PETERSEN KENNETH (DK)
LIST JAN LAURBERG (DK)
PETERSEN KENNETH (DK)
WO1997047415A1 | 1997-12-18 |
US5595614A | 1997-01-21 | |||
US5021085A | 1991-06-04 | |||
FR2765593A1 | 1999-01-08 |
ZHANG J.S ET AL: "AGEING BEHAVIOUR OF SPRAY DEPOSITED 18Ni(250) MARAGING STEEL + 10 VOL% AL2O3 PARTICULATE- REINFORCED METAL MATRIX COMPOSITES", MATERIALS SCIENCE AND ENGINEERING, vol. A225, no. 1-2, - 1997, pages 96 - 104, XP000900931
Hofmann-bang, Zacco A/s (Hans Bekkevolds Allé 7 Hellerup, DK)
1. | A metal matrix composite based on boron steel containing at least 0. 0010% boron by weight, produced by spray forming, comprising ceramic particles with a hardness greater than 800 HV, selected from a group consisting of Al203, AlN, BeO, B4C, CeO2, Cr3C2, MgO, MoSi2, Mo2C, NbC, Si3N4, SiO2, ThO2, TiB2, TiC, VC, WC, WSi, ZrB, ZrC, ZrO. |
2. | A metal matrix composite according to claim 1, where the amount of ceramic particles is up to 30 % (v/v), preferably from 4 to 30 % (v/v), more preferably from 8 to 25 % (v/v), most preferably from 10 to 20 % (v/v). |
3. | A metal matrix composite according to claim 1 or 2, where the average size of the ceramic particles is from 0. 1 cm to 1 mm, preferably from 0. 2 pm to 500 m, more preferably from 20 Um to 180 µm. |
4. | A metal matrix composite according to any of the preceeding claims, where the ceramic particles are selected among Al2O3, TiC, ZrO2, VC, MgO, WC, and Six. |
5. | A metal matrix composite according to any of the preceeding claims, where the boron steel has a nominal composition of 0. 10. 65 % C, 0. 02. 0 % Mn, 0. 00. 5 % Si, 0. 02. 0 % Cr, and 0. 0010. 1 % B. |
6. | A metal matrix composite according to claims 14, where the boron steel has a nominal composition of 0. 16 0. 40 % C, 0. 81. 8 % Mn, 0. 050. 4 % Si, 0. 151. 0 % Cr, and 0. 00150. 02 % B. |
7. | A metal matrix composite according to claims 14, where the boron steel has a nominal composition of 0. 18 0. 30 , C, 0. 91. 4 % Mn, 0. 120. 35 % Si, 0. 200. 5 % Cr, and 0. 0020. 005 % B. |
8. | A metal matrix composite according to claims 57 further comprising minor amounts of Cu, Ti, Al, P, or S. |
9. | A metal matrix composite according to any of the preceeding claims further comprising one or more alloy elements selected among Al, Ti, Li, Mg, Ca, Zr, Ni, V, Y, Nb, S, and P. |
10. | A metal matrix composite according to claim 9, where the alloy elements are selected among Ti, Li, and Mg. |
11. | A metal matrix composite according to claim 9 or 10, where the total amount of alloy elements is from 0. 1 to 10. 5 ^f by weight, preferably between 0. 15 and 6 % by weight, more preferably between 0. 2 and 4 % by weight. |
12. | A method for preparing a metal matrix composite comprising the steps of : providing boron steel containing at least 0. 0010 % boron by weight preferably with a nominal composition of 0. 10. 65 % C, 0. 02. 0 % Mn, 0. 00. 5 % Si, 0. 01. 0 % Cr, and 0. 0010. 02 % B, melting said boron steel, selecting one or more types of ceramic particles having a hardness greater than 800 HV, optionally dividing the steel into two or more streams of melted steel, leading said stream (s) into a spray forming chamber, thereby atomising the melt to form droplets, mixing the ceramic particles with a gas essentially free of oxygen to form a particle/gas mixture, injecting the ceramic particles in between the droplets, by spraying them into the spray forming chamber, collecting the droplets on a substrate, and letting the droplets solidify immediately on the substrate, wherein the ceramic particles are selected from a group consisting of AlOs,A1N, BeO, B4C, Cet2, Cr. 3C, MgO, MoSi, Mo2C, NbC, SiN,,Si0,Th0,TiB, TiC, VC, WC, WSi, ZrB, ZrC, and Zr02. |
13. | A method according to claim 12, wherein the distance between the point of atomising and the substrate is adjustable. |
14. | A method according to claims 1213, wherein said gas is selected among nitrogen, argon, and helium. |
15. | A metal matrix composite produced according to the method of each of the preceeding claims 1215. |
Boron steel is a type of steel that is well known for exhibiting good wear resistance. Therefore boron steel is typically used when extra resistance towards mechanical stress is needed, e. g. in gear-shift levers, agricultural machines and the like.
