J.P. Lin

Formation mechanism of coarse grained zone in annealed high Nb–TiAl–xB ingots

High Nb–TiAl ingots with various boron levels (0, 0.2, 0.5, 0.7 and 1.0 at-%) were investigated using annealing in a single α phase field for various lengths of time, and a coarse grained zone (CGZ) was observed when the boron content was greater than 0.5 at-%. Scanning electron microscopy and transmission electron microscopy were used to study microstructural evolution and boride transformation. Experimental results show that the width of CGZ is closely related with the boron addition and the cooling rate. The formation mechanism is discussed for various nucleation behaviors of boride at the ingot scale during solidification caused by the temperature induced supercooling and the boron induced compositional supercooling, which lead to dissimilar pinning effects of borides at high temperature.

Acid corrosion behaviour of Ti–48Al–6Nb porous alloys with different phase skeletons

Ti–48Al–6Nb porous alloys with different phase skeletons were synthesised by powder metallurgy at different temperatures. TiAl3 skeletons achieved at 700°C were covered by corrosion products and skeletons fractures led to pores collapse. TiAl skeletons were synthesised at 900°C with obvious corrosion pits and pore diameter increasing. And Ti3Al/TiAl skeletons achieved at 1350°C exhibit the best acid corrosion resistance with the least mass loss of 1.853 mg m–2. Skeletons and pore diameters remained stable just with fully lamellar structures emerged. In addition, Nb2Al phases presented better resistance than NbAl3 in the skeletons contributing to acid corrosion resistance of the porous alloys.