CN1312402A

CN1312402A - Technological process of electrophoretic coprecipitation-sintering to prepare gradient metal/biological glass ceramic coating

Info

Publication number: CN1312402A
Application number: CN 01106418
Authority: CN
Inventors: 陈晓明; 韩庆荣; 李世普
Original assignee: Wuhan University of Technology WUT
Current assignee: Wuhan University of Science and Engineering WUSE; Wuhan University of Technology WUT
Priority date: 2001-01-09
Filing date: 2001-01-09
Publication date: 2001-09-12
Anticipated expiration: 2021-01-09
Also published as: CN1133759C

Abstract

The present invention makes biological glass (BG) granules and hydroxyapatite (HA) granules possess identical charged characteristics is the selected proper dispersion medium so as to implement codeposition of BG powder material and HA powder material on the matrix as electrode, at the same time continuously changes the composition of electrophoretic liquor to make the component of coating layer produce gradient change. Because the deposition condition of said coating layer is related to the electric field intensity between two electrodes, it utilizes the continuous change of deposition voltage so as to obtain a coating layer with a certain pore structure gradient, and said coating layer is subjected to sintering treatment so as to obtain the metal/biological glass ceramic gradient coating layer with excellent binding strength.

Description

Technology for preparing metal/biological glass ceramic gradient coating by electrophoretic codeposition-sintering method

The invention relates to a series of gradient coating composite materials such as metal/bioactive glass/hydroxyapatite and the like prepared on the surfaces of various metals with complex shapes and a preparation method thereof.

The ceramic coating is prepared on a substrate (particularly a metal substrate) with excellent mechanical properties, so that the comprehensive advantages of the substrate material and the ceramic material are exerted, and the attention is attracted more and more. In order to obtain a coating composite with excellent properties, it is necessary to design the coating to have a certain composition and structural gradient. In order to achieve these goals, in recent years, many methods have been developed at home and abroad to solve the coating problem. Such as: self-propagating high-temperature synthesis technology (SHS), laser cladding method, Sol-Gel (Sol-Gel) method and the like, but the methods have the problems of high cost, complex process and the like. At present, the plasma spraying process is applied more and more mature, the method is a linear process, the temperature is very high in the spraying process, the application and the coating performance are greatly influenced, and in addition, the coating cannot be realized on a complex surface.

The invention aims to provide a nonlinear coating process, which can prepare a uniform coating on a substrate with a complex shape and a porous surface, and has the advantages of low cost and simple process; can be produced continuously and operated intermittently; the feed liquid can be recycled, and no pollutant is discharged; it is suitable for large-scale production, and is an electrophoretic codeposition-sintering method.

Electrophoretic deposition (EPD) refers to the integration of two processes, electrophoresis and deposition. Electrophoresis refers to the phenomenon that colloidal particles move directionally in a dispersion medium under the action of an external electric field; sedimentation refers to the agglomeration of particles into a denser mass. In fact, the electrophoretic fluid does not necessarily need to be colloidal, and all colloidal suspension dispersions consisting of suitably treated particles having a particle size of less than 10 μm are suitable for electrophoretic deposition by the apparatus of the present study. In the case of colloidal suspension dispersions, the properties exhibited are similar to those of colloidal dispersions in that the particles have an electric double layer structure and are charged with a galvanic potential and, therefore, are capable of directional movement under the action of an electric field, and when they move to the vicinity of the substrate serving as an electrode, the electric double layer is compressed due to an increase in the electrolyte concentration or the strong electric field, with the result that the Zeta potential of the particles in the vicinity of the electrode is lowered, thereby causing the particles to flocculate. At this time, the distance between the particles is small, and London-Van der Waals attraction between the particles is dominant, thereby forming a close-packed coating on the substrate. The surface of the coating raw material particles is subjected to coordinated modification treatment, so that the coating raw material particles can be charged with the same kind of charges, and the particles with different components can be sequentially deposited or co-deposited on the substrate by adjusting the deposition voltage according to the sensitivity of the coating raw material particles to an electric field, so that a coating green body with the composition and the pore structure in gradient change is obtained. The coating prepared by electrophoretic deposition is only a compact and packed blank, the bonding strength of the coating and the substrate is very low, the bonding of the coating and the substrate can be enhanced through sintering, and simultaneously, the blank is also densified. The gradient coating has no obvious interface, so that the thermal stress is relieved, and the bonding strength and the stability of the coating are improved. This is not comparable to other coating processes in combination with heat treatment.

The present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a process flow diagram of the present invention;

FIG. 2 is a schematic view of an electrophoretic co-deposition apparatus according to the present invention.

(1) -a direct current power supply (pulsed); (2) -a voltmeter; (3) -an ammeter; (4) -a cathode; (5) -an anode; (6) -a liquid charger; (7) -an electrophoresis tank; (8) -a constant flow pump; (9) -an adjustment groove; (10) magnetic stirrers (with heating).

The invention is further explained in detail with reference to fig. 2.

Firstly, optimally designing the composition and the structure of a coating according to the performance requirement of a coating composite material to be manufactured; then preparing coating powder, screening a dispersion medium, and carrying out surface modification on the coating powder by combining the analysis of the charging characteristics of the coating powder in the dispersion medium. The preparation method mainly takes Bioactive Glass (BG) particles and HA particles as coating raw materials, realizes codeposition on a substrate (metal) as an electrode, determines process parameters (including a deposition electric field, suspension concentration, component regulation and stirring state) according to the deposition condition of the coating raw materials, and then carries out electrophoretic codeposition. The electrophoretic deposition device can well realize the preparation of the gradient functional ceramic coating. The specific process is that the slurry flows from bottom to top in the electrophoresis tank under the action of the constant flow pump and the overflow, so that the functions of well stirring, controlling the temperature of the electrophoresis liquid and adjusting the components of the electrophoresis liquid are achieved, and the continuous change of the components in the electrophoresis tank can be ensured.

