Process for treating a turbomachine part

Abstract

The invention relates to a process (P) for treating a part (1), in particular a turbomachine, comprising the following steps: (S1) supplying a surface stress (F), intended to be applied to a contact surface (5) of the part (1), and at least one radius of curvature (R), (S2) determining a volume stress acting in the material of the part (1) below the surface, comprising calculating an analytical expression for the volume stress as a function of the surface stress and the radius of curvature, (S3) for each treatment in a set of thermochemical treatments, determining a hardness and a residual stress of the part (1), (S4) identifying, within the set of acceptable treatments, for which the hardness and the residual stress correspond to a mechanical strength of the part (1) greater than a threshold strength taking into account the volume stress.and a treatment duration is less than or equal to a threshold duration, (S6) application of one of the acceptable treatments to the part (1). Figure to be published for the abstract: Figure 2,

Description

Title of the invention: Method for treating a turbomachine part DOMAIN

[0001] The invention relates to the field of turbomachinery and in particular to turbomachine parts that are subjected to mechanical stresses requiring a certain level of rolling fatigue resistance. Such parts are found notably in power transmission devices. STATE OF THE ART

[0002] Certain components in a turbomachine, particularly gears or power transmission devices, are designed to be in mechanical contact with other components under high stress. They must exhibit significant rolling fatigue resistance. Rolling fatigue of a component whose surface is subjected to mechanical stress corresponds to a fracture or break in the material of the component below the surface, the mechanical stresses being the cause of the fracture or break. This fracture produces a crack in the component, a crack that propagates through the component and, in particular, towards the surface subjected to stress. The fracture can be described as a crack initiation. The fracture occurs at a certain depth below the surface and can be designated by the abbreviation EPIP, which stands for "deep-initiated spalling."In particular, failure can occur at a specific depth where shear stresses are at their maximum.

[0003] To ensure that a part exhibits sufficient rolling fatigue resistance, it is known to apply a thermochemical treatment configured to reach a treatment depth that is a multiple of the specific depth at which shear stresses are maximum. The treatment depth can thus be chosen to be two or three times the specific depth. However, such treatment depths require very long thermochemical treatment times, close to 500 hours or even more. Such times pose difficulties in maintaining treatment consistency over its duration, in the cost of manufacturing the part, and obviously in the manufacturing time of the part.

[0004] There is therefore a need for an optimized method of strengthening the rolling fatigue resistance of a turbomachine part. EXPOSED

[0005] One aim of the present presentation is to propose a method for strengthening the rolling fatigue resistance of a turbomachine part optimized compared to the prior art.

[0006] The objective is achieved through a process for treating a part, in particular a turbomachine part, the process comprising the following steps: - provision of a surface constraint, intended to be applied to a contact surface of the part, and at least one radius of curvature of the contact surface, - determination of a volume stress acting within the material of the part below the surface, the determination including a calculation of an analytical expression of the volume stress as a function of the surface stress and the radius of curvature, - for each treatment within a set of thermochemical treatments, determination of the hardness and residual stress of the part subjected to the treatment, - identification within the set of acceptable treatments for which: • Hardness and residual stress correspond to a mechanical resistance of the part greater than a threshold resistance, the threshold resistance taking into account the stress in volume, and • a treatment duration is less than or equal to a threshold duration, and - application of one of the acceptable treatments to the part.

[0007] Such a process is advantageously and optionally complemented by the following various features taken alone or in combination: - the identification of acceptable treatments includes an identification of first treatments of the assembly for which the hardness and residual stress correspond to a mechanical resistance of the part greater than the threshold resistance, and / or an identification of second treatments among the first treatments for which the duration of the treatment is less than or equal to the threshold duration; - the process includes determining the depth of the part exhibiting the lowest mechanical resistance, with the identification of the first treatments based on the lowest mechanical resistance; - the process includes a step of identifying third treatments among the acceptable treatments, for which a surface hardness of the part subjected to the treatment is greater than or equal to a threshold hardness, the treatment applied being chosen from among the third treatments; - the process includes a step of identifying fourth treatments among the acceptable treatments for which a layer of material of the part to be removed following the application of the treatment has a thickness less than or equal to a threshold thickness, the applied treatment being chosen from among the fourth treatments, the process possibly including a step of

