DE102004020058B4 - A method of depositing a layer of a shape memory alloy - Google Patents

Abstract

A method for depositing a layer (15) of a shape memory alloy on a substrate (14), wherein the composition of the shape memory alloy is selected so that a one-way effect, two-way effect or superelastic behavior is obtained, as substrate (14) a technical single crystal with austenitic or martensitic Crystal structure is used, and the deposition conditions are chosen so that the layer (15) epitaxially grow on the substrate.

Description

The The invention relates to a method for depositing a layer a shape memory alloy on a substrate, where the shape memory behavior of the layer while of the deposition is generated.

Such methods are for example from US 6,358,380 B1 and from the US 5,061,914 known. According to these references, the layer of the shape memory alloy is deposited on a substrate by a PVD method, wherein the PVD method is carried out at a temperature at which crystallization of the microstructure in the form of the high temperature phase of the shape memory alloy to be deposited is possible during the deposition. In this way, an annealing step separate from the production of the layer for effecting the crystallization can be saved while forming the high-temperature phase in the microstructure. As a shape memory alloy, for example, NiTi can be deposited. The alloy composition of the deposited layer can be influenced by the composition of the target used in the PVD process.

According to the DE 101 32 125 A1 It is furthermore known that textured metal layers can be deposited by epitaxial growth on a textured substrate by means of electrodeposition. These deposited layers can continue to serve as a substrate for the deposition of high-temperature superconductors and must be matched in their texture to the texture required for the high-temperature superconductor. For the electrode position, a bath with AgPd, AgSn, Al, Au. AuNi, AuCo, Bi, Cr, Cu, CuSn, CuZn, Fe, In, Mn, Ni, NiP, NiFe, NiW, NiCo, Pb, PbSn, Pd, PdNi, PdCo, Pt, Rh, Sn, SnNi.

In the US 6,043,451 describes a process for coating substrates with nitinol, in which under certain conditions, the coating may have superelastic properties. Such coatings are primarily applied to substrates which are exposed to corrosive environmental conditions, such. As vehicles, ships, pumps, sensors or aircraft.

task The invention is a method for depositing a shape memory alloy indicate during which the deposition of the shape memory behavior without limiting the variability of the process limiting parameters, such as the process temperature, must be noted.

These Task is inventively characterized solved, that a technical single crystal is used as substrate, the a one of the phase states the shape memory alloy corresponding crystal structure, wherein the deposition conditions be adjusted so that the layer epitaxially on the substrate grows up. In the epitaxial growth of the layer so the crystal structure transfer of the substrate to the layer, thereby automatically adopting one of the phase states of the shape memory alloy becomes. This usually shows a low-temperature phase, also referred to as martensite, or a referred to as austenite high-temperature phase on. As the shape memory effect of shape memory alloys based just on the phase transformation between these two phases, is made by making one of the phases through the epitaxial The shape memory behavior of the layer grows up automatically generated.

The The crystal structure of the layer thus becomes during the epitaxial growth enforced. Therefore, no heat treatment of the layer is advantageous or while the generation necessary. A strong heating of the layer (with NiTi over 400 ° C) can therefore omitted, so that, for example, the layer also on temperature-sensitive Substrates can be generated.

According to one Embodiment of the invention, it is provided that the layer through a PVD process is deposited. This can be beneficial to a proven Technology used be, especially for very small quantities a cost-effective production the layer allows.

A Another embodiment of the invention provides that the layer is galvanic is deposited. This can be especially for large quantities economical Layers of the shape memory alloy produce.

Especially advantageous in the electrodeposition is that the alloy composition the layer by variations of the electrical Abscheidepotentials can be adjusted. Unlike the PVD method so must for different Alloy compositions of the layer no targets with different Compositions are kept. Rather, the layer composition can be by simple variations of the electrical parameters of the galvanic Set deposition process. The deposition potential can during the galvanic deposition, for example, by adjusting the Abscheidestromdichte can be varied when the current density-potential curve associated with the deposition process is known.

The exact alloy composition the deposited layer is of particular importance, as it depends on the transition temperature between the phases of the shape memory alloy and thus the temperature dependence of the shape memory effect. This is independent of whether the one-layer effect, the two-way effect or the superelastic behavior of shape memory alloys should be used with the deposited layer.

