Patent Application
20170218522
The present invention relates to the field of producing surfaces on metallic workpieces with improved adhesion to organic polymers and/or biological materials and/or ceramic materials.
The invention relates to a surface-treated metallic workpiece of titanium and/or titanium alloys with titanium as a main component and/or nickel-titanium alloys as well as Nitinol, wherein the treated surface of the metal is free from inclusions, precipitations of other metals, alkaline earth metals and/or aluminum, intermetallic phases, and/or mechanically intensely defect-rich areas, and the surface has a first roughness and a second roughness, wherein the first roughness is provided by depressions in the form of pores, the pores having a diameter in the range between 0.5 and 50 μm, are open towards the surface, and are closed towards the workpiece, and at least a portion of the pores have an undercut, and the second roughness is provided by statistically distributed elevations and depressions in the range of 100 nm and less.
Furthermore, the invention relates to a production method for a surface-treated workpiece.
It is known in principle that an increase in the roughness of a metal workpiece surface can be helpful in improving the adhesion of outer layers. In particular, trenches, pores or local elevations can be structures on the workpiece surface which can be filled or surrounded by a flowable polymer, prepolymer or monomer, so that after it's curing the polymer film is fixed as a result of mechanical anchoring.
In medicine, the use of implants with porous surfaces for better fixation of the surrounding organic tissue has been known for more than 20 years.
Titanium and its alloys are a widely used material for implants in particular because of the high biocompatibility, good corrosion resistance and low toxicity.
The roughness of the implant made of titanium or its alloys necessary for successful osseointegration can be achieved by diffusion welding, sintering, sand blasting, plasma spraying, successive etching or other methods.
From Hacking et al. “Acid-etched microtexture for enhancement of bone growth into porous-coated implants” [Journal of Bone and Joint Surgery 85, 1182] it is known, that for forming a microtexture etching may be advantageous over sintering.
It is known from US 2007/0187253 A1 to remove beta (β) phases from Ti-6Al-4V alloys near the surface so as to produce a nanotopographic surface. The process is limited to the structuring of Ti-6Al-4V alloys. The described method is likewise limited to the removal of the β phase, if this is not formed, it can not be used, and further, other impurities and mechanical defects not given by the β phase remain on the surface and thus also do not contribute to favorable topography.
A further disadvantage of the process is that the structuring of the Ti-6Al-4V alloy surface requires the incorporation into an electrochemical cell with appropriate electrical contacting, which means that the contact point of the workpiece must not come into contact with the electrolyte, in order to ensure defined and reproducible electrochemical conditions during the process, and thus the entire workpiece can not be surface-modified.
It is an object of the invention to provide metallic workpieces which have a particularly favorable topography.
It is also an object of the invention to provide metallic workpieces with a favorable topography constituted of the metals titanium, zirconium, hafnium, vanadium, niobium, tantalum and the alloys of these metals as well as the nickel-titanium alloy known under the name “Nitinol”.
It is also an object of the invention to provide metallic workpieces which are free from inclusions and dispersions or precipitations of other metals and/or intermetallic phases as well as defect areas on their surface.
In addition, the object of the invention is to provide a method for patterning the surface, which can also be applied to workpieces made of titanium and/or titanium alloys of different compositions, as well as to other metals and alloys.
It is also an object of the invention to provide a process which, in addition to the β phase, also removes further impurities or mechanical defects from the surface and thus increases the purity of the surface.
Furthermore, it is an object of the invention to provide a method which makes it possible to structure complete workpieces, even with a complex shape.
The object of the invention is achieved by the provision of a metallic workpiece of the metals titanium, zirconium, hafnium, vanadium, niobium, tantalum and/or their alloys, as well as the nickel-titanium alloy known under the name “Nitinol”, of which the treated surface is largely free of inclusions and/or precipitations of other metals and/or intermetallic phases as well as mechanically strongly defect-rich regions (e.g., dislocation nests) and wherein the workpiece has a topography, which is defined by a first and a second roughness and wherein the first roughness is defined by depressions in the form of pores, and wherein the pores are open towards the surface and are closed towards the workpiece, and wherein at least 25%, preferably 50%, of the pores have an undercut, and wherein the second roughness is determined by statistically distributed elevations and depressions in the range of 100 nm and less.
