Study On The High Frequency Induction Oxidation Process Of Titanium Alloy TC4 In Flow Field Of Active Dry Air

Titanium alloy has a series of excellent properties, such as great specific strength, strong corrosion resistance, better high-temperature resistance and lower density etc. In recent years, Titanium alloy as one of the most far-ranging and applied materials in 21st centuries will be mainly used in many fields such as: aviation and airspace, oceanic engineering, petrochemical industry and medical sanitation industry etc. So it has widely application in foreground, at the same time, it attracts people's extensive attention. TC4 is a kind ofα+βtitanium alloy. TC4 as one of the most progressively used titanium alloy possesses fine compositive performances, for example better plasticity and impact toughness. But because it shows poor wearing resistance, especially eroding resistance, and it also appears easily scratched, occluded. These shortcomings have restricted its application. The properties of alloy is depending on its structure. And the structure is related on chemical composition, forming, processing, heat treatment technology and surface treating. However, surface treating technology is important to improve their properties in application of alloy.High-frequency induction oxidation is a new technology to form oxidation layer on metal surface. Compared with other surface treatment techniques, it shows the advantages as follows: low energy cost, high efficiency, and no pollution to environment. In the thesis, the preparation of oxidation layer of TC4 titanium alloy by high-frequency induction oxidation from 800℃to 1000℃in flow field of active dry air has been studied. The factors effect on performances of oxidation layer were tested and analyzed. By use of thickness tester, hardness meter, SEM observation, XRD and XPS analysis, the morphology and constitution of layer were studied. At last, forming mechanism of oxidation layer was also discussed.By analysis of test results, some laws were shown as follows: (1) relation between different treating temperature and the oxidation layer's properties; (2)relation between the treating time and the oxidation layer's properties; (3) foundation of oxidation kinetics models. It indicates that from 800℃to 1000℃, the thickness and hardness of oxide layer increased with power exponent by the increasing of treating time and treating temperature, and that only in 10 minutes the layers oxidized obtained is compact and uniform within the range of this temperature. The oxidation layers are mainly consisted of TiO2 and Al2O3. The thickness of layer is 10～30μm, and the microhardness is 500～1400HV.In comparing to the micro-plasma oxidation process and thermal oxidation process, the high frequency induction oxidation technique has the shortest treating time and the highest efficiency, and the performances of oxide layer is relatively better. Simultaneously, it does no pollution to the environment. The properties of oxidation layer obtained by high-frequency induction oxidation is also better than the other processes. Compared with the oxygen, the process which was dealt with in flow field of active dry air can low economy cost. Therefore, the high-frequency induction oxidation process is promising technique in surface treating of titanium alloy.