HK1180642B

HK1180642B - Part assembly method

Info

Publication number: HK1180642B
Application number: HK13107941.0A
Authority: HK
Inventors: Yves Winkler; Stewes Bourban; Alban Dubach
Original assignee: The Swatch Group Research And Development Ltd.
Priority date: 2010-06-22
Filing date: 2011-06-22
Publication date: 2017-05-19

Description

Method for assembling parts

Technical Field

The invention relates to a method for permanently assembling at least a first component made of a first material and at least a second component made of a second material, in which permanent assembly the second component is used to constrain (imprisoner) the first component.

The technical field of the invention is the field of precision machinery. More particularly, the present invention relates to the field of methods for manufacturing amorphous metal components.

Background

The present invention relates to the assembly of two parts to each other in order to obtain two parts assembled together by clamping or, conversely, two parts movable with respect to each other.

In order to obtain movable assemblies (for example, rotating bearings), several manufacturing steps are known: first of all at least three parts to be movably mounted are very finely machined. It follows that at least two of these components must be assembled by screws, gluing, welding or other methods in order to partially constrain the third component that will remain mobile. Manufacturing such a movable assembly requires that the final clearance between the two components be sufficient to allow the two components to move relative to each other. This gap must not be too large, otherwise there is a risk of one component shifting relative to the other, which is undesirable. Such assemblies are therefore complex and expensive to manufacture.

To produce a fixed/sealed assembly, the threads for the assembly may be formed or the components may be bonded, brazed, welded or riveted to one another.

Certain problems may arise. In fact, sometimes the above known methods cannot be used. First, these methods cannot be used because they are not possible. For example, it is not possible to make threads on brittle materials without damaging the part.

Secondly, these methods cannot be used because undesirable effects, such as degassing of the adhesive material, can occur.

Disclosure of Invention

The present invention relates to a method of fixing two parts to each other, which overcomes the drawbacks of the prior art by enabling a first part to be simply and effectively fixed to a second part, wherein the assembly can be fixed or mobile.

The invention therefore relates to the above-mentioned assembly method, said method being characterized in that it comprises the following steps:

-selecting as a first material a metal alloy capable of becoming at least partially amorphous, a second material different from the first material;

-taking a part formed of said second material;

-shaping the first part and simultaneously assembling the first part onto the second part, the first material being subjected, at the latest at the moment of shaping, to a treatment allowing the first material to become at least partially amorphous, the first and second parts being subjected to a thermal cycle as follows: first a temperature gradient to ensure expansion of at least the second part; followed by a cooling gradient to cause the second component to contract around the first component, thereby constraining the first component;

-dimensioning said at least one second component and said at least one first component as appropriate and selecting the coefficient of thermal expansion of said second material in comparison with the coefficient of thermal expansion of said first material so as to:

-obtaining a permanent assembly of the second component clamped on the first component if the product of the coefficient of thermal expansion of the second material and the cooling gradient is greater than the product of the coefficient of thermal expansion of the first material and the cooling gradient;

-obtaining a permanent assembly with at least one degree of freedom between the second component and the first component if the product of the coefficient of thermal expansion of the second material and the cooling gradient is smaller than the product of the coefficient of thermal expansion of the first material and the cooling gradient.

One advantage of the present invention is that it allows the two components to be very simply secured to each other. In fact, the coefficient of expansion of the material plays a role meaning that no clamping means or means for obtaining a gap need be used. The gap or clamping between the two components is achieved directly by the choice of materials and their coefficients of expansion. Likewise, the grip or gap can be easily adjusted by the particular choice of material used.

In a first advantageous embodiment, the method comprises the steps of:

-defining the thermal cycle such that the temperature-increasing gradient increases the first material, selected as a metal alloy capable of becoming at least partially amorphous, above its melting temperature, causing the first material to at least partially lose any crystalline structure, and such that the temperature-decreasing gradient decreases the first material below its glass transition temperature, allowing the first material to become at least partially amorphous.

