Resolved Shear Stress Research Articles

Study on the plasticity enhancing mechanism of silver-based solid solution for electronic packaging

Ag-based solid solutions have gained significant attention in the electronic packaging field due to their remarkable plasticity. In this work, the generalized planar fault energy (GPFE), critical strength and stresses, and electronic properties after adding solutes with different types and size misfits were studied for Ag-based solid solutions. Furthermore, we explored the underlying mechanism behind the impact of solutes on the plasticity of Ag and confirmed it through transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) analyses. Importantly, we introduced the novel concepts of size and chemical misfit factors, electronic factors, and twinning factor into the plasticity enhancement mechanism of Ag-based solution systems. The predictions based on these factors were in agreement with experimental observations using TEM and HRTEM. Remarkably, the (Ag)–Bi system exhibited the lowest critical resolved shear stress for slip and twinning, as well as the most superior plasticity, positioning it as a crucial candidate for future development. This study presents a scientific framework for designing and developing Ag-based solid solutions with excellent plasticity, encompassing size/chemical factors, electronic factors, and twinning factor.

Effects of shear strain on shock response in single crystal iron

With large-scale non-equilibrium molecular dynamics simulations and in situ x-ray diffraction analysis, we conducted a systematic investigation into the effects of pre-existing shear strain (γxy) on the shock response of single crystal iron. Our findings reveal significant effects of γxy on the deformation of the crystal structure during shock loading, leading to noticeable alterations in the propagation of shock waves. Specifically, during the elastic stage, the presence of γxy results in a reduction of shock strength, consequently diminishing the magnitude of elastic lattice strain (εe). In the plastic stage, γxy stimulates the α–ε phase transformation, and structure deformation undergoes a transition from the sequential activity of dislocation-to-transformation to the synchronous activity of dislocation and transformation. This transition inhibits the propagation of plastic waves and consequently broadens the elastic regime. Additionally, the introduction of γxy activates different slip systems, as it alters the corresponding resolved shear stress. Concurrently, the presence of γxy triggers the activation of different high-pressure phase variants. Our investigation sheds light on the fundamental physics of iron under shock compression and the influence of pre-existing shear strain on its behavior.

Kink bands promote exceptional fracture resistance in a NbTaTiHf refractory medium-entropy alloy.

Single-phase body-centered cubic (bcc) refractory medium- or high-entropy alloys can retain compressive strength at elevated temperatures but suffer from extremely low tensile ductility and fracture toughness. We examined the strength and fracture toughness of a bcc refractory alloy, NbTaTiHf, from 77 to 1473 kelvin. This alloy's behavior differed from that of comparable systems by having fracture toughness over 253 MPa·m1/2, which we attribute to a dynamic competition between screw and edge dislocations in controlling the plasticity at a crack tip. Whereas the glide and intersection of screw and mixed dislocations promotes strain hardening controlling uniform deformation, the coordinated slip of <111> edge dislocations with {110} and {112} glide planes prolongs nonuniform strain through formation of kink bands. These bands suppress strain hardening by reorienting microscale bands of the crystal along directions of higher resolved shear stress and continually nucleate to accommodate localized strain and distribute damage away from a crack tip.

Fatigue Analysis of the Nickel-Based Superalloy Inconel 617 by Fatigue Experiments and EBSD Data-Based Finite Element Simulations in Correlation with E·m Theories

