Method for treating a turbine engine component

Abstract

The invention relates to a method (P) for treating a component (1), in particular of a turbine engine, comprising the following steps: - (S1) providing a surface stress (F), intended to be applied to a contact surface (5) of the component (1), and at least one radius of curvature (R); - (S2) determining a volume stress exerted in the material of the component (1) below the surface, comprising calculating an analytical expression of the volume stress as a function of the surface stress and the radius of curvature; - (S3) for each treatment of a set of thermochemical treatments, determining a hardness and a residual stress of the component (1); - (S4) identifying in the set acceptable treatments for which the hardness and the residual stress correspond to a mechanical strength of the component (1) that is greater than a threshold strength taking into account the volume stress, and a treatment duration is less than or equal to a threshold duration; and - (S6) applying one of the acceptable treatments to the component (1).

Description

[0001] Process for treating a turbomachine part

[0002] DOMAIN

[0003] The invention relates to the field of turbomachines and in particular to parts of the turbomachine which are subjected to mechanical stresses requiring a certain rolling fatigue resistance. Such parts are found in particular in power transmission devices.

[0004] STATE OF THE ART

[0005] Some parts in a turbomachine, particularly in gears or power transmission devices, are intended to be in mechanical contact with other parts under high stress. They must have significant rolling fatigue resistance. Rolling fatigue of a part whose surface is subjected to mechanical stress corresponds to a break or fracture in the material of the part below the surface, the mechanical stresses being the cause of the break or fracture. This fracture produces a crack in the part, a crack that propagates in the part and in particular towards the surface subjected to the stresses. The fracture can be called crack initiation. The fracture occurs at a certain depth below the surface and can be referred to by the abbreviation EPIP which stands for "deep spalling initiated at depth".The fracture can in particular occur at a particular depth where the shear stresses are maximum. To ensure that a part has sufficient rolling fatigue resistance, it is known to apply a thermochemical treatment configured to reach the part at a treatment depth which is a multiple of the particular depth where the shear stresses are maximum. The treatment depth can thus be chosen equal to two or three times the particular depth. Such treatment depths, however, require very long thermochemical treatment times, close to 500 hours or even longer. Such times pose difficulties in terms of consistency of the treatment over its duration, the manufacturing cost of the part and obviously the manufacturing time of the part.

[0006] There is therefore a need for an optimized process for strengthening the rolling fatigue resistance of a turbomachine part.

[0007] EXPOSED

[0008] An aim of the present presentation is to propose a method for strengthening the rolling fatigue resistance of a turbomachine part that is optimized compared to the prior art.

[0009] The aim is achieved by means of a method for treating a part, in particular a turbomachine part, the method comprising the following steps:

[0010] - provision of a surface stress, intended to be applied to a contact surface of the part, and at least one radius of curvature of the contact surface,

[0011] - determination of a volume stress acting in the material of the part below the surface, the determination comprising a calculation of an analytical expression of the volume stress as a function of the surface stress and the radius of curvature,

[0012] - for each treatment of a set of thermochemical treatments, determination of a hardness and a residual stress of the part subjected to the treatment,

[0013] - identification in the set of acceptable treatments for which: o the hardness and residual stress correspond to a mechanical resistance of the part greater than a threshold resistance, the threshold resistance taking into account the volume stress, and o a treatment duration is less than or equal to a threshold duration, and - application of one of the acceptable treatments to the part.

[0014] Such a method is advantageously and optionally supplemented by the following different characteristics taken alone or in combination:

[0015] - the identification of acceptable treatments includes an identification of first treatments of the set for which the hardness and the 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;

[0016] - the method comprises determining a depth of the part having a lower mechanical resistance, the identification of the first treatments being based on the lower mechanical resistance;

[0017] - the method comprises a step of identifying third treatments from 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;

[0018] - the method comprises a step of identifying fourth treatments from 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 treatment applied being chosen from among the fourth treatments, the method possibly comprising a step of removing the layer of material following the application of the treatment;

[0019] - the method comprises, before applying the treatment, a simulation step, in particular by finite elements, of the mechanical resistance of the part; - the assembly comprises at least one type of treatment chosen from nitriding, nitrocarburizing, cementation and carbonitriding;

[0020] - 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.

[0021] The disclosure also relates to a turbomachine part obtained by a method such as has just been presented, a turbomachine comprising such a part and an aircraft comprising such a turbomachine.

