SE453891B - COATED HARD METAL PRODUCT, WITH HIGH TEMPERATURE AND PURPOSE STABILITY AND PROCEDURE FOR PRODUCING THIS - Google Patents

Description

453 891 2 alumina which are commercially available. The main disadvantage that prevents a more extensive use of alumina tools is their low strength, which seldom exceeds 70 kp / mmz, when using standard type cross-fracture testing or bending testing. This should be compared with a strength of 140-310 kp / mm * or even more for cemented carbide cutting tools. The low strength of alumina tools limits their usefulness to cutting machining under conditions in which the tool is not subjected to heavy stresses, for example cutting finishing. The low strength of alumina also precludes the use of this material in certain types of replaceable cutting bodies which are subjected to high stresses when locked in tool holders.

It is an object of the present invention to provide a hard, abrasion resistant material which combines the extremely high abrasion resistance of alumina with the relatively high strength and hardness of cemented carbide.

A further object of the invention is to improve the abrasion resistance of hard metals without significantly reducing the strength. Yet another object of the invention is to provide a process for producing a highly adhesive, non-porous, dense coating of alumina on cemented carbide substrates.

The above objects and other objects according to the invention are fulfilled by vapor deposition under carefully controlled conditions of a coating consisting mainly of α-alumina with a thickness of 1-10 μm on a cemented carbide substrate. The product comprises a cemented carbide substrate and a completely dense (usually exceeding 99% of theoretical density) α-aluminum coating, which is strongly and adhesively bonded to the substrate. The coated product has an abrasion resistance which is substantially equivalent to the abrasion resistance of alumina-based cutting materials and a wash breaking limit of at least 105 kp / mm * and in most cases more than 140 kp / mm ”. At very high cutting speeds, exceeding about 450 surface meters / minute in some applications and possibly higher in other applications, the higher heat resistance of solid (solid) alumina can lead to higher abrasion resistance. In all cutting tests of a kind other than the use of speeds exceeding these levels, the abrasion resistance of coated products according to the invention has been found to be substantially as high as in alumina cutting materials.

According to the invention, a coating thickness can be used within a wide range of 1-10 μm. As will be shown in more detail below, some applications require even narrower ranges within the stated limits, for example, 1-3 μm has been found to be optimal for machining high temperature resistant alloys and for use in milling and 6-10 um has been shown to be optimal for machining steel.

In the process according to the invention, aluminum halide, water vapor and hydrogen gas are passed over the carbide support at a temperature of 900-150 ° C, the amount ratio of water vapor / hydrogen gas being kept between about 0.025 and 2.0 and preferably between 0.05 and 0.20.

Attempts or proposals to coat a variety of substrates with alumina have previously been referred to in the literature.

As far as is known, however, coating of a cemented carbide substrate with alumina to form a completely dense and adhesive coating has not previously been stated. Nor has the surprising combination of properties which characterize products according to the invention previously been achieved with either coated or uncoated cutting tool materials.

Products according to the invention stand out in a number of respects. The strength compared to comparable prior art coated cemented carbide materials is considerably higher and the cutting properties are superior in terms of tool life at medium and higher cutting speeds. The basis for these 453 891 4 data will be apparent from the discussion and test results set forth therein. following.

The term "sintered carbide" or "cemented carbide" as used herein means one or more transition metal carbides of metals of Group IVb, Vb and VIb of the Periodic Table which are sintered or bonded with one or more matrix metals belonging to the group of iron, nickel and cobalt . A typical cemented carbide contains WC in a cobalt matrix or TiC in a nickel matrix.

In pure or simple WC-Co carbides, it has been found that the bond between the substrate and the coating is improved if the surface of the substrate contains a thin (less than 5 μm) carbon-poor (carbon deficit) eta-phase (W3Co3C) layer of a type which is well known in the cemented carbide industry. Such a layer can be provided by using slightly decarburizing conditions at the beginning of the coating cycle. With such simple cemented carbide grades, the strongest bond between the alumina coating and the substrate is obtained at a relatively small coating thickness, ie. thickness less than about 8 pm.

