U.S. patent application number 13/643485 was filed with the patent office on 2013-03-14 for method for producing a monocrystalline body from a magnetic shape memory alloy.
This patent application is currently assigned to ETO MAGNETIC GMBH. The applicant listed for this patent is Anne Drevermann, Markus Laufenberg, Emmanouel Pagounis, Laszlo Sturz. Invention is credited to Anne Drevermann, Markus Laufenberg, Emmanouel Pagounis, Laszlo Sturz.
Application Number | 20130062032 13/643485 |
Document ID | / |
Family ID | 44546013 |
Filed Date | 2013-03-14 |
United States Patent
Application |
20130062032 |
Kind Code |
A1 |
Laufenberg; Markus ; et
al. |
March 14, 2013 |
METHOD FOR PRODUCING A MONOCRYSTALLINE BODY FROM A MAGNETIC SHAPE
MEMORY ALLOY
Abstract
A method for producing an MSM actuator element, having a crystal
orientation along a first crystal axis, from a monocrystalline MSM
body by introducing a molten alloying material into a molding shell
and subsequently solidifying the alloying material, comprising the
following steps: providing a molding shell which comprises a
nucleation region (24), a selector region (26) and a crystal region
(28) and is oriented along a longitudinal axis (22) at least in
some sections, introducing the molten MSM alloying material, in
particular NiMnGa-based alloying material, into the molding shell
without providing a separate nucleation crystal, compacting the MSM
alloying material by generating a solidification front moving from
the nucleation region across the selector region into the crystal
region along a solidification path.
Inventors: |
Laufenberg; Markus;
(Radolfzell, DE) ; Pagounis; Emmanouel;
(Radolfzell, DE) ; Drevermann; Anne; (Aachen,
DE) ; Sturz; Laszlo; (BG Vaals, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Laufenberg; Markus
Pagounis; Emmanouel
Drevermann; Anne
Sturz; Laszlo |
Radolfzell
Radolfzell
Aachen
BG Vaals |
|
DE
DE
DE
NL |
|
|
Assignee: |
ETO MAGNETIC GMBH
Stockach
DE
|
Family ID: |
44546013 |
Appl. No.: |
13/643485 |
Filed: |
May 26, 2011 |
PCT Filed: |
May 26, 2011 |
PCT NO: |
PCT/EP2011/058695 |
371 Date: |
October 25, 2012 |
Current U.S.
Class: |
164/69.1 |
Current CPC
Class: |
C30B 29/52 20130101;
C30B 11/00 20130101; B22D 23/00 20130101; H01L 41/47 20130101; H01L
41/20 20130101; C30B 11/14 20130101; H01F 1/0308 20130101 |
Class at
Publication: |
164/69.1 |
International
Class: |
B22D 23/00 20060101
B22D023/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 28, 2010 |
DE |
10 2010 021 856.1 |
Claims
1-12. (canceled)
13. A method for producing an MSM actuator element, having a
determined crystal orientation along a first crystal axis, from a
monocrystal MSM body by introducing a molten alloying material into
a molding shell and subsequent solidification of the alloying
material, comprising the steps of: (a) providing a molding shell
which comprises a nucleation region, a selector region and a
crystal region having a first crystal axis oriented in the
direction of a longitudinal axis at least in some sections; (b)
introducing a molten MSM alloying material into the molding shell
without providing a separate nucleation crystal; (c) compacting the
MSM alloying material by generating a solidification front moving
from the nucleation region across the selector region into the
crystal region along a solidification path, wherein the
solidification path in the crystal region runs along the
longitudinal axis, forms a region which is deflected from the
longitudinal axis in the selector region, the maximum deflection of
which, relative to the longitudinal axis, is greater than a maximum
cross-sectional width in the selector region, wherein the
longitudinal axis has an angular deviation of less than 10.degree.
from the first crystal axis; and (d) dividing the solidified MSM
alloying material into a plurality of MSM actuator elements by cuts
perpendicularly to the longitudinal axis.
14. The method according to claim 13, wherein the solidification
path in the selector region forms a region which is deflected in a
spike-like manner with two angled sections, the entry and exit side
of which is aligned in alignment to the longitudinal axis.
