JPS5842255B2 - MCRALY - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to alloys, and more particularly to nickel, cobalt or nickel-cobalt coated alloys with improved high temperature corrosion resistance.

Modern jet engine superalloys are susceptible to oxidative attack and hot corrosion at very high temperatures, and therefore such superalloys may be coated with superalloys having a different composition and having greater resistance to oxidative attack and corrosion. It is known that this is common.

There are generally two basic types of coatings.

One such method is an aluminide coating such as that disclosed in U.S. Pat. No. 3,102,044 or U.S. Pat. Formed by diffusion.

Another format is the surface-mounted MCrAI
Y-type coatings, such as Ni CrAIY as described in US Pat. No. 3,754,903.

CoCr as described in U.S. Pat. No. 3,676,085
AIY, U.S. Patent Application No. 4 filed May 13, 1974
N1CoCrAIY as described in US Pat. No. 69186, FeCr as described in US Pat.
It is a coating such as AI Y.

A particularly useful coating, the MCrAIY coating, is approximately 8-30% chromium, 5-15% chromium, in substantial weight percent.
aluminum, up to 1% of a reactive metal selected from yttrium, scandium, thorium and other rare earth elements, the balance selected from the group consisting of nickel, cobalt and nickel-cobalt, preferably about 0.012 It was applied to a thickness of -0.015 crIl.

In contrast to such surface-mounted coatings, diffusion aluminide coatings are typically applied by reacting the aluminum with the deoxygenated surface of the article to be protected.

This aluminide layer is formed as a guard band of varying component concentrations that have consumed the matrix components.

This aluminide layer oxidizes to form an inert protective oxide.

In U.S. Pat. Nos. 3,677,789 and 3,692,554 a separate layer of a metal selected from the platinum group is applied prior to the aluminum diffusion process.

However, many modern alloys have complex properties, and because the coating components are partially derived from the components of the base alloy, it is difficult to control the coating components to form a suitable protective oxide.

Moreover, in diffusion techniques, the coating does not naturally form homogeneously; for example, for metals of the platinum group, they are concentrated in high concentrations on the surface.

The existence of such a gradient is of course disadvantageous.

This is because the ingredients change with use and the coating loses its effectiveness.

Although such prior coating compositions provided improvements over previous alloy compositions, further improvements were needed, particularly with respect to, for example, high temperature corrosion resistance.

The present invention seeks to provide a nickel, cobalt and nickel-cobalt coated alloy composition with improved high temperature corrosion resistance.

In particular, the present invention provides substantially 8-3% by weight
Reactive metal selected from the group consisting of 0% chromium, 5-15% aluminum, 1% or less yttrium, scandium, thorium and other rare earth elements, 3-12
% of a noble metal selected from the group consisting of platinum or rhodium, nickel, cobalt and the remainder selected from the group consisting of nickel-cobalt.
It is an object of the present invention to provide a type IY alloy coating composition.

The inclusion of noble metals as alloying components produces substantially uniform diffusion throughout the composition, homogenizing the properties of the MCrAIY type surface-mounted coating.

In one preferred embodiment, the reactive metal is yttrium and the noble metal is 5-10% platinum.

In another embodiment, the reactive metal is
'Jium, and the noble metal is 5% rhodium.

The invention will now be described in detail by way of example embodiments with reference to the accompanying drawings.

The alloys of the present invention exhibit significantly improved high temperature corrosion resistance,
It is believed to be particularly useful as a coating for current superalloys.

The alloy according to the invention is itself corrosion resistant and does not depend on reaction with the substrate for its protective effect.

Furthermore, these alloys are uniform throughout their thickness and therefore exhibit more durable and reliable protective properties than the aluminide coatings described above.

The desired result was selected from the group consisting of approximately 830% chromium, 5-15% aluminum, 510% platinum or rhodium, and less than 1% yttrium, scandium, thorium, and other rare earth elements, by weight percent. It is obtained by a basic alloy with a remainder consisting of reactive metals, nickel and/or cobalt.

One preferred alloy is 0.5% yttrium and 5-1
0% platinum is used.

By adding a certain amount of platinum or rhodium as an alloy coating to this MCrAIY type coating, not only the sulfidation resistance is significantly increased, but also the reactive gold fi(Y,
Sc, Th, La, and other rare earth elements, which normally confer oxide adhesion to the underlying substrate, can promote oxide adhesion even in the absence of these elements. What was discovered is astonishing.

Regarding the method of applying this alloy as a coating to the surface to be protected, the presence of platinum or rhodium in the coating alloy generally rules out the use of vapor deposition techniques since platinum or rhodium has a low vapor pressure. .

However, other techniques are available for obtaining coatings of suitable composition.

For example, it has been recognized that the coating may be applied using a simultaneous MCrAIY type vapor deposition and platinum or rhodium spraying process.

Alternatively, the coating may be accomplished by plasma flash techniques.

