KR20100114391A - High velocity oxy-fuel(hvof) spray coating process of wc-crc-ni powder for the improvement of durability of metallic components - Google Patents

Abstract

PURPOSE: An HVOF(High Velocity Oxy-Fuel) spray coating method of WC-CrC-Ni powder for the improvement of durability of a metal part is provided to improve the wear resistance and life span of a high-speed rotating element. CONSTITUTION: An HVOF spray coating method of WC-CrC-Ni powder is characterized in that the feed rate of O2 is 38FMR, the feed rate of H2 is 53FMR, the feed rate of powder is 25g/min, and the spray distance is 7 inches. WC-CrC-Ni powder comprises W68wt.%, C5wt.%, Cr21wt.%, and Ni6wt.%.

Description

High Velocity Oxy-Fuel (HVOF) spray coating process of WC-CrC-Ni powder for the improvement of durability of metallic components}

According to the present invention, the four process factors (hydrogen flow rate, oxygen flow rate, and flow rate) of a tungsten carbide (WC) alloy are used to obtain a wear-resistant coating layer on a high-speed rotating body such as air bearing spindles by OCP: Spraying distance and powder supply amount) to obtain the optimum conditions based on the experimental design method and to coat.

Traditional hard chromium plating has been widely used in places where the wear, heat resistance, corrosion resistance and the like are deposited on the metal surface.

을 배출시키고 세라믹코팅의 취성문제를 가지고 있다.However, chromium plating is not only difficult to use above 400 ℃ but also highly toxic carcinogen during plating.

Has a problem of brittleness of ceramic coating.

In recent years, this technology has been applied to industries such as automobiles and aircrafts that require longer lifespan of parts under harsh atmospheres such as abrasion or corrosion by coating the surface of materials with HVOF (High Velocity Oxy-Fuel). It is becoming.

The world's leading producers of air bearings, Wstwind Air Bearing and JEVCO International, produce more than 120,000 RPM air bearings by adopting hard chrome-plated spindles.

As the RPM of the high-speed rotor increases, high heat is generated and corrosion wear is severe, and more expensive materials are used.

However, the metal material has a severe thermal deformation at high temperatures and a decrease in physical properties, which has a limit on improving its lifespan compared to the cost increase of raw materials, and the shaft is fixed at high temperatures.

In order to improve this, Cr hard plating was performed, but problems such as sticking phenomenon and coating dropout also appeared in plating.

In the case of aluminum-based oxide, the wear resistance and heat resistance to the shaft are excellent when no contact with the bushing occurs, but the bearing does not endure the impact due to the increased friction with the bushing at the start and stop of the air bearing spindle. Because of this dropping, the coating inherent properties cannot be exhibited.

Aluminum-based spray coating applied by some domestic companies is slightly better in rust resistance than Cr hard, but because of its low impact resistance, it does not contribute much to the life of parts.

As a result, domestic electronics and semiconductor companies prefer expensive imported products to produce world-class products.

The present invention is the optimal spraying to form a coating layer using the experimental design method for the four process factors (hydrogen flow rate, oxygen flow rate, spraying distance and powder supply amount) required for the optimal spraying process of tungsten carbide-based alloy for extending the life of the air bearing spindle The purpose is to present the conditions.

In the present invention, the ultra-fast flame spraying method (HVOF) provides an optimum spraying condition for abrasion resistant coatings on high-speed rotors with an O₂ supply rate of 38 FMR (1FMR = 12 scfh (Standard Cubic Feet per Hour) = 0.34m³ / h), and an H₂ supply rate of 53FMR. It provides an optimal spray coating method for powder supply speed of 25g / min and injection distance of 7inch for tungsten carbide series alloy.

The present invention has the effect of improving the wear resistance of an ultra-high speed rotating body such as an air bearing spindle to extend the life.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figure 1 (a) and (b) is an enlarged view of the WC-CrC-Ni powder, (c) is an XRD results, Figure 2 is an XRD of the WC-CrC-Ni coating under 9 conditions, Figure 3 Is a SEM cross-sectional view of the WC-CrC-Ni coating under 9 conditions, Figure 4 is a surface morphological SEM results of the WC-CrC-Ni coating under 9 conditions, Figure 5 is a surface characteristic (hardness, porosity , Surface roughness) and process variables, Figure 6 is a cross-sectional and surface morphological SEM results of the WC-CrC-Ni coating sprayed by the optimal process, Figure 7 is WC-CrC-Ni by the optimum spraying process The hardness and porosity of the coating.

