title: Influence of microstructural modifications induced by ultrasonic impact treatment on hardening and corrosion behavior of wrought Co-Cr-Mo biomedical alloy.
abstract: In this work, biomedical Co-28Cr-6Mo alloy is subjected to ultrasonic impact treatment (UIT). XRD, TEM and SAED analyses show that the plastic deformation induced by the UIT process results in a complex microstructural formation in surface layer of Co-28Cr-6Mo alloy. The peculiar feature observed in the alloy structure by TEM is the formation of Lomer-Cottrell locks originated by simultaneous sliding of Shockley partial dislocations in intersecting planes. At the beginning of the UIT process (till the strain extent e ≈ 0.2), dislocation pile-ups are gathered in front of the Lomer-Cottrell locks stimulating the formation of a great number of chaotic stacking faults (SFs) packets (incompletely transformed martensite), which are predominant with regard to the occurrence of ε-martensite and micro-twins. The incompletely transformed martensite hinders the shear translation through the twin boundaries and suppresses grain subdivision in surface layer of Co-28Cr-6Mo alloy at the UIT process used. On-going deformation to e ≈ 0.4 leads to further modification of microstructure in the micron-scale γ-grains, which consists of numerous Lomer-Cottrell locks, chaotic subtraction SFs, intersected nano-twins and fine lathes of ε-martensite with average size of approx. 50-100 nm. The observed structural features (at e ≈ 0.4) allow adequately explaining noticeable increase in microhardness without any cracks/cleavages in surface layer. Enhanced corrosion resistance of Co-28Cr-6Mo alloy, which manifests itself with less negative corrosion potential and lower corrosion and passivity currents in potentiodynamic curve, is promoted by the UIT induced oxide films and the following structural features: the CSL type of γ/ε interfacial boundaries, uniformly distributed fine carbides, and high fraction of the grains oriented with close packed (111)γ and (0002)ε planes parallel to the surface of the UIT-processed specimen.
authors.affiliation: Kurdyumov Institute for Metal Physics, NAS of Ukraine, 36 Academician Vernadsky blvd. UA, -03142, Kyiv, Ukraine.
authors.forename: Yu N
authors.initials: YN
authors.lastname: Petrov
authors.affiliation: Kurdyumov Institute for Metal Physics, NAS of Ukraine, 36 Academician Vernadsky blvd. UA, -03142, Kyiv, Ukraine.
authors.forename: G I
authors.initials: GI
authors.lastname: Prokopenko
authors.affiliation: Kurdyumov Institute for Metal Physics, NAS of Ukraine, 36 Academician Vernadsky blvd. UA, -03142, Kyiv, Ukraine. Electronic address: mordyuk@imp.kiev.ua.
authors.forename: B N
authors.initials: BN
authors.lastname: Mordyuk
authors.affiliation: Kurdyumov Institute for Metal Physics, NAS of Ukraine, 36 Academician Vernadsky blvd. UA, -03142, Kyiv, Ukraine.
authors.forename: M A
authors.initials: MA
authors.lastname: Vasylyev
authors.affiliation: National Technical University "Kyiv Polytechnic Institute", 37 Peremohy AvenueUA-03056, Kyiv, Ukraine.
authors.forename: S M
authors.initials: SM
authors.lastname: Voloshko
authors.affiliation: Kurdyumov Institute for Metal Physics, NAS of Ukraine, 36 Academician Vernadsky blvd. UA, -03142, Kyiv, Ukraine.
authors.forename: V S
authors.initials: VS
authors.lastname: Skorodzievski
authors.affiliation: Kurdyumov Institute for Metal Physics, NAS of Ukraine, 36 Academician Vernadsky blvd. UA, -03142, Kyiv, Ukraine.
authors.forename: V S
authors.initials: VS
authors.lastname: Filatova
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D002858:Chromium Alloys / Q000737:chemistry*; D003343:Corrosion; D006244:Hardness; D013499:Surface Properties; D014465:Ultrasonics
chemical_list: D001672:Biocompatible Materials; D002858:Chromium Alloys
keywords: Corrosion; Electron microscopy; Hardness; Microstructure; Ultrasonic impact treatment; Wrought Co-Cr-Mo alloy