Diffracting-grain identification from electron backscatter diffraction maps during residual stress measurements: a comparison between the sin²ψ and cosα methods

Abstract

X-ray diffraction (XRD) is a widely used technique to evaluate residual stresses in crystalline materials. Several XRD measurement methods are available. (i) The sin2ψ method, a multiple-exposure technique, uses linear detectors to capture intercepts of the Debye–Scherrer rings, losing the major portion of the diffracting signal. (ii) The cosα method, thanks to the development of compact 2D detectors allowing the entire Debye–Scherrer ring to be captured in a single exposure, is an alternative method for residual stress measurement. The present article compares the two calculation methods in a new manner, by looking at the possible measurement errors related to each method. To this end, sets of grains in diffraction condition were first identified from electron backscatter diffraction (EBSD) mapping of Inconel 718 samples for each XRD calculation method and its associated detector, as each method provides different sets owing to the detector geometry or to the method specificities (such as tilt-angle number or Debye–Scherrer ring division). The X-ray elastic constant (XEC) ½S 2, calculated from EBSD maps for the {311} lattice planes, was determined and compared for the different sets of diffracting grains. It was observed that the 2D detector captures 1.5 times more grains in a single exposure (one tilt angle) than the linear detectors for nine tilt angles. Different XEC mean values were found for the sets of grains from the two XRD techniques/detectors. Grain-size effects were simulated, as well as detector oscillations to overcome them. A bimodal grain-size distribution effect and `artificial' textures introduced by XRD measurement techniques are also discussed.

Effects of Residual Stress Induced by Laser Shock Peening on Fatigue Crack Propagation Behavior in Directed Energy Deposition Stainless Steel

“…The region where outlier data points appear has only a few grains involved in diffraction, resulting in a lower peak intensity. [ 30 ] The accuracy of the peak positions is poor, and the presence of inter‐microcrystalline strains may affect the stress test results of coarse‐grained materials, leading to measurement errors. The residual stress experimental values in the Y ‐direction (S22) ranged from 162.3 to 210.5 MPa, with an average value of about 184 MPa.…”

Assessment of Process, Parameters, Residual Stress Mitigation, Post Treatments and Finite Element Analysis Simulations of Wire Arc Additive Manufacturing Technique

“…The macroscopic in-plane stress σ 11 and σ 22 are adapted from lattice strain data by use of sin 2 ψ method [136]. In Sin 2 Ψ methods, the stress measurement was determined by the exclusion of the radiation cone and line detectors [151].…”

Investigation of the Mechanical Properties and Microstructure of the Co40NiCrMo Alloy Used for STACERs and Prepared by the CSPB Process and the Winding and Stabilization Method

“…To explore the residual stress distribution state, the X-ray diffraction technique for residual stress measurement can be used, which is usually associated with sin 2 Ψ, a method based on the interception of the diffraction cone and line detectors. To overcome the loss of information, cos α, an alternative method using a single exposure to collect the entire diffraction cone via a 2D detector, was employed [17]. The present paper compared both the sin 2 Ψ and cos α methods in the residual measurement of STACER and determined the values for STACERs with good service behaviors.…”