JPS61127873A - Corrosion resistant coating - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates generally to coating steel and titanium substrates, and more particularly to coating steel and titanium gas turbines without loss in fatigue life. A novel two-layer corrosion-resistant coating on engine compressor blades is inspired.

[Prior art and its problems]

Gas turbine engine compressor blades are conventionally made from steel or titanium alloys. These wings are subject to severe erosion when operating in sand and dust environments. Blade erosion reduces compressor efficiency, thus requiring early blade replacement.

Many types of corrosion-resistant coatings are currently available, including tungsten and carbon (U.S. Pat. No. 414-820).
), platinum metal (U.S. Pat. No. 3,309,292), and boron (U.S. Pat. No. 2,822,502). However, these coatings, which have been identified in the industry to provide corrosion resistance to substrates such as tungsten and steel alloy compressor blades, can promote rapid deterioration in the fatigue properties of the substrate and cause cracking. and create points of failure, thereby reducing the service life of the substrate. This effect on the fatigue life of the substrate is due to the fact that prior art corrosion-resistant coatings are hard materials that promote a decrease in the fatigue strength of the substrate by creating residual stresses and associated strains in the substrate. This seems to be due to the fact that

Therefore, there is a need in the art for erosion resistant coatings that do not adversely affect the fatigue life of the substrates to which they are applied.

[Purpose of the invention]

The object of the invention is therefore to provide a new coating which does not have the above-mentioned disadvantages.

Another object of the invention is to provide a two-layer coating with good erosion resistance that does not adversely affect the fatigue life of the substrate to which it is applied.

It is a further object of the present invention to minimize retention stresses and associated distortions in erosion resistant coatings to reduce their negative impact on the fatigue life of the coated substrate.

Yet another object of the present invention is to provide a coating that can be used in high temperature corrosive atmospheres such as those in which gas turbine compressor components operate.

Yet another object of the present invention is to provide a coating having wide application that provides corrosion resistance to a variety of gas turbine compressor components without degrading the fatigue life of those components.

[Key points of the invention]

These and other objects of the invention are achieved by an erosion-resistant coating consisting of two successively applied layers, each of a different material. The second applied coating layer is formed of a tungsten-carbon alloy corrosion resistant material.

The first coating layer or intermediate layer applied directly to the titanium or steel substrate is made of a ductile material, such as platinum, palladium or nickel, which penetrates into the first coating layer or completely forms the first coating. Diffusion of material through the layer and into the substrate can be prevented. This protects the substrate from deterioration of material or design properties. Residual stresses and associated tensile strains in the coating are reduced by applying the second layer onto the first layer at a relatively low temperature, i.e. from about 500 to about 140
It is minimized by applying at 0°F and providing a coating with a fine grain and/or columnar grain structure.

The practice of the present invention provides an erosion-resistant tungsten-carbon alloy coated titanium or steel alloy such that adverse effects on the fatigue life of the substrate as previously encountered with erosion-resistant coatings of this type are substantially eliminated. A manufactured base material is provided.

[Detailed description of the invention]

In the coatings of the present invention, a ductile first layer applied immediately adjacent to a titanium or steel alloy substrate forms a diffusion barrier so that the second layer diffuses into the substrate and It is believed to prevent deterioration of the substrate, and does not itself deteriorate the properties of the substrate on which it is applied. Most corrosion-resistant coatings of the tungsten-carbon alloy type are brittle, and the constituents of these coatings (e.g., carbon, boron, nitrogen, and oxygen) are capable of bonding to the base alloy at the temperatures commonly used to apply the coating. embrittle. For example, previous studies on titanium carbide/nitride coatings on titanium have confirmed that a brittle alpha skin layer is formed on the titanium substrate. In the practice of the present invention, the ductile first layer applied to the substrate acts as a barrier to the diffusion of embrittling components of the second tungsten-carbon alloy layer into the substrate layer, and also acts as a crack suppression means. This is believed to result in improved fatigue life performance of the substrate by suppressing crack propagation rates.

