RU2758655C2 - Method for diffusion welding of metals with metal ceramics - Google Patents

Abstract

FIELD: welding.

SUBSTANCE: invention relates to a method for diffusion welding of metals with metal ceramics and can be used for producing a worked-in turbine sealing with a multi-layered shell. The method for diffusion welding of metals with metal ceramics includes pressing the powder of a metal ceramic material into the cavity of a metal part in a cold state to a porosity of 5 to 25%, heating in a vacuum and sintering. Heat treatment of the main part is executed prior to diffusion welding to relieve stresses and stabilise the dimensions thereof, and preliminary fractional separation of the initial powder charge is executed prior to pressing.

EFFECT: proposed invention provides a possibility as a result to increase the bending strength of the connection of metal with metal ceramics after diffusion welding and eliminate cracks and tears.

1 cl, 2 tbl, 2 dwg, 1 ex

Description

The invention relates to the technology of diffusion welding of a metal part with a cermet and can be used to manufacture a run-in seal for turbines with a multilayer shell.

A known method of manufacturing sintered products, including pressing the original powder, sintering and cooling at certain temperature intervals (Patent No. 876303, IPC B22F 3/16, H01F 1/22, 30.10.1981 - analogue).

The disadvantage of this method is the fact that the elimination of warpage is achieved by leveling the temperature across the section during isothermal holdings without taking into account possible warpage of products during stamping and machining by relieving the stresses that have arisen during their manufacture, as well as phase transformations during the heat treatment of the base material ...

The closest analogue is the method of diffusion welding of metals with cermets, according to which the powder of cermet material UMB-4C is pressed into the cavity of a metal part at a temperature below the recrystallization temperature to a porosity of 5-25% (Patent No. 738802, IPC V23K 19/00, 05.06.1980 ).

The value of porosity after pressing is determined by the initial granulometric composition of the powder of the cermet material UMB-4S, which has a composition: 92% nichrome Kh20N80 and 8% boron nitride.

In accordance with GOST 13084-88, nichrome powder ПХ20Н80 is produced in three size classes: 280, 160 and 56.

To ensure a bending strength of at least 10 kg / mm ^{2, it is} proposed to use a fraction of size class 56 (granulometric composition is presented in Table 1).

In this case, the powder of this size class consists of 50% of particles with a size from 0.16 to 0.056 mm and less.

The flexural strength of the joint after diffusion welding according to patent No. 738802 is 19, 15 kg / mm ² , and with a porosity after pressing-in of more than 25%, it is less than 7 kg / mm ² . At the same time, according to the technical requirements for the manufacture of a running-in seal for turbines with a multilayer shell, the bending strength of the joint is at least 10 kg / mm ² .

Diffusion welding is carried out in conventional vacuum furnaces at a temperature of 1170 ° C with a holding time of 3 hours.

At the set temperature regime, diffusion welding with the formation of a diffusion joint and sintering of UMB-4S cermets take place at the same time.

Under the influence of deformation and internal elastic stresses arising in a two-layer workpiece, the cermet pressure is created on the surface of the metal part, which is necessary to perform diffusion welding.

The density of cermets during sintering is determined by the particle size distribution of the powder: percentage of the fraction yield, particle size and the sintering process.

In the process of sintering, due to volumetric shrinkage, an increase in the density of cermets occurs as a result of the formation of bonds between individual particles, spheroidization of pores and closure of through porosity.

This process is accompanied by the creation of sufficiently high internal stresses, which, under unfavorable conditions, lead to the destruction of the diffusion joint with the formation of cracks and separations in the cermet.

The disadvantage of this method is that the powder of cermet material UMB-4C, consisting of 92% of nichrome powder of size class 56 (GOST 13084-88), 50% consists of particles ranging in size from 0.16 to 0.056 mm or less without limitation.

None of these methods take into account the process of shrinkage of the cermet powder in the sintering process, which causes the destruction of the connection of metals with cermet in the sintering process. It is known that the process of shrinkage of the powder composition depends on the size and shape of the powder particles, as well as the factors of pressing pressure, sintering temperature (Ya.E. Geguzin "Physics of sintering". Publishing house "Nauka", 1967, pp. 268-270).

The technical result, which the invention is aimed at, is to increase the bending strength of the metal-cermet joint after diffusion welding and to eliminate cracks and tears.