15. The method according to claim 13, wherein the solidification
path in the selector region forms a helix-shaped or zigzag-shaped
region.
16. The method according to claim 13, wherein the longitudinal axis
is aligned vertically to a flat cooling device associated with the
nucleation region.
17. The method according to claim 13, wherein the crystal region
extending in an elongated manner along the longitudinal axis has an
effective cross-sectional area for the solidification front of
>3 cm.sup.2.
18. The method according to claim 13, wherein the crystal region
extending in an elongated manner along the longitudinal axis has an
effective cross-sectional area for the solidification front of
>7 cm.sup.2.
19. The method according to claim 13, wherein the crystal region
extending in an elongated manner along the longitudinal axis has an
effective cross-sectional area for the solidification front of
>12 cm.sup.2.
20. The method according to claim 13, wherein the MSM alloying
material for producing the solidification front is cooled so that a
temperature gradient in the melt, occurring in the selector region,
adjacent to the solidification front, is between 0.3 K/mm and 20
K/mm.
21. The method according to claim 13, wherein the MSM alloying
material for producing the solidification front is cooled so that a
temperature gradient in the melt, occurring in the selector region,
adjacent to the solidification front, is between 1 K/mm and 15
K/mm.
22. The method according to claim 13, wherein the MSM alloying
material for producing the solidification front is treated by
bringing about a relative speed between the molding shell and the
temperature gradient, so that the solidification front in the
selector region moves at a speed of between 0.1 mm/min and 50
mm/min along the solidification path.
23. The method according to claim 13, wherein the MSM alloying
material for producing the solidification front is treated by
bringing about a relative speed between the molding shell and the
temperature gradient, so that the solidification front in the
selector region moves at a speed of between 0.3 mm/min and 5 mm/min
along the solidification path.
24. The method according to claim 13, wherein the solidification
front moves along the solidification path through an at least
partially cross-sectionally rectangular crystal region.
25. The method according to claim 24, wherein a cross-sectionally
rectangular inner contour of the crystal region determines a
crystal orientation of the MSM alloying material, which is
solidified in a monocrystalline manner, in at least a second
crystal axis orthogonal to the first crystal axis.
26. The method according to claim 13, wherein the alloying material
has Ni, Mn, Ga and at least Co in the composition
Ni.sub.aMn.sub.bGa.sub.cCo.sub.dFe.sub.eCu.sub.f, wherein a, b, c,
d, e and f are indicated in atom-% and fulfill the conditions
44.ltoreq.a.ltoreq.51; 19.ltoreq.b.ltoreq.30;
18.ltoreq.c.ltoreq.24; 0.1.ltoreq.d.ltoreq.15;
0.ltoreq.e.ltoreq.14.9; 0.ltoreq.f.ltoreq.14.9; d+e+f.ltoreq.15;
a+b+c+d+e+f=100.
27. The method according to claim 13, wherein the compacting of the
MSM alloying material takes place along a plurality of
solidification paths which are adjacent to one another and
separated from one another.
28. The method according to claim 13, including dividing of the MSM
alloying material, which is solidified in the crystal region, into
the plurality of MSM actuator elements without previous
metrological determining of a crystal orientation in the solidified
MSM alloying material.
29. The method according to claim 13, wherein the alloying material
is NiMnGa.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to method for producing a
monocrystalline MSM body for the production of an MSM actuator and
such a monocrystalline MSM body, as is produced by the method.
[0002] MSM actuators (also designated "MSM-actuators") are
generally known from the prior art and utilize the effect that
under the influence of a magnetic field, so-called magnetic shape
memory materials (MSM=Magnetic Shape Memory) carry out an expansion
movement which--typically lying along the expansion direction in
the single-figure percent range relative to a length of a
respective body--can be the basis for a drive and in this respect
can be for instance an alternative to known actuators realized by
means of permanent magnets and/or electromagnets.
