| In this paper, the ingots of Ti-Al alloys including Ti3 Al, Ti Al, Ti Al3 intermetallic compound were prepared by vacuum non-consumable electrode arc smelting method,and the ingot composition were homogenized through the annealing.A ordered porous anodic oxide layer coated titanium-aluminium alloys have been fabricated by the method of anodic oxidation in sodium hydroxide(Na OH) based electrolyte and sulfuric acid(H2SO4) based electrolyte,which containing a small quantity of hydrogen peroxide(H2O2) and of hydrofluoric acid(HF) respectively. The relationships between the anodic oxidation parameters on the surface morphology and thickness of porous anodic oxide layer were investigated; the formation mechanism of nanotubes array on the Ti3 Al was discussd. The composition and phase composition of anodic oxide layer were analyzed. High temperature cycle oxidation experiments of anodic oxidation samples were carried out in static air at 700℃ and 800℃ respectively.The influence of anodic oxidation parameters on the oxidation resistance of the matrix was investigated; Top morphologies and cross sections morphologies after high temperature oxidation were analyzed;the reason for oxidation resistance of nano-porous anodic oxide layer was discussed.Ti3Al, Ti Al and Ti Al3 specimens were anodized in sodium hydroxide(Na OH) based electrolyte with a small quantity of hydrogen peroxide(H2O2) at different voltage. Double layer porous structure formed on three kind of specimens at 30 V voltage, three-dimensional bicontinuous ligament–pore structure of outer layer and nano-porous structure of inner layer. The oxide layer was mainly composed of Al, Ti O2, Al2O3 and Al(OH)3. Under 60 v voltage, a ordered porous anodic oxide layer formed only on the Ti Al surface, anodized for 15 min, anodic oxidation layer composed by the bright white nanotube arrays, which average tube size was 103 nm. With the increase of time, the nanotube array layer replaced by the ordered porous structure, whose average pore diameter was 438 nm.After anodic oxidation treatment in sulfuric acid(H2SO4) based electrolyte with a small quantity of hydrofluoric acid(HF), two different structures of porous anodic oxide layer have been obtained, nanotube array structure coated Ti3 Al and ordered porous structure coated the others Ti-Al alloys. The diameter of single tube(hole) in porous anodic oxidation layer increased linearly with the increase of voltage and decreased with the increase of Al content. Thickness was mainly related to voltage, time and temperature, and increased with the increase of voltage, time and temperature respectively. The maximum thickness can reach to 1.4μm. The oxide layer was mainly composed of Ti O2 and Al2O3, the proportion of Al2O3 in oxide layer increased with the increase of Al content.In the static air at 700 ℃, oxidation resistance of Ti3 Al and Ti Al specimens after anodic oxidation treatment was improved greatly. In the static air at 800 ℃, the anodic oxidation layer had a poor protective effects on the Ti3 Al matrix. For Ti Al intermetallic compounds, the anodic oxidation samples showed excellent oxidation resistance except the 0% HF handle samples. The parabolic slope constant(Kp) of 50 V handle sample was about 1/1024 for the untreated sample.The Kp of 1 h handle was about 1/221 for the untreated sample. The Kp of 0.35% HF handle sample was about 1/3320 for the untreated sample. The improvement of oxidation resistance was mainly attributed to F- effect and the densification of porous structure in the static air at high temperature. |
PDF Full Text Request