Baumgärtner, S.

Bonnekoh, C.

Hoffmann, A.

Hoffmann, J.

Reiser, J.

Zaefferer, S.

KITopen

KIT – The Research University in the Helmholtz AssociationReducing the brittle-to-ductile transition temperature of tungsten to −50 °C by cold rolling a a b a a cC. Bonnekoh , J. Reiser , S. Zaefferer , S. Baumgärtner , J. Hoffmann , A. Hoffmanna b cKarlsruhe Institute of Technology, Germany, Max-Planck-Institut für Eisenforschung GmbH, Germany, Plansee SE, AustriaInstitute for Applied Materials - Applied Materials Physics (IAM-AWP)High-Temperature Materials Group, Campus NorthHermann-von-Helmholtz-Platz 176344 Eggenstein-Leopoldshafenhttp://www.iam.kit.edu/awp Conclusion Severely cold rolled W exhibits a tremendous low BDTT of around −50 °C. Cold deformation transforms W in a grain boundary rich material with a growing fraction of HAGBs. The hyperbolic hardening is interpreted as residual stresses in addition to the hardening caused by the Hall–Petch effect. Because of the finding of an unexpected low dislocation density within most grains, the source of these residual stresses is assumed to be located close to the grain boundaries. The author supposes that W transforms into a grain boundary-controlled material, with highly stressed grain boundaries which are promoting dislocation nucleation. A highly boosted dislocation emission rate leads in accordance with Roberts et al. to a lowered BDTT.Please also note the talk of J. Reiser et al. in session Refractory Metals - Materials 1, RM9 on tuesday 15:20, and the poster of S. Bonk et. al. Rm62 both dealing with severe cold rolled W.−200 0 200 400 600 800050100150 −600 K Results Electron channeling contrast imaging (ECCI) was applied to get a first idea of the dislocation structure and the number of dislocations. An unexpected low dislocation density was observed. A massive shift of the BDTT of around −600 °C took place during cold rolling. Further tests revealed a negligible size effect of about 50 K. Reduction of the BDTT is caused by microstructural modifications during the severe cold rolling.Grain boundary character maps of a low deformed sample and of a highly deformed specimen are represented with view in T-direction. HAGBs are drawn in black, LAGBs are grey. −450 K0.3 μm3 μm 3 μm φ =1.8 CRRDNDRDND Motivation  Background Kapplied1. nucleate2. glideshielding dislocationsanti-shieldingdislocations−1n 	∝	λsourcesAccording to Roberts (1993) the BDTT correlates with the emission of dislocations close to the tip. If grain boundaries act as dislocation sources, the BDTT will decrease with reduced grian size.blunting of the crack tipcrackfrontKeﬀectivegrainboundariesThe selected approach of our tungsten research team is the toughening of W and the shifting of its high BDTT of ~600 °C by applying a cold deformation achieved by severe cold rolling. Tungsten is a promising candidate as a first wall material in fusion reactors and for the piping system of solar powered power stations running a liquid natrium based heat exchange system. Despite its outstanding properties, the extreme brittleness of commercial tungsten pre-vents a successful usage as structural material until now.A reduction of the BDTT by a significant margin is inevitable before W can be applied as a powerful structural material.0 50 100 1500.5fracture toughness at RT /MPa m  Kappliedλ0.4 μmRDNDRDND0.5 −1 1 MPa m  s brittle semi-br. ductile cold rolled, φ =1.8CR as sintered cold rolled, φ =4.1CR φ =1.8 CR φ =4.1CR φ =4.1CRTwo maxima are observed for both materials. The weakly deformed microstructure exhibits a high amount of LAGBs. The HAGB-peak of the severely deformed specimen correlates with the texture components.0 10 20 30 40 50 6002468101214 φ =1.8CR φ =4.1CRHAGBLAGB2° - 15° 15° - 62.8°φCRφCRdisorientation /deg.−3frequency /10temperature /°C 0.5fracture toughness /MPa m requirement for structural applicationsWP91Al O2 3W-4VW-4TiW-26ReW-5TaNb Mo Ta W   25 25 25 25 Aquirre et al. 2010Ashby et al. 2006Bürgel et al. 2014Gludovatz et al. 2010Konopik et al. 2010Palacios et al. 2013Wurster et al. 2011Zou et al. 20170.2 0.4 0.6 0.8 1.0 1.2540580620660φ =4.1CRφ =3.4CRφ =3.0CRφ =2.5CRφ =1.8CR−1 d  ﬁt−0.5 d  ﬁtA strong work hardening was detected. Interestingly, the hardening exceeds the predictions of the Hall–Petch law. A hyperbolic approach describes very well the hardening behavior of fine-grained and ultrafine-grained tungsten.mean grain size in ND /µmmicrohardness /HV0.1rxx 396 ±8 HV0.1 

Reducing the brittle-to-ductile transition temperature of tungsten to -50⁰C by cold rolling

https://publikationen.bibliothek.kit.edu/1000070583/4194709

Reducing the brittle-to-ductile transition temperature of tungsten to -50⁰C by cold rolling

Abstract

Similar works

Full text

Available Versions

KITopen