In a second advantageous embodiment, the method comprises the steps of:

-transforming the first material into a preform and subjecting the first material to a treatment allowing the first material to become at least partially amorphous;

-defining the thermal cycle of the first material transformed into a preform so that the preform is subjected to a temperature between its glass transition temperature and its crystallization temperature;

-pressing the preform so that the at least one second component constrains the at least one first component;

-cooling the assembly to allow the first material to retain the at least partially amorphous character.

In a third advantageous embodiment, the method comprises the step of depositing an intermediate layer on the second component; the method further comprises a final step of dissolving the intermediate layer so as to increase the gap between the first part and the second part if the product of the coefficient of thermal expansion of the second material and the cooling gradient is smaller than the product of the coefficient of thermal expansion of the first material and the cooling gradient.

In another advantageous embodiment, the method comprises the steps of: -making at least one relief on said second component so as to increase the mechanical adhesion between said first and second component.

In another advantageous embodiment, said at least one relief is formed by machining.

In another advantageous embodiment, the first material or the second material, selected as a metal alloy capable of becoming at least partially amorphous, is subjected to a treatment allowing the first material or the second material to become fully amorphous.

One advantage of the present invention is that it is very easy to implement. In fact, this method uses amorphous metals with the following special characteristics: for each alloy, at a given temperature range [ Tg-Tx ]]The amorphous metal softens but remains amorphous (where Tx is the crystallization temperature and Tg is the glass transition temperature) for a certain period of time (e.g., for Zr)_41.24Ti_13.75Cu_12.5Ni₁₀Be_22.5Alloy, Tg 350 ℃, Tx 460 ℃). Thus, these metals can be shaped under relatively low stress and at low temperatures, allowing simplified processes to be used. Because the viscosity of the alloy is in the temperature range Tg-Tx]The use of this type of material also allows extremely small geometries to be repeatedly machined with great precision, since the temperature drops sharply and the alloy therefore adapts to all the details of the cavity (n). For example, for platinum-based materials, the forming occurs at a temperature of about 300 ℃ at which the viscosity of the alloy is as high as 10³Pa.s, stress of 1MPa, not 10 at temperature Tg¹²Viscosity in Pa.s. This means that these components can be manufactured and assembled simultaneously.

The invention also relates to a method for permanent assembly between at least a first component formed of a first material and at least a second component formed of a second material, in which permanent assembly the second component is intended to constrain the first component, characterized in that it comprises the following steps:

-selecting as said second material a metal alloy capable of becoming at least partially amorphous, the first material being different from the second material;

-taking a part formed of said first material;

-shaping the second part and simultaneously assembling the second part onto the first part, the second material being subjected, at the latest at the moment of shaping, to a treatment allowing the second material to become at least partially amorphous, the second part and the first part being subjected to a thermal cycle as follows: first an elevated temperature gradient to ensure expansion that allows the first and second components to be assembled together; followed by a cooling gradient to cause the second component to contract around the first component, thereby constraining the first component;

Drawings

The objects, advantages and features of the assembly method according to the invention will be more clearly seen from the following detailed description of at least one embodiment of the invention, given purely by way of non-limiting example, illustrated in the accompanying drawings, in which:

fig. 1 to 6 schematically show a first embodiment of the method according to the invention.

Fig. 7 to 11 schematically show a second embodiment of the method according to the invention.

Fig. 12 to 18 schematically show a variant of the first embodiment of the method according to the invention.

Fig. 19 schematically shows a variant of the second embodiment of the method according to the invention.

Detailed Description

The invention relates to the assembly of a first component 1 and a second component 2, the first component 1 having a coefficient of thermal expansion of α₁Of a first material, the second component 2 being made of a material having a coefficient of thermal expansion of α₂Is made of the second material of (1). The second part is arranged to restrain the first part 1.

