NUM>, with the first pipe <NUM> positioned near the second pipe <NUM>. The first pipe <NUM> has a radius R<NUM>, and the second pipe <NUM> has a radius R<NUM>. The center axis O<NUM> of the first pipe <NUM> is positioned on a circle C<NUM> having a first diameter D<NUM> around the rotation axis O. The second pipe <NUM> has a center axis O<NUM> at the same position as that of the rotation axis O, and its periphery coincides a circle C<NUM> having a second diameter D<NUM> (= 2R<NUM>) around the rotation axis O. Because the first diameter D<NUM> is larger than the second diameter D<NUM> [D<NUM> ≥ <NUM> (R<NUM> + R<NUM>)], the first nozzle 11a is located outside, while the second nozzle 12a is located inside, when the pipe assembly <NUM> is rotated around the rotation axis O.

Though the nozzles (first nozzles) 11a of the first pipe <NUM> and the second nozzles 12a of the second pipe <NUM> are directed oppositely (<NUM>° direction) in the depicted example, it is of course not restricted as long as a center angle of the first nozzle 11a and the second nozzle 12a is within <NUM>-<NUM>°.

<FIG> shows an example of third pipe assemblies <NUM> for introducing the mixture gases A and B into a CVD furnace <NUM> without contact. This pipe assembly <NUM> comprises four first pipes <NUM>, <NUM>, <NUM>, <NUM> and one second pipe <NUM>, both end portions of the first and second pipes <NUM>, <NUM>, <NUM>, <NUM>, <NUM> being integrally fixed by holding members (not shown). Each first pipe <NUM> has a vertical line of nozzles (first nozzles) 11a, and the second pipe <NUM> has two pairs of vertical lines of nozzles (second nozzles) 12a, 12a, 12a, 12a arranged in perpendicular diametrical directions (<NUM>°). The nozzles (first nozzles) 11a, 11a, 11a, 11a of all first pipes <NUM>, <NUM>, <NUM>, <NUM> are directed outward.

The first pipe <NUM> has a radius R<NUM>, and the second pipe <NUM> has a radius R<NUM>. The center axis O<NUM> of each first pipe <NUM> is positioned on a circle C<NUM> having a first diameter D<NUM> around the rotation axis O. Accordingly, four first pipes <NUM>, <NUM>, <NUM>, <NUM> are located at equal distance from the rotation axis O. The center axis O<NUM> of the second pipe <NUM> is at the same position as that of the rotation axis O, with its periphery located on a circle C<NUM> having a second diameter D<NUM> (= 2R<NUM>) around the rotation axis O. Because the first diameter D<NUM> is larger than the second diameter D<NUM> [D<NUM> ≥ <NUM> (R<NUM> + R<NUM>)], the first nozzles 11a, 11a, 11a, 11a are outside, while the second nozzles 12a, 12a, 12a, 12a are inside, when the pipe assembly <NUM> is rotated around the rotation axis O. Though a center angle θ of the center axes O<NUM>, O<NUM> of the adjacent first pipes <NUM>, <NUM> to the rotation axis O is <NUM>° in the depicted example, it is not restricted but may be <NUM>-<NUM>°.

The temperature of forming the hard titanium aluminum nitride coating is preferably <NUM>-<NUM>. When the coating-forming temperature is lower than <NUM>, the resultant hard titanium aluminum nitride coating has too high a chlorine content, resulting in low hardness. On the other hand, when the coating-forming temperature exceeds <NUM>, the reaction is too accelerated, forming a granular crystal structure, and thus resulting in poor oxidation resistance.

The reaction pressure of forming the hard titanium aluminum nitride coating is preferably <NUM>-<NUM> kPa. When the reaction pressure is less than <NUM> kPa, the above characteristic microstructure cannot be obtained. On the other hand, when the reaction pressure exceeds <NUM> kPa, the resultant hard titanium aluminum nitride coating has a granular crystal structure, and thus poor oxidation resistance.

Though not particularly restrictive, upper layers may be formed on the hard titanium aluminum nitride coating by a known chemical vapor deposition method. The upper-layer-forming temperature may be <NUM>-<NUM>. Starting material gases used for forming the upper layers are exemplified as follows:.

