KR20130003300A - High velocity oxygen fuel (hvof) spray coating of cobalt alloy powder for durability improvement of high speed spindle operating without lubricant - Google Patents

Abstract

PURPOSE: A HVOF coating with a cobalt powder for improving the durability of a non-lubricated high velocity rotary body is provided to coat the surface of the high velocity rotary body with a cobalt alloy powder by using the HVOF, thereby improving the eco-unfriendly problem of an EHC coating. CONSTITUTION: An HVOF coating with a cobalt alloy powder is a method for coating the surface of a high velocity rotary body with the cobalt alloy powder using the HVOF. The coating is implemented at 38 to 42 FMR(Flow Meter Reading)( 3.59X10-3 to 3.96X10-3m3 per second) of oxygen flow rate, 60 to 75 FMR(5.66X10-3 to 7.08X10-3m3 per second) of hydrogen flow rate, 30 grams per minute of powder supply velocity, and at a spray distance of 5 inches. The high velocity rotary body is formed with an Inconel series or a titanium alloy. The velocity of a spray gun is set to 3 millimeters per second. A manufactured coating material is air cooled by using 180 psi(pound per square inch) of argon gas as powder carrier gas.

Description

High Velocity Oxygen Fuel (HVOF) Spray Coating of Cobalt Alloy Powder for Durability Improvement of High Speed Spindle Operating Without Lubricant}

The present invention relates to a coating method of cobalt powder using an ultra-high speed flame spraying method (HVOF) for improving durability of a non-lubricating high speed rotating body.

For the past 60 years, electrolytic hard chromium plating (EHC) has been widely used in the manufacture of hard surface coatings where they require abrasion, heat and corrosion resistance. However, according to recent studies EHC process has been a problem in terms of health and the environment posed due to produce a well-known cause of cancer Cr ^{6 +} ion mist.

On the other hand, studies on coating methods that can replace EHCs are active, and deposition techniques such as high-velocity oxy-fuel thermal spraying (HVOF), laser deposition, discharge plasma sintering and vacuum or atomic plasma spraying Known.

However, there is no development of a specific coating method for obtaining a cobalt coating for improving the durability of the non-lubricated high-speed rotating body in relation to the cobalt coating using HVOF.

Accordingly, an object of the present invention to provide a coating method of cobalt alloy powder that can improve the durability of the non-lubricated high-speed rotating body while improving the non-friendly problem, which is a problem of the electrolytically treated hard chromium plating (EHC) used in the prior art. There is.

In order to achieve the above object, the present invention is characterized in that the coating of cobalt alloy powder using a super-high speed flame spraying method (HVOF) on the surface of the non-lubricated high-speed rotor, of the cobalt alloy powder using a high speed flame spraying method (HVOF) It provides a coating method.

The - (7.08X10-3 m3 / sec 5.66X10-3) - More specifically, the coating is ^{38-42 FMR (3.59X10 -3 3.96X10 -3 m} 3 / sec) oxygen flow rate, 60-75 of FMR It can be carried out with coating conditions having a hydrogen flow rate, a powder feed rate of 35 g / min, and a spray distance of 5 inches.

The inventors of the present invention, the cobalt alloy powder coating layer has a characteristic that the brittle oxide produced by the local overheat generated when sliding in contact with the other object acts as a solid lubricant, and improves the wear resistance, thereby cobalt It was conceived that the durability of the rotating body could be improved by coating the alloy powder on a part that is susceptible to friction and frictional heat such as an ultra-high speed rotating body, and the coating method of such a cobalt alloy powder was optimized by using an ultra-fast flame coating method. The invention has been completed.

Therefore, the coating method of the present invention can be applied to the coating for improving the durability of the high-speed rotating body, such as air bearing spindles without using a lubricant, and more specifically, the high-speed rotating body is made of Inconel series or titanium alloy It may be, and more specifically, may be made of Inconel 718 or Ti64, but is not limited thereto.

The coating method according to the present invention is coated with cobalt alloy powder on the surface of a high-speed rotating body by using an ultra-high speed flame spraying method (HVOF), while improving the environmentally-friendly problem of the conventional electrolytically treated hard chromium plating (EHC) without lubrication and high speed. Durability of the rotating body can be improved.

