DE3816310A1 - Process for enriching titanium in the immediate surface zone of a component consisting of a nickel-based superalloy containing at least 2.0 % by weight of titanium, and use of the surface enriched according to the process - Google Patents

Abstract

Process for enriching titanium in the surface zone of a component consisting of a nickel-based superalloy with at least 2.0 % by weight of Ti to an average content of at least 25 % by weight down to a depth of at least 2 mu m, with a total depth of the enriched surface zone of at least 4 mu m, by a heat treatment, lasting for at least 1 hour, at 1100 to 1200@C in a nitrogen-containing atmosphere under a pressure of 0.1 to 10<5> Pa. Use of the surface zone as a wear-resistant, TiN-containing layer or as a substrate for the application of an additional anticorrosive and antioxidant layer of an Ni/Cr/Al/Si/Y/Ta/Co alloy. In the latter case, the titanium-enriched zone serves as a barrier layer for the Al against migration towards the interior and as an Al reservoir in subsequent operation. <IMAGE>

Description

Process for the enrichment of titanium in the immediate Surface zone of a component made of at least 2.0% by weight Titanium-containing nickel base superalloy and use the surface zone enriched by the process.

Technical field

Gas turbines for the highest demands. Increase in effectiveness grades requires higher gas temperatures and thus warmer Materials, more suitable material combinations and better ones Constructions for the individual components. The most important and most critical component is the turbine blade, taking protection layers against erosion, wear, corrosion and oxidation gain in importance at high temperatures.

The invention relates to the further development mechanically and / or gas turbine blades subject to high thermal stress and their protective layers, the advantageous properties dispersion-hardened alloys are increasingly used should. This also expands the problem circle of stable protective layers with a long service life and their Adhesion to the base material.  

In particular, it relates to an enrichment process of titanium in the immediate surface zone of a component from a nickel containing at least 2.0% by weight of titanium base superalloy to an average salary from at least 25% by weight to a depth of at least 2 µm with a total depth of the enriched surfaces zone of at least 4 µm.

It also relates to the use of titanium according to the Process enriched surface zone on a component a thermal machine.

State of the art

The demand for higher gas turbine efficiencies leads to an increase in gas temperatures and thus to an increase the thermal and mechanical stress the components, especially the blades. Add to that the Demand for better resistance to wear, Erosion, corrosion and oxidation in a wide temperature Area. Because one and the same material is contradictory One is not able to optimally meet requirements Forced to separate tasks: High temperature resistant Core material plus suitable protective layer. This is true additionally for all blade materials (super alloys), but especially for oxide dispersion hardened alloys. In order to be able to further increase the gas temperatures also used cooled hollow blades. To the mechanical load on the rotor body and the weight reduce, the wall thickness of the hollow blades continues to increase reduced. The inside wall temperatures rise, so that one is also forced to use internal protective layers against erosion, corrosion, oxidation etc. At the complexity of the geometry of modern refrigerated Buckets is the production of suitable, more durable, non-flaking protective layers inside the blade a problem that has hardly been solved satisfactorily.  

Protective layers - in particular Al ₂ O ₃ -forming surface zones - as they are also required for materials that have been hardened by oxide dispersion, can in principle be produced using the following processes:

• - Diffusion pack process (Pt / Al): galvanic application a 5 to 10 µm thick Pt layer as a diffusion barrier. Packing in Ni / Al powder and heat treatment. Since the Pt to Part diffuses to the surface, leaving its barrier effect in operation after. This method is also suitable not for complicated blade geometries with internal cooling.
• - Chemical precipitation from the vapor phase (CVD = chemical vapor deposition): substances are in the vapor / gas phase reacted at high temperatures and the reak tion products deposited on the substrate. The layer thickness is based on the geometry ("viewing distance") of the substrate dependent, so that in hollow bodies, at protruding corners and undercuts do not guarantee a sufficiently thick Precipitation is present.
• - Salt bath electrolysis: use of high temperature fluoride bathing as an electrolytic means of transport for e.g. Al, Si, Ti, B, rare earths etc. Here, too, is the electroly precipitation and its diffusion and anchoring with the core material (cathode) depending on the direction, so that the procedure for intricately designed hollow bodies can hardly be used.
• - Chemical nickel deposition: deposition of nickel hypophos phid (Ni + 4 - 7% P) and conversion into nickel phosphide. Use of nickel-boron as a reducing agent. The disadvantage consists in the introduction of P and B, which elements are difficult to remove.
• - Physical precipitation (vacuum evaporation) from the Vapor phase (PVD = physical vapor deposition): After this Processes include protective layers with high Cr and Al content of Ni / Cr / Al / Si / Y / alloys Ta / Co generated. Can hardly be used for hollow bodies.  
• - Vacuum plasma spraying: alloys forming outer layers of the Ni / Cr / Al / Si / Y / Ta / Co type can be observed under observation know more precautions after this procedure be injected. For hollow bodies (internally cooled turbines shoveling) this method is not to be used.

