Method for measuring crystal misorientation of a single-crystal blade

Abstract

Method for measuring crystal disorientation of a monocrystalline blade Method for measuring crystal disorientation of a monocrystalline blade (10) comprising a material formed of dendrites (30) having a main trunk (32) extending in a main direction (Z') and branches (34), the method comprising defining a reference frame (XYZ) of the blade comprising a radial direction (Z), mechanically and chemically treating the blade (10) in a base plane (P1) to acquire a first image (I1) by micrography, mechanically and chemically treating the blade (10) in a comparison plane (P2) radially offset from the base plane (P1) by a distance (D), to acquire a second image (I2) by micrography, processing the first and second images (I1, I2) so as to compare the position of the main trunk (32) of each dendrite (30) between the two images (I1,I2) and thus deduce the orientation of the main direction (Z') of the dendrites (30) with respect to the radial direction (Z). Figure for the abstract: Fig. 4.,

Description

Title of the invention: Method for measuring the crystal disorientation of a single-crystal blade Technical field

[0001] The present disclosure relates to the field of single-crystal blades, and in particular the three-dimensional optical measurement of the crystal orientation of these blades. More specifically, the present disclosure relates to a method for measuring the crystal disorientation of a single-crystal blade. Prior art

[0002] Rotating aircraft engines must meet demanding criteria of airworthiness, quality and performance. Their performance is generally correlated with the temperatures of the combustion gases circulating at the turbines and in particular their blades. These blades are subjected to very high temperatures, for very long periods, and rotate at very high rotational speeds. Given these stresses, the blades are mainly subjected to fining.

[0003] To withstand these stresses, these blades are generally made from so-called “monocrystalline” or “monograin” superalloys which, by definition, have the advantage of not having grain boundaries, which improves their resistance.

[0004] The manufacture of single-crystal turbine blades is based on a foundry process in which, starting from a molten alloy, the selection of a seed and the control of the growth direction of the dendrites generated during cooling determine the final orientation of the grain. Dendrites are branched crystals appearing during solidification of the alloy and having a three-dimensional structure, comprising a central shaft, or main trunk forming a main direction of the dendrite, and branches extending from the main trunk, in secondary directions transverse to the main direction.

[0005] These dendrites can be revealed by known micrographic preparation methodologies, including cutting the blade, polishing and chemical or electrochemical etching. The dendrites thus highlighted on the section plane take the form of a cross whose center indicates the position of the main trunk, and the branches correspond to the ramifications.

[0006] Furthermore, the resistance of the blades to stresses and in particular to fining is directly correlated to the primary orientation of the crystal constituting them, called primary crystalline orientation, relative to the radial direction in which the centrifugal stresses linked to the rotation of the turbine are exerted. In other words, the resistance of the blades depends on the orientation of the main direction of the dendrites relative to the ideal theoretical axis (i.e. 0° relative to the radial direction) targeted for a blade. The angle between the main direction of the dendrites and the radial direction (the ideal theoretical axis) should typically be less than 15°, this value constituting a compromise between the cost price and the scrap rate due to crystal disorientation.

[0007] Turbine blades are therefore frequently the subject of investigations aimed at observing their crystalline orientations and highlighting this variable (difference between the main direction of the dendrites and the radial direction of the blades), in order to identify the causes and modes of damage to these blades, in particular deformations, cracks, and ruptures.

[0008] Furthermore, the efficiency and quality of these investigations are essential factors which contribute to ensuring the necessary responsiveness for possible actions aimed at improving flight safety. However, current investigation methods have a certain number of drawbacks. Indeed, known radiocrystallography methods, such as the "Laue" method, require specialized equipment not usually available in a traditional metallographic laboratory, which implies the delegation of these investigations, and therefore time and costs for carrying out orientation measurements which are not compatible with the requirements of efficiency and responsiveness of these investigations.

[0009] Other methods, more accessible in terms of technical means, do not provide satisfactory reliability and quality of measurements. Indeed, depending on the methods used, it can be particularly difficult to reliably identify the main trunks, or to distinguish the direction in which the dendrites are disoriented relative to the radial direction.

