JPS60211083A - Process for stripping thermal barrier coating - Google Patents

Abstract

PURPOSE:To strip off a thermal barrier coating easily and completely by pretreating it with a mineral acid soln., then posttreating with an acidic soln. of mineral acid contg. ammonium chloride or ammonium bromide. CONSTITUTION:A single or/and a multilayered thermal barrier coating comprising alkaline earth metal ceramic, transition metal ceramic, transition metal alloy, etc. is pretreated with a soln. of mineral acid, then posttreated with ca. 5-30pts.vol. pref. 15-20pts.vol. treating liquid basing on the unit weight of the material to be treated, of an acidic soln. of mineral acid at <=ca. 100 deg.C, pref. 80-95 deg.C under reflux of water, to strip off the thermal barrier coating without damaging the surface of the base material. Suitable mineral acid is inorg. acid such as HCl, H2SO4, H3PO4, etc. and the suitable concn. of the acid is ca. 3-35%, pref. 5-20%. The concn. of said ammonium chloride or ammonium bromide is ca. 3-30%, pref. 5-20%.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION The present invention relates to a method for removing the original thermal barrier coating, which is extremely difficult to remove, during injection gas coating of the combustion chamber of a jet engine. The object of the present invention is to provide a method for simple and complete peeling.

BACKGROUND OF THE INVENTION Conventionally, the following methods have been used to remove thermal barrier coatings consisting of single-layer/multilayer coatings made of alkaline earth metal ceramics, transition metal ceramics, and transition metal alloys. That is, firstly, it is treated with a strong acid solution or a strong alkaline solution at high temperature,
The second method is to remove component elements in the form of salt, and the second method is mechanical polishing. However, although the first method uses high temperatures, it takes a considerable amount of time to peel off, and the peeling itself tends to cause spots.

Additionally, it has the disadvantage that it tends to cause corrosion of the base material, and there are also problems with the adhesion of re-coating. Furthermore, there are also problems in terms of recent energy conservation measures and pollution control measures such as waste steam and waste liquid treatment. Although the second method reduces shrinkage, there are problems such as breakage accidents and deformation of the base material due to a decrease in the thickness of the base material.

Furthermore, peeling occurs, and as with the first method, there is also a problem in adhesion during recoating.

Structure of the Invention As a result of intensive study in view of these points, the present inventors have found that:
In the first method, it has been discovered that a mineral acid solution containing ammonium chloride or ammonium bromide promotes peeling of the coating without damaging the base material surface,
This has led to the present invention. That is, the present invention relates to alloys of transition metals in periods 4, 5, and 6 of the periodic table, such as chromium, cobalt, nickel, zirconia, and yttrium, and ceramic derivatives thereof, and single-layer/and multi-layer coatings of alkaline earth metal ceramics. After pretreatment with mineral acid solution, the thermal barrier coating consists of
This is a stripping method for thermal barrier coatings, which is characterized by thermal embedding and post-treatment in a mineral acidic solution containing ammonium chloride or ammonium bromide.

In the present invention, the mineral acid in the mineral acid solution in pre-treatment and the mineral acid solution in post-treatment is an inorganic acid such as hydrochloric acid, sulfuric acid, or phosphoric acid. In one heat treatment of the present invention, it is essential to use ammonium chloride or ammonium bromide. This is thought to be due to the effect of converting the thermal barrier coating, which is an oxide that is insoluble or poorly soluble in acids and alkalis, into a soluble or easily soluble ammonium complex. That is, by using a specific ammonia compound in place of conventional acid or alkali stripping methods, stripping of thermal barrier coatings becomes extremely easy.

In the present invention, the 8 conditions are appropriately selected depending on the acidic solution of ammonia halide used, but the reaction is carried out under reflux of water at 100°C or lower, preferably 80 to 95°C, for about 5 to 8 hours. Bye. The amount of processing liquid at that time is 5 to 3 per unit weight of the original sample.
0 capacity, preferably about 15 to 20 capacity. Also,
The concentration of mineral acid in the pre-treatment and post-treatment is about 3 to 35% by weight, preferably about 5 to 20% by weight. If the concentration of mineral acid is lower than 3% by weight, peeling will be insufficient, and if it is higher than 35% by weight, it is not preferable due to problems with the material of the device and waste water. Furthermore, the concentration of ammonium chloride or ammonium bromide is 3 to 30% by weight, preferably 5 to 20% by weight.
That's about it. If the ammonium compound concentration is lower than 3% by weight, peeling will be insufficient, and if it is higher than 30% by weight, no particular improvement in effectiveness will be observed.

Hereinafter, the present invention will be explained in more detail with reference to Examples. All numbers in the examples indicate weight %.

Example 1 Multilayer flow consisting of magnesium zirconate, cobalt chromium ψ aluminum e yttrium alloy. After washing the coating with water, it is further refluxed at 90° C. for 3 hours in an aqueous solution of 5% hydrogen chloride containing 15% ammonium chloride.

　′ Wash with water and then dry. Peeling The peeling of the coating is insufficient and patchy.

Example 2. After refluxing, the peeled surface of the sample, which was thoroughly washed with water and dried, had the same surface condition as shown in FIG.

Example 3 The peeled surface of a sample with a flow diameter of 3°, thoroughly washed with water and dried has the same surface condition as in FIG.

Example 4. After refluxing, the peeled surface of the sample, which was thoroughly washed with water and dried, had the same condition as shown in FIG.

Example 5 The peeling state of the 5° scratch was good, and no corrosion or grain boundary erosion was observed.

Example 6 After treatment at 90°C for 2 hours, a 5%* hydrogen hydride aqueous solution containing 15% ammonium chloride was heated to ~90°C. The peeling state of the tings was good, and no corrosion or grain boundary erosion was observed.

[Brief explanation of the drawing]

FIG. 1 shows a micrograph (X100) of the surface condition after peeling according to the method of the present invention. FIG. 2 shows a micrograph (X100) of the coating surface condition before peeling. Figure 3 A and B show concentrated hydrochloric acid aqueous solution (35% by weight) of the conventional method.
A (X60) and B (X100) are micrographs showing the peeled state after refluxing for 5 hours. 4 and 5 show micrographs (X500) of the cross section after peeling according to the method of the present invention. Patent applicant Iwa 1) Masami drawing? '('i!＞(no change in rF) Date of amendment order: July 31, Showa Go (shipping date)
The column for a brief description of the drawings on page 8 of the specification is amended as follows. "Figure 1 shows a micrograph (X100) of the surface condition of the metal structure after peeling by the method of the present invention. Figure 2 shows a micrograph (X100) of the coating surface condition of the metal structure before peeling. Figures 6A and B show concentrated hydrochloric acid aqueous solution (65% by weight) of the conventional method.
A' (X60) and B (X100) are micrographs of the metal structure in a peeled state after refluxing for 5 hours. FIGS. 4 and 5 show micrographs (X500) of cross-sections of metal structures after peeling according to the method of the present invention. ”

Claims (3)

[Claims] (1) A thermal barrier coating consisting of a single layer or/and a multilayer coating is pretreated with a mineral acid solution and then subjected to fl heat treatment in a mineral acid solution containing ammonium chloride or amthonium bromide. How to remove barrier coating. (2) The stripping method according to claim 1, wherein the mineral acid is at least one acid selected from inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid. (3) The peeling method according to claim 1, wherein the passion treatment is carried out under reflux of a mineral acid solution containing ammonium chloride or ammonium bromide.