Preferred substrates containing both WC and TiC and / or TaC have been found to be able to form an intermediate non-metallic layer, which appears to improve the bond between the substrate and the coating. The intermediate layer is also assumed to contain an oxide phase of Ti or Ta. When using substrates containing TiC and / or TaC, the coating thickness may be greater than when using substrates of WC only.

It should be noted that the term "alumina" for the coating does not exclude the presence of minor amounts (usually not more than 5% of the coating) of other materials, for example Ti, Ta, Co, Mg, Ca or Cr, which do not significantly affect the properties or function. of the coated product.

Due to the high demands normally placed on cemented carbide cutting materials, the properties of coatings and the manner in which these are bonded to the substrate, as well as the effect on the strength of the substrate, are extremely critical. The coating layer must have high integrity in terms of density and evenness - porosity or non-uniformity are unsuitable. The coating must also be tightly and adhesively bonded to the cemented carbide substrate to prevent flaking or separation during use. The coating must also not significantly reduce the strength of the cemented carbide substrate. Products according to the present invention have been subjected to extensive testing and have been found to meet all the requirements set forth above. The coatings are uniform and completely dense and are strongly bonded to the substrate and the coated composite material maintains a high proportion of the strength, usually more than 85% of the transverse breaking limit of the uncoated substrate. The fact that these properties of the coated product have been successfully achieved is quite surprising, especially in view of the considerable reductions in strength previously obtained when applying abrasion-resistant coatings on hard metal substrates. Coated materials according to the invention also provide a surface unit in machining operations which appears to be completely equivalent in quality to the quality obtained with solid alumina cutting materials, which are considered to give the best surface finish.

Description of preferred embodiments The very good properties of the alumina-coated product according to the invention depend on careful control of the process parameters. The process involves the use of a gaseous mixture of hydrogen, water and an aluminum halide, for example aluminum trichloride. Carbon monoxide and carbon dioxide can, if desired, also be added. The primary total deposition reaction is: 3H2O + 2AlCl3 - å Al2O3 + 6HCl.

The most important constituents of the gas reaction mixture are therefore water vapor and aluminum chloride vapor. However, the aluminum chloride vapor can be formed in many ways during the deposition reaction, for example by heating solid AlCl3 powder or by passing chlorine gas over aluminum metal. The water vapor is most conveniently obtained by reaction of hydrogen and carbon dioxide in the deposition chamber to form carbon monoxide and water vapor by the water gas reaction: H2 + co2; :: šco + nzo.

The amount of water vapor formed in this way depends on the temperature and the initial concentration of hydrogen, carbon dioxide, carbon monoxide and water vapor in the supplied gas stream. In order to obtain a coating of good quality with the desired thickness within the temperature range 900-150 ° C, the volume ratio between water vapor and hydrogen gas present after the water gas reaction should be between about 0.02 and 2.0.

Hydrogen has been shown to be necessary in the vapor deposition process in order to obtain a dense, adhesive coating. Hydrogen appears to ensure oxidation of aluminum at the carbide surface.

Oxidation in the reaction zone above the carbide substrate gives a condition known as "dusting" and must be avoided. The absence of hydrogen gives a porous coating which is not completely dense. Thus, three necessary constituents of the process are aluminum halide vapor, water vapor and hydrogen. In a preferred form, the process uses aluminum chloride vapors, hydrogen and carbon dioxide, the latter component reacting with H2 to form water vapor.

The amount of water vapor present after the reaction of known added concentrations of H 2 and CO 2 as well as CO and H 2 O, if these constituents are used, can be calculated using the following equation: \ / 2 ._ 2a in which a = 1 - K; K = the equilibrium constant of the water gas reaction: b = (C0) i - (H2O) i + K ((H2) i + (CO2) i + 2 (H2O) i); : ch c = K ((n2) i (Co2) i + (H2) i (H20) i + (H20) i (co2) i + (H2o) i.

