Cermet powder

Abstract

A cermet powder includes a) from 50 to 90 wt-% of at least one hard material, and b) from 10 to 50 wt-% of a matrix metal composition. The wt.-% for a) and b) are based on a total weight of the cermet powder. The matrix metal composition comprises i) from 40 to 75 wt-% of iron and nickel, ii) from 18 to 35 wt-% of chromium, iii) from 3 to 20 wt.-% of molybdenum, and iv) from 0.5 to 4 wt-% of copper. The wt-% for i) to iv) are based in each case on a total weight of the matrix metal composition. A weight ratio of iron to nickel is from 3:1 to 1:3.

Claims

1. A sintered cermet powder comprising: a) from 50 to 90 wt-% of at least one hard material; and b) from 10 to 50 wt-% of a matrix metal composition, the wt.-% for a) and b) being based on a total weight of the cermet powder, the matrix metal composition comprising: i) from 40 to 75 wt-% of iron and nickel, ii) from 18 to 35 wt-% of chromium, iii) from 3 to 20 wt.-% of molybdenum, and iv) from 0.5 to 4 wt-% of copper, the wt-% for i) to iv) being based in each case on a total weight of the matrix metal composition, and a weight ratio of iron to nickel being from 3:1 to 1:3, wherein the sintered cermet powder is produced by a process comprising the steps of: mixing or milling the at least one hard material powder with the matrix metal composition which is provided as a powder so as to obtain a powder mixture, and sintering the powder mixture so as to obtain the sintered cermet powder mixture.

2. The sintered cermet powder as recited in claim 1, wherein the matrix metal composition further comprises v) cobalt.

3. The sintered cermet powder as recited in claim 2, wherein the cobalt is present in an amount of up to 10 wt-% based on the total weight of the matrix metal composition.

4. The sintered cermet powder as recited in claim 1, wherein the matrix metal composition further comprises vi) a modifier.

5. The sintered cermet powder as recited in claim 4, wherein the modifier is selected from Al, Nb, Ti, Ta, V, Si, W and mixtures thereof.

6. The sintered cermet powder as recited in claim 4, wherein the modifier is present in an amount of up to 5 wt-% based on the total weight of the matrix metal composition.

7. The sintered cermet powder as recited in claim 1, wherein the matrix metal composition consists essentially of: i) from 40 to 75 wt-% of iron and nickel; ii) from 18 to 35 wt-% of chromium; iii) from 3 to 20 wt-% of molybdenum; iv) from 0.5 to 4 wt-% of copper; v) from 0.0 to 10 wt-% of cobalt; and vi) from 0.0 to 5 wt-% of at least one modifier; the wt-% for i) to vi) being based in each case on the total weight of the matrix metal composition, and the weight ratio of iron to nickel being from 3:1 to 1:3.

8. The sintered cermet powder as recited in claim 1, wherein the matrix metal composition comprises from 15 to 50 wt-% of iron.

9. The sintered cermet powder as recited in claim 1, wherein the matrix metal composition comprises from 15 to 50 wt-% of nickel.

10. The sintered cermet powder as recited in claim 1, wherein the matrix metal composition comprises from 20 to 33 wt-% of chromium.

11. The sintered cermet powder as recited in claim 1, wherein the matrix metal composition comprises from 4 to 15 wt-% of molybdenum.

12. The sintered cermet powder as recited in claim 1, wherein the matrix metal composition comprises from 0.7 to 3 wt-% of copper.

13. The sintered cermet powder as recited in claim 1, wherein the weight ratio of iron to nickel in the matrix metal composition is from 1:2 to 2:1.

14. The sinteed cermet powder as recited in claim 1, wherein the at least one hard material is a metal carbide.

15. The sintered cermet powder as recited in claim 14, wherein the metal carbide is selected from WC, Cr.sub.3C.sub.2, VC, TiC, B.sub.4C, TiCN, SiC, TaC, NbC, Mo.sub.2C and mixtures thereof.

16. The sintered cermet powder as recited in claim 1, wherein the cermet powder comprises an average particle size of from 10 to 100 m as determined in accordance with ASTM C1070.

Description

DETAILED DESCRIPTION

(1) Corrosion resistance is determined here under practical conditions in the form of emissions of the matrix metals, rather than electrochemical methods, such as potentiograms, which cannot quantify service time under practical conditions.

(2) It has now surprisingly been found that the abovementioned problems can be solved via a cermet powder comprising one or more hard materials and a specific matrix metal composition.

