Constant load creep tests on isothermally forged Udimet 720Li, an advanced superalloy for gas turbine disc application, were run in the stress/temperature field 900-450MPa/650-700 ℃ producing rupture times in the 20-...Constant load creep tests on isothermally forged Udimet 720Li, an advanced superalloy for gas turbine disc application, were run in the stress/temperature field 900-450MPa/650-700 ℃ producing rupture times in the 20-5000h range. The creep curves have shown a predominant accelerating creep stage, that has been described by the following equation: where ε min depends on stress and temperature, while parameter C depends mainly on stress. A strain dependent damage, defined by the parameter C, causes the accelerating creep stage at stresses lower than 750MPa, whilst its contribution to the creep strain acceleration is less important at higher stresses. The model rationalizes the different behaviors at high and low stress and has been validated with variable stress and temperature creep behavior.展开更多
The isothermal oxidation behavior of Ni_3Al containtng 15 at.% Fe and NiAl containing 30 at.% Fe was studied for 100 h at 850, 950, 1050 and 1150℃, respectively. The results show that the oxidation kinetics of the tw...The isothermal oxidation behavior of Ni_3Al containtng 15 at.% Fe and NiAl containing 30 at.% Fe was studied for 100 h at 850, 950, 1050 and 1150℃, respectively. The results show that the oxidation kinetics of the two alloys obey a parabolic law at various temperatures and every parabolic curve possesses two oxidation rate constants. The morphology, microstructure and the chemical composition of the oxide scales were examined using optical metallography, X-ray diffraction analysis, scanning electron microscopy and electron probe microanalysis. The oxide scale of Ni_3Al containing 15 at.% Fe consists mainly of NiO, NiFe_2O_4, and FeAl_2O_4, and that of NiAl containing 30 at.% Fe consists of Fe_2O_3 and (Fe,Ni)Fe_2O_4, contrasting sharply to the oxide scales of pure Ni_3Al and NiAl which consist of Al_2O_3. The oxide scales on the surfaces of Ni_3Al and NiAl containing Fe are not too dense and not too cohesive to the matrix,so their oxidation resistance is not too good.展开更多
文摘Constant load creep tests on isothermally forged Udimet 720Li, an advanced superalloy for gas turbine disc application, were run in the stress/temperature field 900-450MPa/650-700 ℃ producing rupture times in the 20-5000h range. The creep curves have shown a predominant accelerating creep stage, that has been described by the following equation: where ε min depends on stress and temperature, while parameter C depends mainly on stress. A strain dependent damage, defined by the parameter C, causes the accelerating creep stage at stresses lower than 750MPa, whilst its contribution to the creep strain acceleration is less important at higher stresses. The model rationalizes the different behaviors at high and low stress and has been validated with variable stress and temperature creep behavior.
文摘The isothermal oxidation behavior of Ni_3Al containtng 15 at.% Fe and NiAl containing 30 at.% Fe was studied for 100 h at 850, 950, 1050 and 1150℃, respectively. The results show that the oxidation kinetics of the two alloys obey a parabolic law at various temperatures and every parabolic curve possesses two oxidation rate constants. The morphology, microstructure and the chemical composition of the oxide scales were examined using optical metallography, X-ray diffraction analysis, scanning electron microscopy and electron probe microanalysis. The oxide scale of Ni_3Al containing 15 at.% Fe consists mainly of NiO, NiFe_2O_4, and FeAl_2O_4, and that of NiAl containing 30 at.% Fe consists of Fe_2O_3 and (Fe,Ni)Fe_2O_4, contrasting sharply to the oxide scales of pure Ni_3Al and NiAl which consist of Al_2O_3. The oxide scales on the surfaces of Ni_3Al and NiAl containing Fe are not too dense and not too cohesive to the matrix,so their oxidation resistance is not too good.