The parentheses indicate the concentration of the gaseous components indicated in parentheses, expressed in partial pressure, and indices (f) and (i) denote the final concentration or equilibrium concentration and the constituent or initial concentration. The amount of H2 present and thus the H2O / H2 ratio can be determined by the relationship: A series of coated products were prepared according to the invention by passing aluminum chloride vapor, hydrogen and carbon dioxide over cemented carbide cutting plates. The samples were prepared at varying initial gas compositions and at varying final H 2 O / H 2 concentrations. In all cases the deposition was carried out at 1050 ° C and a deposition cycle lasting 45 minutes was used with 2-3 g of aluminum chloride and an aluminum chloride generator temperature of about 200 ° C.

The use of more AlCl3 shifts the desired H2O / H2 ratio to a higher value and vice versa. The coatings were deposited on a cemented carbide substrate with the following composition in weight percent: WC 72%, Co 8.5%, TiC 8%, TaC 11.5%. Table I below shows the effect of the gas composition on the coating thickness. When carrying out the coating with both higher and lower values of the ratio H 2 O / H 2 (ie outside the range of about 0.025 to 2.0), it was not possible to obtain a coating of sufficient thickness, i.e. > l pm. The quality of the coating was good on all specimens with a greater coating thickness than 1 μm. The quality of the coating was judged to be good if the coating could withstand an adhesion test, whereby the coated article was displaced under a diamond tip of the type used in Rockwell hardness tests, using a load of 2 kp on the diamond tip. If the coating resisted flaking or crumbling during this test, the coating was considered to be of good quality. Although the coating did not resist this effect, it could be of acceptable quality.

The nature of the coating obtained was determined using X-ray diffraction analysis and optical microscopy. Rönt- O. Genetic analysis showed that the coating consisted of α-Al 2 O 3 455 891 8 higher deposition temperatures (exceeding 1150 ° C), significant amounts of the compound W 3 Co 3 C (eta phase) began to form due to reaction of the cemented carbide substrate with the coating atmosphere. Optical microscopy showed a gray, translucent coating of AIZO3, which was completely dense and well bonded to the substrate of the samples in which the coating quality was found to be good. A very thin (less than 1 μm) coating of another non-metallic compound was present between the Al 2 O 3 layer and the cemented carbide substrate, if the substrate contained TiC and / or TaC. The presence of this thin layer may be desirable in order to obtain a higher bond strength between the coating and the substrate, ie. a bonding strength sufficient for the material to meet the adhesion test specified above.

The preferred temperature range for the deposition of the coating is 900 to 220 ° C. At lower temperatures, the deposition rate becomes very low and the coating is poorly bonded to the substrate. At higher temperatures, too strong a reaction occurs between the coating atmosphere and the cemented carbide substrate, which weakens the bond between the coating and the substrate and reduces the strength of the finished composite body.

The strength of the Al2O3-coated cemented carbide composite material was measured (as were all strength measurements given in this context) using a slightly modified standard cross-fracture test (ASTM No. B4066-63T), which included a load with three rollers and a thickness-to-thickness ratio. 3.5 to 1. Using a deposition temperature of 1050 ° C and a cemented carbide substrate of the type set forth in the first ten examples in Table I, the average strength of rods having a coating thickness of S-7 was pm (the preferred thickness of this substrate in terms of abrasion resistance) to 169 kp / mm '. This means only a slight reduction (11%) from the strength value of 190 kp / mm 'measured on the uncoated cemented carbide substrates. Table II lists the properties when cutting metal of coated cutting plates manufactured according to the invention and compares these properties with the corresponding properties of non-coated cutting plates. Examples 11-17 relate to replaceable cutting plates measuring 12.7 x 12.7 x 4.1 mm coated with Al 2 O 3 at 100 ° C using the steam deposition method set forth in Examples 1-10.

Coating thicknesses in the range of 1-10 μm were used.