Regarding the second layer of erosion resistant coating, the coating is applied under conditions such that its residual stresses and tensile strains are minimized to promote retention of fatigue life in the substrate. Even small amounts of strain in the coating tend to induce cracking in the substrate which adversely affects its fatigue life. In particular, the stress in the coating is a function of the difference in coefficient of thermal expansion between the coatings (Δα) and the temperature difference (in Δ) between the substrate (room temperature) and the coating deposition temperature. Therefore, the stress (ρ) in the coating can be expressed by the formula: %.

According to this equation, the stress in the coating can be reduced by reducing Δα by using a coating material with a coefficient of expansion that approximates that of the substrate, or by using lower temperatures when depositing the coating. This can be lowered by

Erosion-resistant coating of tungsten-carbon alloy is 18
It is customary to apply the tungsten-carbon alloy corrosion-resistant coating at a temperature of about 500 to about 1400"F, thereby forming a base. An improved fatigue life of the material is achieved.

Any suitable eutectic mixture is included in combination with the bilayer coating of the present invention. Although any suitable substrate may be used, particularly good results are obtained using stainless steel or titanium alloys in combination with the novel two-layer coating disclosed herein.

The first layer of the coating according to the invention contains palladium, platinum or nickel. Any suitable palladium-, platinum-, or nickel-containing metal may be used, but nickel or palladium is preferred, especially when the substrate to be coated is a stainless steel chain, and titanium alloys are used as the substrate to be coated. In this case, platinum or nickel is preferred. This palladium, platinum or nickel containing layer is
As mentioned above, it acts as a diffusion barrier and protects the substrate during further coating with a hard tungsten-carbon alloy overcoat.

Each layer of the coating of the present invention can be of any suitable thickness. The first layer containing palladium, platinum or nickel is from about 10,001 to about 1,002 inches and the second layer of tungsten-carbon alloy is from about 10,005 to about 1,000 inches.
Particularly good results are obtained with approximately [LO03 inches.

Any suitable coating technique can be used to apply the first layer of coating to the substrate. Typical methods include electrolytic plating, sputtering, ion plating, electrocladding, back coating, and chemical vapor deposition, among others.

Any suitable technique may be used, but electrolytic plating, sputtering, chemical vapor deposition or ion plating methods are preferably used. Similarly, any suitable technique can be used to deposit the corrosion-resistant tungsten-carbon layer over the palladium, platinum or nickel interlayer.

Preferred methods for achieving this low temperature deposition include chemical vapor deposition/controlled nucleation thermochemical vapor deposition, sputtering, physical vapor deposition, and electrolytic plating methods.

In carrying out the coating method of the present invention, the surface of the substrate to be coated is first shot peened to create compressive stresses therein. The shot peened surface is then thoroughly cleaned with detergents, chlorinated solvents, or acidic or alkaline cleaning agents to remove any residual oil or contaminants such as light metal oxides, scale, etc.

To ensure good adhesion of the first layer of platinum, palladium or nickel, the cleaned substrate is activated to finally remove the adsorbed oxygen. As mentioned above, the first layer is applied to the surface of the substrate by conventional coating techniques such as electrolytic plating, chemical vapor deposition (CvD), sputtering or ion plating. If the selective coating method is electrolytic plating, activation of the substrate surface is conveniently carried out by anodic or cathodic cleaning by passing the required electrical current therethrough in an alkaline or acidic cleaning bath. Plating is then applied using a conventional plating bath, such as Watt's nickel sulfate-chloride bath or a platinum/palladium amino nitride/diamin nitride bath. CVD to apply coating
If selected, activation is carried out by passing hydrogen gas over the substrate surface. CVD is then carried out, using volatile halides of the metal to be deposited and reacting these gases with a gas such as hydrogen at a suitable temperature, e.g., below 1400"F, to deposit the metal layer. Do the following.

If sputtering is selected as the method of applying the coating, bias sputtering can be used to activate the substrate.

Deposition of the first metal interlayer is carried out by sputtering or ionic vapor blasting using high purity Targetera F of the metal selected to form the interlayer.

