Method for determining the risk of recrystallized grains appearing during the manufacture of a mechanical part

Abstract

Method for determining a risk of the appearance of recrystallized grains during the manufacture of a mechanical part Method (1) for determining a risk of the appearance of recrystallized grains during the manufacture of a mechanical part by casting an alloy with a metallic component in a mold, the method (1) comprising the following steps: 1) a step (E1) implementing a mechanical test on a test piece so as to characterize an imposed plastic deformation of said test piece as a function of an imposed temperature; 2) a step (E2) implementing a heat treatment for resolving said test piece, said heat treatment for resolving being capable of creating the recrystallized grains;6) a step (E6) of comparing the value of the plastic deformation potential (Pε) or the value of the plastic energy potential (PE) calculated with a threshold value, the exceeding of which corresponds to the existence of a risk of the appearance of recrystallized grains in the test piece. Figure for the abstract: Fig. 1;

Description

Title of the invention: Method for determining a risk of the appearance of recrystallized grains during the manufacture of a mechanical part FIELD OF THE INVENTION

[0001] The present invention relates to the field of manufacturing mechanical parts with a metallic component, and more particularly the reduction of the frequency of appearance of recrystallized grains likely to form during the production of the mechanical part. TECHNOLOGICAL BACKGROUND

[0002] In the field of transport, whether air, sea, rail or automobile, the safety and reliability of vehicles, such as aircraft in air transport, is an absolute priority for manufacturers. The operability of mechanical parts, playing a critical role in the operation of these vehicles, must then be ensured throughout one or more journeys of each vehicle.

[0003] The certification of such mechanical parts aims in this sense to guarantee that each of these parts meets technical requirements, called certification requirements, established by the relevant regulatory authorities. This certification process requires a rigorous evaluation of the design, production and performance of such parts. Thus, only mechanical parts that meet these certification requirements can be used in the construction, maintenance and / or repair of these vehicles, thus helping to minimize operational risks and prevent potential accidents that could be caused by these vehicles.

[0004] However, it is common for the mechanical parts produced to have variations (or deviations), for example dimensional or intrinsic variations, due to various factors such as the different successive manufacturing processes of the mechanical part, the materials used, the environmental conditions, etc. Such variations can become “critical” with respect to specific certification requirements, making certain mechanical parts potentially non-compliant and therefore unusable.

[0005] For example, when manufacturing an aeronautical type mechanical part such as a turbine blade, made of a nickel-based superalloy, specific requirements related to aerodynamic performance, heat resistance and durability are taken into account to assess whether the blade can be mounted in a rotor structure and become operational. This blade is manufactured by the implementation of the lost wax casting process known to the person skilled in the art and the steps of which are recalled below.

[0006] A wax model of the blade is made to be an exact replica of the final piece and will serve as a template for the ceramic mold (shell). Several wax models are then grouped together to form a cluster which is then attached to a channel system that will allow the molten metal to be poured into the mold. The cluster is then covered with a layer of refractory ceramic material, creating a ceramic mold that will be able to withstand the high temperatures of the casting process. The cluster is then heated to melt the wax, leaving a hollow ceramic mold.

[0007] The nickel-based superalloy is melted at extremely high temperatures and then poured into the ceramic mold. The molten metal then fills the mold cavity, forming the turbine blade. The molten metal then cools and solidifies in the mold, taking the shape of the blade. It is then essential to carefully control the cooling process to ensure an optimal microstructure, whether columnar or single-crystal, of the superalloy before the mold is removed and the part is subjected to heat treatments to optimize its mechanical strength and high-temperature stability so as to meet the certification requirements for it.

[0008] More particularly, traction and compression phenomena are likely to occur during cooling of the alloy because the latter has a higher coefficient of thermal expansion than the ceramic mold, which itself has a higher coefficient of thermal expansion than the ceramic core (structure inside the ceramic mold delineating the channels of the blade in this example). In other words, the alloy contracts more quickly than the ceramic mold, and contracts more quickly than the ceramic core during cooling. Thus, due to these differentials in coefficients of thermal expansion, the contraction is uneven and therefore creates mechanical stresses in the cooling alloy.

[0009] These generated mechanical stresses can be particularly pronounced in certain areas of the blade and lead, when they exceed a certain threshold, to a plastic and local deformation of the metal and therefore to a definitive accumulation of dislocations in the blade. These dislocations can however become problematic when they manage to reorganize themselves in such a way as to form a new grain leading to the presence of grain boundaries (perimeters of recrystallized grains), which means that the structure of the part is no longer monocrystalline. This reorganization of the dislocations generally occurs when a high temperature resolution heat treatment is applied to homogenize the chemistry of the entire part. This heat treatment allows the previously created dislocations to move freely within the material.

