Patent Publication Number: US-6669794-B1

Title: Method for treating an object with a laser

Description:
FIELD OF THE INVENTION 
     The present invention concerns a treatment method for an object made of a material exhibiting martensitic transformation, in particular a shape memory material. 
     The invention applies to the manufacture of active or passive monolithic structures (i.e. one single piece of material), made of shape memory material, and in particular to the manufacture of monolithic actuators, connectors, active components for fixing and grippers, of very small dimensions, made of shape memory material. 
     DESCRIPTION OF THE PRIOR ART 
     The following two documents should be consulted as regards shape memory materials: 
     [1] Engineering Aspects of Shape Memory Alloys, T. W. Duerig et al., Ed. Butterworth-Heinemann, 1990 
     [2] Shape memory materials, Edited by K. Otsuka and C. M. Wayman, Cambridge University Press, 1998, chapter 10, pages 21 to 237 
     The following document which divulges particular applications of these materials should also be consulted: 
     [3] French Patent Application No. 9615013 of Dec. 6, 1996, “Dispositif de préhension en matériau à mémoire de forme et procédé de réalisation”, an invention by Y. Bellouard, J. E. Bidaux and T. Sidler—see also International Application No. PCT/EP97106966, International Publication No. WO 98/24594. 
     It will be recalled that shape memory materials have several solid phases in mestastable equilibrium. The change of phase from a solid phase to another may be induced under stress (super-elasticity) and/or by temperature change (shape memory effect). 
     When the change of phase is heat induced, it may be accompanied by a macroscopic shape change. Thus a shape memory material which is apparently plastically deformed in its low temperature phase, called the “martensite phase” can return to its initial shape by being heated to its high temperature phase, called the “austenite phase”. 
     The characteristic temperatures of the beginning and end of the austenite-martensite transformation are respectively designated M a  and M f . The characteristic temperatures of the beginning and end of the martensite-austenite transformation are respectively designated A s  and A f . 
     Particular care must be taken that there exists only one “memorised” shape in a shape memory material, namely the austenite shape: the phenomenon is thus not intrinsically reversible. 
     Obtaining an intrinsic reversible effect for such a material requires either the use of a very particular manufacturing method of the material (for example the method known by the name of “Melt Spinning”), or the use of a thermo-mechanical treatment commonly called the “education method” which will in a way “memorise” a preferred martensite shape. 
     Another known technique consists in exploiting the fact that the mechanical characteristic of the material evolves with the change of phase. Thus, a mechanical assembly including on the one hand an element made of such a material and on the other hand another element whose characteristic remains constant will have two stable operating points corresponding to the temperature and stress zones defining the solid phases of this shape memory material. 
     However, when one wishes to obtain an actuator of very small dimensions, it is very difficult to make such an assembly. This is why, a known technique consists in creating a single piece structure which is also called a monolithic structure: the actuator is then manufactured in a single same element made of a memory shape material. 
     In this regard, the following document should be consulted: 
     [4] Y. Bellouard et al., “A concept for monolithic SMA microdevices”, Journal de Physique IV, n o 11, p.603-608 (1997). 
     The difficulty is thus to be able to obtain a reversible effect and for such purpose to obtain different mechanical properties in this same element: In order to do this, it is necessary to heat the latter locally so that only a part thereof can have a shape memory effect while the other part remains passive. 
     However, in order for a displacement to occur, it is imperative to achieve mechanically an initial pre-deformation of the element (except if there is a two-way memory effect). 
     EP-A-0 086 357 A discloses a method for manufacturing a crank case wherein the surface layer material of the case is transformed from a ferritic state to a substantially martensitic state. 
     MESSER K ET AL: “STAND DES LASERSTRAHLHAERTENS” HAERTEREI TECHNISCHE MITTEILUNGEN, DE, CARL HANSER VERLAG, MUNCHEN, vol. 52, no. 2, Mar. 1, 1997 (1997-03-01), pages 74-82 discloses the laser beam hardening of iron based alloys. 
     MIGLIOREL L R: “HEAT TREATING WITH LASERS” ADVANCED MATERIAL&#39;S &amp; PROCESSES, US, AMERICA SOCIETY FOR METALS. METALS PARK, Ohio, vol. 154, no. 2, Aug. 1, 1998 (1998-08-01), pages H25-H29 discloses the treatment by laser of steels. 
     FR-A-2 393 075 discloses the annealing of a non ferrous metal part by means of a laser. 