1 is a photograph of the microstructure of the cobalt alloy powder T800.
2 is a cross-sectional photograph of a T800 coating layer.
3 is an XRD graph of a T800 coating layer.
4 is a graph showing the change in hardness according to the spray process conditions.
5 is a graph showing a change in surface roughness according to the spray process conditions.
6 is a graph showing the change in surface porosity according to the spray process conditions.
7 is a graph showing a change in the friction coefficient according to the change in hardness for each temperature.
8 is a graph showing a change in wear traces of the T800 coating layer and the counterpart according to temperature.
9 is a sectional view of a breakthrough site.
10 is a graph of the results of the tensile strength of each test group.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the following examples. However, the following examples are intended to illustrate the contents of the present invention, but the scope of the present invention is not limited to the following examples. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

< Example  1> T800  coating

Micro size powder (5-30 μm in diameter, Satellite Co. Inc.) was coated to a 300-350 μm thickness using a JK3000 HVOF device.

As a powder material for preparing a coating, commercial cobalt alloy T800 (Co-45.7 wt.%, Mo-28.4 wt.% And Cr-17.6 wt.%) Of Satellite was used as shown in Table 1.

Chemical composition ratio of T800 (wt.%) Co  Mo  Cr  Si  Fe  Ni   O  C   P  Honey. 28.4 17.6 3.10 0.68 0.65 0.02 0.02 0.01

As can be seen in Figure 1, the cobalt alloy powder is a mixture of spherical particles having a diameter of 5 to 30㎛.

The cobalt alloy powder maintains excellent strength from 253 ° C to 705 ° C, has excellent oxidation resistance up to 980 ° C, and high creep strength at 700 ° C. Coated on an Inconel 718 substrate. In the pretreatment process, the substrate was ultrasonically cleaned in acetone solution for 5 minutes and then blasted with 60 mesh alumina (Al₂O₃) for 3-5 seconds to increase the bonding strength between the substrate and the coating layer.

In the spray process, the conditions were controlled by spray distance, oxygen and hydrogen gas flow rates, and powder feed rates, and coated according to 16 processes designed by the Taguchi experimental program using four spray parameters with three levels. Spray gun speed was set to 3 mm / s and argon gas of 180 psi was used as powder carrier gas. The prepared coating was air cooled.

The melting point of the εCo phase of the Co-Mo and Co-Cr systems of the T800 alloy powder is lower than the melting point of pure Co, 1495 ° C. The sprayed particles of various sizes melt, partially melt or soften at temperatures above 3,500 ° C. due to the flame during the spraying time of 0.1-1 ms according to the coating process of the present invention.

Hot particles of various sizes and speeds are accelerated to 1,000 m / s and hit cold coating surfaces. When bumping, a bond with the surface is formed, and subsequent bumping of the particles forms a thick coating layer of a layered structure as shown in FIG. 2.

Attached and thinned particles are quenched at a very high cooling rate of up to 10 ⁶ K / s, forming a highly adhesive coating layer. As shown in FIG. 3, the Co phase in the XRD of the coating layer maintains crystallinity, but other components are solidified in an amorphous state.

< Example  2> Coating layer analysis and friction and wear characteristics analysis

Surface microstructure and coating layer analysis were performed using an optical microscope, SEM. The hardness value was calculated from the average value measured 9 times at the center of the cross section of the coating layer by the Micro Vickers Hardness Tester, and the tissue photograph of the coating layer obtained using the optical microscope was analyzed by an image analyzer. The porosity of the coating layer is shown as the average of the times. Surface roughness was obtained by averaging seven measurements using a surface roughness tester to obtain surface roughness.

The friction and wear characteristics of the coatings were tested with a reciprocating wear tester (TE77 AUTO, Plint & Partners) at 25 ° C and 538 ° C (1000 ° F) without lubricant. As a counterpart, stainless steel balls (SUS 304 and Hv227) with a diameter of 9.53 mm were used, with a reciprocating sliding distance of 2.3 mm, a frequency of 35 Hz, a speed of 0.161 m / s, a load of 10 N, and a sliding time of 4 minutes. It was.

The hardness, roughness and porosity were dependent on the spray process conditions, and the results of 16 different conditions are shown in FIGS. 4, 5 and 6, and the most optimized conditions were oxygen and hydrogen flow rates and powder feed rates at 5 inch spray distance. the respective times were 38 ~ 42FMR - - (7.08X10-3 m3 / sec 5.66X10-3 ) and 30g / min days ^{(3.59X10 -3 3.96X10 -3 m 3 /} sec), 60 ~ 75FMR.

The hardness of the coating layer 560-640 Hv was higher than the substrate Inconel 718 (~ 410 Hv) and light spindle material Ti64 (~ 350 Hv). It can be usefully used for improving durability.

Average surface roughness was found to be 2.2-3.0 μm. The impact and quenching of the fast particles and gases onto the coating surface resulted in the formation of a rough surface.