[0022] DESCRIPTION OF FIGURES

[0023] Other characteristics and advantages will emerge from the following description, which is purely illustrative and not limiting, and must be read in conjunction with the attached drawings in which:

[0024] - Figure 1 is a schematic representation of a part subjected to mechanical stress on the surface;

[0025] - Figure 2 is a schematic representation of a method for treating a turbomachine part;

[0026] - Figure 3 is a schematic representation of a fatigue cycle of a part and its mechanical resistance;

[0027] - Figure 4 is a schematic curve representing a hardness of a part as a function of a depth below the surface;

[0028] - Figure 5 is a schematic curve representing a residual stress of a part as a function of a depth below the surface;

[0029] - Figure 6 is a schematic representation of a mechanical resistance margin of a part as a function of parameters of a treatment applied to this part. DETAILED DESCRIPTION OF THE INVENTION

[0030] In relation to figure 1, a first part 1, in particular of a turbomachine, is in contact with a second part 3.

[0031] The first part 1 may in particular be part of a power transmission device in the turbomachine, such as for example a gear.

[0032] The second part 3 applies a force F to the first part 1 which is directed along a z axis. In reaction, the first part applies a force -F to the second part 3 which is opposite to the force F. The forces F and -F are exerted within a contact surface 5 between the first part 1 and the second part 3.

[0033] The contact surface 5 extends in x and y directions perpendicular to the z axis. The z axis is an axis normal to the contact surface 5.

[0034] Force F is a surface stress intended to be applied to the contact surface 5 of the first part 1 during operation of the turbomachine.

[0035] We also speak of contact pressure or pressure to designate a local distribution of surface stresses linked to the imposed force F.

[0036] The first part 1 must be able to withstand mechanical resistance. In particular, the first part 1 must withstand rolling fatigue.

[0037] 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 for each point of the contact surface 5 of the pressure force which is exerted at this point.

[0038] 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. If the first part 1 does not have a spherical shape at the level of the contact surface 5, it is then possible to define several radii of curvature, for example two radii of curvature corresponding to the directions x and y.

[0039] It is also possible to enter more than two radii of curvature and to introduce additional directions in which the radii of curvature are measured, if the surface shape is more complex. Each radius of curvature is defined from a center of curvature.

[0040] It should be noted that the first part 1 may be in motion during operation of the turbomachine so 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 of the first part 1 over time by the value of the force F or the stress field over time, the value of the surface over time, a position and a direction of the axis normal to the surface over time, the radius(es) of curvature of the surface over time.

[0041] If the first part 1 is rotating during operation of the turbomachine, the functions mentioned above can be periodic.

[0042] Turbomachine part treatment process

[0043] In relation to Figure 2, a method P is proposed for treating a part 1, in particular the first part 1 as described previously.

[0044] During a first step S1 of the method 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 S1, at least one radius of curvature R of the contact surface 5 is also provided. More generally, if the part 1 is in motion during the operation of the turbomachine, the value of the force F - or the stress field - 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 may be provided.

[0045] Alternatively, instead of providing the force F, it is possible to provide a maximum permissible stress. Such a maximum permissible stress corresponds to the force F for which a certain risk of damage is accepted.

[0046] During 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.

[0047] This volume constraint can be determined in particular along the z axis which is the axis normal to the surface 5.

[0048] 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 then referred to as determining a stress field.

[0049] 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.

[0050] Analytical expressions are, for example, stress expressions associated with an elliptical contact of Hertz type between the first part 1 and the second part 3.

[0051] Various analytical expressions available in the literature can 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 authored by Howard R. Thomas and Victor A. Hoertsch.

[0052] In the case where the part 1 is in periodic movement, in particular during the operation of the turbomachine, and the variations of the force F over time have been provided, it is possible to obtain a graphical representation of the volume stress of the first part 1.

[0053] An example of such a representation is given in Figure 3. Curve 11 is a fatigue cycle which is covered at each period of the movement of the first part 1. Each point on curve 11 represents a moment of this period and gives:

[0054] - on the abscissa, the hydrostatic pressure or stress to which part 1 is subjected at this moment of the cycle, and

[0055] - on the ordinate, the shear stress exerted in the material of part 1 under the contact surface 5.

[0056] Shear can be mesoscopic shear which translates shear at the scale of a few grains of material.

[0057] In order to mechanically strengthen it, different thermochemical treatments can be applied to part 1.