     CHEMICAL ABSTRACTS, vol. 126, no. 24, Jun. 16, 1997 (1997-06-16) Columbus, Ohio, US; abstract no. 319898, VILLERMAUX, F. ET AL: “Corrosion kinetics of laser treated NiTi shape memory alloy biomaterials” &amp; MATER. RES. SOC. SYMP. PROC (1997), 459 (MATERIALS FOR SMART SYSTEMS II), 477-482, 1997 discloses the laser treatment of shape memory alloys. 
     WO-A-89 10421 discloses heat treatment of shape memory alloys. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to overcome the problem of local change (i.e. at least in a pre-defined zone) of the microstructure of an object made of a material exhibiting martensitic transformation, in particular a shape memory material. 
     “Local change of the microstructure” of such an object means: 
     the local crystallisation of the object when the material is amorphous 
     or the local recrystallisation of the object when the material is work-hardened 
     or the secondary local crystallisation of the object when the material is already crystallised (for example to induce locally a transformation temperature change) 
     or the controlled formation of precipitates or the annihilation of crystalline faults, locally, in the object (with a view to locally changing the mechanical properties of the latter). 
     More precisely, the present invention concerns a treatment method for an object made of a material able to undergo martensitic transformation, in particular a shape memory material this method being characterised in that at least a pre-defined zone of this object is irradiated by a laser beam able to heat this zone sufficiently, to a temperature lower than the melting temperature of the material, to cause, in said zone, a microstructure change selected from among a crystallisation, recrystallisation, secondary crystallisation controlled formation of precipitates and annihilation of crystalline faults, said zone being heated to a temperature and for a time which are not able to cause amorphisation of the material. 
     This laser beam is thus used to anneal the object locally by bringing the latter to a much higher temperature T than the temperature A f  of the shape memory material of which the object is made. 
     However, it should be noted that the temperature and the annealing time are such that amorphisation of the material cannot be obtained. 
     It should also be noted that the material could even have been annealed in a furnace prior to implementing the method of the invention. 
     Irradiating a zone of an element made of shape memory alloy by means of a laser beam is of course known, from European Patent document Nos. 0360455A and 031 0294A (Catheter Research Inc.). The use of a laser to modify and alter the crystalline structure so that the martensitic transformation can no longer occur is divulged therein. The notion of altering is important in the sense where, in the case of these documents, the laser is used to “destroy” and not to “construct” a crystal lattice. This means that the element is annealed beforehand then locally “amorphised” to prevent the migration of contaminating ions such as the silver ions in the NiTi matrix of the element. It is thus a method with an object contrary to the object of the method of the present invention. Indeed, the object of local annealing by laser is to crystallise or recrystallise locally a material exhibiting martensitic transformation (in particular a shape memory material) and not to amorphise it. Amorphisation by heating can be obtained when the rise in temperature is very high, i.e. close to the melting temperature, and cooling occurs extremely quickly. 
     The method of the present invention has numerous advantages: 
     This method can be implemented with an inexpensive device and allows annealing of structures made of shape memory material to be achieved simply, without using a furnace (the duration of the treatment according to the invention being much shorter than that of annealing effected by means of a furnace). Moreover, such a method can easily be implemented in a production line. 
     This method allows small pre-defined zones to be annealed in complex structures, in a very precise manner. 
     This method is compatible with great freedom of conception of the structures with which it is to be implemented (whereas local annealing by means of an electric current would require a well defined and dimensioned current path). 
     With this method, the rise in temperature occurs very quickly and cooling depends only on the size of the object to be annealed. This allows annealing qualities, which are difficult to obtain with a furnace, to be obtained. By way of example, hardening at the end of annealing is no longer necessary with the invention. 
     This method is very well suited to the production of micro-electro-mechanical systems or MEMS, may be integrated in a microsystem manufacturing method and allows quick production of the latter. 
     This method is the only one which allows reversible actuators, of very small dimensions, to be obtained without the use of stress obtained by mechanical pre-deformation effected by an operator. The invention allows this pre-deformation to be introduced during annealing. 
     The applications of the invention are numerous and are located in particular in the microtechniques (MEMS): it allows for example micro-switches to be manufactured for fibre optics, modulators, grippers, active fixations, axes of translation and axes of rotations, which are monolithic. 
     According to a first particular implementation mode of the method of the invention, said irradiation of the zone is also used to cause permanent deformation of this zone allowing the object to be stressed. In this case, the laser is thus used to pre-deform the object by annealing. 
     According to a second particular implementation mode, before and during, or after irradiation of the zone, the object is stressed by the deformation of said object. In this case, an initial mechanical pre-deformation of the object is thus made, unlike the preceding case. 