[0008]

[0009]

[0010]

[0011]

[0012] removal of the layer of material following the application of the treatment; - the process includes, before the application of the treatment, a simulation step, in particular by finite elements, of the mechanical resistance of the part; - the assembly includes at least one type of treatment chosen from nitriding, nitrocarburizing, cementation and carbonitriding; - the set includes a subset of treatments of the same type of treatment, each treatment of the subset corresponding to a particular pair of temperature and duration of treatment. The presentation also covers a turbomachine part obtained by a process as just described, a turbomachine comprising such a part and an aircraft comprising such a turbomachine. DESCRIPTION OF THE FIGURES Other features and advantages will become clear from the following description, which is purely illustrative and not exhaustive, and should be read in conjunction with the attached drawings on which: - Fig. 1 is a schematic representation of a part subjected to a mechanical stress on the surface; - Fig. 2 is a schematic representation of a process for treating a turbomachine part; - Fig. 3 is a schematic representation of a fatigue cycle of a part and its mechanical resistance; - Fig. 4 is a schematic curve representing the hardness of a part as a function of depth below the surface; - The [Fig.5] is a schematic curve representing a residual stress of a part as a function of a depth below the surface; - Fig. 6 is a schematic representation of a mechanical resistance margin of a part as a function of parameters of a treatment applied to that part. DETAILED DESCRIPTION OF THE INVENTION Turbomachine component under surface stress In relation to [Fig.1], a first part 1, in particular of a turbomachine, is in contact with a second part 3. The first part 1 can in particular be part of a power transmission device in the turbomachine, such as a gear. The second part 3 applies a force F to the first part 1, which is directed along the z-axis. In reaction, the first part applies a force F to the second part 3. force -F opposite to force F. The forces F and -F are exerted within a contact surface 5 between the first piece 1 and the second piece 3.

[0013] The contact surface 5 extends along directions x and y perpendicular to the z-axis. The z-axis is an axis normal to the contact surface 5.

[0014] The force F is a surface stress intended to be applied to the contact surface 5 of the first part 1 during the operation of the turbomachine.

[0015] Contact pressure or pressure is also used to designate a local distribution of surface stresses related to the imposed force F.

[0016] The first part 1 must be able to withstand mechanical stress. In particular, the first part 1 must be able to withstand rolling fatigue.

[0017] More precisely, it is possible to define a surface pressure field which is exerted on the first part 1. The surface pressure field corresponds to a data point for each point of the contact surface 5 of the pressure force which is exerted at that point.

[0018] The contact surface 5 of the first part 1 has at least one radius of curvature R. The radius of curvature R is defined from a center of curvature C which is placed on the side of the first part 1 of the contact surface 5 if the first part 1 is concave at the level of the contact surface 5.

[0019] If the first part 1 does not have a spherical shape at the contact surface 5, it is then possible to define several radii of curvature, for example two radii of curvature corresponding to the x and y directions.

[0020] It is also possible to introduce more than two radii of curvature and to introduce additional directions along which the radii of curvature are measured, if the shape of the surface is more complex. Each radius of curvature is defined from a center of curvature.

[0021] It should be noted that the first part 1 may be in motion during the operation of the turbomachine, such that the applied stress, or the applied stress field, on the contact surface 5 of the first part 1 varies over time. In this case, it is possible to describe the mechanical stress on the first part 1 over time by the value of the force F or the stress field over time, the value of the surface area over time, a position and direction of the axis normal to the surface over time, and the radius(s) of curvature of the surface over time.

[0022] If the first part 1 is rotating during the operation of the turbomachine, the functions mentioned above can be periodic.

[0023] Method for treating the turbomachine part

[0024] In relation to [Fig.2], a process P is proposed for treating a part 1, in particular the first part 1 as described previously.

