Search

The pitting corrosion behaviour of 27%Cr–7%Ni (2707) hyper‐duplex stainless steel (HDSS) at ambient temperature has been assessed using a novel bipolar electrochemistry test set‐up. Application of this technique generates a linear potential gradient at the surface of the HDSS 2707 test piece, which allows assessment of the pitting corrosion behaviour at ambient temperature. Pit nucleation and associated growth kinetics can be obtained and characterised. To assess pitting corrosion in high‐alloyed HDSS, the normal bipolar test method had to be modified by superimposing an auxiliary potential. This new test set‐up was demonstrated by characterising the nucleation of pits and associated pit growth kinetics. The latter occurred either at austenite/ferrite interphase or inside ferrite phase, with pit growth within the ferrite phase in the HCl environment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lean duplex stainless steel was heat treated at 1000℃ to 1350℃. • Pit nucleation and growth kinetics were obtained at room temperature. • Heat treatments at 1000℃ had the highest pitting corrosion resistance. • A new microstructure design containing isolated small ferrite grains is proposed. The corrosion performance of type 2101 lean duplex stainless steel (LDSS) after different solution annealing heat treatments is investigated. The austenite to ferrite phase ratios and morphologies are correlated to their localised corrosion responses, with the application of bipolar electrochemistry providing access to pit nucleation and growth kinetics. The propagation of pitting corrosion via selective dissolution of the ferrite phase is observed, pointing towards a direct effect of ferrite morphology on pit shape. The corrosion behaviour of solution heat treatments are compared and ranked, providing information for improving and optimising the corrosion resistance of LDSS 2101 microstructures. [ABSTRACT FROM AUTHOR]

• Bipolar electrochemistry to probe localised corrosion in stainless steel rebars is introduced. • The full spectrum of anodic-to-cathodic corrosion response is accessible. • Pit growth kinetics and 3D pit ratio development are reported. • Trans-passive corrosion and selective phase dissolution are observed and discussed. The corrosion performance of stainless steel rebars is assessed by using bipolar electrochemistry. This method produces a quasi-linear potential gradient across the sample, with the technique providing rapid access to test for the nucleation and growth of pits across a wide range of applied potentials. The localised corrosion behaviour and resulting growth kinetics of Types 304L and 316L austenitic stainless steels (ASSs) are compared to Type 2101 and 2205 duplex stainless steels (DSSs). The difference in selective phase dissolution between pitting and trans-passive corrosion in DSSs is compared, with critical pitting potential, pit nucleation numbers, growth kinetics, volume loss, and aspect ratio of these four stainless steels discussed. [ABSTRACT FROM AUTHOR]

In present work, mechanical alloying (MA) is employed to produce composite powders of titanium (Ti) containing 0.25 wt% graphene nanoplatelets (GNPs). Four composite powder samples are prepared by carrying out high energy ball milling (HEBM) at different milling times. Subsequent cold compaction and pressureless sintering are performed to obtain sintered compacts. Influence of ball milling time on powder characteristics, crystallographic as well as morphological evolution, relative density, compressibility, corrosion rates and mechanism, sinterability and hardness of the composites have been investigated. The plastic deformation capacity and yield stress of the composite powders are analyzed using linear compaction equations. X-ray diffraction has confirmed the non-occurrence of titanium carbide (TiC) formation during MA. Scanning electron microscopy has not only revealed a transformation in morphology of Ti particle from bulk shape to flaky but also has shown a strong adherence of GNPs on Ti particles. Electrochemical characterization results indicate that exchange current density for 6 h ball milled sample is quite high that leads to a thicker TiO 2 resulting in pitting corrosion. Sinterability and micro hardness values are found to be highest for 2.5h ball milled composite in comparison to others. • Effect of milling times on structural and electrochemical properties are investigated. • TiC phase formation increases as milling duration is increased. • The corrosion rates are not much affected with the addition of 0.25 wt% graphene. • 6h ball milled composite reveals the presence of TiO 2 leading to pitting corrosion. • Sinterability and micro hardness are found highest for 2.5h ball milled composite. [ABSTRACT FROM AUTHOR]