Method for optimizing the friction welding of an assembly of at least two parts made of a nickel-chromium alloy hardened by γ'' phase precipitation, joined by friction welding

Abstract

A method for optimizing the friction welding of an assembly of at least two parts made of a nickel-chromium alloy hardened by γ'' phase precipitation, joined by friction welding. The method comprises, prior to a friction welding step of the two parts (12, 14) to form the assembly (10), a solution heat treatment step of said parts to obtain them in an annealed state, and a surfacing step of each of said parts during which each part is surfaced to have an arithmetic mean roughness (Ra) greater than 3.2 µm. These heat treatment and surfacing steps optimize the friction welding step, particularly during the initial friction phase, by limiting the thermal and mechanical stresses exerted on said parts during the friction welding step. Figure 3

Description

Title of the invention: Method for optimizing friction welding of an assembly of at least two parts made of a nickel- and chromium-based alloy hardened by y-phase precipitation assembled by friction welding

[0001] The present application relates to a method for optimizing the friction welding of an assembly of at least two parts made of a nickel- and chromium-based alloy hardened by γ-phase precipitation and assembled by friction welding.

[0002] In the aeronautical field, nickel and chromium-based alloys, such as Inconel® 718 type alloys, are commonly used, because parts made with these alloys have high mechanical characteristics over a wide temperature range compared to other parts used in aeronautics made from different alloys.

[0003] In a known manner, a method for manufacturing an assembly of parts made of a nickel and chromium-based alloy comprises a first step of receiving said parts, said parts being for example in an annealed or hardened state, a second step of friction welding said parts together, followed by a third step of deburring and checking the weld, and finally a fourth step of post-welding tempering heat treatment in two sub-steps: a first sub-step for obtaining an assembly in an annealed state, followed by a second sub-step for obtaining an assembly in a hardened state.

[0004] The parts are pre-machined to have an arithmetic mean roughness (Ra) of between 0.5 pm and 1.0 pm. However, parts with such a roughness Ra have a reduced friction capacity, which also reduces the efficiency of linear friction welding.

[0005] Another method of manufacturing an assembly of nickel and chromium-based alloy parts comprises a first step of receiving said parts in a hardened state, a second step of friction welding said parts together, followed by a third step of deburring and checking the weld.

[0006] In aeronautics, parts or assemblies made of nickel and chromium alloy in a hardened state are generally used, particularly in critical areas, because these parts or assemblies have better tensile and fatigue properties at high temperatures than parts or assemblies which are not in a hardened state.

[0007] The present invention aims to propose an improvement to the existing method of manufacturing an assembly of parts made of chromium and nickel alloy.

[0008] To this end, the invention relates to a method for optimizing welding by friction of an assembly of at least two parts made of a nickel-chromium-based alloy hardened by y-phase precipitation”, each part comprising at least a first face, said parts being assembled, in one step, to each other, at their first face, by friction welding.

[0009] According to the invention, the method comprises, before the friction welding step, a step of heat treatment of each of said parts during which each part is heated from an initial temperature to a first predetermined temperature and maintained at this first predetermined temperature for a first determined duration, then cooled to the initial temperature, so as to obtain said parts in an annealed state, and a step of surfacing each of said parts during which the first face of each part is surfaced so as to have an arithmetic mean roughness (Ra) greater than 3.2 pm.

[0010] Advantageously, the surfacing step, consisting of preparing the surface of each part for the friction welding step, makes it possible to obtain parts having a predetermined roughness Ra in order to facilitate and accelerate the friction welding step, in particular during the initial friction phase bringing the thermal energy to the interface between the parts to be welded together.

[0011] Furthermore, since the parts are in an annealed state prior to the friction welding step, this makes it possible to limit the forces exerted on said parts and to better accommodate the thermal and mechanical stresses during the friction welding step. Furthermore, this makes it possible to avoid cracking phenomena in the assembly obtained.

[0012] According to one characteristic, the surfacing step consists of cutting the first face of at least one or each of said parts. In particular, the surfacing step consists of water jet cutting the surface of one or each of the parts, so as to have a roughness Ra greater than 3.2 μm.

[0013] According to another characteristic, the surfacing step consists of machining the first face of at least one or each of said parts. In particular, the surfacing step consists of machining the surface of one or each of the parts, by means of roughing tools, or an abrasive disc, or even an abrasive belt, so as to have a roughness Ra greater than 3.2 μm.