Nickel-based superalloys exhibit pronounced elastic anisotropy and, hence, the local grain orientation strongly affects the stress and strain distribution in the material under mechanical loadings. Therefore, the crack initiation and failure behaviour of components made from nickel-based superalloys are complex and hardly predictable. A better fundamental understanding of the phenomena that occur in nickel-based superalloys under a quasistatic and cyclic load is therefore desired. Previously, a continuum mechanics-based model has been successfully developed, considering the grain structure, the elastic anisotropy, and the Schmid factor, based on data from electron backscatter diffraction (EBSD). The E·m model was confirmed by the finite element method (FEM) simulations and experimental observations regarding the resulting average stresses and strains in the individual grains as well as the formation of slip bands under a quasistatic load with few restrictions. The behaviour under cyclic loadings has been investigated in this work to correlate the mechanical behaviour, simulated by the previously developed FE models, with the local stiffness and Schmid factors considering fatigue failure. For this purpose, the fatigue behaviour of Inconel 617 samples was characterised up to the high-cycle fatigue (HCF) regime, accompanied by EBSD measurements for stress amplitudes that resulted in strains close to the elastic–plastic regime. The EBSD data were used to create digital twins of the samples to simulate the mechanical reaction to a displacement similar to the associated strain of the fatigue tests. An analysis of the fractured samples by scanning electron microscopy was performed to retrace the location of the crack initiation supported by the EBSD measurements before and after fatigue testing. Two samples were investigated in detail that showed different fracture types. Sample 1 showed transcrystalline failure in a grain that showed a high Young’s modulus, Schmid factor, and resolved shear stress that indicates a failure due to the properties of the grain itself. In contrast, an intercrystalline failure was observed for sample 2 that showed large differences in the orientation and, hence, largely different mechanical properties in the area of failure as well. The observed failure types, the resulting stresses and strains calculated by the FE model, and the consideration of the E·m model showed an agreement of all the methods. Therefore, the findings of this work complement previous investigations of the mechanical behaviour of coarse-grained anisotropic nickel-based superalloys with a focus on the orientations of the grains towards the loading direction.

A phase-field model of concurrent Suzuki segregation and partial dislocation glide

Co–Al–W-base superalloys with the classic γ−γ′ microstructure offer exciting high temperature property profiles. High temperature deformation in such alloys involves shearing of the γ′ phase by a a/3〈112〉 superpartial to create a superlattice intrinsic stacking fault (SISF) while the trailing a/6〈112〉 partial is pinned at the γ−γ′ interface. Experiments indicate that Suzuki segregation to such faults lowers their energy, which in turn lowers the resistance to partial dislocation glide. However, quantifying the extent of solute segregation and its impact on the dynamics of partial dislocation glide from experiments is challenging. In order to fulfill the purpose computationally, in this paper, we present a phase-field model of the phenomenon of concurrent solute segregation and partial dislocation glide. Our simulations reveal that under creep conditions in a representative pseudobinary alloy belonging to the Co–Al–W system, there is a marked increase in the partial dislocation velocity due to solute segregation. The rise in dislocation velocity due to segregation is found to be more significant for lower resolved shear stresses on the dislocation. Higher solute interdiffusivity also leads to enhanced partial glide velocities. Our model can be extended to multicomponent systems, which can, in turn, be used to accelerate the design of novel Co-base superalloys by predicting the kinetics of the displacive-diffusive shearing of the γ′ phase for prospective alloy systems.

Fractography of Stress Corrosion Cracking of 20% Cold Worked Type 304 H Stainless Steel Containing δ-Ferrite in Oxidizing Primary Water

Fractography of stress corrosion cracking (SCC) of 20% cold worked Type 304 H stainless steel containing δ-ferrite was studied using a compact tension (CT) specimen in oxidizing primary water with a scanning electron microscope (SEM) and electron back scattered diffraction (EBSD). The stress corrosion crack propagated mostly in transgranular stress corrosion cracking (TGSCC) mode and sometimes in intergranular stress corrosion cracking (IGSCC) mode. TGSCC paths were along the {111} plane with both high resolved shear stress and high resolved tensile stress. IGSCC preferentially propagated along the grain boundary perpendicular to the loading axis. The findings in this work suggest that TGSCC proceeds through formation of a weakening zone at the head of the crack tip by interaction of slip and corrosion and then cracking of the weakened zone by tensile stress.