(3) In an embodiment, the present invention provides a cermet powder comprising: a) from 50 to 90% by weight of one or more hard materials; and b) from 10 to 50% by weight of a matrix metal composition, where the data by weight are based on the total weight of the cermet powder, characterized in that the matrix metal composition comprises: i) from 40 to 75% by weight of iron and nickel, ii) from 18 to 35% by weight of chromium, iii) from 3 to 20% by weight of molybdenum, iv) from 0.5 to 4% by weight of copper, where the data by weight for the metals i) to iv) are based in each case on the total weight of the matrix metal composition, and where the ratio by weight of iron to nickel is in the range of from 3:1 to 1:3.

(4) The cermet powders of the present invention have excellent suitability as thermal spray powders. These powders can be used for surface coating, for example, of metal substrates. The cermet powders of the present invention can, for example, be applied to a wide variety of components by thermal spraying processes, such as plasma spraying or high-velocity flame spraying (HVOF) or other flame spraying processes, arc spraying, laser spraying, or application welding, for example, the PTA process, the objective being to give the respective component the desired surface properties.

(5) The cermet powders of the present invention comprise one or more hard materials in an amount of from 50 to 90% by weight, for example, in an amount of from 60 to 89% by weight, for example, from 70 to 88% by weight, based in each case on the total weight of the cermet powder. The cermet powders of the present invention can comprise typical hard materials. Examples can, for example, include metal carbides such as a hard material, for example, those selected from the group consisting of WC, Cr.sub.3C.sub.2, VC, TiC, B.sub.4C, TiCN, SiC, TaC, NbC, Mo.sub.2C, and mixtures thereof.

(6) Preference is in particular given to the hard materials WC and/or Cr.sub.3C.sub.2.

(7) The cermet powders of the present invention have a matrix metal composition which is present in an amount of from 10 to 50% by weight, for example, from 11 to 40% by weight, for example, from 12 to 30% by weight, based in each case on the total weight of the cermet powder. The matrix metal composition is a determining factor for the excellent properties of the cermet powders of the present invention.

(8) In an embodiment, the present invention provides the use of a matrix composition comprising: i) from 40 to 75% by weight of iron and nickel; ii) from 18 to 35% by weight of chromium; iii) from 3 to 20% by weight of molybdenum; iv) from 0.5 to 4% by weight of copper; where the data by weight for the metals i) to iv) are based in each case on the total weight of the matrix metal composition, and where the ratio by weight of iron to nickel is in the range of from 3:1 to 1:3, for producing a cermet powder.

(9) In an embodiment of the present invention, the matrix metal composition can, for example, comprise, as an additional metal: v) cobalt, for example, in an amount of up to 10% by weight, based on the total weight of the matrix metal composition.

(10) In an embodiment of the present invention, the matrix metal composition can also comprise: vi) modifiers, for example, selected from the group consisting of Al, Nb, Ti, Ta, V, Si, W, and any desired mixtures thereof.

(11) The usual amount of the modifiers present is up to 5% by weight, based on the total weight of the matrix metal composition.

(12) In an embodiment of the present invention, the matrix metal composition to be used in the present invention can consist essentially of the following components: i) from 40 to 75% by weight of iron and nickel; ii) from 18 to 35% by weight of chromium; iii) from 3 to 20% by weight of molybdenum; iv) from 0.5 to 4% by weight of copper; v) optionally up to 10% by weight of cobalt; vi) optionally up to 5% by weight of one or more modifiers; where the data by weight for the metals i) to vi) are based in each case on the total weight of the matrix metal composition, and where the ratio by weight of iron to nickel is in the range of from 3:1 to 1:3.

(13) Excellent properties can be achieved with a matrix metal composition which comprises from 15 to 50% by weight, for example, from 20 to 45% by weight, of iron.

(14) In an embodiment of the present invention, the matrix metal composition comprises from 15 to 50% by weight, for example, from 20 to 45% by weight, of nickel.

(15) The presence of chromium, molybdenum and copper in the matrix metal composition achieves the excellent properties of the cermet powder or of the surface coatings produced therefrom.

(16) In an embodiment of the present invention, the matrix metal composition can, for example, comprise from 20 to 33% by weight, for example, from 20 to 31% by weight, of chromium.

(17) In an embodiment of the present invention, the matrix metal composition can, for example, comprise from 4 to 15% by weight of molybdenum, for example, from 5 to 10% by weight of molybdenum.

