Of Hf-containing Nial-based Eutectic Alloy Oxidation And Mechanical Properties Study

Multiphase intermetallic NiAl-based alloy with the composition of NiAl-28Cr-5.85Mo-0.15Hf has been directionally solidified(DS) by conventional Bridgeman apparatus. The microstructure, BDT, elevated temperature compressive deformation and tensile creep are investigated by XRD, SEM and TEM. Furthermore, The effect of RE on the oxidation behavior of NiAl-28Cr-5.5Mo-0.5Hf alloy is also studied.The (DS) NiAl-28Cr-5.85Mo-0.15 alloy prepared by conventional DS technique is composed of three phases, which are NiAl matrix, lamellar Cr(Mo) phase and semicontinuousely distributed Hf solution phase. The tensile results indicate that NiAl-28Cr-5.85Mo-0.15Hf alloy exhibits apparent brittle-to-ductile transition temperature(BDTT). At temperature just above the BDTT, the fracture morphology changed from NiAl cleavage and debonding along the NiAl and Cr(Mo) phase boundary to completely dimple in nature. The tensile creep curve is composed of the typical primary creep stage, steady-state creep stage and the accelerated creep stage. Based on the stress exponent and the activation energy for creep, the dominant creep deformation mechanism is controlled by the dislocation climb. The creep fracture is controlled by the crack formation and crack propagation. The creep fracture data can be analysed by the Monkman-Grant relationship.The effect of RE on the oxidation behavior of NiAl-28Cr-5.5Mo-0.5Hf alloy is studied. The isothermal oxidation kinetics of the alloy containing various content REEs obeys the parabolic law at 1100癈. The weight gain of the alloy containing small addition is lower than that of the matrix alloy. When the addition is up to 0.5wt%, the weight gain dramatically increases. The weight gain of the alloy containing 0.05wt%Ce and 0.1 wt% Nd is lowest among that of the Ce-doped and Nd-doped alloy, respectively. The oxidation scale of 0.005, 0.05wt%Nd alloy includes small portion of e-Al2O3. The CeO2 and Nd2O3 form in theoxidation scale of 0.5Ce- doped and 0.5wt%Nd-doped alloy, respectively. The RE addition results in a change of the constituent scales contents, gets rid of the microhole in the oxidationscale and eliminates the internal oxidation.