The base material used in the experiment of the present invention used Inconel 718 material having a strong adhesive strength with the coating layer without a binder layer and used in a corrosive environment.

The powder to be used in the experiment was WC-CrC-Ni powder prepared by the spray drying method having the chemical composition shown in Table 1.

The coating process was pre-treatment, thermal spraying and post-treatment. In the pretreatment process, the base material was blasted with 60 mesh alumina (Al₂O₃) to increase the adhesion between the base material and the coating layer.

In the thermal spraying process, the thermal spraying was carried out for 9 different conditions as shown in Table 2 using the Taguchi experiment design method, with the spraying conditions varying with the flow rate of oxygen and hydrogen gas, the spraying distance, and the powder feed rate.

The spraying equipment used JK3000, the gun speed (Gun Speed) was sprayed at a constant 3mm / sec, and the carrier gas (Carrier Gas) of the thermal spraying powder used Ar.

Cooling of the specimen was carried out by air cooling without an external cooling device.

The microstructure and composition of the coating layer were analyzed by XRD, optical microscope, scanning electron microscope, and EDS, and measured 9 times at the center of the cross section of the coating layer using a Micro Vickers hardness tester. The porosity of the coating layer was obtained from the tissue photograph obtained by the optical microscope with the average value of five times through an image analyzer, and the surface roughness was analyzed by the average value measured three times at the center of the surface for the unpolished specimen.

Table 1 Chemical Composition Ratio of WC-CrC-Ni Powder

ingredient W C Cr Ni WC-CrC-Ni 68 5 21 6

Table 2 Nine conditions for optimal spraying process

O₂flow rate (FMR) H₂flow rate (FMR) Feed rate (g / min) Spray distance (inch) One 30 53 25 6 2 30 57 30 7 3 30 61 35 8 4 34 53 35 7 5 34 57 25 8 6 34 61 30 6 7 38 53 30 8 8 38 57 35 6 9 38 61 25 7

WC-CrC-Ni powder has a form in which high hardness WC particles are mixed in Cr and Ni bases serving as binders, and FIG. 1 shows the SEM and XRD results of the powder of WC-CrC-Ni.

, Cr₂O₃, WC, Cr₃Ni₂, Ni₃C 결정상이 존재하고 있으며 스프레이 드라잉법으로 제조된 분말의 평균 입도는 15~30㎛이다.XRD Analysis

, Cr₂O₃, WC, Cr₃Ni₂, Ni₃C crystal phases exist, and the average particle size of the powder produced by spray drying is 15 ~ 30㎛.

WC-CrC-Ni powder is dissolved or partially dissolved by a high temperature flame of up to about 3,500 ° C., and these splats are deposited on the substrate at a high speed of up to about 1,000 m / s.

XRD results of the WC-CrC-Ni coating prepared by Taguchi design scheme are shown in FIG. 2.

As a result of XRD, WC, W₂C, Cr₂O₃ and Cr₃Ni₂ phases existed, and during the High Velocity Oxy-Fuel, the droplets were decomposed into metals and graphite above the pyrolysis temperature of the powder during 0.1 ~ 1ms flight in the hot flame. It is because of this.

3 and 4 show the cross-sectional and surface morphological SEM results of the WC-CrC-Ni coating specimen prepared by the high speed flame spraying method.

The thickness of the coating is about 350 ~ 400㎛ and the adhesion is good because the surface of the substrate is very dense due to the increase of the actual surface area as a result of blasting with alumina of 60 mesh on the base material.

Cross sections and surfaces form a porous coating.

This is because carbon generated by the pyrolysis of WC reacts with oxygen to produce gas and escapes through the coating layer.

The relationship between the surface characteristics and the process variables in each process is shown in FIG. 5.

The hardness value is 913 ~ 1033Hv, which is about 2 times higher than the material used for general mechanical parts.The hardness value is 38FMR, 53FMR hydrogen, spraying distance 8inch, and the highest hardness at 30g / min powder supply. Indicated.