According to the gradient design condition of the coating, a colloidal suspension dispersion system prepared from a coating raw material (BG) with a dominant inner layer is directly added into an adjusting tank, a colloidal suspension dispersion system of other coating raw materials is added from a liquid adding device, and the components of the electrophoretic plating solution can be continuously changed and the gradient coating can be realized according to the preset design by controlling the adding speed of the colloidal suspension dispersion system.

And finally, sintering the coating according to a determined temperature system (sintering in a large atmosphere, atmosphere protection sintering and vacuum sintering can be selected according to requirements) to strengthen the combination of the coating and the substrate.

The invention successfully develops the Ti6A14V/BG/HA bioactive glass-ceramic gradient coating composite material by adopting an electrophoresis codeposition process, and the bonding strength of the coating and a matrix can reach more than 20 MPa. The main technical process is as follows: 1. design of the coating

Firstly, a Na with a lower melting point and a thermal expansion coefficient similar to that of Ti6A14V is developed₂O-CaO-SiO₂-P₂O₅The system Bioactive Glass (BG) is used as a high-temperature adhesive between Ti6A14V and Hydroxyapatite (HA), and the internal stress of the coating is reduced and the bonding strength of the coating is improved through the gradient distribution of BG and HA in the coating. Secondly, BG particles "encapsulated" by HA are prepared by inducing crystallization of HA on the surface of BG, and BG is changedThe charged nature of the particle surface, achieved co-deposition of BG and HA on Ti6a14V as an electrode to obtain a gradient coating. 2. Preparationof coating raw materials

Melting developed biological glass, pulverizing with water and gas flow, preparing BG powder of below 3 μ M in anhydrous ethanol by gravity settling classification, and dispersing in 0.005M Ca (NO)₃)₂To the suspension was added dropwise 0.003M (NH)₄)₂HPO₄And NH₄OH, temperature controlled at 40-50 ℃, pH =11-12, and with constant stirring, the following reaction takes place:

after 6 hours of reaction, the solution was allowed to stand for one week, the surface floaters were removed, and then filtered and washed with distilled water. And (4) drying, adding absolute ethyl alcohol, and performing ball milling to obtain colloidal suspension with known slurry concentration.

The hydroxyapatite is prepared by a double decomposition reaction method: 0.03M of (NH)₄)₂HPO₄Dropwise adding to 0.05M Ca (NO)₃)₂While stirring, keeping pH =11-12 and T =65 deg.C, reacting for 8h, standing the mother solution for 10 days, removing surface floating matter, filtering, washing with distilled water, drying in vacuum drier, adding absolute ethanol, and ball milling to obtain colloidal suspension with known slurry concentration. 3. Electrophoretic co-deposition

Ultrasonically dispersing prepared BG suspension and HA suspension for half an hour, respectively adding into an adjusting tank and a liquid adding device, and opening a magnetic stirrer and a constant flow pump; with Ti6A14V through 1500# SiC metallographical sand paper polishing, pickling, acetone ultrasonic cleaning, heavy distillation water washing, after the drying as the negative pole, Pt is the positive pole, 1cm of dipolar interval, and deposition voltage is 30V, treat that deposit 30s back, add HA suspension to the adjustment tank through separating funnel, adjust dropwise add speed, make the volume of the HA suspension that adds in the adjustment tank in whole deposition process can be equivalent with the volume of the BG suspension that adds originally. And co-depositing for 1-7min, and taking out the sample and drying in a dryer after the deposition is finished. 4. Sintering treatment

And (3) placing the dried coating sample in a tubular furnace, and sintering under the protection of argon atmosphere at the treatment temperature of 850-1000 ℃, keeping the temperature for 1h, wherein the heating rate is less than 3 ℃/min, and the cooling rate is less than 2 ℃/min. 5. Results

The expansion coefficient of the glass melted by the prepared HA modified BG powder is matched with that of Ti6A14V, the glass is an ideal coating high-temperature bonding material, the glass and HA are used as raw materials, electrophoretic deposition is adopted, the co-deposition of BG and HA can be realized, and a Ti6A14V/BG/AH gradient coating can be obtained by sintering. The adopted process parameters are as follows: the deposition voltage is 30V, the deposition time is 5min, after the coating is sintered (heat preservation is carried out for 1h) at 925 ℃ under the protection of argon atmosphere, the coating with the optimal thickness of about 50 mu m can be obtained, and the bonding strength of the coating and the substrate can reach more than 20 MPa; the cross section of the coating is observed and analyzed by an electron microscope, and the coating is proved to be a gradient coating in a strict sense.

Claims

1. The technology for preparing the metal/biological glass ceramic gradient coating by the electrophoresis codeposition-sintering method is characterized by comprising the following steps: firstly, modifying coating powder to enable all coating raw materials to realize codeposition on a substrate (metal, such as titanium alloy and the like) serving as an electrode; the gradient bioceramic coating with high bonding strength is obtained by continuously changing the concentration of different components in a coating colloid suspension dispersion system, preparing a gradient coating through electrophoretic codeposition and sintering.

2. The electrophoretic codeposition-sintering process for preparing metal/bioglass ceramic gradient coating according to claim, wherein Bioactive Glass (BG) particles are selected as high temperature binder for coating raw materials, and BG and HA particles are in gradient change in the coating.