Material removal through wear and erosion (hard body erosion) now also plays a role in internal cooling increasing role. Among the wear-resistant materials offers itself among other things titanium nitride TiN, which a Hardness of over 1100 HV (Vickers units). Is TiN particularly erosion-resistant and also shows against fretting corrosion good behavior.

In principle, titanium can be applied to a substrate by flame spraying and plasma spraying. However, this always creates more or less porous layers, which practically always have a certain content of TiO ₂ . These oxide skins make it practically impossible to further treat them chemically, for example to obtain TiN. Therefore, the success of such a high-temperature use of titanium - even in the case of a mere intermediate layer or the basis for further layers - is at least doubtful.

In view of the steadily increasing mechanical, thermal and chemical stresses in the area of the gas flow exposed components of a gas turbine there is a large one Need to further develop suitable material combinations wrap and look for new combinations. This applies in particular especially for the extensive area of protective layers increased resistance to erosion, corrosion and oxidation especially in the upper temperature range.

Presentation of the invention

The invention has for its object on a component a layer made of a titanium-containing nickel-based superalloy with at least 25 wt .-% titanium by enrichment in the To produce surface zone. The layer should be with the bottom  material without jagged transitions and in Do not flake off or unfavorably ver to change. The layer should either serve as an outer boundary with advantageous physical properties or as an intermediate layer (diffusion barrier) for highly stressed components thermal machines (gas turbine blades) are used can. The method should also be independent of the geometry of the component even for complicated shapes, especially difficult accessible hollow body applicable without great expense be.

This object is achieved in that the component is subjected to a heat treatment in the temperature range between 1100 and 1200 ° C for at least 1 h in a nitrogen-containing atmosphere under a pressure of 0.1 to 10 ⁵ Pa in the aforementioned method.

The task is also solved in that the titanium enriched surface zone as against erosion and wear resistant, non-chipping, with the base material firmly connected, at least partially made of titanium nitride TiN existing surface layer of a thermally and mechanically highly stressed component of a thermal machine used becomes.

In addition, the task is solved in that the titanium Enriched surface zone as the basis for application one resistant to high temperature corrosion and oxidation capable of containing Cr, Al, Si, Y, Ta and Co. Nickel alloy existing protective layer and as a barrier layer against Al diffusion from said protective layer inside of the base material and as an Al reservoir for the said Protective layer in the operation of a mechanical, thermal and chemically highly stressed component of a thermal machine is used.  

Way of carrying out the invention

The invention is illustrated by the following figures described exemplary embodiments.

It shows:

Fig. 1 is a diagram of the titanium content in function of the distance from the ideal surface (hypothetical) for ver different nickel-base superalloys with different Lichem titanium content,

Fig. 2 shows a schematic cross section through the surfaces near portion of a component enriched in the surface zone of titanium,

Figure 3 is a schematic cross-section through the surfaces close match is a component having a titanium-enriched zone and a protective layer against high-temperature corrosion and -Oxydation. State at the beginning and in a first operating phase,

Figure 4 is a schematic cross-section through the surfaces close match is a component having a titanium-enriched zone and a protective layer against high-temperature corrosion and -Oxydation. State in a later phase of operation,

Fig. 5 is a perspective view in several sections of the hollow airfoil of an internally cooled gas turbine bucket including nozzle for abrasive blasting.

In Fig. 1, a diagram is shown which shows the titanium content as a function of the distance from the ideal surface for different nickel-based superalloys as the base material with different titanium content. The curves are hypothetical in nature and only show the basic, expected titanium distribution. Depending on the test conditions , the values may differ. The distance x is plotted in µm on the abscissa. The ordinate refers to the total Ti content in% by weight. Most of the titanium is in the form of the nitride TiN. Curve 1 relates to an oxide dispersion-hardened nickel-base superalloy with a Ti content of 2.5% by weight as the base material after it has been annealed in air under greatly reduced pressure. Curve 2 applies to a cast nickel superalloy with a Ti content of 3.4% by weight, which was annealed in nitrogen under greatly reduced pressure. Curve 3 relates to a cast nickel super alloy with a Ti content of 3.7% by weight, which was heat-treated in nitrogen under atmospheric pressure. Curve 4 applies to a wrought nickel superalloy with 2.5 wt.% Ti content, which was annealed in nitrogen under reduced pressure.