     The non-irradiated part of the object can be all in one piece or, conversely, this non-irradiated zone may include at least two zones which are separated by the irradiated zone. 
     According to a particular embodiment of the invention, the object is a thin element and zones of this elements, which are distributed over said element with a view to rigidifying the latter, are irradiated, by means of said laser beam. 
     In the present invention, the energy transmitted to the material by the laser can be varied as a function of the position of the laser beam on the object. 
     In order to do this, one can for example vary, as a function of this position, the power of the laser, the duration of the laser pulse, the sequence of successive shots, or vary the zone sweep speed by the laser beam. 
     The invention also concerns objects obtained via methods according to the invention. 
     According to a first particular embodiment of the invention, the object constitutes a plane monolithic device at least one part of which is able to undergo a reversible movement in the plane of the device, as a function of the temperature of the zone which has been crystallised or recrystallised by irradiation. 
     According to a first example, this device constitutes a gripper including a fixed part and a moving arm forming a return spring one end of which is connected to this fixed part by said zone, the moving arm being deformed by a user after crystallisation or recrystallisation of this zone by irradiation, to subject the gripper to stress. 
     According to a second example, this device constitutes an actuator including at least a fixed part and at least a moving part, this moving part being connected to the fixed part by a first element, which constitutes said zone and forms the motor element of the actuator, and by a second element which is able to exert a return force on the moving part. 
     According to a third example, this device constitutes an actuator including a first zone crystallised or recrystallised by irradiation by the laser beam, this first zone being used to put the actuator under stress, and a second zone crystallised or recrystallised by irradiation by the laser beam, this second zone forming the motor-element of the actuator and being distinct from the first zone. 
     According to a second particular embodiment of the invention, the object constitutes a monolithic device including a first plane part and a second part able to undergo a reversible movement outside the plane of the first part, as a function of the temperature of the zone which has been crystallised or recrystallised by irradiation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood upon reading the description of embodiment examples given hereinafter, purely by way of non-limiting indication, with reference to the annexed drawings, in which: 
     FIG. 1 is a schematic view of a device allowing the method of the invention to be implemented, 
     FIG. 2 is a schematic view of an object wherein the non annealed part is not in all in one piece, 
     FIG. 3 is a schematic view of an object wherein the non annealed part is all in one piece, 
     FIG. 4 is a schematic view of a strip rigidified by a method according to the invention, 
     FIG. 5 is a schematic view of a translation stage along an axis, the manufacture of which uses the method of the invention, 
     FIG. 6 is a schematic view of a gripper the manufacture of which uses the method of the invention, 
     FIG. 7 is a schematic view of an optical switch, the manufacture of which uses the method of the invention, 
     FIG. 8 is a schematic view of an actuator, the manufacture of which uses the method of the invention, 
     FIG. 9A is a schematic top view of another actuator, the manufacture of which uses annealing in accordance with the method of the invention while FIG. 9B is a profile view of this other actuator after annealing, 
     FIG. 10 is a schematic view of a translation table which is provided with guide elements, with articulations, and the manufacture of which uses the method of the invention, and 
     FIGS. 11 to  25  illustrate schematically other applications of the present invention. 
    
    
     DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS 
     FIG. 1 is a schematic view of a device allowing implementation of a method according to the invention. 
     According to this method, one or several zones such as zone A of an object  2  made of a material exhibiting martensitic transformation, for example a shape memory material, is irradiated, by a laser beam  4 . This beam  4  is able to bring zone A to a sufficient temperature T for crystallisation, recrystallisation, or secondary crystallisation of this zone, or the controlled formation of precipitates or annihilation of crystalline faults in this zone. Further, as has been seen, the heating time and temperature are such that amorphisation of the material does not occur. 
     Purely by way of non-limiting indication, the shape memory material of which object  2  is formed, is a NiTi alloy for which a temperature T of the order of 500° C. is suitable. 
     However, other shape memory materials, such as CuZnAl or NiTiCu can be used in the invention. 
     One may also use, in the invention, the materials described in document [1], chapter 1, pages 3 to 20, drafted by C. M. Wayman and entitled, “Introduction to martensite and shape memory”. 
     The device of FIG. 1 includes a laser  6 , for example a diode laser of the type marketed by the Siemens company under the reference S/N 150001B and the wavelength of which is equal to 810.5 nm. 
     Object  2  is mounted on a positioning system with three degrees of freedom which is symbolised by the axes X, Y and Z which are perpendicular to each other and which allows object  2  to be placed in laser beam  4  transmitted by diode  6 . 
