Do you know the surfaceDo you know the surface

Do you know the surfaceDo you know the surface

Original title: Do you know the surface treatment of titanium and titanium alloy? Titanium is easy to react with O, H, N and other elements in the air and Si, Al, Mg and other elements in the investment at high temperature, and a surface contamination layer is formed on the surface of the casting, so that the excellent physical and chemical properties of the casting are deteriorated, the hardness is increased, the plasticity and elasticity are reduced, and the brittleness is increased. The density of titanium is small, so the inertia of titanium liquid flow is small, and the fluidity of molten titanium is poor, resulting in low casting flow rate. Due to the large temperature difference (300 ℃) between the casting temperature and the mold, the cooling is fast, and the casting is carried out in a protective atmosphere, it is inevitable that there are defects such as pores on the surface and inside of titanium castings, which have a great impact on the quality of castings. Therefore, the surface treatment of titanium casting is more important than other dental alloys. Because of the unique physical and chemical properties of titanium, such as small thermal conductivity, low surface hardness, low elastic modulus, high viscosity, low conductivity and easy oxidation, the surface treatment of titanium is very difficult, and it is difficult to achieve the desired effect by conventional surface treatment methods. Special processing methods and operation methods must be adopted. The later surface treatment of the casting is not only to obtain a smooth and bright surface, reduce the accumulation and adhesion of food and plaque, maintain the normal oral microecological balance of the patient, but also to increase the aesthetic feeling of the denture; More importantly, through these surface treatment and modification processes, the surface properties and suitability of castings are improved, and the physical and chemical properties of dentures, such as wear resistance, corrosion resistance and stress fatigue resistance, are improved. I. Removal of Surface Reaction Layer The surface reaction layer is the main factor affecting the physical and chemical properties of titanium castings. Before the grinding and polishing of titanium castings, the surface contamination layer must be completely removed to achieve satisfactory polishing effect. The surface reaction layer of titanium can be completely removed by the method of acid cleaning after sand blasting. 1. Sand blasting For the sandblasting treatment of titanium castings, it is generally better to use white corundum coarse blasting, and the sandblasting pressure is smaller than that of non-precious metals, which is generally controlled below 0.45Mpa. Because when the injection pressure is too high, the sand impacts the titanium surface to produce intense sparks, and the temperature rise can react with the titanium surface, forming secondary pollution and affecting the surface quality. The time is 15 to 30 seconds, and only the burnt-on sand, the surface sintering layer and part of the oxidation layer on the surface of the casting are removed. The rest of the surface reaction layer structure should be removed quickly by chemical pickling. 2. Pickling Pickling can quickly and completely remove the surface reaction layer without contamination of other elements on the surface. Both HF-HCl and HF-HNO3 pickling solutions can be used for titanium pickling, but HF-HCl pickling solution absorbs more hydrogen, while HF-HNO3 pickling solution absorbs less hydrogen, so the concentration of HNO3 can be controlled to reduce hydrogen absorption, and the surface can be brightened. Generally, the concentration of HF is about 3% ~ 5%. The suitable concentration of HNO3 is about 15% ~ 30%. Pickling surface titanium plate TA 1 pure titanium plate Expand the full text Sand-blasted titanium plate, pure titanium plate II. Treatment of casting defects Internal defects of internal pores and shrinkage cavities: They can be removed by iso-hot static pressing technology (hot isostatic pressing), but they will affect the accuracy of the denture. It is better to use X-ray flaw detection, grind the exposed pores on the surface, and use laser repair welding. The surface pore defect can be directly repaired by laser local welding. III. Grinding and polishing 1. Mechanical grinding: Titanium has high chemical reactivity, low thermal conductivity, high viscosity, titanium plate gr7 , low grinding ratio of mechanical grinding, and is easy to react with abrasive tools. Ordinary abrasives are not suitable for grinding and polishing of titanium. It is better to use superhard abrasives with good thermal conductivity, such as diamond, cubic boron nitride, etc. The polishing speed is generally 900 ~ 1800 m/min. It is appropriate ? Otherwise, the titanium surface is prone to grinding burns and micro-cracks. Titanium plate with grinding surface and polished surface Milling surface Milling surface Titanium plate Titanium alloy plate 2. Ultrasonic grinding: through the action of ultrasonic vibration, the abrasive particles between the grinding head and the ground surface produce relative motion with the ground surface to achieve the purpose of grinding and polishing. The advantage is that it is easy to grind grooves, pits and narrow parts which cannot be ground by conventional rotary tools, but the grinding effect of larger castings is not satisfactory. 