Coating the second layer of tungsten-carbon alloy over the first metal layer is accomplished by conventional coating techniques such as CVD1 sputtering at temperatures not exceeding 1400 DEG F., as described above.

If C'VD is selected for the deposition of the tungsten-carbon alloy, a gaseous mixture of WF6, H2, a suitable fertile compound containing carbon, oxygen and hydrogen, and an inert gas diluent such as argon. is encysted in the first layer and about 8
00 to about 1200 degrees Fahrenheit, and the gas mixture is reacted and deposited onto the heated substrate.

If sputtering +3 is selected for the deposition of the tungsten-carbon alloy, a high purity alloy target is prepared and a sputtering coating equipment is used to coat the material on the target layer onto the substrate coated with the first layer. EXAMPLES AND COMPARATIVE EXAMPLES Several of the coating techniques described above were used in connection with the present invention and are described in the following examples to briefly illustrate the invention.

The individual 0450 stainless steel surfaces were first thoroughly cleaned of all dirt, fat, and other undesirable materials, and then conditioned by shot peening at step 1. Next, use a sticky note to clean the surface of the substrate.
Electrolytic plating was performed with nickel or palladium footings having a thickness of α2 to α8 mils using Watt's nickel sulfamate or palladium aminonitrate plating baths, respectively. 9588-97.8% tungsten and 112-6.
A second coating consisting of a tungsten-carbon alloy containing 12% carbon was deposited over the first coating by a CvD coating method. In this method, evaporation was achieved by reacting a gaseous mixture of WF, H, and an organic compound containing carbon, oxygen, and hydrogen with tungsten. Deposition began after preheating the substrate to 1000° F. for 30-60 minutes, and this temperature was maintained throughout the coating operation. Deposition times were adjusted to obtain a coating thickness of approximately 1-3 mils. The hardness of the tungsten-carbon alloy coating is 2050 k/fntt”.

(2) Erosion resistance of coated samples The coated substrate samples were tested for erosion resistance using an S, S, White erosion tester. When using this device,
Diameter 1 separating the coated sample from this sample
The sample was sandblasted by impacting the sample at a predetermined impact angle from a /2 inch nozzle. The conditions under which the erosiveness test by sand impact was conducted are as follows: Sand---1------S, S
, White Ago, 50 prn Air pressure------------50p
s 1 Powder flow rate-----------
60A C” Sample/nozzle spacing-1
After setting it in the α5 inch*S, S-White apparatus, the powder chamber was vibrated 60 times per second to produce the desired powder flow rate.

The samples were sand blasted for 5 minutes at a sand impact angle of 90° and 90°.

Erosive wear of the samples was measured as the volume of coating material lost per minute of sand impingement. The results of the erosive wear test are shown in Table 1 below.

The procedure of this example was repeated for comparison purposes, but with C45
No coating was applied to the stainless steel substrate. The results of this comparative erosion and wear test are also shown in Table 1.

Table 1 Relative corrosion resistance test of C450 edge and uncoated caBa steel coated with W-C alloy F! Sample volume loss rate (-7m1nX10
-') Coating Sand impact angle Nl/W-C alloy 5.0 5. OPd
/W-C joint area 5.0 5.0 No footing 70.0 7α0th ■
Referring to the table, it can be readily seen that the uncoated samples exhibited at least 14-25 times greater erosion rates than the coated samples.

2. Fatigue Life of Coated Samples Fatigue Bending Plate Test (Modified Claus) Samples were coated according to this example and then subjected to fatigue testing in a bending plate testing apparatus by clamping both ends of the sample. An uncoated C450 stainless steel substrate was used as a control for baseline determination. The A ratio (
aa/5rn) = 1 and mechanically vibrated to failure at a frequency f = 30 Hz. Stress levels were varied in the range of 55-60 kgi. Failure was indicated by destruction of the test specimen.

The results of the fatigue test are shown in Table 2 below.

Table ■ Fatigue test results Test sample Stress level Coating until failure (Ksl) Number of cycles Nl/WC combined 55 1 (L2X
106 No coating 55 4
．． 6X10'Pd/W-C alloy 60
4.6X10' coating 7ZL
60 2.0 It is immediately apparent that no deterioration was shown.

