Fastin situphase and stress analysis during laser surface treatment: A synchrotron x-ray diffraction approach

Abstract

An in situ stress analysis by means of synchrotron x-ray diffraction was carried out during laser surface hardening of steel. A single exposure set-up that based on a special arrangement of two fast silicon strip line detectors was established, allowing for fast stress analysis according to the sin2ψ x-ray analysis method. For the in situ experiments a process chamber was designed and manufactured, which is described in detail. First measurements were carried out at the HZG undulator imaging beamline (IBL, beamline P05) at the synchrotron storage ring PETRA III, DESY, Hamburg (Germany). The laser processing was carried out using a 6 kW high power diode laser system. Two different laser optics were compared, a Gaussian optic with a focus spot of ø 3 mm and a homogenizing optic with a rectangular spot dimension of 8 × 8 mm2. The laser processing was carried out using spot hardening at a heating-/cooling rate of 1000 K/s and was controlled via pyrometric temperature measurement using a control temperature of 1150 °C. The set-up being established during the measuring campaign allowed for this first realization data collection rates of 10Hz. The data evaluation procedure applied enables the separation of thermal from elastic strains and gains unprecedented insight into the laser hardening process.

20 Hz synchrotron X-ray diffraction analysis in laser-pulsed WC-Co hard metal reveals oscillatory stresses and reversible composite plastification

“…Recently, a novel in-situ characterisation approach based on a millisecond synchrotron X-ray diffraction (XRD) analysis coupled with a pulsed laser sample treatment was introduced by Kostov et al [12]. The complex experimental set-up makes it possible to characterise temporal evolutions of lattice strain, stress and microstructure, as well as to perform real-time monitoring of phase transformations of rapidly heated samples in the laser focus of several millimetres, which overlaps with the synchrotron X-ray beam footprint on the investigated sample surface.…”

“…In the current work, this well-established synchrotron X-ray set-up [12] was used to in-situ characterise WC-Co inserts coated with a PVD TiCN/Al2O3 bilayer, which was locally heated using a high-power diode laser (HPDL) up to a maximum temperature of 1300°C, applying (i) a single and (ii) five successive heating cycles. The objectives were (i) to test the transferability of the synchrotron XRD set-up to the field of cutting inserts analysis, (ii) to evaluate the time-dependent evolution of stresses and finally the formation of residual stresses, the evolution of microstructure and (iii) to assess thermally driven mechanisms governing stress build-up and relaxation.…”

Fast Temporal and Spatial Resolved Stress Analysis at Laser Surface Line Hardening of Steel AISI 4140

“…Results of in-situ diffraction studies during processing help deepen the process understanding and can be used to improve and validate process simulation and thereby allow accurate process predictions. The adaption of the single exposure technique [5] into an experimental setup for laser surface hardening as presented in [6,7] allows for the real-time monitoring of phase transitions and strain evolutions. Here, a specially designed process chamber was commissioned with measuring and evaluation strategies established that allows for the separation of thermal and elastic strains for each exposure.…”

MYTHEN Detector – Perspectives in Residual Stress Measurements

“…In particular, deformations in coarse-grained nanocrystalline nickel were followed in situ, and subsequently residual dislocations described [9]. This was followed by series of in situ stress measurements carried out at Karlsruhe Institute of Technology, where two monomodular (1K) MYTHEN detectors were employed in sin 2 ψ method [10][11]. While the implementation of both MYTHEN 1K and 24K systems in stress measurements on synchrotron sources yielded excellent results, laboratory measurements are still not described.…”