| γ-Ti(46-48)Al is used widely in aerospace engine manufacturing areas as a kind of high-temperature structural materials because of superior performance. But for titanium alloy the high temperature oxidation resistance will drop down above 850℃, so It is an urgent need to solve the problem. At present, it is nearly no research at titanium alloy chemical metal polishing pieces in domestic and foreign. This thesis has two purposes based on the above two issues. Prepare the Chemical conversion coating by chemical methods to reduce the surface roughness, and then to improve the alloy high temperature oxidation resistance.In this paper, the effect of the components and process parameters in the slurry on titanium alloy was studied both in the process of chemical conversion film formation and to the surface gloss change or the sample weight loss rate. The research method is using orthogonal and single factor experiment. In this paper, the influence of three-acid polishing liquid to reaction rate was debated, including how to choose THinhibiterHT and brightener. Optimize the technology to manufacture chemical conversion film. The conversion coating based on HF/H3PO4 inγ-TiAl alloy surface was investigated. SEM, XRD and EDX showed that the composite coating was composed of Ti, O and a mass of Al, with a uniform dry riverbed structure.The dynamics and oxidation mechanism of the original sample and the specimens with chemical conversion film in the 850℃thermal shock experiment, 850℃high temperature 900℃were discussed. And the alloy after chemical treatment showed good anti-stripping ability in the thermal shock experiment, While the oxidation rate and the oxidation layer of the original sample in the oxidation process grow quickly. In 900℃cyclic oxidation experiments, the alloy samples with chemical conversion film showed extremely good oxidation resistance, and the oxide layer grow slowly, besides the samples surface is uniformity with small oxide grains hard to collapse. SEM and EDS analysised the cross section showed the oxidation layer continuous, inseparable and with significant level. In 850℃cyclic oxidation experiments, the weight mass was larger in the original sample than that in the alloy treated. The scanning microscopes showed that the original sample oxidized at 850℃for 20h generated compact rutile dendrite. Experimental results show that chemical treatment to improve the performance of titanium alloy is more suitable for a particular environment and temperature.The performance of the chemical conversion film of the samples with different surface roughness was studied. The chemical conversion film display the similar morphology though they have different surface roughness, but with totally different composition. It is easier to form the intact and superior performance oxide film with a large amount of Al. It is found the smaller the surface roughness, shorter to get a good chemical conversion film.At last, the mechanism of the chemical conversion coating of titanium alloy how to effect the high temperature oxidation resistance was discussed view of the chemical polishing and chemical conversion film formation theory.
|
PDF Full Text Request