[0058] It is possible to predetermine in advance a certain number of candidate treatments which can be applied to part 1, and thus form a set, or catalogue, of possible thermochemical treatments.

[0059] During a third step S3, for each treatment of the set of thermochemical treatments, a hardness of the part 1 subjected to the treatment is determined. During a third step S3, a residual stress of the part 1 subjected to the treatment is also determined.

[0060] 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. The hardness is, for example, a Vickers hardness which is expressed in HV units. The residual stress is a mechanical stress that the thermochemical treatment leaves inside the treated part 1. The treatment can in fact put part 1 under mechanical tension, tension that can be measured in the form of a pressure expressed in Pascal units.

[0061] The hardness and residual stress can be evaluated at different depths in the workpiece 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 the treated workpiece 1.

[0062] Figure 4 illustrates an example of a hardness curve 7 as a function of the depth of the treated part 1.

[0063] Figure 5 illustrates an example of a residual stress curve 9 as a function of the depth of the treated part 1.

[0064] There are databases that allow the hardness and residual stress of a part 1 to be determined based on the chemical composition of the part 1 and the treatment applied to it.

[0065] A machine learning module trained on such bases can also make such estimates.

[0066] During a fourth step S4, in a set of candidate treatments, certain so-called acceptable treatments are identified for which: o the hardness and the residual stress correspond to a mechanical resistance of the part 1 greater than a threshold resistance, the threshold resistance taking into account the volume stress, and o a duration of the treatment is less than or equal to a threshold duration.

[0067] 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.

[0068] Mechanical strength is an object comparable to the volume stress determined previously. The mechanical strength of part 1 corresponds, for example, to a fatigue limit 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 initiation occurs.

[0069] Mechanical resistance can be assessed in particular at a particular depth of the part 1, which has a lower mechanical resistance. The identification of the first treatments is then based on this lower mechanical resistance.

[0070] An example of a fatigue curve 13 is given in Figure 3.

[0071] The mechanical resistance of part 1 is compared to a threshold resistance, the threshold resistance taking into account the volume stress.

[0072] For example, in relation to Figure 3:

[0073] - 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;

[0074] - a point D of the limit fatigue curve 3 is identified, points D and M having the same abscissa of hydrostatic stress;

[0075] - a point O on the hydrostatic stress abscissa axis is identified, corresponding to a shear equal to zero, points O, D and M having the same hydrostatic stress abscissa;

[0076] - the OM / OD ratio is determined, which is a shear ratio, this ratio being unitless;

[0077] - 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 lower than the threshold coefficient.

[0078] An OM / OD ratio greater than or equal to the value one corresponds to a limit fatigue curve which crosses or is located below the fatigue cycle. This situation corresponds to a very high risk of initiation, as part 1 does not have sufficient mechanical strength to withstand the fatigue cycle.

[0079] An OM / OD ratio lower than the value 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.

[0080] If the OM / OD ratio is less than one, the more this ratio decreases, the further the fatigue limit curve is located above the fatigue cycle, and the more the mechanical resistance of part 1 is higher than the mechanical stress corresponding to the fatigue cycle. In other words, the more the OM / OD ratio decreases, the more part 1 has a significant safety margin at initiation.

[0081] Acceptable treatments are also treatments whose duration of treatment is less than or equal to a threshold duration. The threshold duration can be set, for example, at 100 hours or 150 hours.

[0082] According to a first variant of the fourth step S4, the identification of acceptable treatments may, optionally, include

[0083] - a first variant S4-1, during which an identification of first treatments of the set for which the hardness and the residual stress correspond to a mechanical resistance of the part 1 greater than the threshold resistance and

[0084] - a second variant S4-2, during which 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. 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.

[0085] The second variant S4-2 of the fourth step S4 may comprise a sub-step S4-3 of identification, or third variant S4-3, of third treatments from 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.

[0086] In this second variant S4-2, the treatment applied is chosen from a subgroup of acceptable treatments by adding a new condition which concerns the surface hardness of part 1 after treatment. The surface hardness must be greater than a threshold hardness. The threshold hardness can be chosen to be equal to 500 Hv or 700 Hv.

[0087] If in the third step S3 the hardness at different depths in the first part 1 below its surface was determined, it is possible to already have the value of the surface hardness corresponding to a zero depth.

[0088] 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.

[0089] The third variant of the fourth step S4 may comprise a sub-step S4-4 of identifying fourth treatments from among the acceptable treatments or the 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.

