Real-time study of transients during high-temperature creep of an Ni-base superalloy by far-field high-energy synchrotron X-ray diffraction

Abstract

The high-temperature mechanical behavior of single-crystal Ni-base superalloys has been formerly studied by in situ triple-crystal synchrotron X-ray diffractometry (TCD). However, the 1/300 s recording frequency does not allow real-time tests. It is shown here that real-time monitoring is possible with far-field diffractometry in transmission. The use of a far-field camera enables one to follow a diffraction spot with high angular precision and high recording speed. This technique allows measurement of the mechanical response of an AM1 Nibase single-crystal superalloy following steep load jumps and relaxations during high-temperature creep tests. Local crystal misorientation is revealed and rafting (oriented coalescence) is examined. This new technique is compared with TCD, in order to highlight its benefits and drawbacks.

X-Ray Diffraction Contrast Tomography for Probing Hydrogen Embrittlement in Heat-Treated Lean Duplex Stainless Steel

“…In addition, the advantage of DCT to observe a large number of 3D grains at the same time will be lost, but the far-field method using parallel X-rays will provide a more accurate observation. A study reported in a literature indicates that a change of mismatch of 10 −5 orders in Ni-based alloy during creep test is detectable as a change of several diffraction spots (Tréhorel et al, 2018). To apply the far-field method, a strong parallel X-ray source is required, and a synchrotron will be suitable rather than a laboratory instrument.…”

High-Temperature Dislocation Climb in the γ′ Rafts of Single-Crystal Superalloys: The Hypothesis of a Control by Dislocation Entry into the Rafts

“…Thus and can differ only by a few per cent and the logarithmic term can be linearized.) By combining equations (5) and (6) we can also derive a variation law for the osmotic force:…”

“…This can be done in a non-destructive way by hard X-Rays high resolution diffractometry [4]. Thanks to the very intense beams provided by synchrotron sources the acquisition time of a (200) peak can be reduced to less than ten seconds [5]: we can determine not only the behavior of both rafts and channels under steady state conditions, but also their transient plasticity following a change in load and/or temperature. Within the present paper we shall focus on the high temperature behavior of the γ' rafts and try to establish basic equations with parameters which can be fitted to the results of in situ real time tests.…”

The Effect of Crystal Defects on 3D High-Resolution Diffraction Peaks: A FFT-Based Method

“…X-ray diffraction (XRD) is one of the most powerful non-destructive tools to investigate materials, as their wavelength is commensurate with the distance between atoms within a crystal [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ]. Successive improvements of both the X-ray sources (from X-ray tubes to third generation synchrotrons) and detectors (from photographic plates and gas counters to fast two-dimensional arrays) have led to a tremendous increase in the quantity of data recorded per unit time, allowing real time in situ or in operando measurements [ 10 , 11 ]. It is now possible to determine the 3D grain microstructure of a bulk material with a submicron resolution (using topo-tomography), to follow the evolution of the elastic strain state of the grains of a polycrystal during mechanical tests (3D-XRD, far field diffractometry), or to measure the distribution of strains within a few grains in real time (2D diffractometry) [ 12 , 13 ].…”