(18) The copper content is important, in particular together with the specific iron-nickel ratio, for the corrosion properties. Excellent corrosion results were achieved with a matrix metal composition comprising, for example, from 0.7 to 3% by weight, for example, from 0.9 to 2.0% by weight, of copper.

(19) The ratio by weight of iron to nickel in the matrix composition likewise contributes to the corrosion-resistance of the cermet powder of the present invention.

(20) In an embodiment of the present invention, the ratio by weight of iron to nickel in the matrix metal composition can, for example, be from 1:2 to 2:1, for example, from 1:1.5 to 1.5:1.

(21) In an embodiment of the present invention, the cermet powders of the present invention can, for example, be used as thermal spray powders. Certain particle sizes have proven to be particularly suitable. In an embodiment of the present invention, the average particle size of the cermet powders of the present invention can, for example, be from 10 to 100 m, determined by means of laser scattering according to ASTM C1070.

(22) The present invention also provides a process for producing the cermet powder of the present invention.

(23) In an embodiment, the present invention provides a process for producing a cermet powder comprising: a) mixing or milling of one or more hard-material powders with a pulverulent matrix metal composition which comprises: i) from 40 to 75% by weight of iron and nickel, ii) from 18 to 35% by weight of chromium, iii) from 3 to 20% by weight of molybdenum, iv) from 0.5 to 4% by weight of copper, where the data by weight for the metals i) to iv) are based in each case on the total weight of the matrix metal composition, and where the ratio by weight of iron to nickel is in the range of from 3:1 to 1:3; b) sintering the powder mixture; and c) optionally pulverizing the mixture sintered in step b).

(24) The mixing or milling in step a) of the process of the invention for producing cermet powder can, for example, take place via dispersion of the pulverulent hardness-imparting materials (hard materials), and also of the pulverulent matrix metal composition, in a liquid. In the case of milling, the dispersion is then milled in a milling step, for example, in a ball mill or in an atrittor.

(25) In an embodiment of the present invention, the matrix metal composition can, for example, take the form of alloy powder.

(26) In an embodiment, the process of the present invention for producing cermet powder can, for example, include mixing via a dispersion in a liquid, optionally followed by milling, followed, via removal of the liquid, by a granulation step, which can, for example, take place via spray drying. The spray granulate can then be classified and, in a thermal process step that follows, can be sintered so that the mechanical strength of the granulate is sufficient to restrict disintegration of the granulate during the thermal spraying process in a manner which allows reliable conduct of the thermal spraying process. The sintering of the powder mixture can, for example, take place under reduced pressure and/or in the presence of inert gases, for example, selected from the group consisting of hydrogen, argon, nitrogen and mixtures thereof, at any desired pressure.

(27) When an inert gas that avoids oxidation is used, the sintering can also be carried out in the approximate region of atmospheric pressure. The sintering step usually provides a powder or a loose sintered cake which can be converted back to powder. The powders obtained are similar in size and appearance to the spray granulate. Agglomerated/sintered spray powders offer freedom in the selection of the components (for example, their contents and particle sizes), and, by virtue of their good flowability, have good metering properties in the spraying process. In an embodiment of the present invention, very fine-particle hardness-imparting materials, for example, with an average particle size below 20 m, as determined by means of laser scattering according to ASTM C1070, can be used for the cermet powders of the present invention and for the purposes of the production process of the present invention for cermet powder. The use of such fine-particle hardness-imparting materials leads to very smooth wear surfaces, and this in turn leads to low coefficients of friction and to long service times.

(28) Sintered/crushed cermet powders or, respectively, spray powders can be produced analogously, except that the powder components are not necessarily mixed wet in dispersion, but can instead be mixed dry, and are optionally tableted or compacted to give other moldings. The sintering step that follows takes place analogously, but compact, strong sintered structures are usually obtained, which require exposure to mechanical force for conversion back to powder form. In these instances, however, the resultant powders with average particle sizes from 10 to 100 m are typically of irregular shape and are characterized by fractured surfaces. These thermal spray powders have markedly poorer flowability, which can be disadvantageous for a constant application rate during thermal spraying, but is still practicable.

(29) The cermet powders of the present invention, or the cermet powders obtainable according to the process of the present invention for producing cermet powder, can be used as a thermal spray powder. The present invention therefore further provides the use, as a thermal spray powder, of the cermet powders of the present invention or of the cermet powders obtainable via the process of the present invention for producing cermet powder.

