Superalloy powder

Abstract

The invention discloses a Ni— or Co-based superalloy powder enriched with at least one fusing element: B, such that each grain of powder includes said at least one fusing element distributed among the other elements of the superalloy. A powder of this kind already has the requisite final composition, both in terms of constituent elements of the superalloy and in terms of fusing element(s). In particular, the proportion of B and, optionally, Si is adapted for use of the powder without a preliminary step of mixing with another powder. Use of this powder to fabricate components, in particular plates, by sintering, or mixed with a cement, or as a constituent of a mixture for injection molding of metallic powders.

Description

The object of the invention is a superalloy powder.

In the field of aeronautical engineering and industrial turbines, the severe operating conditions imposed on certain components such as turbine blading and nozzles have dictated the need to manufacture these components in Ni— or Co-base superalloy. To assemble these components or to repair them by hardfacing (that is to say by localized deposition of material on the component), current techniques reliant on fusion welding are found wanting or unsuitable for use. Also, as described in the document FR 2 822 741, brazing-diffusion methods have been developed using so-called bi-component mixtures of two metallic powders. These mixtures include:

a first superalloy powder of chemical composition similar to that of the material to be repaired, and

a second powder of nickel (Ni) or cobalt (Co) base containing 2 to 6% by weight of fusing elements such as boron (B) or silicon (Si).

The presence of fusing elements in the second powder makes it possible to lower the melting point of the latter and to work at a temperature at which the second powder is liquid, while the first powder remains in the solid state.

These bi-component mixtures nevertheless have a number of drawbacks such as the difficulty of making a uniform mixture of two powders, problems of segregation of the powders during storage of the mixture, or problems of proportioning each powder in the mixture. For example, when sintering a bi-component mixture and the quantity of fusing element in certain regions of the mixture is not sufficient, a porous sintered material is obtained. Conversely, an excess of fusing element in certain regions of the mixture causes excessive fusion resulting in deformation of the sintered material, which then fails to conform to the required dimensions.

To overcome these problems, a solution described in FR 2 822 741 envisages a means of incrusting the grains of the second powder onto the grains of the first powder by mechanical synthesis. In practice, however, this incrustation technique is found to be limited: this technique is found to be rather difficult to put into effect, in particular by virtue of the fineness of the second powder used, which causes health problems. Moreover this technique only partially improves the homogeneity.

It is also known to chemically encapsulate the grains of the superalloy powder in layers of Ni—B and/or Ni—Si. From an industrial standpoint, this method is difficult to use in that it is very time-consuming and very difficult to put into effect when the alloys are composed of a considerable number of elements in small proportions.

The purpose of the invention is to propose an alternative to the existing solutions, offering good results in terms of uniformity of distribution of the fusing element(s) within the powder, which is reflected in particular by the absence of deformation of components fabricated by sintering.

To achieve this purpose, the object of the invention is a Ni— or Co-based superalloy powder according to claim 1 or claim 5.

It is not necessary to mix the powder of the invention with another powder as in FR 2 822 741, as the powder of the invention already has the final composition that is needed, both in terms of constituent elements of the superalloy and in terms of fusing element(s). In particular, the proportion of B and, optionally, of Si is adapted for utilization of the powder without a step of preliminary mixing with another powder (as explained above, the proportion of fusing elements has a determining influence on the behavior of the powder during heat treatment of the latter).

In addition, in the powder of the invention, said fusing element forms an integral part of the superalloy: it is not chemically deposited or mechanically incrusted on the surface of the superalloy grains, as in the known techniques referred to above.

In short, in the powder of the invention, the constituent elements of the superalloy, including the fusing element, are present in each grain of powder and are therefore distributed within the powder in a perfectly homogeneous manner. The problems of localized porosity and excessive fusion, associated with too low a proportion or too high a proportion of fusing element in certain regions of the powder, are thus avoided.

Advantageously, to manufacture the powder of the invention, use is made of a technique of atomizing a precursor liquid mixture, including the elements of said superalloy and said at least one fusing element.

The invention and its advantages will be better understood by reading the detailed description that follows. This description makes reference to the attached figures in which:

FIG. 1 is a photograph of a plate made by sintering from a powder according to the invention; and

FIG. 2 is a photograph of a plate made by sintering from a bi-component mixture of powders.

Irrespective of the type of powder according to the invention, given by way of example below, each powder is a Ni— or Co-based superalloy powder which includes at least the three elements Ni, Co and Cr (chromium).

These powders were made using an atomization technique from a precursor liquid mixture including the elements of the superalloy (Ni, Co, Cr . . . ) and at least one fusing element (B and, optionally, Si). This liquid mixture was obtained by fusing alloys by induction, under vacuum, in a crucible equipped with a burette allowing the liquid mixture to flow out at a low rate of flow. Inert gas jets under high pressure, flowing at a velocity close to that of sound, are used to atomize the mixture leaving the burette. The mixture then breaks down into fine droplets which then assume a spheroidal shape under the effect of surface tension and cool down very rapidly in an atomization chamber. In our case, the inert gases used are argon or nitrogen for example.

