Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
METAL POWDER FOR THERMAL COATING OF SUBSTRATES
Document Type and Number:
WIPO Patent Application WO/2003/042422
Kind Code:
A1
Abstract:
The invention concerns the use of a diffusion alloy metal powder for thermal coating of substrates. The powder comprises a pre-alloyed iron base powder particles having molybdenum particles diffusion alloyed to the particles of the base powder.

Inventors:
HOLMQVIST ULF (US)
HALLEN HANS (BE)
Application Number:
PCT/SE2002/000943
Publication Date:
May 22, 2003
Filing Date:
May 17, 2002
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
HOEGANAES AB (SE)
HOLMQVIST ULF (US)
HALLEN HANS (BE)
International Classes:
B22F9/08; B22F1/00; B22F1/148; B22F9/20; B32B15/01; C22C38/22; C22C38/44; C23C4/06; C23C4/08; C23C10/36; (IPC1-7): C23C4/06; C23C4/08
Domestic Patent References:
WO2001032946A12001-05-10
Foreign References:
US4561892A1985-12-31
JPH08209202A1996-08-13
JPS63137102A1988-06-09
JPH03264642A1991-11-25
US6095107A2000-08-01
US4954171A1990-09-04
Other References:
None
Attorney, Agent or Firm:
AWAPATENT AB (Box 5117 Malmö, SE)
Download PDF:
Claims:
CLAIMS
1. Metal powder for thermal coating of substrates said powder essentially consisting of prealloyed iron base powder particles having molybdenum particles diffu sion alloyed to the base powder particles.
2. Powder according to claim 1 wherein the molybde num particles originate from reduced molybdenum trioxide.
3. Powder according to claim 1 or 2 wherein the amount of molybdenum diffusion alloyed to the particles of the base powder is above 2, preferably above 3, and most preferably above 4 % by weight of the metal powder.
4. Powder according to any one of the preceding claims wherein the amount of molybdenum diffusion alloyed to the particles of the base powder is between 2 and 15, preferably between 3 and 10 %, and most preferably between 4 and 10 % by weight of the metal powder.
5. Powder according to any one of the preceding claims, wherein the prealloyed base powder is a gasat omised powder.
6. Powder according to any one of the preceding claims, wherein the prealloyed base powder is a water atomised powder.
7. Powder according to any one of the preceding claims wherein the prealloyed base powder includes at least one of the elements selected from the group con sisting of carbon, silicon, manganese, chromium, molybde num, vanadium and tungsten.
8. Powder according to any one of the preceding claims having a particle size below 50ohm, preferably be tween 25 and 210 hum..
9. Powder according to any one of the preceding claims having a particle size below 90Am, preferably be tween 65Am.
10. Powder according to any one of the preceding claims for thermal coating of aluminium substrates. AMENDED CLAIMS [received by the International Bureau on 26 September 2002 (26.09. 02); original claims 110 replaced by new claims 114 (2 pages)] 1. Use of a metal powder for thermal coating of substrates, said powder essentially consisting of pre alloyed iron base powder particles having molybdenum particles diffusion alloyed to the base powder particles.
11. 2 Use according to claim 1, wherein the molybdenum particles originate from reduced molybdenum trioxide.
12. 3 Use according to claim 1 or 2, wherein the amount of molybdenum diffusion alloyed to the particles of the base powder is above 2, preferably above 3, and most preferably above 4 % by weight of the metal powder.
13. 4 Use according to any one of the preceding claims wherein the amount of molybdenum diffusion alloyed to the particles of the base powder is between 2 and 15, preferably between 3 and 10 %, and most preferably between 4 and 10 % by weight of the metal powder.
14. 5 Metal powder for thermal coating of substrates, said powder essentially consisting of prealloyed iron base powder particles having molybdenum particles diffu sion alloyed to the base powder particles.
15. 6 Powder according to claim 5, wherein the molybde num particles originate from reduced molybdenum trioxide.
16. 7 Powder according to claim 5 or 6, wherein the amount of molybdenum diffusion alloyed to the particles of the base powder is above 2, preferably above 3, and most preferably above 4 % by weight of the metal powder.
17. 8 Powder according to any one of the claims 57, wherein the amount of molybdenum diffusion alloyed to the particles of the base powder is between 2 and 15, preferably between 3 and 10 %, and most preferably between 4 and 10 % by weight of the metal powder.
18. 9 Powder according to any one of the claims 58, wherein the prealloyed base powder is a gasatomised powder.
19. 10 Powder according to any one of the claims 59, wherein the prealloyed base powder is a wateratomised powder.
20. Powder according to any one of the claims 510, wherein the prealloyed base powder includes at least one of the elements selected from the group consisting of carbon, silicon, manganese, chromium, molybdenum, vanadium and tungsten.
21. Powder according to any one of the claims 511, having a particle size below 500ym, preferably between 25 and 210 Um.
22. Powder according to any one of the claims 512, having a particle size below 9ohm, preferably below 65hum.
23. Powder according to any one of the claims 513 for thermal coating of aluminium substrates.
Description:
METAL POWDER FOR THERMAL COATING OF SUBSTRATES.