[0010] The turbine blade, no longer having a monocrystalline or columnar structure, then has a serious defect leading to it being considered defective because it does not comply with the specific certification requirements. Indeed, the monocrystalline or columnar structure gives the blade the ability to withstand extremely high operating temperatures, which allows the engines to operate at higher temperatures and thus improve their performance. In addition, a blade having a monocrystalline or columnar structure is less likely to deform under stress at high temperature and has better resistance to aging in particular. Thus, when the blade becomes polycrystalline, i.e.Having grain boundaries, the blade has limitations in terms of heat resistance and high temperature performance which can lead to significant safety risks when placed in the high-pressure turbine of a turbomachine for example.

[0011] Furthermore, such a defect cannot be repaired without compromising the performance of the mechanical part. As such, the mechanical part is generally replaced by another mechanical part of the same type and function which meets said requirements. However, since the mechanical part is made of a so-called complex alloy and requires special waste management which can be difficult to implement, a non-compliant part can then contribute to environmental pollution.

[0012] There is therefore a critical challenge linked to the preservation of the monocrystalline or columnar structure of these mechanical parts made of alloy, in particular nickel-based superalloy, during the process of their manufacture.

[0013] One solution consists in attempting to predict the appearance of recrystallized grains during the manufacture of the mechanical part because, as indicated above, the latter have a negative, or even harmful, impact on the mechanical properties of the part. Since the formation of recrystallized grains is influenced by two known factors, i.e. the plastic deformation and the temperatures at which these plastic deformations undergone by the part take place during its manufacture, one approach consists in developing a chart designed to determine the risk of the appearance of recrystallized grains during the manufacture of a mechanical part as a function of the temperature and plastic deformation energy or plastic deformation conditions to which the mechanical part is subjected.In other words, this chart provides graphical information that allows operators to improve manufacturing conditions so as to minimize the unwanted formation of recrystallized grains.

[0014] For this purpose, a series of mechanical tests is undertaken on test pieces. These tests aim to characterize the plastic deformation of the test pieces. generating recrystallization in response to different applied stress values ​​and for different controlled temperatures. Then, a heat treatment operation is carried out on the test piece to reveal those that have been recrystallized. Finally, the plastic deformation energy or plastic deformation is measured and is associated with the temperature observed during the test on the test piece while integrating the information concerning the presence of recrystallized grains. This thus makes it possible to create an abacus which will serve as a reference to guide the operators during the casting of the alloy in the mold so that the conditions of temperature and plastic energy or plastic deformation of deformations undergone by said metal part to be manufactured are below a given threshold of risk of appearance of recrystallized grains. Such an abacus is called isothermal because it is derived from isothermal tests.

[0015] However, there is a key limitation to this approach. The main difficulty is that isothermal tests are not representative of the manufacturing process which is anisothermal, making certain comparisons uncertain.

[0016] To solve this problem, two approaches are suggested. First, it is possible to carry out a large number of anisothermal tests, but this proves difficult, particularly at very high temperatures. Second, it is possible to collect a large number of manufacturing results for different geometries. However, this approach is neither always feasible nor economically viable, particularly when seeking to establish an abacus for a new alloy.

[0017] There is also an additional limitation to these anisothermal approaches. The main difficulty lies in the fact that it is extremely complex to cover all possible thermomechanical paths, which makes some comparisons uncertain. In other words, if a simulated thermomechanical path does not precisely match the reference chart over certain temperature ranges, the reliability of the comparison must be questioned. Thus, this approach of comparing thermomechanical paths is effective but its major limitation lies in the difficulty of covering all possible scenarios.

[0018] There is therefore a need to obtain a criterion that has two essential characteristics. First, this criterion must be able to consider the thermomechanical history of the cooling process, which means that it must take into account how the material has been subjected to variations in temperature and deformation over time. Second, it must be based on simple tests, preferably isothermal tensile tests from an isothermal chart. PRESENTATION OF THE INVENTION

[0019] To this end, the present disclosure relates to a method for determining a risk of the appearance of recrystallized grains during the manufacture of a mechanical part by casting an alloy with a metallic component into a mold, the method comprising the following steps: 1) a step implementing a mechanical test on a test piece so as to characterize an imposed plastic deformation of said test piece as a function of an imposed temperature; 2) a step implementing a heat treatment for resolving said test piece, said heat treatment for resolving being capable of creating recrystallized grains; 3) a step implementing a macrographic attack to determine the appearance of recrystallized grains in the test piece; 4) a step of acquiring data from an abacus of critical thresholds of plastic deformation likely to lead to the appearance of recrystallized grains as a function of a succession of temperature values; 5) a step of calculating a plastic deformation potential as a function of critical plastic deformation thresholds acquired on the chart and measured plastic deformation values ​​for a plurality of temperatures of the thermomechanical path of the test piece; and 6) a step of comparing the value of the calculated plastic deformation potential with a threshold value, the exceeding of which corresponds to the existence of a risk of the appearance of recrystallized grains in the test piece.

