Residual stress determination in a shot-peened nickel-based single-crystal superalloy using X-ray diffraction

Abstract

A residual stress depth profile up to 1 mm is determined with the Ortner method in a single crystal of a nickel-based superalloy which has been subjected to shotpeening. An optimization procedure is assessed to minimize uncertainties connected to Bragg angle, mosaic spread and numerical stability. The theoretical background is reviewed to highlight the connections between Bragg angle positions and the stress tensor components in different coordinate systems and also to obtain a mathematically consistent formulation. Transformation matrices required to express the strain components with respect to the initial state are provided for the general case. It is shown that, when a stress gradient occurs beneath the sample surface plane, the value of the 33 component of the stress tensor determined from measurements is twice its true value. For a sample surface oriented along a h100i crystallographic direction, the data analysis shows that the compressive stresses which develop in the 150 mm-thick surface layer are compensated for by small tensile stresses developing at long scale rather than a specific layer of finite size featuring high tensile stresses. At least 17 Bragg angles are required to have stable solutions with standard deviations close to 30 MPa. Maximum compressive stresses of 1000 or 1400 MPa depending on the assumption used to describe the initial state occur at a 30 mm depth.

Investigations into the Surface Strain/Stress State in a Single-Crystal Superalloy via XRD Characterization

“…However, for the γ phases, there exists an intrinsic stress in the γ phase. Erdong Wu's research [17] on a complete heat-treated DD10 single-crystal superalloy by neutron diffraction also showed a tetragonal distortion with c/a >1. In addition, the angular distortions of the γ phase are enhanced during the aging treatment.…”

“…The principle and brief introduction of the stress measurement and the relevant calculation as well as the involved elastic constants are described in the next paragraph. Details can be seen elsewhere in the papers [17,23]. As a typical two-phase (γ/γ′) coherent structure, a doublet fitting of these six {331} and two {004} diffraction peaks was performed in this paper.…”

“…Seeing the Reference [17] (Morançais, A.; M. Fèvre. Residual stress determination in a shot-peened nickel-based single-crystal superalloy using X-ray diffraction.…”

“…In the last 20 years, works have been conducted to investigate the strain/stress state in SC nickel-based superalloys. The strain/stress state of Ni-based SC superalloy samples that went through thermo-mechanical fatigue, creep-deformation, and shot-peening have been experimentally studied [15][16][17]. B. Marty.…”

“…In the previous works dealing with Ni-based SC superalloys strain/stress research, the macro-stress was always involved, and its correlations with the material performance were discussed [15][16][17]20]. However, the Ni-based SC superalloys were composed of an fcc γ-matrix and coherently aligned L1 2 -ordered γ -precipitates and had a unique two-phases mismatch structure [21,22], which has not been taken into consideration in the aforementioned works.…”