A first stage compressor blade fabricated from AM350 stainless steel was coated with a Ni/W-C coating according to this example. Total coating thickness should be 2-5 mils and coating hardness should be 1950-2050 kP.
/mm”.:!-y The wing was tested for fatigue life using a B-7 Ip tester, and the wing was
It was possible to excite an air jet at the frequency of the basic bending method while firmly fixing it in the shape groove. The test was conducted at room temperature and the conditions for this test were as follows: Fundamental frequency (Nf) = 600-700Hz Stress level =
= 105 kgi Deflection = 179 mils The failure point was indicated by the loss of natural frequency at a rate of 10 cycles/sec. In this B7Ive test, the allowable vine fatigue life is 3o to 000 cycles.

The blade with the first coating was determined to have a fatigue life of 430,000 cycles, and the blade with the second coating was determined to have a fatigue life of 385,000 cycles, so the coated blade We investigated the details of the fatigue life of these wings and confirmed the fact that the corrosion-resistant coating does not degrade the fatigue life of the substrate on which it is applied.

〔Effect of the invention〕

With reference to the above example, some of the many advantages of the present invention will be readily apparent. For example, novel coatings have been developed which prevent or reduce the corrosion of metals, such as metals and their alloys, particularly in operating environments such as gas turbine engines. This is achieved with little deterioration of the material properties of the coated structure.

Although specific components of the present invention have been described above, many other modifications are possible that may affect, enhance, or otherwise improve the coatings of the present invention.

These modifications are also intended to be encompassed by the present invention.

Although several embodiments have been shown herein, many modifications and changes will occur to one skilled in the art after reading this disclosure. These are also intended to be included in the present invention.

・、−Nino

Claims (13)

[Claims] (1) A two-layer coating consisting of a first layer made of palladium, platinum or nickel, and a second layer made of a tungsten-carbon alloy and covering the first layer. 2. The coating of claim 1, wherein: (2) a second layer is deposited over the first layer at a temperature of about 500 to about 1400 degrees Fahrenheit. (3) the first layer has a thickness of about 0.0001 to about 0.002 inches, and the second layer has a thickness of about 0.0005 to about 0.
．． 3. A coating according to claim 1 or claim 2, wherein the coating has a diameter of 0.004 inches. (4) A base material and a coating covering it, which is a two-layer coating consisting of a first layer made of palladium, platinum, or nickel, and a second layer made of a tungsten-carbon alloy and covering the first layer as an upper layer. wherein the first layer of the coating is in direct contact with the substrate,
An article in which a coating imparts corrosion resistance to a substrate without loss of fatigue life. (5) The article according to claim 4, wherein the base material is steel or titanium alloy. (6) depositing a second layer of tungsten and carbon on top of the first layer of palladium, platinum or nickel;
A method of making a two-layer coating, wherein the deposition is carried out at a temperature of about 500 to about 1400 degrees Fahrenheit. (7) Low temperature adhesion of the second layer to the first layer by CVD/C
7. The method according to claim 6, which is carried out by NTD, sputtering, physical vapor deposition, or electroless plating. (8) A method according to claim 6 or claim 7, wherein the first layer is deposited on the substrate before being overcoated with the second layer. (9) The method according to claim 8, wherein the base material is steel or titanium alloy. (10) The method according to claim 8 or 9, wherein the first layer is deposited on the substrate by electrolytic plating, sputtering, or ion plating. (11) Applying a first layer of palladium, platinum or nickel in direct contact with the substrate to the substrate, then applying a second layer overlying this first layer, the second layer being tungsten. - A method of imparting corrosion resistance to a substrate without loss of fatigue life of the substrate, characterized in that it consists of a carbon alloy. (12) Place the second layer on top of the first layer at about 500°F to about 1400°F.
12. The method according to claim 11, wherein the deposition is carried out at a temperature of . (13) The method according to claim 11, wherein the base material is made of steel or titanium alloy.