WO2012146808A1

WO2012146808A1 - Method for coating materials by means of the thermal spraying of compositions

Info

Publication number: WO2012146808A1
Application number: PCT/ES2012/070125
Authority: WO
Inventors: Kudama Abdul RAZZAQ HABIB; Iván CERVERA GONZÁLEZ; Juan José SAURA BARREDA
Original assignee: Universitat Jaume I De Castellón
Priority date: 2011-04-29
Filing date: 2012-02-28
Publication date: 2012-11-01
Also published as: ES2391321A1; ES2391321B1

Abstract

The invention relates to a method for coating materials, comprising the thermal spraying of compositions on the surface thereof. The method consists in: spraying the composition onto the surface of the material, and subjecting the coated material to a step-based thermal treatment which gradually varies the temperature of the assembly in a stepped manner. Preferably, the composition is sprayed using one of the techniques selected from the group including oxy-fuel, plasma spray and high-velocity oxy-fuel (HVOF), thereby forming coatings of different thicknesses, preferably in the form of a layer. The invention also relates to any coated material that can be obtained using the aforementioned method.

Description

METHOD FOR COATING MATERIALS THROUGH THERMAL PROJECTION

OF COMPOSITIONS SECTOR OF THE TECHNIQUE

The method of coating materials by thermal projection on their surface of chemical compositions can be used in those industrial applications where it is necessary to protect materials against chemical deterioration, for example by oxidation at high temperature, and / or mechanical, by wear. The field of application is very wide: furnaces for the ceramic industry, pump shafts for the chemical and petrochemical industry and blades for the aeronautical industry, etc. It also allows the recharge of worn parts, which can be coated by the procedure described.

STATE OF THE TECHNIQUE

The growing demand for engineering products for applications in machinery elements that have to work in both severe tribological and corrosive media, such as shaft protection sleeves, thermocouple sheaths, electrical insulators, pump shafts, baking ovens in the ceramic industry, etc. require specific surface designs. While the surface texture of said devices is achieved by mechanical treatments, the surface chemical composition is usually controlled by surface modification in the form of coatings. Although there are different techniques available to deposit materials on each type of substrate, thermal spray processes are widely used to deposit coatings of different thicknesses in various industrial applications.

Some of the best known compositions for coating materials against mechanical wear and high temperature corrosion are alumina and MCrAlY superalloy.

Thermal projection of alumina base coatings The thermal projection processes commonly used to project AI ₂ O ₃ base coatings are: flame spray (OF), air plasma (APS -Atmospheric Plasma Spray-) and high-speed oxifuel (HVOF).

The spray spray alumina base powder (OF) technique has disadvantages compared to the APS and HVOF techniques, in that the structures obtained are larger in size, have larger cracks and porosity. On the other hand, this technique has the advantage of being more economical, easy to use and greater adaptability to manufacturing processes in short series or for the recovery of worn parts.

The thermal spray technique of alumina powders, as well as plasma superalloy has the advantage of the high temperature reached (10,000-15,000 ° C) which is suitable for melting all or part of the ceramic powder particles (> 2,000 ° C ). In addition, the relatively high speed achieved by said particles produces a deformation thereof by impact, thereby achieving dense deposits with good substrate binding. Through this technique (APS) there is the possibility that some oxides can be formed when it is a metallic material, something that does not occur with ceramic coatings.

The projection technique of alumina-based powders, as well as super-alloy by HVOF, creates particle velocities between 300-1000 m / s, resulting in an increase in the impact force resulting in a higher density and adhesion of the coating. . In this process the temperature reached is approximately 3300 ° C.

Commercial alumina (corundum) particles are presented in the stable form CC (rhombohedral), which undergoes a total or partial transformation in metastable phases during thermal projection: γ (cubic), δ (tetragonal or orthorhombic), Θ (monoclinic) , among other. The formation of These phases are favored by the low cooling rate of the coatings since they are ceramic materials with low thermal conductivity.

MCrAlY super alloy thermal projection

Thermally projected MCrAlY superalloy coatings are used as protective layers against high temperature oxidation of both Ni base superalloys and austenitic stainless steels.

MCrAlY coatings have excellent resistance to dry corrosion and oxidation at high temperatures. These coatings form an oxide layer on the outer surface, and immediately under this layer the material is impoverished in aluminum; also, an interdiffusion zone is formed in contact with the substrate.

The two most important processes for applying this coating are physical vapor deposition by electron beam (EBPVD) and plasma spray (PS). The EBPVD process produces a structure of crystals perpendicular to the surface of the substrate, and this structure can be improved by closing the defects by shot peening treatments and laser treatments. For its part, the PS process is carried out in low pressure chambers to minimize the formation of oxides when depositing the alloy.

During the oxidation process of MCrAlY coatings, the aluminum-rich β phase grains become γ ^' phase islands, leaving the γ matrix phase less resistant to oxidation.

