Creep Parameters of Single Crystal Nickel-Base Superalloys with Different Orientations and Their Relationship with Creep Behavior

Abstract:

By means of the tests of creep performance and the measurements of internal friction stresses, the effective creep parameters of the [001]-, [011]- and [111]-oriented single crystal nickel-base superalloys after being crept to steady-state stage under the conditions of high temperatures/low stresses along [001], [011] and [111] orientations respectively, and their relationship with the creep performance and deformation mechanism have been studied. Results show that, with the increase of creep temperatures and decrease of applied stresses, the internal friction stresses of the three alloys decrease. Under the same conditions, the order of the internal friction stresses is σi[001] > σi[111] > σi[011]. The inclined and continuous “roof”-type γ channels in the [011]- and [111]-oriented alloys before and after creep are responsible for the low internal friction stress and poor creep resistance of the two alloys. The effective creep activation energy of the [001] oriented alloy is Qe[001]= 281.32 KJ/mol, indicating that the deformation mechanism during steady-state creep stage is the dislocation climb controlled by element diffusion. The effective creep activation energy of the [011]-oriented alloy is Qe[011]= 139.74, and the low value is related to the open ? matrix channels possessing small resistance for dislocation slip. The effective creep activation energy of the [111]-oriented alloy is Qe[111]= 182.61 kJ/mol, and the relatively larger value compared to that of the [011]-oriented alloy is related to the lamellar γ’ rafts and the cross slip of dislocations in the [111]-oriented alloy.

Key words:creep; internal friction stress; single crystal nickel-base superalloy; microstructure; effective creep parameters