[0003] In addition to the alloy which is used (typically an alloy
on the basis of NiMnGa), the crystal orientation in which the MSM
element is present is critical for the effectiveness of such an MSM
actuator or respectively MSM actuator element: Methods to be
assumed as being known from the prior art for the production of
monocrystalline MSM material have the characteristic that a crystal
orientation resulting by the introduction of a molten alloying
material into a molding shell and subsequent cooling or
respectively solidification of the alloying material is stochastic,
with the result that an alignment of the crystal axes is not
predeterminable and must then be developed by subsequent
manufacturing steps of the MSM body. FIG. 5 shows such an
arrangement of the prior art: An MSM monocrystal 10 which has been
solidified and elongated in the previously described manner has a
geometric longitudinal axis 12 determined by the molding shell.
Largely in a stochastic manner during the solidification of the
material, however, a crystal orientation has formed in the
monocrystal 10, which is described by way of example by a first
crystal axis 14 and a second crystal axis 16 orthogonal thereto
(wherein the third axis is then automatically fixed orthogonally to
them both). This then leads to an MSM element 18 (after prior
determining of the crystal axes by measuring) being able to be cut
out from the finished monocrystal, which has a maximum dimension
delimited by the geometric relationships which are shown (with a
large amount of waste material, accordingly). Consequently, this
leads to the fact that with prevalent longitudinal dimensions of
monocrystalline MSM elements in the range between 10 mm and 30 mm
and with desired cross-sections of typically between 5 mm.sup.2 and
30 mm.sup.2 correspondingly large monocrystals 10 (FIG. 5) must be
produced, in order to also be able to manufacture the desired
minimum dimensions for the MSM element for the case of unfavourable
crystal orientations. It is obvious that this procedure, which is
to be assumed as being known, is inefficient in many respects; on
the one hand, waste material occurs to a considerable extent
through the necessary cutting processes (typically carried out by
wire eroding), on the other hand in each case a measuring of the
produced monocrystal is necessary with regard to determining the
crystal orientation (typical procedure by X-ray diffractometry), in
order to create the prerequisite at all for the subsequent
cutting.
[0004] It can also be seen from observing by way of example the
geometric relationships of FIG. 5 that the maximum achievable
dimensions (e.g. a longitudinal extent of an MSM element which is
to be produced) are limited.
[0005] It is known from the prior art that so-called nucleation
crystals (seed crystals) can influence a crystal orientation in a
monocrystal production process. For this purpose substantially a
suitable monocrystal, oriented in the desired manner, is
incorporated into the process at the start of the process, on which
the crystal which is to be produced ideally nucleates in a
monocrystalline manner. However, this procedure is also problematic
in many respects; not only are suitable nucleation crystals costly
and difficult to handle in particular for industrial manufacturing
processes outside a laboratory environment, also such nucleation
crystals require a very precise process management, in order to
achieve the correct nucleation behaviour (with further possible
disadvantages to the MSM effect of a produced MSM element if the
nucleation crystal has material which is foreign to the alloy).
Therefore, in addition to the obvious need for an increase in
efficiency according to the problem described above, the need also
exists for procedural simplification, with the aim of enabling
processes which are simple to operate and are potentially
large-scale for the production of monocrystal MSM bodies.
[0006] With regard to the further prior art, reference is made to
the following documents:
[0007] 1. M. ZHU et al.: "Preparation of single crystal CuAlNiBe
SMA and its performances", JOURNAL OF ALLOYS AND COMPOUNDS, Vol.