Fig. 2 shows a schematic cross section through the near-surface part of a component made of a nickel-based super alloy, which has a titanium-enriched surface zone. 5 is the base material (Ni superalloy), 6 is the surface zone enriched in titanium, which continuously merges into the base material 5 without a visible interface. The dash-dotted line is drawn as the ideal, invisible boundary 7 between base material 5 and zone 6 enriched with titanium. The thickness of the zone 6 enriched in titanium is denoted by "a" . "a" ranges between approx. 2 µm and 10. . . 20 µm. The expression p N ₂ with the arrowhead pointing at the surface indicates the nitrogen partial pressure required to carry out the process.

Fig. 3 shows a schematic cross section through the near-surface part of a component made of a nickel-based super alloy with a titanium-enriched zone and a protective layer against high-temperature corrosion and oxidation in the state at the beginning and in a first operating phase. 5 is the base material (Ni superalloy), 6 the zone enriched in titanium (in the present case as an intermediate layer), which merges into the base material 5 without a visible interface. 7 is the ideal boundary between base material 5 and zone 6 enriched in titanium with the thickness "a" . 8 represents a protective layer resistant to corrosion and oxidation at high temperature. This layer consists of a nickel alloy containing the elements Cr, Al, Si, Y, Ta and Co. 9 is the interface which is unevenly formed for the purpose of good anchoring between the zone 6 enriched with titanium and the protective layer 8 . The unevenness of 9 is mostly created by sandblasting. The thickness of the protective layer is denoted by "d" and is usually 100 µm to 250 µm. The figure shows the state immediately after manufacture or at the start of operation (first operating phase). Part of the aluminum in layer 8 diffuses into zone 6 (concentration gradient), which is indicated by the downward-pointing arrow provided with the symbol "Al" . On the other hand, the zone 6 prevents the change of the aluminum into the interior of the base material 5 .

Fig. 4 shows a schematic cross section through the near-surface part of a component made of a nickel-based superalloy with a zone enriched in titanium and a protective layer against high-temperature corrosion and oxidation in the state of a later operating phase. The individual layers and the reference numerals correspond those of Fig. 3. in consequence of the depletion (consumption) of aluminum the protective layer 8 moves the latter now from the zone 6 back into the latter. This is indicated by the symbol "Al" and an upward dashed arrow.

In Fig. 5 is a perspective view of the sections provided with hollow airfoil an internally cooled gas turbine blade is shown. In addition, a section (longitudinal section) of the nozzle of a device for abrasive blasting is shown in the same way. 10 represents a hollow, internally cooled airfoil (detail) of a guide or rotor blade of a thermally and mechanically highly stressed gas turbine. 11 are circumferential grooves on the entire inner circumferential surface (only partially shown), 12 are corresponding beads in between (also only partially drawn). 11 and 12 serve to enlarge the surface, to improve the impact cooling and to improve the construction (distribution, material savings) of the blade. 13 is a nozzle and 14 is a baffle plate of a device, not shown, for abrasive blasting of the inner surface of the airfoil 10 . The beam is indicated by sharp-edged, abrasive particles 15 (only drawn in the central part of the beam), and its direction is indicated by dash-dotted lines and arrows.

Embodiment 1 See Figs. 1, 2, 5

A thermally highly stressed vane of a gas turbine was treated in the following manner. The airfoil 10 was hollow, had grooves 11 and beads 12 (ribs) on the inside and consisted of an oxide dispersion-hardened nickel-base superalloy with the trade name MA 6000 from INCO in the zone-annealed, recrystallized, coarse-grained state (longitudinally oriented stem crystals). The base material 5 had the following composition:

Cr = 15% by weight W = 4.0% by weight Mo = 2.0% by weight Al = 4.5% by weight Ti = 2.5% by weight Ta = 2.0% by weight C = 0.05% by weight B = 0.01% by weight  Zr = 0.15% by weight Y₂O₃ = 1.1% by weight Ni = rest

The airfoil 10 with the wing profile had the following external dimensions:

Total length = 190 mm Largest width = 82 mm Greatest thickness = 24 mm Profile height = 30 mm Average wall thickness = 3 mm

The machined from full prismatic semi-finished blade profile was processed in order to increase the surface and improve the cooling on its inside by the method of electro-erosion in such a way that a whole number of circumferential grooves 11 and beads 12 was formed.