The invention will be better understood from the following examples.

Example 1 Ni-8Cr-6AI doped with platinum and rhodium
The alloy was made by conventional arc melt drop casting technology.

The test piece with the composition shown in the graph of Figure 1 is 1crrL×IC
rrL×0.2 crrL, and a high temperature corrosion test was conducted as follows.

Alloy specimens were spray coated with an aqueous solution of Na2so4, dried and weighed.

After achieving a coating of 0.5■-C7rL"Na25O, the specimens were oxidized for 20 hours at 1.000 DEG C. in an atmosphere of 0.02.

The weight of the specimen was recorded continuously as a function of time, and changes in weight were converted to weight increments per unit area.

This is shown in FIG.

As shown, adding 25 weight percent platinum did not significantly improve the performance of the Ni-8Cr-6AI alloy in this test.

However, significant improvements in performance were obtained when 5 or 10 weight percent platinum was added.

The test piece of Ni-8Cr-6Al-5Rh alloy is 1opt.
It was almost the same as that of the alloy.

Example 2 Test specimens were made as in Example 1 with the compositions shown in FIGS. 2 and 3.

These specimens were subjected to high temperature cyclic oxidation tests and surprisingly it was found that specimens containing platinum or rhodium had improved oxide adhesion of Al2O3 formed on the alloy.

It has been found that alloys with 5-10 weight percent pt are superior to 2.5 weight percent Pt alloys, and the latter are significantly superior to alloys without such modification.

Oxide adhesion on Ni-8Cr-6AI-5Rh alloy at 1200°C is higher than that on Ni-8C at the same temperature.
It was found to be equal to that of r-6AI-10Pt.

Example 3 All alloy test pieces are 1c1rlX0.8cfIIX0.1
-0.2CrfL, respectively Ni -17
Cr-12AIO, 5Y, Ni-17Cr-12A
I-5Rh-0,5Y, Ni-17Cr-12
Al-10Pt0.5Y1Co-17Cr-11AI-
0,5Y, C0-17Cr-11AI-5Rh-0,
5Y, C.

17Cr-11AI-10Pt-0,5Y, dimensioned and weighed, and then 0.5Y.
5 2. Coated with OWI9AmNa2SO.

These specimens were then subjected to 14 cycles of testing.

Each cycle included oxidizing in air at 955° C. for 20 hours, cooling to room temperature, rinsing, and reweighing.

This sequence was repeated until destruction.

The results obtained for a set of specimens at 955° C. using 2 m9/crtt of salt are shown in FIG.

CoCrAIY is basically more resistant to high temperature corrosion than Ni CrAIY, but CoCrAIY or Ni
It will be appreciated that the addition of pt or Rh to either CrAIY can dramatically improve its high temperature corrosion resistance.

Example 4 Ni-17Cr-12AI-0,5Y, respectively
Ni-17Cr-12A1-5Rh-0,5Y, N
i-17Cr-12AI-5Pt ~0.5Y, N
An eroded bar made of i17Cr-12AI-10Pt-0,5Y was repeatedly subjected to a high-temperature corrosion burner test at 955° C. using 35 ppm of seawater mixed into the fuel prior to combustion.

Severe corrosion occurred on the tips of both the Ni Cr AI Y-based composition and the rhodium modified composition after 110 hours.

High temperature zone failure was observed in all bars between 300 and 400 hours.

Specimens modified with rhodium lasted somewhat longer than those of the basic composition.

Although the rhodium modified composition showed little improvement in this test, the nature of the failure was unusual and the results are somewhat questionable and not conclusive.

In contrast, the platinum modified composition exhibited surprisingly increased high temperature corrosion resistance compared to the base composition.

This composition showed no signs of failure up to 675 hours,
At this point the test was terminated.

It is to be understood that the foregoing description is provided to disclose the invention to the extent that it may be practiced by one skilled in the art, and is not intended to limit the scope of the invention.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the sulfidation properties of various NiCrAl alloys at 1000°C. Figures 2 and 3 are respectively in air at 1100℃ and 1
Figure 1 shows the oxidation properties of various NiCrAl alloys at 200°C. Figure 4 shows temperature at 955°C.2. Orl19-am ”Na2S
Various CoCrAIY and N1CrAI in O4
It is a graph showing the high temperature corrosion characteristics of Y. Figure 5 is 955°C, 0.5Tn?・+, m ”N
1 is a graph showing the high temperature corrosion characteristics of Ni CrAIY alloy in a2 SO4.

Claims (1)

[Claims] l For MCrAIY type coating alloys, the coating composition is substantially 8-30% chromium, 5-15% by weight.
% aluminum, up to 1% of reactive metals selected from the group of yttrium, scandium, thorium and other rare earth elements, 3-12% of precious metals selected from the group consisting of platinum and rhodium, nickel, cobalt and nickel. and a remainder selected from the group consisting of leucobalt.