In the present case, the first component 1 is made of an at least partially amorphous material comprising at least one metallic element as an at least partially amorphous metal alloy. However, it is conceivable to manufacture the second part 2 from an at least partially amorphous material comprising at least one metallic element, while the first part 1 is manufactured from any material. Preferably, the first part 1 and/or the second part 2 are made of a fully amorphous metal alloy, which may be the same or different. The metal element may be of a noble metal type.

The amorphous metal properties of the movable component 1 are used to assemble the second component 2 and the first component 1. In fact, it is possible to use,amorphous metals are very advantageous for forming, allowing parts with complex shapes to be manufactured simply with high precision. This is because the amorphous metal has the following special characteristics: for each alloy, at a given temperature range [ Tg-Tx ]]The amorphous metal may soften but remain amorphous (where Tx is the crystallization temperature and Tg is the glass transition temperature) for a certain period of time (e.g., for Zr_41.24Ti_13.75Cu_12.5Ni₁₀Be_22.5Alloy, Tg 350 ℃, Tx 460 ℃). Thus, these metals can be shaped under relatively low stress and at low temperatures, allowing simplified processes such as thermoforming to be used. Because the viscosity of the alloy is in the temperature range Tg-Tx]The use of this type of material also allows extremely small geometries to be repeatedly machined with great precision, since the temperature drops sharply and the alloy therefore adapts to all the details of the cavity. For example, for platinum-based materials, the forming occurs at a temperature of about 300 ℃ at which the viscosity of the alloy is as high as 10³Pa.s, stress of 1MPa, not 10 at temperature Tg¹²Viscosity in Pa.s.

The first step, as shown in fig. 2, consists in taking the second part 2 as a support. The support 2 is formed of a material referred to as a "second material", which may be any material. The second part 2 constrains the first part 1.

The second step, shown in fig. 3, consists in taking the first material, i.e. the material forming the first component 1.

The third step, as shown in fig. 4 to 6, consists in shaping the first material, which is an amorphous metal, so as to form the first component 1 and assembling the first component 1 to the second component 2. For this purpose, a thermoforming process is used.

First, a preform 4 of amorphous material is manufactured. The preform 4 is made up of components similar in appearance and dimensions to the final component. Typically, the preform 4 takes the shape of a circular disc if it is desired to manufacture, for example, circular components. It is important that the preform 4 already has an amorphous structure. To this end, the material or materials forming the first material are brought to a liquid state by raising the temperature of these materials above their melting temperature. These materials are then homogeneously mixed to form the first material. The mixture is then cast into the mould parts 5a, 5b of a mould 5 having the desired shape. The mixture is then cooled as quickly as possible so that the atoms have no time to be structured, so that the first material becomes at least partially amorphous.

As shown in fig. 4, the preform 4 is then placed on the second component 2 to cover the second component 2. The hot press is then heated to a particular temperature of the material, preferably between the glass transition temperature Tg and the crystallization temperature Tx of the material. So that the first component 1 and the second component 2 are raised to the same temperature. It is of course also conceivable for the second component 2 to be raised to a different temperature than the first component 1.

Once the hot press is at this temperature, pressure is applied to the preform 4 to fill the cavity 6 in the second part as shown in fig. 5. The pressing operation is performed for a predetermined period of time.

Once the pressing time is reached, the first material is cooled below the Tg temperature to form the first component 1. The pressing and cooling must be fast enough to prevent the first material from crystallizing. In fact, for a given first material at a given temperature between its glass transition temperature Tg and the crystallization temperature Tx, there is a maximum duration beyond which the material begins to crystallize. The duration decreases as the temperature approaches its crystallization temperature Tx and increases as the temperature approaches its glass transition temperature Tg. Thus, for each temperature/alloy pair, the amorphous material starts to crystallize if the time spent at the temperature comprised between Tg and Tx exceeds a certain value. Typically for Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5Alloy and 440 c, the pressing time should not exceed about 120 seconds. Thus, the thermoforming retains the at least partially amorphous initial state of the preform 4.

