GB2053744A

GB2053744A - Manufacturing blades, e.g. turbine blades

Info

Publication number: GB2053744A
Application number: GB8022019A
Authority: GB
Original assignee: MTU Motoren und Turbinen Union Muenchen GmbH
Current assignee: MTU Aero Engines GmbH
Priority date: 1979-07-21
Filing date: 1980-04-04
Publication date: 1981-02-11
Also published as: DE2929634A1; FR2461762A1; NL8003868A; FR2461762B1; DE2929634C3; DE2929634B2; GB2053744B

Abstract

The manufacture of titanium or titanium-base alloy blades especially turbine blades, including the steps of forming at the blade surface by nitriding, boronising or carburizing, a thin diffusion layer and subsequently peening the blades.

Description

SPECIFICATION Improved titanium or titanium-base alloy blades This invention relates to a method for manufacturing titanium or titanium-base alloy blades, especially turbine blades.

In order to improve the integrity of the surface of titanium or titanium-base alloy turbine blades against especially aggresive media at elevated tem peratures and against erosion, use is increasingly made of protective surface layers. It is a known practice, with turbine blades of nickel or of nickelbase alloys, to use aluminizing, plasma spraying or other coating processes where a protective layer, which may equally be applied in the form of a brush-on medium, is applied to the surface of the turbine blade.

With the conventional method it is difficult to achieve adequate adhesion of the protective coating to the base material, adequate resistance against fretting and adequate fatigue strength.

An object of the present invention is to improve the surface integrity of titanium or titanium-base alloy turbine blades to achieve a high resistance against corrosion and concurrently maximum safety from fretting, and any type of erosion.

According to the present invention we propose a method of manufacturing titanium or titanium-base alloy blades, wherein a thin diffusion layer is produced on the surface of-the blade by nitriding, boronising or carburizing and wherein the blades are subsequently peened.

Unlike conventional methods, which deposit an additional corrosion-inhibiting surface layer on a base material, a thin surface layer of the base material is subjected to nitriding by diffusion, and is hardened as a result. Peening of the thin and hard diffusion zone causes plastic deformation of the peaks of the surface roughness profile which serves to reduce the notch effect. Peening additionally sets up compressive stresses in the rim layer, so improving the fatigue performance. Other advantages of the present invention are that it makes possible varying the thickness of surface layer to suit the protective function intended, and that the cost of the manufacture is less than by the conventional method.

The preferred temperature for nitriding and carburizing is from 750 to 950 C, and 950"C for boronising.

In salt bath cyaniding the dwell times may be from 15 minutes to 3 hours, in gas nitriding up to 15 hours, and in ion nitriding up to 30 hours.

For carburizing and boronising the dwell time need not be quite as long as for gas nitriding or ion nitriding, so that dwell times between 1 and 10 hours are sufficient.

For peening, use is preferably made of Al203 grit, which produces particularly good surface finishes.

1. A method of manufacturing titanium ortitanium-base alloy blades, wherein a thin diffusion layer is produced on the surface of the blade by nitriding, boronising or carburizing and wherein the blades are subsequently peened.

2. A method according to Claim 1,wherein nitriding and carburizing runs is carried out at a temperature in the range 750"C to 9500C, and boronising is carried out at a temperature of 950"C.

3. A method according to Claim 1 or 2, wherein the dwell time for salt bath nitriding is 15 minutes to 3 hours, for gas nitriding is up to 15 hours and for ion nitriding is up to 30 hours 4. A method according to any one of Claims 1 to 3, wherein the dwell times for carburizing are between 1 and 10 hours and for boronising between 2 and 10 hours.

5. A method of manufacturing a titanium or titanium-base alloy turbine, substantially as hereinbefore described.

6. Atitanium or titanium-base alloy turbine blade when made by the method according to any one of the preceding claims.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improved titanium or titanium-base alloy blades This invention relates to a method for manufacturing titanium or titanium-base alloy blades, especially turbine blades. In order to improve the integrity of the surface of titanium or titanium-base alloy turbine blades against especially aggresive media at elevated tem peratures and against erosion, use is increasingly made of protective surface layers. It is a known practice, with turbine blades of nickel or of nickelbase alloys, to use aluminizing, plasma spraying or other coating processes where a protective layer, which may equally be applied in the form of a brush-on medium, is applied to the surface of the turbine blade. With the conventional method it is difficult to achieve adequate adhesion of the protective coating to the base material, adequate resistance against fretting and adequate fatigue strength. An object of the present invention is to improve the surface integrity of titanium or titanium-base alloy turbine blades to achieve a high resistance against corrosion and concurrently maximum safety from fretting, and any type of erosion. According to the present invention we propose a method of manufacturing titanium or titanium-base alloy blades, wherein a thin diffusion layer is produced on the surface of-the blade by nitriding, boronising or carburizing and wherein the blades are subsequently peened. Unlike conventional methods, which deposit an additional corrosion-inhibiting surface layer on a base material, a thin surface layer of the base material is subjected to nitriding by diffusion, and is hardened as a result. Peening of the thin and hard diffusion zone causes plastic deformation of the peaks of the surface roughness profile which serves to reduce the notch effect. Peening additionally sets up compressive stresses in the rim layer, so improving the fatigue performance. Other advantages of the present invention are that it makes possible varying the thickness of surface layer to suit the protective function intended, and that the cost of the manufacture is less than by the conventional method. The preferred temperature for nitriding and carburizing is from 750 to 950 C, and 950"C for boronising. In salt bath cyaniding the dwell times may be from 15 minutes to 3 hours, in gas nitriding up to 15 hours, and in ion nitriding up to 30 hours. For carburizing and boronising the dwell time need not be quite as long as for gas nitriding or ion nitriding, so that dwell times between 1 and 10 hours are sufficient. For peening, use is preferably made of Al203 grit, which produces particularly good surface finishes. CLAIMS

3. A method according to Claim 1 or 2, wherein the dwell time for salt bath nitriding is 15 minutes to 3 hours, for gas nitriding is up to 15 hours and for ion nitriding is up to 30 hours

4. A method according to any one of Claims 1 to 3, wherein the dwell times for carburizing are between 1 and 10 hours and for boronising between 2 and 10 hours.