JPS58130280A - Selective chemical removal of hard surface coating from superalloy substrate - 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 The present invention relates to the removal of Ceramic, Celmet, and Kinzumi coatings from high strength, high temperature metal substrates, and more particularly, using an aqueous acidic stripping bath equipped with high energy density agitation means. It concerns the removal of these hard surface coatings from superalloys, particularly nickel-based substrates.

One of the most difficult requirements of chemical stripping techniques is the preparation of "hard surface" coatings, i.e. metal surfaces such as nickel-based jet engine combustion chambers (kH), which can be removed by detonation guns, gas machines, and flame spray methods. The objective was to develop a composition that chemically removes fused particle coatings that are applied to surfaces such as surface coatings, which are typically applied as a thin layer to provide protection against high temperature oxidative gas flow. , these include the heat-resistant Ceramic ivy, Celmet and nickel-based mixtures.

The prior art lacks an efficient surface chemical stripper that can rapidly and selectively remove such coatings without damaging the underlying substrate. The characteristics of the techniques used so far are: -Mechanical methods such as mechanical caroing, polishing, and blast polishing1. and non-mechanical methods such as chemical immersion in solutions such as hydrochloric acid and the use of molten salt baths that only soften the ceramic and ceramic coatings. However, mechanical methods are very time consuming.
Moreover, the metal substrates frequently used in "high technology" applications are susceptible to large dimensional deviations that can easily damage very expensive parts of the equipment. Although some ceramic coatings are softened by conventional chemical methods, it is still necessary to mechanically remove the ceramic coating along with the underlying inner adhesive coating. Molten salt baths are cumbersome to operate and are only effective for a limited number of coating and substrate combinations.

Nine, these techniques are all deficient in removal speed, operating cost, and effectiveness of results. US Patent No. 269
No. 8781 discloses a sulfuric acid solution containing a self-efficacious nitroaromatic additive for removing oxide scale and electrodeposited nickel from steel substrates. However, there is no teaching indicating that Ceramic, Celmet, or hard surface metal coatings can be chemically removed from nickel-based substrates. The object of the present invention is to create effective compositions and associated methods for the same.

Another object of the present invention is to provide a composition and associated method effective for selectively and non-corrosively removing a hard, high temperature resistant ceramic, nickel-based adhesive coat from a nickel-based substrate. It's about releasing JIJ.

Another object of the present invention is to devise a method for selectively stripping hard surface coatings from metal surfaces of jet engine components without causing dimensional deviations on the surfaces undergoing stripping treatment.

The above and other objects of the present invention are to provide a novel composition for selectively removing hard surface coatings, particularly heat resistant selank, celmet and nickel based coatings from high strength, high temperature resistant metal substrates, particularly nickel based substrates; It was completed by the discovery of a method to The release composition should have a concentration of Hp, preferably about 9O-450y/l and a specific gravity of 1.84C66"Ba at 66°Ba.
'e1.84Bpac,! ! rav, ), most preferably about 250-300 y/l; about 20 y/l
to a saturated water-soluble nitro-substituted aromatic compound, preferably about 100-1201/1) tanitrobenzene sulfo y1! Sodium; about 0-70 y/l of water-soluble fluorine-containing species, preferably about 10-20 y/l of fluoroborous NRS about 0-1. Ol/l of surfactant, preferably L (d about 0-α, a member of the group of diphenyl ether sulfonates of 51/l; the remainder being about 2-9 of the solution.
Consists of 0 weight 1* violet water.

The stripping method of the present invention involves removing a hard surface coating on a metal substrate, typically a heat-resistant ceramic, ceramic or nickel-based coating, using the above-mentioned acidic residual bath solution, preferably sulfuric acid, soluble fluorine-containing acid, soluble nitro-substituted aromatic contact with a solution consisting of a group compound, a surfactant, and water, and the contact is continued until the hard surface coating is selectively removed from the metal surface. Contact is made with the coated substrate at 1
20-1807. Most preferably 150-15
A nine-solution bath maintained at 0"F is heated to at least about 4 watts/ln", preferably about 7-8" by ultrasonic agitation means, preferably a fully powered ultrasonic generating transducer.
This is done by immersion while being actively stirred by a power source. Once the coating has been completely removed, the substrate is removed from the f# solution, rinsed, and ready for the next application.

