PRODUCTION METHOD OF A THICK COATING WITH LAYERED STRUCTURE

Abstract

A method of producing a layered thick coating which has antibacterial properties, high-wear resistance and low friction coefficient on the surfaces of metallic materials. The objective is to provide a layered thick coating production method, which enables to form a titanium oxide layer exhibiting bioactive property on the outermost surface of the coating, and to produce a structurally denser coating as the zinc contained in the coating causes liquid phase sintering thereby filling the discontinuities in the coating structure.

Claims

1. A method of production of a thick coating with layered structure, which enables to form a wear resistant, antibacterial and bioactive layered thick coating having low friction coefficient, the method comprising: increasing surface roughness of a substrate material to a level of 2-5 m for the thick coating b a sanding process, wherein the substrate material is CoCrMo alloy; preparing a powder composition containing 90%-95% of pure titanium having a particle size of (<44 m) and 5%-10% of pure zinc having a particle size of (<44 m) for a coating process, forming coating on the substrate surface via cold gas dynamic spraying technique; adding at least one ceramic powder selected from the group consisting of ZrO.sub.2, ZnO, and Al.sub.2O.sub.3 into the powder composition in order to increase the wear resistance in a final product; adding at least one antibacterial metallic powder selected from the group consisting of Zn, Cu, and Ag into the powder composition in order to increase the antibacterial property in the final product; mechanically cleaning a coating surface via SiC grinding paper, and, polishing the coating surface by using a diamond or alumina suspension; applying thermal oxidation process on the coating surface in air atmosphere at 500-600 C. temperature for an average of 60 hours by means of the thermal oxidation, producing a titanium oxide layer with a thickness of 2-3 m formed on an outermost surface; obtaining the wear resistant, antibacterial and bioactive layered thick coating having a thickness up to 200 m as the final product.

2. (canceled)

3. The method of claim 1, wherein, a temperature of metallic powders during a spraying process is kept at 150-200 C. in order to ensure that a structure of the sprayed metallic powders is the same as a structure of coating during a cold gas dynamic spraying process.

4. (canceled)

5. The method of claim 1, wherein, the thick coating is formed on the substrate surface via cold gas dynamic spraying by using air of 6 bars or higher pressure via a cold gas dynamic spraying technique.

6. The method of claim 1, wherein, a titanium and zinc containing metallic coating having a thickness of 100-200 m is produced via a cold gas dynamic spraying process.

7.-9. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Production method of a thick coating with layered structure developed to fulfill the objective of the present invention is illustrated in the accompanying figures, in which;

[0023] FIG. 1. is a view of the graphic of the friction coefficient obtained from the wear test against an alumina ball of 6 mm diameter under 4 Newton load on CoCrMo alloy and the coating produced by the method of the invention.

[0024] FIG. 2. is a view of the SEM photograph of the result of bio-activity test application on the coating in a simulated body fluid.

[0025] FIG. 3. is a view of a macro scale photograph of the result of the application of disc diffusion antibacterial test on the coating by using S-aureus bacteria.

[0026] The components shown in the figures are each given reference numbers as follows: [0027] CoCrMo_A. CoCrMo Alloy [0028] KN. Coated sample [0029] KY. Coating surface [0030] CH. Hydroxyapatite precipitated in SBF [0031] BAB. Area decontaminated from bacteria

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] A thick coating production method of the present invention, which enables to form a wear resistant, antibacterial and bioactive layered thick coating having low friction coefficient, comprises the steps of [0033] increasing surface roughness of the substrate material (CoCrMo alloy) to a level of 2-5 m for the coating (by sanding process), [0034] preparing powder mixtures comprising 95-90% by weight of titanium powder (pure, size <44 m) and 5-10% by weight of zinc powder (pure, size <44 m) for the coating process, [0035] forming coating on a substrate surface via cold gas dynamic spraying by using air of 6 bar or higher pressure, [0036] mechanically cleaning (via SiC grinding paper) and polishing (by using diamond or alumina suspension) the coating surface, [0037] applying thermal oxidation process on the coating surface in air atmosphere at 500-600 C. temperature for an average of 60 hours, [0038] obtaining the wear resistant, antibacterial and bioactive layered thick coating having low friction coefficient as the final product.

[0039] Within the scope of the invention, the powder mixture comprising zinc and titanium is coated on the metallic substrate (CoCrMo alloy) surface via cold gas dynamic spraying method. Various components (metallic and/or ceramic based powders such as Ag, ZrO, ZnO) are added to the powder mixture depending on the requirements (antibacterial property, etc.) for the final product. The surface of this coating is subjected to thermal oxidation with the purpose of forming titanium oxide on the outermost surface of the coating. The zinc contained in the coating causes liquid phase sintering during thermal oxidation whereby fills in the discontinuities that might be present in the coating structure and thus enables to form a structurally denser coating.