478, No. 1-2, 10 Jun. 2009, page 404-410;
[0008] 2. H. ESAKA et al.: "Analysis of single crystal casting
process taking into account the shape of pigtail", MATERIALS
SCIENCE AND ENGINEERING A, Vol. 413-414, 15 Dec. 2005, pages 151,
155;
[0009] 3. GB 2 330 099 A;
[0010] 4. C. Li et al.: "Preparation of Single Crystal of TiNi
Alloy and its Shape Memory Performance", PROC. OF SPIE. Vol. 7493,
2009, pages 7493L1-74931L8;
[0011] 5. K. ROLFS et al.: "Double twinning in NiMnGaCo", ACTA
MATERIALIA, Vol. 58, No. 7, 1 Apr. 2010, pages 2646-2651;
[0012] 6. U.S. Pat. No. 5,062,469 A;
[0013] 7. M. LANDA et al.: "Ultrasonic characterization of
Cu--Al--Ni single crystals lattice stability in the vicinity of the
phase transition", ULTRASONICS, Vol. 42, No. 1-9, 1 Apr. 2004,
pages 519-526; 8. F. XIONG et al.: "Fracture mechanism of a
Ni--Mn--Ga ferromagnetic shape memory alloy single crystal" JOURNAL
OF MAGNETISM and MAGNETIC MATERIALS, Vol. 285, No. 3, 1 Jan. 2005,
pages 410-416.
[0014] It is therefore an object of the present invention to
provide a method for the production of a monocrystal MSM body and a
corresponding monocrystalline MSM body, which are improved with
regard to utilization of material and efficiency of the associated
monocrystal material, in particular to reduce waste of the
monocrystal material for the production of one or more MSM elements
from the monocrystalline MSM body and in addition to make the
necessity of a nucleation crystal unnecessary.
SUMMARY OF THE INVENTION
[0015] The object is achieved by providing a method to provide a
monocrystal MSM body, (preferably for use as an actuator or
respectively actuator element), which proceeds from the fact that
the divided body (and divided further into individual actuator
elements) resulting from the method of the present invention is
further treated with typical (and otherwise known) heat treatment
steps and/or magnetomechanical training steps, in order to achieve
or respectively optimize the magnetic shape memory behaviour. In
accordance with a further development, it is also in particular
included by the invention to subject individual or the plurality of
MSM actuator elements to a heat treatment after the division, in
order to stimulate the magnetic shape memory behaviour;
alternatively, this heat treatment can also take place on the
compacted MSM alloying material before the division into the
plurality of MSM actuator elements. Provision is also made within
preferred further developments of the invention to move the
separated (distributed) MSM actuator elements in the manner of a
training in a targeted and predetermined manner in order to
stimulate the shape memory behaviour. Provision is made here in
particular (and otherwise also assumed as known), that a separated
element is moved in a targeted manner in the provided expansion
direction, for instance by the application of tensile and/or
pressure forces, in order to thus carry out the training with the
aid of such mechanical strokes.
[0016] In an advantageous manner according to the invention, the
production of the monocrystal MSM body--preferably on the basis of
a NiMnGaX alloying material, wherein X has optionally one or more
elements of the group Co, Fe and Cu--without the necessity to
provide a (separated) nucleation crystal, rather solely from the
introduction of the molten MSM alloying material into the
especially configured molding shell according to the invention.
More precisely, the latter has a longitudinal axis and is deflected
in the region of the selector region from this longitudinal axis,
according to the invention by a deflection which exceeds the
maximum cross-sectional width in the selector region. Thereby,
provision is made within the scope of the invention to realize a
longitudinal sectional geometry of the solidification path
deflecting according to the invention by the formation of the
selector region so that this deflection is greater in the
cross-sectional direction than a maximum cross-section width in the
selector region, in other words, the region of the maximum
deflection lies outside a projection of the cross-section in the
crystal region to the entry of the selector region along the
longitudinal axis.
[0017] According to a further development, this deflection has in
longitudinal section the form of at least one spike, alternatively
a spiral, a helix or another angle configuration.
[0018] Through this advantageous provision, the crystal structure
of the solidifying or respectively then solidified MSM material
then undergoes in a manner according to the invention a crystal
orientation which orients itself on the longitudinal axis, more
precisely runs along the direction of the longitudinal axis of the
molding shell (or respectively deviates therefrom by an angle
deviation which according to the invention is <10.degree.,
according to a further development is advantageously <6.degree.,
again according to a further development and advantageously is less
than 3.degree.).
