Determination of stress gradients in a thermally grown oxide layer using x-ray diffraction

A method based on X-ray diffraction and absorption theory is proposed whereby the stress distribution across Cr2O3 scales grown on Ni-30Cr and Ni-30Cr-0.5Y alloys is evaluated both at room temperature and under growth conditions. In-situ stress measurements at 1000 degrees C show that although the oxide on Ni-30Cr-0.5Y possesses a lower average stress than that grown on Ni-30Cr, the interfacial oxide stress is greater for the Y-doped alloy. The compressive in-plane residual stresses at interfaces can be as high as -3600 MPa, while surface in plane stresses ranged from -200 to -400 MPa. The addition of yttrium significantly strengthens the oxide/alloy interface in experiments at 900 degrees C, 1000 degrees C and 1100 degrees C thus enabling the oxide td sustain much higher residual stresses upon cooling compared to scales on Ni-30Cr.