Furthermore, the object of the invention is achieved by a method for producing the workpiece according to the invention which comprises the following steps
i. photochemical etching of the surface in an electrolyte under illumination
ii. chemical etching in acid solution
As workpieces the metals titanium, zirconium, hafnium, vanadium, niobium, tantalum and/or their alloys are suitable. Examples of suitable titanium alloys can be found in Materials Properties Handbook: Titanium Alloys, R. Boyer, G. Welsch, and E. W. Collings, eds. ASM International, Materials Park, Ohio, 1994. Particularly suitable among these are titanium grade 2, Ti-6Al-4V (grade 5) and derivatives of this alloy (grades 23-25, grade 29), Ti-3Al-2.5V (grade 9) and derivatives of these alloys (e.g., grade 18 and grade 28) as well as NiTi (Nitinol). In the case of niobium, suitable alloys would be e.g. C-103, C-129Y, C3009, Cb 752, FS85 and Nb1Zr.
In this case, it is generally advantageous to clean the workpiece of coarse soiling and grease/oil before the first etching step i. The cleaning is carried out in a manner which is generally known to a person of ordinary skill in the art, for example by rinsing with water-miscible organic solvents, e.g., by an acetone bath or a bath consisting of 70% isopropanol and 30% deionized water.
During the photochemical etching step i, a chemically greatest possible surface smoothness is produced. The electrolyte is preferably a strongly oxidizing acid.
Among oxidizing acids, those skilled in the art generally understand such acids which, in addition to the reaction potential resulting from the protons, still participate in a redox reaction. The anion of the oxidizing acid oxidizes the metal and is thereby reduced. The occurrence of the oxidizing effect here also depends on the concentration of the acid and the temperature in the manner known to the worker of ordinary skill. Typically, strongly oxidizing acids come from the group known as oxygen acids. The strong oxidizing acid is preferably selected from the group consisting of sulfuric acid (H2SO4), nitric acid (HNO3), peroxomonosulfuric acid (H2SO5), chloric acid (HClO3), perchloric acid (HClO4), chromic acid (H2CrO4), arsenic acid (H3AsO4), hydrogen peroxide (H2O2) and/or a combination of these acids and/or one or a combination of these acids diluted with water (H2O).
The illumination can be performed with LED arrays e.g. based on Enfis Uno Tag Arrays. The nominal irradiance (radiant flux) should be between 200 and 450 mW. The wavelengths can be in the range between 190 and 780 nm.
The shape of the sample container and the distance to the illumination source are to be selected in dependence on the sample geometry in such a way that homogeneous illumination is possible. Typically, a distance of 8 cm between sample surface and LED array was chosen.
The photochemical etching step i takes place at a temperature between 10° C. and 50° C., preferably between 15° C. and 40° C., particularly preferably between 20° C. and 25° C. (room temperature).
The duration of the photochemical etching step i is 5 to 30 hours, preferably 10 to 25 hours, more preferably 15 to 22 hours.
After photochemical etching, the sample is rinsed several times in a manner well known to those skilled in the art, e.g., with deionized water and subsequently dried e.g. by simple air drying before being placed in the etching bath ii.
The chemical etching step ii serves to remove inclusions and/or precipitations and/or mechanically defective areas and takes place in acidic solution. The acidic solution is a combination of a strongly oxidizing acid and an oxide-dissolving acid.
Acid-dissolving acids are understood as meaning those acids which are capable of converting metal oxides into metal salts with formation of water. Preferably, the oxide-dissolving acids are selected from the group consisting of hydrochloric acid (HCl), hydrofluoric acid (HF), bromic acid (HBr), iodic acid (HI), a combination of these acids and/or one or a combination of these acids in dilution with water (H2O).
The etching solution for etching step ii (etching solution ii) can be selected from the group consisting of sulfuric acid (H2SO4), hydrochloric acid (HCl), hydrofluoric acid (HF), where appropriate, diluted with water.
The etching solution is typically based on a 1:1 mixture of concentrated sulfuric acid (96-98%) and concentrated hydrochloric acid (37%) or hydrofluoric acid (40%). Optionally, the ratio between concentrated sulfuric acid and concentrated hydrochloric acid/conc. hydrofluoric acid may be varied, e.g., to a ratio of 1:2. This etching solution ii can also be diluted by the addition of deionized water.