A Full-Field Crystal Plasticity Study on the Bauschinger Effect Caused by Non-Shearable Particles and Voids in Aluminium Single Crystals

In the present work, the goal is to use two-scale simulations to be incorporated into the full-field open software DAMASK version 2.0.3 crystal plasticity framework, in relation to the Bauschinger effect caused by the composite effect of the presence of second-phase particles with surrounding deformation zones. The idea is to achieve this by including a back stress of the critical resolved shear stress in a single-phase simulation, as an alternative to explicitly resolving the second-phase particles in the system. The back stress model is calibrated to the volume-averaged behaviour of detailed crystal plasticity simulations with the presence of hard, non-shearable spherical particles or voids. A simplified particle-scale model with a periodic box containing only one of the spherical particles in the crystal is considered. Applying periodic boundary conditions corresponds to a uniform regular distribution of particles or voids in the crystal. This serves as an idealised approximation of a particle distribution with the given mean size and particle volume fraction. The Bauschinger effect is investigated by simulating tensile–compression tests with 5% and 10% volume fractions of particles and with 1%, 2%, and 5% pre-strain. It is observed that an increasing volume fraction increases the Bauschinger effect, both for the cases with particles and with voids. However, increasing the pre-strain only increases the Bauschinger effect for the case with particles and not for the case with voids. The model with back stress of the critical resolved shear stress, but without the detailed particle simulation, can be fitted to provide reasonably close results for the volume-averaged response of the detailed simulations.

A viscoplastic self-consistent analysis of tensile anisotropy and tension-compression asymmetry in rare-earth magnesium alloy

The anisotropy and tension-compression asymmetry of rare-earth magnesium (Mg-RE) alloys have attracted significant attention. In this study, the room-temperature tensile anisotropy and tension-compression asymmetry of the extruded Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr alloy were investigated utilizing techniques such as optical microscopy (OM), electron backscatter diffraction (EBSD), and viscoplastic self-consistent (VPSC) modeling. Among the tensile samples, the T0 sample (with axis parallel to extrusion direction) exhibits the greatest tensile yield strength (TYS) of 270 MPa and ultimate tensile strength (UTS) of 336 MPa, the T45 sample (with axis inclined at a 45° angle to extrusion direction) and T90 sample (with axis perpendicular to extrusion direction) exhibit lower TYS and UTS. The C0 sample shows a slightly greater compressive yield strength (CYS) of 290 MPa. The ratio of TYS/CYS is approximately 1.07. This study significantly adjusts the VPSC hardening parameters through the Schmid factor of deformation mechanisms in Mg-RE alloy, particularly increasing the τ0 (critical resolved shear stress, CRSS) and τ1 values for basal <a> slip and {10-12} twinning. The ratios of CRSS for other deformation mechanisms to basal <a> slip are approximately as follows: CRSSTwin/CRSSBas = 2, CRSSPri/CRSSBas ≈ 2.7 and CRSSPyr/CRSSBas ≈ 3.3, while these ratios in traditional alloys are generally higher. The stress-strain curves and pole figures obtained from the modified VPSC model demonstrate excellent agreement with experimental results. According to the VPSC simulation results, the primary factor contributing to tensile anisotropy is the disparity in the activation levels of slip systems. The inclusion of rare-earth elements mitigates the tension-compression asymmetry by reducing the difference of CRSS between different deformation mechanisms.

Deformation behavior and magnetic properties of equiatomic FeNi single crystals

An equiatomic Fe–Ni alloy in its disordered A1 structure is a soft magnetic alloy. On ordering to the L10 ordered phase, it shows significant magneto-crystalline anisotropy and a strong permanent magnet behavior and is of interest as a rare earth-free permanent magnet. However, synthesis of an L10 phase in a bulk form remains a challenge due to its low critical ordering temperature Tc and consequent extremely slow ordering kinetics. This phase is present in asteroids, and how it was formed remains unclear. The likely mechanism is enhanced diffusion kinetics due to extreme dislocation densities and vacancy concentrations produced by deformation during asteroid collisions and the presence of S. Prior to examining extreme deformation in an FeNi alloy comparable to that in asteroid collisions, low strain rate deformation behavior, magnetic properties, and the structure of undoped and S-doped [100]-oriented FeNi single crystals were carried out. Controlled deformation at a strain rate of 1 × 10−5/s showed the yield point to be 89 MPa, and the critical resolved shear stress was 25.7 MPa. The dislocation densities obtained were ∼1017/m2. The saturation magnetization value was ∼147–151 emu/g both before and after deformation, comparable to NdFeB magnets. Coercivity increased slightly from ∼0.04–0.4 to ∼5 Oe after deformation due to an increase in dislocation density. The x-ray diffraction scan of S-doped and deformed single crystals after annealing at 300 °C, just below Tc, showed no evidence of L10 order. These data serve as a baseline for extreme strain rate deformation where much higher dislocation densities and vacancy concentrations can be obtained to facilitate L10 order.