     This laser beam is sent to zone A via, successively, a collimation lens  8 , a semi-transparent mirror  10 , a diaphragm  12  and a lens  14  for focusing the beam on the object. 
     As is seen in FIG. 1, a camera  16 , for example a CCD camera, is provided for observing irradiated zone A via, successively, lens  14 , diaphragm  12 , semi-transparent mirror  10  and an optical device  18 . 
     This camera allows the position of the object to be adjusted in laser beam  4 . 
     The electric current supply of the laser diode includes an arbitrary signal generator (not shown) allowing laser-pulses of a determined power and duration to be obtained. 
     The advantage of having one or several zones in the crystalline state and one or several zones in the amorphous or hardened state in the same shape memory material is that two or more different mechanical properties can be obtained (for example shape memory effect, super-elasticity, different transformation temperatures) in the same material. One can thus manufacture an actuator whose active part is the laser annealed zone, the non-annealed zones having another active role (movement at different temperatures) or passive role (for example as a guide or return spring) in the actuator. 
     FIG. 2 is a schematic view of a thin strip  20  made of a non-annealed shape memory material, for example an amorphous material. 
     A zone  22  of circular shape of this thin strip has undergone annealing by laser beam in accordance with the invention. 
     Zones  24  and  26  which have not undergone annealing can be seen in FIG.  2 . Zone  24  is surrounded by zone  22  and zone  26  surrounds zone  22 . 
     Owing to the shape of annealed zone  22 , these zones  24  and  26  are stressed, thus providing a reversible shape memory effect and the possibility of obtaining a reversible actuator. 
     In the example of FIG. 2, the zone which is not annealed by laser is not all in one piece: it is formed of zones  24  and  26  separated by zone  22 . 
     Conversely, in the example of FIG. 3, another thin strip  20  made of a shape memory material which is not locally annealed, for example an amorphous material, is seen, a substantially rectilinear zone  28  of which has undergone laser annealing in accordance with the invention, this zone  28  extending from one edge of strip  20  towards the centre of the latter. Consequently, zone  30  which is not subjected to laser annealing is all in one piece. 
     This zone  30  is again subjected to stress thus providing a reversible shape memory effect. 
     When the invention is implemented, it is possible to vary the annealing temperature by varying the power of the laser beam or, more generally, the energy transmitted to the object by the laser (by varying the intensity of the supply current of diode  6  in the example of FIG. 1) during annealing, as a function of the position of the laser spot on the object to be treated. 
     It is known that transformation temperatures evolve with the annealing parameters (time, temperature). 
     One may for example sweep the zone to be annealed for the purpose of varying locally the characteristic temperatures of the shape memory material from which the object is made, i.e. the parameters M s , M f , A s  and A f  of this material. 
     This has the advantage of extending the martensite-austenite transition zone of the material. 
     It should be noted that the shape memory material annealed in accordance with the invention can become super-elastic in the annealed zone. 
     The method of the invention can thus also be used when one wishes to make a shape memory material super-elastic locally. 
     FIG. 4 illustrates schematically an other application of the invention to the stiffening of a thin strip  20  made of shape memory material. 
     Points  32  of strip  20  are annealed by laser, these points being distributed in a substantially uniform manner on the surface of the strip. 
     Stresses are thus created locally in strip  20  around laser impact points  32 . This allows the strip to be rigidified, in particular when loaded in bending. 
     FIGS. 5,  6 ,  7 ,  8  and  9 A,  9 B illustrate schematically various devices which are capable of having very small dimensions and the manufacture of which uses a method according to the invention. 
     Purely by way of non-limiting indication, these devices can be made with dimensions of less than 500 μm and thicknesses of the order of 1 μm to 200 μm so that they can be considered micro-devices. 
     In the case of each of FIGS. 5 and 6, an operator has to deform the device so as to stress the latter after having annealed a part of this device in accordance with the invention. 
     However, in the case of FIG. 5, deformation by an operator can also occur before (and during) annealing. 
     In such case, the device is first fixed onto a support via its pads; the central mobile part is moved by the operator then held stressed and the springs compressed by this stress are annealed. Then the device returns to a position of equilibrium. 
     In the case of deformation effected after annealing (case of the example considered hereinbelow), the device is free, a part (the two springs on the left of FIG. 5) is annealed; then the device is stressed and secured. 
     Conversely, in the case of each of the devices of FIGS. 7,  8  and  9 A,  9 B, the permanent deformation, induced by annealing, of the zone which undergoes annealing, can be exploited; the annealing thus allows the device to be stressed. 