[0019] It is thereby then advantageously achieved through the
present invention that (with this then negligible orientation error
in the practical realization) a monocrystal is produced, the
crystal orientation of which no longer occurs stochastically, but
rather is marked by the mechanical alignment of the molding shell
along the longitudinal axis (or respectively of the course section
formed in a deflected manner according to the invention for the
solidification in the selector region). The advantageous
consequence resulting therefrom for series production is evident:
Not only is the waste which is necessary in a further treatment or
respectively in the dividing of the solidified material into a
plurality of MSM elements drastically reduced, also through the
procedure according to the invention at least the crystal
orientation is fixed with regard to the longitudinal axis through
the procedure according to the invention, in other words, before a
possible further treatment of the monocrystal for the realization
of the MSM element(s), a laborious step of orientation measurement
(for instance by means of X-ray diffractometry) would be
superfluous.
[0020] If then, as provided advantageously and according to a
further development the molding shell (in particular in the
selector or respectively crystal region) is configured so as to be
rectangular in cross-section, in addition the crystal orientation
of the solidifying or respectively solidified MSM material can be
influenced along a second crystal axis running orthogonally to the
first crystal axis (and hence automatically to the third orthogonal
axis), so that as a result in this way then also the complete
three-dimensional crystal orientation of a resulting crystal is
determined in the space (again without the necessity of
measuring).
[0021] Within the practical realization of the invention, it is
particularly favourable and preferred to provide the longitudinal
axis in vertical direction, so as to provide it approximately
perpendicularly to an (otherwise known) cold plate as cooling
device in or at the nucleation region of the molding shell. If the
molding shell is then (in an otherwise known manner) moved from a
warmth or respectively heat environment, opposed to the
longitudinal axis, with a drawing speed, alloying material which is
introduced into this molding shell in liquid state solidifies owing
to the temperature gradient then in an upward direction along a
solidification path, which is able to be described through the
longitudinal axis and, deviating therefrom, is deflected according
to the invention in the selector region. According to a further
development advantageously the solidification--or respectively
cooling behaviour of the molding shell is arranged here so that in
cross-section (radially) no significant temperature gradient is
present from the interior outwards in the melt adjacent to the
solidification front, and a temperature gradient of the melt close
to the solidification front is set at values of between 0.3 K/mm
and 20 K/mm, wherein a particularly preferred range of values for
producing the desired crystal orientation lies in the range between
1 K/mm and 15 K/mm. Additionally or alternatively, it is favourable
according to a further development to arrange the cooling rate,
described by the speed of movement of the solidification front
along the solidification path (or respectively a drawing speed of
the molding shell relative to the temperature gradient), at a range
of between 0.1 ram/min and 10 mm/min, wherein a particularly
preferred range lies between 0.3 mm/min and 5 mm/min.
[0022] In this way a monocrystalline solidification behaviour is
then advantageously achieved, which forms the first crystal axis of
the crystal structure at least along the longitudinal axis (or
respectively shows between these axes a maximum angular deviation
of less than 10.degree., typically less than 6.degree. or even less
than 3.degree.). For the case where according to a further
development advantageously also the cross-section of selector
region and/or crystal region (i.e. the plane perpendicular to the
longitudinal axis) is configured so as to be rectangular, more
preferably square), in addition an influencing (parameter) of the
orthogonal second or respectively third crystal axis can be
achieved in the direction of the rectangular longitudinal edges in
cross-section, so that in the ideal case of an e.g. elongated and
cross-sectionally rectangular crystal region of the molding shell,
this region determines the three-dimensional orientation of a
monocrystal which is solidified therein. According to a further
development, it is particularly advantageous within the scope of
the invention to carry out a division, following the
solidification, (always) perpendicularly to the longitudinal axis
(Z axis), because indeed in this respect, with the previously
described maximum deviations, the crystal orientation is already
fixed.