[0020] By using the data from the so-called isothermal chart on the one hand, that is to say constructed from isothermal tensile tests unlike the anisothermal chart constructed from anisothermal tensile tests, while on the other hand integrating data from the thermomechanical path of the cooling process of the test piece, the criterion for determining the risk of the appearance of recrystallized grains in the test piece (the plastic deformation potential) takes into account the two characteristics defined above. The potential is then able to consider the thermomechanical history of the cooling process while relying on simple tests, here isothermal tensile tests which come from said chart.

[0021] Furthermore, it has been demonstrated that this criterion is indeed consistent with experimental observations by casting tests of simplified parts having a significant geometry of the mechanical part to be manufactured and / or by comparison with anisothermal mechanical tensile tests. Of course, the expression “and / or” must be interpreted here as corresponding to an inclusive “or”. In other words, the verification of the conformity of said potential can be implemented by said casting tests or by comparison with anisothermal mechanical tensile tests, or well by combining the implementation of casting tests and comparison with anisothermal tensile mechanical tests.

[0022] Thus, following these tests on specimens, the risk of the appearance of recrystallized grains during the manufacture of a mechanical part is better controlled, which significantly, or even totally, reduces the risk of manufacturing a mechanical part which could be considered non-compliant with the certification requirements and therefore liable to be withdrawn or destroyed.

[0023] According to one embodiment of the invention, the plastic deformation potential corresponds to a cumulative value of ratios, each ratio comprising as a numerator a difference between two successive values ​​of plastic deformation of the thermomechanical path of the test piece recorded at two successive temperatures of the thermomechanical path, and comprising as a denominator a critical threshold of plastic deformation acquired by the abacus and interpolated as a function of two successive temperatures of the abacus which are closest to the two successive temperatures of the thermomechanical path.

[0024] Since the recrystallization phenomenon is likely to occur as a function of the temperatures at which the most significant variations in plastic deformation occur, it is advantageous for the plastic deformation potential to be calculated as a function of these elements. In other words, the potential takes into account the temperatures at which major changes in deformation occur.

[0025] The present disclosure also relates to a method for determining a risk of the appearance of recrystallized grains during the manufacture of a mechanical part by casting an alloy with a metallic component into a mold, comprising the following steps: 1) a step implementing a mechanical test on a test piece so as to characterize an imposed plastic deformation energy of said test piece as a function of an imposed temperature; 2) a step implementing a heat treatment for resolving said test piece, said heat treatment for resolving being capable of creating recrystallized grains; 3) a step implementing a macrographic attack to determine the appearance of recrystallized grains in the test piece; 4) a step of acquiring data from an abacus of critical thresholds of plastic energy likely to lead to the appearance of recrystallized grains as a function of a succession of temperature values; 5) a step of calculating a plastic energy potential as a function of critical thresholds of plastic energy acquired on the abacus and measured values ​​of energy of plastic deformation for a plurality of temperatures of the thermomechanical path of the specimen; and 6) a step of comparing the value of the calculated plastic energy potential with a threshold value, the exceeding of which corresponds to the existence of a risk of the appearance of recrystallized grains in the test piece.

[0026] This method for determining a risk of the appearance of recrystallized grains proposes an alternative solution to the technical problems identified above. More particularly, this method concerns the use of a criterion relating to a plastic energy potential, instead of a criterion relating to plastic deformation, and which will also be compared to a threshold value to determine whether or not there is a risk of the appearance of recrystallized grains. Thus, to calculate this criterion, it is proposed to use an isothermal chart of critical thresholds of plastic energy (also called "plastic deformation energy") likely to lead to the appearance of recrystallized grains as a function of a succession of temperature values.

[0027] In the same way, the abacus is also said to be isothermal, which means that this criterion, the plastic deformation energy potential, is able to consider the thermomechanical history of the cooling process of the test piece while relying on simple tests.

[0028] Also, whether the criterion relates to plastic deformation energy or plastic deformation, it is consistent with experimental observations which can be carried out by casting tests of simplified parts and / or by comparison with anisothermal mechanical tensile tests.

[0029] According to one embodiment of the invention, the plastic energy potential corresponds to a cumulative value of ratios, each ratio comprising as a numerator a difference between two successive values ​​of plastic energy of the thermomechanical path of the test piece recorded at two successive temperatures of the thermomechanical path, and comprising as a denominator a critical threshold of plastic energy acquired by the abacus and interpolated as a function of two successive temperatures of the abacus which are closest to the two successive temperatures of the thermomechanical path.