[0040] The method of the present invention relates to producing a layered thick coating which exhibits antibacterial property, and has high wear resistance and low friction coefficient on the surfaces of metallic materials. In the said method, the powder mixture comprising zinc and titanium is coated by using cold gas dynamic spraying method (2.sup.nd process) over a metallic substrate whose surface is roughened (1.sup.st process), and then this coating is subjected to thermal oxidation (3.sup.rd process) for forming titanium oxide on the outermost surface.

[0041] Thanks to the fact that the metallic powders, which are sprayed during the cold gas dynamic spraying applied after the process of surface roughening, do not rise to relatively high temperatures, composition of the coating formed on the surface of the metallic substrate materials is not different from the powder composition. During the cold gas dynamic spraying process, the fact that the temperature of the sprayed metallic powders does not exceed 150-200 C. enables the structure of the sprayed powders to be the same as the coating structure that is formed. A notable oxidation is not observed on the powders during spraying. In this method, the coating properties obtained can be changed in a wide range by means of the metallic and/or ceramic based powders that will be added to the sprayed powder mixture at different ratios. For example; in cases where wear is critical, ceramic powders (e.g. (ZrO.sub.2, ZnO); and in cases where antibacterial property is critical, antibacterial metallic powders (e.g. Zn, Cu, Ag) can be added to titanium powders. The titanium based coating produced by cold gas dynamic spraying is subjected to thermal oxidation in atmospheric condition at 500-600 C. Thickness of the titanium oxide layer formed on the outermost surface of the coating increases depending on the period of thermal oxidation, and this thickness reaches 3 m in 60 hours at 600 C. The zinc contained in the coating during thermal oxidation causes liquid phase sintering whereby fills in the discontinuities that might be present in the coating structure and thus forms a structurally denser coating. As a result of these processes, hardness of the coating increases, its wear resistance is improved and its friction coefficient decreases. In addition to these, the coating exhibits improved bioactivity and antibacterial property.

[0042] In the method of the present invention, the powder sprayed on the substrate material whose surface is roughened contains 5-10% by weight of zinc in order to provide a low friction coefficient to the coating. As a result of the cold gas dynamic spraying process, a titanium and zinc containing metallic coating having a thickness up to 200 m can be formed on the substrate material. When aluminum, silver, ceramics, etc. are added in powder form to the sprayed mixture, the properties of the coating can be changed in a wide range. In the method of the present invention, while the material to be coated contains a mixture of different powders, the coating that is obtained stands out with its bioactivity as well as its antibacterial property and the low friction coefficient it exhibits during the wear test. Presence of a high ratio of titanium in this coating (preferably 90-95% by weight) is associated with the high affinity of titanium to oxygen. By means of the thermal oxidation process (in atmospheric conditions for 60 hours at 500-600 C.), which is the 3.sup.rd process of the invention, a titanium oxide layer with a thickness of 2-3 m is formed on the outermost surface. As a result of this process, the coating is converted into a layered structure and acquires the feature of exhibiting high hardness and wear resistance as well as low friction coefficient.

[0043] The coating formed in the scope of the invention is suitable for the engineering applications (automotive, aircraft, etc.) wherein friction and wear are active. Under dry ambient conditions where no lubrication is carried out, friction coefficient of this coating under 4N load is <0.1. Due to this feature thereof, the layered coating of the present invention has the potential of limiting use of the lubricant, which is used for reducing friction and wear in engineering applications, and which has negative impacts on the environment. The coating applied on the CoCrMo alloy was subjected to wear test by a reciprocating wear test device against an alumina ball with 6 mm diameter under a 4 Newton load under dry sliding conditions (normal atmospheric conditions) and the graphic of the obtained friction coefficient is shown in FIG. 1. The wear tests conducted in a dry sliding condition that the coating of the present invention provides important advantages in protecting the substrate material by increasing the wear resistance and decreasing the friction coefficient in engineering applications where wear and friction are important.

[0044] The fact that titanium oxide is bioactive enables the coating of the present invention to be used in biomedical sector (For example: for orthopedic implants requiring biocompatibility together with high wear resistance). The zinc added to the coating has the advantage of providing antibacterial property to the coating as well as low friction coefficient. Therefore, the layered coating of the present invention can also find use in sectors where antibacterial surfaces are sought. Taking into consideration the positive effects of zinc on the biological activity in the human body, the fact that the coating contains zinc makes the layered coating of the invention even more attractive for the medical sector. In this context, bioactivity test was applied in simulated body fluid and disc diffusion antibacterial activity test was applied by using S-aureus bacteria to the coating, and the results are shown in FIGS. 2 and 3, respectively. The results of the wear, bioactivity and antibacterial activity tests disclose that the layered coating of the present invention contributes to improvement of the performance and properties of the implants.

[0045] The facts that the coating of the invention does not harm the mechanical properties of the metallic materials and improves bioactivity and antibacterial properties and decreases friction coefficient while increasing wear resistance show that the method of the present invention can constitute an alternative to the state of the art applications. Components whose surfaces are coated by the present method have structures and properties suitable for being used in various engineering applications in sectors such as automotive, aircraft, chemical, biomedical, etc.