RU2669257C1 - Method for obtaining structured porous coating on titanium - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention relates to a method for modifying a surface of titanium to produce a structured porous layer comprising nano- and micropores, and can be used in medical technology in the manufacture of biologically compatible endoprostheses and implants for traumatology, orthopedics, plastic surgery, dental implants, for the preparation of the surface of titanium implants for the application of bioactive coatings, as well as for the manufacture of catalyst carriers and composite materials that are used in various fields of technology. Method comprises treating the surface of titanium in an argon medium by moving a laser beam with a power of no more than 300 W, preferably 250–270 W, at a speed of at least 20 mm/s, preferably 25–35 mm/s, with the simultaneous supply to the irradiation zone of the titanium carbide powder fraction 80/100 mcm, the subsequent acid etching by immersion in nitric acid for 3–5 days, washing and drying at a temperature of 50–100 °C.EFFECT: technical result of the invention is an increase in the surface area of the porous coating on titanium due to the formation of a hierarchical structure of the porous layer including micro- and nanosized pores, which increases the adhesion of the impregnating material in the preparation of composite coatings and the speed of integration of implants.3 cl, 3 ex, 2 dwg

Description

The invention relates to a method for modifying a titanium surface to obtain a structured porous layer containing nano- and micropores, and can be used in medical technology in the manufacture of bioprotective endoprostheses and implants for traumatology, orthopedics, plastic surgery, dental implants, for preparing the surface of titanium implants for applying bioactive coatings, as well as for the manufacture of catalyst supports and composite materials that are used in various Other technical areas.

From the standpoint of chemical and electrochemical biocompatibility, titanium is the most preferred metal for the manufacture of endoprostheses, orthopedic and other implants. Its modulus of elasticity, which characterizes the ability to absorb loads without breaking, is close to the modulus of elasticity of the bone. Titanium oxide as a bioinert material does not cause the formation of fibrous tissue, as a result of reparative osteogenesis occurs in direct contact with the surface of the implant, while the use of a porous surface provides effective biological fixation of prostheses in the bone by ingrowth. However, to enhance the reaction of bone formation, bioactive materials are required, characterized by the formation of a close chemical bond with bone. To ensure the best conditions for osseointegration, it is necessary to match the bone structure of not only the coating composition, but also the structure of the implant surface. For reliable technological fastening on the implant of a coating of biologically active material, it is necessary to create a porous surface of a certain type.

A known method of producing a multilayer porous coating on titanium (CN 104800887, publ. 2015.07.29), comprising applying titanium particles to the implant matrix, the subsequent formation of a porous coating by sintering in vacuum at a temperature below 1000 ° C. The gaps between the titanium particles on the surface of the implant communicate with micropores in the titanium particles of its matrix in such a way that an open pore system is formed, while the pore diameter of the porous system varies from 20 to 700 μm. The titanium-containing multilayer coating includes a highly porous titanium coating. The dimensions of the pore channel vary over a wide range, which favorably affects osteosynthesis and biological fixation. In addition, the adhesion between the coating and the matrix material is increased. Since the synthesis is carried out at a low temperature, the mechanical properties of the matrix material do not change. Known technology provides the possibility of strict quality control of the resulting coating and is suitable for large-scale production. Moreover, the disadvantages of the method include a relatively high energy consumption, as well as the need to use expensive equipment to maintain a high temperature of 1000 ° C and vacuum. In addition, from the description it is not entirely clear how and with what accuracy the pore size is controlled in such a wide range (20-700 microns).

A known method for producing titanium materials with gradient porosity by the method of electric spark plasma sintering, combining the effects of high temperature, axial pressure, low voltage and high current in the presence of an electromagnetic field (Fundamental research. 2014. No. 12, part 5. P. 947-951). PTS-1 grade titanium powder is mixed with chemically pure sodium chloride powder as a temporary pore filler, the mixture is sintered at a pressure of 10 MPa and the material is consolidated by electrospark plasma treatment at a temperature of 700 ° C. Then the temporary filler is removed by dissolving it in distilled water. The resulting material is characterized by a high proportion of pore space (up to 50%), optimal pore size (100-160 μm) and high mechanical and adhesive properties. In another embodiment of the method, in one step, the pre-prepared mixture of titanium powder and a temporary filler is baked onto a substrate of cast technically pure titanium grade VT1-0 in one step. A smooth porosity gradient of the obtained implant allows to reduce mechanical stresses and the likelihood of peeling of the porous layer from the titanium matrix. The main disadvantages of this method are associated with high energy consumption and high cost of equipment for creating high temperatures and pressures (SPS method). In addition, in the known method, the formation of "porous pores" is not ensured - a two-level micro- and nanoporous structure in the surface layer

