RU2426816C2 - Procedure for preparing surface of impeller of turbine before application of heat-proof coating - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: blades are subjected to diffusion annealing at temperature 850±10°C in vacuum during time interval facilitating formation of surface layer of blades identical to base metal of blades by strength; further, blades are mechanically cleaned at depth 15-30 mcm and are chemically treated. Diffusion annealing is carried out in vacuum of 10^-3 mm of m.c. during 30-60 minutes. Surface layer of blades is mechanically treated by means of electro corundum.

EFFECT: production of strong surface layer identical to base metal of turbine impeller by chemical composition eliminating cracks and other defects on surface.

3 cl, 1 ex

Description

Technical field

The invention relates to the field of mechanical engineering and, in particular, to a method for preparing the surface of a turbine impeller before applying heat-resistant coatings, mainly ion-plasma spraying, to its surface, which can be used in turbopump units of liquid propellant rocket engines.

State of the art

The application of durable and heat-resistant coatings to the blades of the impellers of turbines by ion-plasma spraying requires an operation to eliminate various defects from their surface layer that arose during the manufacture of the blades, both by mechanical and electrical discharge methods.

A known method of preparing the surface of the blades before applying a heat-resistant coating by electron beam spraying, including the operation of grinding, plastic surgery - hardening and subsequent recrystallization annealing at a temperature of 1200 ° C, which helps to create a fine-grained structure in their surface layer (author. Certificate. USSR No. 1448760, MKI C23C 14/02, 1987).

Known technology has significantly improved the fatigue strength of turbine blades made of a nickel-based alloy by a mechanical method.

However, this method of preparing the surface of the blades before applying a heat-resistant coating cannot be applied if they are manufactured by the EDM method for the following reasons:

- in the process of electric discharge machining in the surface layer of the blades, a change in the chemical composition occurs, leading to a deterioration in adhesive ability;

- in addition, cracks and sludge adhering to it, which have strong adhesion to the base metal, remain on the blade surface. This circumstance can lead to a distortion of the surface layer, and hence to a sharp deterioration in the fatigue strength of the blades, as well as to a decrease in the adhesive strength of the applied coating.

Disclosure of invention

The objective of the invention is the creation of a technology for preparing the surface of the blades of the turbine impeller made by electric discharge machining, which would make it possible to obtain a surface layer of the blades identical in chemical composition to the base metal, and also to prevent the appearance of cracks and other defects on their surface.

The problem is solved due to the fact that in the method of preparing the surfaces of the blades of the turbine impeller subjected to electrical discharge machining from a heat-resistant nickel-based alloy, before spraying the heat-resistant coatings of the blades, they are subjected to diffusion annealing at a temperature of 850 ± 10 ° С in vacuum for a time providing the creation of a surface layer of the blades , identical in strength to the base metal of the blades, then mechanical cleaning of the blades to a depth of 15-30 microns and their chemical cleaning are carried out.

Other differences of the proposed method are:

- diffusion annealing is carried out in a vacuum of 10 ^-3 mm RT. Art. within 30-60 minutes.

- mechanical cleaning of the surface layer of the blades is carried out using electrocorundum.

EFFECT: obtaining a dense and durable surface layer of turbine impeller blades without foreign particles and cracks, suitable for applying a heat-resistant coating on it with the required adhesion.

An example implementation of the invention

The blades of the turbine impeller are made by EDM on the Roboform machine. As a result of this treatment, various kinds of defects arise on their surface: cracks, sagging, sludge. In addition, a change in the chemical composition occurs in the surface layer, leading to a deterioration in its adhesive ability. To eliminate this negative effect, the impeller of the turbine with blades is subjected to diffusion annealing, for which it is placed in a vacuum oven, heated to a temperature of 850 ± 10 ° C and kept there for 30-60 minutes in a vacuum of 1 · 10 ^-3 mm RT. Art. This treatment allows, due to diffusion processes, to create a homogeneous and equal-strength surface layer with the base metal, partially remove the influx and loosening. Next, mechanical cleaning of the surfaces of the blades to a depth of 15-30 microns is carried out through the use of electrocorundum as a working abrasive tool. As a result of this stripping, sludge, sag and cracks are removed.

To completely clean the surface of the blades from residual phenomena, after cleaning, use the operations of its chemical treatment, washing and drying. As a chemical treatment, operations such as degreasing and chemical etching are used.

Industrial application

The proposed technology can be used when applying a heat-resistant nickel coating to the blades of the impellers of turbines of liquid rocket engines.

Claims (3)

1. The method of preparing the surfaces of the electroerosive blades of the impeller of a turbine made of a heat-resistant nickel-based alloy before spraying heat-resistant coatings, characterized in that the blades are subjected to diffusion annealing at a temperature of 850 ± 10 ° C in vacuum for a time that ensures the creation of a surface layer of the blades, identical in strength to the base metal of the blades, then the mechanical cleaning of the blades to a depth of 15-30 microns and their chemical cleaning. 2. The method according to claim 1, characterized in that the diffusion annealing is carried out in a vacuum of 10 ^-3 mm RT. Art. within 30-60 minutes 3. The method according to claim 1, characterized in that the mechanical cleaning of the surface layer of the blades is carried out using electrocorundum.