3. Electrolytic mechanical compound grinding: a conductive grinding tool is used, electrolyte and voltage are applied between the grinding tool and the grinding surface, and the surface roughness is reduced and the surface gloss is improved under the combined action of mechanical and electrochemical polishing. The electrolyte is 0.9 NaCl, the voltage is 5V, and the rotation speed is 3000 rpm/min. This method can only grind flat surfaces, and the grinding of complex denture brackets is still in the research stage. 4. Barrel grinding: The centrifugal force generated by the revolution and rotation of the grinding barrel is used to make the denture in the barrel move relative to the abrasive to reduce the surface roughness. Grinding is automatic and efficient, but it can only reduce the surface roughness but not improve the surface gloss, and the precision of grinding is poor, so it can be used for deburring and rough grinding before fine polishing of denture. 5. Chemical polishing: Chemical polishing is to achieve the purpose of leveling and polishing through the oxidation-reduction reaction of metal in chemical medium. The method has the advantages that the chemical polishing has nothing to do with the hardness of the metal, the polishing area and the structural shape, all parts in contact with the polishing solution are polished, no special complex equipment is needed, the operation is simple and convenient, and the method is more suitable for polishing the titanium denture bracket with a complex structure. However, the process parameters of chemical polishing are difficult to control, and it is required to have a good polishing effect on denture without affecting the accuracy of denture. A better titanium chemical polishing solution is prepared from HF and HNO3 in a certain proportion, wherein HF is a reducing agent and can dissolve titanium metal to play a role in leveling, the concentration is less than 10%, and HNO3 plays a role in oxidation to prevent excessive dissolution and hydrogen absorption of titanium, and can also play a role in brightening. Titanium polishing solution requires high concentration, low temperature and short polishing time (1 ~ 2 min.). 6. Electrolytic polishing: It is also called electrochemical polishing or anodic dissolution polishing. Due to the low conductivity and strong oxidation performance of titanium, it is almost impossible to polish titanium with aqueous acidic electrolytes such as HF-H3PO4 and HF-H2so. After external voltage is applied, the titanium anode is oxidized immediately, so that anodic dissolution cannot be carried out. However, the use of anhydrous chloride electrolyte at low voltage has a good polishing effect on titanium, and small specimens can be mirror-polished, but for complex restorations, it can not achieve the purpose of complete polishing. Perhaps the method of changing the shape of the cathode and adding a cathode can solve this problem, which needs further study. IV. Surface Modification of Titanium 1. Nitriding: a golden yellow TiN coating was formed on the surface of titanium denture by chemical heat treatment techniques 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. However, the technology is complex and the equipment is expensive, so it is difficult to achieve clinical application for surface modification of titanium denture. 2. Anodizing: The anodizing technology of titanium is relatively easy. In some oxidizing media, under the action of applied voltage, the titanium anode can form a thicker oxide film, thereby improving its corrosion resistance, wear resistance and weather resistance. H2SO4, H3PO4 and organic acid aqueous solution are generally used as the electrolyte for anodizing. Titanium anodizing and coloring 3. Atmospheric oxidation: Titanium can form a thick and firm water-free oxide film in high temperature atmosphere, which is effective for general corrosion and interstitial corrosion of titanium, and the method is relatively simple. 5. Coloring In order to increase the aesthetic feeling of the titanium denture and prevent the titanium denture from being continuously oxidized and discolored under natural conditions, surface nitriding treatment, atmospheric oxidation and anodic oxidation surface coloring treatment can be adopted to form light yellow or golden yellow on the surface so as to improve the aesthetic feeling of the titanium prosthesis. The anodizing method makes use of the interference effect of the titanium oxide film on the light to naturally generate colors, and can form colorful colors on the titanium surface by changing the bath voltage. VI. Other surface treatments 1: Surface roughening: In order to improve the bonding performance between titanium and decorative resin, the surface of titanium must be roughened to increase its bonding area. The Surface of titanium is usually roughened by sandblasting in clinic, but the sandblasting will pollute the aluminum oxide on the surface of titanium. We use the oxalic acid etching method to get a good roughening effect, the surface roughness (Ra) can reach 1.50 ± 0.30 μm after etching for 1 H, and the Ra is 2.99 ± 0.57 It is more than twice the Ra (1.42 ± 0.14 μm) of sand blasting alone, and its bond strength is improved by 30%. 2. Surface treatment for high temperature oxidation resistance: In order to prevent the rapid oxidation of titanium at high temperature,ti6al4v, 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 kind of surface treatment is very effective for the oxidation of titanium at high temperature. Perhaps the coating of this kind of compound on the surface of titanium is beneficial to the combination of titanium and porcelain, and further research is needed. More Titanium and Titanium Alloy Surface Treatment Titanium Plate Titanium Anodizing Please Pay Attention to Ruida Titanium Industry Return to Sohu to See More Responsible Editor:. yunchtitanium.com


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