This method severely disturbs the approx. 10 µm immediate surface zone (crystal lattice) and has to be removed. This was done by abrasive sandblasting of the blade interior with sharp-edged particles 15 by means of the nozzle 13 and the deflection plate 14 . The exterior of the airfoil 10 was machined by conventional grinding. Care was taken to ensure that the surface roughness was low (approx. 2 to 4 µm) both inside and outside. The blade was then placed in a closed chamber with air of reduced pressure (poor "vacuum") and heated. The heat treatment was carried out under a pressure of 0.5 Pa at a temperature of 1200 ° C. for 1 hour. After cooling in the oven, the shovel was examined. A thin, very hard, shiny gold layer of TiN had formed on its surface. The examination with the microsensor showed a considerable accumulation of the titanium in the surface zone. The concentration had approximately the course of curve 1 in FIG. 1 (hypothetically). The thickness of the highly enriched surface zone averaged 2 µm on both the outer and the inner surface of the blade and was very uniform. The entire enriched zone was about 4 µm deep. The surface zone had a height of over 1000 HV (Vickers) and consisted mainly of TiN.

The hard surface zone 6 merged into the base material 5 without a visible border, adhered excellently to the latter, was insensitive to thermal shock and did not flake off. It could be used directly as an anti-erosion layer. This is of particular importance with regard to the internal cooling of the blade, since wear-causing particles must be expected in some areas in view of the insufficiently cleaned cooling air.

Embodiment 2 See Figs. 1, 2, 5

A highly stressed, internally cooled rotor blade for a gas turbine was manufactured from a cast nickel-based superalloy with the trade name IN 738 from INCO. The base material 5 had the following composition:

Cr = 16.0% by weight Co = 8.5% by weight Mo = 1.75% by weight W = 2.6% by weight Ta = 1.75% by weight Nb = 0.9% by weight Al = 3.4% by weight Ti = 3.4% by weight Zr = 0.1% by weight B = 0.01% by weight C = 0.11% by weight Ni = rest

The airfoil 10 had an airfoil profile with the following external dimensions:

Total length = 200 mm Largest width = 90 mm Greatest thickness = 23 mm Profile height = 28 mm Average wall thickness = 3.5 mm

The turbine blade was produced in one piece by the precision casting method with all the grooves 11 and beads 12 arranged in the interior of the blade 10 . In order to have a clean surface zone suitable for further treatment, the blade was cleaned and then chemically etched.

Then the blade was exposed to a nitrogen atmosphere at a temperature of 1100 ° C under a pressure of 10 Pa for 2 h. The titanium migrated from the inside of the base material 5 to the outside and accumulated in the surface zone 6 . After the workpiece had cooled, an intense golden yellow color could be determined on its surface. The investigation showed a Ti curve approximately according to curve 2 in FIG. 1 (hypothetically). The thickness of zone 6 enriched with Ti was approximately 4 μm (high concentration) or 8 μm (low concentration). The majority of the titanium was bound to nitrogen as TiN. For the use of zone 6 enriched in titanium as a surface layer with high resistance to erosion and wear, the statements made under example 1 apply.

Embodiment 3 See Fig. 1, 2, 3, 4, 5

A thermally highly stressed guide blade for a gas turbine was produced, which had an internally cooled hollow blade 10 . A cast nickel-based superalloy with the trade name IN 939 from INCO with the following composition was used:

Cr = 22.4% by weight Co = 19.0% by weight Ta = 1.4% by weight Nb = 1.0% by weight Al = 1.9% by weight Ti = 3.7% by weight Zr = 0.1% by weight C = 0.15% by weight Ni = rest

The airfoil 10 with the wing profile had the following external dimensions:

Total length = 170 mm Largest width = 70 mm Greatest thickness = 20 mm Profile height = 26 mm Average wall thickness = 3 mm

The turbine blade was manufactured as a precision casting with grooves 11 and beads 12 in the interior of the blade. The raw cast blade was processed outside and inside by sandblasting with sharp-edged particles 15 in order to create favorable conditions for the production of the subsequent layers. Care was taken to ensure that the interior, which should only have an anti-erosive surface zone, was as smooth as possible. In contrast, a certain minimum roughness (approx. 5-10 μm) was desirable on the outer lateral surface of the airfoil 10 , in order to ensure better adhesion conditions for the additional protective layer to be applied, with high corrosion and oxidation resistance. The entire blade was cleaned and chemically etched.