[0010] There is therefore a need to overcome at least in part the aforementioned drawbacks, by providing a method for measuring the crystalline orientation of a monocrystalline blade which is at the same time reliable, efficient, and technically accessible so as to meet the requirements of efficiency and reactivity of these investigations. Statement of the invention

[0011] The present disclosure relates to a method for measuring crystal disorientation of a single-crystal blade, the blade extending radially between a blade root and a blade tip and comprising a material formed of dendrites having a main trunk extending in a main direction between the blade root and the blade tip, and branches extending transversely to the main direction, the method comprising: - the definition of a reference frame of the blade comprising a radial direction of the blade, - mechanical and chemical treatment of the blade in a base plane perpendicular to the radial direction so as to acquire a first image by micrography in said base plane, - mechanical and chemical treatment of the blade in a comparison plane perpendicular to the radial direction and radially offset from the base plane by a predetermined distance, so as to acquire a second image by micrography in said comparison plane, - processing the first and second images in order to compare the position of the main trunk of each dendrite between the two images and thus deduce the orientation of the main direction of the dendrites relative to the radial direction of the blade.

[0012] It is understood that the reference frame of the blade is a Cartesian frame comprising the normal radial direction of the blade, and a plane perpendicular to the radial direction, the base plane being parallel to this plane perpendicular to the radial direction.

[0013] In this method, the mechanical and chemical treatment of the blade on two planes makes it possible to acquire a micrographic image on these two planes, i.e. the base plane and the comparison plane. It is thus possible to compare the position of the main trunk of each dendrite between these two images, and therefore to measure, for each dendrite, the offset of its main trunk between these two planes, knowing moreover the predetermined distance separating the two planes.

[0014] Comparing the position of the main trunks, by processing the first and second images, makes it possible to deduce the primary growth axis of the dendrites of the single crystal, and consequently to deduce the crystalline orientation of the blade, more precisely the disorientation of the crystals with respect to the radial direction.

[0015] This method has the advantage of reliably and precisely measuring the primary crystalline orientation of the blade, with sample preparation means readily available in a traditional metallographic laboratory, without requiring specialized equipment likely to generate significant costs and delays, and being incompatible with the efficiency and responsiveness requirements of these investigations.

[0016] In some embodiments, the method comprises, prior to mechanically and chemically treating the blade in the base plane, making a radial reference notch, the base plane and the comparison plane being arranged to intersect the reference notch.

[0017] It is understood that the radial reference notch extends mainly in the radial direction, perpendicular to the plane of the reference mark perpendicular to the radial direction. The presence of the notch is advantageous in that it constitutes a mark making it possible to facilitate the superposition of the first image and the second image during their processing, and therefore to improve the precision of said processing and the results obtained.

[0018] In some embodiments, the first and second images each comprise at least a portion of the reference notch, wherein processing the first and second images comprises superimposing the first and second images by superimposing said portion of the reference notch.

[0019] It is understood that the first and second images each comprise the same portion of the reference notch, which makes it possible to improve the precision of the superposition and the results obtained during the processing of the images.

[0020] In some embodiments, the base plane is defined by a radial end of the blade root.

[0021] This makes it possible to improve the speed and efficiency of the process, the base plane being already present and not requiring significant machining work, apart from its polishing before the chemical treatment. It will also be noted that defining the base plane, and consequently the comparison plane, in the blade root, and not at another location on the blade, makes it easier to carry out investigations aimed at determining the crystalline orientation, the quantity of material being greater at the blade root.

[0022] In some embodiments, the predetermined distance between the base plane and the comparison plane is between 0.15 and 0.35 mm.

[0023] This distance makes it possible to obtain a reliable estimate of the primary growth axis of the dendrites, and therefore of the crystalline orientation, while limiting the quantity of material to be removed by machining to prepare the comparison plane, and therefore improving the efficiency of the process.

[0024] In some embodiments, the method comprises measuring the radial positioning of the base plane relative to a reference plane of the blade, and measuring the radial positioning of the comparison plane relative to said reference plane.

[0025] By measuring the radial positioning, along the radial direction, of the base plane and the comparison plane relative to the same reference plane, it is possible to know precisely the predetermined distance between these two planes and their relative position with respect to each other. This makes it possible to further improve the accuracy of the measurement of the crystal orientation.

[0026] In some embodiments, the reference plane is defined by a radial end of the blade tip.

[0027] The plane defined by the radial end of the blade head being easily identifiable, and precisely locatable, this makes it possible to simplify the implementation of the method and to further improve its efficiency.