FIELD OF THE INVENTION The present invention concerns thermal spray pow- ders, their production and use. Specifically the inven- tion concerns the spray powders for thermal coating of aluminium substrates.

BACKGROUND OF THE INVENTION Different methods for producing coatings on alumin- ium substrates are previously known. These methods are used in eg aluminium engine block having cylinder liners which are formed by thermal spraying.

U. S. Pat. No. 2, 588, 422 discloses an aluminum engine block having cylinder liners which are formed by thermal spraying. These liners are built up in two layers on the untreated surface of the engine block, the top layer being a hard slide layer such as steel about 1 mm in thickness and the lower layer being a molybdenous interlayer about 50 microns in thickness. The interlayer, containing at least 60% molybdenum, does not constitute a slide layer, but is necessary in order to bind the hard slide layer to the aluminum block. Preferably, the interlayer is made up of pure molybdenum. The slide layer is a layer of hard metal, as for example carbon steel, bronze or stainless steel, in which the steel may be an alloy containing nickel, chromium, vanadium or molybdenum for example. In principle, this two-layer structure provides a good slide layer, but the cost of the double coating is substantial.

In recent thermal spraying methods the thermal spray powders are made up by a mixture of powdered steel with powdered modybdenum such as described in the US patent 6 095 107. The risk of segregation due to differences in properties between the base steel powder and the powder of crushed molybdenum is however a problem which may re-

sult in non-uniform coatings. Another disadvantage is that comparatively large amounts of molybdenum are re- quired due to the segregation effect.

OBJECTS OF THE INVENTION A main object of the present invention is to provide an inexpensive metal powder for thermal coating of sub- strates, especially for aluminium.

Another object is to provide a powder which does not segregate and wherein the amount of expensive molybdenum alloying metal can be reduced in comparison with cur- rently used methods.

A further object is to provide a thermal powder, which has high deposition efficiency and gives excellent coating quality.

Another object is to provide a thermal powder giving coatings of suitable porosity and oxide content and wherein the pores are predominantly closed, isolated and have an advantageous range of pore diameters.

SUMMARY OF THE INVENTION These objects are obtained by a metal powder com- prising a pre-alloyed iron base powder having particles of molybdenum, such as reduced molybdenum trioxide, dif- fusion alloyed to the particles of the base powder.

DETAILED DESCRIPTION OF THE INVENTION The type and particle size of the iron base powder is selected in view of the desired properties of the fi- nal coating and the substrate. The base powders are pref- erably pre-alloyed with elements desired in the coating.

Also a minor part of the molybdenum content may be in- cluded in the pre-alloyed powder. Other elements which may be included in the pre-alloyed base powder are C, Si, Mn, Cr, V and W. The pre-alloyed powder may be prepared by atomisation with water or gas. The particle sizes of the base powder are below 500 Am preferably between 25

and 210 Am for PTA and less than 90 ym, preferably less than 65 Am for HVOF or plasma spraying.

