Deformation-induced phase transformation in a Co-Cr-W-Mo alloy studied by high-energy X-ray diffraction during in-situ compression tests. (1st February 2019)

• Record Type: Journal Article
• Authors: Weißensteiner, Irmgard; Petersmann, Manuel; Erdely, Petra; Stark, Andreas; Antretter, Thomas; Clemens, Helmut; Maier-Kiener, Verena
• Is Part Of: Acta materialia. Volume 164(2019)
• Page Start: 272
• Page End: 282
• Publication Date: 2019-02-01
• Subjects: Co-Cr-W -- In-situ -- High-energy X-ray diffraction -- Martensitic phase transformation -- Crystallography; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2018.10.035
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: 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. Graphical abstract: Image 1