[0014] According to one characteristic, the first predetermined temperature is between 900°C and 1100°C, preferably between 950°C and 1000°C, and the first determined duration is between 1 hour and 3 hours.

[0015] According to one characteristic, after the friction welding step, the method comprises a step of heat treatment of the assembly during which the assembly is heated from an initial temperature to a second predetermined temperature and maintained at this second predetermined temperature for a second determined duration, then cooled to a third predetermined temperature, then maintained at this third predetermined temperature for a third determined duration, then cooled to the initial temperature, so as to obtain said assembly in a hardened state.

[0016] Advantageously, this heat treatment step makes it possible to obtain an assembly in a post-welding hardened state, which makes it possible to optimize the properties of the weld in comparison with a process in which the friction welding step occurs directly on parts in a hardened state.

[0017] According to one characteristic, the second predetermined temperature is between 680°C and 760°C, the second determined duration is between 7 hours and 9 hours, the third predetermined temperature is between 580°C and 660°C, and the third determined duration is between 7 hours and 9 hours.

[0018] According to one characteristic, during the step of heat treatment of the assembly, the assembly is cooled from the second predetermined temperature to the third predetermined temperature at a cooling rate of between 45°C / hour and 55°C / hour.

[0019] According to one characteristic, the surfacing step is carried out prior to the step of heat treatment of the parts.

[0020] According to another characteristic, the step of heat treatment of the parts is carried out prior to the surfacing step, the surfacing step being carried out on said parts in the annealed state.

[0021] According to one characteristic, during the surfacing step, the first face of each part is surfaced so as to have an arithmetic mean roughness greater than or equal to 10 μm.

[0022] According to another characteristic, during the surfacing step, the first face of each part is surfaced so as to have an arithmetic mean roughness greater than or equal to 30 μm.

[0023] Advantageously, parts having a roughness Ra greater than or equal to 10 pm, or even greater than or equal to 30 pm, allows, during the friction welding stage, to accentuate the friction energy created during the first oscillation cycles of the part(s).

[0024] Other characteristics and advantages will emerge from the description of the invention which follows, a description given by way of example only, with reference to the appended drawings, among which:

[0025] [Fig-1] is a diagram illustrating an assembly of two parts made of nickel and chromium based alloy welded by linear friction,

[0026] [Fig.2] is a diagram illustrating an assembly of two nickel-chromium alloy parts welded by continuous drive friction,

[0027] [Fig.3] is a diagram illustrating an assembly of two alloy parts based on nickel and chrome welded by inertia friction,

[0028] [Fig.4] is a diagram illustrating an assembly of two alloy parts based on nickel and chrome welded by orbital friction,

[0029] [Fig.5] is a flowchart of the steps in the welding optimization process by friction according to one embodiment of the invention;

[0030] [Fig.6] is a graph illustrating the evolution of the temperature (T) as a function of the time (t) during the friction welding optimization process according to one embodiment of the invention; and

[0031] [Fig.7] is a flowchart of the steps in the welding optimization process by friction according to another embodiment of the invention.

[0032] As shown in Figures 1 to 4, an assembly 10 is composed of a first part 12 made of a nickel and chromium-based alloy friction-welded to a second part 14 made of a nickel and chromium-based alloy and thus forming a weld joint 16. In particular, a first face F12 of the first part 12 is welded to a first face F14 of the second part 14.

[0033] The parts 12, 14 are shown as being parallelepiped in shape, but may be of different shapes. For example, the parts 12, 14 may be generally cylindrical in shape with a circular base. Of course, the assembly is not limited to the first and second parts, but may include a plurality of other parts made of nickel and chromium-based alloy, friction-welded together so as to form the assembly.

[0034] In [Fig.l], the parts 12, 14 are welded together by linear friction welding (known in English as "Linear Friction Welding"). In particular, during the linear friction welding of two parts 12, 14, a pressure (represented by the arrows P) is exerted on each part 12, 14 in the direction of the other part 12, 14 in order to bring them into contact, at their first face F12, F14, and one of the parts 14 is put into translation, or more precisely into linear oscillation, relative to the other part 12 (according to the double arrow TL). Alternatively, a pressure is exerted on one of the parts in the direction of the other part which is kept stationary in the pressure direction, in order to bring them into contact, at their first face, and one of these parts is put into translation relative to the other part.The mechanical friction between the first faces F12, F14 of the parts 12, 14 which are in contact generates heat, which makes it possible to visco-plastically deform and mix the alloys of the parts 12, 14 at the contact interface between the parts 12, 14 (i.e. at the level of the welding joint 16), and thus to weld them to each other.