According to one special embodiment of the method is provided that the Separation process is carried out at a temperature at which the shape memory alloy is present in the phase state to be deposited. When in deposition has a temperature at which the phase state, which is predetermined by the epitaxial growth, anyway in the shape memory alloy would make out Thus, the forming layer can advantageously particularly low stress grow up, causing the layer a low density of structural defects having. This has a positive effect on the formation of the shape memory effect and on the long-term behavior of the layer.

According to a variant of the invention, the layer is detached from the substrate after its production. As a result, the substrate, which is expensive to produce as a technical monocrystal, can advantageously be used repeatedly for the production of layers. The layer as such can advantageously be further processed as semifinished product. Alternatively, the layer may also remain on the substrate, the composite formed in this way being used as a functional unit (cf. US 5,061,914 ).

Becomes the layer is detached from the substrate, so it is advantageous if the detachment process at a temperature carried out is where the shape memory alloy is present in that phase state, which differs from the crystal structure of the substrate is different. As a result, that is achieved by that the phase transformation in the layer tensions in the interface between the layer and the substrate are generated there weakening the Bindings in the crystal lattice, whereby the replacement of the Layer is advantageously facilitated.

Further Details of the invention are described below with reference to the drawing described. Show here

1 an embodiment of a galvanic bath for producing the layer according to the invention and

2 and 3 schematic representations of the crystal lattice of an embodiment of the layer on the substrate.

According to 1 is in a container 11 a galvanic bath 12 provided in which a roller 13 about half dips. The roller 13 is provided at its periphery with a martensitic or austenitic, designed as a technical single crystal steel strip, which is a substrate 14 for the deposition of a layer 15 formed of a shape memory alloy.

By applying a potential U to the roller designed as a working electrode 13 and a counter electrode 16 The layer is on the rotating in the direction of arrow roller 13 deposited and grows in thickness until it is the galvanic bath 12 leaves. The galvanic bath 12 can by means of a heater 17 For example, be heated so that the temperature of the galvanic bath in the high-temperature phase of the shape memory alloy is on the substrate 14 should be deposited. Once the shift 15 the galvanic bath 12 leaves, cools them, causing their crystal lattice is transferred to the low-temperature phase, so that stresses between the substrate 14 and the layer 15 arise. These support a detachment of the layer on a guide roller 18 , from where the layer can be wound as a band on a supply roll, not shown.

through Many of the galvanic process can be used the known shape memory alloy be deposited. Particularly suitable for electrochemical deposition are the alloy systems AgCd, AuCd, CuSn, CuZn and MnCu.

In 2 is the mechanism of epitaxial growth of the layer 15 on the substrate 14 shown schematically. The substrate has an austenitic structure and may consist of, for example, an austenitic steel Fe. On the substrate 14 copper atoms Cu and tin atoms Sn are deposited, the layer 15 growing up epitaxially. In this case, the crystal structure of the substrate 14 accepted. The epitaxial deposition of the layer 15 takes place at a temperature at which the shape memory alloy CuSn has an austenitic crystal structure.

After deposition of the layer 15 can by cooling the same according to 3 a phase transformation of the layer 15 into a martensitic crystal structure (martensitic phase transformation). Since the substrate retains its austenitic crystal structure, the different lattice structures of martensite and austenite create in a parting plane 19 between substrate 14 and layer 15 Tensions due to forced distortion of adjacent grids. This will cause the layer to peel off 15 from the substrate 14 facilitated.

Claims (6)

Method for depositing a layer ( 15 ) of a shape memory alloy on a substrate ( 14 ), wherein the composition of the shape memory alloy is selected such that a one-way effect, two-way effect or superelastic behavior is obtained, as substrate ( 14 ) a technical single crystal with austenitic or martensitic crystal structure is used, and the deposition conditions are chosen so that the layer ( 15 ) grows epitaxially on the substrate. Method according to claim 1, characterized in that the layer ( 15 ) is deposited by a PVD method. Method according to claim 1, characterized in that the layer ( 15 ) is electrodeposited. A method according to claim 3, characterized in that the alloy composition of the layer ( 15 ) is adjusted by varying the electrical deposition potential. Method according to one of the preceding claims, characterized in that the layer ( 15 ) after their preparation from the substrate ( 14 ) is replaced. Method according to claim 5, characterized in that the detachment process performed at a temperature is where the shape memory alloy is present in that phase state, which differs from the crystal structure of the substrate is different.