A zone melting device for the in situ observation of directional solidification using high-energy synchrotron x rays.

Directional solidification (DS) is an established manufacturing process to produce high-performance components from metallic materials with optimized properties. Materials for demanding high-temperature applications, for instance in the energy generation and aircraft engine technology, can only be successfully produced using methods such as directional solidification. It has been applied on an industrial scale for a considerable amount of time, but advancing this method beyond the current applications is still challenging and almost exclusively limited to post-process characterization of the developed microstructures. For a knowledge-based advancement and a contribution to material innovation, in situ studies of the DS process are crucial using realistic sample sizes to ensure scalability of the results to industrial sizes. Therefore, a specially designed Flexible Directional Solidification (FlexiDS) device was developed for use at the P07 High Energy Materials Science beamline at PETRA III (Deutsches Elektronen-Synchrotron, Hamburg, Germany). In general, the process conditions of the crucible-free, inductively heated FlexiDS device can be varied from 6 mm/h to 12 000 mm/h (vertical withdrawal rate) and from 0 rpm to 35 rpm (axial sample rotation). Moreover, different atmospheres such as Ar, N2, and vacuum can be used during operation. The device is designed for maximum operation temperatures of 2200 °C. This unique device allows in situ examination of the directional solidification process and subsequent solid-state reactions by x-ray diffraction in the transmission mode. Within this project, different structural intermetallic alloys with liquidus temperatures up to 2000 °C were studied in terms of liquid-solid regions, transformations, and decompositions, with varying process conditions.

Fast in situ phase and stress analysis during laser surface treatment: a synchrotron x-ray diffraction approach.

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 sin(2)ψ 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 mm(2). 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.

Critical consideration of precipitate analysis of Fe-1 at.% Cu using atom probe and small-angle neutron scattering.

An Fe-1 at.% Cu model alloy was examined by atom probe (3DAP) and small-angle neutron scattering (SANS) to verify the accordance of the gained results. The Fe-Cu alloy was heat-treated for various times at 500°C, forming Cu-rich precipitates within the Fe matrix. The chemical compositions of the precipitates and matrix found by 3DAP were used to calculate the magnetic scattering contrast. Additionally, a magnetic moment of the precipitates that contain a significant amount of Fe was taken into account for the calculation of magnetic scattering contrast. This in turn is used for the evaluation of the magnetic scattering curves gained by SANS. Both the 3DAP data as well as the scattering curves were analyzed with regard to radius, number density, and volume fraction of the precipitates as a function of aging time. The results yielded by both techniques are in good agreement and correspond to the development of the hardness of the alloy. Minor differences can be related to the cluster search algorithm used for the analysis of the 3DAP data as well as Fe overestimation based on different field phases.