The first part 1 and the second part 2 are then removed from the mould 5 as shown in figure 6 to form the final part.

It is contemplated that the second component may be made of amorphous metal and the first component 1 may be made of any material.

A variant of thermoforming uses the principle of casting. The amorphous metal components are mixed in liquid form, that is, at a temperature at least equal to the melting temperature. The mixture is then cast into a mold having the shape of the part to be manufactured, and the mixture is then rapidly cooled so that the atoms have no time to be structured.

According to the invention, the first material and the second material are advantageously chosen such that the coefficient of thermal expansion α is obtained₁And coefficient of thermal expansion α₂The coefficient of thermal expansion of a material determines that the material will, when its temperature increases, according to the equation α -L₀Δ T swell, wherein:

Δ L represents the change in length in meters (m);

α denotes the coefficient of linear expansion in degrees Kelvin to the first negative power (K)^-1)；

L₀Denotes the initial length in meters (m);

ΔT＝T-T₀and represents a change in temperature in kelvin (K) or degrees celsius (deg.c).

This means, for example, for a 30m steel bar, since the steel has 12.0 × 10^-6When subjected to a temperature change of positive Δ T-60 ℃, the steel bar will expand to a length of 30.0216 m. Thus, when the temperature is reduced, the steel bar will contract and return to its original length.

This principle is utilized in the case of the present invention. In fact, thermoforming is performed at a temperature higher than room temperature, which means that the materials forming the first and second components 1, 2 expand, as they undergo a gradient of temperature increase. During cooling, i.e. during the cooling gradient, the first and second materials will shrink. In the case of thermoforming, the gradient is the same, since both the first and the second part are placed between the same mould parts 5a and 5 b. If the coefficients of thermal expansion are different, the contraction will be different. Naturally, if the first component 1 and the second component 2 do not experience the same temperature rise, the gradient will be different for the two components and the degree of contraction will also be different, since the contraction depends on the temperature rise gradient, the coefficient of thermal expansion and the size.

In the case of casting, the fact that the molten alloy is poured into the mould results in an increase in the temperature of the second part 2 located in the mould 5. It is believed that the temperatures of the two materials will approach each other through heat transfer.

In the first embodiment, the first member 1 and the second member 2 are assembled in a movable manner to form the unit 3. For example, it is conceivable for the unit 3 to be a ball joint or a wheel rotatably mounted on a spindle. It is also conceivable that the unit 3 is two tubes fitted loosely to each other. As shown in fig. 1, the unit comprises a support 2 which is a second part on which a movable part 1 which is a first part is mounted.

According to the invention, advantageously, the coefficient of thermal expansion α of the first component 1₁Coefficient of thermal expansion α with the second member 2₂Different. This results in the first part 1 being movable relative to the second part 2. The difference in the coefficients of thermal expansion results in the appearance of gaps or the appearance of clamping to each other. The use of an at least partially amorphous material comprising at least one metallic element skillfully makes it possible to simultaneously carry out the operation of manufacturing a part made of an at least partially amorphous material comprising at least one metallic element and the operation of assembling said part to another part.

The gap between the two movable parts is defined by the following factors: the difference in the coefficients of thermal expansion of the first and second materials, the temperature at which thermoforming is performed and the first and second components 1, 1Dimension in the case of mobile assembly, i.e. in the case of a gap 12 between the two parts 1 and 2, the coefficient of thermal expansion α₁Specific heat expansion coefficient α₂Large coefficient of thermal expansion α₁Specific heat expansion coefficient α₂The larger the gap 12, the larger the fact that the first component 1 must contract more than the second component 2 because the first component 1 is constrained in the second component 2, to this end, the coefficient of thermal expansion α₂And the product of said temperature reduction gradient has a specific heat expansion coefficient of α₁And the product of the temperature reduction gradient is small.