The blade was then annealed for 3 hours at 1150 ° C. in a nitrogen atmosphere under a pressure of 10 ⁵ Pa (approximately 1 bar). A comparatively thicker, titanium-enriched zone 6 of a total of approx. 15 µm depth (high enrichment to approx. 10 µm depth) was formed both on the lateral surface and inside, approximately in accordance with the concentration curve according to curve 3 ( FIG. 1).

The hard surface zone 6 of 1100 HV (Vickers) on the inside (cooling channel) of the airfoil 10 was used directly as a layer against solid erosion. The corresponding outer zone 6, however, served as the basis (intermediate layer) for the application of a protective layer 8 against corrosion and oxidation at high temperatures. A nickel alloy of the Ni / Cr / Al / Si / Y / Ta / Co type with the following composition was used for this protective layer 8 :

Cr = 23% by weight Al = 9.5% by weight Si = 2.5% by weight Y = 0.5% by weight Ta = 1.0% by weight Co = 10.0% by weight Ni = rest

The protective layer 8 was applied to the outer lateral surface of the airfoil 10 by vacuum plasma spraying in a thickness of approximately 100 μm. Zone 6 acts in the vorlie case thanks to its high titanium content as a diffusion barrier against migration of the aluminum from the protective layer 8 towards the inside into the base material 5 . At the same time, it serves as a reservoir for the aluminum during operation. The latter diffuses slowly into zone 6 in the first operating phase, where it forms inter alia with the titanium the intermetallic compounds TiAl and Ti ₃ Al. This process can also be at least partially initiated before commissioning by an additional heat treatment of the blade.

In a later operating phase - when protective layer 8 is depleted of aluminum - the intermetallic compounds disintegrate again and the aluminum migrates from zone 6 back to layer 8 . In order to be able to perform the additional function of the reservoir, zone 6 should therefore have a certain minimum thickness and a high Ti content, the largest possible proportion of which should be in metallic form. The processes must therefore be optimized in this direction.

Embodiment 4 See Figs. 1, 3, 4

A blade for a gas turbine was produced from a wrought nickel-based superalloy with the trade name Nimonic 80A. The base material 5 had the following composition:

Cr = 19.5% by weight Al = 1.4% by weight Ti = 2.4% by weight Zr = 0.06% by weight Mn = 0.30% by weight Si = 0.30% by weight B = 0.003% by weight C = 0.06% by weight Ni = rest

The full airfoil designed without cooling channels showed the following Dimensions on:

Total length = 175 mm Largest width = 92 mm Greatest thickness = 23 mm Profile height = 29 mm

The turbine blade was pre-forged and by mechanical Editing brought into the final form. Thereupon was their surface roughened by abrasive sandblasting (upper surface roughness approx. 10 µm) to ensure liability for the later to improve the protective layer to be applied. It followed chemical etching of the surface.

The blade was then exposed to a nitrogen atmosphere at a temperature of 1100 ° C. and a pressure of 1000 Pa for 6 h. Zone 6 enriched with titanium reached a depth of approx. 10 µm (thickness of the part with high accumulation approx. 6 µm) and a hardness of approx. 1050 HV (Vickers). The course of the composition roughly corresponded to curve 4 ( FIG. 1).

Zone 6 was used as the basis for the application of a protective layer 8 against corrosion and oxidation. The protective layer 8 of the Ni / Cr / Al / Si / Y / Ta / Co type had the following composition:

Cr = 20.5% by weight Al = 11.5% by weight Si = 2.5% by weight Y = 0.5% by weight Ta = 1.0% by weight Co = 12.0% by weight Ni = rest

The protective layer 8 was applied in a thickness of 200 μm to the outer surface of the airfoil by the vacuum plasma spraying method. Otherwise, the statements made in Example 3 about this protective layer apply.