(30) The cermet powders of the present invention moreover have excellent suitability for surface coating, in particular, of metal substrates or of components.

(31) The present invention therefore further provides the use, for surface coating purposes, of the cermet powders of the present invention or of the cermet powders obtainable via the process of the present invention for producing cermet powder. The surface coating can, for example, take place via a thermal spraying processes, for example, via plasma spraying or high-velocity flame spraying or other flame spraying processes, or arc spraying, or laser spraying, or application welding.

(32) The cermet powders of the present invention or cermet powders obtainable via the present process of the present invention for producing cermet powder impart excellent properties to the components coated therewith, in particular, in respect of protection from wear under corrosive environmental conditions, for example, at pH below 7 and in the presence of any chloride ions that may be present.

(33) The present invention therefore further provides a process for producing a coated component, the process comprising the application of a coating via thermal spraying of a cermet powder of the present invention or of a cermet powder obtainable via the process of the present invention for producing cermet powder.

(34) The present invention further provides a coated component obtainable by the production process of the present invention. The component coated in the present invention can be used for protection from wear under corrosive environmental conditions, for example, at pH below 7, and in the presence of any chloride ions that may be present.

(35) In an embodiment of the present invention, the coated component can, for example, be a part of an apparatus which comes into contact with media which comprise acids and/or which comprise chloride ions. By way of example, coated components of the present invention can be displaceable parts of valves or are piston rods.

(36) The examples below illustrate the present invention without any resultant restriction of the present invention thereto.

Example 1

Comparative Example

(37) Spray powders with compositions as set forth in Table 1 were compacted for 10 min at 1000 C. to give compact moldings with identical specific surface area, by means of hot pressing. The peripheral layers were smoothed by means of abrasive SiC paper. The cylindrical moldings were then exposed for 28 days to 500 ml of the media (1N hydrochloric acid, 1N sulfuric acid, and 1N citric acidthe latter corresponding to mol/l) at 20 C. with air ingress. 180 ml were then removed, and the content of the elements of which the matrix was composed was determined.

(38) The mechanical properties wear resistance and cavitation resistance were determined on sprayed layers. The sprayed layers were also subjected to the ASTM B117 salt-spray test, and the change was recorded after 1000 hours.

(39) Coatings made of the spray powders were also produced on ST37 structural steel and on V4A stainless steel. A JP5000 HVOF burner was used for this purpose. The data in Table 1 are in percent by weight.

(40) TABLE-US-00001 TABLE 1 Prior-Art Spray Powders No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7 WC (%) 86 73 85 85 70 85 Cr.sub.3C.sub.2(%) 75 20 Matrix (%) 14 25 7 15 15 30 15 Fe(%) 6 63.3 70 Co(%) 71 5 Ni (%) 80 100 57 14 67 Cr (%) 29 20 16 18 20 20 Al (%) 10 Nb (%) 4 Mo (%) 16 2.7 9 Cu (%) Matrix emission 2283 5684 420 3269 2510 4360 3083 (mg/180 ml, 28 days, 1N HCl) Matrix emission 2366 5151 1835 2202 2620 2570 3222 (mg/180 ml, 28 days, 1N H2SO4) Matrix emission 316 2486 11 125 1352 106 3141 (mg/180 ml, 28 days, 1N citric acid) Properties of sprayed layer: Wear (ASTM 20 41 15 41 33 41 23 G65-04, mg) Cavitation wear 5 5 7 5 10 7 5 (mg/h) according to ASTM G32 on level coating Change in salt-spray disc. none none none disc. none none test according to ASTM B117 (1000 h) disc. means discoloration.

(41) The data by weight for Fe (%) to Cu (%) are based on the total weight of the matrix composition. The total content of matrix is stated in the Matrix (%) row, and is based on the total weight of the spray powder. The % data for the carbides are based on the total weight of the spray powder. In the spray powders of Nos. 4 to 7, the matrix took the form of an alloy since a corresponding alloy powder was used to produce the spray powder. No. 7 corresponds to a preferred embodiment described in DE 10 2006 045 481 B3.

(42) It is clear from the results that no known material performs adequately in all respects. WCCr3C2-Ni 83/20/7 (No. 3) is the only material with adequate resistance to hydrochloric acid and citric acid, but not to sulfuric acid. The resistance of all of the spray powders of Nos. 1-7 to sulfuric acid is generally poor.