[0030] Since the recrystallization phenomenon is likely to occur as a function of the temperatures at which the most significant variations in plastic energy occur, it is advantageous for the plastic energy potential to be calculated as a function of these elements. In other words, the potential takes into account the temperature at which major changes in deformation occur.

[0031] According to one embodiment of the invention, the plastic energy is calculated as a function of the total plastic deformation undergone by the test piece during the mechanical test.

[0032] According to one embodiment of the invention, said total plastic deformation is determined from the elastic deformation and the thermal expansion undergone by the test piece during the mechanical test.

[0033] It should be noted that the calculation of the total plastic deformation as well as the plastic energy remain classic calculations which are well known and accessible to those skilled in the art.

[0034] According to one embodiment of the invention, the mechanical test on the specimen is a tensile test interrupted before rupture.

[0035] According to one embodiment of the invention, the mechanical test is carried out at an imposed deformation speed.

[0036] The imposed deformation rate can be conformed to the deformation rate observed during the manufacturing process.

[0037] According to one embodiment of the invention, step 2) of implementing the heat treatment is carried out at a temperature above 1200°C.

[0038] The present disclosure further relates to a computer program comprising instructions executable by a processor, which, when executed by the processor, implement the method for determining a risk of the appearance of recrystallized grains as defined above.

[0039] The computer program may be coded in any programming language and may take the form of source code, object code, or intermediate code between the source code and the object code, such as a partially compiled form or any other desired form.

[0040] The present disclosure also relates to a computer-readable data medium, on which the computer program as defined above is recorded.

[0041] Such a data medium may be an internal or external hard drive, a USB key, a CD-ROM, a memory card or a cloud (or "cloud"). Of course, this list is non-exhaustive and may include any other data medium known to the person skilled in the art and which is not cited in this patent application. Brief description of the drawings

[0042] Other aims, characteristics and advantages of the invention will be better understood on 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: - [Fig.l] [Fig.l] schematically illustrates a process for determining the risk of recrystallized grains appearing during the manufacture of a mechanical part, in particular a turbine blade, by casting an alloy with metal component in a mold according to a first embodiment of the invention; - [Fig.2] [Fig.2] schematically illustrates the process of determining the risk of appearance of recrystallized grains according to a second mode of implementation of the invention; - [Fig.3A] [Fig.3A] illustrates an isothermal chart of critical thresholds of plastic deformation likely to lead to the appearance of recrystallized grains as a function of a succession of temperature values; and - [Fig.3B] [Fig.3B] illustrates a graph representing the evolution of a plastic deformation potential for a first thermomechanical path and for a second thermomechanical path. It should be noted that in all the figures, common elements are identified by identical numerical references. DETAILED DESCRIPTION OF THE INVENTION

[0043] Casting manufacturing is a fundamental process for creating mechanical parts from metal, alloy, or other materials by melting the material and molding it into a desired shape.

[0044] The term “mechanical part” means any part designed to perform a specific function, for example in the field of rail, maritime, automobile or air transport.

[0045] In the context of air transport, a mechanical part may be a turbine blade intended to be mounted in a rotor structure of a high-pressure turbine. It is also known to produce the turbine blade from a nickel-based superalloy. For example, mention may be made of the nickel-based superalloy known as AMI, known as the first-generation alloy, or the CMSX4® superalloy.

[0046] Such a blade needs to have a monocrystalline or columnar structure, i.e. consisting of a single crystal without grain defects (or, in the case of a columnar structure, of several crystals substantially oriented in the same direction), which gives it significant mechanical resistance to centrifugal forces and aerodynamic forces, for example. However, when the structure of the blade becomes polycrystalline, it then has a serious defect leading to it being considered defective because it does not comply with the specific requirements for air certification.

[0047] It is therefore important to control the appearance of grains in the structure of the blade, during its manufacture by casting.

[0048] For this purpose, a method is proposed for determining a risk of the appearance of recrystallized grains during the manufacture of the mechanical part. In other words, This process makes it possible to assess the probability of the formation of such recrystallized grains. It is thus implemented upstream of the manufacture of the mechanical part so as to avoid, if the process confirms the existence of this risk, manufacturing it with such grains in its structure and thus removing or destroying it.

[0049] [Fig.l] presents a flowchart describing the various successive steps of method 1 for determining the risk of the appearance of recrystallized grains during the manufacture of a mechanical part, in particular the turbine blade in the air sector. [Fig.l] illustrates the steps of method 1 according to a first embodiment of the invention.

[0050] Method 1 begins with a step E1 implementing a mechanical test on a test piece so as to characterize an imposed plastic deformation of said test piece as a function of an imposed temperature. The mechanical test here involves the use of a testing machine, such as a tensile machine to apply a mechanical stress to the test piece. For example, such a machine makes it possible to carry out tensile tests at temperatures up to 1200°C, or even higher. The maximum temperature to be reached is ideally higher than the solvus of the y' phase for the superalloy considered, or even up to the solidus of the alloy.

