Gradient of Residual Stress and Lattice Parameter in Mechanically Polished Tungsten Measured Using Classical X-rays and
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W) is an elastically isotropic metal with a body-centered cubic (bcc) structure, having the highest melting temperature (3422 °C) and the lowest thermal expansion coefficient (4.5 9 10−6 m/mK[1]) of any pure metal. Its density, equal to 19.3 g/cm3, is the same as that of gold and higher than that of uranium. Only a few currently known stable pure metals have a higher density (i.e., Os, Ir, Pt, Rh, Np, and Pu).[2] Tungsten thermal conductivity is equal to 174, 159 and 146 W/mK for temperatures of 300, 400 and 500 K, respectively.[3] Relatively high strength and stiffness at high temperatures, together with an excellent corrosion resistance as well as a relatively low price, ADRIAN OPONOWICZ, ANDRZEJ BACZMAŃSKI, and SEBASTIAN WROŃSKI are with the AGH-University of Science and Technology, WFiIS, al. Mickiewicza 30, 30-059 Kraków, Poland. MARIANNA MARCISZKO-WIĄCKOWSKA and KAMILA KOLLBEK are with the AGH-University of Science and Technology, ACMIN, al. Mickiewicza 30, 30-059 Kraków, Poland. Contact e-mail: marciszk@agh. edu.pl MANUELA KLAUS and CHRISTOPH GENZEL are with the Abteilung für Mikrostruktur- und Eigenspannungsanalyse, HelmholtzZentrum Berlin für Materialien und Energie, Albert-Einstein-Str. 15, Berlin 12489, Germany. MIROSŁAW WRÓBEL is with the AGH-University of Science and Technology, WIMiIP, al. Mickiewicza 30, 30-059 Kraków, Poland. Manuscript submitted March 12, 2020. METALLURGICAL AND MATERIALS TRANSACTIONS A
makes tungsten one of the most commonly utilized hard metals, for example in the military, aerospace, nuclear, electronic and chemical industries.[4] Tungsten can be used to produce structures working at a high temperature, radiation shields, and parts of a nuclear fusion reactor,[5–10] multipinhole collimators for magnetic resonance devices,[11] electrical switching contacts, magnetrons for microwave ovens, laser printers, air cleaners, and chemical reactors, etc.[12] Surface finishing, such as polishing, is required for many engineering applications. Polishing not only increases the surface smoothness and thereby reduces the stress concentrators, but also changes the stress state in the subsurface layers. In addition, the reduction of surface roughness and the generation of compressive residual surface stresses have a positive effect on fatigue life, which is important in many industrial applications. Polished tungsten products are widely available on the market (e.g., References 13 through 16) and several studies have been devoted to the effects of mechanical polishing on the performance and durability of parts made from this material. Like many body-centered cubic metals, tungsten exhibits a sudden ductile to brittle transition, which occurs at relatively high temperature (i.e., it is ductile above and brittle below ca. 130 °C). Therefore, the reduction of cracking tendency is particularly important in the case of tungsten surface.[13–16] It
was found by Yuan et al.[17] that surface residual stresses induced by mechanical polishing can strongly influence the surface cracking behavior occurring due to
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