[0023] As a result, therefore the present invention not only
enables a drastic reduction in manufacturing steps or respectively
upstream testing steps (because ideally any measuring of the
crystal orientation can be dispensed with), the invention also
permits MSM elements to be produced which are optimized with regard
to dimension from the restricted interior of a molding shell,
because in particular already in the described molding process by
solidification along a solidification direction corresponding to
the longitudinal axis of the molding shell and a crystal alignment
effected therewith, a maximum length dimension is able to be
produced. It is then to be expected in particular that MSM elements
can be produced efficiently and with small manufacturing
expenditure (and hence potentially on a large scale) as the basis
for the production of MSM actuators (also by further dividing, e.g.
sawing), which reach length dimensions of more than 20 mm, in
particular more than 40 mm and/or permit a cross-sectional area of
15 mm.sup.2 or more.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Further advantages, features and details of the invention
will emerge from the following description of preferred example
embodiments and with the aid of the figures; these show in:
[0025] FIG. 1 a geometric schematic diagram of a molding shell
arrangement for carrying out the method according to a first
example embodiment of the invention;
[0026] FIG. 2 an illustration analogous to FIG. 1, but with a
different geometrical configuration in the form of a
cross-sectionally rectangular crystal region of the molding
shell;
[0027] FIG. 3 a diagrammatic illustration of a cylindrical MSM
monocrystal and of a crystal orientation drawn therein
diagrammatically on realization of the invention;
[0028] FIG. 4 an illustration analogous to FIG. 3, but with a
monocrystal body in the shape of a rectangular block to illustrate
the crystal orientation of an MSM actuator element (likewise in the
shape of a rectangular block) provided diagrammically therein
and
[0029] FIG. 5 a diagrammatic illustration of an MSM monocrystal
realized according to a generic method from the prior art with
crystal axes oriented therein stochastically, and with the limited
cut possibilities resulting therefrom for an MSM actuator
element.
DETAILED DESCRIPTION
[0030] FIG. 1 illustrates the principle by which the present
invention can be realized according to a first example embodiment.
A so-called molding shell is shown for the production of
monocrystalline bodies by the so-called Bridgman method, which,
extending from a cold plate 20 perpendicularly along a longitudinal
axis (dot-and-dashed line 22), forms a nucleation region 24,
subsequently a selector region 26 and a crystal region 28. Suitably
molten alloying material is introduced into the device through an
upper opening 30, and the liquid alloying material then solidifies
from below upwards (arrow direction 32) with the formation of a
correspondingly upward moving solidification front, the speed of
movement of which is predetermined by a suitable temperature
influence.
[0031] FIG. 1 (as also the analogous FIG. 2) illustrate how
according to the invention the solidification path takes place not
perpendicularly and linearly along the longitudinal axis 22, but
rather has a linear course which is bent in longitudinal section
from FIG. 1 or respectively FIG. 2; more precisely, in the selector
region 26 the molding shell is configured so that its interior
channel which is effective for the solidification (from the
direction from below upwards) firstly is deflected by an angle
.quadrature. of approximately 40.degree. and then has a further,
but oppositely deflected section, until the channel at the upper
end of the selector region is again in alignment cross-sectionally
with the cross-section on the base side. In accordance with the
invention, advantageously this deflection, which in the illustrated
example embodiment at its maximum lateral deflection transcends
over the projection of the cross-section in the crystal region or
respectively in the base region adjacent to the cold plate 20,
advantageously provides for a longitudinal orientation of the
crystal structures in vertical direction, i.e. in the direction of
the axis 22. In the solidified state, this then leads in the region
of the crystal region 28 to the monocrystal which is present there
having an orientation which has at least a first crystal axis
orientated in the direction of the longitudinal axis (wherein here
according to the invention a maximum angle error of 10.degree.,
typically however of less than 6.degree. or even less than
3.degree. can be achieved).
[0032] FIG. 2 shows a variant of the example embodiment of FIG. 1;
here in the crystal region 28', the channel extending vertically
along the longitudinal axis 22 is square in cross-section, so that,
in addition to a crystal axis orientation in vertical direction,
additionally the two crystal axes orthogonal thereto extend
parallel to the edge courses of the crystal region. FIG. 3 or
respectively 4 illustrate these geometrical relationships, in this
respect in accordance with the forms of realization of FIG. 1 or
respectively FIG. 2: FIG. 3 shows the result of a monocrystal body
solidified in a hollow cylindrical crystal region. The direction of
the longitudinal axis (here: z-axis) corresponds approximately to
the alignment of the crystal longitudinal axis c with the described
small possible angle error. Owing to the cylinder structure (i.e.