These cutting plates were then used for machining SAE 1045 steels with Brinell hardness 190 (BHN) at a speed of 210, 300 and 450 surface meters / minute, feed rate 0.25 mm per revolution and cutting depth 2.5 mm. The cutting time for a flank wear of 0.25 mm is stated in Table II together with the pit wear depth at the time for flank wear 0.25 mm. The cross-breaking limit is also stated. For comparison purposes, the cutting properties and strength values for uncoated substrate material, Examples 18 and 19, a commercially available, solid, alumina-based (89% Al 2 O 3, 11% TiO) cutting plate material, Examples 20 and 21, and for a TiC -coated hard-metal cutting plate, all experiments being carried out under the same conditions.

It can be seen that the cutting properties of the cemented carbide tool material are very significantly improved by the Al 2 O 3 coating and that this improvement is significantly greater than that of a TiC coating on the same substrate. It also appears that the degree of improvement obtained depends on the coating thickness up to a value of about 7 μm and that a certain tendency for deterioration arises at 10 μm. At the optimum torque of 7 microns for this substrate, the performance characteristics of the tool coated with Al 2 O 3 were equivalent to the performance characteristics of the tool made of solid Al 2 O 3 at all three tested speeds. However, the strength of the Al2O3-coated cutting plate was considerably higher than that of the solid Al2O3 plate and also higher than the strength of the same substrate with a TiC coating.

Due to the limited strength, it has not been possible to use solid alumina as a cutting material in replaceable cutting plates of the type used in bolt-type holders (pin-type holders). These replaceable cutting plates have a centrally arranged hole for a bolt which locks the cutting plate in position. The strength of such a cutting plate must be sufficient to withstand the locking stresses. The strength of coated materials according to the invention is high enough to enable the use of such cutting plates.

The present invention therefore makes it possible to use replaceable cutting plates for such purposes, which have higher abrasion resistance than some comparable cutting plates currently available.

Table III below shows the application properties of the coated cutting plates according to the invention when cutting a nickel-based high-temperature alloy, Inconel 718 in solution-aged state (hardness 390 Brinell units BHN).

The results, Example 25, are compared with the use properties of uncoated cemented carbide of the same composition (Example 26) and in addition with a commercial tool of solid alumina (Example 27). The cutting plates were of the replaceable type with a negative clearance angle (reversible and rotatable) with the dimensions 12.7 x 12.7 x 4.1 mm. The cemented carbide base for the material of Examples 25 and 26 was 94% WC and 6% Co.

The substrate was coated with Al 2 O 3 at 1050 ° C using the vapor deposition process described above in connection with Examples 1 ~ 1C.

The properties of the cutting plate coated with 2.5 μm Al 2 O 3 were significantly better than the properties of the uncoated cemented carbide cutting plate of the same substrate composition. Experiments with other coating thicknesses have determined that the optimum thickness for this type of machining (ie of high temperature alloys) is in the range of 1-3 μm.

