The influence of pre-oxidation on the liquid zinc corrosion resistance of high Nb-TiAl alloys was investigated. The pre-oxidation was performed by heating the specimens, buried in silica powder and encapsulated in a silica tube under a vacuum of 1.3x10-5 Pa at 950℃ for 12 h. Experimental results showed that the preoxidized sample exhibited much higher liquid zinc corrosion resistance than that for the comparative samples. This excellent liquid zinc corrosion resistance was attributed to the formation of high-quality oxide scale during peroxidation. The corrosion of all the samples in liquid zinc was caused by a localized breakdown in the oxide scales. The continuous and dense oxide scale formed during preoxidation substantially may prevent the liquid zinc from diffusing to the substrate, and its good continuity may also reduce the possibility of localized breakdown in the oxide scale.
The effects of heat treatments on typical microstructures of directionally solidified（DS） Ti-45Al-8Nb-（W,B,Y）（molar fraction,%） alloys prepared by the Bridgeman method were studied.Two typical DS microstructures including full lamellae with cellular growth morphology and massive structure with dendritic growth morphology were examined.The results show that the heat treatment of 1250 ℃ for 24 h ＋ 900 ℃ for 30 min＋air cooling can efficiently eliminate the B2 phase in the DS alloys and change the massive structure of the rapid DS alloy into lamellar microstructure.Columnar lamellar colonies with widths of 150-200 μm and 50-100 μm respectively were observed in intercellular and dendritic arm regions.The heat treatment of 1 400 ℃ for 12 h＋900 ℃ for 30 min＋air cooling could simultaneously remove the B2 phase,massive structure and solidification segregations from the DS alloys,however,it caused severe growth of grains.