[0051] By "imposed" temperature, we mean that the mechanical test is carried out at a specific (constant) temperature. In this sense, the test piece can be placed in a furnace that maintains the temperature at the desired value. The maximum test temperature is ideally the solvus, or even beyond the solvus of the alloy, up to the solidus of the alloy.

[0052] By "imposed" plastic deformation is meant a controlled application of mechanical stress to the specimen until a plastic deformation of a specific value is characterized.

[0053] Method 1 continues with the implementation of a step E2 in which the test piece is subjected to a resolution heat treatment. For example, the resolution heat treatment may have a temperature of approximately 1240°C when the alloy is AM1 (first generation alloy) and a temperature of approximately 1300°C when the alloy is CMSX4®. The person skilled in the art knows that these temperatures are only exemplary for these two alloys.

[0054] The resolution heat treatment is likely to generate recrystallized grains. As stated above, the dislocations in the crystal structure of the alloy can reorganize when a high-temperature resolution heat treatment is applied to the test piece, thus leading to the formation of grain boundaries in its structure, which is therefore no longer monocrystalline. It is therefore important to determine at this level whether recrystallized grains have appeared in the test piece.

[0055] For this purpose, the test piece is then subjected during a step E3 to a macrographic attack to determine the appearance of recrystallized grains in the test piece. The macrographic attack is preferably carried out by chemical treatment. A macrographic control subsequently makes it possible to visualize the presence of recrystallized grains in the test piece.

[0056] Furthermore, carrying out a large number of tests under the same conditions (temperature and plastic deformation value imposed) proves to be impractical given the time required for this undertaking and the difficulty in obtaining reliable data.

[0057] For at least one of these reasons, it is proposed to use an abacus as a model for predicting a risk of the appearance of recrystallized grains under specific temperature and plastic deformation conditions (or plastic energy in the context of a second mode of implementation of the method). Such an abacus is based on experimental data and behavior equations and is therefore more reliable for predicting a risk of recrystallization.

[0058] Method 1 then continues with a step E4 of acquiring data from an abacus of critical thresholds of plastic deformation likely to lead to the appearance of recrystallized grains as a function of a succession of temperature values.

[0059] Such an abacus 2 is presented as an example in [Fig.3A]. Abacus 2 shows the evolution of the risk of appearance of recrystallized grains as a function of different temperatures and plastic deformation values. More particularly, abacus 2 is said to be isothermal, i.e. constructed from isothermal tensile tests, here at temperatures ranging from 750°C to 1200°C on the abscissa axis X. Abacus 2 shows on the ordinate axis Y the evolution of the plastic deformation values.

[0060] The risk of the appearance of recrystallized grains is partitioned into three adjacent zones: a first zone ZI in which there is a significant risk of the appearance of recrystallized grains, a second zone Z2 in which the risk of the appearance of recrystallized grains is lower, and a third zone Z3 in which the risk of the appearance of recrystallized grains is almost zero.

[0061] In this example, the so-called "critical" thresholds of plastic deformation likely to lead to the appearance of recrystallized grains are therefore relative to the first zone Z1. Thus, if the temperature imposed on the test piece is 900°C and the imposed plastic deformation is 0.020, the point of intersection between these two data is located in the first zone Z1, which means that there is a significant risk of the appearance of recrystallized grains.

[0062] It should be noted that the data extracted from the abacus 2, for example the so-called critical thresholds and the corresponding temperatures, can be stored in a memory to be used in the next step E5. The memory can be of the ROM type (for “Read Only Memory”), in the form of a CD ROM or in the form of magnetic storage media such as a floppy disk or a hard disk.

[0063] The advantage of using the so-called isothermal chart 2 is that it is constructed from simple tensile tests. However, the data in chart 2 alone cannot provide sufficiently reliable data to determine whether or not there is a risk of recrystallization. Indeed, it is important to take into account the thermomechanical history of the cooling process of the specimen.

[0064] In this respect, method 1 continues with step E5 of calculating a plastic deformation potential as a function of critical plastic deformation thresholds acquired on chart 2 and measured plastic deformation values ​​for a plurality of temperatures of the thermomechanical path of the test piece.

[0065] It is noted that the recrystallization phenomenon is likely to occur depending on the temperatures at which the most significant variations in plastic deformation occur. The plastic deformation potential is then calculated based on these elements. In other words, the potential takes into account the temperatures at which major changes in plastic deformation occur.