Well-known technology, particularly related to the construction of gas turbine engines that use superalloys currently useful in jet engines and aeronautical applications.1 Known technology in Shiba & C includes metals that are exposed to severe oxidative conditions at high temperatures. It is necessary to coat the surface with a thin (several ajl) coating of a gold-14 protective layer or a non-gold N4 protective layer. These coatings are commonly referred to as hard surface coatings and can be made of any of a number of high-strength, corrosion-resistant materials; ``Nickel-based'', defined as ``nickel-rich metal mixtures that can function as either nickel-based materials'', ceramic materials or Celmet, as well as some mixtures of these materials, can be used. The four-hard coating, which is frequently used as a protective layer in aircraft combustion chambers, is a three-layer system and has an order 91 composition.

Adhesive coat + 3-5lit lNi so*+c
r15% intermediate: I-): 4-6Li1. Mi80%
-Cr2Q- and MyO-ZrO snow 35-65 [hardware outer coat: /;, -1Q ail, Mho-
ZrO.

The hard surface coatings that have begun to be applied to the combustion chambers of jet engines are as follows: ca2s, 18% Cr 112, Yo5
, Hi balance B: Y stabilized zirconia It can be exfoliated from metals (more specifically, metal superalloys that have both high temperature resistance and high strength at high temperatures). In particular, the coating on the nickel thread alloy, such as the well-known Hast. The coating is applied to the substrate using a variety of circumferential techniques (detonation guns, plasma blasts and flame blast particle applications).

All of these well-known application techniques essentially consist of grinding the composition into a fine powder, heating this powder until it reaches a molten state, and then turning the molten material, accelerated in a gas plasma, into a fine, very fine powder. It consists of spraying onto the substrate to be coated in the form of a dilute gold RZ cast, which hardens to form an extremely tough protective coating.

The present invention is further directed to improved compositions and associated methods for removing these virginally applied coatings.

In order for a powerful chemical stripping agent to function effectively, it is necessary to overcome several problems first.

The peeling composition has a speed of /fI, for example, 1/2 Q
It must be possible to strip at rates on the order of 300 ml/hour, and the chamber must be ventilated to remove toxic vapors produced by the practice of this process. This ventilation is always a major consideration in both laboratory and factory environments and applications. Such a solution was found by creating an aqueous acidic bath with the following composition: In other words,
Sulfuric acid is also ``4'' (any commercially available brand, but preferably concentrated, 9, e.g. 66B4F), an essential component of the solution -1'6 o i!, 80.cD concentration is about 9O-
450 y/11 preferably in the range of about 250-500 y/l. If too little acid is used, the bath will not have the acid strength necessary to remove the coating at a reasonable rate, but if more than -10,000, 45 Qy/l is used, strong stripping results will not be obtained and economical The justification is electric. However, from -poor to theoretically H, O, may occupy up to 90% of the solution.

The 20th essential Jj that acts as an oxidizing agent in the stripping solution! In the broadest embodiment of the present invention, the base is a water-soluble nitro-substituted aromatic compound, more specifically, rice [! it
water-soluble nitro-substituted benzene compounds, such as the compounds disclosed in US Pat. No. 2,698,781. Most preferably, a suitable alkali metal salt or an alkaline earth metal salt (preferably an ammonium group) of nitropene/bisulfonic acid or sodium sulfonic acid is most preferred. ) are valid. It is believed that this group of chemicals acts as a reaction accelerator in solution, but the theory is not intended to be binding. 2) #l11t of the Ellllllll compound is approximately 20
y/l to saturation, about 2O-120y//
69, and a high concentration, for example 6O-120y/7, is most preferred.

