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Shanxi AoYuDa New Materials Co., Ltd

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Relying on the unique technology and resources of BaoTi group and northwest non-ferrous metals research institute, the company specializes in the production and sales of titanium and titanium alloy series, tantalum niobium series, zirconium series, nickel series and other metal materials, accessories and equipment.

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The company has a complete set of quality assurance system from raw materials to manufacturing, process testing, finished product inspection and after-sales service, which strictly guarantees the quality of products.

Surface treatment technology of titanium

Titanium is easy to react with O, h, N and Si, Al, Mg in the air at high temperature. The surface pollution layer is formed on the surface of the casting, which makes its excellent physical and chemical properties worse, hardness increases, plasticity and elasticity decrease, and brittleness increases.

The density of titanium is small, so the inertia of liquid titanium is small, and the fluidity of molten titanium is poor, which leads to low casting flow rate. The temperature difference between casting and mold is large (300 ℃), and the cooling is fast. The casting is carried out in protective atmosphere. The surface and interior of titanium castings are inevitably with porosity and other defects, which have a great influence on the quality of castings.  

Therefore, the surface treatment of titanium castings is more important than other dental alloys. Because of its unique physical and chemical properties, such as small thermal conductivity, low surface hardness, low elastic modulus, high viscosity, low conductivity and easy oxidation, it is very difficult to surface treatment of titanium, and it is difficult to achieve ideal results by conventional surface treatment methods. Special processing methods and operation methods must be adopted.

The later surface treatment of castings is not only to obtain smooth and bright surface, reduce the accumulation and adhesion of food and plaque, maintain the normal balance of oral microecology of patients, but also increase the aesthetic feeling of dentures. More importantly, through these surface treatment and modification process, the surface properties and suitability of castings are improved, and the wear resistance, corrosion resistance and stress fatigue of dentures can be improved Physical and chemical properties of labor.  

1、 Removal of surface reaction layer

The surface reaction layer is the main factor affecting the physical and chemical properties of titanium castings. Before the titanium castings are polished, the surface contamination layer must be completely removed before the titanium castings are polished to achieve satisfactory polishing effect. The surface reaction layer of titanium can be completely removed by acid washing after sand blasting.  

1. sand blasting: generally, the white corundum is used for the sand blasting of titanium castings, and the pressure of sand blasting is smaller than that of non precious metals, and generally controlled below 0.45MPa. Because, when the spray pressure is too high, the sand particles impact the titanium surface to produce intense sparks, and the temperature rise can react with the titanium surface, forming secondary pollution, which affects the surface quality. The time is 15-30 seconds, only the sand, sintering layer and part and oxide layer on the surface of casting can be removed. The other surface reaction layer structure should be removed by chemical pickling.  

2. pickling: pickling can quickly and completely remove the surface reaction layer, and the surface will not produce other elements pollution. HF HCl and HF HNO3 acid solutions can be used for acid washing of titanium. However, HF HCl acid solution has a large amount of hydrogen absorption, while HF HNO3 acid solution has a small amount of hydrogen absorption, which can control the concentration of HNO3 to reduce hydrogen absorption and can be treated with light treatment. Generally, the concentration of HF is about 3% - 5%, and the concentration of HNO3 is about 15% - 30%.  

2、 Treatment of casting defects

Internal porosity and shrinkage hole internal defects: hot isostatic pressing can be removed, but it will affect the accuracy of denture. It is better to wear the exposed pores and repair welding with laser after X-ray inspection. The surface porosity defects can be repaired by laser local welding directly.  

3、 Grinding and polishing

1. mechanical grinding: Titanium has high chemical reactivity, low thermal conductivity, high viscosity, low mechanical grinding grinding ratio, and easy to react with abrasive grinding tools. Ordinary abrasives are not suitable for grinding and polishing titanium. It is better to use super hard abrasive with good thermal conductivity, such as diamond and cubic boron nitride. The polishing line speed is generally 900-1800m / min. otherwise, the surface of titanium is easy to be burnt and microcracked.  

2. ultrasonic grinding: by ultrasonic vibration, the grinding particles between the grinding head and the ground surface can move relatively with the ground surface to achieve the purpose of grinding and polishing. The advantages of the method are that the groove, nest and narrow parts which can not be ground by conventional rotary tools are easy, but the larger grinding effect of casting is not satisfactory.  