     It is to be specified that deformation of the object always occurs during laser annealing. This deformation is small with respect to the deformation which an operator can induce. 
     This deformation will thus be exploited a priori in devices which amplify it (case of the examples of FIGS. 7 and 9A,  9 B) or in the case of very small movements (example of FIG.  8 ). 
     This deformation may be a permanent contraction or expansion, depending upon the parameters of the laser pulse. 
     Moreover, in the case of each of FIGS. 5 to  8 , there is a plane monolithic device a part of which is able to undergo a reversible movement in the plane of the device. 
     Conversely, the device of FIGS. 9A and 9B is a monolithic device including a first part which is plane and a second part which is able to undergo a reversible movement outside the plane of the first part. 
     Furthermore, in the case of each of the devices of FIGS. 7 and 9A,  9 B, the element used for pre-stressing the device is also the active element of the device, while, in the case of the device of FIG. 8, the element used for pre-stressing the device is different from the active element of the device. 
     The device of FIG. 5 is a translation stage along an axis X. 
     This device is cut out by laser from a thin strip made of shape memory alloy. 
     It can be seen that this device includes a central mobile part  34 , two springs  36  secured, on one side, to the latter and, on the other side, to two pads  38 , two other springs  40  secured, on one side, to the mobile part and, on the other side, to two other pads  42 . 
     The two springs  36 , located on the left of the Figure, are heated to their annealing temperature by a laser beam in accordance with the invention. 
     The two springs  40 , located on the right of the Figure, remain substantially at ambient temperature (approximately 20° C.). 
     After cooling the entire device to ambient temperature, the four springs are pre-stressed along axis X (axis of translation) and the device is secured via the four pads on a plane substrate  44 . 
     The operating principle of this device is as follows: springs  36  are heated above the transformation temperature Ax which is of the order of 60° C. for an NiTi or NiTiCu alloy. 
     The heating can be achieved for example by an electric current which is made to flow in the two springs. 
     The latter transform into austenite, thus return to their initial shape and pull the mobile part towards the left. 
     During cooling, these two springs  36  return to their martensitic state and the mobile part is pulled towards the right because of the elasticity of springs  40  which have not been annealed and which form return springs for the device. 
     Another possible operating mode (deformation before—and during—annealing) was explained above. 
     The device of which FIG. 6 is a schematic top view, is a micro-gripper which is cut by laser from a thin strip of shape memory material. 
     This device includes a fixed part  46 , including two securing zones  48 , and an actuating part  50  intended to form a return spring. 
     One end of this actuating part is connected to fixed part  46  via a semi-circular part  52 , intended to be laser annealed in accordance with the invention. 
     The other end  54  of the actuating part and a zone  56  of the fixed part, which is located facing this other end  54 , constitute the jaws of the device. 
     For the local annealing of zone  52  a laser beam is projected onto the latter. 
     After returning to ambient temperature, the arm of the gripper (i.e. part  50  thereof) is then deformed outside its elastic domain in order to define the open position of the gripper. 
     This device thus remains open and has a certain elasticity. 
     If one wishes to pick up an object with the gripper, the whole of the device is heated for example by means of a Peltier element. The gripper closes because of the force generated by the phase transformation in the annealed part. 
     During cooling, when the actuating part has returned to the martensite state, the return spring is able to pull the arm in its open position. 
     The device of FIG. 7 is an optical switch which is cut, for example by laser, from a thin strip of amorphous shape memory material. 
     It includes an arm  58  intended to move so that one of its two ends can interrupt or, conversely, allow a light beam from a fibre optic  60  to pass. 
     In the other end of this arm there is a virtual rotational centre  62 . 
     One can also see a fixed part  64  of the device, in the shape of a C, which is connected to a side of the end of arm  58  where the virtual rotational centre is located via an element  66  forming a spring and to the other side of this end via another element  68  intended to be annealed by laser in accordance with the invention. 
     Two substantially rectilinear guide elements  70  can also be seen, also connecting fixed part  64  to this end of the arm where the virtual rotational centre is located such that virtual extensions of these two elements  70  intersect at the virtual rotational centre. 
     It is to be specified that the element forming a spring  66  and element  68  intended to be annealed by laser are located on either side of a line L which passes through the virtual rotational centre and which is substantially perpendicular to arm  58 . 
     Let us suppose that element  68  becomes elongated during annealing. 
     The austenitic shape of this element  68  is thus an elongated shape. 