Likewise, the higher the thermoforming temperature, the larger the gap at room temperature. The assembled final gap 12 can also be altered by applying greater or lesser stress during cooling to at least Tg.

The use of amorphous metal allows to achieve a mobile assembly while manufacturing the first component 1, without making the method more complex, but on the contrary simplifying it.

The excess material may be removed, for example, by chemical or mechanical means. Excess material may be removed before or after cooling.

Alternatively, the second component 2 is made of an amorphous metal or an amorphous metal alloy, while the first component 1 is made of any material. The second part 2, which is a support, comprises a cavity 6, in which cavity 6 the first part 1 is accommodated. The method used is a thermoforming method as described above.

In the first modification shown in fig. 12 to 18, an additional step may be provided between the first step and the second step. This additional step consists in depositing the intermediate layer 9 on the part not made of amorphous metal, that is, when the first part is cast in the cavity 6 of the second part 2, the intermediate layer 9 on the walls 7 of said cavity 6, or in the case of the alternative embodiment of the first embodiment, the intermediate layer 9 on the walls 7 of the first part 1. The intermediate layer 9 may be deposited by CVD, PVD, electrodeposition, galvanic deposition or other methods. After the third step, this layer 9 is therefore interposed between the first component 1 and the second component 2. The intermediate layer 9 may then be selectively dissolved in a chemical bath in order to increase the gap 12 between said first part 1 and said second part 2. Dissolution is possible because a gap 12 was previously created between the first component 1 and the second component 2, allowing the chemical solvent to penetrate into the gap and thus removing all the intermediate layers.

In the second embodiment, the first member 1 and the second member 2 are fixedly assembled to form one unit. The ability of amorphous metal to conform perfectly to all details of the surface during hot working can be used to seal the assembly if the difference between the coefficients of thermal expansion of the materials used for parts 1 and 2 is chosen appropriately. For example, it is conceivable that the unit 3 is a sealed assembly formed by two tubes or watch hands fixed to a mandrel. As shown in fig. 7, the unit includes a support member 2 which is a second member, and a first movable member 1 which is a first member is fixed to the second member 2. The method used shown in fig. 8 and 11 is the same as that of the first embodiment. The method uses a hot forming method, and the first component 1 or the second component 2 may be made of an amorphous metal or an amorphous metal alloy, as in the first embodiment.

In this embodiment, the sealed assembly or clamping of the second component to restrain the first component is accomplished by selecting the first material and the second material in a manner that results in a coefficient of thermal expansion α₁Specific heat expansion coefficient α₂More specifically, the dimensions of the first and second components and the coefficient of thermal expansion α are determined₁And α₂So that said coefficient of thermal expansion α₂And the product of the temperature reduction gradient is greater than the thermal expansion coefficient α₁And the cooling gradient is large. The second part, which constrains the first part, is thus much more contracted than the first part, thereby clamping said first part.

As a result, the first and second materials shrink during cooling of the first and second components. Because of the different coefficients of thermal expansion, the degree of contraction is different. In this example, the second component is larger than the first componentThe clamping force is thus determined by the difference in the coefficients of thermal expansion of the first and second materials, the temperature at which thermoforming is performed, and the dimensions of the two components, the coefficient of thermal expansion α₂Specific heat expansion coefficient α₁The more large, the greater the clamping force. Likewise, the higher the thermoforming temperature, the greater the clamping force at room temperature. The final clamping force of the assembly can also be varied by applying greater or lesser stress during cooling to at least Tg.

In a variation of the second embodiment as shown in fig. 19, an additional step may be provided between the first step and the second step. The additional steps consist in: the inner wall 10 of the second component 2 is machined when the first component 1 is made of an amorphous material, or the outer wall 11 of the first component 1 is machined when the second component is made of an amorphous material. The machining consists in machining rough areas, for example reliefs 13. This increases the mechanical adhesion and/or sealing between the first component 1 and the second component 2 during thermoforming.