[0066] More particularly, the plastic deformation potential can be calculated using the above variables in the following equation (1): p yr / (1) Or : - PE represents the plastic deformation potential; - the interval [To - Tf] represents the temperatures of the thermomechanical path of the specimen during its cooling; - epicorresponds to a plastic deformation value measured at a specific temperature from the interval [To - Tf]; - Aepi corresponds to the difference between two successive values ​​of plastic deformation of the thermomechanical path of the test piece at two successive temperatures of the thermomechanical path; and - ( T, ) corresponds to an interpolated critical threshold of plastic deformation on chart 2 as a function of two successive temperatures Ti of chart 2 for which the corresponding critical thresholds of plastic deformation are available through the chart. These two temperatures Ti are substantially close to the two successive temperatures of the thermomechanical path.

[0067] To illustrate this step E5, a first thermomechanical path CH1 of a region of a part which led to the visual appearance of grain boundaries during step E3 is plotted graphically on the chart 2 of [Fig.3A]. Similarly, a second thermomechanical path CH2 of a second region of the part which did not lead to the visual appearance of grain boundaries during step E3 is illustrated in this same [Fig.3A].

[0068] Since the first thermomechanical path CH1 is located between the temperature range of 1300 to 750°C and the measured temperatures of the first thermomechanical path CH1 (with their respective plastic deformation values) are 1300°C, 1270°C, 1200°C, 1150°C, 1100°C, 950°C, 900°C, 850°C and 750°C, it is appropriate, in order to calculate the plastic deformation potential PE, to take the difference in plastic deformation values ​​Aepi between each two successive temperature values ​​resulting from the increments of the thermomechanical calculations.

[0069] As an example, the plastic deformation between the successive temperatures resulting from the increments of the thermomechanical calculations is given by the thermomechanical calculation (difference between the two plastic deformations at the two increments) (Aepi). Concerning the denominator of the ratio presented in equation (1), the critical thresholds are interpolated linearly as a function of the thresholds critical of the two temperatures Ti of the abacus corresponding to the interval in which is the temperature increment studied.

[0070] The critical threshold is thus raised for all successive temperatures measured from the first thermomechanical path CH1.

[0071] Similarly, the second thermomechanical path CH2 is located between the temperature ranges of 1300 to 750°C. The measured temperatures of the second thermomechanical path CH2 (with their respective plastic deformation values) are 1300°C, 1270°C, 1200°C, 1150°C, 1100°C, 950°C, 900°C, 850°C and 750°C. It is appropriate, to calculate the plastic deformation potential PE, to note the difference in plastic deformation values ​​Aepi between each two successive temperature values ​​resulting from the measured temperatures of the second thermomechanical path CH2.

[0072] As an example, the plastic deformation between the successive temperatures resulting from the increments of the thermomechanical calculations is given by the thermomechanical calculation (difference between the two plastic deformations at the two increments) (Aepi). Concerning the denominator of the ratio presented in equation (1), the critical thresholds £^(77 ) are interpolated linearly as a function of the critical thresholds of the two temperatures Ti of the chart corresponding to the interval in which the temperature increment studied is located.

[0073] The critical threshold is thus raised for all successive temperatures measured in the second thermomechanical path CH2.

[0074] Following the calculation of the plastic deformation potential Pe, the method 1 continues with a step E6 of comparing the value of the calculated plastic deformation potential Pe with a threshold value. Exceeding this threshold value corresponds to the existence of a significant risk of the appearance of recrystallized grains in the test piece (first zone ZI of the chart 2).

[0075] For example, when the threshold value is equal to 1, the plastic deformation potential Pe indicates a significant risk of the appearance of recrystallized grains in the test piece if it is greater than 1. Conversely, the plastic deformation potential Pe indicates a very low risk of the appearance of recrystallized grains in the test piece if the maximum limit of the recrystallization potential is less than 1.

[0076] [Fig.3B] illustrates a graph 3 showing on the Y axis the evolution of the plastic deformation potential Pe for the first thermomechanical path CH1 and for the second thermomechanical path CH2, and this as a function of temperatures ranging from 1300°C to 750°C on the X axis.

[0077] More particularly, it can be seen in [Fig.3B] that the first thermomechanical path CH1 exhibits a significant change in the plastic deformation potential Pe between 1000°C and 900°C, leading to an exceeding of the threshold value which is here equal to 1. Thus, contrary to what is indicated in chart 2 of [Fig.3A], that is to say that the first thermomechanical path CH1 does not enter the first zone ZI and therefore presents little or no risk of recrystallized grains appearing, the plastic deformation potential Pe clearly shows that the first thermomechanical path CH1 actually leads to an increased risk of recrystallized grains appearing.

[0078] Concerning the second thermomechanical path CH2, it is recalled that it is noted in [Fig.3A] that this second thermomechanical path CH2 enters at the temperature 950°C in the first zone ZI. Thus, the second thermomechanical path CH2 is supposed to present an increased risk of an appearance of recrystallized grains in the test piece concerned. However, as the second thermomechanical path CH2 only presents small differences in plastic deformation between two successive temperatures, or at least much smaller differences than those of the first thermomechanical path CH1, the value of the plastic deformation potential Pe is here much lower than that of the first thermomechanical path CH1 as illustrated in [Fig.3B]. Thus, in this example, the plastic deformation potential Pe reaches the value of 0.6 which remains below the threshold of 1.