[0028] In some embodiments, the mechanical treatment comprises machining and / or polishing a surface of the blade in the base plane and in the comparison plane, and the chemical treatment comprises applying an acid to the machined and polished surfaces of the blade.

[0029] When the base plane is considered at the radial end of the blade root, only polishing of this radial end surface of the blade root is necessary. To define the comparison plane, more machining is necessary, in which a larger amount of material is removed over the predetermined distance.

[0030] In some embodiments, processing the first and second images comprises exploiting them, the exploiting comprising mapping the position of the main trunk of the dendrites in the first image and in the second image.

[0031] The processing of the first and second images comprises the exploitation of these images, consisting of identifying the position of the main trunks on each image, either manually or by digital methods. It is therefore understood that the position of a main trunk can be identified by a point corresponding to the center of the cross formed by the dendrite in the plane, and that the exploitation of each of the first and second images reveals a cloud of points revealing the position of the main trunks of each of the dendrites.

[0032] In certain embodiments, the method comprises, after the exploitation of the first and the second image, a mathematical and / or statistical and / or trigonometric processing of the processed images so as to determine an average main direction of the dendrites, and to measure a primary angle between the average main direction and the radial direction.

[0033] When the first and second images that have been exploited are superimposed, in particular by superimposing the portion of the reference notch, it is possible to visualize the variation in the position of the main trunks from one image to the other. Thus, this variation for each of the main trunks can constitute input data that can be averaged, for example by statistical processing, which makes it possible to determine an average primary growth axis of the dendrites, and therefore an average main direction of the dendrites. From the latter, it is possible to determine a primary angle between the average main direction and the radial direction, for example via a trigonometric calculation. It is thus possible to determine a primary angle of crystalline disorientation precisely, and by using simple and easily accessible processing tools.

[0034] In some embodiments, the method comprises, for each dendrite and in the first image and the second image, measuring secondary angles between branches of a dendrite.

[0035] The measurement of secondary angles can be carried out after the acquisition of each image, or during the exploitation of these. The measurement of secondary angles, in addition to the primary angle, makes it possible to evaluate crystallographic disorientations even more precisely.

[0036] In some embodiments, the method includes determining Euler angles of the blade defined by the primary angle and secondary angles of the dendrites.

[0037] Knowledge of the Euler angles, and therefore of the Euler frame, makes it possible to know precisely the crystalline orientation of the blade in relation to the blade reference frame.

[0038] In some embodiments, the single crystal blade is a turbine blade. Brief description of the drawings

[0039] The invention and its advantages will be better understood upon reading the detailed description given below of different embodiments of the invention given as non-limiting examples. This description refers to the appended pages of figures, in which:

[0040] [Fig.l] [Fig.l] represents a perspective view of a monocrystalline turbine blade;

[0041] [Fig.2] [Fig.2] schematically represents a) a side view of a dendrite, b) an image obtained by micrographs in a plane P of the blade of [Fig.l], c) a 3D modeling of a dendrite;

[0042] [Fig.3] [Fig.3] schematically represents a) a 3D modeling of a dendrite having an orientation inclined relative to the radial direction of the blade, b) a 2D view of the modeling of the image a) in a section plane perpendicular to the radial direction;

[0043] [Fig.4] [Fig.4] represents a perspective view of a single-crystal turbine blade at different stages of a crystal misorientation measurement method according to the invention;

[0044] [Fig.5] [Fig.5] schematically represents the acquisition of a first image by micrography in a first PI plane of the blade;

[0045] [Fig.6] [Fig.6] schematically represents the acquisition of a second image by micrography in a second plane P2 of the blade;

[0046] [Fig.7] [Fig.7] schematically represents the exploitation of the first and second images and the mapping of the positions of the main trunks on each of the images;

[0047] [Fig.8] [Fig.8] schematically and in a simplified manner represents the superposition of the first and second images and the variation in the position of the main trunks;

[0048] [Fig.9] [Fig.9] schematically represents the different stages of a process of measurement of crystal disorientation of a monocrystalline blade according to the invention. Description of the embodiments

[0049] [Fig. 1] illustrates a moving blade 10, for example metallic, of a high-pressure turbine of a turbomachine. The turbine blade is formed of a monocrystalline material. Of course, the present invention can also be applied to other moving or fixed blades of the turbomachine formed of a monocrystalline material.

