JPS5917189B2 - Thermally protected superalloy structure - Google Patents

Description

[Detailed description of the invention] The present invention relates to thermally protected superalloy structures.

Plasma-sprayed metal/ceramic thermal barrier coatings using stabilized zirconium oxide protect metal elements exposed to high temperature conditions, and generally overcome the effects of substrate metal depth and thermal transitions. Widely used to reduce Such systems are commonly used in combustion chambers, intermediate ducts and afterburner liners in gas turbine engines, but they are also used to protect vane platforms and airfoils at various stages. It is good to be treated. The most important feature of such coatings is their thermally insulating properties. This is because the magnitude of the reduction in base metal temperature and transient thermal stress is related to the low thermal conductivity of the oxide component and the thickness of the coating.
Generally, the properties required for practical thermal barrier coatings are as follows. (a) Low thermal conductivity.

(b) have sufficient tack to resist cracking due to thermal stress, i.e. have good interparticle and substrate adhesion;

(c) the metal constituents are maximally metallurgically uniform;
and have oxidation/high cavity corrosion resistance.

(d) The coefficient of thermal expansion between the ceramic and the matrix alloy is as close as possible.

(e) The required crystal structure (cubic zirconia) is fully stabilized to minimize the effects of nonlinear thermal expansion caused by structural transformation.

(f) Repairs are possible during manufacturing and after sale.

Several ceramic monometallic systems based on magnesia stabilized zirconia are currently employed in the art. Generally, the base metal is HastellOyX,
A nickel- or cobalt-based superalloy such as TD-Nickel, or Hayness 188, with a bond layer of Nickel-5(f) aluminum or Nickel-20% chromium alloy and an intermediate metal layer of stabilized zirconia ceramic. and a top layer of stabilized zirconia. Such a layer is plasma sprayed onto the base metal, and those skilled in the art have recognized that performance can be improved and coating costs reduced by a nominally continuous gradient treatment process, which reduces the concentration of zirconia. ,
It increases continuously from O% at the interface between the bond layer and the base metal to almost 100% at the outer surface. Typically such coatings are deposited to a thickness of about 380 microns. Details of various such techniques can be found in U.S. Pat.
, 091,548 and 3,522,064.

One of the currently preferred ceramic components is zirconia, which may be used alone or mixed with materials such as magnesium oxide, calcium oxide, yttrium oxide, La2O3, cl2O3, and these materials are more desirable. It is known to stabilize zirconia in the cubic crystal form.

Accordingly, one of the best means currently known to those skilled in the art for protecting nickel and cobalt-based superalloys from high temperature environments consists of a zirconia-based ceramic coating. This coating is adhered to a base coating of Nickel-chrome or Nickel-aluminum alloy, and in this coat 4' ink the concentration of ceramic increases gradually or discontinuously from the substrate to the upper coating. are doing. Although such advanced systems are known to perform well, it has been found that when failure occurs, it occurs due to oxidative degradation of the metal components and subsequent spalling of the ceramic top layer. Ivy.

Furthermore, when damage occurred, it was difficult to repair the damaged article because the metal components were resistant to available acid removal solutions. In accordance with the present invention, it has been found that by appropriate selection of the bond coat metal, significant improvements in thermal barrier performance and repairability of the article can be obtained. Accordingly, one object of the present invention is to provide improved ceramic/metal thermal barrier coatings for nickel and cobalt-based superalloys.

This and other objects of the invention will become readily apparent from the following description. According to the heather invention, as a bond coating and grading metal for zirconia-based ceramic,
The thermal resistance of the barrier is improved by using an alloy consisting of 25% chromium, 10-18% aluminum, less than 1% yttrium and the balance a material selected from the group consisting of cobalt, iron, nickel and nickel-cobalt. was found to be surprisingly improved.

Such materials are known as MCrAlY alloys and are described in U.S. Pat. Nos. 3,542,530 and 3,676,085.
No. 3,754,903 and U.S. Patent Application No. 469,186, co-filed May 13, 1974 (U.S. Pat.
, No. 026). The concentration of the bond coating and zirconia preferably varies continuously from 0% ceramic at the interface between the base material and the bond coating to 100% ceramic at the exposed surface; It should be understood that if a device to vary the concentration drastically is not available, one or more layers of discontinuously increasing concentrations of zirconia may be used. The zirconia used in this coating is preferably stabilized into a cubic crystalline form by the use of an amount of calcium or magnesium oxide, as is well known in the art.