The hard titanium aluminum nitride coating formed on the substrate is smoothed by brushing, buffing, blasting, etc., to achieve a surface state having excellent chipping resistance. Particularly when a hard-coated cutting edge is treated by wet or dry blasting using ceramic powder of alumina, zirconia, silica, etc., the hard coating is provided with smoothed surface and reduced residual tensile stress, thereby getting improved chipping resistance.

The present invention will be explained in further detail by Examples below, of course without intention of restricting the present invention thereto. In Examples and Comparative Examples below, the flow rate (L/minute) is expressed by L per every minute at <NUM> atom and <NUM>, and the thickness is expressed by an average value.

Milling insert substrates (WDNW140520-B) of WC-based cemented carbide comprising <NUM>% by mass of Co, <NUM>% by mass of TaC, and <NUM>% by mass of CrC, the balance being WC and inevitable impurities, which are schematically shown in <FIG>, and property-evaluating insert substrates (SNMN120408) of WC-based cemented carbide comprising <NUM>% by mass of Co, <NUM>% by mass of CrC, <NUM>% by mass of ZrC, <NUM>% by mass of TaC, and <NUM>% by mass of NbC, the balance being WC and inevitable impurities were set in the CVD furnace <NUM> shown in <FIG>, and the temperature in the CVD furnace <NUM> was elevated to <NUM> while flowing an H<NUM> gas. Thereafter, a starting material gas comprising <NUM>% by volume of an H<NUM> gas, <NUM>% by volume of an N<NUM> gas, <NUM>% by volume of a TiCl<NUM> gas, and <NUM>% by volume of a CH<NUM>CN gas was flown at a flow rate of <NUM> L/minute into the CVD furnace <NUM>, at <NUM> and <NUM> kPa. Thus, a <NUM>-µm-thick titanium carbonitride coating was formed on each substrate by chemical vapor deposition.

Introduced into the CVD furnace <NUM> using the pipe assembly <NUM> shown in <FIG>, which was rotated at a speed of <NUM> rpm, after the temperature and the pressure in the CVD furnace <NUM> were lowered to <NUM> and <NUM> kPa, respectively, while flowing an H<NUM> gas, were (a) a mixture gas A comprising <NUM>% by volume of a TiCl<NUM> gas, <NUM>% by volume of an AlCl<NUM> gas, <NUM>% by volume of an N<NUM> gas, and <NUM>% by volume of an H<NUM> gas, through the first nozzles 11a, 11a of the first pipes <NUM>, <NUM>, and (b) a mixture gas B comprising <NUM>% by volume of an H<NUM> gas, <NUM>% by volume of an N<NUM> gas, and <NUM>% by volume of an NH<NUM> gas, through the second nozzles 12a of the second pipe <NUM>. The total flow rate of the mixture gases A and B was <NUM>/minute. Thus, a <NUM>-µm-thick hard titanium aluminum nitride coating having a composition represented by Ti<NUM>Al<NUM>N<NUM> (atomic ratio) was formed on each titanium carbonitride layer by chemical vapor deposition, to produce the hard-coated tools (milling inserts).

The thicknesses of the titanium carbonitride coating and the hard titanium aluminum nitride coating of each hard-coated tool were measured by the following procedure. Each coating surface was lapped slantingly at an angle of <NUM>° to obtain a lapped surface, and the lapped surface exposing the thickness-direction cross sections of the hard coatings was observed by an optical microscope of <NUM>,<NUM> times at five arbitrary points to measure the thickness of each layer, and the measured thicknesses were arithmetically averaged. The results are shown in Table <NUM>.

To identify the crystal structure, CuKα<NUM> rays (wavelength λ: <NUM>) were projected onto a hard coating surface on a rake face of the property-evaluating insert (SNMN120408) at tube voltage of <NUM> kV and tube current of <NUM> mA, by an X-ray diffraction apparatus (EMPYREAN available from PANalytical). The X-ray diffraction pattern obtained in a 2θ range of <NUM>-<NUM>° is shown in <FIG>. In this X-ray diffraction pattern, diffraction peaks of the Ti(CN) coating and diffraction peaks of the hard titanium aluminum nitride coating having an fcc structure were observed together with a diffraction peak of WC in the WC-based cemented carbide substrate. It is clear from the X-ray diffraction pattern of <FIG> that the hard titanium aluminum nitride coating has a single structure of fcc.