This technical result is achieved using the method of diffusion welding of a metal part made of a nickel-based alloy EP666 with cermet, which includes pressing a powder of a cermet material into the cavity of a metal part in a cold state to a porosity of 5-25%, heating them in vacuum and sintering, and according to the invention, before diffusion welding, heat treatment of a metal part is carried out by heating the part without powder in a vacuum furnace to T = 1160 ± 5-10 ° C with holding for 3 h and a vacuum of no more than 5 × 10 ^-4 mm Hg. Art., cooling with a furnace to 700 ° C with an exposure of 15 h, cooling with a furnace in a heating chamber to 400 ± 10 ° C and cooling with a furnace to 150 ° C in a cooling chamber without an argon admission, and before pressing, preliminary fractional separation of the initial powder of cermet material with a decrease in the volumetric content of particles less than 0.056 mm to reduce its volumetric shrinkage during sintering.

One of the conditions for obtaining a strong joint in the process of diffusion welding is to ensure a uniform gap between the cermet and the base material. At the same time, volumetric changes in a part made of EP666 alloy, which occur as a result of phase transformations and the resulting stresses during the performance of sintering modes, are extremely undesirable and should be minimized (FF Khimushin "Heat-resistant steels and alloys." ., pp. 270-276).

To relieve the stresses arising in the manufacture of parts (stamping, machining, etc.), and to stabilize the phase composition of the KhN55MBYu alloy, a preliminary heat treatment of the part is carried out before diffusion welding and sintering.

The reason for the violation of the integrity of the diffusion joint at the cermet-metal interface is that during sintering, in addition to pressing the cermet layer against the walls of the metal part due to thermal expansion, the volume of cermet decreases due to shrinkage of the powder during sintering (photo 1, 2).

Photo 1 shows the destruction of the diffusion joint UMB-4S - EP666, and photo 2 - the diffusion joint UMB-4S - EP666 without destruction.

In order to exclude the shrinkage of the cermet powder in the sintering process, which causes the destruction of the metal-cermet compound, fractional separation of the powder is carried out.

To improve the quality and stabilize the composition of the PKh20N80-56-24 powder, fractional separation is carried out with a limitation of the percentage of particles less than 0.056 mm. The proposed manufacturing method provides for preliminary fractional separation (screening) of the powder charge to obtain a granulometric material ПХ20Н80-56-24 of the following composition.

The particle size distribution is shown in table 2.

Example

An outer sealing ring with an inner cavity filled with UMB-4C cermet powder is made of EP666 alloy.

Preliminary heat treatment of the sealing ring, without UMB-4S powder in the cavity, is performed in 4 passes as follows.

1 run - heating the part without powder in a vacuum oven according to the mode:

T = 1160 ± ⁵ ₁₀ ° C, warming up according to the control exposure - 3 hours.

Vacuum - no more than 5 × 10 ^-4 mm Hg, cool with an oven to 700 ° C, hold for 15 hours.

Cool with oven (in the heating chamber) to 400 ± 10 ° C. Cool with an oven (in a cooling chamber) without puffing argon to t≤150 ° C.

2nd entry - vacuum powder drying.

3 pass - vacuum powder drying (if necessary).

4 pass - sintering.

Heat to 600 ± 10 ° C - hold for 3 hours (8 ° / min).

Heat to 800 ± 10 ° C - 1 hour (4 ° / min).

Heat to 1160 ⁺⁵ ° C - 6 hours 50 ¹ (0.8 ° / min).

Further with the oven up to 700 ° C, exposure - 15 hours.

Cool with an oven to 400 ° C and then in a cooling chamber with an argon flood.

Thus, the claimed invention made it possible to increase the bending strength of the metal-cermet joint after diffusion welding and to eliminate cracks and tears.

Claims (1)

A method of diffusion welding of a metal part made of an EP666 nickel-based alloy with cermet, including pressing a powder of a cermet material into the cavity of a metal part in a cold state to a porosity of 5-25%, heating them in vacuum and sintering, characterized in that heat treatment is carried out before diffusion welding of a metal part by heating the part without powder in a vacuum furnace to T = 1160 ± 5-10 ° C with holding for 3 h and a vacuum of no more than 5 × 10 ^-4 mm Hg, cooling with an oven to 700 ° C with holding 15 h, cooling with a furnace in a heating chamber to 400 ± 10 ° C and cooling with a furnace to 150 ° C in a cooling chamber without argon puffing, and before pressing in, preliminary fractional separation of the initial sintered metal powder is carried out with a decrease in the volume content of particles in it less than 0.056 mm to reduce its volumetric shrinkage during sintering.

Images