     At ambient temperature, since element  68  is in its martensitic state, spring  66  tends to compress element  68 . Arm  58  returns (approximately) to its initial position. 
     When it is heated, element  68  passes into the austenitic phase, becomes elongated and causes arm  58  to rotate in the anti-clockwise direction (upwards in the example of FIG.  7 ). 
     The shape of elements  66  and  68  may be adapted depending upon the desired characteristics. 
     It is to be specified that the two elements  70  are facultative guide means. 
     The device of FIG. 8 is formed from a thin strip of shape memory material. 
     It is an actuator including a fixed part  72  having substantially the shape of a rectangular frame two sides  74  of which are not annealed by laser while the other two sides  76  are annealed by laser in accordance with the invention. 
     Moreover, this device includes a mobile part  78  comprised between the two sides  76  and this mobile part is connected to the two non-annealed sides  74  respectively by an element  80  which is also annealed by laser in accordance with the invention and by another element  82  which is not annealed forming a return spring. 
     The moving part is intended to move in translation substantially parallel to the two annealed sides  76 . 
     When it is annealed, element  80  expands very little. 
     When the two sides  76  are annealed (by a laser beam to anneal these sides in the same conditions), these two sides expand more than element  80  and subject the device to traction stress. 
     If this element  80  is heated (without of course annealing it again), it contracts and pulls mobile part  78 . 
     When the device returns to ambient temperature, the element forming a spring  82  pulls the moving part  78 . 
     The device shown in top view in FIG. 9 a  is cut from a thin strip of amorphous shape memory material. 
     This device includes an arm  84  one end of which is extended by two bars  86  respectively secured to two pads  88 . 
     A bar  90  is comprised between these two bars  86  and one of its ends is also secured to this end of arm  84 . 
     The other end of bar  80  is secured to a pad  92 . 
     The device thereby obtained is secured to a plane support (not shown) via pads  88  and  92 . 
     Central bar  90  is then annealed by laser in accordance with the invention. 
     Deformation, which may be a contraction or expansion depending on the parameters of the laser pulse, as was seen above, and which is induced during annealing, causes arm  84  to be displaced out of the plane of the support as shown in FIG. 9B which is a schematic profile view of the device after laser annealing. 
     It can be seen in FIG. 9B that the device is secured to its support  94  such that arm  84  is located outside this support. 
     In the example of FIG. 9B is has been assumed that the laser annealed arm has become elongated. 
     The non-annealed bars  86  form return springs which were stressed during annealing. 
     If the whole device or only the annealed bar is heated (for example by a Peltier element or by Joule effect or by a very low power laser beam) so as to obtain the martensitic transformation of annealed bar  90 , the latter is deformed, which causes the whole of arm  84  to move. 
     The device of FIGS. 9A and 9B can be used as an optical switch or more generally as an actuator. 
     By combining two or three devices of this kind a gripper may even be formed, the two or three mobile arms of the latter then being used to grip an object. 
     The present invention has other applications: 
     The object treated in accordance with the invention may be a monolithic structure including particular zones, for example, articulations, and the particular zones are then irradiated by the laser beam to make them super-elastic. 
     In another example, the object is a single piece system which is made multi-functional by irradiating, by means of the laser beam, various zones of this system, and transmitting, to such zones, by means of the laser, different energies, the zones being intended for example to form different actuators acting at different temperatures. 
     In yet another example, the object is a monolithic structure including zones which are irradiated by the laser beam at different energies to obtain a shape memory effect in certain zones, for example in order to form actuators therefrom, and to make the other zones super-elastic, for example in order to form guide articulations with these other zones. 
     This is schematically illustrated in FIG.  10 . 
     The single piece system made of shape memory material shown in FIG. 10 includes a translation device  96  which can be compared to the device of FIG.  5  and which includes a mobile table  98  connected to two securing pads  100  via two springs  102 . 
     The pads are intended to be secured to a support (not shown). 
     The system further includes an other device  104  intended to be secured to the support by its two ends  106 . 
     This other device  104  includes a mobile stabilising bar  108  and elements  110  intended to form articulations. 
     As is seen in FIG. 10, bar  108  is secured to fixed ends  106  via certain of elements  110  and mobile table  98  via other elements  110 . 
     Elements  110  are annealed by a laser beam in accordance with the invention so that they form super-elastic flexible elements. 
     One of the two springs  102  is also annealed by a laser beam in accordance with the invention, for example the left spring, so that it has a shape memory effect. 
     The other spring, which is not annealed by the laser beam, constitutes a return spring. 
