Alloy composition for the manufacture of protective coatings, its use, process for its application and super-alloy articles coated with the same composition

Abstract

Alloy composition for the manufacture of protective coatings, comprising cobalt, nickel, chromium, aluminum, yttrium and iridium in amounts so as to obtain the phases α, β and σ, in particular for coating a super-alloy article. Preferably, such super-alloy article is a turbine component.

Claims

1. An alloy composition for the manufacture of protective coatings, the alloy composition comprising, by weight, cobalt in amounts from 10 to 30%, nickel in amounts from 30 to 70%, chromium in amounts from 15 to 20%, aluminum in amounts from 8 to 12%, yttrium in amounts from 0.1% and 2%, and iridium in amounts from 0.5 to 3.5%.

2. The composition according to claim 1, further comprising rhenium.

3. The composition according to claim 2, wherein the composition comprises less than 2% by weight of rhenium.

4. The composition according to claim 2, wherein the rhenium is present in an amount of from 0.5% to 1.5% by weight.

5. The composition according to claim 2, wherein the amounts of cobalt, nickel, chromium, aluminum, yttrium, rhenium and iridium are such to obtain the formation of phases α and σ.

6. The composition according to claim 5, wherein the amounts of cobalt, nickel, chromium, aluminum, yttrium, and iridium are such to obtain the formation of a phase β.

7. The composition according to claim 5 wherein the amounts of cobalt, nickel, chromium, aluminum, and iridium are such to obtain the formation of a phase γ.

8. The composition according to claim 1, comprising, by weight, 24.1% of cobalt, 47.59% of nickel, 16.8% of chromium, 9.7% of aluminum, 0.41% of yttrium, and 1.40% of iridium.

9. The composition according to claim 1 wherein the composition is present in powder form.

10. The composition according to claim 1, wherein the composition consists of, by weight, from 10% to 30% of cobalt, from 30% to 70% of nickel, from 15% to 20% of chromium, from 8% to 12% of aluminum, from 0.1% to 2% of yttrium, from 0.5% to 3.5% of iridium.

11. The composition according to claim 1, wherein the composition consists of, by weight, from 10% to 30% of cobalt, from 30% to 70% of nickel, from 15% to 20% of chromium, from 8% to 12% of aluminum, from 0.1% to 2% of yttrium, from 0.5% to 3.5% of iridium, and less than 2% of rhenium.

12. The composition according to claim 11, wherein the amount of rhenium is from 0.5% to 1.5% by weight.

13. A method of making an alloy composition for the manufacture of protective coatings in powder form wherein the composition comprises by weight from 10% to 30% of cobalt, from 30% to 70% of nickel, from 15% to 20% of chromium, from 8% to 12% of aluminum, from 0.1% to 2% of yttrium and from 0.5% to 3.5% of iridium wherein the method comprises an atomization process carried out directly on the alloy in molten state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the accompanying drawings:

(2) FIGS. 1 and 2 show the SEM micrographs of the four coatings made in the Examples;

(3) FIGS. 3 and 4 show microstructural details of one of the four coatings made in the Examples; and

(4) FIGS. 5 and 6 show the microstructures of the four coatings made in the Examples observed under an optical microscope following etching.

EXAMPLE

(5) Preparation of the coating composition in powder form.

(6) The pulverisation step comprises a first manufacturing step of the master alloy ingots and the subsequent steps of re-melting and atomising the master alloy in an atomisation gas system.

(7) The master alloy ingots are made using a vacuum induction oven. The VIM (Vacuum Induction Melting) technology is the most versatile melting process for the production of nearly all Fe, Ni and Co based special alloys, and is also the only allowed for some aeronautic applications, not only for the production of ingots but also of castings.

(8) There were thus melted Ni, Co, Cr and Ir filling elements with purity no lower than 99.9%, by means of a water cooled copper coil through which passes an alternating current that is wound about the refractory crucible thus generating eddy currents in the filling material which is heated by joule effect.

