The surface treatment and application of titanium metal can be summarized from three aspects:
1. Artisan surface treatment
Titanium is used in building materials such as roofs and outer walls of Daxia, as well as decorations such as eyes, watches and pendants. These uses utilize the excellent corrosion resistance of titanium, but also require bright, glossy and fashionable surfaces. Sense and other craftsmanship processing.
(1) Surface finishing
1. Grinding
2. Annealing and pickling - tarnished/grey surface
3. Vacuum annealing + pickling --- glossy/dark grey surface
4. Shot peening (50-500um glass (1018, 0.00, 0.00%) beads) ---- surface showing plow skin
5. Dense stripe processing: 150-240# abrasive belt grinding to make it have long and continuous grinding stripes.
6. Pattern embossing processing (concave-convex processing) -- embossed pattern with concave and convex on the processing surface. (The method of embossing by chemical etching or mechanical engraving.
7. Chemical etching---pattern
(2) Mirror finishing - Titanium is a difficult material for mirror finishing.
1. Soft belt polishing: hardened layer on the machined surface, low efficiency, liquid: alumina + water + KOH, polyurethane belt
2. Chemical polishing: Influencing factors: temperature, time and polishing liquid.
3. Electropolishing: Anhydrous organic electrolyte has better electropolishing effect on titanium.
(3) Coloring
Titanium surface is originally silver-white, in order to improve its ingenuity, it can be colored, that is, colored stainless steel. Its main colors are green bronze, red bronze, sapphire blue, wine red, coffee red, titanium gold, emerald green, black gold, rose gold and so on.
1. Atmospheric oxidation method: It is a method of heating in the atmosphere in an electric furnace, etc., the reflected light of the oxide film formed on the surface of the titanium and the reflected light passing through the inside of the oxide film and reflected at the interface between the oxide film and the titanium interfere with light to develop color. . Low cost, poor coloring uniformity and reproducibility, not suitable for decoration.
Chroma: Time: 5min. 300℃ unchanged
350℃ metallic color 550 purple 750 red purple
Yellowish 600 Blue Violet 800 Glossy Gray
Light yellow 650 sky blue 850 bright gray
500 light brown 700 yellow green
2. Anodizing method
It is the process of forming an oxide film on the metal surface by electrolysis. The affinity of titanium and oxygen is high, and various color film layers can be obtained with the change of process conditions during electrolysis in a specific electrolyte. Anodizing coloring is also called electrolytic coloring. When titanium is anodic electrolyzed in an oxygen-containing medium, an oxidation reaction occurs at the anode, and titanium and oxygen combine to form an oxide film of titanium. The principle of titanium anodic oxidation coloring is that the reflected light on the surface of the oxide film and the internal reflected light at the oxide film-titanium interface cause light interference to develop color. The anodic oxidation coloring of titanium is voltage-dependent. When electrolyzed at different voltages, oxide films with different thicknesses can be formed, which show different colors due to the interference of light. Titanium oxide film has high strength, good chemical stability, bright color, uniform color, simple process, low cost, and high decoration and use value. It has been used in the industry for the coloring of building decoration materials and various handicrafts.
In order to improve the aesthetics of dental prostheses, American scholar Wang (1995) conducted a preliminary study on the anodizing coloration of titanium. In 0.1M H2SO4 electrolyte, under the electrolysis voltages of 10v, 15v and 25v, the titanium surface showed golden yellow, light blue and blue hue changes, respectively. The same golden yellow appearance was obtained by tinting tests on 3 units of titanium fixed bridges at 10v. It is considered that anodizing coloring method can be used for coloring the surface of titanium dentures. Its coloring process and corrosiveness and color stability in oral environment need to be further studied.
3. Nitriding method (CVD\PVD\PCVD\ion implantation method) (titanium nitride is golden yellow).
Using modern surface modification and chemical heat treatment technologies such as glow discharge plasma nitriding, physical chemical vapor deposition, multi-arc ion plating, nitrogen ion implantation and laser beam nitriding, a layer of golden yellow TiN structure can be formed on the titanium surface. So as to achieve the purpose of surface modification and strengthening. After the titanium denture parts are nitrided, the surface is golden yellow nitride layer, which can improve the aesthetic effect of the denture, and improve the physical and chemical properties of the denture, such as wear resistance and corrosion resistance, but the technology is complex, the equipment is expensive, and the processing cost of the titanium denture will also be reduced. Higher, surface nitriding treatment is used for the coloring and modification of titanium dentures. At present, it is still difficult to achieve clinical practical application.
2. Corrosion-resistant surface treatment
Due to the excellent corrosion resistance of titanium itself, surface treatment to further improve its corrosion resistance is generally not carried out. In crevice corrosion and pitting corrosion, surface treatment is sometimes used.