The invention is not restricted to the exemplary embodiments. According to the present method, the immediate surface zone 6 of any component made of a nickel-base superalloy containing at least 2.0% by weight of titanium can have an average content of at least 25% by weight of titanium to a depth of at least 2 μm total depth of the enriched surface zone 6 of at least 4 µm can be enriched. The proposed heat treatment takes place in the temperature range between 1100 and 1200 ° C for at least 1 h in an atmosphere containing nitrogen under a pressure of 0 to 10 ⁵ Pa. An upper limit of the duration of exposure is not due to technical, but only due to economic considerations, which is why it is unnecessary in the claim. The atmosphere consists of technically pure nitrogen or air, whereby attention must be paid to the partial pressure of nitrogen. The surface zone 6 is advantageously freed beforehand by mechanical processing or chemical treatment of oxide layers and / or disturbed structural zones.

The base material 5 of the component preferably consists of an oxide dispersion-hardened nickel-based superalloy with 15-20% by weight Cr, 4.5-6% by weight Al, 2% by weight Mo, 3.5-4% by weight W, 2.5 wt% Ti, 0-2 wt% Ta, 0.15-0.19 wt% Zr, 0.01-0.05 wt% C, 0.01 wt % B, 1.1% by weight Y ₂ O ₃ , balance Ni.

The surface zone 6 enriched according to the method is used as an erosion-resistant and wear-resistant, non-flaking surface layer which is firmly bonded to the base material 5 and at least partially consists of TiN, in particular as an inner layer in the case of hollow blades, or as a basis for applying high-temperature anti-corrosion / Antioxidation layer 8 , where it acts as a diffusion barrier and as a reservoir for aluminum. The protective layer 8 against corrosion and oxidation preferably consists of an alloy with 20.5-23% by weight Cr, 9.5-11.5% by weight Al, 2.5% by weight Si, 0.5% by weight % Y, 1% by weight Ta, 10-12% by weight Co, balance Ni.

Claims (9)

1. A method for enriching titanium in the immediate surface zone ( 6 ) of a component made of a nickel-based superalloy containing at least 2.0% by weight of titanium to an average content of at least 25% by weight to a depth of at least 2 μm at a total depth ( a ) of the enriched surface zone ( 6 ) of at least 4 µm, characterized in that the component undergoes a heat treatment in the temperature range between 1100 and 1200 ° C for at least 1 h in an atmosphere containing nitrogen under a pressure of 0.1 is subjected to 10 ⁵ Pa. 2. The method according to claim 1, characterized in that the nitrogen-containing atmosphere from technically pure Nitrogen exists. 3. The method according to claim 1, characterized in that the nitrogen-containing atmosphere consists of air and has a pressure of 0.1 to 10 Pa. 4. The method according to claim 1, characterized in that the surface zone ( 6 ) of the component before the heat treatment by mechanical processing or chemical treatment of oxide layers and / or disturbed structure zones is freed. 5. The method according to claim 1, characterized in that the component made of an oxide dispersion hardened nickel-base superalloy with 15-20 wt .-% Cr, 4.5-6 wt .-% Al, 2 wt .-% Mo, 3.5 -4 wt% W, 2.5 wt% Ti, 0-2 wt% Ta, 0.15-0.19 wt% Zr, 0.01-0.05 wt% C, 0.01% by weight B, 1.1% by weight Y ₂ O ₃ , balance Ni. 6. Use of the surface zone ( 6 ) enriched in titanium according to the method according to one of the preceding claims as resistant to erosion and wear, non-flaking, firmly bonded to the base material ( 5 ), the at least partially consisting of titanium nitride TiN surface layer of a thermally and mechanically highly stressed component of a thermal machine. 7. Use according to claim 6 as internal wear solid protective layer of one equipped with cooling channels hollow gas turbine blade. 8. Use of the surface zone ( 6 ) enriched in titanium according to the method according to one of claims 1 to 5 as a basis for applying a high-temperature corrosion and oxidation resistant, containing a Cr, Al, Si, Y, Ta and Co containing nickel alloy existing protective layer ( 8 ) and as a barrier layer against Al diffusion from said protective layer ( 8 ) into the interior of the base material ( 5 ) and as an Al reservoir for said protective layer ( 8 ) in the operation of a mechanically, thermally and chemically highly stressed component thermal machine. 9. Use according to claim 8 as an inner and / or outer intermediate layer of a hollow gas turbine blade equipped with cooling channels, the outer protective layer ( 8 ) of an alloy with 20.5-23% by weight Cr, 9.5-11, 5% by weight Al, 2.5% by weight Si, 0.5% by weight Y, 1% by weight Ta, 10-12% by weight Co, balance Ni.