GB2222678A

GB2222678A - Ultrasonic measuring of crystalline properties

Info

Publication number: GB2222678A
Application number: GB8919737A
Authority: GB
Inventors: Juergen Wortmann; Wolf-Dieter Feist
Original assignee: MTU Motoren und Turbinen Union Muenchen GmbH
Current assignee: MTU Aero Engines GmbH
Priority date: 1988-09-06
Filing date: 1989-08-31
Publication date: 1990-03-14
Anticipated expiration: 2009-08-31
Also published as: DE3830233A1; GB8919737D0; FR2636141A1; DE3830233C2; FR2636141B1; GB2222678B

Description

2222,,678 APPARATUS FOR THE DETERMINATION OF CRYSTALLINE STRUCTURE

-------------- The invention relates to apparatus for determining the crystalline structure of a test piece.

The crystalline structure of a crystalline component is of considerable importance for resistance in use and service life. For example, in the case of monocrystalline bodies the arrangement of the crystalline structure, i.e. the lattice orientation related to a predetermined direction, has a significant effect on the qualities in use of the component. When there are fairly large deviations there occurs a considerable reduction of the long-time rupture strength of the monocrystalline component e.g. a turbine blade.

In the case of polycrystalline components the size of the intercrystalline angle, i.e. of the angle of the lattice orientations of two adjacent grains, is of great importance. From this also conclusions may be drawn as regards the resistance in use of the object.

When there are extensive deviations there occurs a considerable reduction of the long-time rupture strength of the mono-crystalline component e.g. a turbine blade.

In the case of polycrystalline components the size of the intercrystalline angle, i.e. of the angle which the lattice orientations of two adjacent grains form with each other, are of great importance. From this conclusions may be drawn as regards the resistance in use of the object.

A further quality characteristic is the occurrence of foreign and recrystallisation grains. All three types of deviations may well be able to reduce the service life of turbine blades by more than the factor 1000.

The utilisation of ultra-sound for the determination of crystalline orientation is known from the work "Ultraschall-Messtechnik (Ultrasonic Measurement Engineering) by Horst-Dieter Tietz, Berlin, pp. 145-146. The process disclosed in that work, however, requires for coupling a regularly formed smooth metal surface. The drawback associated with this is that it is possible only to test testing bodies with a specific external outline, such as cylinder, plate or sphere, inasfar as sensors are not adapted precisely to the surface of the element, which is very costly. With test bodies having irregularly curved surfaces this method cannot be used.

Determination of the orientation of monocrystals is usually carried out using X-ray fine structure determination (Laue method). This method detects lattice structures in regions close to the surface. There are drawbacks with this; the method does not supply any information as to structures in the volume, and it requires before measurement the removal of mechanically deformed surface layers; it cannot therefore be used on finished processed parts, such as turbine blade vanes.

One object of the invention is to enable accurate crystallographic measurement of test pieces of any shape at low cost.

According to the invention we propose apparatus for the 1 determination of the crystalline structure of a crystalline test piece by means of ultrasonic waves radiated from a transmitting test head and received by a reception test head, wherein the transmitting test head and the reception test head are aligned with each other and immersed in a liquid medium, the heads and a test piece which, is use is arranged between them, being relatively movable to detect an intensity maximum of the ultra sound passing through the test piece.

The invention enables, for the first time, crystal lattice determination of test pieces of any shape, e.g.

turbine blades. Further, volume testing is possible, i.e. rays are passed through the component, as a result of which imperfections and grain boundaries situated inside the body become detectable.

Furthermore, it is not necessary to process the surface of the component; testing may be carried out on finished components. There used to be no interference with its dimensions.

Conveniently, the liquid medium is water. This makes possible a simple exchange of maintenance or soiling, and uncomplicated handling.

The test piece is preferably arranged in fixed position and the transmitter testing head and the reception testing head are movable together. By this means large and heavy test pieces can be simply fixed and the expenditure of technical means for the moving device (goniometer) remains small.

In an alternative embodiment the transmission testing head and the reception testing head are stationary, and the test piece is movable; in the case.of relatively. small and light test pieces such as turbine blades this permits simple construction.

The moving device (goniometer) for the moved component is designed in such a manner that the moved element is movable in six degrees of freedom; preferably three in translation and three in rotation.

