Multilayer coating

Abstract

A multilayer coating obtained by carrying out the steps of (1) applying a ZnNi layer to a substrate material, in particular to a steel; (2) carrying out a first heat treatment in a temperature range from 135-300 C., preferably from 185-220 C., for a time period of at least 4 hours, preferentially of at least 23 hours; (3) applying a metal-pigmented top coat to the ZnNi layer; and (4) carrying out a second heat treatment in a temperature range from 150-250 C., preferably from 180-200 C., for a time period of at least 10 minutes, prefer-ably of at least 20 minutes, preferentially of at least 30 minutes.

Claims

1. A method of manufacturing an aircraft component with a multilayer coating, the method comprising: (1) applying a low hydrogen embrittlement ZnNi layer directly to a substrate material, wherein the substrate material is steel; (2) carrying out a first heat treatment in a temperature range from 135-300 C. for a time period of at least 23 hours; (3) passivating the low hydrogen embrittlement ZnNi layer; (4) applying a metal-pigmented top coat to the low hydrogen embrittlement ZnNi layer, wherein the top coat comprises a mixture of zinc flake layers and aluminum flake layers which are connected by an inorganic matrix; and (5) carrying out a second heat treatment in a temperature range of between 180 and 200 C. for a time period of at least 10 minutes.

2. The method in accordance with claim 1, wherein the first heat treatment temperature range is from 185-220 C.

3. The method in accordance with claim 1, wherein the substrate material is shot peened with an intensity of at most 0.1 mm Almen A before step (1).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be described in more detail in the following with reference to the enclosed Figures. In this respect, a number of the Figures are related to a series of experiments which have been carried out and which show the advantages of the multilayer coating in accordance with the invention. There are shown:

(2) FIG. 1 a comparison of the corrosion resistance of the coating in accordance with the invention with respect to conventional coatings;

(3) FIGS. 2a-c a time-to-rupture diagram, an enlarged shot of a ruptured surface and an REM shot of a ruptured surface of a steel coated with the multilayer coating in accordance with the invention;

(4) FIGS. 3a-e a time-to-rupture diagram, an enlarged shot of a ruptured surface and two REM shots of a ruptured surface of a steel coated with the multilayer coating in accordance with the invention; and

(5) FIGS. 4a-c a time-to-rupture diagram, an enlarged shot of a ruptured surface and an REM shot of a ruptured surface of a steel coated with the conventional ZnNi layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) A total of 5 different strips can be recognized in FIG. 1, with the two left hand strips showing a multilayer coating in accordance with the invention on a steel. The strip arranged in the middle shows a steel which has only been coated with a ZnNi layer and the two right hand strips show a steel which has only been coated with a metal-pigmented top coat, but does not have a ZnNi layer.

(7) The coatings shown in FIG. 1 were all subjected to an identical corrosion test so that now the corrosion resistance of the different coatings can be assessed using an optical examination. It can immediately be recognized that the multilayer coating in accordance with the invention has a very much better corrosion resistance than the coating not in accordance with the invention likewise shown in FIG. 1. Almost no traces of corrosion can be recognized. The two right hand strips which do not have a zinc-nickel layer have in particular been very pronouncedly attacked by corrosion. The strip of a steel coated with a zink-nickel layer arranged at the middle has a somewhat less advanced corrosion state.

(8) This result is confirmed since in a re-embrittlement experiment in accordance with NAVAL Warfare (45%/24h+5%/1 h) the behavior of the multilayer coating in accordance with the invention on a steel, in particular on a high-strength steel, is better with respect to corrosion-caused, hydrogen-induced damage than a steel having an LHE ZnNi layer.

(9) The total impression that the multilayer coating in accordance with the invention is superior to a conventional ZnNi layer is also confirmed on the basis of the series of experiments shown in the following.

(10) In this respect, incremental-step load tests are carried out under a media load in 3.5% NaCl solution at room temperature on nick-break specimens from the material 300 M with different coating variants in accordance with ASTM F519. After the examination, a ruptured surface analysis takes place for determining operationally-caused, hydrogen-induced damage due to the corrosion load (re-embrittlement tests).

(11) The series of experiments comprises the following specimens in total:

(12) 2 sets @ 4 nick-break specimens, Number: 1a, in the state: LHE ZnNi (LLI)+passivation+HT 190 C./23 h+TC P35 (5 m)+HT 190 C./30 min (in accordance with the invention)

(13) 2 sets @ 4 nick-break specimens, Number: 1 b, in the state: LHE ZnNi (LLI)+passivation+HT 190 C./23 h+TC P35 (10 m)+HT 190 C./30 min (in accordance with the invention)

(14) 1 set @ 4 nick-break specimens, Number: 1c, in the state: LHE ZnNi (LU)+passivation+HT 190 C./23 h (comparison example)

(15) The orienting re-embrittlement tests are carried in accordance with the test routine shown below.