Additionally, the zirconia may contain other oxides such as Y2O3 and La2O3, or metastabilizers such as Cl2O3, which are known to be permanent cubic stabilizers for zirconia. By choosing the compressive strength and coefficient of thermal expansion corresponding to the properties of the metal matrix, the properties of the ceramic part can be made suitable for thermal shock resistance by mixing with cubic stabilized zirconia. Non-stabilizers such as nickel oxide, zinc oxide and cobalt oxide may be added. These specific techniques do not themselves form part of the heather invention, and the term "zirconia" as used hereafter includes zirconia-based ceramic materials, which may be pure zirconia or the examples mentioned above. It can be any of zirconia mixed with one or more additives. The thermal barrier coatings of the present invention may be applied by techniques well known in the art using commercially available equipment.

In the following example, the nozzle (AlO6F45H-1), 4
0 kilowatt power supply
lPS-61M) and Nimoku's powder feeder (Plasm
It was attached using a minigun (PlasmadynemOdellO68) using a plasmadynemOdellOO8A).

One powder feeder contained bond coated alloy and the other powder feeder contained zirconia, both pressurized with argon. By varying the flow rates of the individual powder feeders, thermal barrier coatings with continuously varying concentrations were obtained. The choice of powder particle size of the material is not critical and it has been found that for the equipment used it is preferred that the particle size of the bond coated alloy is in the range 0.03 to 0.05 m1&. The particle size of this material is not critical, but is specific to the equipment used, as smaller particle sizes tend to melt too quickly and block the nozzle of the spray gun.
Example 1 A Haste 110yX plate was coated with zirconia stabilized with continuously varying concentrations of nickel chromium and MgO for 100 hours and 200 hours at approximately 980°C.
A static oxidation test was performed for an hour.

Metallographic examination of the coating structure after this test revealed that the nickel chromium component had been significantly oxidized after 100 hours. Other samples are 109
It was oxidized for 1 hour at 5°C and then water quenched.
Metallographic examination of the structure of the coating after such treatment shows that the degraded nickel is almost completely oxidized, with cracks running through the coating and perpendicular to the direction of the base metal. Ivy.

6 containing zirconia stabilized with 17% MgO
The same goes for Hastell Oy test was conducted.

Metallographic examination of such samples after tests corresponding to the examples described above showed that the bond coating was less oxidized and therefore the expected working life of the coating was longer. . Fluidized bed tests were also conducted on various samples, in which the material was heated to 980°C for 2 minutes.
It was cooled for 2 minutes in a chamber vortex. Testing was continued for 100 cycles using samples containing cobalt, chromium, aluminum, and yttrium, and adhesion of the coating to the substrate alloy, gold, was satisfactory, and metallographic tests showed that the components were partially It was only oxidized to However, the nickel chrome sample was completely oxidized. Example 2 Actual size Ha from JT8D-17 gas turbine engine
Several stellOyX burner cylinders are taken out, and the above-mentioned MgO/ZrO2 concentration changes continuously on the inner peripheral surface.
- coated with cobalt/chromium/aluminum/yttrium alloy and experimentally tested on engines.

Claims (1)

Claims: 1. A substrate of a material selected from the group consisting of nickel-based or cobalt-based superalloys, a metal bond coating on the substrate, and a zirconia-based ceramic thermal barrier coating on the metal bond coating. For thermally protected superalloy structures, the metal bond coating is substantially 15 to 4
0% chromium, 10-25% aluminum, 1%
A superalloy structure characterized in that it is an alloy consisting of yttrium and the remainder of a material selected from the group consisting of iron, cobalt, nickel and a mixture of nickel and cobalt. 2. The material of the ceramic thermal barrier coating is mixed with the alloy of the metal bond coating in such a manner that the concentration of ceramic material increases continuously from the interface with the substrate to the finished surface. A superalloy structure according to scope 1.