Defects induced through rapid solidification in a Co–20 Cr alloy

Martensitic transformation in cobalt alloys has been widely explored due to its complex nature. Recent studies demonstrated that rapid solidification enhances the γ–FCC → ε–HCP transformation through a high density of ε–martensite nucleating defects formation (i. e. vacancy supersaturation, sub – mi...

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Bibliographic Details
Published in:	Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 844; p. 143161
Main Authors:	Ramirez – Ledesma, A.L., Luna – Manuel, J.C., Lopez, H.F., Juarez – Islas, J.A.
Format:	Journal Article
Language:	English
Published:	Lausanne Elsevier B.V 02-06-2022 Elsevier BV
Subjects:	Alloys Athermal martensite Chromium base alloys Cobalt base alloys Cobalt–based alloys Defects Internal defects Martensite Martensitic transformation Martensitic transformations Mechanical properties Rapid solidification Recrystallization Retained austenite Staking Supersaturation Thickening Transmission electron microscopy Internal defects Cobalt–based alloys Martensitic transformation Transmission electron microscopy Athermal martensite
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Summary:	Martensitic transformation in cobalt alloys has been widely explored due to its complex nature. Recent studies demonstrated that rapid solidification enhances the γ–FCC → ε–HCP transformation through a high density of ε–martensite nucleating defects formation (i. e. vacancy supersaturation, sub – micron sized voids, staking faults/ε – martensite plate intersections, among others), resulting in almost 100% ε–martensite. In this work, the rapid solidified (RS) alloy exhibits a complex microstructure consisting of an athermal ε–martensite matrix with residual austenite (γ–phase) as the γ → ε transformation was kinetically dominant. Thus, a variety of defects are exposed, and critical theoretical modeling is derived from TEM experimental evidence, consequently, their interactions as a stair–rod dislocations are proposed. A disclosure concerning how these defects’ interaction influence the mechanical behavior of the studied Co–20 Cr alloy in the as – cast and heat – treated (at 1023 K/750 °C for 1 h) conditions is presented. In particular, annealing was found to be highly effective in promoting alloy strength and ductility. Apparently, internally straining is considerably reduced through thermally activated recovery mechanisms including ε–plate thickening and alloy recrystallization. •The martensitic transformation complexity in Co–Cr alloys is once again exposed.•Rapid solidification enhances martensitic transformation via high density – defects formation.•A critical theoretical modeling regarding martensite/defects interactions is proposed.•A full hexagonal phase exhibits outstanding ductility after an isothermal treatment.
ISSN:	0921-5093 1873-4936
DOI:	10.1016/j.msea.2022.143161