A variant in which an intermediate layer is added between the component 1 and the component 2 must also be mentioned. By selecting a material for the layer having a different coefficient of thermal expansion than the component 1 and the component 2, the layer allows the clamping force to be adjusted over a larger range.

In a variant, this layer can also be used for fixing in order to avoid damaging the components to be assembled on the amorphous metal, in particular in the case of the assembly of brittle materials, such as silicon. Soft layers (copper, gold, silver, indium, etc.) that plastically deform before the brittle material breaks when the assembly is stressed due to cooling can thus be deposited on the brittle material.

In another variant, the first component 1 or the second component 2 may be locally heated to locally expand the material of the first component 1 or the second component 2. This thereby allows the first and second components to be assembled to each other. Preferably, this variation can be used in the second embodiment.

It will be evident that various modifications and/or improvements and/or combinations which are obvious to a person skilled in the art may be made to the various embodiments of the invention listed above without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method of permanent assembly between at least a first component (1) formed of a first material and at least a second component (2) formed of a second material, in which permanent assembly the second component is intended to constrain the first component, characterised in that it comprises the following steps:

-taking a part formed of said second material;

-shaping the first part (1) and simultaneously assembling it onto the second part, at the latest at the moment of said shaping, the first material being subjected to a treatment which allows it to become at least partially amorphous, the first and second parts being subjected to a thermal cycle as follows: first a temperature gradient to ensure expansion of at least the second part; followed by a cooling gradient to cause the second component to contract around the first component, thereby constraining the first component;

-dimensioning the at least one second component and the at least one first component as appropriate and having a coefficient of thermal expansion (α) with the first material₁) By comparison, the coefficient of thermal expansion of the second material is selected (α)₂) So as to:

-if the coefficient of thermal expansion of the second material (α)₂) And the cooling gradient is greater than the coefficient of thermal expansion of the first material (α)₁) And said cooling gradient is high, a permanent assembly is obtained in which said second component is clamped to said first component;

-if the coefficient of thermal expansion of the second material (α)₂) And the cooling gradient is greater than the coefficient of thermal expansion of the first material (α)₁) And said cooling gradient is small, a permanent assembly is obtained in which there is at least a degree of freedom between said second part and said first part.

2. The permanent assembly method according to claim 1, characterized in that it comprises the following steps:

3. The permanent assembly method according to claim 1, characterized in that said forming comprises the steps of:

-transforming the first material into a preform (4) and subjecting the first material to a treatment allowing the first material to become at least partially amorphous;

-pressing the preform so that the at least one second component (2) constrains the at least one first component (1);

4. A permanent assembly method according to claim 1, characterised in that it comprises a step of depositing an intermediate layer (9) on the second component; the method further comprises a final step of dissolving the intermediate layer so as to increase the gap (12) between the first component (1) and the second component (2) if the product of the coefficient of thermal expansion of the second material and the cooling gradient is smaller than the product of the coefficient of thermal expansion of the first material and the cooling gradient.

5. A permanent assembly method according to claim 2, characterised in that it comprises a step of depositing an intermediate layer (9) on the second component; the method further comprises a final step of dissolving the intermediate layer so as to increase the gap (12) between the first component (1) and the second component (2) if the product of the coefficient of thermal expansion of the second material and the cooling gradient is smaller than the product of the coefficient of thermal expansion of the first material and the cooling gradient.

6. A permanent assembly method according to claim 3, characterised in that it comprises a step of depositing an intermediate layer (9) on the second component; the method further comprises a final step of dissolving the intermediate layer so as to increase the gap (12) between the first component (1) and the second component (2) if the product of the coefficient of thermal expansion of the second material and the cooling gradient is smaller than the product of the coefficient of thermal expansion of the first material and the cooling gradient.