circular shape in the x-y plane in FIG. 3), the two further axes,
orthogonal to one another and to the vertical axis c, are
stochastic in their alignment. In contrast, the further development
of FIG. 2 (geometry according to FIG. 4) offers the possibility, by
provision of the square cross-sectional contour (running here
parallel to the x- or respectively y-direction), to develop the
second (a) or respectively third (b) crystal axis parallel
accordingly, so that as a result of the carrying out of the method
described in FIG. 2 or respectively FIG. 4 a monocrystal is
achieved, which through its shape in the form of a rectangular
block already to the greatest possible extent also describes its
actual crystalline orientation and in this respect is potentially
not (or only minimally) in need of further treatment. Also, the
result of the production method according to FIG. 1 (FIG. 3) is
already advantageous in so far as here with the crystal axis (c),
running in the direction of the longitudinal extent (z) of the
molding shell and of the blank which is solidified therein, a
relevant alignment is fixed for instance for the expansion
behaviour of an MSM body, and also such a cylindrical body is then
able to be used without further (or only with minimal) further
treatment, if the precise alignment of the a- or respectively
b-crystal axes is not concerned.
[0033] The execution of the method is described below with the aid
of a practical example:
[0034] Primary alloying material is produced as so-called master
alloy by induction melting from the materials NiMnGa, in accordance
with composition for an MSM alloy, by induction melting. A typical
melting temperature is set at a range of between 50.degree. and
400.degree. above the liquefaction temperature of the respective
alloy. Typically, the melting takes place under an Ar atmosphere
between 100 mbar and 1200 mbar.
[0035] The liquid master alloy is poured into a ceramic molding
shell which has a geometry in accordance with FIG. 1. This molding
shell is moved in the Bridgman method relative to a temperature
gradient from a hot zone into a cold zone, so that the
solidification front runs through the molding shell from bottom to
top. This speed of the movement of the solidification front
typically lies at 0.3 mm/min; the temperature gradient in the melt
close to the solidification front is set at a value of typically 3
K/mm. After running through the selector region, which is
advantageously deflected according to the invention, the MSM
material solidifies with a crystal axis aligned vertically, i.e.
along the direction of the longitudinal axis 22, so that after
concluding solidification and cooling, a cylinder can be removed
from the crystal region 28 as an MSM body of the geometry shown in
FIG. 3. This now offers the possibility of immediately realizing an
MSM actuator with a movement-(expansion) direction extending
axially; alternatively, from this body, by determining a
crystalline transverse axis, the prerequisite can be created so
that with little waste and minimized loss on the covering surface
side, one or more MSM elements which are cross-sectionally
rectangular or respectively in the shape of a rectangular block can
be created with a defined crystal orientation also in the
transverse direction. For such a separation, in particular cuts
perpendicular to the Z-axis present themselves, because indeed in
this respect the orientation is already developed.
[0036] To stimulate or respectively realize a complete shape memory
functionality of actuators realized in the described manner, the
material is heat-treated (either as a whole body before the
separation, alternatively by heat treatment of the divided
individual actuator elements). It is also advantageous to train
these elements after dividing in their movement--or respectively
expansion behaviour, wherein for this purpose, typically over some
strokes, in the provided expansion--or respectively movement
direction a movement is imprinted into the material by
corresponding input of tensile force or respectively pressure
force.
[0037] Whereas the arrangement described above and the operation
thereof for realizing the method according to the invention are to
be understood generically and in principle (and configured and
adapted in a suitable manner by the specialist in the art), it is
in particular also within the scope of the present invention to
provide in the manner of a multi-armed molding shell a plurality of
solidification paths along selector--and crystal regions which are
respectively separated from one another but nevertheless
adjacent.
[0038] The ranges of application of an MSM body which is produced
by the present invention are potentially unlimited; it is
advantageously to be expected that the present invention
nevertheless considerably simplifies and configures more
economically the large-scale production of such bodies which are
clearly defined with regard to the crystal geometry, so that in
future further fields of application are developed for MSM
actuators.
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