Patent Application
20110044841
The invention relates to a method for producing microscopically small components.
The production of components with dimensions greater than 50 μm is known. To produce components of this type, preforms are first produced by microcasting or powder metallurgical methods. These preforms are subsequently machined by micro-machining in order to thus give them the desired final contour.
The disadvantage of methods of this type is that complex machines with dimensions that are substantially below 500 μm cannot be constructed with the aid of components produced in this manner. The reason for this is that a complex machine comprising several components and assembled from individual free components is always ten to fifty times larger than the individual components of which it is composed. The production of components with dimensions less than 1 μm has hitherto been possible only lithographically. Free components that are not coupled to a substrate cannot be obtained in this manner at a reasonable expense.
In particular for applications in medicine, for example for dispensing medications or for diagnostics using implanted microsystems, however, it is desirable to have complex machines available, the dimensions of which are considerably less than 500 μm.
The object of the invention is therefore to disclose a method with which free components not bonded to a substrate and with a size of less than 10 μm can be produced.
The object is attained by the invention through a method with the steps (a) production of a precipitation hardenable, alloy comprising at least two phases, in which alloy a first phase forms a matrix structure in which a second phase is embedded in the form of discrete particles of a size less than 10 μm, preferably less than 1 μm; (b) dissolution of the matrix and separation of discrete particles from the alloy and (c) mechanical deformation by forging respectively a separated particle with at least one striking tool to form the desired element.
The advantage of the method according to the invention, which can also be referred to as nanoforging, is that components with a size of less than 50 μm can be produced. It is furthermore advantageous that components with reproducible dimensions can be produced, since the particles used as output blocks likewise have a size that is reproducible in a high grade manner.
It is furthermore advantageous that large production runs of components can be produced quickly through the method, since a large number of particles can be obtained very quickly through the use of the precipitation hardenable alloy.
It is also advantageous that the method manages without lithographic or powder metallurgical processes, which reduces the expenditure in terms of equipment. Furthermore, the method makes it possible to produce components from a plurality of high-strength alloys, with which lithographic or powder metallurgical methods do not provide satisfactory results.
Within the scope of the present specification, the term γ, γ′ refers very generally to two different phases. In a preferred embodiment the first phase is a γ phase and the second phase is a γ′ phase in terms of physical metallurgy. The discrete particles are then, for example, γ′ particles.
A matrix structure is understood to mean that it is interconnected such that it can be dissolved and the particles contained therein, in particular the γ′ particles contained therein, can thus be separated from the γ matrix. In particular the γ′ particles are separated by row-type and column-type areas in which the γ phase is present. Preferably the alloy has more than 10, in particular more than 100, γ′ particles, which are separated from one another by areas in which the γ phase is present.
The size of the γ′ particles means in particular the maximum side length of a minimal cuboid envelope. To determine the size of a γ′ particle, the cuboid around the relevant γ′ particle is therefore determined, which cuboid completely surrounds the γ′ particle and has the smallest volume among all of the cuboid envelopes of this type, and the maximum side length thereof established. This side length represents the size of the γ′ particle.
A separation of the γ′ particles from the superalloy means in particular that the γ′ particles are separated from the rest of the matrix structure, in particular therefore from the γ phase. The forging comprises in particular a freeform forging in which the separated γ′ particle is forged with a hammer on a flat base, and a die forging in which the γ′ particle is struck by a hammer in a die or is deformed or shaped between two dies.
In a preferred embodiment the γ′ particles are embodied essentially in a cuboid form. An essentially cuboid form should be understood to mean that a strict mathematical cuboid form is not necessary. Instead, it is sufficient if, for example, the longest side of a cuboid envelope of minimal volume around the relevant γ′ particle is no more than 15% longer than the shortest side of the corresponding cuboid envelope.
The maximum edge length of the cuboid or the cube is preferably less than 10 μm, preferably less than 1 μm. The advantage of this is that particularly small components can be produced.
Preferably, the dissolution of the matrix is carried out chemically and/or electrochemically. Through this the matrix is dissolved particularly quickly and effectively, without the γ′ particles being excessively affected.