[0079] Consequently, contrary to what is indicated in chart 2 of [Fig.3A], the second thermomechanical path CH2 presents a very low risk of the appearance of recrystallized grains in the corresponding test piece.

[0080] Thus, it is demonstrated that by using the data from the isothermal chart 2 while considering the thermomechanical history of the cooling process, it is possible to obtain with much more reliability whether a thermomechanical path is likely to lead to the appearance of recrystallized grains. Indeed, the reliability of the use of the plastic deformation potential Pe has been verified and confirmed by casting tests of simplified parts or by comparison with anisothermal tensile mechanical tests.

[0081] Furthermore, this verification or confirmation may constitute an additional optional step E7 of method 1 and which is illustrated in dotted lines in [Fig.l]. This step may therefore occur after step E6 so as to confirm whether the thermomechanical path risks leading to the appearance of recrystallized grains.

[0082] [Fig.2] illustrates a flowchart describing the various successive steps of method 1 for determining the risk of the appearance of recrystallized grains during the manufacture of a mechanical part, in particular the turbine blade in the air sector. [Fig.l] illustrates the steps of method 1 according to the second embodiment of the invention.

[0083] In this second embodiment of method 1, only steps E4, E5 and E6 are modified. More precisely, instead of calculating the potential relating to plastic deformation as set out in the first embodiment of the invention, a potential relating to plastic energy is calculated. For this purpose, in step E44 (E4 in [Fig.l]), the chart 2 of critical thresholds of plastic deformation likely to lead to the appearance of recrystallized grains is used as a function of a succession of temperature values. The plastic deformation data of chart 2 then make it possible to present them in the form of data relating to plastic energy.

[0084] Indeed, the person skilled in the art is able, by using his general knowledge, to transform an abacus relating to plastic deformation into an abacus relating to the plastic energy absorbed by the alloy when it undergoes said plastic deformation.

[0085] A plastic deformation energy potential is then calculated at step E55 (E5 in [Fig.l]) and according to the following equation (2) and using chart 2 showing the evolution of the plastic energy instead of the plastic deformation on the ordinate: yTf AEpl (2) E Or : - PE represents the plastic energy potential; - the interval [To - Tf] represents the temperatures of the thermomechanical path of the specimen during its cooling; - Epicorresponds to a plastic energy value measured at a specific temperature from the interval [To - Tf]; - AEpi corresponds to the difference between two successive values ​​of plastic energy of the thermomechanical path of the specimen at two successive temperatures of the thermomechanical path; and - ) corresponds to an interpolated critical threshold of plastic energy on the abacus 2 whose ordinate axis here represents the evolution of the plastic energy values, as a function of two successive temperatures Ti of the abacus 2 for which we have through the abacus the corresponding critical thresholds of plastic energy. These two temperatures Ti are substantially close to the two successive temperatures of the thermomechanical path.

[0086] Following the calculation of the potential of the plastic deformation energy PE, the method 1 continues with a step E66 (step E6 in [Fig.l]) of comparing the value of the calculated plastic energy potential PE with said threshold value. As indicated above, exceeding this threshold value corresponds to the existence of a significant risk of the appearance of recrystallized grains in the test piece (first zone ZI of the chart 2).

[0087] For example, when the threshold value is equal to 1, the plastic energy potential PE indicates a significant risk of the appearance of recrystallized grains in the test piece if it is greater than 1. Conversely, the plastic energy potential PE indicates a very low risk of the appearance of recrystallized grains in the test piece if the maximum limit of the plastic deformation energy potential is less than 1, for example 0.2.

[0088] Whether the calculated potential is the plastic deformation potential Pe or the plastic energy potential PE, the same observations are made concerning the first thermomechanical path CH1 and the second thermomechanical path CH2. In other words, it is noted that the first thermomechanical path CH1 does indeed present a significant risk of the appearance of recrystallized grains in the corresponding test piece, contrary to what is shown in [Fig.3A], and that the second thermomechanical path CH2 does indeed present a very low risk of the appearance of recrystallized grains in the corresponding test piece.

[0089] In the same way, the reliability of the use of the PE plastic deformation energy potential was verified and confirmed by casting tests of simplified parts or by comparison with anisothermal tensile mechanical tests. Furthermore, this verification or confirmation may constitute the additional optional step E7 of method 1 according to the second embodiment of the invention and which is illustrated in dotted lines in [Fig.2]. This step may therefore take place after step E66 so as to confirm whether the thermomechanical path risks leading to the appearance of recrystallized grains.