Average surface porosity was found to be 0.01-0.04%. The pores are created as the hot coating shrinks by cooling, or as a result of the release of gases trapped therein in a high-speed collision process with molten particles and the coating layer.

Referring to FIG. 7, the coefficient of friction (FC) of the coating layer was found to be less than half of the coefficient of friction of the non-coated Inconel 718 substrate. This suggests that the T800 coating can be usefully used as a wear resistant coating for improving the durability of sliding machine elements.

No obvious correlation was observed between the coefficient of friction and the hardness of the coating layer, which is believed to be due to the greater effect of lubrication of sliding wear particles on the hardness of the T800 coating.

As can be seen in FIGS. 7 and 8, the coefficient of friction and wear traces decrease as the sliding surface temperature increases from 25 ° C. to 538 ° C., which increases the lubrication effect of Co oxide at higher temperatures. Because. At high temperatures, crude Co oxides such as CoO and Co ₃ O ₄ are rapidly formed on the coating surface by sliding. The crude steel oxide is easily consumed by sliding and serves as a lubricant to reduce the coefficient of friction.

< Example  3> Ti64  Superficial T800  Coating Adhesion Analysis

The adhesion of the coating layer (T800 / Ti64) on the Ti64 substrate was investigated through a tensile tester FM-10E according to ASTM C633 and known methods ("Process Instruction" Sermatech Korea Ltd., control number PI-1-02 (1999) 17). . The crosshead traveling rate was 0.05 in / min.

The adhesive strength of the binder FM1000 (epoxy adhesive binder) was set to a minimum binding force of 10000 psi, and the tensile bond strength (TBS) was obtained by averaging three measured values.

T800 (260 μm) / Ti64, Binder NiCr (110 μm thick, 80% Ni, 20% Cr) / Ti84 and triple coated T800 / NiCr / Ti64 to determine the effect of NiCr binder on T800's bond and adhesion and T800 adhesion It was used to

NiCr Effects of Substrate (Ti64) / Binder NiCr (110 μm Thickness, 80% Ni, 20% Cr), Ti64 / T800 (260 μm) and Ti64 / NiCr / T800 on the Adhesion of T800 to Ti64 and Adhesion of Ti64 / T800 It was used to measure the effect of the binder.

Triple coating; NiCr (Ti64) / Binder NiCr (110 μm thick, 80% Ni, 20% Cr), Ti64 / T800 (260 μm) and Ti64 / NiCr / T800 on the adhesion of T800 to Ti64 and the adhesion of Ti64 / T800 It was used to measure the effect of the binder.

As can be seen in FIGS. 9 and 10, the tensile bond strength (TBS) and tensile fracture location (TFL) of Ti64 / NiCr are 11,600psi and top coat-near of NiCr, respectively. top). 9 shows that the Ti64 / NiCr bond coating begins to break at a tensile strength of 11,600 psi.

TBS and TFL of Ti64 / T800 appeared to be near middle of 8,770 psi and T800 coating, respectively. Bond coating of NiCr did not increase the TBS of Ti64 / T800, which can be seen from the almost identical TBS and TFL of Ti64 / T800 and Ti64 / NiCr / T800.

The TBS of Ti64 / T800 was higher than the tensile strength of T800 coating (8,770 psi), which can be seen from the fact that no clear fracture was observed in the center of T800 coating in tensile failure strength. This suggests that Ti64 / T800 coatings can be usefully used as a coating for wear resistance of lightweight alloy Ti64 high speed rotors.

Having described the specific parts of the present invention in detail, it will be apparent to those skilled in the art that such specific descriptions are merely preferred embodiments, and thus the scope of the present invention is not limited thereto. will be. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims (3)

A method of coating cobalt alloy powder using an ultra-high speed flame spraying method (HVOF), characterized by coating a cobalt alloy powder using a high speed flame spraying method (HVOF) on the surface of a high speed rotor.
The method of claim 1,
The coating is ^{38-42 FMR (3.59X10 -3 - 3.96X10 -3} m 3 / sec) oxygen flow rate, 60-75 FMR of - hydrogen flow rate of (5.66X10-3 7.08X10-3 m3 / sec), 30 g A coating method of cobalt alloy powder using HVOF, characterized in that it is carried out under a coating condition having a powder feed rate of / min, and a spray distance of 5 inches.
The method according to claim 1 or 2,
The high-speed rotating body is made of Inconel-based or titanium alloy, characterized in that the coating method of cobalt alloy powder using ultra-high speed flame spraying method (HVOF).

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