However, the demand for materials with improved wear resistance increases. Lots of different ways of improving the steel and the method for producing it have been attempted.
It has been tried to enforce several kinds of metals by forming a metal matrix composite, e. g. by various types of spray forming. Ceramic particles typically used are carbides, oxides, and nitrides.
Until now the incorporation of said particles has not proven any significant results regarding enhanced strength and some tests have even showed an increased tendency to stress within the metal matrix.
It is an object of the present invention to provide a metal matrix composite that does not exhibit the above- mentioned problems.
It is another object of the present invention to provide a metal matrix composite which exhibits improved wear resistance.
It is a further object of the present invention to provide a suitable method for producing a metal matrix composite with improved wear resistance.
Further, it is an object of the invention to provide a metal matrix composite and a method for producing said matrix that is economically acceptable.
These and other objects are obtained by the invention as defined in the claims.
"Ageing behaviour of spray-deposited 18Ni (250) maraging steel + 10 vol. % Al_0 particulate reinforced metal matrix composites", by J. S. Zhang describes a metal matrix composite based on maraging steel having a nominal composition of 18% Ni, 5% Mo, 5, 5% Co, 0. 4% Ti, 0. 1% Al balanced with Fe, where 10 % (v/v) of Altos has been added.
The finding in this article regarding the ageing of steel material does not imply any improved wear resistance. Furthermore, the steel tested in the above-mentioned article does not contain boron.
The metal matrix composite according to the invention is based on boron steel, defined as containing at least 0. 0010 % boron by weight, preferably 0. 001-0. 1 % boron, more preferably 0. 0015-0. 02 % boron, and most preferably 0. 002-0. 004 % boron by weight. The carbon steel may preferably be hardened and tempered.
The metal matrix composite may be produced by any conventional kind of spray forming, however, it is preferred that the metal matrix composite is produced by the method according to the invention.
The metal matrix composite comprises ceramic particles, which should preferably exhibit a considerable hardness, i. e. the ceramic particles should exhibit a hardness greater than 800 HV, preferably greater than 1200 HV, more preferably greater than 1800 HV.
The ceramic particles may be selected from a group of materials consisting of Al-, O-,, AlN, BeO, B4C, Ce0, CrC :, MgO, MoSi2, MoC, NbC, Si N4, SiO, ThO, TiB, TiC, VC, WC, WSi, ZrB, ZrC, and ZrO2. Preferably the ceramic particles are selected among Al-03, TiC, ZrO, VC, MgO, WC, and SiO-.
The amount of ceramic particles added has great influence on the wear resistance. The optimal amount may depend on the combination of materials in the matrix, the actual condition for use of the matrix, as well as the average particle size.
The average distance between two ceramic particles may influence the wear resistance, as it is more difficult for a particle in the material which is worn against the present material, hereinafter named as a wearing particle, to dig into the surface of the matrix between the ceramic particles, if the average distance between the particles is less than the average particle size of the wearing particle. A high content of ceramic particles with a small particle size in combination with a short distance between them therefore provides a preferred embodiment.
The amount of ceramic particles added may e. g. be up to 30 % (v/v), preferably from 4 to 30 % (v/v), more preferably from 8 to 25 (v/v), most preferably from 10 to 20 % (v/v).
If the matrix material itself is too soft, wearing particles of a larger size than the ceramic particles may be able to dig out the ceramic particles from the surface of the matrix. If, however, the matrix is sufficiently hard, the wearing particle will not be able to dig into the material, and the ceramic particles will actually crack the wearing particles.