[0035] In [Fig.2], the parts 12, 14 are welded together by continuous drive friction welding (known in English as “Continuous Drive Friction Welding"). In particular, during continuous drive friction welding of two parts 12, 14, pressure (represented by the arrows P) is exerted on each part 12, 14 in the direction of the other part 12, 14 in order to bring them into contact, at their first face F12, F14, and one of the parts 14 is rotated relative to the other part 12 (along the arrow R), so as to generate heat by friction, and thus weld the parts 12, 14 to each other.

[0036] In [Fig. 3], the parts 12, 14 are welded together by inertia friction welding (known in English as "Inertia Friction Welding"). In particular, during the inertia friction welding of two parts 12, 14, one of the parts 14 is rotated (according to the arrow R), then a pressure (represented by the arrow P) is exerted on the other part 12 in the direction of the rotating part 14 in order to bring them into contact at their first face F12, F14. The rotation of the part 14 is then stopped, but the contact between the parts 12, 14 continues to produce heat by inertia, which makes it possible to viscoplastically deform and mix the alloys of the parts 12, 14, and thus to weld them to each other.

[0037] In [Fig. 4], the parts 12, 14 are welded together by orbital friction welding (known in English as "Orbital Friction Welding"). In particular, during orbital friction welding of two parts 12, 14, a pressure (represented by the arrows P) is exerted on each part 12, 14 in the direction of the other part 12, 14 in order to bring them into contact, at their first face F12, F14, and each of the parts 12, 14 is rotated (according to the arrows R), so as to generate heat by friction, and thus weld the first faces F12, F14 of the parts 12, 14 to each other.

[0038] [Fig.5] represents the different stages of an embodiment of the friction welding optimization method according to the invention applied to the assembly 10, and [Fig.6] illustrates the evolution of the temperature (T) as a function of time (t) during the embodiment of this method.

[0039] The parts 12, 14 are previously manufactured, at a step E10. In particular, the parts 12, 14 are previously taken from a semi-finished product, such as a connecting rod, a plate or even a sheet metal.

[0040] The parts 12, 14 are made of an alloy based on nickel (chemical symbol Ni) and chromium hardened by precipitation of the y” phase. The y” phase of the nickel and chromium alloy parts is composed of trinickel-niobium (chemical symbol Ni3 Nb). The parts 12, 14 are made of the same material, or of different nickel and chromium alloys hardened by precipitation of the y” phase. The parts 12, 14 are made of an alloy comprising approximately 50% nickel, 20% chromium, 20% iron, 5% niobium (chemical symbol Nb), 3% molybdenum and some other alloying elements, such as aluminum or titanium, or residual in lower concentration. Parts 12, 14 can be made with type 718 alloys (nickel and chromium based alloys) hardened by precipitation of the Y phase”-

[0041] In order to form each part 12, 14, a nickel and chromium-based alloy is first forged, rolled, molded, extruded, or obtained by additive manufacturing, so as to obtain a blank of each part 12, 14.

[0042] Each blank of the parts 12, 14 thus formed then undergoes a step E12 of solution heat treatment, so as to obtain parts 12, 14 in an annealed state.

[0043] Solution treatment consists of a step of gradual temperature increase, followed by a controlled cooling step. Thus, solution treatment consists of heating a part, from an initial temperature T0, to a first predetermined temperature TPI, maintaining this first predetermined temperature TPI for a first determined duration dDl, then cooling the part to the initial temperature T0. Solution treatment is a heat treatment which aims to dissolve at least part of the phases of the alloy which precipitated during the previous steps of its manufacture. Solution treatment makes it possible to facilitate the relaxation of the stresses accumulated during the previous steps of the manufacture of the parts.

[0044] A part is said to be in an annealed state after having undergone a heating cycle. The first predetermined temperature TPI is between 900°C and 1100°C, and the first determined duration dDl is between 1 hour and 3 hours. Preferably, the first predetermined temperature TPI is between 950°C and 1000°C. This first predetermined temperature TPI corresponds to the solution temperature of the δ phase of the parts 12, 14. The δ phase of the nickel and chromium alloy parts is composed of Ni3Nb. The γ phase of the nickel and chromium alloy parts is metastable and following long exposure to a temperature above 650°C, it transforms into the δ phase, which leads to softening of the nickel and chromium alloy. This first predetermined duration dDl makes it possible, depending on the dimensions of the parts 12, 14, to reach the first predetermined temperature TPI at the heart of each part 12, 14.