[0090] Although the present invention has been described with reference to specific 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. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0091] It is also obvious that all the characteristics described with reference to the method are transposable, alone or in combination, to a device and vice versa. For example, this method can be executed by a device or a plurality of devices combined with each other and / or connected to a computer. The person skilled in the art is able to decide on the hardware means to be used to enable the implementation of the different steps of the method.

Claims

Claims

1. Method (1) for determining a risk of the appearance of recrystallized grains during the manufacture of a mechanical part by casting an alloy with a metallic component in a mold, the method (1) comprising the following steps: 1) a step (El) implementing a mechanical test on a test piece so as to characterize an imposed plastic deformation of said test piece as a function of an imposed temperature; 2) a step (E2) implementing a heat treatment for resolving said test piece, said heat treatment for resolving being capable of creating the recrystallized grains; 3) a step (E3) implementing a macrographic attack to determine the appearance of recrystallized grains in the test piece;4) a step (E4) of acquiring data from an abacus (2) of critical thresholds of plastic deformation likely to lead to the appearance of recrystallized grains as a function of a succession of temperature values; 5) a step (E5) of calculating a plastic deformation potential (PE) as a function of critical thresholds of plastic deformation acquired (^) on the abacus (2) and of measured values ​​of plastic deformation (epi) for a plurality of temperatures of the thermomechanical path (CH1, CH2) of the test piece; and 6) a step (E6) of comparing the value of the calculated plastic deformation potential (PE) with a threshold value, the exceeding of which corresponds to the existence of a risk of the appearance of recrystallized grains in the test piece.;

2. Method (1) according to claim 1, in which the plastic deformation potential (PE) corresponds to a cumulative value of ratios, each ratio comprising as numerator a difference between two successive values ​​of plastic deformation (Aepi) of the thermomechanical path (CH1, CH2) of the test piece recorded at two successive temperatures of the thermomechanical path (CH1, CH2), and comprising as denominator a critical threshold of plastic deformation (g^) acquired by the abacus (2) and interpolated as a function of two successive temperatures of the abacus (2) which are the closest of the two successive temperatures of the thermomechanical path (Chl, CH2).

3. Method (1) for determining a risk of the appearance of recrystallized grains during the manufacture of a mechanical part by casting an alloy with a metallic component in a mold, comprising the following steps: 1) a step (El) implementing a mechanical test on a test piece so as to characterize an imposed plastic deformation of said test piece as a function of an imposed temperature; 2) a step (E2) implementing a heat treatment for resolving said test piece, said heat treatment for resolving being capable of creating the recrystallized grains; 3) a step (E3) implementing a macrographic attack to determine the appearance of recrystallized grains in the test piece; 4) a step (E44) of acquiring data from an abacus (2) of critical thresholds of plastic energy (e^) capable of leading to the appearance of recrystallized grains as a function of a succession of temperature values;5) a step (E55) of calculating a plastic energy potential as a function of critical plastic energy thresholds acquired on the chart (2) and measured plastic energy values ​​(Epi) for a plurality of temperatures of the thermomechanical path (CH1, CH2) of the test piece; and 6) a step (E66) of comparing the value of the calculated plastic energy potential (PE) with a threshold value, the exceeding of which corresponds to the existence of a risk of the appearance of recrystallized grains in the test piece.;

4. Method (1) according to claim 3, in which the plastic energy potential (PE) corresponds to a cumulative value of ratios, each ratio comprising as numerator a difference between two successive values ​​of plastic energy (AEpi) of the thermomechanical path of the test piece recorded at two successive temperatures of the thermomechanical path (CH1, CH2), and comprising as denominator a critical threshold of plastic energy acquired by the abacus (2) and interpolated as a function of two successive temperatures of the abacus (2) which are closest to the two successive temperatures of the thermomechanical path (CH1, CH2).

5. Method (1) according to claim 3 or 4, wherein the plastic energy (Epi) is calculated as a function of the total plastic deformation undergone by the test piece during the mechanical test.

6. Method according to claim 5, in which said total plastic deformation is determined from the elastic deformation, the thermal deformation, undergone by the test piece during the mechanical test.

7. Method (1) according to any one of the preceding claims, wherein the mechanical test on the test piece is a tensile test interrupted before rupture.

8. Method (1) according to any one of the preceding claims, in which the mechanical test is carried out at an imposed deformation rate.

9. Method (1) according to any one of the preceding claims, in which step 2) of carrying out the heat treatment is carried out at a temperature above 1200°C.

10. A computer program comprising instructions executable by a processor, which, when executed by the processor, implement the method (1) of determining a risk of the appearance of recrystallized grains according to claims 1 to 9.

11. Computer-readable data carrier, on which the computer program according to claim 10 is recorded.

Images