Also according to the invention we propose a method of using the apparatus for detecting crystal lattice orientation in a test piece, comprising relatively rotating the heads and the test piece about an axis until an intensity maximum is achieved, and then relatively rotating about an axis perpendicular thereto, until again an intensity maximum is achieved. Thereby the two angle components situated perpendicularly to each other of the crystal orientation angle are determined. As the observed intensity maxima are very steep, a very precise angular determination can be achieved by means of the invention.

For determination of corn boundaries within a polycrystalline test piece, after rotation to the first maximum, a linear relative movement between the test piece and measuring probe is performed until there occurs a discrete modification of echo intensity. By renewed rotation until the achievement of echo maximum the extent of the corn magnitude angle in the rotation plane is directly detected.

The two processes can be advantageously combined so as to achieve a greater process ecomony. In particular an automatic and quantitative evaluation of higher precision and at greater speed is achieved. In a further embodiment of the invention a process is described for the identification of foreign grains in which there is effected a linear shaped scanning of the test piece e.g. in the orientation of maximum echo intensity. The advantage of this process lies in that it is possible to identify grains of differing orientation present in the volume.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing, which is a diagrammatic representation of the construction of the measuring device.

A dip tank 12 is shown which is filled with water as a coupling medium. A test piece 1 in the form of a monocrystalline turbine blade is securely fixed in the dip tank 12 by means of a clamping device 13. test head 2 and a reception test head 3 are mounted aligned on each other by means of a mechanical holder 4 which is movable in at least six freedome degrees by means of a goniometer 5 not shown in detail.

By means of a pulse generator 7 a trigger signal is produced that is used by switching an ultrasonic transmission pulse and for the activation of a reception part 8. The ultrasonic transmitter 6 triggered by the pulse generator 7 produces a signal which impacts a A transmission transmission test head 2 by means of the lead 14a.

The ultrasonic signal passes through the coupling medium (water) and the test piece 1, and is taken up by the reception test head 3. By means of the line 14b the signal reaches the receiver 8 with coupled high frequency amplifier. An oscilloscope 9 is used for viewing the progress of the intensity and a gating circuit 10 with duration measurement device determines the ultrasonic duration.

A control unit 11 for setting the goniometer may be operated as desired either by hand by means of the input device 15 or by evaluation of the signals from the receiver 8 and the gating circuit 10. In the last instance a fully automatic determination of the desired data is effected. Depending on the measuring programme it will be possible to ascertain grain boundaries or to identity foreign grains.,

Claims

1. Apparatus for the determination of the crystalline structure of a crystalline test piece by means of ultrasound waves radiated from a transmitting test head and received by a reception test head, wherein the transmitting test head and the reception test head are aligned with each other and immersed in a liquid medium, the heads and a test piece which, in use, is arranged between them, being relatively movable to detect an intensity maximum of the ultra sound passing through the test piece.

2. Apparatus according to claim 1, wherein the liquid medium is water.

3. Apparatus according to claim 1 or claim 2, wherein the test piece is stationarily mounted and the transmitting test head and the reception test head are movable together.

4. Apparatus according to claim 1 or claim 2, wherein the transmitting test head and the reception test head are stationarily mounted and the test piece is movable.

5. Apparatus according to any preceding claim wherein relative movement is effected by means having six degrees of freedom.

6. Apparatus according to claim 5, wherein said means for effective relative movement has three degrees of free translation and three degrees of free rotation.

7. Apparatus for the determination of the crystalline -B- structure of a test piece constructed and arranged substantially as herein described with reference to and as illustrated in the accompanying drawings.

8. A method for determining the crystal lattice orientation of a crystalline test piece using apparatus according to any one of claims lto 7 comprising relatively rotating the heads and the test piece about an axis until an intensity maximum is reached, and subsequently effecting relative rotation about an axis perpendicular thereto, until an intensity maximum is again arrived at.

9. A method for determining grain boundaries using apparatus according to any one of claims 1 to 7, comprising relatively rotating the heads and the tes piece about an axis until an intensity maximum is achieved, effecting of intensity takes place, and thereafter effecting relative rotation about an axis perpendicular thereto until an intensity maximum is again arrived at.

10. A method for identification of foreign bodies using apparatus according to any one of claims 1 to 7, comprising relatively moving the heads and the test piece such that a line-shaped scanning of the test piece (1) is effected in the orientation of maximum echo intensity.

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