[0025] During a first step SI of the process P, a surface stress F, or the stress field, is provided. The surface stress F is intended to be applied to a surface of the part 1. During a first step SI, at least one radius of curvature R of the contact surface 5 is also provided.

[0026] More generally, if part 1 is in motion during the operation of the tur-bomachine, the value of the force F - or of the stress field - can be provided over time, the value of the surface over time, the position and direction of the axis normal to the surface over time, the radius or radii of curvature of the surface over time.

[0027] Alternatively, instead of providing the force F, it is possible to provide a maximum allowable stress. Such a maximum allowable stress corresponds to the force F for which a certain risk of damage is acceptable.

[0028] In a second step S2, a volume stress acting in the material of the first part 1, under the contact surface 5, is determined. This volume stress corresponds to a local effect of the force F under the contact surface 5.

[0029] This volume constraint can be determined in particular along the z-axis which is the axis normal to the surface 5.

[0030] This determination can be carried out for different distances to the contact surface 5 measured along the z-axis, i.e. for different depths of the part 1 below the contact surface 5. This is referred to as the determination of a stress field.

[0031] For each depth, an analytical expression giving in particular shear stresses at different depths can be used, and in particular at the depth where the shear stresses are maximum.

[0032] Analytical expressions are, for example, expressions of constraints associated with an elliptical Hertz-type contact between the first part 1 and the second part 3.

[0033] Various analytical expressions available in the literature may be used, such as those appearing in the English-language publication "Stresses due to the pressure of one elastic Solid upon another" University of Illinois Engineering Experiment Station Bulletin No. 212 published in July 1930 and whose authors are Howard R. Thomas and Victor A. Hoertsch.

[0034] In the case where part 1 is in periodic motion, in particular during the operation of the turbomachine, and where the variations of the force F over time have been provided, it is possible to obtain a graphical representation of the volume stress on the first part 1.

[0035] An example of such a representation is given in [Fig. 3]. Curve 11 is a cycle fatigue that is traversed at each period of the movement of the first part 1. Each point on the curve 11 represents a moment of this period and gives: - on the x-axis, the hydrostatic pressure or stress to which part 1 is subjected at this moment of the cycle, and - on the ordinate, the shear stress exerted in the material of part 1 under the contact surface 5.

[0036] The shear can be a mesoscopic shear which translates the shear at the scale of a few grains of matter.

[0037] In order to strengthen it mechanically, various thermochemical treatments can be applied to part 1.

[0038] It is possible to predetermine in advance a number of candidate treatments which can be applied to part 1, and thus form a set, or catalogue, of possible thermochemical treatments.

[0039] In a third step S3, for each treatment in the set of thermochemical treatments, a hardness of the treated part 1 is determined. In a third step S3, a residual stress of the treated part 1 is also determined.

[0040] In other words, for each treatment, an estimate of the hardness and residual stress of part 1 is made, if part 1 were subjected to this thermochemical treatment.

[0041] Hardness is, for example, a Vickers hardness which is expressed in HV units.

[0042] Residual stress is a mechanical stress left by the heat treatment chemical inside the treated part 1. The treatment can indeed put part 1 under mechanical stress, a stress which can be measured as a pressure expressed in Pascal units.

[0043] Hardness and residual stress can be evaluated at different depths in part 1 below its surface, so that during the third step S3, it is possible to determine a hardness curve and a residual stress curve as a function of the depth of part 1 being processed.

[0044] Fig. 4 illustrates an example of a hardness curve 7 as a function of the depth of the treated part 1.

[0045] Fig. 5 illustrates an example of a residual stress curve 9 as a function of the depth of the treated part 1.

[0046] There are databases that allow the hardness and residual stress of a part 1 to be determined as a function of the chemical composition of the part 1 and the treatment applied to it.

[0047] A machine learning module trained on such bases can also make such estimates.