If the particle size of the ceramic particle is equal to or larger than the particle size of the wearing particle, the wearing particle will, provided the hardness of the matrix is sufficient, be unable to remove the ceramic particle. In a preferred embodiment the average size of the ceramic particles is therefore selected in view of the final use of the product.
The average size of the ceramic particles may be from 0. 1 Am to 1 mm, preferably from 0. 2 ßm to 500 Am, more preferably from 20 zm to 180 Am.
The composite material is based on steel, which is a suitable material exhibiting the desired properties, such as malleability, capability of being tempered to a hardness sufficient to support the ceramic particles when they are subjected to hard wear and sufficiently ductility.
As the particles during wear will be crack initiating, it is important that the matrix material is able to be work hardened in order to minimize any spreading of possible crackings.
These properties may be influenced by the composition of the steel, depending of the type of ceramic used.
Preferred embodiments comprise metal matrix composites
based on boron steel with nominal compositions as follows : 0. 1-0. 65 % C, 0. 0-2. 0 % Mn, 0. 0-0. 5 % Si, 0. 0-2. 0 % Cr, and 0. 001-0. 1 % B, or <BR> <BR> 0. 16-0. 40 % C, 0. 8-1. 8 % mon, 0. 05-0. 4 ° Si, 0. 15-1. 0 % Cr, and 0. 0015-0. 02 % B, or 0. 18-0. 30 % C, 0. 9-1. 4 % Mn, 0. 12-0. 35 % Si, 0. 20-0. 5 % Cr, and 0. 002-0. 005 % B.
The metal matrix composite according to the invention may further comprise impurities, such as minor amounts of Cu, Ti, Al, Ni, P, or S.
The metal matrix composite may further comprise one or more alloy elements selected among Al, Ti, Li, Mg, Ca, Zr, Ni, V, Y, Nb, S, and P, preferably selected among Ti, Li, and Mg. The total amount of alloy elements may be between 0. 1 and 10. 5 % by weight, preferably between 0. 15 and 6 % by weight, more preferably between 0. 2 and 4 % by weight.
The invention further relates to a method for preparing a metal matrix composite comprising the steps of : -providing boron steel containing at least 0. 0010 % boron by weight, preferably with a nominal composition of 0. 1-0. 65 % C, 0. 0-2. 0 % Mn, 0. 0-0. 5 % Si, 0. 0-1. 0 % Cr, and 0. 001-0. 02 -I B, -melting said boron steel, -selecting one or more types of ceramic particles having a hardness greater than 800 HV,
-optionally dividing the steel into two or more streams of melted steel, -leading said stream (s) into a spray forming chamber, thereby atomising the melt to form droplets, -mixing the ceramic particles with a gas essentially free of oxygen to form a particle/gas mixture, -injecting the ceramic particles in between the droplets, by spraying them into the spray forming chamber, -collecting the droplets on a substrate, and -letting the droplets solidify immediately on the substrate, wherein the ceramic particles are selected from a group consisting of Al O., AlN, BeO, B4C, Ce0, Cr3C2, MgO, MoSi-, Mo-C, NbC, Si>N4, SiO, ThO, TiB, TiC, VC, WC, WSi, ZrB2, ZrC, ZrO2.
The boron steel may of course have a different nominal composition, e. g. one of the above-mentioned compositions.
By melting said boron steel, it is understood that the steel is subjected to a temperature between 1500 and 1800 °C<BR> Oc.
The ceramic particles should exhibit a hardness greater than 800 HV, preferably greater than 1200 HV and most preferably greater than 1800 HV.
The melted steel may optionally be divided into two or more streams ; preferably the steel is divided into 2 streams.
The ceramic particles are mixed with a gas essentially free of oxygen, which gas may be e. g. nitrogen, argon, and helium.
In order to obtain a product of the desired quality it is important that during the entire spray forming procedure the droplets have the acquired temperature when hitting the surface of the substrate or the steel collected on said surface. Therefore, in a preferred embodiment according to the invention, the distance between the point of atomising and the substrate is adjustable.
On one hand, the temperature of the droplets should preferably be sufficiently high to keep the droplets melted in the initial contact with the substrate, so as to amalgamate on the substrate. On the other hand, the temperature of the droplets should preferably be sufficiently low to allow for a fast solidification of the material.