On the fractured surface (hard titanium aluminum nitride coating, etc.) of each hard-coated tool, microstructure observation was conducted by SEM (S-<NUM> available from Hitachi, Ltd. ) and a field-emission transmission electron microscope FE-TEM (JEM-2010F available from JEOL Ltd. ), and mapping analysis was conducted by an energy-dispersive X-ray spectrometer EDS (UTW-type Si (Li) semiconductor detector available from NORAN) attached to JEM-2010F.

<FIG> is a SEM photograph (magnification: <NUM>,<NUM> times) of a fractured hard coating surface on a rake face of the property-evaluating insert (SNMN120408). It is clear that the hard titanium aluminum nitride coating had a columnar crystal structure.

<FIG> is a TEM photograph (magnification: <NUM>,<NUM> times) of the hard titanium aluminum nitride coating, <FIG> is a TEM photograph (magnification: <NUM>,<NUM> times) enlargedly showing a portion A in <FIG>, and <FIG> is a cross-sectional, dark-field STEM image (magnification: <NUM>,<NUM> times) enlargedly showing the portion A in <FIG>. <FIG> and <FIG> reveal that the hard titanium aluminum nitride coating had a first relatively flat crystal phase <NUM> (pale gray portion B), and a second thin-film-like (network-like) crystal phase <NUM>, the first crystal phase <NUM> being surrounded by the second crystal phase <NUM> (dark gray or black portion C). <FIG> reveals that that the first crystal phase <NUM> had an average of maximum lengths Dav of <NUM> and an average of maximum diameters Daw of <NUM>.

<FIG> corresponding to <FIG> and <FIG> shows the mapping analysis (plane analysis) results of Al and Ti. <FIG> reveals that the first crystal phase <NUM> contained more Al and less Ti, while the second crystal phase <NUM> contained less Al and more Ti.

<FIG> shows the nanobeam diffraction (NAD) of a portion B (high-Al TiAlN) in <FIG>, and <FIG> shows the nanobeam diffraction (NAD) of a portion C (high-Ti TiAlN) in <FIG>. The nanobeam diffraction conditions in JEM-2010F were acceleration voltage of <NUM> kV and camera length of <NUM> in portions B and C. It was found from <FIG> that both of the first crystal phase (high-Al TiAlN) and the second crystal phase (high-Ti TiAlN) had a fcc structure.

It was found from <FIG> that the first relatively flat crystal phase of high-Al TiAlN having an fcc structure was surrounded by the second crystal phase of thin, network-like, high-Ti TiAlN having an fcc structure.

In a cross section of the property-evaluating insert (SNMN120408), the composition of the hard titanium aluminum nitride coating was measured at five arbitrary points at its thickness-direction center by an electron probe microanalyzer EPMA (JXA-8500F available from JEOL, Ltd. ), under the conditions of acceleration voltage of <NUM> kV, irradiation current of <NUM> A, and a beam diameter of <NUM>. The measured values were arithmetically averaged to determine the composition of the hard titanium aluminum nitride coating. The results are shown in Table <NUM>.

In a cross section of the hard coating of the property-evaluating insert (SNMN120408), the compositions of high-Al TiAlN grains and high-Ti TiAlN grains in the hard titanium aluminum nitride coating were analyzed at five arbitrary points at a thickness-direction center of the above coating, by an energy-dispersive X-ray spectrometer EDS [UTW-type Si (Li) semiconductor detector available from NORAN, beam diameter: about <NUM>] attached to FE-TEM (JEM-2010F), and the measured values were arithmetically averaged. The results are shown in Table <NUM>.

The surface hardness of the hard coating was measured <NUM> times by a nanoindentation method using a nanoindentation hardness tester (ENT-<NUM> available from Elionix Inc. ) with a Si single crystal as a standard sample, at a maximum load of <NUM> mN, and a load speed of <NUM> mN/second, for a keeping time of <NUM> second, and arithmetically averaged. The results are shown in Table <NUM>.

Each milling insert <NUM> was fixed to a tip portion <NUM> of a tool body <NUM> of the indexable rotary cutting tool (ASRT5063R-<NUM>) <NUM> shown in <FIG> by a setscrew <NUM>, to evaluate the tool life of the hard coating under the following milling conditions. The flank wear width of the hard coating was measured by an optical microscope (magnification: <NUM> times). The tool life is expressed by the total cutting length when the maximum wear width of the flank exceeded <NUM>. The results are shown in Table <NUM>.

