The density of titanium alloy is small, so the inertia of titanium liquid is small when flowing, and the poor fluidity of molten titanium leads to low casting flow rate. The temperature difference between the casting temperature and the casting mold (300℃) is large, the cooling is fast, and the casting is carried out in a protective atmosphere. The surface and interior of the titanium casting inevitably have defects such as pores, which have a great impact on the quality of the titanium casting. The following describes titanium alloy forgings surface treatment method.
1. Removal of the surface reaction layer
The surface reaction layer is the main factor affecting the physical and chemical properties of the titanium casting. Before the titanium casting is ground and polished, the surface contamination layer must be completely removed in order to achieve a satisfactory polishing effect. The surface reaction layer of titanium can be completely removed by pickling after sandblasting.
Surface treatment method of titanium alloy forgings
1. Sandblasting: The sandblasting treatment of titanium castings is generally better to use white corundum for rough blasting, and the pressure of sandblasting is smaller than that of non-precious metals, generally controlled below 0.45Mpa. Because, when the injection pressure is too large, the sand particles impact the titanium surface to generate intense sparks, and the temperature rise can react with the titanium surface, resulting in secondary pollution and affecting the surface quality. The time is 15 to 30 seconds, only to remove the sticky sand, surface sintered layer and part of the oxide layer on the surface of the casting. The rest of the surface reaction layer structure should be quickly removed by chemical pickling.
2. Pickling: Pickling can quickly and completely remove the surface reaction layer, and the surface will not be polluted by other elements. Both HF-HCl series and HF-HNO3 series pickling solutions can be used for titanium pickling, but HF-HCl series pickling solution has a large hydrogen absorption capacity, while HF-HNO3 series acid washing solution has a small hydrogen absorption capacity, which can control HNO3 The concentration of HF can reduce the absorption of hydrogen, and the surface can be brightly treated. Generally, the concentration of HF is about 3%~5%, and the concentration of HNO3 is about 15%~30%.
2. Treatment of casting defects
Internal pores and shrinkage holes Internal defects: can be removed by hot isostatic pressing, but it will affect the accuracy of dentures. It is best to use X-ray inspection to remove exposed pores on the surface and use laser repair welding. Surface porosity defects can be directly repaired by laser local welding.
3. Grinding and polishing
1. Mechanical grinding: Grade 2 Titanium Round Bar has high chemical reactivity, low thermal conductivity, high viscosity, low mechanical grinding and grinding ratio, and is easy to react with abrasives. Ordinary abrasives are not suitable for grinding and polishing titanium. It is better to use good thermal conductivity. For superhard abrasives, such as diamond, cubic boron nitride, etc., the polishing line speed is generally 900~1800m/min.
2. Chemical polishing: Chemical polishing is the purpose of leveling and polishing through the redox reaction of metal in chemical medium. The advantage is that chemical polishing has nothing to do with the hardness of the metal, the polishing area and the structural shape, and all the parts in contact with the polishing liquid are polished, no special complex equipment is required, the operation is simple, and it is more suitable for the polishing of complex structure titanium denture brackets. However, the process parameters of chemical polishing are difficult to control, and it is required to have a good polishing effect on the denture without affecting the accuracy of the denture.
4. Coloring
In order to increase the beauty of titanium dentures and prevent the discoloration of titanium dentures from continued oxidation under natural conditions, surface nitriding treatment, atmospheric oxidation and anodizing surface coloring treatment can be used to make the surface light yellow or golden yellow, and improve the quality of titanium dentures. beauty. The anodic oxidation method utilizes the interference effect of the titanium oxide film on light to naturally develop color, and can form colorful colors on the titanium surface by changing the cell voltage.
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