In a surprising manner, during cooling, there is no separation of the fusing element(s) from the other elements of the alloy. All of these elements remain within each droplet, and therefore within each grain of powder.

Unless otherwise indicated, the percentages given below are percentages by weight.

In a first type of superalloy powder according to the invention, based on Ni, the superalloy enriched with fusing elements essentially includes: 14 to 19.6% of Co; 8.2 to 15.3% of Cr; 2.6 to 4.7% of Mo; 2.25 to 3.5% of Al; 1.95 to 3.1% of Ti; 0 to 2% of Si; 0.4 to 1.3% of B; and a remainder of Ni.

The presence of impurities in the powder is not ruled out (hence the use of the term “essentially”). For example, carbon (C), zirconium (Zr), and phosphorus (P) may be found in minimal proportions, for example in the order of, or less than, 0.06%.

In a first example (a) of the first type of superalloy powder according to the invention, the superalloy enriched with fusing elements essentially includes: 16.4 to 19.6% of Co; 8.2 to 12.8% of Cr; 2.6 to 4.4% of Mo; 2.25 to 3.3% of Al; 1.95 to 2.9% of Ti; 0.8 to 2% of Si; 0.5 to 1.3% of B; and a remainder of Ni.

In a second example (b) of the first type of superalloy powder according to the invention, the enriched superalloy essentially includes: 14 to 16% of Co; 12 to 15.3% of Cr; 3.35 to 4.7% of Mo; 2.9 to 3.5% of Al; 2.5 to 3.1% of Ti; 0.4 to 1% of B; and a remainder of Ni. In the example (b), B is the sole fusing element.

In a second type of superalloy powder according to the invention, based on Co, the enriched superalloy essentially includes: 17.2 to 22.2% of Cr; 26.75 to 30% of Ni; 0 to 1.5% of Si; 0.8 to 1% of B; 0.1 to 0.5% of C; 0 to 0.37% of Zr; 0 to 3% of Ta; and a remainder of Co.

The cobalt-base powders of the second type can include impurities, such as phosphorus P, in minimal proportions, for example in the order of, or less than, 0.04%.

Table 1 below summarizes the compositions of the example powders (a) and (b), cited above, and of an example powder (c) corresponding to the second type of superalloy powder according to the invention.

	TABLE 1
	Composition in % by weight
Ex	Ni	Co	Cr	Mo	Al	Ti	Si	B	C	Zr	P	Ta
(a)	base	16.4	8.2	2.6	2.25	1.95	0.8	0.5	0	0	0	0
		19.6	12.8	4.4	3.3	2.9	2	1.3	0.06	0.05	0.01	0
(b)	base	14	12	3.35	2.9	2.5	0	0.4	0	0	0	0
		16	15.3	4.7	3.5	3.1	0	1	0.06	0.06	0.02	0
(c)	26.75	base	17.2	0	0	0	0	0.8	0.1	0	0	—
	30		22.2	0	0	0	1.5	1	0.5	0.37	0.04	—

All of these examples of superalloy powder may be used in the implementation of any brazing-diffusion method applied during the manufacture or repair of components made of nickel-based or cobalt-based alloys, in particular in the field of aeronautical engineering. This can include assembly of components, filling of cracks, or fissures, on a component or hardfacing of the surface of a component with a view to correcting a superficial defect or restoring certain properties or geometric dimensions of the latter.

Depending on the applications, placement of the filler powder can be effected in different ways.

For the filling of cracks, the raw powder can be used mixed with a cement, for example of the type Nicrobraz 320. It will be noted that the mixture obtained can be applied in the form of beads.

In certain applications, and in particular in the case of hardfacing of a component surface, the application can be effected in the form of a compact filler piece. Said compact filler piece is obtained from the powder either by a fabrication technique imparting compaction by sintering the powder, or by techniques of injection molding of metallic powders.

FIG. 1 shows an example of a compact filler piece made by sintering from a superalloy powder according to the invention. It takes the form of a plate designed to be used to build up the surface of a component.

This plate was made from a powder of the first type cited above, according to the following steps: kilning of the raw powder; distribution of the latter in a mold matching the dimensions and thickness of the desired sintered material; arrangement of the mold in a furnace to expose it to heat treatment. As an example of heat treatment, it is possible to apply (for a furnace pressure of 0.13 Pa) a progressive temperature rise to 1,160° C., holding at this temperature for approximately 10 minutes, followed by gradual cooling.

For comparison, a compact filler piece was made by sintering from a mixture of bi-component powder of known type. FIG. 2 shows the piece obtained.

In practice, it was found that the invention made it possible to dispense with the handling and storage of several different types of powders, and to avoid any powder mixing stage, which is critical from a health and safety perspective.