The chemical etching step ii is preferably carried out at room temperature. The sample is preferably added directly after the etching solution has been prepared. The etching bath is typically not stirred, since gas evolution occurs during etching, the gas evolution causing intermixing of the etching solution. The volume of the etching solution used is selected in such a way that the etching solution is present in excess in comparison to the sample volume and thus the sample volume is completely wetted. The etching step ii generally takes place at room temperature, without the introduction of external heat, but using the resulting heat of reaction.
The duration of the chemical etching step ii is between 1 and 6 hours and can be extended by diluting the etching bath. When the etching solution ii is undiluted, the duration of the etching step ii is preferably 2 to 4 hours, more preferably 3 hours.
After the chemical etching step ii, the surface-treated workpiece is repeatedly rinsed in a manner well known to the person of ordinary skill in the art, e.g. with deionized water and subsequently dried e.g. by simple air drying.
The workpieces according to the invention have a high purity and freedom of mechanical defects on the surface after the two-stage etching treatment.
Exemplary embodiments of the invention are described below with reference to the accompanying figures.
Therein:
Because of this topography comprised of a roughness in the nanoparticle and the pores with a diameter of 0.5 μm to 50 μm, preferably 1 μm to 40 μm, particularly preferably 2 μm to 20 μm with an undercut, the materials according to the invention are outstanding for the adhesive bonding with other materials. The workpieces can thus be used in the field of medical implant technology.
The workpieces according to the invention can be used e.g. for dental implants or artificial hip joints. For dental implants, the osseointegration of the Ti implant is of great importance for the long-term stability of the implant. The topography of pores with an undercut and the nanoroughness in the pores ensure excellent mechanical interlocking between bone and implant. With the Ti surface patterning, a purification of the Ti surface can also take place, which can result in a lower release of alloy metal ions from the implant, e.g. Al or V ions. This is especially significant e.g. for artificial hip and knee joints.
In the art, the workpieces according to the invention are particularly important in the field of composite materials, since the bonding of the various materials is important. Thus, the workpieces according to the invention can be used for composite turbine blades. The composite consists in this case of a layer sequence of fiber-reinforced polymer and Ti sheets, which are connected to one another. For this connection, optimum adhesion between polymer and Ti sheet is of the utmost importance. The pore undercuts and the nanoroughness of the pores provide the mechanical interlocking between the Ti sheet and the polymer.
In order not to limit the generality of the teaching, the invention will be explained in the following in some examples:
The sample (turbine blade) was sandblasted and then cleaned for 5 min in acetone and dried in air. The sample is then etched for 24 h in concentrated H2SO4 at room temperature without external temperature control under illumination with an ENFIS Uno Day Red LED array operated at a nominal irradiance of 400 mW (300 mA and a wavelength of 620 nm) at a distance of approximately 8 cm from the sample surface. After this step, the sample was repeatedly cleaned in deionized water and dried in air. Subsequently, the sample was etched for 3 h in a freshly prepared fresh solution of HCl and H 2 SO 4 in a volume ratio of 1:1 without external temperature control. The sample was then repeatedly washed in deionized water and dried in air. The volumes of the respective etching solution were chosen such that a complete wetting of the sample is assured. The etching solutions were not stirred during the etching.
The scanning electron micrographs (SEM) in
The sample was degreased for 5 min in acetone and cleaned and air-dried. The sample is then etched for 20 h in concentrated H2SO4 at room temperature without external temperature control under illumination with an ENFIS Uno Tag Red LED array operated at a nominal irradiance of 400 mW (300 mA and a wavelength of 620 nm) at a distance of approximately 8 cm from the sample surface. After this step, the sample was repeatedly cleaned in deionized water and dried in air. Subsequently, the sample was etched for 3 h in freshly prepared etching solution consisting of HCl and H2SO4 in a volume ratio of 1:2 without external temperature control. The sample was then repeatedly washed in deionized water and dried in air. The volumes of the respective etching solution were chosen such that a complete wetting of the sample is assured. The etching solutions were not stirred during the etching.