7. A method of permanent assembly according to claim 3, characterised in that it comprises the following steps: -making at least one relief on said second component so as to increase the mechanical adhesion between said first component (1) and said second component (2).

8. The permanent assembly method according to claim 7, characterized in that said at least one relief is formed by machining.

9. Assembly method according to claim 1, characterized in that said first material, chosen as a metal alloy capable of becoming at least partially amorphous, is subjected to a treatment that allows it to become completely amorphous.

10. The permanent assembly method according to claim 1, characterized in that said first material, chosen as a metal alloy capable of becoming at least partially amorphous, is subjected to a heat treatment allowing said first material to become at least partially crystalline after the assembly step.

11. A method of permanent assembly between at least a first component (1) formed of a first material and at least a second component (2) formed of a second material, in which permanent assembly the second component is intended to constrain the first component, characterised in that it comprises the following steps:

-taking a part formed of said first material;

-shaping the second part (2) and simultaneously assembling it onto the first part, at the latest at the moment of said shaping, the second material being subjected to a treatment which allows it to become at least partially amorphous, the second part and the first part being subjected to a thermal cycle as follows: first a temperature gradient to ensure expansion of at least the first part; followed by a cooling gradient to cause the second component to contract around the first component, thereby constraining the first component;

12. The permanent assembly method according to claim 11, characterized in that it comprises the following steps:

-defining the thermal cycle such that the temperature-increasing gradient increases the second material, selected as a metal alloy capable of becoming at least partially amorphous, above its melting temperature, causing the second material to at least partially lose any crystalline structure, and such that the temperature-decreasing gradient decreases the second material below its glass transition temperature, allowing the second material to become at least partially amorphous.

13. The permanent assembly method according to claim 11, wherein the molding step comprises the steps of:

-transforming the second material into a preform (4) and subjecting the second material to a treatment allowing the second material to become at least partially amorphous;

-defining the thermal cycle of the second material transformed into a preform so that the preform is subjected to a temperature between its glass transition temperature and its crystallization temperature;

-cooling the assembly to allow the second material to retain the at least partially amorphous character.

14. A permanent assembly method according to claim 11, characterized in that it comprises a step of depositing an intermediate layer (9) on the first component (1); the method further comprises a final step of dissolving the intermediate layer so as to increase the gap (12) between the first part and the second part if the product of the coefficient of thermal expansion of the second material and the cooling gradient is smaller than the product of the coefficient of thermal expansion of the first material and the cooling gradient.

15. A permanent assembly method according to claim 12, characterized in that it comprises a step of depositing an intermediate layer (9) on the first component (1); the method further comprises a final step of dissolving the intermediate layer so as to increase the gap (12) between the first part and the second part if the product of the coefficient of thermal expansion of the second material and the cooling gradient is smaller than the product of the coefficient of thermal expansion of the first material and the cooling gradient.

16. A permanent assembly method according to claim 13, characterized in that it comprises a step of depositing an intermediate layer (9) on the first component (1); the method further comprises a final step of dissolving the intermediate layer so as to increase the gap (12) between the first part and the second part if the product of the coefficient of thermal expansion of the second material and the cooling gradient is smaller than the product of the coefficient of thermal expansion of the first material and the cooling gradient.

17. The permanent assembly method according to claim 13, characterized in that it comprises the following steps: -making at least one relief on said first component so as to increase the mechanical adhesion between said first component and said second component.

18. The permanent assembly method according to claim 17, wherein the at least one relief is formed by machining.

19. Assembly method according to claim 11, characterized in that said second material, chosen as a metal alloy capable of becoming at least partially amorphous, is subjected to a treatment allowing said second material to become completely amorphous.

20. The permanent assembly method according to claim 11, characterized in that said second material, chosen as a metal alloy capable of becoming at least partially amorphous, is subjected to a heat treatment allowing said second material to become at least partially crystalline after the assembly step.