Atmospheric oxidation treatment: Titanium is protected in high temperature atmosphere, which makes the oxide film thicker, and its film thickness increases with the increase of temperature and the extension of time. Atmospheric oxidation treatment is effective for overall corrosion and crevice corrosion of titanium. The method is relatively simple, but the durability is not very reliable. This is because atmospheric oxidation treatment only thickens the oxide film. In a corrosive environment, pure titanium will thicken the oxide film. Thinning over time, eventually leading to corrosion. The time for which its corrosion resistance is maintained is determined by the atmospheric oxidation treatment conditions (T, t) and the severity of the corrosive environment. It is difficult to predict this time. Component materials that require long-term stable operation generally do not use this method.
Precious metal coating: The corrosion resistance of titanium is maintained by the oxide film formed on the surface. The formation reaction of this oxide film is generally expressed by the following formula:
Ti +2H2O jujube→TiO2 +4H+ +4e?/P> This reaction is an anodic reaction, so as long as the potential of titanium is increased, the reaction can proceed further to the right, which means the stability and resistance of the titanium oxide film. Corrosive enhancement. However, to increase the potential of titanium, it is necessary to apply a high voltage from the outside, and at the same time, it is difficult to apply a uniform voltage when the area is large, so it is not often used. Generally, precious metals do not corrode in harsh environments and exhibit high potential. Taking advantage of this, the titanium surface is coated with noble metal, and the potential of titanium is moved to the more expensive side (the direction of the higher potential), thereby improving its corrosion resistance.
Titanium is usually coated with less expensive Pd, Ru or their oxides (PdO, RuO2) among noble metals.
Coating noble metals or their oxides on titanium is very effective in improving its corrosion resistance, and the corrosion resistance of the coated materials can be comparable to that of Ti?/FONT>0.15Pd alloys. The disadvantage is that during prolonged use in fluids or fluids containing solids, the precious metal film will peel off the titanium surface, although this peeling is rare. At present, Japan is developing a coating method with good density and property, but the cost is higher.
Dry process coating TiC, TiN film (CVD, PVD, PCVD):
TiC, TiN and TiCN have better corrosion resistance than titanium, the methods are gas method, CVD, PVD, PCVD
The gas method must be heated at a temperature much higher than the phase transition point of titanium, so that the structure and shape of the product cannot meet the requirements of use; while the CVD, PVD, and PCVD methods require special equipment and large-scale equipment that can be mass-produced is being developed. medium, high cost. (These treatment methods are rarely used to improve corrosion resistance, but are sometimes used to improve wear resistance. Pb+, Pt+ implantation method (ion beam, electron beam)
Surface modification by ion implantation is very effective in improving corrosion resistance, but the cost is higher.
3. Wear-resistant surface treatment
The disadvantage of titanium is that it has poor wear resistance, and the surface is prone to pitting and other defects. At present, it is difficult to apply to sliding mechanical parts. At present, various surface treatment methods are being actively researched and developed. The methods suitable for titanium surface treatment include wet coating method represented by Cr and Ni, thermal diffusion method, surfacing method and sputtering method, etc. Recently, the more advanced methods are CVD, PVD, PCVD surface strengthening method.
1. Wet coating:
Mainly use Cr plating, Ni-P method, (it is difficult to plate Cr directly on titanium, usually Ni is first plated on the titanium substrate, and then Cr is plated. The electrolytic method has a fast film formation speed and a thickness of several microns, (the decorative coating is only 1um). It is an effective wear-resistant surface treatment method.
2. Thermal diffusion method:
Thermal diffusion processes such as carburizing, nitriding, and boronizing, which are widely used for hardening of steel materials, have also been used recently for titanium. The main introduction is that the ion nitriding method is different from gas nitriding. It uses glow discharge plasma to destroy the oxide film on the titanium surface. Therefore, the pre-nitridation treatment does not require mechanical grinding and pickling to remove the oxide film, and the nitriding efficiency is high. Titanium at 850 degrees, the nitride film thickness increases from 0.7um to 5.0um, the surface hardness reaches 1200-1600Hv, and has good film resistance.
3. Surfacing method:
Titanium surface surfacing hardening modification by plasma transfer arc also has excellent wear resistance. The method is simple, and the treated material does not need to be exposed to the entire high temperature, which can prevent the decline of mechanical properties. But secondary processing is required. It is only suitable for handling thicker large workpieces.
4. Sputtering method:
The method of spraying the dripping molten metal on the surface of the material to be treated by using the high-speed air jet of plasma flow can be processed in the atmosphere without vacuum, and the production efficiency is high. But the adhesion of the coating is not enough.
5. CVD, PCD, PCVD method
6. Ion Implantation