     Purely by way of non-limiting example, shape memory materials which can be used in the invention are as follows: 
     AgCd, AuCd, CuZn, CuZnX (where X=Si, Sn, Al or Ga), CuAlNi, CuSn, 
     CuAuZn, NiAl, TiNi, TiNiX (where X=HF, Cu, Nb, Pd, Co), TiPdNi, InTl, InCd and MnCd. 
     The present invention also applies to objects made of “magnetic” shape memory material. These are materials whose martensite transformation is able to be induced by a magnetic field. This is for example the case of Ni 2 MnGa alloys. With regard to such materials the following may for example be consulted: 
     R. D. James, M. Wuttig, “Magnetostriction of Martensite”, Philosophical Magazine A, 1988, vol. 77, n o 5, p.1273 to 1299. 
     More generally, the present invention applies to all materials exhibiting martensite transformation. 
     The invention may apply to any type of material shaping. Thus, it applies in particular to wires, strips, tubes, springs, rectangular bars of shape memory alloys. 
     FIGS. 11 to  25  illustrate schematically various particular applications of the invention. 
     FIG. 11 is a top view of a schematic, partial cross-section of a wristband, for example a watch wristband, including links in series such as links  112 ,  113  and  114 . This watch wristband further includes clips  115  and  116 , each clip being intended to secure two adjacent links to each other. For example clip  115  is intended to secure links  112  and  113  to each other and clip  116  is intended to secure links  113  and  114  to each other. Each clip, which is located inside one of the links, is made of a shape memory material and includes, in the example shown, a circular peripheral part  117   a  provided with two diametrically opposite stubs  117   b  which are intended to secure the two corresponding links, and a central zig-zag shape zone  117   c  which extends substantially along the diameter corresponding to the stubs. Peripheral part  117   a  is provided with two diametrically opposite extensions  117   d , at 90° with to stubs  117   b . As is seen in FIG. 11, these extensions are provided with elongated holes through which pass respectively two pins  117   e  allowing the clip concerned to be secured to one of the two corresponding links and also assuring guiding of the clip. Each central zone is annealed in accordance with the invention. 
     The design of the wristband allows one or several links to be easily removed or added. To remove a link, one need only remove two adjacent clips, which allows the corresponding link to be removed; the continuity of the wristband is then re-established by means of one of the two clips. To add a link, a clip associated with an already present link is removed, the additional link is added, the clip is replaced to secure the additional link to the link already present and the continuity of the wristband is re-established by means of an additional link. 
     To add or remove a clip, the clip is heated or the corresponding link is heated locally. The annealed zone  117   c  of the clip is then used as an actuator to deform the elastic structure formed by the non-annealed zone, i.e. the remainder  117   a ,  117   b ,  117   d  of the clip. By deforming, this elastic structure may be inserted in a link (see clip  116  of FIG. 11) or removed therefrom. 
     FIG. 12 is an example of a fixing device made of shape memory material with local annealing, obtained by bending a sheet metal of uniform thickness. Local annealing by a method according to the invention may be used to make only the part forming a spring active or super-elastic. Thus, in FIG. 12, the non-annealed zones will be more rigid than the annealed zone, which assures proper gripping. This fixing device may be used for example to fix a stack of small elements  123  such as for example piezoresistive ceramics. 
     In this FIG. 12, the stack has the reference  124 , the fixing device has the reference  126 , the non-annealed zones of the fixing device have the reference  127  and the annealed zone has the reference  128 . The immobilisation of the stack by the fixing device is thermally induced. 
     Moreover, the super-elastic properties in the case of a shape memory material can also be advantageously used to have a force which is quasi-independent of the tolerances of the elements of the stack. 
     FIG. 13 shows a catch spring currently used in horology. The elasticity is provided by the zone annealed locally by a method according to the invention. Owing to the properties of super-elasticity (force saturation effect), a catch spring may be obtained with a holding force which is independent of the tolerances of the object to be held. 
     In FIG. 13 the reference  130  represents a part such as for example a watch crown which is mobile in translation along arrow  132 , the catch spring, made of shape memory material, has the reference  134 , the annealed zone of this spring (central zone) has the reference  136 , the non-annealed zones of the spring (end zones) have the reference  138 . In the case of FIG. 13 the super-elasticity of zone  136  is thermally induced. The support  139  to which one of the two zones  138  is fixed, the other zone  138  being intended to abut the crown  130  will be noted in FIG.  13 . 