The SEM images are shown in
The integral superficial element distribution of the blasted sample (
The sample is cleaned for 5 min in acetone and degreased and dried in air. The sample is then etched for 20 h in concentrated H2SO4 at room temperature without external temperature control under illumination with an ENFIS Uno Day Red LED array operated at 300 mA (400 mW) at a distance of approximately 8 cm from the sample surface. After this step, the sample was repeatedly cleaned in deionized water and dried in air. Subsequently, the sample is etched for 3 h in freshly prepared etching solution consisting of HCl, H2SO4, H2O (deionized) in a volume ratio of 1:1:1 without external temperature control. The sample was then repeatedly washed in deionized water and dried in air. The volumes of the respective etching solutions were chosen such that a complete wetting of the sample is assured. The etching solutions were not stirred during the etching.
a) shows the Ti-6Al-4V surface after the two-step etching process. One can see a fine-formed cup-like surface with a rough nanostructure. The diameters of the cups are about 2 μm. In part, these structures have also grown into one another.
The sample is cleaned for 5 min in acetone and dried in air. Subsequently, the sample is etched for 20 h in an etching solution consisting of concentrated H2SO4 and deionized water (volume ratio 1:1) at room temperature without external temperature control under illumination with an ENFIS Uno Tag Red LED array operated at 300 mA (400 mW) about 8 cm from the sample surface. After this step, the sample was repeatedly cleaned in deionized water and dried in air. The sample is then washed for 3 h in a freshly prepared etching solution consisting of cone. HCl and conc. H2SO4 in the volume ratio 1:1 without external temperature control. The sample was then repeatedly washed in deionized water and dried in air. The volumes of the respective etching solution were chosen such that a complete wetting of the sample is assured. The etching solutions were not stirred during the etching.
a) shows the Ti-6Al-4V surface after the two-stage etching process. A finely formed cup-like surface with a rougher nanostructure than in
The sample was degreased for 5 min in acetone and cleaned and air-dried. Subsequently, the sample is etched for 20 h in concentrated H2SO4 at room temperature without external temperature control under illumination with an ENFIS Uno Day Red LED array at an irradiation strength of 200 mW (200 mA) at a distance of approximately 8 cm from the sample surface. Since the NiTi wire should be structured from all sides at the same time, the NiTi wire was rotated around its own axis at about 10 rpm with stationary, one-sided illumination. After this step, the sample was repeatedly cleaned in deionized water and dried in air. The sample was then etched for 2 h in freshly prepared etching solution consisting of HCl and H2SO4 in a volume ratio of 1:2 without external temperature control. The sample was then repeatedly washed in deionized water and dried in air. The volumes of the respective etching solution were chosen such that a complete wetting of the sample is assured. The etching solutions were not stirred during the etching.
The SEM images in
The sum spectrum of the treated and untreated sample is shown in
The sample was burnished with abrasive paper (4000 SiC grain size) until the cutting or saw marks were removed and then degreased for 5 min in acetone and cleaned and dried in air. The sample is then etched for 20 h in concentrated H2SO4 at room temperature without external temperature control under illumination with an ENFIS Uno Tag Red LED array operated at a nominal irradiance of 400 mW (300 mA and a wavelength of 620 nm) at a distance of approximately 8 cm from the sample surface. After this step, the sample was repeatedly cleaned in deionized water and dried in air. Subsequently, the sample is etched for 3 h in freshly prepared etching solution consisting of HCl and H2SO4 in a volume ratio of 1:1 without external temperature control. The sample was then repeatedly washed in deionized water and dried in air. The volumes of the respective etching solution were chosen such that a complete wetting of the sample is given. The etching solutions were not stirred during the etching.
The EDX element distribution in
The sample was burnished with abrasive paper (4000 SiC grain size) until the cutting or saw marks were removed and then cleaned for 5 min in acetone and dried in air. Subsequently, the sample is etched for 24 h in concentrated H2SO4 at room temperature without external temperature control under illumination with an ENFIS Uno Day UV LED array at 300 mA at a distance of approximately 8 cm from the sample surface. After this step, the sample was repeatedly cleaned in deionized water and dried in air. Subsequently, the sample was etched for 3 h in a freshly prepared fresh solution of HCl and H2SO4 in a volume ratio of 1:1 without external temperature control. The sample was then repeatedly washed in deionized water and dried in air. The volumes of the respective etching solution were chosen such that a complete wetting of the sample is assured. The etching solutions were not stirred during the etching.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2014 110 922.8 | Jul 2014 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2015/100322 | 7/31/2015 | WO | 00 |