Other preferred but not essential bath components include soluble fluorine-containing*, preferably fluoroboric acid HBF4, but other fluorine-containing species capable of generating low concentrations of fluorine ions in an aqueous solution; For example, HP
%NH4HF@, N, AlF6 are particularly preferred. The concentration of fluoride ions is determined by the amount required to produce the desired concentration of fluoride ions in solution, but is generally about 0-701 for substances with a high degree of separation of 1% in aqueous solution.
/l, preferably in the range of about 10-20 y/l. As the fluorine ion concentration increases, the chance of harmful corrosion to the substrate increases, and the upper limit of the amount of fluorine ion that can be added to the @#1m solution increases.

Although not essential, it is preferred to include a small amount of a surfactant, such as 0-50 1/l, preferably about 0-L Oy/l, to be applied as a wetting agent to the surface to be dissolved in the bath.

Particularly preferred compounds for this purpose are diphenyl ether sulfonates, such as compounds of the general formula where R represents an alkyl group or water, and X represents an alkali metal such as sodium. Such a product is commercially available under the trade name "Dowfax 3B2," manufactured by Dakke Cal, Inc., Z.D., Michigan. Most diphenyl ether sulfonic acid alkaline tal salts are suitable equivalents;
In the broadest embodiment of the invention, any surfactant that is hydrolytically and oxidatively stable to the stripper solution can be used as an acceptable substitute. ＠The following composition is completed by adding 2-90% water by weight to bring the bath solution to the desired strength. Water reduces the viscosity of the exfoliation solution and increases the mobility of ionic species in the solution.

Adding water to sulfuric acid has the desirable effect of lowering the cavitation threshold of the solution, ie, the minimum force required to bring the local pressure acting on the solution to a value less than the vapor pressure of the solution. This threshold occurs due to an increase in vapor pressure and a decrease in viscosity and dilution density. 20KHIK for room temperature water)
The cavitation threshold is 2.45Wlih''.

The method of the present invention comprises contacting the hard surface coating with an acidic stripping solution and continuing the contact until the hard surface coating is substantially removed from the metal substrate without dimensional change of the underlying surface. In order for exfoliation to occur at an acceptable rate, it is essential that the solution bath be continuously stirred by suitable stirring means, preferably an ultrasonic generating transducer, either magnetostrictive (preferred) or piezoelectric transducer (D). The transducer must be operated to produce a maximum A power density of about 4 watts/in", preferably about 7-8 watts/*h". Merely stirring according to conventional techniques does not produce the necessary solution agitation in the bath to produce an effective velocity. In combination with an ultrasonic stirrer that inherently supplies energy to the solution, it is possible to It is necessary to maintain the H7 fluid at a temperature of about 110-180"F, and preferably about 150-150"F, during operation to obtain stripping rates.

The present invention will be explained in more detail with the following examples.

Example 1 Hap an aircraft sconce used in a jet engine.
tall-yX (22Cr, 1a5F#, 9[]
Made with M*51-5"b α6W, remaining Ma), length 4
(35ail thickness, H1/Cr 95*) and medium 11coe) (46aal thickness, Misas-cr2ocs
and klg.

55-36-mixture of ZrO@) and an outer coat (61
0m5? The flame softening was carried out over 520 ilk'' of triple layers consisting of 520 ilk (thick, MyO-ZrO, The coating was removed for 10-16 hours. Two 1200 watt side-mounted submersible ultra-high water tanks with 1 liter of 30 gallon hot water tanks were used during the release operation and a square polypropylene Stripping solution (275yXl) contained in a container made of
CDH, o, 66B-', 14 yXl''4 (4
8), 120 gA of Dawfaz-nitrobenzenesulfonic acid 17) Ah α1 yXl of Dawfaz-3B 2
) was used for 6 gallons. A metallographic examination revealed no damage to the base of the cylindrical combustion chamber.