[0048] During a fourth step S4, in a set of candidate treatments, certain so-called acceptable treatments are identified for which: • Hardness and residual stress correspond to a mechanical resistance of part 1 greater than a threshold resistance, the threshold resistance taking into account the stress in volume, and • the duration of treatment is less than or equal to a threshold duration.

[0049] The hardness and residual stress that were determined in the previous step are used here to evaluate the mechanical strength of part 1. There are several examples in the technical literature of laws that link hardness to mechanical strength.

[0050] Mechanical strength is an object comparable to the volume stress determined previously. The mechanical strength of part 1 corresponds, for example, to a limit fatigue curve which gives, as a function of the hydrostatic stress applied in the material, the shear applied in the material of part 1 beyond which stress initiation occurs.

[0051] Mechanical resistance can be assessed, in particular, at a specific depth of part 1, which exhibits lower mechanical resistance. The identification of the initial treatments is then based on this lower mechanical resistance.

[0052] An example of a fatigue curve 13 is given in [Fig.3].

[0053] The mechanical resistance of part 1 is compared to a threshold resistance, the threshold resistance taking into account the volume stress.

[0054] For example, with regard to [Fig.3]: - a point M of a fatigue cycle 11 is identified which has the shortest distance to a limit fatigue curve 13; the shortest distance can be evaluated for each point of the fatigue cycle 11 with respect to any point of the limit fatigue curve 13; - a point D is identified on the limit fatigue curve 13, points D and M having the same hydrostatic stress abscissa; - a point O is identified on the axis of hydrostatic stress abscissas, corresponding to a shear equal to zero, the points O, D and M presenting the same hydrostatic stress abscissa; - the OM / OD ratio is determined, which is a shear ratio, this ratio being dimensionless; - the OM / OD ratio is compared to a threshold coefficient, for example equal to 0.8; and - it is decided that the mechanical resistance of part 1 is greater than the threshold resistance when the ratio is less than the threshold coefficient.

[0055] An OM / OD ratio greater than or equal to the value one corresponds to a curve of The fatigue limit is crossed or is located below the fatigue cycle. This situation corresponds to a very high risk of fatigue initiation, as part 1 does not have sufficient mechanical strength to withstand the fatigue cycle.

[0056] An OM / OD ratio less than the value of one corresponds to a limit fatigue curve located above the fatigue cycle, which indicates that part 1 has a mechanical resistance greater than the mechanical stress corresponding to the fatigue cycle.

[0057] If the OM / OD ratio is less than one, the lower this ratio becomes, the further the limiting fatigue curve is located above the fatigue cycle, and the greater the mechanical resistance of part 1 is compared to the mechanical stress corresponding to the fatigue cycle. In other words, the lower the OM / OD ratio, the greater the safety margin for part 1 to initiate fatigue.

[0058] Acceptable treatments are also those whose duration is less than or equal to a threshold duration. The threshold duration can be set, for example, at 100 hours or 150 hours.

[0059] According to a first variant of the fourth step S4, the identification of acceptable treatments may optionally include - a first variant S4-1, during which an identification of initial treatments of the assembly for which the hardness and residual stress correspond to a mechanical resistance of part 1 greater than the threshold resistance and - a second variant S4-2, in which second treatments are identified among the first treatments for which the duration of treatment is less than or equal to the threshold duration.

[0060] In the first variant S4-1, the identification of treatments allowing sufficient mechanical resistance takes place before the identification of treatments whose duration is not too long.

[0061] The second variant S4-2 of the fourth step S4 may include a sub-step S4-3 of identification, or third variant S4-3, of third treatments among the acceptable treatments for which a surface hardness of the part subjected to treatment is greater than or equal to a threshold hardness, the treatment applied being chosen from among the third treatments.

[0062] In this second variant S4-2, the applied treatment is chosen from a subgroup of acceptable treatments by adding a new condition concerning the surface hardness of the part 1 after treatment. The surface hardness must be greater than a threshold hardness. The threshold hardness can, in particular, be chosen to be equal to 500 Hv or 700 Hv.