[0045] The parts 12, 14 in the annealed state are characterized by a Vickers hardness less than or equal to 300 HV (300 kgf / mm2, or approximately 2942 N / mm2).

[0046] A part in an annealed state no longer has a hardening phase, and is therefore more malleable.

[0047] The first faces F12, F14 of the parts 12, 14 intended to be welded to each other are then prepared, in a step E20. The method thus comprises a step E20 of surfacing each of the parts 12, 14 during which the first face F12, F14 of each part 12, 14 is surfaced so as to have an arithmetic mean roughness (Ra) greater than 3.2 pm. In other words, the surface of the first face F12, F14 of each part 12, 14 is modified to have a roughness Ra greater than 3.2 pm. By "greater" is meant here "strictly greater". Preferably, the roughness Ra of the parts 12, 14 is greater than or equal to 10 pm, and more preferably greater than or equal to 30 pm. The preparation of the surface of the parts 12, 14 makes it possible to obtain parts having a roughness Ra optimized for the friction welding step, that is to say a roughness Ra making it possible to facilitate and accelerate the friction welding step.

[0048] The surfacing step E20 consists of cutting the first face F12, F14 of at least one or each of the parts 12, 14. For example, the surfacing step E20 consists of water jet cutting the surface of the first face F12, F14 of the parts 12, 14.

[0049] The surfacing step E20 is carried out on the parts 12, 14 in the annealed state.

[0050] The method then comprises a step E30 of assembling the parts 12, 14 in the annealed state by friction welding, so as to form the assembly 10. This step E30 is carried out by means of a friction welding apparatus (not shown in the figures).

[0051] All friction welding technologies involving friction can be used, including linear friction welding (illustrated in [Fig.l]), continuous drive friction welding (illustrated in [Fig.2]), inertia friction welding (illustrated in [Fig.3]), or orbital friction welding (illustrated in [Fig.4]).

[0052] As shown in [Fig.6], the friction welding of the parts 12, 14 is carried out at an initial temperature T0. The initial temperature T0 is generally the ambient temperature of the environment of the parts 12, 14. For example, the initial temperature T0 is around 20°C.

[0053] The friction welding step, as well as the friction welding apparatus, are not detailed here, as they are well known to those skilled in the art.

[0054] Then, the method comprises a step E40 of deburring the assembly 10. Deburring consists of removing an involuntary surplus of material which appeared during friction welding, in particular at the weld joint 16. During step E40, the weld is also checked. These steps of deburring and checking the surface of the assembly are not detailed further here, because they are well known to those skilled in the art.

[0055] The method then comprises a step E50 of post-welding heat treatment of the assembly 10 in an annealed state. This step E50 consists of a double tempering hardening heat treatment, and is carried out in a single step.

[0056] Tempering, or also called hardening or aging, consists of heating a part or assembly to a temperature lower than that of solution heating for a determined period, in order to precipitate the hardening intermetallic phases.

[0057] The previously carried out solution step can make it possible to prepare the precipitation of the compounds of the nickel and chromium-based alloy(s) which occurs during the tempering step E50.

[0058] Thus, during step E50, the assembly 10 is heated from an initial temperature to a second predetermined temperature TP2 and maintained at this second predetermined temperature TP2 for a second determined duration dD2, then cooled to a third predetermined temperature TP3, then maintained at this third predetermined temperature TP3 for a third determined duration dD3, then cooled to the initial temperature. The initial temperature of this step E50 here corresponds to the initial temperature T0 before the step E12 of solution heat treatment of the parts 12, 14, but could be slightly different from this initial temperature T0.

[0059] The second predetermined temperature TP2 is between 680°C and 760°C, preferably equal to 720°C. The second determined duration dD2 is between 7 hours and 9 hours, preferably substantially equal to 8 hours.

[0060] The cooling rate VR of the assembly 10 between the second predetermined temperature TP2 and the third predetermined temperature TP3 is between 45°C / hour and 55°C / hour, and in particular equal to approximately 50°C / hour.