Each hard-coated tool (milling insert) was produced in the same manner as in Example <NUM> except for changing the coating conditions of the hard titanium aluminum nitride coating as shown in Tables <NUM>-<NUM> and <NUM>-<NUM>, and its properties and tool lives were evaluated. With respect to the hard titanium aluminum nitride coating of each Example, the measurement results of composition, crystal structure and form, thickness and hardness, as well as an average lateral cross section diameter of columnar crystals are shown in Table <NUM>. The measurement results of composition, crystal structure, Dav and Daw of high-Al TiAlN and the composition and crystal structure of high-Ti TiAlN in each Example are shown in Table <NUM>. The observation results of microstructure of high-Al TiAlN, etc. and the tool life in each Example are shown in Table <NUM>. It is clear from Tables <NUM>-<NUM> that each hard titanium aluminum nitride coating of Examples <NUM>-<NUM> has a columnar crystal structure in which high-Al TiAlN having an fcc structure is surrounded by network-like, high-Ti TiAlN having an fcc structure, as well as a good tool life, as in Example <NUM>.

With the same milling insert substrates of WC-based cemented carbide as in Example <NUM> set in the CVD furnace <NUM>, a mixture gas comprising <NUM>% by volume of a TiCl<NUM> gas, <NUM>% by volume of an N<NUM> gas and <NUM>% by volume of an H<NUM> gas at a flow rate of <NUM>/minute was flown into the CVD furnace at <NUM> and 16kPa, to form a titanium nitride coating having an average thickness of <NUM> on the insert substrate.

A <NUM>-µm-thick hard titanium aluminum nitride coating having a composition represented by Ti<NUM>Al<NUM>N<NUM> (atomic ratio) was formed in the same manner as in Example <NUM>, except for introducing the mixture gas A through the second nozzles 12a of the second pipe <NUM> and the mixture gas B through the first nozzles 11a, 11a of the first pipes <NUM>, <NUM> into the CVD furnace <NUM>, thereby producing the hard-coated tool (milling insert).

The properties and tool lives of the hard-coated tools were evaluated in the same manner as in Example <NUM>. The measurement results of the composition, crystal structure and form, thickness and hardness of the hard titanium aluminum nitride coating, and the average lateral cross section diameter of columnar crystals are shown in Table <NUM>. The measurement results of the composition, crystal structure, Dav and Daw of high-Al TiAlN, and the composition and crystal structure of high-Ti TiAlN are shown in Table <NUM>. The observed microstructure of high-Al TiAlN, etc. and the tool life are shown in Table <NUM>. It is clear from Tables <NUM>-<NUM> that the hard titanium aluminum nitride coating of Example <NUM> had a columnar crystal structure, in which high-Al TiAlN having an fcc structure was surrounded by network-like, high-Ti TiAlN having an fcc structure, as well as a good tool life, as in Example <NUM>.

After forming a titanium carbonitride coating in the same manner as in Example <NUM>, the nozzles 11a, 12a shown in <FIG> (center angle θ: <NUM>°, and H<NUM> = H<NUM>) were used to introduce mixture gases A, B. A <NUM>-µm-thick hard titanium aluminum nitride coating was formed by chemical vapor deposition under the conditions (<NUM> and <NUM> kPa) shown in Table <NUM> in the same manner as in Example <NUM>, except for introducing a mixture gas A comprising <NUM>% by volume of an H<NUM> gas, <NUM>% by volume of an N<NUM> gas, <NUM>% by volume of a TiCl<NUM> gas and <NUM>% by volume of an AlCl<NUM> gas through the first nozzles 11a, and a mixture gas B comprising <NUM>% by volume of an H<NUM> gas, <NUM>% by volume of an N<NUM> gas and <NUM>% by volume of an NH<NUM> gas through the second nozzles 12a, into the CVD furnace <NUM> at a flow rate of <NUM>/minute. The properties and tool lives of the resultant hard-coated tools (milling inserts) were elevated in the same manner as in Example <NUM>. The results are shown in Tables <NUM>-<NUM>.

