Lamellar morphology of directional solidified Ti–45Al–6Nb–xW alloys

Directional solidification of Ti-45Al-6Nb-xW（x=0,0.4,0.8;at%） alloys was performed by Bridgeman method with the stable growth rate of 5,10,and 20 μm·s^（-1）.The differential scanning calorimeter（DSC） results indicate that both the eutectic temperature and the transition temperature of α（Ti_3Al） to γ（TiAl） increase with W content increasing from 0 at%to 0.8 at%.For the stable growth rate of 10 μm·s^（-1）,the orientations of α_2（Ti_3Al）/γ（TiAl）lamellae change from 45°（0 at%W） to 0° and near 0°（0.4at%and 0.8 at%W） to the crystal growth direction,and the spacing of α_2/γ lamellae decreases with W content increasing from 0 at%to 0.4 at%,while it increases when W content is 0.8 at%.With the increase in growth rate from5 to 10 and 20 μm·s^（-1）,the lamellar spacing of α_2/γbecomes smaller,and the lamellar thickness becomes more uniform.

Dynamics evolution of γ' precipitates size and composition interface between γ/γ' phases in Ni-Al alloy at different aging temperatures

The precipitation dynamics of γ’(L1-NiAl)phase and composition interfacial width between γ(fcc Ni)and γ’ phase were investigated using the phase field simulation linking with CALPHAD method.The coarsening rate and particle size distribution(PSD) of γ’ phase,the temporal composition interfacial width of γ/γ’ in Ni-17 at% Al alloy aged at 923,973 and 1023 K were clarified.As the aging temperature increases,the morphology of γ’ phase changes from the interconnected rectangle shape to the separated cuboidal shape.The average particle radius(<r>) of γ’ phase at coarsening stage follows <r> ∞t^(n) with the exponents n=0.21,0.23 and 0.26,respectively.The peak values of simulated PSDs at 923 K are less than the value calculated by the Lifshitz-Slyozov-Wagner(LSW) model,and the width of simulated PSD increases at later stage of precipitation.The normalized radius(r/<r>)which corresponds to the peak value of PSD moves from1.1 to 1.0 as the aging temperature increases from 923 to1023 K,and they are smaller than that of LSW model.The composition interfacial width decreases as the aging progresses and increases as the aging temperature increases.