[0061] The third predetermined temperature TP3 is between 580°C and 660°C, preferably equal to 620°C. The third determined duration dD3 is between 7 hours and 9 hours, preferably substantially equal to 8 hours.

[0062] The assembly 10 is then cooled, from the third predetermined temperature TP3 to the initial temperature, in air at room temperature.

[0063] After this heat treatment, the assembly 10 is mechanically characterized by a Vickers hardness greater than or equal to 400 HV (approximately 3922 N / mm2).

[0064] According to another embodiment shown in [Fig.7], the surfacing step E20 is carried out prior to the solution heat treatment step E12 of the blanks of the parts 12, 14. The surfacing step E20 is therefore carried out on blanks of parts 12, 14 which are not in an annealed state.

[0065] According to another embodiment, the surfacing step E20 consists of machining the first face F12, F14 of at least one or each of the parts 12, 14. For example, the surfacing step E20 consists of machining the surface of the first face F12, F14 of at least one or each of said parts, by means of roughing tools, an abrasive disc, an abrasive belt, or any other means. allowing cutting / modification of the surface.

Claims

Claims

1. Method for optimizing the friction welding of an assembly (10) of at least two parts (12, 14) made of a nickel-chromium-based alloy hardened by y-phase precipitation, each part (12, 14) comprising at least one first face (F12, F14), said parts (12, 14) being assembled, in a step (E30), to each other, at their first face (F12, F14), by friction welding, the method comprising, before the friction welding step (E30), a step (E12) of heat treatment of each of said parts (12, 14) during which each part (12, 14) is heated from an initial temperature (T0) to a first predetermined temperature (TPI) and maintained at this first predetermined temperature (TPI) for a first determined duration (dDl), then cooled to the initial temperature (T0), so as to obtain said parts (12, 14) in an annealed state, characterized in that the method comprises,before the friction welding step (E30), a step (E20) of surfacing each of said parts (12, 14) during which the first face (F12, F14) of each part (12, 14) is surfaced so as to have an arithmetic mean roughness (Ra) greater than 3.2 pm, the surfacing step (E20) consisting of cutting or machining the first face (F12, F14) of at least one or each of said parts (12, 14).,

2. Method according to claim 1, characterized in that the first predetermined temperature (TPI) is between 900°C and 1100°C and in that the first determined duration (dDl) is between 1 hour and 3 hours.

3. Method according to one of claims 1 or 2, characterized in that, after the friction welding step (E30), the method comprises a step (E50) of heat treatment of the assembly (10) during which the assembly (10) is heated from an initial temperature (T0) to a second predetermined temperature (TP2) and maintained at this second predetermined temperature (TP2) for a second determined duration (dD2), then cooled to a third predetermined temperature (TP3), then maintained at this third predetermined temperature (TP3) for a third determined duration (dD3), then cooled to the initial temperature (T0), so as to obtain said assembly (10) in a hardened state.

4. Method according to claim 3, characterized in that the second tem- predetermined temperature (TP2) is between 680°C and 760°C, in that the second determined duration (dD2) is between 7 hours and 9 hours, in that the third predetermined temperature (TP3) is between 580°C and 660°C, and in that the third determined duration (dD3) is between 7 hours and 9 hours.

5. Method according to one of claims 3 or 4, characterized in that, during the step (E50) of heat treatment of the assembly (10), the assembly (10) is cooled from the second predetermined temperature (TP2) to the third predetermined temperature (TP3) at a cooling rate (VR) of between 45°C / hour and 55°C / hour.

6. Method according to one of claims 1 to 5, characterized in that the surfacing step (E20) is carried out prior to the step (E12) of heat treatment of the parts (12, 14).

7. Method according to one of claims 1 to 5, characterized in that the step (E12) of heat treatment of the parts (12, 14) is carried out prior to the surfacing step (E20), the surfacing step (E20) being carried out on said parts (12, 14) in the annealed state.

8. Method according to one of claims 1 to 7, characterized in that during the surfacing step (E20), the first face (F12, F14) of each part (12, 14) is surfaced so as to have an arithmetic mean roughness (Ra) greater than or equal to 10 pm.

9. Method according to one of claims 1 to 8, characterized in that during the surfacing step (E20), the first face (F12, F14) of each part (12, 14) is surfaced so as to have an arithmetic mean roughness (Ra) greater than or equal to 30 pm.

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