According to the present invention the base powder and the alloying powder, i. e. the source of the alloying element, which is preferably molybdenum trioxide, are mixed according the prescribed formulation and the mix- ture is heated to a temperature below the melting point of the obtained mixture. The temperature should be suffi- ciently high to ensure adequate diffusion of the alloying element into the iron base powder in order to form a par- tially or diffusion alloyed powder. On the other hand the temperature should be lower than the temperature required for complete pre-alloying. Usually the temperature is be- tween 700° and 1000°C, preferably between 750° and 900°C, and the reduction is performed in a reducing atmosphere, e. g. hydrogen, for a period of 30 minutes to 2 hours for reduction of the molybdenum trioxide, which is a pre- ferred molybdenum source. As an alternative molybdenum source metallic molybdenum may be used. In this context it may be mentioned that metal powders having molybdenum diffusion alloyed to the base powder particles are previously known from e. g. the Japanese patent publications 8-209 202,63-137102 and 3-264 642. These known powders are, however, used within the powder metallurgical industry for producing sintered products of various shapes and sizes. Furthermore, and in contrast to- the powders according to the present invention, these known powders often have not only molybdenum but also copper and/or nickel diffusion alloyed to the base powder particles. In these known powders the content of the diffusion alloyed molybdenum is usually low, whereas in the inventive powder for thermal coating the diffusion alloyed molybdenum should be high in order to obtain an efficient sliding. So far the most interesting results have been obtained with powders having a content of diffusion alloyed molybdenum above about 4% by weight. It should also be observed that only molybdenum is diffusion

alloyed to the base powder particles in the powder used for thermal spraying according to the present invention.

The upper limit of this diffusion alloyed molybdenum is decided by how much molybdenum the base particles can carry which seems to be about 15 % by weight, see below.

The particle size of the final thermal spray powder is essentially the same as that of the pre-alloyed base powder as the molybdenum particles which are obtained when the molybdenum trioxide is reduced are very small in comparison with the particles of the base powder. The amount of the Mo which is diffusion alloyed to the base powder should be at least 2 % by weight of the total pow- der composition. Preferably the amount of Mo should be between 2 and 15 and most preferably between 3 and 10 t by weight.

The different methods for applying the diffusion al- loyed powders on the metal base substrate are spray or weld cladding process, such as flame spray, HVOF and plasma spray or PTA.

The invention is further illustrated by, but should not be limited to, the following preparation and example.

Example For the experiment on the new material for thermal coating based on water atomised Fe based (Fe-3Cr-0,5Mo) +5% Mo.

Used base materials and chemical analysis: Water atomised iron powder (Fe-3Cr-0,5Mo)-71 pm Molybdenum trioxide Mo03 (Average particle size 3-7 m) Chemical analysis (Fe-3Cr-0, 5 Mo) % 0-tot 1. 22 C 0. 48 Fe Base Ni 0. 05 Mo 0. 52 Mn 0. 10 S 0. 01 P 0. 01 Cr 2. 95 Si <0. 01 Sieve Analysis (Fe-3Cr-0,5 Mo) pu 71-106 0, 1 63-71 0, 8 53-63 4, 7 45-53 23, 4 36-45 23, 1 20-36 33, 3 -20 14, 6

Procedure 92,46% of the water atomised (Fe-3Cr-0,5Mo powder) and 7, 54% of Mo03 were mixed together in a Lodge mixer and the annealing was carried out as follows: Temperature: 820°C Time: 60 min Atmosphere: Reduced atmosphere (type H2, N2, CO2 and mixes of these gases) After annealing the powder cake was crushed and sieved to a particle size below 75 pm.

Sieve analysis and chemical composition (powder mix after annealing): Chemical analysis (Fe-3Cr-0, 5 Mo) % O-tot 1. 5 C 0. 60 Fe Base Ni 0.05 Mo 5. 57 Mn 0. 10 S 0. 01 P 0. 01 Cr 2. 75 Si <0. 1 Sieve Analysis (Fe-3Cr-0,5 Mo) cm % 71-106 0, 1 63-71 1, 4 53-63 6, 5 45-53 34, 1 36-45 20, 4 20-36 30, 8 -20 6, 7

The obtained powder was used in a plasma spraying process for coating an Al base substrate. An unexpectedly homogenous and excellent coating was obtained with a minimum amount of Mo. Figure 1 is a micrograph of this powder having molybdenum diffusion alloyed to the surface of the base powder particles. Figure 2 discloses the coating.