(16) Test routineRe-embrittlement tests

(17) TABLE-US-00001 TABLE 1 Test routine - Re-embrittlement tests Pre-load Passed embrittlement test Incremental, step-wise load 45% F.sub.mK for 24 hours (incremental-step load) Subsequently hourly increase by 5% F.sub.mK Test duration Max. 24 + 10 hours Temperature Room temperature (20 3 C.) Test medium 175 2 ml 3.5% NaCl solution, pH 6.9 0.1 not purged with nitrogen, naturally vented

(18) IaLHE ZnNi (LLI)+Passivation+HT 190 C./23 h+TC P35 (5 m)+HT 190 C./30 min

(19) Two sets each having 4 nick-break specimens are prepared in this specimen. In this respect, an LHE ZnNi (LLI) having a passivation is used as the zinc-nickel layer and is subjected to a first heat treatment at 190 for a time of 23 hours. For this purpose a top coat (=coating) of the type P35 from the Magni corporation is used as the metal-pigmented top coat. It is applied with a thickness of 5 m. Subsequently a second heat treatment is carried out which has the purpose of baking in the metal-pigmented top coat. The second heat treatment at 190 C. lasts 30 minutes. This can be summarized as follows in brief: LHE ZnNi (LLI)+passivation+HT 190 C./23 h+TC P35 (5 m)+HT 190 C./30 min.

(20) A steel of the type 300 M, Lot 065/Z (F.sub.mk=42960 N) is used as the material which serves as the substrate material for the multilayer coating.

(21) The test parameters are as follows: 45% F.sub.mK 24 h+5% F.sub.mK per 1 h; max. 24+10 hours; test medium 3.5% NaCl, pH 7; test bench: Zwick Z050.

(22) TABLE-US-00002 TABLE 2 Result of the test on specimen Ia Results Time to Result rupture in Max. force (>50% Set Specimen hours in % F.sub.mK/N passed) Remark 1 1 33:00:36 90/40500 Passed 2 33:01:12 90/40500 Passed 3 33:01:48 90/40500 Passed 4 33:02:24 90/40500 Passed 2 1 33.00:36 90/40800 Passed 2 33:01:12 90/40800 Passed 3 33.01:48 90/40800 Passed 4 33:01:48 90/40800 Passed

(23) The time-to-rupture diagrams of one of the specimens 1-4 from set 1 and from set 2 are shown in FIG. 2a.

(24) Furthermore, a microscopic representation of the ruptured surfaces of each specimen is shown in FIG. 2b.

(25) FIG. 2c shows 4 representations of a specimen in which enlarged shots of the layer thicknesses in the nick bed of the nick-break specimen and outside the nick can be seen.

(26) The incremental-step load tests show that both examined sets @ 4 specimens withstood a test load of 90% F.sub.mK. The shortest test duration amounts to 33h 36 s in both sets. The metallographic analyses of variant la show that the ZnNi coating is continuously present at the examined specimen. The layer thickness of the metal-pigmented top coat (ZnL layer) amounts to an average of 16.0 m. The layer thickness of the top coat amounts to approximately 33.0 m (FIG. 2c, top illustration). The ZnNi coating has a thickness of 8.5 m in the nick bed and the top coat has a thickness of 20.5 m (FIG. 2c, lower illustrations).

(27) The metallographic analyses of variant 1a show that the ZnNi coating is continuously present at the examined specimen. The layer thickness of the ZnNi coating amounts to 16.0 m on average. The layer thickness of the top coat amounts to approximately 33.0 m (FIG. 2c, top illustrations). The ZnNi coating has a thickness of 8.5 mm in the nick bed and the top coat has a thickness of 20.5 m (FIG. 2c, lower illustrations).

(28) IbLHE ZnNi (LLI)+Passivation+HT 190 C./23 h+TC P35 (10 m) +HT 190 C./30 min

(29) Two sets each having 4 nick-break specimens are prepared in this specimen. In this respect, an LHE ZnNi (LLI) having a passivation is used as the zinc-nickel layer and is subjected to a first heat treatment at 190 for a time of 23 hours. For this purpose a top coat (TC) of the type P35 from the Magni corporation is used as the metal-pigmented top coat. It is applied with a thickness of 10 m. Subsequently a second heat treatment is carried out which inter alia has the purpose of baking in the metal-pigmented top coat. The second heat treatment at 190 C. lasts 30 minutes. This can be summarized as follows in brief: LHE ZnNi (LLI)+passivation+HT 190 C./23 h+TC P35 (10 m)+HT 190 C./30 min.