[0090] In the third variant, the treatment applied 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 part 1 to be removed following the application of the treatment.

[0091] The thermochemical treatment, such as nitriding, applied to part 1 can in fact have the effect of making a surface layer of part 1 brittle or of deforming the surface of part 1. It may be advantageous, by removing a surface layer, to remove the brittle layer or to resume the exact shape of part 1.

[0092] In the third variant, the removed layer must have a thickness less than or equal to a threshold thickness. The threshold thickness may be in particular between 0.5 mm and 1 mm, in particular chosen to be equal to 0.5 mm or 1 mm.

[0093] The thickness of the layer to be removed can be estimated using business rules and / or modeling tools.

[0094] 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.

[0095] During a sixth step S6, a so-called acceptable treatment is chosen and applied to part 1.

[0096] In this third variant, the method 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.

[0097] It should be noted that the three variants of the fourth stage S4 can be cumulative two by two or all three.

[0098] Such a process P allows:

[0099] - to ensure that the chosen treatment has a duration less than the threshold duration, and

[0100] - to ensure that the treated part 1 has sufficient mechanical strength to withstand the expected mechanical stress. Furthermore, the identification of candidate treatments takes a relatively short time thanks to the use of the analytical expression of the volume stress.

[0101] In particular, such an expression makes it possible to avoid using a finite element simulation method, a method which takes much longer to produce a usable result.

[0102] The P method makes it possible to predict for a treated part 1 where and at what contact pressure initiation occurs. These predictions are in agreement with physical rolling fatigue tests.

[0103] Furthermore, the P method makes it possible to control the difference between the mechanical strength of the part 1 and the mechanical stress that is planned to be applied to it. In other words, the P method makes it possible to know the safety margin in terms of mechanical strength. It is possible to control the risk of damage of the deep chipping type where in the prior art until now, safety margins were taken without being quantified.

[0104] Optionally, the method P, as just presented, can 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 expected mechanical effects.

[0105] It is also possible to explore vast domains of geometric and loading properties with the P method in a few minutes to quickly target sub-domains for fine analysis via finite element simulation.

[0106] The thermochemical treatments that can be implemented may comprise at least one type of treatment chosen from nitriding (diffusion of atomic nitrogen from the surface of the part 1 towards the core), nitrocarburizing (nitriding with additional diffusion of carbon), carburizing (diffusion of carbon on the surface of the part 1) and carbonitriding (carburizing with additional diffusion of nitrogen). In particular, the set of treatments, the relevance of which is desired to be assessed, may comprise 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 the treatment. For example, the set of treatments may comprise a subset of nitriding treatments which differ from each other by their duration or their temperature.

[0107] It should be noted that the entire set of treatments can be the subset of treatments of the same type of treatment, that is to say that the set of treatments then corresponds to a single type of treatment which is declined in different durations and at different temperatures.

[0108] 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.

[0109] 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 different durations.

[0110] The duration of treatment is reported on the abscissa along an axis graduated in hours.

[0111] The treatment temperature is plotted on the ordinate along an axis graduated in degrees Celsius.

[0112] For each treatment, the mechanical resistance was evaluated by determining the OM / OD ratio presented above. Curves along which the ratio takes a constant value were plotted on the map.

[0113] One curve has a minimum value of the ratio, namely equal to 0.56, and another curve has a maximum value of the ratio, notably equal to 0.8.

[0114] Each point of the mapping illustrated in figure 6 thus makes it possible to know a nitriding duration, a nitriding temperature and the OM / OD ratio characterizing the mechanical resistance of the part 1, in particular a margin at initiation.

[0115] A first point 16 corresponds, for example, to a treatment duration of between 500 and 600 hours, a temperature of between 530 and 540 degrees Celsius and an OM / OD ratio of between 0.6 and 0.64.

[0116] A second point 19 corresponds, for example, to a treatment time of less than 200 hours, a temperature of approximately 540 degrees Celsius and an OM / OD ratio equal to 0.8.

[0117] 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 part 1 subjected to treatment is greater than or equal to a threshold hardness.

[0118] A first curve 15 plotted on the map corresponds to the equality of surface hardness and threshold hardness.

[0119] Treatments that do not respect the constraint are located above the first curve 15, that is, in the direction of increasing temperatures.

[0120] The treatments that respect the constraint are located below the first curve 15, that is to say in the direction of decreasing temperatures.