The object of the present invention is the development of new methods of coating materials with chemical compositions projected by thermal projection, such that the material obtained has a coating layer that is capable of combining high corrosion resistance at high temperatures and to wear

In short, the present invention emerges as a need to improve the methods of coating by thermal projection of currently existing compositions, which allows its use in more demanding conditions from the point of view of resistance to high temperature oxidation and abrasive wear. This allows to obtain a better performance of systems that operate at high temperature, by increasing it, or increasing the service life of the components.

Another of the applications is the recycling of parts that have suffered wear and that are no longer suitable for commissioning, since it allows them to be recharged by thermal projection of the chemical composition according to the described method.

BIBLIOGRAPHY

- J. Ramírez, A. Gutiérrez-Alejandre, Catal. Today 43 (1998) 123.

- V. Fervel, B. Normand, C. Coddet, Wear 230 (1999) 70.

- L. Chen, L. Wang, Z, Zeng, T. Chu, Surface & Coating Technology, 201 (2006), 599-605.

- R. Tomaszek, L Pawloski, J. Zdanowski, J. Grimblot, I. Laureyns, Surface-Coating Technology, 185 (2004) 225.

I. M. Kusoglu, E. Celik, H. Cetinel, I. Ozdemir, O. Demirkurt, K. Onel, Surface-Coating Technology, vol. 200, 1- 4, (2005) 1173-1177.

- K. A. Habib, J. J. Saura, C. Ferrer, M. S. Damra, E. Giménez, L. Cabedo, Surface-Coating Technology, 201 (2006), 1436-1443.

- Y. Liu, T. E. Fisher, A. Dent, Surface-Coating Technology, 167 (2003) 68-75.

R. Venkataraman, Gantam Das, B. Venkataraman, G.V Narashima, R. Krishnamurthy, Surface-Coating Technology, vol. 201, 6 (2006) p. 3691-37.

- R. Venkataraman, B. Ravikumar, R. Krishnamurthy, DK Das, South. & Coat. Tech., Vol. 201, 6.4 3087-3095 (2006). - T. Narita, F. Lang, K. Zaini, T. Yoshioka, T. Izumi, H. Yakuma, S. Hayashi, Oxid. Of Metals, Vol 68, (2007) 343-363.

- T.J. Najidam, W.G. Sloof, Oxid of metais, Vol. 69, (2008), 1-18.

- S. Wang, Y. Wu, F. Gesmuudo, Y. Niu, Oxid. Of Metals, Vol. 69, (2008), 299-315.

- X. Liu, L. Huang, Z. B. Bao, H. Wei, X. F. Sun, Oxide. Of metais, Vol. 71, (2009), 125-142.

United States Patent n. 7,316,850. Modified MCrAlY coatings on turbine blade tips with improved durability.

Spanish patent n. 2131451 Bl. Quasicrystalline thermal barrier type coatings for the protection of components of hot turbine areas.

DESCRIPTION OF THE INVENTION

The present invention relates to a method for coating materials by thermal projection of a chemical composition, characterized in that it comprises at least the following steps:

- project the chemical coating composition on the surface of the material, and

- subjecting the previously coated material to a stage heat treatment comprising:

^• gradually increase the temperature over a period of time between 5 and 10 minutes, including both limits, from room temperature (which can be considered herein having a value of 25 ° C) to a value between 500 ° C and 600 ° C, including both limits;

maintain the temperature reached in the previous stage for a period of time between 15 and 40 minutes, including both limits; gradually increase the temperature a second time for a period of time between 5 and 10 minutes, including both limits, at a value between 700 ° C and 900 ° C, including both limits;

maintain the temperature reached during a time interval between 15 minutes and 40 minutes, including both limits;

gradually increase the temperature for the third time over a period of time between 5 and 10 minutes, including both limits, to a value between 1000 ° C and 1150 ° C, including both limits;

maintain the temperature reached during a time interval between 200 minutes and 250 minutes, including both limits; Y

gradually decrease the temperature to a value between 20 ° C and 90 ° C, including both limits.

Preferably, the second time the temperature is increased is made up to a range between 700 ° C and 800 ° C, including both limits. Also preferably, the temperature decrease is performed up to a range between 60 ° C and 90 ° C, including both limits, and more preferably still up to room temperature (which can be considered as 25 ° C in the scope of the present invention) .

Preferably, the gradual increase in temperature, in any of the steps described above that involve this action, is carried out at a heating rate between 30 ° C / hour and 60 ° C / hour, including both limits. Also preferably the gradual decrease in temperature is carried out at a cooling rate between 20 ° C / hour and 50 ° C / hour, including both limits. The variation of these speeds in the process is determined based on the furnace conditions where the process is carried out and the structural dimensions and characteristics of the piece (of the material to be coated).

Optionally, the composition is thermally projected onto the surface of the material by one of the techniques selected within the group consisting of: oxifuel, Plasma Spray, and high speed oxyfuel (HVOF), obtaining coatings of different thicknesses, preferably in the form of a layer. The thickness of said coating layer depends on the thickness of the piece to be coated; however, said thickness is between 10% and 30% of the total thickness of the material to be coated. Preferably, the thickness does not exceed 25% of the total thickness of the material to be coated. The projected composition is preferably in powder form.

