The rapid oxidation of titanium at high temperature forms titanium-silicon compound and titanium-aluminum compound on the surface of titanium, which can prevent the oxidation of titanium at a temperature above 700 °C. This surface treatment is very effective for high-temperature oxidation of titanium. Perhaps the coating of such compounds on the surface of titanium is beneficial to the bonding of titanium and ceramics, and further research is still needed. From the perspective of oxidation resistance, the service temperature of titanium alloy should not exceed 500°C. Generally, the difference between the shrinkage of area of the sample with oxide film and the sample without oxide film is measured as the index of oxidation degree. Oxidation is the limit of high temperature of titanium materials. One of the main reasons to use it. The process of titanium material and oxidation synthesis oxide. Titanium materials are stable in air at room temperature, but are easily oxidized when heated in air or in an oxidizing atmosphere. The degree of oxidation depends on the characteristics of the titanium material itself and the concentration of oxygen in the environment, heating time and heating temperature, etc. At high temperatures, titanium materials oxidize rapidly, resulting in brittle alloys and deterioration of mechanical properties.
When studying the phase composition of titanium anode films, it was determined that the oxide films are generally Roentgen (X-ray) amorphous films, which when formed have a low potential breakdown level. According to some authors, under certain voltage conditions The anodic film breakdown found during film formation is always accompanied by crystal formation. Titanium on the surface of the anodized film has a high degree of oxidation resistance. Low-molecular-weight titanium oxides are found under titanium dioxide (TiO2), and the thickness increases when the oxide formation potential is raised, and the low-molecular-weight titanium oxides in the film partially decrease. In the potential region of titanium oxide formation, titanium oxides of composition Ti50B to titanium oxide are found on the surface of titanium. This range of titanium oxides is transformed into titanium dioxide Ti02 (octoside stone) as the anode potential increases. Since then, according to the anode As the potential increases, the composition of the oxide film of titanium changes, and the degree of oxidation changes from zero to very high.
Because the spark temperature is sufficient for the polymorphic transformation of fausidendite to rutile, it has not been elucidated why the quasi-stable variant (variant) of the oxide is observed in the coating. Even as a result of plasma spraying alumina, although the temperature of the sprayed oxide is very high, a low temperature modification is still obtained. This is the case where plasma spraying and micro-arc oxidation are used, the same can be found in the process of forming the coating. It seems that one of the main reasons may be that a small part of the oxide layer melts during the micro-arc oxidation, and the melt in this region cools violently when the micro-arc moves. Short-term discharges help to form the amorphous phase in the coating. As a result of the rapid cooling rate in the electrolyte of the anode micro-segments responsible for the breakdown, quenching of the thin film material occurs without reaching thermodynamic equilibrium and without the formation of a fully crystalline phase. The study of Roentgen’s amorphous form of this film found that there is a polycrystalline structure of deformation (octahedral stone) in the amorphous matrix, and the film formed in sulfuric acid or phosphoric acid is composed of crystalline phase TiO2. This phase is a phase that crystallizes under the voltage increasing condition. Using the crystallography method, it is clarified how brookite forms crystalline products under low-density current conditions. It has been determined that the anode thin film TiO2 is in the modified state of anatase (octahite). Under the condition of forming voltage, the inclusion rutile of modified titanium oxide was found by thin film spark voltage asymptotic method. When the film voltage is further increased, it is completely transformed into rutile.
Improving the oxidation resistance of titanium materials can be achieved by coating and developing more oxidation-resistant alloys. The coating can use surface processing technology to coat a protective metal layer (such as aluminum, platinum, gold, etc.) or a metal-oxide mixture layer (such as Al+SiO2) on the surface of the titanium material to improve the oxidation resistance of the titanium material performance. Using platinum ion plating, Ti-6Al-2Sn-4Zr-2Mo does not oxidize for a long time at 590°C. Using tungsten and platinum as the bottom layer of the coating respectively, the anti-oxidation temperature can be increased to 700°C. Adjusting the composition of titanium alloy can also improve the oxidation resistance of titanium materials. The Pilling-Bedworth ratio of selected alloying elements should be greater than 1, and the Gideon free energy is lower than that of titanium, which is in line with Hauffe’s law. Alloying elements that improve oxidation resistance include: niobium, aluminum, molybdenum, tungsten, tin, silicon, etc. Add these alloying elements to obtain titanium alloys with good oxidation resistance, such as Ti-5A1, Ti-5Al-2.5, Ti-4Al-3Mo-1V, Ti-5.8Al-4Sn-3.5Zr-O.5Mo-O.7Nb -O.35Si-0.06C etc. Ti3A1, Ti-Al, Ti-Al-Nb and other intermetallic compounds have higher anti-oxidation ability. The anti-oxidation temperature of Ti3A1 can reach above 750°C, and that of TiAl can reach above 900°C. The anti-oxidation ability of Ti-A1-Nb is higher than that of TiAl is higher.
When the temperature is higher than 800°C, the oxide film will decompose, and oxygen atoms will enter the metal lattice through the oxide film, resulting in embrittlement. In general, the oxidation kinetics of titanium follows a parabolic law at low temperatures and a linear law at high temperatures. The molecular volume of the oxide film formed by titanium is larger than the volume of metal atoms consumed to form the oxide film, so the formed oxide film can cover the entire surface of the metal. At 500°C, the oxide film formed on the surface of the titanium material has a protective effect, can prevent the penetration of oxygen, and prevent the titanium material from continuing to oxidize. As the temperature continues to rise, the oxide film loses its protective effect, and intense oxidation occurs. Oxygen diffuses through the oxide film to the inside of the metal, forming an obvious gas permeation layer.