Dislocation Density of GlidCop with Compressive Strain applied at High Temperature

Dislocation densities of GlidCop with compressive strain applied at high temperature were examined by X-ray line profile analyses with synchrotron radiation. In order to evaluate the dislocation density, we applied the modified Williamson-Hall and modified Warren-Averbach method. The dislocation densities of GlidCop with compressive strain from 1.1-4 % were in the range of 5.7-8.0×10 m. Introduction GLIDCOP, dispersion-strengthened copper with ultra-fine particles of aluminum oxide, is used as a material for high-heat-load (HHL) components in many accelerator facilities due to its excellent thermal properties. In SPring-8 front ends, this material has been applied to many components such as masks, absorbers and XY slit assemblies, which are to be subjected to a maximum power density of approximately 1 kW mm at a normal incidence for a standard in-vacuum undulator beamline. We investigated the thermal limitation of GlidCop under cyclic HHL conditions using specially designed GlidCop samples because of a progressive increase in the heat load from the insertion device [1]. As part of the investigation, the residual strain of the GlidCop samples was measured using synchrotron radiation and those results were almost in accordance with FEM analyses [2]. On the other hand, evaluation of the plastic strain, which was the main cause of fracture phenomena, was performed qualitatively by comparing the FWHM of the diffraction profiles of samples with unknown plastic strain, with that of samples with known plastic strain [3]. Recently, we investigated the plastic strain of HHL materials, including GlidCop, with regard to dislocation density, as the dislocation density generally correlates with the plastic strain. X-ray line profile analysis has been the most powerful method for investigating the dislocation structure in plastically deformed metal. In this study, we examined the dislocation density of GlidCop with compressive plastic strain loaded at high temperature, as the real components at SPring-8 frontend are subjected to compressive stress at high temperature. The modified Williamson-Hall and modified Warren-Averbach methods were applied to estimate the dislocation density [4]. Experimental Two types of GlidCop samples, TP1 and TP2, were prepared. The grade of GlidCop used was AL15. TP1, which was designed for low cycle fatigue fracture, was identical to those used in our previous studies [1,2]. It was comprised of an absorbing body made of GlidCop with a thickness of 2 mm, as well as a fitting cover and a cooling holder made of stainless steel. Before experiments with synchrotron radiation, cyclic heat loads were applied to the central area of TP1 samples using an Residual Stresses 2016: ICRS-10 Materials Research Forum LLC Materials Research Proceedings 2 (2016) 609-614 doi: http://dx.doi.org/10.21741/9781945291173-103 610 electron beam. The samples were subjected to 50 cycles and absorbed 550 W in each cycle; one cycle period comprised 7 minutes of thermal loading and 5 minutes of thermal unloading. The average maximum temperature of the TP1 samples was approximately 300 oC during the heat cycles. The TP2 samples had known values of compressive strain. TP2 samples consisted of a cylinder with a diameter of 15 mm and a height of 15 mm. These samples were manufactured with compressive strains from 1.1-4 %. Compressive strains were applied at approximately 300 °C. After compression, the central volumes of TP2 samples, with a thickness of 2 mm, were cut by electrical discharge machining. Profile measurements were performed using a transmission-type strain scanning method in the beamline of BL02B1 at SPring-8. Table 1 shows the experimental conditions used for the measurements. The measurements were carried out at the center of samples using Cu (111), (200), (311), (222), (400) and (331) reflections. Table 1. Experimental conditions. Beam line SPring-8/BL02B1 Measurement method Transmission-type strain scanning method