[0050] The blade 10 extends in a reference frame XYZ, Z being the main radial direction in which the blade extends, and the radial plane XY being perpendicular to the radial direction Z. The blade 10 conventionally comprises an aerodynamic surface 12 (or blade) which extends radially between a platform 14 and a blade head 16. It will be noted that, although the blade 10 illustrated in [Fig. 1] has a blade tip bath, the blade 10 could also have a blade head having a heel, without departing from the scope of the invention.

[0051] The aerodynamic surface 12 has a leading edge 18 arranged opposite the flow of hot gases coming from the combustion chamber of the turbomachine, a trailing edge 20 opposite the leading edge 18, a lower surface lateral face 22 and an upper surface lateral face 24 (masked), the lateral faces 22, 24 connecting the leading edge 18 to the trailing edge 20.

[0052] The blade 10 further comprises a blade root 26 intended to be mounted in a cell of a movable turbine disk (not shown). Thus, the blade 10 extends radially between a radially inner end 28 of the blade root 26 and the blade head 16 at the radially outer end. Furthermore, the blade head 16 extends in an outer radial end plane of the blade 10, hereinafter called the reference plane R, the reference plane R preferably being parallel to the XY plane.

[0053] The monocrystalline blade 10 may be manufactured by a known foundry method, in which a molten alloy, for example a nickel-based superalloy, is placed in a ceramic mold and then cooled by directional solidification, during which the cooling of the alloy is controlled so as to obtain a material having the desired quality and properties. In particular, a crystal seed is selected and the direction of crystal growth is controlled during cooling, such selection and control of the growth direction determining the final crystal orientation. The crystals forming the final monocrystalline material take the form of dendrites, having a three-dimensional structure.

[0054] [Fig.2] schematically represents, in image a), a dendrite 30. A dendrite 30 comprises a central shaft, or a main trunk 32, defining a main direction Z', or primary direction, of the dendrite 30, which corresponds to the axis of main growth of the dendrite. The dendrite 30 further comprises branches, or ramifications 34 extending from the main trunk 32 in directions transverse to the main direction Z'.

[0055] The dendrites 30 constituting the material of the blade 10 can be revealed by known micrographic preparation methodologies, comprising cutting the part in a section plane, polishing the surface of the cut part, and chemical or electrochemical attack of said surface, by a suitable acid.

[0056] Image b) of [Fig. 2] schematically represents an example of an image obtained by micrography, from a section made in the blade root 26 of the blade 10 of [Fig. 1], along a section plane P perpendicular to the radial direction Z. Image I obtained in 2D (two dimensions) is inscribed in a plane parallel to the XY plane and reveals a plurality of dendrites 30 having, in this plane, a cross shape. The center of the crosses reveals the position of the main trunks 32 at the plane P, and the branches of the crosses reveal the positions of the ramifications 34.

[0057] Image c) of [Fig.2] is a 3D (three-dimensional) model of a dendrite 30, for example of the dendrite 30 of image a). This model has the shape of an extruded cross, making it possible to define the intrinsic angles of the dendrite 30, i.e. the Euler angles of the dendrite 30. The center of the extruded cross of the model of the dendrite 30 corresponds to the main trunk 32, defining the main direction Z', or primary direction. The branches of the cross, extending from the main trunk 32, correspond to the ramifications 34, which extend in secondary directions Y', Z' transverse to the primary direction Z'.

[0058] The orientation of the Euler frame X'Y'Z' of the dendrite 30 relative to the base frame (or Cartesian frame intrinsic to the blade 10), i.e. the frame XYZ defined previously, makes it possible to determine the crystalline orientation of the blade 10. In particular, the orientation of the primary direction Z' of the dendrites 30 relative to the radial direction Z of the blade 10, which is the ideal theoretical direction of the dendrites 30, defines a primary angle of the crystalline orientation. Furthermore, the angles between the secondary directions X' and Y' define the secondary angles of the crystalline orientation.

[0059] Image c) of [Fig.2] represents an “ideal” case, in which the main direction Z' is parallel and coincident with the radial direction Z (the primary angle is therefore zero), and the secondary angles between the secondary directions X' and Y' are right angles.

