The Effects of Short‐Range Order and Long‐Range Order on the Equilibrium Configuration of Superdislocations in FeCo : 2 at% V — Consequences on Flow Stress

Abstract

The variations in flow stress of Fe-Co: 2 atyo V as a function of test or quench temperature exhibit a maximum near the critical temperature for ordering, T,. Transmission microscope study of thin foils reveals the existence of paired dislocations not only at temperatures below T, but also at temperatures above T, where only short-range order exists; calculations of their equilibrium spacing using the quasi-chemical theory [6] are in agreement with experimental results. The peak in flow stress may be explained assuming that for high values of S (S is the long-range order parameter) the dislocation sources are constituted by paired dislocations which keep parallel configurations when operating, and that for low values of S (or 8 = 0 ) sources are constituted by single dislocations or by paired dislocations with only one of them operating.Lea variations de la, limite blastique du Fe-Co: 2 atyo V en fonction de la tempbrature d'essai ou de la tempbrature de trempe prbsentent un maximum proche de la tempbrature critique d'ordre T,. L'examen de lames minces par microscopie blectronique r6vAle la prbsence de dilocations appariQs non seulement pour des tempbraturea de trempe infbrieures 8. T,, mais aussi pour des ternfiraturea supbrieures oh seul subsiste un ordre 8. courte distance; la thborie quasichimique [6] permet de faire un calcul de leur distance d'bquilibre conforme aux rbsultats expbrimentaux. Le pic de limite bl?stique peut %re interprbth en supposant que pour S grand (8 eat le paramhtre d'ordre 8. grande distance) lea sources de dislocations sont constituQs par des dislocations doubles qui gardent des configurations parallhles au cours de leur dbformation et que pour 8 faible ou nul lea sources sont constit u b s par des dislocations simples ou des dislocations doubles dont une seule des partiellea eat active.

Near equiatomic FeCo alloys: Constitution, mechanical and magnetic properties

“…31, the yield stress exhibits a peak for quench temperatures slightly below the critical temperature (corresponding to S $ 0.4 according to Stoloff and Davies). Identical results have been obtained by Marcinkowski and Chessin [96] and Moine et al [97] (shown in Fig. 31).…”

“…Results from Moine et al [97] for strain rates of 3.375 s À1 and 0.0375 s À1 suggest that the position and amplitude of the peak is independent of strain rate. While the difference between the behaviour of FeCo-2V (Fig.…”

“…Illustration of the mechanism proposed by Stoloff and Davies to explain the influence of order/ disorder (and of temperature through order/disorder) on the yield strength of FeCo based alloys, after [75]. Predictions by Moine et al, for yield strength measured at indicated temperature and after quenching from the indicated temperature, after [97]. Note that the curve for quench temperature has been shifted to lower values for easier comparison.…”

“…Moine et al [97] noted that superlattice dislocations are found even in alloys quenched from above T c . These authors then proposed a quantitative analysis of the problem based on the stress required to activate Franck-Read sources for single and superlattice dislocations.…”

Effect of vanadium on atomic ordering characteristics and anti-phase boundary energies of B2–FeCo alloys

“…A general agreement is achieved on ODT temperature of stoichiometric FeCo alloy as T o z 1000 K which is the highest of any binary B2-FeCo alloy [3]. The lower ductility and flow stress of ordered B2 phase relative to disordered A2 phase and accompanying anomaly around T o are explained by the transition of slip mechanism from superlattice to single dislocations [4,9,16]. Vanadium alloying is proposed to retard the ODT reaction [6,17] and similarly decrease long range order (LRO) parameter [18,19] relative to pure-FeCo quenched from same temperature.…”