In another more preferred embodiment, the heat treatment after the projection of the composition on the surface of the material comprises the following steps:

a) gradually increase the temperature for 7 minutes from room temperature (it is considered to be 25 ° C) to reach 570 ° C,

b) maintain the temperature reached for 20 minutes,

c) gradually increase the temperature a second time for 10 minutes to reach 860 ° C,

d) maintain the temperature reached for 20 minutes,

e) gradually increase the temperature for a third time for 15 minutes to reach 1100 ° C,

f) maintain the temperature reached for 240 minutes, and

g) gradually decrease the temperature to room temperature (25 ° C), in a time of 70 minutes.

The heat treatment described has as its main function the homogenization of the coating composition on the material and the compaction of the microstructure

The chemical coating composition used in the method described herein can be of any type known in the field, but preferably it is of metallic type or a cermet type coating, that is, a mixture of a metal based matrix (such as a superalloy of the M-CrAlY type, where M is a metal that can be nickel) and a ceramic charge (for example, alumina).

Another object of the present invention is any coated material obtainable by the method described.

DESCRIPTION OF THE FIGURES

Figure 1: Heating / cooling ramps for heat treatment of the coating composition according to the present method. The procedure begins at room temperature (25 ° C).

Figure 2: Figure 2 shows a SEM micrograph of a system formed by a piece of a material, of metallic type, and a coating according to Example 1 (of metallic type constituted by a NiCrAlY base and a reinforcement of AI ₂ O3 ). The material zone is represented as (A) and the coating as (B).

EXAMPLES OF REALIZATION

A method according to the example and non-limiting nature of the invention is detailed below by way of example according to what is described herein for coating a material, consisting of a metal part, with a chemical composition.

Example 1. Method of coating a metal part with a cermet type coating composition.

The coating material consists of a composition with a matrix of a NiCrAlY super alloy, where M represents a metal and is Ni, and with an additional charge of a ceramic material, which is alumina. Bliss The composition has a weight ratio between 10-50% ceramic and 50-90% metal matrix, and is in the form of a powder, in which the particles of the metal base are specifically spherical and alumina particles of polygonal type The particle size in both cases does not exceed 45 microns.

The coating composition is used in metal parts, to combat corrosion at high temperatures.

Said powder coating composition is projected onto the surface of the metal part by an oxyacetylene gun, and whose projection conditions are shown in Table I.

Table I Parameters of thermal projection.

After the projection of the composition, the heat treatment of the surface already covered is carried out as follows:

gradually increase the temperature for 7 minutes from room temperature (it is considered to be 25 ° C) to reach 570 ° C;

- maintain the temperature reached for 20 minutes,

- gradually increase the temperature a second time for 10 minutes to reach 860 ° C;

- maintain the temperature reached for 20 minutes;

- gradually increase the temperature for a third time for 15 minutes until reaching 1100 ° C;

keep the temperature reached for 240 minutes; Y

gradually decrease the temperature until room temperature (25 ° C), in a time of 70 minutes.

An SEM micrograph of the coated metal part obtained by the method of the present invention is shown in Figure 2, where the high quality thereof is appreciable based on the absence of porosity and correct adhesion at the interface.

Claims

1. Method for coating materials by thermal projection of a chemical composition, characterized in that it comprises the following steps:

- project the chemical coating composition on the surface of the material, and

gradually increase the temperature over a period of time between 5 and 10 minutes, including both limits, from room temperature to a value between 500 ° C and 600 ° C, including both limits;

^• maintain the temperature reached in the previous stage for a period of time between 15 and 40 minutes, including both limits;

gradually increase the temperature a second time for a period of time between 5 and 10 minutes, including both limits, to a value between 700 ° C and 900 ° C, including both limits;

^• maintain the temperature reached for a period of time between 15 minutes and 40 minutes, including both limits;

^• maintain the temperature reached during a time interval between 200 minutes and 250 minutes, including both limits; Y

^• gradually decrease the temperature to a value between 20 ° C and 90 ° C, including both limits.

2. Method according to claim 1, characterized in that the chemical composition is projected onto the surface of the material by one of the techniques selected from the group consisting of: oxifuel, Plasma Spray and high speed oxifuel (HVOF).

3. Method according to any one of claims 1 or 2, characterized in that the composition forms a coating layer on the material with a thickness between 10% and 30% of the total thickness of the material to be coated.

4. Method according to the preceding claim, characterized in that the coating layer has a thickness equal to or less than 25% of the total thickness of the material to be coated.

5. Method according to any one of the preceding claims, characterized in that the stepwise heat treatment comprises:

gradually increase the temperature for 7 minutes from room temperature to reach 570 ° C;

- maintain the temperature reached for 20 minutes;

- maintain the temperature reached for 240 minutes; Y

- gradually lower the temperature to room temperature, in a time of 70 minutes.

6. Method according to any one of the preceding claims, characterized in that the Chemical coating composition is metallic type or a mixture of metal and ceramic filler.

7. Coated material obtainable from the method described in any one of the preceding claims.