[0060] In practice, foundry manufacturing methods involve inevitable and intrinsic imperfections in the blades, the primary direction Z' therefore not being perfectly aligned with the radial direction Z. [Fig.3] represents, in image a), a model of a dendrite 30, in which the primary direction Z' is inclined, and forms a primary angle 0 with the radial direction Z. Given this inclination, the branches 34 are themselves not perpendicular to each other. Indeed, in a section of the modeling of the dendrite 30 perpendicular to the radial direction Z, shown in image b) of [Fig.2], the secondary directions X', Y' form secondary angles [3, |3'] between them, where [3' = 180° - [3.

[0061] The primary and secondary angles [3, [3' constitute the Euler angles of the dendrite 30, the values ​​of which make it possible to know the orientation of the Euler frame X'Y'Z' relative to the frame XYZ intrinsic to the blade 10, and therefore to know the crystalline orientation of the blade 10.

[0062] It is sometimes necessary to know as precisely as possible the crystalline orientation, and in particular the disorientation of the dendrites 30 with respect to the ideal radial direction (the primary angle 0 must be less than 15°), to identify the causes and modes of damage to these blades, in particular deformations, cracks, and breaks possibly suffered by the blades. The method described below with reference to FIGS. 4 to 9 makes it possible to carry out such investigations efficiently, by means readily available in a traditional metallographic laboratory.

[0063] In the present example, we are interested in a method for measuring the crystal disorientation of a monocrystalline turbine blade as described above and shown in [Fig.l].

[0064] In a first step (step S100), a reference frame intrinsic to the blade 10 is defined. In the present example applied to the turbine blade 10, this reference frame is the Cartesian reference frame XYZ described previously, where Z is the radial direction of the blade 10.

[0065] Next, a reference notch E is made in the blade root 26 (step S200, image a) of [Fig. 4]). Preferably, the notch E is made from the radially inner end 28 of the blade root 26, perpendicular to the plane formed by said radially inner end 28, that is to say perpendicular to the radial plane XY. Preferably, the dimensions and dimensions of the notch E result from an empirical optimization between precision, material and preparation time. In other words, the notch E constitutes a quick reference point to be produced by machining, the dimensions of the notch E being moreover determined and known precisely, so as to improve the precision of the superposition and of the treatments described later.

[0066] A base plane PI is then defined (step S300, image b) of [Fig.4]). In this example, the base plane PI corresponds substantially to the plane formed by the radially inner end 28 of the blade root 26, on which a preparation is carried out. This preparation comprises polishing the radially inner end 28, then chemically etching it in order to reveal the dendrites 30.

[0067] In addition, a measurement of the positioning dimension of the base plane PI is also carried out at this step. To do this, a measurement of the distance between the base plane PI obtained after the preparation, and the reference plane R described previously, can be performed. Thus, step S300 of defining the base plane PI comprises the preparation (step S310) described above, and the measurement of the positioning dimension (step S320).

[0068] The acquisition of a first image II is then carried out in the base plane PI (step S400, [Fig.5]). The first image II is obtained by a micrography method described previously, in the base plane PI, and makes it possible to reveal a plurality of dendrites 30. The acquisition of the first image II is carried out on a portion of the base plane PI encompassing a portion of the reference notch E, for example an edge 29 of the notch in the base plane PI, and an end 291 of said edge 29.

[0069] A comparison plane P2 is then defined (step S500, image c) of [Fig.4]). As for the basic plane PI, the definition of the comparison plane P2 includes the preparation (step S510) and the measurement of the positioning dimension (step S520).

[0070] The comparison plane P2 is parallel to the base plane PI, and is obtained by machining the blade root 26 from the base plane PI (corresponding substantially to the radially internal end 28), and over a predetermined distance D in the radial direction Z. The distance D between the base plane PI and the comparison plane P2 may be for example between 0.15 and 0.35 mm, and is less than the height of the reference notch E. After this machining, the surface obtained is polished, and a chemical attack is carried out, so as to reveal the dendrites 30 in the plane P2. The step S510 of preparing the comparison plane P2 therefore comprises the machining described above, the polishing and the chemical attack.