[0121] Thus, the second point 19 corresponds to a nitriding for which the surface hardness constraint is respected.

[0122] A second curve 17 represents a search for parameters of a nitriding which makes it possible to produce a part whose mechanical resistance is characterized by an OM / OD ratio equal to 0.8, a treatment duration of less than 200 hours and which respects the constraint linked to the second variant of step S4, according to which the surface hardness of the part subjected to the treatment is greater than or equal to a threshold hardness.

[0123] 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 lower than the threshold hardness and the OM / OD ratio is low to the point of giving too large a margin for priming.

[0124] It is possible to determine the OM / OD ratio for the treatments surrounding this initial treatment in the mapping. These determinations make it possible to identify a direction in the mapping along which we are approaching the satisfaction of the constraints. Essentially, this direction corresponds here to higher OM / OD ratios and lower processing times.

[0125] To identify this direction, it is possible to give greater weight to compliance with one of the constraints, for example here the constraint relating to the OM / OD ratio.

[0126] By moving in the map in this identified direction, we arrive at a new nitriding treatment.

[0127] For this new treatment, it is possible to carry out a new identification of the best direction.

[0128] Thus, we are moving gradually towards areas where the constraints are less and less unsatisfied.

[0129] A path 17 intersects in particular the curve with an OM / OD ratio equal to 0.8. On this curve, the condition on the mechanical resistance of part 1 is satisfied.

[0130] When we first arrive at this curve, the treatment duration is greater than 300 hours, that is to say, the treatment duration condition is not satisfied.

[0131] To get closer to satisfying this condition while continuing to respect the condition of the OM / OD ratio, we stay on this curve of OM / OD ratio equal to 0.8 and we 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 intersection of the first curve 15 and the curve of OM / OD ratio equal to 0.8, the optimization is stopped because beyond this first point 19 the constraint relating to surface hardness is no longer satisfied.

[0132] According to the example presented, 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 equal to 0.8 and a surface hardness equal to the threshold hardness.

[0133] It is noted that by applying a thermochemical treatment configured to reach part 1 at a treatment depth which is equal to two or three times the particular depth where the shear stresses are maximum, the treatment times vary between 200 and 400 hours for the same temperature of 539 degrees Celsius.

[0134] It is thus possible to explore, in a reasonable time, the field of possible thermochemical treatments in order to determine a treatment which respects the different constraints.

[0135] It should also be noted that the P process as just described allows initial estimates to be made for parts made from materials for which fatigue characterizations have not yet been carried out.

[0136] Estimated specific properties are used during a material tensile test (yield threshold) to evaluate the strength properties of the area reinforced by thermochemical treatment.

[0137] It is possible to quickly decide on the interest of a Material & Process solution without it having been subject to fatigue characterizations.

Claims

CLAIMS 1. Method (P) for treating a part (1), in particular a part (1) of a turbomachine, the method comprising the following steps: - (S1) provision of 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) of the contact surface (5), - (S2) determination of a volume stress acting in the material of the part (1) under the surface, the determination comprising 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 of a set of thermochemical treatments, determination of a hardness and a residual stress of the part (1) subjected to the treatment, - (S4) identification in the set of acceptable treatments for which: o the hardness and the residual stress correspond to a mechanical resistance of the part (1) greater than a threshold resistance, the threshold resistance taking into account the volume stress, and o a duration of the treatment is less than or equal to a threshold duration, and - (S6) application of one of the acceptable treatments to the part (1).

2. Method (P) according to claim 1, in which the identification (S4) of the acceptable treatments comprises - (S4-1) an identification of first treatments of the set for which the hardness and the residual stress correspond to a mechanical resistance of the part (1) greater than the threshold resistance, 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) having a lower mechanical resistance, the identification of the first treatments being based on the lower mechanical resistance.

4. Method (P) according to any one of the preceding claims, comprising a step (S4-3) of identifying third treatments from 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. Method (P) according to any one of the preceding claims, comprising a step of identifying (S4-4) fourth treatments from 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 treatment applied being chosen from among the fourth treatments, the method possibly comprising a step (S7) of removing the layer of material following the application of the treatment.

6. 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. Method (P) according to any one of the preceding claims, in which the assembly comprises at least one type of treatment chosen from nitriding, nitrocarburizing, cementation and carbonitriding.

8. Method (P) according to claim 7, in which the set 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 the treatment.

9. Turbomachine part obtained by a method (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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