A known method of obtaining a porous titanium coating (CN 101032633, publ. 2007.09.12), providing for cold spraying in vacuum by subsequent sintering, according to which first mixed titanium-magnesium powder is sprayed onto a relief base from titanium or its alloy, which is then sintered in high vacuum at high temperature. Thus obtained porous titanium coating, not containing oxide, has a thickness of more than 0.5 mm, exhibits a system of open and communicating pores with a size of 30-200 μm, a density of 30-65%, while its adhesion to the matrix is 60 MPa, and the module elasticity - 30-50 GPa. The method provides an increase in the strength and durability of implants bearing a large load, such as artificial joints, artificial bones, roots of artificial teeth, etc. Cold spraying while maintaining a vacuum, as well as subsequent sintering in high vacuum at high temperature, are complex energy-consuming operations that require the use of expensive equipment. In addition, the known method does not provide for the formation in the surface layer of titanium of a two-level micro- and nanoporous structure.

Closest to the claimed is a method of obtaining a porous coating on implants from titanium and its alloys (RU 2620428, publ. 2017.05.25), providing for laser surface treatment in argon at a radiation power of 400-500 W and a given speed of translational movement of the laser beam on the surface implant at a speed of 10-20 mm / s while simultaneously supplying to the irradiation zone a titanium carbide powder fraction providing a pore size of 1-5 μm, followed by etching of the surface layer containing grains of titanium carbide in titanium m atrica, in concentrated nitric acid for 3-7 days, washing off the acid and drying at a temperature of 50-100 ° C.

The porous coating obtained on the titanium endoprosthesis and implants obtained in a known manner does not sufficiently facilitate their rapid assimilation and integration, and if used as a carrier in the formation of composite coatings (for example, catalytic, bioactive, etc.), it does not provide sufficiently strong adhesion applied material with a porous coating due to the fact that the known method provides the formation of a coating with simple, and close in size, pores, without a pronounced hierarchy of pores in size.

The objective of the invention is to provide a method for producing a porous coating on titanium, the structure of which provides high adhesion to the impregnating material during the formation of composite coatings and the rapid integration of implants with such a coating.

The technical result of the invention is to increase the surface area of the porous coating on titanium due to the formation of a hierarchical structure of the porous layer, including micro- and nanoscale pores, which helps to increase the adhesion of the impregnating material in the preparation of composite coatings and increase the speed of implant integration.

The specified technical result is achieved by the method of obtaining a porous coating on titanium, providing for the treatment of its surface in argon by moving a laser beam along it with simultaneous feeding of titanium carbide powder into the irradiation zone, followed by acid etching by immersion in nitric acid for several days, washing and drying with at a temperature of 50-100 ° C, in which, in contrast to the known one, laser radiation with a power of not more than 300 W is used, the laser beam is moved along the surface at a speed of at least 20 mm / s, using a powder of titanium carbide fraction 80/100 microns.

Mainly use laser radiation with a power of 250-270 watts, and the laser beam is moved at a speed of 25-35 mm / s.

The method is as follows.

The correspondingly cleaned surface of a titanium product placed in an open container is exposed to a laser beam, translationally moving it along the surface to be processed at a speed of at least 20 mm / s, preferably 25-35 mm / s, while supplying titanium carbide powder fraction 80 / 100 μm into the irradiated zone, which is the melting zone of the titanium substrate, while it is continuously blown with argon. Thus, the whole process is carried out in an argon atmosphere, which, due to its large specific gravity, is prevented from rapidly evaporating into the atmosphere.

During laser processing, only the surface layer of a titanium matrix of a given thickness is melted (melting temperature of titanium is 1660 ° С) without melting of a carbide powder, in which the melting temperature is much higher (3100 ° С). As a result, a composite layer consisting of particles of titanium carbide in a titanium matrix is formed in the surface layer of the titanium alloy.

After etching the treated product in nitric acid for 3-5 days, as a result of which the titanium carbide is completely dissolved, and the titanium matrix, due to the passivation ability, remains unchanged, the product is washed from acid in distilled water and dried in air at 50- 100 ° C.

The resulting porous layer is shown in FIG. 1 and FIG. 2.

In FIG. Figure 1 shows the surface of titanium samples after laser processing with a TiC powder of 80/100 μm fraction and etching (a and b are images taken with an optical microscope at × 10 and × 40 magnification; c, d are images taken using a scanning electron microscope at magnification × 30 and × 150).

In FIG. Figure 2 shows the inner surface of micropores after laser treatment with a TiC powder of the 80/100 micron fraction and etching (a, c, e - “large” micropores with a size of 50-100 microns; b, d, e - “small” nanopores with a size of 200-500 nm ) at various magnifications.

When titanium carbide grains enter the titanium melt, carbon diffusion occurs between two phases: solid particles of titanium carbide TiC and molten titanium.