[0071] The aforementioned distance D can be chosen arbitrarily and approximately, provided that it is included in the range mentioned in the preceding paragraph, and that it remains less than the height of the notch E. To know precisely the positioning dimension of the comparison plane P2 in the XYZ reference frame, the measurement of the positioning dimension (step S520) is carried out, in which the distance between the comparison plane P2 obtained after the preparation, and the reference plane R is measured.

[0072] The precise knowledge of the positioning dimension of the base plane PI carried out in step S320, and of the comparison plane P2 carried out in step S520, makes it possible to precisely deduce the distance between the base plane PI and the comparison plane P2, i.e. the distance D. The precise knowledge of the distance D and of the position of the planes PI, P2 along the radial direction Z allows a more precise evaluation of the primary angle 0, described later.

[0073] On the basis of the comparison plane P2, the acquisition of a second image 12 is carried out (step S600, [Fig. 6]). The second image 12 is obtained in the same manner as for the first image II, i.e. by a micrography method in the comparison plane P2, and makes it possible to reveal the same plurality of dendrites 30 as in the first image II, but in the comparison plane P2.

[0074] In particular, the acquisition of the second image 12 is carried out on a portion of the comparison plane P2 similar to the portion of the base plane PI on which the acquisition of the first image II is made, encompassing the same portion of the reference notch E, comprising the border 29 in the comparison plane P2 (that is to say the same border as in the base plane PI but radially offset by the distance D), and the end 291 of said border 29.

[0075] The images II and 12 thus obtained are then exploited (step S700, [Fig.7]). The exploitation of these images notably comprises the localization of the main trunks 32 on each image II, 12, corresponding to the centers of the crosses revealing the position of the dendrites 30 (step S710). At this step, only the position of the centers 32 in the XY plane is important. Thus, the images II and 12 represented in [Fig.7] take the form of a cloud of points, symbolizing the position of the centers of the crosses, that is to say of the main trunk 32 of each dendrite 30, in the planes P1 and P2 respectively.

[0076] Optionally, it is also possible to measure the secondary orientations, and in particular the secondary angles [3 and |3', on each of the images II and 12 (step S720). More precisely, the secondary angles [3 and [3' can be measured on the image II, then checked on the image 12 in order to validate the measurements carried out on the image II. In addition to the measurement of the primary angle 0 described below, the measurement of the secondary angles [3 and [3' makes it possible to evaluate the crystallographic disorientations more precisely.

[0077] The processing operations described above can be carried out manually, by manually measuring the position of each center 32 on the images II and 12 as well as the secondary angles [3 and |3', or digitally, by means of suitable digital tools allowing these measurements to be carried out. It will also be noted that the order of step S720 is not limiting, the measurement of the secondary angles [3 and [3' can be carried out first on the first image II, just after step S400 of acquiring the first image II, then on the second image 12, just after step S600 of acquiring the second image 12.

[0078] The measurement of the positioning of the main trunks 32 in step S710 makes it possible, for each dendrite 30, to compare the position of the main trunk 32 on the base plane PI (first image II) and on the comparison plane P2 (second image II). For this, the images used in step S700 are then subjected to mathematical and / or statistical and / or trigonometric processing (step S800).

[0079] During this step, the first and second images II, 12 obtained previously are superimposed so as to visualize the evolution of the position of the main trunk 32 of each dendrite 30, between the base plane PI and the comparison plane. P2 (step S810). The reference notch E made in step S200 and included in part on images II and 12 makes it possible to facilitate this superposition and to improve its precision. The notch E in fact serves as a reference, by superimposing the edges 29 and the ends 291 of each image II, 12.

[0080] The result of this superposition is shown schematically in [Fig.8], on which only a sample of about ten pairs of points, symbolizing the position of the main trunks 32, is shown. Each pair of points, for example the pairs 32a, 32b, 32c, represents a single main trunk 32, the position of which has slightly deviated between the first image II and the second image 12, that is to say between the base plane PI and the comparison plane P2. This slight deviation between the planes PI and P2 is represented by the distance e.

[0081] Knowledge of the distance e for each dendrite 30 visible in images II, 12, in particular its amplitude, makes it possible to carry out a statistical measurement on all of the dendrites 30. For example, all of the measured distances e are represented in the form of a Gaussian curve, of which only the peak is retained and considered as the average deviation value of the main trunks 32. Thus, precise knowledge of the distance D and the average deviation value e makes it possible to deduce, by trigonometric calculations, the primary orientation, in particular the primary angle 0 (step S820).

