Effect of small quantities of carbon and nitrogen on the elastic and plastic properties of iron
Zusammenfassung
Die Erscheinung der elastischen Nachwirkung in reinem und technischem Eisen und in Eisenlegierungen wird diskutiert, insoweit sie durch die Anwesenheit von Stickstoff oder Kohlenstoff in fester Lösung verursacht wird.
Es stellt sich heraus, dass die elastische Nachwirkung in allen untersuchten Werkstoffen, soweit sie kubisch raum zentriert sind, anwesend ist und denselben Charakter zeigt.
Die Nachwirkung wird bei den untersuchten Temperaturen hinreichend genau durch eine einzige Relaxationszeit τ beschrieben, welche identisch ist mit dem magnetisch ermittelten Werte. Bei Änderung der Messtemperatur wird ein Maximum in der Dämpfung durchlaufen.
Das obengesagte gilt aber nur für ausgeglühte Proben. Wird die Probe kalt verformt, so verschwindet das erste Maximum und es taucht ein zweites auf bei höheren Temperaturen. Dieses Maximum wird als “Gorski” Dämpfung gedeutet.
Für das erste Maximum wird eine neue Deutung vorgeschlagen, welche von der früher vorgeschlagenen nur wenig verschieden ist.
References (9)
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Ann. Physik, Leipzig
(1937)G. RichterAnn. Physik, Leipzig
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Phys. Rev.
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Cited by (312)
Identification and analysis of a reverse dynamic strain ageing in welded joints of C-Mn steels in the secondary circuit welds of nuclear power plants
2024, Scripta MaterialiaIn an original way, we exploit a restricted region within the dynamic strain ageing domain where a simultaneous increase in strength and uniform elongation has been shown, with increasing free solute concentrations. This unusual reverse dynamic strain ageing was shown to be a marker of the interaction between strain ageing and strain hardening. Analysis, based on a dual experimental and theoretical approach, shows that dynamic strain ageing reduces the ability of the material to exhibit dynamic recovery. This regime operates at very low solute concentrations and saturates above a critical solute concentration. All the results obtained support the dislocations/solutes interactions as the main mechanism.
Carbon diffusivity by means of Snoek relaxation in ternary Fe-26 at%(Al+Ga) alloys with different Al/Ga ratio
2024, Journal of Alloys and CompoundsAnelastic relaxation in the temperature range from 0 to 300°C (0.1–30 Hz) in ternary Fe-26(Al+Ga)-0.1Tb alloys is experimentally studied and analysed with respect to binary Fe3Al and Fe3Ga intermetallic compounds. The Snoek-type relaxation due to cyclic stress-induced carbon atom jumps between octahedral interstices in the α-Fe based solid solution (Fe-C-Al,Ga) is recorded and analysed. The Snoek-type effect in the ternary Fe-26(Al+Ga)-0.1Tb alloys has a higher activation energy (up to ∼1.2 eV) in comparison to α-Fe-C (0.83 eV). The relaxation effect demonstrated significant broadening with respect to Debye peak with a single relaxation time and splitting into two separated peaks at a certain ratio Al/Ga. Snoek-type effect provides a unique opportunity to measure C atom diffusivity at relatively low temperatures. Influence of the chemical composition and the measuring frequency on the activation parameters in Fe-26(Al+Ga)-0.1Tb alloys are reported and analysed to estimate the impact of Al and Ga atoms on C atom diffusivity in α-Fe based solid solution.