In a preferred method γ′ particles bonded on the metal surface are shaken off by means of ultrasound for the separation. The metal surface is thereby in particular that surface of the alloy to which the γ′ particles were connected before the chemical and/or electrochemical dissolution.
The shaking off is carried out particularly preferably in an aqueous solution, which is subsequently centrifuged to obtain the γ′ particles. It is hereby ensured that the γ′ particles can be obtained with a high yield. At the same time γ′ particles are prevented from reaching the air, where they could possibly be inhaled.
Preferably the alloy is monocrystalline, in particular in individual or all γ′ particles. This results in particularly advantageous strength properties of the components produced.
The method is particularly advantageous if the alloy is a nickel-based superalloy, since in this case particularly uniformly shaped and essentially cuboid γ′ particles can be produced and components with a particularly high mechanical strength are obtained. Nickel-based superalloys with 1 to 9% by weight aluminum, 0-8% by weight titanium and 0-15% by weight tantalum, in particular 0-12% by weight tantalum, for example Udimet 710 with 2.3% by weight aluminum and 3% titanium or Waspaloy with 1.3% by weight aluminum and 3% titanium are particularly favorable. Alloys of this type have furthermore proven to be particularly advantageous for the production of γ′ particles.
In general alloys are preferred in which the γ′ particles have an L12 crystal structure. For example, the alloy is alternatively a nickel-iron alloy and the γ′ particles comprise Ni3Fe. In this manner, components with a particularly high ductility are obtained, which are also easy to forge.
It is preferred that the processing surface of the striking tool is smaller than 50 μm, in particular smaller than 5 μm. The size of the processing surface is given as the side length of a square of equal area.
Preferably a manipulator with tungsten tip is used as striking tool and a silicon cantilever arm is used as an anvil. Preferably the silicon cantilever arm has a flat surface. Alternatively, at least one recess functioning as a die is provided in the silicon cantilever arm. This recess preferably has a base area, the maximum dimension of which is less than 5 μm. In this manner particularly small components can be produced.
It has turned out that the recess can be produced with a particularly high precision and in a particularly reproducible manner by nanolithography or microlithography. For forging, in a preferred embodiment a tungsten tip with a plateau is used, the maximum dimension of which is less than 5 μm. A tungsten tip has the advantage of being sufficiently hard so as not to be deformed itself during forging. The maximum dimensions of less than 5 μm furthermore make it possible to observe the forging operation, for example, through a scanning electron microscope.
An exemplary embodiment of the invention is explained in more detail below based on the attached drawings. They show:
a A scanning electron microscope image of a precipitation hardenable nickel-based superalloy comprising two phases, in which a first phase (γ phase) forms a matrix structure in which a second phase is embedded in the form of discrete particles (γ′ phase) of a size less than 10 μm,
b A scanning electron microscope image of the alloy according to
a, 3b, 3c, 3d and 3e show the progress of a production method according to the invention in the form of scanning electron microscope images.
a shows a scanning electron microscope image of a precipitation hardenable alloy, which has two phases, namely a γ′ phase 10 and a γ phase 12. The γ phase 12 represents a first phase and the γ′ phase 10 represents a second phase. The first phase 12 forms a matrix structure, in which the second phase 10 is embedded in the form of a plurality of discrete γ′ particles 14a, 14b, . . . , of a size less than 10 μm. The γ′ particles 14 are arranged in a row-type and column-type manner and separated from one another by the γ phase 12.
The structure shown in
This heat treatment is carried out such that essentially cubic deposits in the form of the γ′ particles 14 of the type Ni3Al with an essentially identical size of 300 nm to 500 nm are obtained: In particular the alloy is heat treated such that the variance of the size distribution based on the average value is below 25%. Details on the production can be found in the article “Nano-structured materials produced from simple metallic alloys by phase separation” in Nanotechnology 16 (2005) 2176-2187.