[0082] Finally, the knowledge of the primary angle θ determined in step S820, and of the secondary angles [3 and [3' determined in step S720, make it possible to determine the Euler angles of the dendrites 30, defining the crystalline orientation of the blade 10 (step S900). It will be noted, however, that this last step S900 (as well as step S720 of determining the secondary angles [3 and |3') is optional, the method being able to stop only at step S820 of determining the primary angle θ. Indeed, the knowledge of the primary angle θ is essential in that it makes it possible to estimate the crystalline disorientation with respect to the radial direction Z, this disorientation being able to explain on its own any damage to the blade 10 occurring. The knowledge of the secondary angles [3 and [3' makes it possible, however, to refine the evaluation of this disorientation.

[0083] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various illustrated / mentioned embodiments may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

Claims

Claims

1. Method for measuring crystal disorientation of a single-crystal blade (10), the blade (10) extending radially between a blade root (26) and a blade tip (16) and comprising a material formed of dendrites (30) having a main trunk (32) extending in a main direction (Z') between the blade root (26) and the blade tip (16), and branches (34) extending transversely to the main direction (Z'), the method comprising: - defining a reference frame (XYZ) of the blade comprising a radial direction (Z) of the blade (10), - mechanically and chemically treating the blade (10) in a base plane (PI) perpendicular to the radial direction (Z), so as to acquire a first image (II) by micrography in said base plane (PI), - mechanically and chemically treating the blade (10) in a comparison plane (P2) perpendicular to the radial direction (Z) and radially offset from the base plane (PI) by a predetermined distance (D),so as to acquire a second image (12) by micrography in said comparison plane (P2), - processing the first and second images (II, 12) so as to compare the position of the main trunk (32) of each dendrite (30) between the two images (II, 12) and thus deduce the orientation of the main direction (Z') of the dendrites (30) relative to the radial direction (Z) of the blade (10).,

2. Method according to claim 1, comprising, before the mechanical and chemical treatment of the blade (10) in the base plane (PI), the production of a radial reference notch (E), the base plane (PI) and the comparison plane (P2) being arranged so as to cut the reference notch (E).

3. A method according to claim 2, wherein the first and second images (II, 12) each comprise at least a portion (29) of the reference notch (E), the processing of the first and second images (II, 12) comprising superimposing the first and second images (II, 12) by superimposing said portion (29) of the reference notch (E).

4. A method according to any one of claims 1 to 3, wherein the base plane (PI) is defined by a radial end (28) of the foot dawn (26).

5. A method according to any one of claims 1 to 4, wherein the predetermined distance (D) between the base plane (PI) and the comparison plane (P2) is between 0.15 and 0.35 mm.

6. A method according to any one of claims 1 to 5, comprising measuring the radial positioning of the base plane (PI) relative to a reference plane (R) of the blade (10), and measuring the radial positioning of the comparison plane (P2) relative to said reference plane (R).

7. A method according to claim 6, wherein the reference plane (R) is defined by a radial end of the blade head (16).

8. A method according to any one of claims 1 to 7, wherein the mechanical treatment comprises machining and / or polishing a surface of the blade (10) in the base plane (PI) and in the comparison plane (P2), and the chemical treatment comprises applying an acid to the machined and polished surfaces of the blade (10).

9. A method according to any one of claims 1 to 8, wherein processing the first and second images (II, 12) comprises exploiting them, the exploiting comprising mapping the position of the main trunk (32) of the dendrites (30) in the first image (II) and in the second image (12).

10. Method according to claim 9, comprising, after the exploitation of the first and second images (II, 12), a mathematical and / or statistical and / or trigonometric processing of the processed images so as to determine an average main direction (Z') of the dendrites (30), and to measure a primary angle (0) between the average main direction (Z') and the radial direction (Z).

11. Method according to any one of claims 1 to 10, comprising, for each dendrite (30) and on the first image (II) and the second image (12), the measurement of secondary angles (|3, |3') between the branches (34) of a dendrite (30).

12. A method according to claims 10 and 11, comprising determining Euler angles of the blade (10) defined by the primary angle (0) and the secondary angles (|3, |3') of the dendrites (30).

13. A method according to any one of claims 1 to 12, wherein the single-crystal blade (10) is a turbine blade.

Images