In order to have a sufficient cooling effect it is preferred that the pressure within the reaction chamber is held above atmosphere pressure.
In order to obtain the desired product another important parameter is that the distribution of the particles is sufficiently homogenous. Further, the porosity of the material should be sufficiently low.
Before processing it is important to reduce the oxygen level in the chambers, which may be accomplished by
evacuating the chambers and subsequently filling them with nitrogen.
The invention also relates to a metal matrix composite produced by the method according to the invention.
In the following the invention is described in more detail with reference to the drawings and the example below.
Figure 1 shows a spray-forming unit suitable for the process according to the invention.
Figure 2 shows a system of gas nozzles.
In figure 1 a spray-forming unit is disclosed. The unit comprises a closed container (1) with a separate melting chamber (2) and an atomisation chamber (3). Inside the melting chamber (2) there is a crucible (4) for melting the metal equipped with an outlet (7) and a stopper rod (5). In the atomisation chamber (3) the substrate (6) is arranged. At the bottom of the container (1) there is an outlet (8) for gasses and excess powder.
Figure 2 shows a system of gas nozzles consisting of three rings for inlet of primary gas (12), secondary gas (13), and particle gas (14) arranged around the outlet (11) from a crucible (not shown in the figure).
Example A boron steel with the following composition was spray formed with addition of A1=0 ; particles with a median size of 135 um.
Composition of the steel matrix in wt-% :
C : 0. 198% Mn : 0. 97% Si 0. 21% Cr : 0. 4% Cu : O. 11% Ni : 0. 4% Mo : 0. 01% V : 0. 01% N : 0. 0065% Ti : 0. 046% B : 0. 0039% Impurities : P : 0. 009% S : 0. 005% Sn : 0. 006% As : 0. 006% Nb : 0. 002% A spray forming unit according to figure 1 was used.
First, the chambers were evacuated and then filled with nitrogen until the pressure was larger than that of the surroundings. In the melting chamber the metal was melted in a crucible. When the melt reached 1630°C (measured in the centre of the stopper rod), the stopper rod was lifted and the melt was let out through the bottom of the crucible. Around the outlet from the crucible three rings of gas nozzles were arranged as described in Fig. 2. As primary gas, used to stabilise the melt stream, nitrogen was used. As the secondary gas, the atomisation gas, nitrogen was used, in order to split the gas into droplets. The particle gas, for carrying the particles
into the spray cone, was nitrogen. Other parameters, such as gas pressure and spray distance were as follows : Primary gas pressure 2. 1 bar Secondary gas pressure 13. 0 bar Particle gas pressure 7. 5 bar Spray distance* 440 mm *Distance between end of outlet and substrate.
Outside the spray-forming chamber (not shown in any of the figs.), the particles are mixed with the gas before they are injected into the chamber. The droplets were collected on a rotating substrate where they amalgamated.
Because of the fast solidification, the matrix retained the particles and they were distributed homogeneously throughout the main part of the cross section area.
The metal matrix composition produced was tested for tensile strength, yield strength, elongation, abrasive wear, and hardness by standard methods.
For comparison the boron steel without the particles were tested in similar ways.
The results are shown below.
Without With particles particles Tensile strength [N/mm-] 993/1031* 1131 Yield strength [N/mm-] 880 (8. 9 vol. %) 1010
Elongation [%] 4. 0 (8. 9 vol. %) 10. 6 Abrasive wear ** Hardened 2. 45 (6. 1 vol. %) 3. 2 and tempered [mm/min] Abrasive wear ** Hardened 1. 62 (6. 1 vol. %) 4. 1 [=/mini Hardness [HV] Hardened 595 680 Hardness [HV] Hardened and 415 385 tempered * The content of particles varied in the material. The specific content was determined to be 8. 9 and 6. 2 % pr. volume, respectively, for each sample of the material.
** The wear test is an ASTM G65 standard abrasive test with modified abrasive particles. The results therefore cannot be compared to other values achieved by that standard.
The results clearly show an improved wear resistance compared to the boron steel without the particles.
Further, the hardness of the material has not been significantly decreased by the addition of particles, and especially the elongation value is considerably higher than it could be expected for a metal matrix composite.
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