TY - JOUR
T1 - Deformation-induced phase transformation in a Co-Cr-W-Mo alloy studied by high-energy X-ray diffraction during in-situ compression tests
AU - Weißensteiner, Irmgard
AU - Petersmann, Manuel
AU - Erdely, Petra
AU - Stark, Andreas
AU - Antretter, Thomas
AU - Clemens, Helmut
AU - Maier-Kiener, Verena
PY - 2019/2
Y1 - 2019/2
N2 - Nickel-free Co-Cr-W-Mo alloys exhibit a very low or even negative stacking fault energy, and therefore a pronounced tendency towards a deformation-induced phase transformation of the metastable face-centered cubic (fcc) γ-phase to the hexagonal close-packed (hcp) low-temperature ε-phase. In order to analyze the phase transformation in-situ and to correlate it to an external strain, compression tests between 30 °C and 400 °C were performed in a deformation dilatometer simultaneously to high-energy X-ray diffraction. Hence, the elastic strains of the fcc unit cell during compression, the external loads for the onset of the phase transformation and the temperature-dependency could be determined. In the parent fcc γ-phase, the evolution of an 101 fiber texture as well as texture inheritance effects and a distinct variant selection could be observed. Further, for the investigated alloy composition it is demonstrated that the continuum concepts of i) a structural stretch tensor and ii) an invariant plane strain perfectly agree with the widely-accepted nucleation theory of ε-martensite formation in Co-Cr alloys via Shockley partial dislocations on every second {111}
γ plane. Both, the observed transformation texture as well as crystallographic transformation strains reveal the importance of shear stresses in this system.
AB - Nickel-free Co-Cr-W-Mo alloys exhibit a very low or even negative stacking fault energy, and therefore a pronounced tendency towards a deformation-induced phase transformation of the metastable face-centered cubic (fcc) γ-phase to the hexagonal close-packed (hcp) low-temperature ε-phase. In order to analyze the phase transformation in-situ and to correlate it to an external strain, compression tests between 30 °C and 400 °C were performed in a deformation dilatometer simultaneously to high-energy X-ray diffraction. Hence, the elastic strains of the fcc unit cell during compression, the external loads for the onset of the phase transformation and the temperature-dependency could be determined. In the parent fcc γ-phase, the evolution of an 101 fiber texture as well as texture inheritance effects and a distinct variant selection could be observed. Further, for the investigated alloy composition it is demonstrated that the continuum concepts of i) a structural stretch tensor and ii) an invariant plane strain perfectly agree with the widely-accepted nucleation theory of ε-martensite formation in Co-Cr alloys via Shockley partial dislocations on every second {111}
γ plane. Both, the observed transformation texture as well as crystallographic transformation strains reveal the importance of shear stresses in this system.
UR - http://www.scopus.com/inward/record.url?scp=85055900993&partnerID=8YFLogxK
U2 - 10.1016/j.actamat.2018.10.035
DO - 10.1016/j.actamat.2018.10.035
M3 - Article
SN - 1359-6454
VL - 164.2019
SP - 272
EP - 282
JO - Acta materialia
JF - Acta materialia
IS - February
ER -