Example 2 The cylindrical combustion chamber of a military jet engine is 275y/'
Oa (ilt acid Ha" oa (66°"), 1
45 g/l fluoroboric acid IIBF4 (48 ti),
J? and 116, g7t immersed in a stripping solution containing sodium nometanitrobenzene sulfonate. 130
After 20 hours with 1707, 6 layers of coating were removed from the 1000 watt bottom-mounted ultrasonic transducer and 2 gallons of stripping solution was placed in a 5 gallon square polypropylene container. A stainless steel tank was used. No damage to the base was observed.

Hajte ((ey
! 90 pieces! /l of concentrated sulfuric acid H, 80, (66°Be'
), 72 yXl of metanitrobenzene sulfo/1 wave sodium, 46 yXl of sodium sulfate yα day 0
4. 1.2 l/l ammonium thiocyanate was immersed in a stripping solution containing kHl and ticH.

Ultrasonic agitation at 145-150″F for 45 minutes produces several
1 thick coating was removed from the specimen.

According to the invention, ceramics, celmetres and nickel-based materials can be converted from metals, especially nickel-based superalloys to gold! Ij4
Not only can a wide range of hard surface coatings be removed from these substrates without causing any dimensional or structural changes, but also can be removed from these substrates without damaging the underlying materials. Can be removed.

Obviously, eleven modifications may be made to the invention in light of the above description. Therefore, within the scope of the appended claims, the invention can be practiced in a different manner from the above description.

Continued from page 1 0 Inventor Debra Nee Burns 242 South Lewis Avenue, Lombard, Illinois, United States of America

Claims (1)

[Claims] (1) Contains about 90-450 p/l of ``-04 and about 20-240 y/l of a water-soluble nitro-substituted aromatic compound,
A composition for the selective removal of hard surface metal coatings, in particular ceramic, Celmet and nickel-based mixtures, from high strength, high temperature resistant substrates, characterized in that the remainder consists of water. 2. The composition of claim 1, further comprising about 0-70 y/l of water-soluble fluorine-containing particles which dissociate to form a source of fluorine ions in solution. The composition according to claim 2, characterized in that: 14)! 1. $0. about 250-300 y/l, water solubility = ) 1-substituted benzene compound about 6O-120
y/1. , a water-soluble fluorine-containing [about 10-20 y/l], which produces a source of fluorine ions in solution, separated by about 0-1. A composition for selectively removing hard surface coatings, particularly Ceramic, Celmet and nickel-based mixtures, from high strength, high temperature resistant substrates, containing Op/l and the balance consisting of water. +5) The -d product according to claim 4, which contains about 270-281/7 H-Oa. (6) Sodium metanitrobenzene sulfonate as a water-soluble nido-substituted benzene compound at about 101)-120
The composition according to claim 6, characterized in that it contains y/l. (7) A composition according to claim 4, characterized in that it contains about 10-20 L/l of fluoroboric acid as the water-soluble fluorine-containing species. +8) The composition according to claim 4, which contains about 0-α5s of sodium diphenyl ether sulfonate as the diphenyl ether sulfonate. (9) Hard surface coating liquid temperature about 120-180F
The hard surface coating is brought into contact with the acidic stripping solution of claim 1 in a suitable container maintained at a constant temperature and continuously agitated by ultrasonic agitation means so that the hard surface coating does not damage the underlying metal substrate. A hard surface coating containing a selank, celmet and nickel based mixture is coated with a high strength, high temperature resistant coating, characterized in that the contacting is continued until the metal substrate is substantially removed from the metal substrate, and the substrate is then removed from the solution bath. A method for selectively removing chemical substances from a substrate. During the ulJ operation, the temperature of the solution is approximately 1.30-150
9. The method according to claim 9, characterized in that the temperature is maintained at 7'. 10. The method of claim 9, wherein the ultrasonic agitation means is an ultrasonic generating transducer that continuously supplies the solution with a power density of at least 4 watts/male during operation. The power density of the converter is 7-8 watts) / i+&
The method according to claim VB, item 11, characterized in that the composition of the solution bath is a self-contained composition of claim 4, JAd. The method described in Section 9.