Rhenium-containing protective coating with high corrosion and oxidation resistance

The present invention relates to a protective coating for metallic components, in particular gas turbine components from superalloys nickel or cobalt-based. protective coatings for metallic components, the corrosion resistance thereof and / or to increase resistance to oxidation, are in accordance with the Known in the art in great number. Most of these Coatings are known by the collective name MCrAlY, where M represents at least one element selected from iron, nickel, cobalt and is further essential constituents chromium, aluminum and Yttrium or yttrium equivalent element from the group of the rare earths are. Typical coatings of this type are known for example from U.S. Patent 4,005,989. From US-PS 4,034,142 is also known that an additional amount of Silicon, the properties of such protective coatings further can improve. From EP-A 0194392 are still numerous special compositions for protective coatings of above type with admixtures of other elements for various known applications. It is also the element rhenium with Admixtures to 10% (by weight) among many other Optional components mentioned. Due to the consistently low chromium content all described in this document under layers of 20% and little else specified broad areas of However, possible admixtures is not specified Coatings qualified for special conditions, the z. B. in stationary gas turbines with high inlet temperature occur if this except at full load even in partial load operation be operated over prolonged periods, or related uses, such. as in aircraft engines.

From U.S. Patent 4,451,299 a protective coating is of Type MCrAlY produced with the following composition:<sl><li>15 to 45% chromium</li><li>7 to 20% aluminum</li><li>0.1 to 5% yttrium</li><li>0 to 10% of at least one of the metals platinum, rhenium, Silicon, tantalum, and manganese,</li></sl>wherein M is at least one of the metals iron, cobalt and nickel is. The patent relates particularly to the improvement the oxidation resistance of protective coatings by superficial melting.

Starting from this prior art it is the object of the present Invention to provide a protective coating high corrosion resistance both at intermediate temperatures comprises as well at high temperatures. The corrosion and to oxidation properties in the temperature range from 600 to 1150 ° C are improved so that in particular those protective coatings in stationary gas turbine plants with inlet temperatures for example, above 1200 ° C, which in the partial load or full-load work, can be used. Also, the corrosion resistance and oxidation resistance of Coatings for other applications to be increased.

This object is achieved by a protective coating reached which contains the following components (in weight per cent):<sl><li>1 - 20% rhenium,</li><li>22 - 50% chromium,</li><li>0 - 15% aluminum, whereby the share of chromium and aluminum, together at least 25% and at most 53% is,</li><li>0.3 to 2% of a total of at least one reactive element the group of rare earths, in particular Yttrium,</li><li>0 - 3.% silicon,</li></sl>Remainder of at least one of the elements of iron, nickel, cobalt, preferably only nickel and / or cobalt. The protective coating can the usual incidental impurities course and the usual for alloys of this type admixtures contain. It is also known from the literature that not affect certain optional components, a protective coating or from various points of their production even improve or their properties. The present Invention is also protective coatings with a total proportion choosing components of max. 15%, in particular in the range of few percent comprise. Typical known from the literature Optional components for protective coatings and their shares are:<sl><li>0 - 5% hafnium,</li><li>0 - 12% tungsten,</li><li>0 - 10% manganese,</li><li>0 - 15% tantalum,</li><li>0 - 5% titanium,</li><li>0 - 4.% niobium,</li><li>0 - 2.% zirconium.</li></sl>

The present invention utilizes the fact that rhenium as an admixture in protective coatings their life under corrosive or oxidizing influences can improve significantly with its Action despite the lower price the positive effects of Platinum and other platinum group metals is similar. The addition of rhenium therefore, for different purposes optimized layers continue to improve.

cheap as such for applications. B. in stationary gas turbines Areas have 1 - 15% rhenium, preferably 4 - 10%, more preferably about 7% were found. For this application is in the With regard to the ductility of an aluminum content 7-9%, preferably from about 8% suitable. To at intermediate temperatures to achieve a good corrosion resistance to about 900 ° C, should be a proportion of chromium 28-32% are provided. In this case, supports a portion of 1 - 2% silicon, the effect of chromium and aluminum and promotes the adhesion of itself because the aluminum content forming protective aluminum oxide. A portion of 25-35% Nickel improves Ductility and simultaneously reduces the interdiffusion over the base material of the coated component, provided it is a nickel-based base material or a superalloy These high-nickel. The remaining balance cobalt gives good corrosion properties at high temperatures, the be further improved by the rhenium content.

above for stationary gas turbines with high inlet temperature for example 1200 ° C is therefore the following composition qualified:<sl><li>1 - 15% rhenium, preferably 4 - 10%,</li><li>25 - 35% nickel, preferably about 30%,</li><li>28-32% chromium, preferably about 30%,</li><li>7-9% aluminum, preferably about 8%,</li><li>1-3% silicon, preferably about 1.5%</li><li>0.3 to 2% yttrium, preferably about 0.6%,</li></sl>

Balance cobalt, incidental impurities and optional components as mentioned above. A preferred area of ​​application for these protective coatings are the front blades and components in the entry area of ​​a stationary gas turbine with at Full load high inlet temperature, the time, also in the partial load range intended to operate.

For other applications, eg. As aircraft engines, a rhenium content also the life there for use layers increase. For this purpose, the following composition as an example specify:<sl><li>1 - 15% rhenium, preferably 4 - 10%,</li><li>22-26% chromium,</li><li>9-15% aluminum, preferably 10 - 13%,</li><li>0.3 to 2% of a total of at least one reactive element the group of rare earths, in particular yttrium,</li><li>0-30% cobalt, preferably 0 - 15%,</li><li>0-3% silicon, preferably 1-2%,</li></sl>

Balance mainly nickel, and impurities and Optional components as mentioned above.

Even with layers that are particularly resistant to corrosion at about 600 to 850 ° C (so-called HTK II) are adapted to bring a Admixture according to the invention of rhenium advantages such. B. the following composition:<sl><li>1 - 15% rhenium, preferably 4 - 10%,</li><li>25 - 50% chromium, preferably 35 - 45%,</li><li>0 - 3.% aluminum, preferably a 0 - 1%</li><li>0.3 to 2% yttrium, preferably 0.6%</li><li>0.3 to 3% silicon, preferably 1-2%,</li></sl>

Remainder being mainly at least one of the elements of iron, Cobalt, nickel, as well as impurities and as optional components mentioned above.

The present invention is not limited to the procedures set Examples, but generally includes the improvement of against corrosion and oxidation under various conditions specified layers by adding small or larger Shares of rhenium.