3. electrolytic mechanical compound grinding: conductive grinding tool is adopted to apply electrolyte and voltage between grinding tool and grinding surface. Under the joint action of mechanical and electrochemical polishing, the surface roughness can be reduced and surface gloss can be improved. The electrolyte is 0.9nacl, voltage is 5V, and the speed is 3000rpm/min. this method can only grind plane, and the grinding of complex denture support is still in the research stage.  

4. barrel grinding: the centrifugal force produced by the rotation and rotation of the grinding barrel is used to reduce the surface roughness by making the denture and abrasive in the barrel move relative to friction. The grinding automation and efficiency are high, but can only reduce the surface roughness, but can not improve the surface gloss. The grinding precision is poor, which can be used for deburring and rough grinding before the fine polishing of denture.  

5. chemical polishing: chemical polishing is to achieve the purpose of leveling and polishing by oxidation-reduction reaction of metal in chemical medium. The advantages of the method are that chemical polishing is independent of metal hardness, polishing area and structure shape. All parts contacting polishing fluid are polished, without special complicated equipment, easy operation and suitable for polishing of complex titanium denture bracket. But the process parameters of chemical polishing are difficult to control, so it is required that the denture can be polished well without affecting the precision of denture. The better titanium chemical polishing solution is HF and HNO3 are prepared in a certain proportion. HF is a reducing agent, which can dissolve titanium metal and play a leveling role. The concentration is less than 10%. HNO3 plays an oxidation role, preventing the excessive dissolution and hydrogen absorption of titanium, and can also produce bright effect. Titanium polishing solution requires high concentration, low temperature and short polishing time (1-2min).  

6. electrolytic polishing: also known as electrochemical polishing or anode dissolution polishing. Because of the low conductivity of titanium and strong oxidation performance, the aqueous acid electrolyte such as hf-h3po4 and hf-h2so electrolyte can hardly be polished. After applying external voltage, the titanium anode will be oxygen free, which makes the anode dissolution impossible. However, the use of anhydrous chloride electrolyte has good polishing effect on titanium at low voltage. The mirror surface polishing can be obtained for small specimens. However, for complex restoration, the purpose of complete polishing can not be achieved. It is still necessary to further study that the method of changing the shape of cathode and adding cathode can solve this problem.  

4、 Surface modification of titanium

1. nitriding: the surface of titanium denture is formed by chemical heat treatment technologies such as plasma nitriding, multi arc ion plating, ion implantation and laser nitriding, so as to improve the wear resistance, corrosion resistance and fatigue resistance of titanium. But the technology is complex and the equipment is expensive, so it is difficult to achieve clinical application for the surface modification of titanium denture.  

2. anodizing: the anodizing technology of titanium is relatively easy. In some oxidizing medium and under the action of applied voltage, titanium anode can form thick oxide film, thus improving its corrosion resistance, wear resistance and weather resistance. Generally, the electrolyte of anodizing is H2SO4, H3PO4 and organic acid aqueous solution.

3. atmospheric oxidation: titanium can form a thick and strong anhydrous oxide film in high temperature atmosphere. It is effective for titanium corrosion and clearance corrosion. The method is simple and convenient.  

5、 Coloring

In order to increase the aesthetic feeling of titanium denture and prevent the color change of titanium denture under natural conditions, surface nitriding treatment, atmospheric oxidation and anodizing method can be used to make the surface form pale yellow or golden yellow, and improve the aesthetic feeling of titanium denture. Anodizing method uses the interference of titanium oxide film on light and naturally colors. It can form colorful color on titanium surface by changing the groove voltage.  

6、 Other surface treatment

1: Surface coarsening: in order to improve the bonding performance between titanium and the finishing resin, the surface of titanium must be roughened to improve its bonding area. In clinical practice, sandblasting is often used, but sandblasting can cause the pollution of alumina on titanium surface. We use oxalic acid etching method to obtain good coarsening effect. The surface roughness (RA) can reach 1.50 ± 0.30 μ m after etching for 1h, 2.99 ± 0.57 μ m for 2h etching, more than one time higher than that of RA (1.42 ± 0.14 μ m) of sand spraying alone, and the bonding strength is improved by 30%.  

2: Surface treatment of high temperature oxidation resistance: in order to prevent the rapid oxidation of titanium at high temperature, titanium silicon compounds and titanium aluminum compounds are formed on the surface of titanium, which can prevent the oxidation of titanium at temperatures above 700 ℃. This surface treatment is very effective for titanium oxidation at high temperature. Maybe coating the compound on titanium surface is beneficial to the bonding of titanium ceramics, so further research is needed.