However, with the claimed processing parameters: limited laser irradiation power not exceeding 300 W and a high speed of the laser beam (at least 20 mm / s), firstly, a relatively low temperature of the modified surface layer is sufficient to melt titanium, but insufficient for the active diffusion of titanium carbide particles into the titanium matrix, and, secondly, a high heating and cooling rate and, accordingly, a high melting and crystallization rate of the local zone of the surface treated ti, whereby the diffusion processes and redistribution of the active carbon, which began at the interface of two phases - a melt titanium metal and solid titanium carbide, terminated quickly.

With increasing power and going beyond the claimed range, intense heating of the processed surface layer is observed, which can lead to intensive dissolution of titanium carbide in the titanium matrix.

With a decrease in the speed of movement of the laser beam, the duration of local maintenance of high temperature and active interaction of the two above-mentioned phases with redistribution of carbon increases.

In addition, the use of a relatively large fraction of titanium carbide powder (80/100 μm) with a relatively low surface energy of the particles also slows down the rate of diffusion and redistribution of carbon between the phases of titanium and titanium carbide in comparison with the processes using finely dispersed carbide powders titanium under the same processing conditions.

Thus, due to the above combination of parameters of the proposed method, the formation of a porous layer on titanium proceeds under conditions that impede the completion of the dissolution of titanium carbide and redistribution of carbon, and leads to the formation of a specific "nano-rough" interface between the particles of titanium carbide and the surrounding titanium matrix.

After etching of titanium carbide on the surface of the titanium product, a porous hierarchically structured (“two-level”) surface layer is obtained with a thickness of 200-300 μm with a predominant large pore size of 50-100 μm and 200-500 nm for second-level pores formed on the inner surface of large pores, as shown in FIG. 2.

Examples of specific implementation of the method

The surface of the samples was treated using a universal robotic complex for laser powder deposition, consisting of a KUKAKR 30-3NA robot, a KUKA KRC4 control system, a KUKADKP-400 positioner, and an LS-1-K ytterbium fiber laser with a continuous laser power of 100 to 1000 W (length waves λ = 1,070 μm). Processing parameters: the diameter of the laser beam on the treated surface was 0.6 mm, the step of the displacement of the laser beam between the passages was 0.5 mm, the distance from the nozzle plane to the processed object was 10 mm. The variable parameters were the laser radiation power and the linear velocity of the laser beam moving along the surface. Titanium samples were horizontally mounted in a special container open on top to hold argon.

A titanium carbide powder with a particle size of 80/100 microns was used.

The surface of the obtained coating was examined on a Hitachi S5500 high-resolution scanning electron microscope with a Thermo Scientific energy dispersion attachment, INCA 350 Energy on a ZeisEVO 40XVPc scanning electron microscope, and an optical microscope. The average micropore sizes and the thickness of the porous layer were estimated using the graphic options that the software packages for these devices are equipped with.

Example 1

Plates 40 × 20 × 2 mm in size made of technically pure titanium - VT1-0 alloy (%, Ti 98.6-99.7, Fe up to 0.18, C up to 0.07, Si up to 0.1) were processed in the atmosphere argon with a purge at a laser power of 250 W, moving the beam at a speed of 25 mm / s. Etching was carried out by immersion in concentrated (36.5%) nitric acid for 3 days. Samples were washed from acid in distilled water and dried in air at 50 ° C.

The thickness of the obtained porous coating is 200-250 microns. The micropore size is 80-100 microns, nanopores - 300-500 nm.

Example 2

Plates of size 40 × 20 × 2 mm made of technically pure titanium were processed under the conditions of Example 1 at a laser radiation power of 270 W, moving the laser beam at a speed of 30 mm / s. Etching, washing and drying was carried out analogously to example 1.

The thickness of the obtained porous coating is 250-300 microns. The micropore size is 70-100 microns, nanopores - 200-400 nm.

Example 3

Plates of technically pure titanium were processed in an argon atmosphere at a laser radiation power of 270 W, moving the beam at a speed of 30 mm / s. Etching in concentrated nitric acid was carried out for 5 days. After washing, the plates were dried in air at 100 ° C.

The thickness of the obtained porous coating 270-300 microns. The micropore size is 80-110 microns, the nanopore size is 150-500 nm

Claims (3)

1. A method of obtaining a structured porous coating on titanium, comprising treating a titanium surface in an argon medium by moving a laser beam along it while simultaneously supplying titanium carbide powder to the irradiation zone, subsequent acid etching by immersion in nitric acid for 3-5 days, washing and drying at a temperature of 50-100 ° C, characterized in that they use laser radiation with a power of not more than 300 W, the laser beam is moved on the surface at a speed of at least 20 mm / s, while using titanium carbide powder fractions of 80/100 microns. 2. The method according to claim 1, characterized in that they use laser radiation with a power of 250-270 watts. 3. The method according to claim 1, characterized in that the laser beam is moved along the surface at a speed of 25-35 mm / s.

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