[0063] If in the third step S3, the hardness was determined at different depths in the first piece 1 below its surface, it is notably possible to already have the surface hardness value corresponding to a zero depth.

[0064] Such a condition is applied to acceptable treatments so that the identification of acceptable treatments takes place before the application of the condition on surface hardness.

[0065] The third variant of the fourth step S4 may include a substep S4-4 of identifying fourth treatments among the acceptable treatments or third treatments for which a layer of material of the part 1 to be removed following the application of the treatment has a thickness less than or equal to a threshold thickness, the treatment applied being chosen from among the fourth treatments.

[0066] In the third variant, the applied treatment is chosen from a subgroup of candidate treatments possibly respecting the condition on surface hardness by adding a new condition which concerns a layer of material of the part 1 to be removed following the application of the treatment.

[0067] Thermochemical treatment, such as nitriding, applied to part 1 can indeed cause a surface layer of part 1 to become brittle or deform the surface of part 1. Removing a surface layer can be advantageous, either by removing the brittle layer or by restoring the exact shape of part 1.

[0068] In the third variant, the removed layer must have a thickness less than or equal to a threshold thickness. The threshold thickness may, in particular, be between 0.5 mm and 1 mm, specifically chosen to be equal to 0.5 mm or 1 mm.

[0069] The thickness of the layer to be removed can be estimated using business rules and / or modeling tools.

[0070] This condition is applied to acceptable treatments or third treatments so that the identification of acceptable treatments or third treatments takes place before the application of the condition on the thickness of the layer to be removed.

[0071] During a sixth step S6, an acceptable treatment is chosen and applied to part 1.

[0072] In this third variant, the process P is completed by a seventh step S7 which takes place after the application of the treatment to the part 1 and which consists of removing the surface layer of the part 1.

[0073] It should be noted that the three variants of the fourth step S4 can be cumulative two by two or all three.

[0074] Such a process P allows: - to ensure that the chosen treatment has a duration shorter than the threshold duration, and - to ensure that the treated part 1 has sufficient mechanical resistance to withstand the intended mechanical stress.

[0075] Moreover, the identification of candidate treatments takes a relatively short time thanks to the use of the analytical expression of the volume constraint.

[0076] In particular, such an expression makes it possible not to use a finite element simulation method, a method which is much longer to give a usable result.

[0077] The process P makes it possible to predict, for a treated part 1, at what location and at what contact pressure a crack initiation will occur. These predictions are consistent with physical bearing fatigue tests.

[0078] Furthermore, process P makes it possible to control the difference between the mechanical strength of part 1 and the mechanical stress that is expected to be applied to it. In other words, process P makes it possible to determine the safety margin in terms of mechanical strength. It is possible to control the risk of deep spalling damage where, in the prior art, safety margins were taken without being quantified.

[0079] Optionally, the process P, as just presented, may include a simulation step S5, in particular by finite elements, of the mechanical resistance of the part 1. The simulation step S5 preferably takes place before the application of the treatment, so as to verify by simulation that the treatment will indeed have the intended mechanical effects.

[0080] It is also possible to explore with the P method vast domains of geometric properties and loading in a few minutes to quickly target subdomains to be analyzed in detail via finite element simulation.

[0081] The thermochemical treatments that can be implemented can include at least one type of treatment chosen from nitriding (diffusion of atomic nitrogen from the surface of part 1 to the core), nitrocarburizing (nitriding with additional diffusion of carbon), carburizing (diffusion of carbon to the surface of part 1) and carbonitriding (carburizing with additional diffusion of nitrogen).

[0082] In particular, the set of treatments, the relevance of which is to be assessed, may include a subset of treatments of the same type, each treatment in the subset corresponding to a particular combination of temperature and treatment duration. For example, the set of treatments may include a subset of nitriding treatments that differ from one another in their duration or temperature.

[0083] It should be noted that the entire set of treatments can be a subset of treatments of the same type of treatment, that is to say, the set of treatments then corresponds to one and the same type of treatment which is broken down into different durations and at different temperatures.