(30) A steel of the type 300 M, Lot 065/Z (F.sub.mk=42960 N) is used as the material which serves as the substrate material for the multilayer coating.

(31) The test parameters are as follows: 45% F.sub.mK 24 h+5% F.sub.mK per 1 h; max. 24+10 hours; test medium 3.5% NaCl, pH 7; test bench: Zwick Z050.

(32) TABLE-US-00003 TABLE 3 Result of the test on specimen Ib Results Time to Result rupture in Max. force (>50% Set Specimen hours in % F.sub.mK/N passed) Remark 1 1 33:00:36 90/40600 Passed 2 33:01:12 90/40600 Passed 3 33:01:48 90/40600 Passed 4 33:02:24 90/40600 Passed 2 1 26:08:24 55/25800 Passed 2 26:09:00 55/25800 Passed 3 26:09:42 55/25800 Passed 4 26:10:30 55/25800 Passed

(33) The time-to-rupture diagrams of one of the specimens 1-4 from set 1 and from set 2 are shown in FIG. 2a.

(34) Furthermore, a microscopic representation of the ruptured surfaces of each specimen is shown in FIG. 2b.

(35) The incremental-step load tests show that the two examined specimen sets withstood considerably different test loads. That is, the four specimens of set 1 withstood a test load of 90% F.sub.mK; those of set 2 only 55% F.sub.mK. The shortest test duration in set one is 33 h 36 s and in set two 26 h 8 min 24 s.

(36) The metallographic analyses on specimen 1, set 1, show that the ZnNi coating has a thickness on average of 13.3 m and the top coat has a thickness of 29.0 m (FIG. 3c, upper illustrations). On specimen 1, set 2, the layer thicknesses amount on average to 16.3 m with ZnNi and to 24.0 m in the top coat (FIG. 3d, upper illustrations).

(37) The tests furthermore show that the ZnNi coating at the tested sets 1 and 2 is differently pronounced in the region of the nick bed. Specimen 1, set 1 thus has both a ZnNi coating having a thickness of 5.0 m and a top coat of 12.5 m down to the nick bed (FIG. 3c, lower illustrations). Specimen 1, set 2, in contrast, only has traces of the ZnNi coating (FIG. 3d, lower illustrations). The top coat in this specimen is furthermore not continuously pronounced down to the nick bed.

(38) The scanning electron microscopic rupture-surface analysis of specimen 1 of the second step shows that it has considerable damage as a result of hydrogen embrittlement after the incremental-step load test (FIG. 3e, lower illustration). The top right illustration of FIG. 3e shows the top coat in the region of the nick bed.

(39) The metallographic analyses on specimen 1, set 1, show that the ZnNi coating has a thickness on average of 13.3 m and the top coat has a thickness of 29.0 m (FIG. 3c, upper illustrations). On specimen 1, set 2, the layer thicknesses amount on average to 16.3 m with ZnNi and to 24.0 m in the top coat (FIG. 3d, upper illustrations).

(40) The tests furthermore show that the ZnNi coating at the tested sets 1 and 2 is differently pronounced in the region of the nick bed. Specimen 1, set 1 thus has both a ZnNi coating having a thickness of 5.0 m and a top coat of 12.5 m down to the nick bed (FIG. 3c, lower illustrations). Specimen 1, set 2, in contrast, only has traces of the ZnNi coating (FIG. 3e, lower illustrations). The top coat is furthermore not continuously pronounced down to the nick bed.

(41) The scanning electron microscopic rupture-surface analysis of specimen 1 of the second step shows that it has damage as a result of hydrogen embrittlement after the incremental-step load test (FIG. 3e, lower illustration). The upper illustration of FIG. 3e shows the top coat in the region of the nick bed.

(42) IcLHE ZnNi (LLI)+Passivation+HT 190 C./23 h

(43) In this series of experiments, a set of 4 nick-break specimens is prepared, wherein the coat applied to the steel here is not the multilayer coating in accordance with the invention.

(44) A zinc-nickel layer, more precisely a layer of an LHE ZnNi (LLI), with a passivation is used as the coating for the steel of the type 300 M and is subjected to a heat treatment of 190 C. for a duration of 23 hours. This can be summarized as follows in brief: LHE ZnNi (LLI)+passivation+HT 190 C./23 h.