(43) Spray powder No. 4 with a matrix alloy similar to HastelloyC, and No. 6 also have good mechanical properties and good resistance to citric acid, but are not resistant to mineral acids.

(44) Spray powder No. 5 with 316 L stainless steel has very low corrosion-resistance and exhibits unacceptable discoloration in the salt-spray test.

Example 2

Partly Inventive, as Indicated by *

(45) Moldings and sprayed layers were produced analogous to Example 1. The powders according to Nos. 8 and 9 used two alloy powders of identical nominal composition but from different production processes (spraying of the alloy from the melt and cooling of the resultant melt droplets by means of water and, respectively, argon injected through a nozzle). No. 10 comprises, as a matrix, an FeNi 50/50 alloy powder, and also a chromium metal powder used as further component of the matrix. It can therefore be assumed that, in the agglomerated/sintered spray powder, the matrix was not completely and uniformly alloyed with Cr. The data in Table 2 are in percent by weight.

(46) TABLE-US-00002 TABLE 2 Spray Powders No. 8* No. 9* No. 10 WC (%) 85 85 87.5 Cr3C2 (%) Matrix (%) 15 15 12.5 Fe (%) 31 31 36 Co(%) Ni (%) 31 31 36 Cr (%) 27 27 28 Al (%) Nb(%) Mo(%) 6.5 6.5 Cu (%) 1.3 1.3 Matrix emission (mg/180 ml, 28 216 151 1740 days, 1N HCl) Matrix emission (mg/180 ml, 28 151 92 1141 days, 1N H.sub.2SO.sub.4) Matrix emission (mg/180 ml, 28 68 61 608 days, 1N citric acid) Properties of sprayed layer Wear (ASTM G65-04, mg) 26 26 15 Cavitation wear (mg/h) 6 5 8 Change in salt-spray test none none discoloration

(47) The data by weight for Fe (%) to Cu (%) are based on the total weight of the matrix composition. The total content of matrix is stated in the Matrix (%) row, and is based on the total weight of the spray powder. The % data for the carbides are based on the total weight of the spray powder.

(48) The iron- and nickel-containing spray powders Nos. 8 to 10 surprisingly exhibit relatively good resistance to mineral acids in comparison with those having a matrix based on nickel, on cobalt, or indeed on iron. This is surprising to the extent that iron is substantially less inert than nickel. Even the incomplete alloy of the matrix with Cr in No. 10 gives better results in sulfuric acid than any of the powders of Example 1. It appears that FeNi alloys have better acid resistance than the range-endpoints Ni and Fe, and the acid resistance therefore appears to be dependent on the Fe:Ni ratio, as well as on the other elements present.

(49) The acid resistance of the FeNi matrix is further improved in powders Nos. 8 and 9 by the chromium alloyed in the matrix here, and also by the additional materials Mo and Cu. Since, however, the high Mo contents in powders 4 and 6 do not lead to improved acid resistance, it must be concluded that, alongside the Fe/Ni ratio, the copper content is substantially concomitantly responsible for the good corrosion results.

Example 3

Comparative Example, Pure Matrix Alloys

(50) TABLE-US-00003 TABLE 3 Matrix Metal Composition No. 11 No. 12 No. 13 (316L) (NiCr80/20) (NiCr50/50) Fe (%) 68 Co (%) Ni (%) 13 80 50 Cr (%) 17 20 50 Al (%) Nb (%) Mo (%) 2 Cu (%) Matrix emission 948 115 256 (mg/180 ml, 28 days, 1N HCl) Matrix emission 944 110 131 (mg/180 ml, 28 days, 1N H2SO4) Matrix emission 25 1 35 (mg/180 ml, 28 days, 1N citric acid)

(51) These results show that the pure matrix alloys performs substantially better in relation to corrosion than when they are used as matrix in the thermal spray powder. It must be assumed that contact corrosion between the matrix on the one hand and the hard material on the other hand is responsible for the poor performance of the thermal spray powders.

(52) The pure matrix alloys in the form of spray powders have no wear resistance because of the absence of hard materials.

(53) Nos. 8 and 9 according to the present invention are successful in achieving the acid resistance of pure NiCr 80/20 combined with the wear resistance of commercially available spray materials, as described in Examples 1 to 3.

(54) The present invention is not limited to embodiments described herein; reference should be had to the appended claims.