Increasing the powder supply has the effect of increasing the hardness by reducing the thermal decomposition by lowering the powder temperature by the absorption of heat by the powder.

The change in the flow rate of oxygen and hydrogen showed a big change.

The porosity showed 0.27 ~ 1.50% change according to each condition, and showed the smallest porosity at oxygen flow rate 38FMR, hydrogen flow rate 61FMR, spraying distance 7inch and powder feed 25g / min. It can be seen that the effect is very large.

The surface roughness (Ra) was changed from 3.526 to 4.754㎛ according to each condition. The surface roughness (Ra) showed the smallest surface roughness when the oxygen flow rate 38FMR, the hydrogen flow rate 53FMR, the spraying distance 7inch and the powder feed 25g / min. Showed the biggest change.

The optimum process for each surface characteristic was selected through the surface characteristics analysis of the specimens prepared by the experimental design method as shown in Table 2. Decided.

Optimum coating process is based on hardness, oxygen flow rate 38FMR, hydrogen flow rate 53FMR, spraying distance 7inch and powder feed 25g / min.

The surface characteristics of the WC-CrC-Ni thermal sprayed coating layer were evaluated by the optimum process.

6 shows cross-sectional and surface morphological SEM and EDS results of the WC-CrC-Ni coating layer sprayed by the optimum process.

The thickness of the coating layer is about 320.

As a result of the cross-sectional analysis, a 320㎛ coating layer having very dense interface with the base metal was produced and the adhesion was considered to be good.

WC dust is disperse | distributed to the binder base rich in coating layers Ni and Cr.

7 shows the results of analyzing the hardness and porosity of the coating layer.

The hardness value of the optimal spraying process was 1,150Hv, which was 117Hv (about 11%) higher than the maximum value of 1,033Hv of Taguchi process.

The porosity was 1.2%, which was 0.93% (about 344%) higher than the Taguchi process's minimum value of 0.27%.

As a result of HVOF spray coating of WC-CrC-Ni powder, the following conclusions were obtained.

1.The diameter of WC-CrC-Ni powder coated on the Inconel 718 substrate by the high speed flame spraying method by 9 processes is 15 ~ 30㎛ and the average thickness, hardness, porosity and surface roughness of 350 ~ 400㎛ , 965Hv, 2.65%, 4.4 mu m.

2. XRD analysis of the WC-CrC-Ni HVOF coating revealed a new phase that did not exist in the powder due to thermal decomposition during the HVOF process.

3. The optimum process of coating WC-CrC-Ni is O₂ feed rate 38FMR, H₂ feed rate 53FMR, powder feed rate 25g / min, spraying distance 7inch.

4. The hardness value of the WC-CrC-Ni coating layer with HVOF as the optimum process was 1,150Hv, which is 117Hv (about 11%) higher than the maximum value of 1,033Hv of Taguchi process.

Figure 1 (a) and (b) is an enlarged view of the WC-CrC-Ni powder, (c) is an XRD results

2 is XRD of WC-CrC-Ni coating under 9 conditions

3 is a SEM cross-sectional view of the WC-CrC-Ni coating under 9 conditions

Figure 4 is a surface morphological SEM results of the WC-CrC-Ni coating under 9 conditions

5 is a correlation between surface characteristics (hardness, porosity, surface roughness) and process variables

Figure 6 is a cross-sectional and surface morphological SEM results of the WC-CrC-Ni coating sprayed by the optimal process

7 is a hardness and porosity of the WC-CrC-Ni coating by the optimum spraying process

Claims (2)

In the method of coating the tungsten carbide-based alloy powder by the ultra-fast flame spraying method (HVOF) to improve the durability of the high-speed rotating body, The spraying conditions are optimized for the high-speed flame spray coating process of tungsten carbide-based alloy powder for the durability improvement of metal parts, characterized in that the spraying conditions are: O 2 feed rate 38FMR, H 2 feed rate 53FMR, powder feed rate 25g / min, spraying distance 7inch. The method of claim 1, wherein the composition of the tungsten carbide-based alloy powder is W68wt.%, C5wt.%, Cr21wt.%, Ni6wt.% Characterized in that the ultra-high speed flame spraying of tungsten carbide-based alloy powder for the durability of the metal parts How to optimize the coating process.

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