Dependence Of Stacking Fault Energy Research Articles

In Situ Bulk Observations and Ab Initio Calculations Revealing the Temperature Dependence of Stacking Fault Energy in Fe\u2013Cr\u2013Ni Alloys

The dependence of stacking fault energy ({gamma }_{text{SFE}}) on temperature in austenitic Fe–Cr–Ni alloy powders was investigated by in situ high energy synchrotron X-ray diffraction and ab initio calculations in the temperature range from − 45 °C to 450 °C. The X-ray diffraction peak positions were used to determine the stacking fault probability and subsequently the temperature dependence of γSFE. The effect of temperature on the diffraction peak positions was found to be mainly reversible; however, recovery of dislocations occurred above about 200 °C, which also gave an irreversible contribution. Two different ab initio-based models were evaluated with respect to the experimental data. The different predictions of the models can be explained by their respective treatment of the magnetic moments for Cr and Ni, which is critical for the alloy compositions investigated. Ab initio calculations, taking longitudinal spin fluctuations (LSF) into consideration within the quasi-classical phenomenological model, predict a temperature dependence of {gamma }_{rm SFE} in good agreement with the experimentally evaluated trend of increasing γSFE with increasing temperature: left|Updelta {gamma }_{rm SFE}/Updelta Tright|=0.05 {text{mJ}} {text{m}}^{-2}/{text{K}}. The temperature effect on γSFE is similar for all three investigated alloys: Fe–18Cr–15Ni, Fe–18Cr–17Ni, Fe–21Cr–16Ni (wt pct), while their room temperature {gamma }_{rm SFE} are evaluated to be 22, 25, 20 mJ m−2, respectively.

The Stacking Fault Energy and its Dependence on the Interstitial Content in Various Austenitic Steels

The stacking fault energy (SFE) is an intrinsic property of metals and is involved in the deformation mechanism of different kind of steels, such as TWIP (twinning induced plasticity), TRIP (transformation induced plasticity), HNS (high nitrogen), and high strength steels. The dependence of the SFE on the content of interstitial elements (C, N) is not yet fully understood, and different tendencies have been found by different authors. In order to study the influence of the interstitial elements on the SFE, experimental measurements extracted from literature were collected and analyzed to predict the individual and combined effect of carbon and nitrogen in different systems. The referenced austenitic steels are Fe-22Mn-C, Fe-30Ni-C, Fe-15Cr-17Mn-N, Fe-18Cr-16Ni-10Mn-N, Fe-18Cr-9Mn-C-N, Fe-18Mn-18Cr-C-N and Fe-(20-30)Mn-12Cr-C-N. The calculation of the SFE is based on the Gibbs free energy of the austenite to ε-martensite transformation (ΔGγàε), which is calculated by means of the Calphad method. The revision of the measured values reveals that on different ranges of interstitial contents the SFE behaves differently. At lower values (C, N or C+N up to 0.4%), a local minimum or maximum is found in most of the systems. At higher concentration levels, a proportional dependence seems to occur. These observations agree with the theory of the dependence of SFE on the free electron concentration. Alloying with Mn or Ni has a strong influence on the electronic configuration and magnetic properties of the austenite and therefore on the SFE. The results of this study provide valuable information for materials design, especially in the context of alloying with C, N or C+N.

Influence of stacking-fault energy on high temperature creep of alpha titanium alloys

The stacking-fault energy (SFE) has been incorporated in the calculation of the steady-state creep rate of commercially-pure titanium and Ti–(1–10) mol.% Al alloys. Their creep behaviour was found to follow power-law creep when the dependence of SFE on the aluminium content was taken into account in the calculation. The possible contribution due to the formation of short range ordered structure is also discussed, with the conclusion that the decrease in SFE with increasing aluminium addition is the major factor for the strengthening effect in α Ti–Al alloys.

A thermodynamic model for the stacking-fault energy

A general thermodynamic model for calculating the energy of stacking faults is presented and applied to f.c.c. Fe–Cr–Ni alloys. A distinction is made between ideal stacking faults and real stacking faults which are associated with an ideal stacking-fault energy (SFE) and an effective SFE, respectively. The ideal SFE is characterized by a chemical energy volume term and an interphase surface energy term, whereas the effective SFE is defined by an additional strain energy volume term. The chemical and strain energy terms are evaluated from theoretical considerations. The interphase surface energy is calculated based on a comparison with experimental values obtained from Transmission Electron Microscopy (TEM) measurements. The results of this analysis show a good agreement between the calculated and experimental values. The model enables the determination of the ideal and effective stacking fault energies as a function of the Cr and Ni contents. The SFE dependence on the Cr vs Ni contents has the shape of a hyperbola.

Dislocation cell structure relationd =Kϱ−1/2: The stacking fault energy dependence ofK

The Holt relation d = Kϱ−1/2 between dislocation cell diameter d and average dislocation density ϵ is found to apply to Mo–50wt% Re when K = 4. Comparison with other published dislocation cell data shows that K does not remain constant, but varies from metal to metal. The effect of stacking fault energy on the K value is demonstrated to be significant. Il a ete constate que la relation de Holt d = Kϱ−1/2 entre le diametre de la dislocation de la cellule et la densite 7egr; de la dislocation moyenne est applicable a Mo-50 wt% Re quand K = 4. Une comparaison avec d'autres donnees publiees sur la dislocation de la cellule fait ressortir que K ne demeure pas constant, mais varie de metal a metal. Il est demontre que l'effet d'emmagasinement d'energie de fuite sur la value K est significatif.