Plasticity induced anelasticity: The atomistic origin
2024, International Journal of PlasticityPlastic deformation is associated with developments in both dislocation density and residual strain. This study used multi-scale diffraction-based, X-ray as well as electron diffraction, measurements to quantify and relate them. Though both increased with progressive tensile deformation, an inverse orientation dependent relationship clearly emerged. In particular, higher elastically strained regions were accommodated by dislocation walls of lower residual strain. These experimental observations provided a combined perspective of elastic-plastic strain gradients in experimental plasticity. This study was then extended towards anelasticity, or internal friction, as induced by plastic deformation and elastic-plastic strains. Plastic deformation is known to enhance internal friction loss factor, , which then leads to the so-called dislocation enhanced Snoek (DES) peak. However, the atomistic origin of DES, role of elastic versus plastic strain, has never been established. Experimental nano dynamic mechanical analysis (nano-dma) measurements were used to bring out the plasticity induced DES of near-(001) grains. Experimental DES, however, scaled with both dislocation density and residual strain. This ambiguity necessitated use of numerical simulations to decouple respective contributions. Firstly, continuum finite element simulations indicated a stronger impact of residual stress, than the total stress, on the experimental DES. Further, atomistic modeling simulated (i) single-crystal nano-dma response and (ii) corresponding developments in residual stress as well as dislocation density. In particular, the DES emerged as an attribute of the non-uniform residual strain field(s) associated with dislocation(s). The corresponding change(s) in the anisotropies of local activation energy landscape, for interstitial diffusion of carbon, determined the enhanced Snoek response. Our experiments plus numerical modeling, thus brought out, and for the first time, a unique atomistic perspective towards anelasticity induced by plastic deformation.
The bake hardening value is one of the vital strength indexes of dual-phase steel, representing the strengthening ability of materials after pre-strain and baking, playing an important role in vehicle safety and lightweight design. Studying and improving the strain aging mechanism of dual-phase steel helps one to understand the material characteristics and enhances its utilization value. However, the ultra-high strength dual-phase steel is often prone to fracture outside the gauge length of a tensile specimen of the bake hardening value test. No suitable theory explains the fundamental law of dislocation pinning during the saturation stage at present. This paper used FEA, DIC, SEM, TEM, internal friction, and metallographic methods to study the strain aging behavior of dual-phase steels under different pre-strain, bake time, and bake temperature conditions. The results show that the fracture outside the gauge length is related to factors such as the uneven distribution of pre-strain and the ultra-high upper yield strength. The rolling pin shape tensile specimen testing has successfully solved this testing problem. The measured results at the saturation stage of dislocation pinning are in good agreement with the fitting results of the dislocation pinning strengthen mechanism based on the probability event quantization assumption.
Tetragonal dipole dominated Zener relaxation in BCC-structured Fe-17at.%Ga single crystals
2023, Acta MaterialiaThe stress-induced reorientation of the low-symmetry defects due to substitution atom pairs can give rise to an internal friction peak (Zener relaxation) and the first-nearest-neighbor substitutional atom pairs are plainly considered as the dominant contribution. Here, the Zener relaxation in the body-centered cubic (BCC) FeGa single crystals with different orientations was investigated, which against intuition originates primarily from the stress-induced reorientation of the second-nearest-neighbor Ga-Ga atom pairs. This Ga-Ga atom pair configuration is prevalent at high temperatures as directly observed by high-temperature in situ electron microscopy experiments. This phenomenon establishes non-ambiguously a direct correlation between Zener relaxation strengths and magnetostrictive properties. In addition, it was found that the diffusion activation energy of Ga atoms in FeGa single crystals is significantly lower than that in other iron-based alloys, suggesting that this value is closer to the actual diffusion activation energy of Ga atoms in FeGa alloys. These findings offer valuable insights into the study of short-range ordering in BCC alloys and the exploration of their functional properties.
Phase-field modeling of dislocation–interstitial interactions
2023, Journal of the Mechanics and Physics of SolidsThe mechanical behavior of body-centered cubic (BCC) materials can be dramatically affected by the presence of interstitial solute atoms. We present a new phase-field dislocation dynamics formulation to include the diffusion of interstitials. Short-range interactions are accounted for by a concentration-dependent lattice energy, and long-range interactions are accounted for by modifications to the elastic energy. The interstitial diffusion law introduces gradients that require methods for minimizing Gibbs oscillations, which is done via a modified Green’s function. The formulation is general to any solute-solvent system and is applied here to Nb-O as a model system, whose interstitial parameters are obtained from ab initio calculations. The effect of O on the core structures of Nb edge and screw dislocations is calculated. The diffusion of O to form interstitial atmospheres around dislocation cores is simulated, as well as the critical stresses required for dislocations to break away or cross slip from these atmospheres. Future applications of the method to simulate complex interstitial embrittlement mechanisms are discussed.