     FIG. 14 shows the curve of variations in force F exerted by spring  134  on crown  130  as a function of the displacement δ of such spring. This curve shows the mechanical behaviour of annealed zone  136 . It can be seen that F varies little over a wide range Δ of displacements δ. 
     FIG. 15 shows a wire  140  made of shape memory material only an end part  142  of which is annealed by a method according to the invention. This wire may be used as a guide wire in mini-invasive surgery to guide a catheter. Only the end is super-elastic, which enables the curves of the arteries and veins of the human body to be followed without damaging tissue. Rigid part  144  assures good rigidity in torsion, thus avoiding the “whiplash” effect. 
     The super-elasticity of part  142  is mechanically induced. 
     Initially, wire  140  is located in a catheter  146 . End  142  is then pushed out of the catheter (towards the right in FIG. 15) and this end bends because of its super-elasticity. 
     FIG. 16 shows an example of a biopsy clamp  148  which can be used in min-invasive surgery to take tissue samples from the human body. This clamp made of shape memory material forms a lasso of which only the loop  150  is annealed by a method according to the invention. This loop  150  may be closed for example by a weld  152 . The non-annealed part  154 , which is more rigid, allows good torsion and flexion rigidity. 
     The super-elasticity of loop  150  is mechanically induced: initially the clamp is in a catheter  156 . The end corresponding to the loop is pushed out of the catheter (towards the right in FIG. 15) and this end takes the form of the loop because of its super-elasticity. 
     FIG. 17 shows an example of an endocalibrator or stent  158  made of shape memory material. In the case of endocalibrators or stents, local annealing by a method according to the invention allows more or less rigid zones to be created independently of the type of meshing. Thus, the non-annealed zones will not have the same expansion at the catheter outlet as the annealed zones. For example, a cone-shaped stent may be made by progressive annealing on the stent meshing. In FIG. 17, the end  160  of the stent is non-annealed. The rest of the stent is progressively annealed, i.e. the annealing temperature is varied to obtain a variable super-elastic transformation start stress, to the other end  162 . In the case of FIG. 17, the super-elasticity is mechanically induced; initially stent  158  is in a catheter (not shown). The stent is then pushed out of the catheter and the stent takes its cone shape as seen in FIG.  17 . 
     FIGS. 18 to  21  show other examples of stents made of shape memory material, obeying the same principle as that of FIG.  17 . In the case of FIG. 18, there is a stent  164  capable of taking an elongated shape with two diameters. Other spatial geometries are possible for a stent: in the case of FIG. 19 stent  166  takes a shape with two ends of greater diameter than the rest of the stent. In the case of FIG. 20, stent  168  takes a flared shape. In the case of FIG. 21, stent  170  takes a shape which bulges at the centre. 
     FIG. 22 is a schematic view of a damping system made of shape memory material and including two parts  172  and  174  connected by two zig-zag shaped and substantially parallel elements  176  and  178 . Element  176  is not annealed while element  178  is annealed by a method according to the invention. It is known that shape memory alloys have the property of having a very high dampening rate in martensite (this being due to internal friction in the material). With local annealing, a spring with an integrated damping device can be made. Thus non-annealed element  176  behaves like a normal spring while annealed element  178  is able of acting as a damping device 
     FIG. 23 is a schematic view of an unfolded monolithic watch wristband  180  made of shape memory material. Only the ends parts  182  and  184  of the wristband, which have to be secured to the watch case (not shown) are not annealed. The central part  186  of the wristband, which is comprised between parts  182  and  184  is thus annealed by a method according to the invention and the annealing may be progressive depending upon the desired level of rigidity. Various decorative elements (not shown), for example ceramic plates, may be added to the structure thereby obtained. Such a wristband may be made to measure. 
     FIG. 24 is a schematic partial view of a stent  188  made of shape memory material. The whole of the stent meshing is annealed by a method according to the invention, except a limited number N of meshes with &lt;N&lt;10 (zone referenced  190  in FIG.  24 ). 
     FIG. 25 illustrates schematically an application of the stent of FIG.  24 . This stent  188  is placed in an artery  192 . Another artery  194  which communicates with artery  192  but is blocked by the meshing of stent  188  can also be seen. In order to overcome this drawback, the non-annealed meshes are plastically deformed using a surgical balloon  196  brought into contact with these meshes by passing through artery  194  and of the type of those used to unfold steel stents. These deformed meshes allow blood circulation to be re-established in artery  194 . 
     Owing to a guide-wire inserted beforehand in artery  192  and bifurcating in artery  194 , the balloon can also be introduced via artery  192  by passing through the interior of the stent itself and then bifurcating at artery  194 .