[0084] It is possible to visualize a subset of treatments of the same type of treatment according to a map where the duration of the treatment and the mechanical resistance of part 1 are illustrated.

[0085] Figure 6 is an example of such a mapping. It corresponds to the case where the set of treatments only includes nitriding treatments of different temperatures and durations.

[0086] The duration of the treatment is shown on the x-axis along a graduated axis in hours.

[0087] The treatment temperature is plotted on the ordinate along an axis graduated in degrees Celsius.

[0088] For each treatment, the mechanical resistance was evaluated by determining the OM / OD ratio, which was presented above. Curves along which the ratio takes a constant value were plotted on the map.

[0089] One curve has a minimum value of the ratio, in particular equal to 0.56, and another curve has a maximum value of the ratio, in particular equal to 0.8.

[0090] Each point of the map illustrated in [Fig.6] thus makes it possible to know a duration of nitriding, a temperature of nitriding and the OM / OD ratio characterizing the mechanical resistance of part 1, in particular a margin for initiation.

[0091] A first point 16 corresponds, for example, to a treatment time of between 500 and 600 hours, a temperature between 530 and 540 degrees Celsius and an OM / OD ratio between 0.6 and 0.64.

[0092] A second point 19 corresponds, for example, to a treatment time of less than 200 hours, a temperature of about 540 degrees Celsius and an OM / OD ratio of 0.8.

[0093] On such a map, it is possible to represent the constraint linked to the second variant of step S4, according to which the surface hardness of the part 1 subjected to treatment is greater than or equal to a threshold hardness.

[0094] A first curve 15 drawn on the map corresponds to the equality of the surface hardness and the threshold hardness.

[0095] Treatments which do not comply with the constraint are located above the first curve 15, that is to say in the direction of increasing temperatures.

[0096] The treatments which respect the constraint are located below the first curve 15, that is to say in the direction of decreasing temperatures.

[0097] Thus, the second point 19 therefore corresponds to a nitriding for which the surface hardness constraint is respected.

[0098] A second curve 17 represents a search for parameters of a nitriding process that makes it possible to produce a part whose mechanical resistance is characterized by an OM / OD ratio equal to 0.8, a treatment time of less than 200 hours and which complies with the constraint linked to the second variant of step S4, according to which the surface hardness of the part subjected to treatment is greater than or equal to a threshold hardness.

[0099] The first point 16 corresponds to an arbitrary starting point corresponding to a treatment which is not satisfactory, in particular because its duration is too long, its surface hardness is less than the threshold hardness and the OM / OD ratio is low to the point of giving too large a margin for initiation.

[0100] It is possible to determine the OM / OD ratio for the processes surrounding this initial process in the mapping. These determinations make it possible to identify a direction in the mapping along which one approaches the satisfaction of the constraints. Essentially, this direction corresponds here to higher OM / OD ratios and shorter processing times.

[0101] It is possible, in order to identify this direction, to give in particular a greater weight to compliance with one of the constraints, for example here the constraint relating to the OM / OD ratio.

[0102] By moving in the map along this identified direction, we arrive at a new nitriding treatment.

[0103] For this new treatment, it is possible to proceed again with an identification of the best direction.

[0104] Thus, we move step by step towards areas where the constraints are less and less unsatisfied.

[0105] A path 17 intersects in particular the curve with a ratio OM / OD equal to 0.8. On this curve, the condition on the mechanical resistance of part 1 is satisfied.

[0106] When we first arrive at this curve, the duration of the treatment is greater than 300 hours, that is to say that the condition of duration of the treatment is not satisfied.

[0107] To approach the satisfaction of this condition while continuing to respect the OM / OD ratio condition, we remain on this curve with an OM / OD ratio of 0.8 and follow it automatically in the direction of decreasing durations using numerical penalties, for example. By following this curve, the duration decreases until it falls below 200 hours. When we reach the first curve 15, at the second point 19, the intersection of the first curve 15 and the curve with an OM / OD ratio of 0.8, the optimization is stopped because beyond this first point 19 the constraint relating to surface hardness is no longer satisfied.