(45) In this respect, no further coating is applied to the ZnNi layer. No second heat treatment takes place either.

(46) A steel of the type 300 M, Lot 065/Z (F.sub.mk=42960 N) is used as the material which serves as the substrate material for the coating.

(47) The test parameters are as follows: 45% F.sub.mK 24 h+5% F.sub.mK per 1 h; max. 24+10 hours; test medium 3.5% NaCl, pH 7; test bench: Zwick Z050.

(48) TABLE-US-00004 TABLE 4 Result of the test on specimen Ic Results Time to Result rupture in Max. force (>50% Set Specimen hours in % F.sub.mK/N passed) Remark 1 1 26:10:12 55/25800 passed 2 26:15:00 55/25800 Passed 3 26:16:12 55/25800 Passed 4 26:17:24 55/25800 Passed

(49) The time-to-rupture diagram of specimen 1-4 is indicated in FIG. 4a.

(50) Furthermore, a microscopic representation of the ruptured surfaces of each specimen is shown in FIG. 4b.

(51) The incremental-step load tests show that the examined specimens withstood a test load 55% F.sub.mK. The shortest test duration amounts to 26 h 10 min 12 s.

(52) The metallographic analysis shows that the ZnNi coating is present down to the nick bed. The layer thickness of the ZnNi coating amounts to 9.0 m on average and to 6.5 m in the nick bed (FIG. 4c).

(53) A summary of the results is presented in overview form in the following in Table 5.

(54) TABLE-US-00005 TABLE 5 Summary of the results of the re-embrittlement test in table form Test Result Specimen Max. force duration (>50% designation State Set No. in % F.sub.mK/N h:min:s passed) Ia LHE ZnNi (LLI) + 1 1 90/40500 33:00:36 Passed Passivation + 2 90/40500 33:01:12 Passed HT 190 C./23 h + 3 90/40500 33:01:48 Passed TC P35 (5 m) + 4 90/40500 33:02:24 Passed HT 190 C./30 min 2 1 90/40800 33:00:36 Passed 2 90/40800 33:01:12 Passed 3 90/40800 33:01:48 Passed 4 90/40800 33:01:48 Passed Ib LHE ZnNi (LLI) + 1 1 90/40600 33:00:36 Passed Passivation + 2 90/40600 33:01:12 Passed HT 190 C./23 h + 3 90/40600 33:01:48 Passed TC P35 (10 m) + 4 90/40600 33:02:24 Passed HT 190 C./30 min 2 1 55/25800 26:08:24 Passed 2 55/25800 26:09:00 Passed 3 55/25800 26:09:42 Passed 4 55/25800 26:10:30 Passed Ic LHE ZnNi (LLI) + 1 1 55/25800 26:10:12 Passed Passivation + 2 55/25800 26:15:00 Passed HT 190 C./23 h 3 55/25800 26:16:12 Passed 4 55/25800 26:17:24 Passed IIe LHE ZnNi (LLI) + 1 1 55/25800 26:07:48 Passed Passivation + 2 55/25800 26:09:36 Passed HT 190 C./23 h + 3 55/25800 26:17:24 Passed HT accord. to LHT4-4103 4 55/25800 26:27:00 Passed

(55) It can be deduced from Table 5 that the multilayer coating in accordance with the invention has exceptional corrosion resistance which is superior to the comparison specimens, provided that the layer arrangement is formed as continuous and does not have a defect close to the nick bed of the nick-break specimen as in specimen Ib, set 2.

(56) An overview of the layer thicknesses of the different specimens is shown in the following in table form.

(57) TABLE-US-00006 TABLE 6 Summary of the layer thickness determination in table form Layer thickness in m Nick bed Jacket surface Specimen ZnNi TopCoat ZnNi TopCoat designation Set No. MV* MV* MV** MV** Comments Ia 2 2 8.5 20.5 16.0 33.0 Ib 1 1 5.0 12.5 13.3 29.0 Ib 2 1 0.0 0.0 16.3 24.0 Hardly any ZnNi and no Top coat traceable in the nick bed Ic 1 1 6.5 0.0 9.0 0.0 IIe 1 1 7.5 0.0 18.7 47.0 *Mean value from two measured values **Mean value from three measured values

(58) It can therefore be recognized that on a presence of a multilayer coating in accordance with the invention, the corrosion resistance is considerably increased with respect to conventional coatings. This is due to the reduced hydrogen embrittlement due to the multilayer coating in accordance with the invention.