(9) The magnetic agitation, which the process generates in the bath, ensures the homogenisation and the more accurate control of molten chemistry and temperature, and the transport of material needed to perform the chemical-physical reaction needed, for example, for degassing by means of rotary vacuum pumps.

(10) It also allows an exact composition and product reproducibility.

(11) Later, Al is added, a further degassing is performed and it is added, by means of a loading system placed on the top of the oven, the yttrium, reactive component of the composition.

(12) After mixing of the bath, it is performed the chemical analysis and possible additions of principle elements in the case of lacking in the composition. Finally, the molten metal is cast into ingots.

(13) With the aforesaid process, it was obtained the master alloy for the protective coatings, whose chemical composition is shown in Table 2.

(14) TABLE-US-00002 TABLE 2 Powder Id Ni Co Cr Al Ir Y A 86 Bal 24.1 16.8 9.7 1.4 0.41

(15) The resulting ingots were later subjected to an atomising gas step, the most common method for producing spherical metallic powders adapted for spraying systems.

(16) Such step consists in the re-melting of the ingots in a ceramic crucible by magnetic induction. After melting and after having reached the correct superheating temperature, the liquid metal is passed from the crucible, through a nozzle, to inside the atomisation chamber where is it struck by a jet of inert pressurised gas, generally nitrogen, helium or argon, which disintegrates the molten metal into small particles.

(17) When the liquid metal encounters the high speed gas, indeed, it is separated into droplets, therefore rapidly cooled by the gassy atmosphere present in the chamber with the subsequent formation of powder.

(18) The ratio between quantity of gas which strikes the molten metal and the molten metal itself determines the particle size of the manufactured powder. The following process parameters allow to vary this gas/metal ratio, such as: gas pressure metallostatic pressure fluid flow rate material viscosity gas temperature

(19) Higher is the ratio, finer is the size of the obtained powder, and vice versa. The dependence of the gas/metal ratio on the material properties imposes that for each new alloy there are conducted preliminary tests for searching the optimal process parameters.

(20) The powder formed by the master alloy A86 was deposited by VPS on a monocrystal solidified nickel based super-alloy substrate. Four different thermal spraying methods varying the process parameters which allowed to obtained 4 different coatings (id. 228-05_1, 228-05_2, 228-05_3, 229-05_1) were used.

(21) FIGS. 1 and 2 show the SEM micrographs (10000×) of the 4 coatings made. In particular, FIG. 1a) shows a SEM 10000× micrograph for sample 228-05_1 and FIG. 1b) shows a SEM 10000× micrograph for sample 228-05_2; FIG. 2a) shows a SEM 10000× micrograph for sample 228-05_3 and FIG. 2b) shows a SEM 10000× micrograph for sample 229-05_1.

(22) Furthermore, FIGS. 3 and 4 show microstructural details for coating 229-05_1 at lower magnification (100× and 1000×). In particular, FIG. 3a) shows a SEM 100× micrograph for sample 229-05_1, while FIG. 3b) shows a SEM 1000× micrograph for sample 229-05_1; FIG. 4 shows SEM 1000× micrographs for sample 229-05_1, which shows microstructural details: a) inside the coating; b) coating-substrate interface.

(23) In particular, two distinct phases can be observed in FIGS. 1-4: the lattice γ and the phase β dispersed in it; in particular, in coatings 228-05_2 and 229-05_3 such phases appear to be form macroaggregates indicating a coarser structure.

(24) FIGS. 5 and 6 show instead the microstructures of the four samples observed under an optical microscope following etching with nitric acid, acetic acid and hydrofluoric acid which confirm the previous observations. In particular, FIG. 5a) shows an optical micrograph after etching with nitric, acetic and hydrofluoric acid for sample 228-05_1, while FIG. 5b) shows an optical micrograph after etching with nitric, acetic and hydrofluoric acid for sample 228-05_2; FIG. 6a) shows an optical micrograph after etching with nitric, acetic and hydrofluoric acid for sample 228-05_3; and finally, FIG. 6b) shows an optical micrograph after etching with nitric, acetic and hydrofluoric acid for the sample 229-05_1.