Furthermore, by using a single powder containing within each grain the composition necessary to produce a plate (that is to say all the elements of the superalloy and at least one fusing element), the sintering temperature is substantially reduced relative to the temperature required for a bi-component mixture. By virtue of the homogeneity of the powder and the reduction of sintering temperature, a notable improvement is obtained in the uniformity of the properties of the sintered plate and good preservation of the dimensions and shape of the latter, in particular retention of the desired dimensions and good flatness.

Conversely, FIG. 2 illustrates the deformation problems that may be encountered during sintering of a bi-component mixture.

The homogeneity of the superalloy powder of the invention is also reflected in an improvement in the mechanical properties of the zone built up using said plate.

In another example of use of the powder according to the invention, a compact filler piece can be made using known techniques of injection molding of metallic powder. These techniques generally make it possible to obtain components of more complex shapes than those made by simple molding followed by sintering.

To this end, the powder is mixed with a binder in a mixer. The binder includes, for example, polypropylene, ethylene, vinyl acetate and paraffin. The mixing time must be such that plastification of the mixture is obtained. The mixture is then cooled before being milled. The granular material thus obtained can be fed into the hopper of a press and injected into molds of dimensions specific to the compact filler piece to be produced. The molded blank is then chemically stripped from the mold and said blank is sintered.

It was found that certain of the example powders in Table 1 were more amenable to certain uses among the following uses a, b and c:

• • a) use of the powder mixed with a cement, to fill cracks for example;
  • b) use of the powder to produce compact filler pieces, in particular plates, by sintering; and
  • c) use of the powder as a constituent of a mixture for injection molding of metallic powders.

The preferred uses of each example powder are indicated in Table 2 below.

	TABLE 2
	Example	Use a	Use b	Use c
	(a)	Yes	Yes	Yes
	(b)	Yes	Yes
	(c)	Yes	Yes

Claims

1. Superalloy powder, characterized in that the superalloy is enriched with at least one fusing element: B, such that each grain of powder includes said at least one fusing element distributed among the other elements of the superalloy and in that the superalloy is composed of, in weight percent:

14 to 24% of Co;

8.2 to 20% of Cr;

0 to 4.7% of Mo;

2.25 to 8% of Al;

0 to 3.1% of Ti

0 to 3.3% of Si;

0 to 4.5% of Ta;

0 to 0.6% of Y;

up to 1.3% of B; and

a remainder of Ni.

2. Superalloy powder according to claim 1, wherein said superalloy enriched with fusing element is composed of, in weight percent:

14 to 19.6% of Co;

8.2 to 15.3%ofCr;

2.6 to 4.7% of Mo;

2.25 to 3.5% of Al;

1.95 to 3.1% of Ti

0 to 2% of Si;

0.4 to 1.3% of B; and

a remainder of Ni.

3. Superalloy powder according to claim 2, wherein said superalloy enriched with fusing element is composed of, in weight percent:

16.4 to 19.6% of Co;

8.2 to 12.8% ofCr;

2.6 to 4.4% of Mo;

2.25 to 3.3% of Al;

1.95 to 2.9% of Ti

0.8 to 2% of Si;

0.5 to 1.3% of B; et

a remainder of Ni.

4. Superalloy powder according to claim 2, wherein said superalloy enriched with fusing element is composed of, in weight percent:

14 to 16% of Co;

12 to 15.3% of Cr;

3.35 to 4.7% of Mo;

2.9 to 3.5% of Al

2.5 to 3.1% of Ti

0.4 to 1% of B; and

a remainder of Ni.

5. Superalloy powder, characterized in that the superalloy is enriched with at least one fusing element: B, such that each grain of powder includes said at least one fusing element distributed among the other elements of the superalloy and in that the superalloy is composed of, in weight percent:

17.2 to 23% of Cr;

26.75 to 32.4% of Ni;

0 to 2.5% of Si;

0 to 0.5% of C;

0 to 0.4% of Zr;

0 to 3% of Ta;

0 to 0.5% of Y;

0 to 8% d'Al;

up to 1.2% of B; and

a remainder of Co.

6. Superalloy powder according to claim 5, wherein said superalloy enriched with fusing element is composed of, in weight percent:

17.2 to 22.2% of Cr;

26.75 to 30% of Ni;

0 to 1.5% of Si;

0.8 to 1% of B;

0.1 to O.5% of C;

0 to 0.37% of Zr;

0 to 3% of Ta; and

a remainder Co.

7. Superalloy powder according to any one of claims 1 to 6, obtained by atomization of a liquid mixture including the elements of said superalloy and said at least one fusing element.

8. Use of a superalloy powder according to any one of claims 1 to 7 for the fabrication of components, in particular plates, by sintering.

9. Use of a superalloy powder according to any one of claims 1 to 7 mixed with a cement.

10. Use of a superalloy powder according to any one of claims 1 to 7 as a constituent of a mixture for injection molding of metallic powders.