After forming a titanium carbonitride coating in the same manner as in Example <NUM>, the nozzles 11a, 12a shown in <FIG> (center angle θ: <NUM>°, and H<NUM> = H<NUM>) were used to introduce mixture gases A, B. A <NUM>-µm-thick hard titanium aluminum nitride coating was formed by chemical vapor deposition under the conditions (<NUM> and <NUM> kPa) shown in Table <NUM> in the same manner as in Example <NUM>, except for introducing a mixture gas A comprising <NUM>% by volume of an H<NUM> gas, <NUM>% by volume of an Ar gas, <NUM>% by volume of a TiCl<NUM> gas and <NUM>% by volume of an AlCl<NUM> gas through the first nozzles 11a, and a mixture gas B comprising <NUM>% by volume of an N<NUM> gas and <NUM>% by volume of an NH<NUM> gas through the second nozzles 12a, into the CVD furnace <NUM> at a flow rate of <NUM>/minute. The properties and tool lives of the resultant hard-coated tools (milling inserts) were evaluated in the same manner as in Example <NUM>. The evaluation results are shown in Tables <NUM>-<NUM>.

A hard titanium aluminum nitride coating was formed in the same manner as in Example <NUM>, except that the nozzles 11a, 12a shown in <FIG> (center angle θ: <NUM>°, and H<NUM> = H<NUM>) were used to introduce mixture gases A, B, and that the starting material gas compositions and coating conditions (<NUM> and <NUM> kPa) shown in Table <NUM> were used. The properties and tool lives of the resultant hard-coated tools (milling inserts) were evaluated in the same manner as in Example <NUM>. The results are shown in Tables <NUM>-<NUM>.

As shown in Table <NUM>, in any hard titanium aluminum nitride coatings of Comparative Examples <NUM>-<NUM>, high-Al TiAlN was not surrounded by network-like, high-Ti TiAlN. The hard titanium aluminum nitride coatings of Comparative Examples <NUM>-<NUM> had granular crystal structures, though they had an fcc structure. The hard titanium aluminum nitride coating of Comparative Example <NUM> had a granular crystal structure in which hard titanium aluminum nitride layers having an fcc structure and hard titanium aluminum nitride layers having an fcc + hcp structure were alternately laminated.

Each hard-coated tool (milling insert) of Examples <NUM>-<NUM> had a tool life of <NUM> or more (expressed by cutting distance), as long as <NUM> times or more those of Comparative Examples <NUM>-<NUM>. Such high performance appears to be achieved by excellent wear resistance and oxidation resistance of each hard-coated tool (milling insert) of Examples <NUM>-<NUM>, which were obtained by the above characteristic microstructure of the hard titanium aluminum nitride coating.

Claim 1:
A method for producing a hard-coated tool having a hard titanium aluminum nitride coating by chemical vapor deposition, comprising
(<NUM>) using a mixture gas A comprising a TiCl<NUM> gas, an AlCl<NUM> gas, an N<NUM> gas, and an H<NUM> gas, and a mixture gas B comprising an NH<NUM> gas, an N<NUM> gas, and an H<NUM> gas as starting material gases;
(<NUM>) rotating first and second nozzles (11a, 12a) arranged with different distances from the rotation axis (O).
(<NUM>) disposing a tool substrate (<NUM>) around said first and second nozzles (11a, 12a); and
(<NUM>) ejecting said mixture gas A and said mixture gas B separately from said first and second nozzles (11a, 12a),
wherein with the total amount of said mixture gases A and B as <NUM> % by volume,
the content of the TiCl<NUM> gas is <NUM> % to <NUM> % by volume,
the content of the AlCl<NUM> gas is <NUM> % to <NUM> % by volume and
the content of the N<NUM> gas is <NUM> % to <NUM> % by volume,
the balance being an H<NUM> gas in said mixture gas A, and
the content of the NH<NUM> gas is <NUM> % to <NUM> % by volume and
the content of the N<NUM> gas is <NUM> % - <NUM> % by volume,
the balance being an H<NUM> gas in said mixture gas B, wherein
a volume ratio H<NUM>(A) / H<NUM>(B) of the H<NUM> gas in said mixture
gas A to the H<NUM> gas in said mixture gas B is <NUM> to <NUM>.