[0108] According to the example shown, the optimized thermochemical nitriding treatment corresponds to a temperature of 539 degrees for a duration of 93.5 hours. It corresponds to an OM / OD ratio of 0.8 and a surface hardness equal to the threshold hardness.

[0109] It should be noted that by applying a thermochemical treatment configured to achieve part 1 has a processing depth that is equal to two or three times the particular depth where the shear stresses are maximum, the processing times vary between 200 and 400 hours for the same temperature of 539 degrees Celsius.

[0110] It is thus possible to explore, in a reasonable time, the range of possible thermochemical treatments in order to determine a treatment that meets the various constraints.

[0111] It should also be noted that the P process as just described allows for initial estimates to be made for parts made of materials for which fatigue characterizations have not yet been carried out.

[0112] Estimated specific properties are used during a tensile test of the material (plasticity threshold) to evaluate the strength properties of the area reinforced by a thermochemical treatment.

[0113] It is possible to quickly determine the interest of a Material & Process solution without it having been subjected to fatigue characterizations.

Claims

Demands

1. A method (P) for processing a part (1), in particular a part (1) of a turbomachine, the method comprising the following steps: - (SI) provision of a surface constraint (F), intended to be applied to a contact surface (5) of the part (1), and at least one radius of curvature (R) of the contact surface (5), - (S2) determination of a volume constraint acting in the material of the part (1) below the surface, the determination including a calculation of an analytical expression of the volume stress as a function of the surface stress and the radius of curvature, - (S3), for each treatment in a set of treatments thermochemicals, determination of the hardness and residual stress of the part (1) subjected to treatment, - (S4) identification within the set of acceptable treatments for which: • Hardness and residual stress correspond to a mechanical resistance of the part (1) greater than a threshold resistance, the threshold resistance taking into account the stress in volume, and • the duration of treatment is less than or equal to a threshold duration, and - (S6) application of one of the acceptable treatments to the part (1).

2. A method (P) according to claim 1, wherein the identification (S4) of acceptable treatments comprises - (S4-1) an identification of first treatments of the assembly for which the hardness and residual stress correspond to a mechanical strength of the part (1) greater than the threshold strength, and / or - (S4-2) an identification of second treatments among the first treatments for which the duration of the treatment is less than or equal to the threshold duration.

3. Method (P) according to claim 2, comprising a determination of a depth of the part (1) exhibiting lower mechanical resistance, the identification of the first treatments being based on the lower mechanical resistance.

4. A method (P) according to any one of the preceding claims, comprising a step (S4-3) of identifying third treatments among the acceptable treatments, for which a surface hardness of the part (1) subjected to the treatment is greater than or equal to a threshold hardness, the treatment applied being chosen from among the third treatments.

5. A method (P) according to any one of the preceding claims, comprising an identification step (S4-4) of fourth treatments among the acceptable treatments for which a layer of material of the part (1) to be removed following the application of the treatment has a thickness less than or equal to a threshold thickness, the applied treatment being chosen from among the fourth treatments, the method being able to comprise a step (S7) of removing the layer of material following the application of the treatment.

6. A method (P) according to any one of the preceding claims, comprising, before the application of the treatment, a step (S5) of simulation, in particular by finite elements, of the mechanical resistance of the part (1).

7. A process (P) according to any one of the preceding claims, wherein the assembly comprises at least one type of treatment selected from nitriding, nitrocarburizing, cementation and carbonitriding.

8. Method (P) according to claim 7, wherein the assembly comprises a subset of treatments of the same type of treatment, each treatment of the subset corresponding to a particular pair of temperature and duration of treatment.

9. Turbomachine part obtained by a process (P) according to any one of the preceding claims.

10. Turbomachine comprising a turbomachine part according to claim 9.

11. Aircraft comprising a turbomachine according to claim 10.

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