Subsequently the material, namely the γ′ phase 10 and the γ phase 12, is electrochemically etched in an aqueous electrolyte, wherein the alloy is switched as an anode. The etching parameters are thereby selected such that the matrix, namely the γ phase 12, is dissolved. Further details on the etching parameters can be found in the above-referenced article. The process of etching is interrupted at intervals of half an hour to two hours. The situation shown in
Subsequently the superalloy in an aqueous solution is transferred into an ultrasonic bath. γ′ particles 14 bonded on the metal surface are thereby shaken off into the aqueous solution. This solution enriched with γ′ particles 14 is subsequently centrifuged and the γ′ particles 14 are separated.
In a following process step in a vacuum chamber (not shown) of a scanning electron microscope under high vacuum an individual γ′ particle 14 is picked up with the aid of one or more, in the present case two, manipulators 16, 18 (cf.
The manipulators 16, 18 are controlled by means of a joystick and have drives 30 or 32, by means of which the tungsten needles 22, 24 can be positioned with a positional accuracy of 0.5 nm.
After the placement of a γ′ particle 14 on the silicon cantilever arm 20, the γ′ particle 14 is processed by means of a striking tool 33. The striking tool 33 comprises a hammer in the form of a tungsten tip 34. The tungsten tip 34 is attached to a piezoelectric hammer drive 36 and has a positional accuracy in the direction towards the silicon cantilever arm 20 of 1 nm.
The hammer drive 36, the silicon cantilever arm 20 and the two manipulators 16, 18 are arranged in pairs with respect to one another such that the connecting line between manipulator 16 and silicon cantilever arm 20 on the one hand and manipulator 18 and tungsten tip 34 on the other hand run perpendicular with respect to one another.
Forces up to 2 mN can be applied with the aid of the hammer drive 36. The strength of the force applied is recorded by a force transducer 38, which is arranged in a drive 40 for the silicon cantilever arm 20.
The forging operation takes place at room temperature (23° C.). In an alternative embodiment, the silicon cantilever arm 20 comprises an electric heating device (not shown). If desired, the γ′ particle 14 is thus brought to an increased temperature and subsequently processed. It is furthermore possible after a forging at room temperature to heat the γ′ particle 14 by means of the electric heating device in order to trigger recrystallization processes and/or to heal dislocations.
All of the components shown in
In an alternative embodiment the silicon cantilever arm 20 has a recess produced by nanolithography or microlithography. This recess has a base surface, the maximum dimension of which is, for example, less than 1 μm by 1 μm. For mechanical deformation by forging, a single γ′ particle 14 is separated with the aid of the manipulators 16, 18 and placed at a position above the recess. Subsequently, the γ′ particle 14 is struck or pressed into the die with the tungsten tip 34 as a hammer. In this manner, a deformed component with a precisely contoured surface and with a size of less than 1 μm is obtained. A method of this type can be used, for example, to produce gear wheels with a size of less than 10 μm.
It is possible, but not necessary, to strike the γ′ particle 14 completely into the die. Alternatively, the γ′ particle 14 is placed above the die and struck partially into the die. A residue of the γ′ particle 14 remaining outside the die is subsequently removed.
In an alternative method, instead of a high vacuum a weaker vacuum is used, for example a moderate vacuum. It is then advantageous to set the lowest possible air humidity, for example, of less than 10%.
A method according to the invention can comprise the steps of a wetting of the silicon cantilever arm 20 and/or of the tungsten tip 34 with a lubricant layer. This process step is advantageous if there is a risk that the component produced from the γ′ particle 14 will adhere firmly to the silicon cantilever arm 20 or to the tungsten tip after the forging. The wetting with a lubricant layer is achieved, for example, in that a diffusion pump oil such as diffusion pump oil 705 from Dow Corning is evaporated so that it condenses on the silicon cantilever arm 20 or the tungsten tip 34.
a shows the tip 26 of the tungsten needle 22 of the manipulator 16 (cf.
b shows the tungsten tip 34, at the tip of which the γ′ particle 14 is located. The γ′ particle 14 is placed on the silicon cantilever arm 20 (
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DE06/01915 | 10/28/2006 | WO | 00 | 4/21/2009 |