Thicknesses exceeding 3 pm resulted in reduced tool life in some tests. The superior strength of the Al2O3 coated article is clear from the rapid destruction of the Al2O3 solid tool of Example 27, while no breakage or flaking was observed on the Al2O3 coated tools of Example 25. 455 891 ll H mNo.om ~ oo mßm.o mNo.o oøo ~ o ooo.om> m ~ o ø fl .HV wN.v Hwo_o mHo.o ooo ~ o ooN ~ o ooß.o ooA ~ om HV w ~ .N >> N ~ o mN fl. ø oøo.o ooo.o oow.o oov.owm www.om «Ho ßom.o ooo.o oom_o om ~ .o om« .o ß m> mæ.o ß> ~ .om ~ mo øoo. o ooo.o oo «.o oow.owm mo ~ .o mæoo.o ~« oo ooo.o ooH_o omæ.o omo.omw ßNH.o mmo.o mww.o coo.o omH.o ooH_o om>. ovw Nma.o wm fi å. maßåv 000.0 ooo.o omH ~ o ommiu m m. ~ m «oo Hmmo.o H ~ mo ooo.o ooo.o owo.o owm.o N HV mNo.o ßH ~ oo wmm.o øoo_o ooo.o ~ No.om> mo H A21, + www. + .oN =. +. ~ m. ^ o ~ mv .oU. ^ ~ ou. . ~ =. fi wmewxm | mmcmmwMm% Wm + ^ ONmv xuhnu fi m fi uuma .ux fl> Ew fi xoænu fi m fi uummmmcmmua _: | mcO fl uxmwuwmwcwuum> H a fl mßmh 453 891 12 .ou w m M HU «H0 m. .HH _uHa H m .oz H Nß H mwH m> ~ .o «com m _. vw HNH m> ~. ° æH QH ~ m HHHmHwau ~ w = wa m = H = mmmHwn | uHe HN ae H_ ° @H> m = H = »@ = se H_ ° mm Hmo.o HHHu .cHE m.« conv | = NN mw Hmo.o om oem 1 _. HN mw m ~ o. ° Hm QHN | mo ~ H <> Hmm «z ON mwH« m ~ .o m com 4. ~ HHmumEwuw: nmmHwßo mH om fl NOHHQ w cam I H fi HmumE © ums © mm fl wnO wa NHH w> o_o wm Qom ~ H _. ßH HNH w ~ H.o HH Qom H ~ HHm »weøH« ß Hm m = H = mmwH @ Q | Ho ~ H <@H EE H.o wH> mcHcumc EE H.o mw fl mßoo.o HHHu .c fl ë N.v omv ß _. ma æwH mo ~ .o Hm OHN oH ._ vH mwH m ~ o.o Hm QHN ß ._ mH w> H Hm ° .o Nm QHN H _. NH ~ wH @> Q_Q m QHN H HHH ~ HweøHH: mm mcH = mmwHwp1Ho ~ H <HH «EE \ mx HEEV HCHEV u5cHE HEEV Hmm mcwum mcHcuwcu> mmmHm mc fl cpwcuæmmm fix m0m Efi m0m. nwuwëuh lmmc fi c | nm> H ms fi nmouw HH fi u flfi ß uwsm fi ummsnmxw | mwmHmm HH H fl wß fl ß 453 891 13 mc fl uwpmumw m ~ uucmx w fl ummc H | 0 Hd> HwwmZ ßm fm «Z fi weuuw: uw fi wno mm m.w m.N H fl muwäwums wa m: fl: mmmHmn | mO ~ fl <mm. so ÉÉ: 25: mæuwuuw fi muwxw Émewxm mc fl cumcuæmmm fl m xm fi xuowu se Sá 33 m2. Lwm fi cwmm fl wm HHH Hawßmä

Claims (4)

453 891 14 PATENT CLAIMS Coated cemented carbide product, in particular cutting body, with high strength and abrasion resistance, comprising a cemented carbide substrate provided with a coating consisting mainly of alumina, characterized in that the coating consists of a completely dense coating of oxide with a thickness of 1-10 μm obtained by vapor deposition at 900-150 ° C from a mixture of aluminum halide vapor, hydrogen gas and water vapor or carbon dioxide, at a H 2 O / H 2 ratio of between 0.025 and 2.0. Process for the production of a coated cemented carbide product, in particular a cutting body, with high strength and abrasion resistance, characterized in that a mixture of aluminum halide vapor, hydrogen gas and water vapor or carbon dioxide is passed over a cemented carbide substrate at 900 ° C. 220 ° C for precipitating a completely dense coating of J (alumina on the cemented carbide substrate, the amount of water vapor: hydrogen being preferably between 0.025 and 2.0). 3. A process according to claim 2, characterized in that the aluminum halide is aluminum chloride. 4. A method according to claim 2 or 3, characterized in that the water vapor is prepared during the coating process by reacting hydrogen gas with carbon dioxide.