CRITICAL ASSESSMENT 1: Outstanding issues in crystallographic variant selection in displacive transformations

Abstract

Variant selection has been a well researched subject in metallurgy and materials science in recent decades. The emergence of experimental techniques capable of determining crystallographic orientation at the grain level has provided insight into the fundamental processes underlying variant selection. The theory, however, is far from complete. Fundamental questions, such as the specific roles of stress and strain in variant selection, have yet to be fully resolved. It remains unclear whether variant selection is a nucleation controlled phenomenon or growth controlled. The possibility of using unconventional forces such as magnetic or electrical fields to influence variant selection is of interest, but needs further research. Any phenomenon related to phase transformation gains importance only when it can be controlled to improve material properties, and it is still unclear how variant selection can be applied to this end. The literature is critically assessed and an attempt is made to identify areas for future research with potential to allow effective application of variant selection.

A roadmap for tailoring the strength and ductility of ferritic/martensitic T91 steel via thermo-mechanical treatment

“…where U is interaction energy, τ is the shear stress resolved on the habit plane of a variant, σ is arising from the prior formed thicker martensite laths as shown in early studies [55,56]. Detailed review of variant selection is given by Kundu recently [58]. Gong et al suggested that a bainite transformation may be accelerated by ausforming [59].…”

Charpy impact property related to {100} cleavage fracture in 15CrODS steel

“…[4][5][6][7][8][9] A role of {100} cleavage fracture has been reported in line pipe steels. [10][11][12] Garcia-Junceda et al 13 found out an occurrence of delamination fracture associated with {100} cleavage plane in the hot extruded bar of 14CrODS steel. Kimura and Inoue 14 controlled the delamination fracture along the {100} cleavage plane in a low alloy steel formed by caliber-rolling during a tempering, and they attained extremely high absorbed energy at around room temperature, called inverse temperature dependence of toughness.…”

Critical Assessment 8: Outstanding issues in electropulsing processing

“…Implementation of electromagnetic field to crystal orientation selection is an interesting topic. 45 It is reported that electropulsing causes sudden reduction of electrical resistance and change of atomic element distribution in packed oxide powders. 46 The observed change of electrical resistance proves not to be due to thermal effects but is rather dominated by field induced dielectric breakdown.…”

“…Implementation of electromagnetic field to crystal orientation selection is an interesting topic. 45…”