Microstructure and enhanced strength and ductility of Ti-Zr-O alloys prepared by a laser powder bed fusion process

Non-toxic and biocompatible Ti-Zr-O alloys with excellent comprehensive properties of strength and ductility were prepared from Ti-ZrO2 powder mixtures by a laser powder bed fusion (LPBF) process. The substitutional Zr atoms and interstitial O atoms, formed by decomposition of ZrO2 during laser irradiation, were dissolved into crystal lattice of Ti, resulting in significant increases in lattice constant c and axial ratio c/a. The Ti-Zr-O alloys were characterized by fine needle-like microstructure with weakened texture compared to pure Ti. The needle-like microstructure may be generated through the growth of α-nuclei according to the Burgers orientation relationship during β→α phase transformation, and the reduction of crystallographic anisotropy in the Ti-Zr-O alloys is due to the formation of α grains with multiple variants. The LPBFed Ti-Zr-O alloys exhibited significantly enhanced strength and maintained good ductility, overcoming the strength-ductility trade-off dilemma. For example, the yield strength and ultimate tensile strength (UTS) of the Ti-1.48Zr-0.66 O alloy reached 1014 MPa and 1073 MPa, respectively, and its elongation at fracture remained at 17 %. The strength enhancement is due to the solid solution strengthening of O and Zr and grain refinement strengthening, of which the solid solution strengthening of interstitial O atoms is the most dominant contributor to the improvement in strength of the LPBFed Ti-Zr-O alloys. The good ductility is mainly attributed to the activation of pyramidal slips due to reduced critical resolved shear stress (CRSS) ratios between pyramidal and prismatic planes, especially dislocation slips along <c + a> directions on the pyramidal planes due to the fine-grained microstructure. The activation of multiple slip systems, including prismatic and pyramidal slips, contributes to the improved ductility of the LPBFed Ti-Zr-O alloys.

A novel D022-strengthened medium entropy alloy with outstanding strength-ductility synergies over ambient and intermediate temperatures

Precipitation-strengthened medium/high-entropy alloys (MEAs/HEAs) have great potential for high-temperature applications. In this study, we designed a novel Ni45.9Fe23Cr23V4Nb3Mo1B0.1 (at.%) MEA alloy, hardened by the D022 (Ni, Fe, Cr)3(Nb, V)-type nanoprecipitates, with an excellent strength-ductility combination from room to elevated temperatures. Specifically, the tensile strengths, at 700 and 800 °C, could be maintained as high as 845 and 589 MPa, respectively; meanwhile, elongations at all testing temperatures exceeded 25 % without any intermediate-temperature embrittlement. The temperature-dependent deformation mechanisms were unraveled using multi-scale characterizations, which involved profound slip planarities, such as stacking fault (SF) networks and deformation twins (DTs). Furthermore, the critical resolved shear stress (CRSS) to initiate SFs in both face-centered cubic (FCC) and D022 phases was evaluated, and the possible reasons for the origin of anomalous DTs at 800 °C were discussed in detail. The main findings demonstrate that the shearable D022 nanoparticles can provide the FCC matrix with considerable dislocation storage capacity, reinforcing strain hardening at ambient and intermediate temperatures. This work provides fundamental insights into the controllable design and deformation mechanisms of high-performance D022-strengthened MEAs/HEAs.

Temperature-Dependent Mechanical Anisotropy in Textured Zircaloy Cladding

This work evaluates deformation activity in textured zircaloy-4 cladding with the aim of elucidating the mechanisms that govern mechanical behavior across a temperature range anticipated in reactor service. In particular, the dependence of mechanical anisotropy on temperature and stress state (ratio of applied stresses) is examined via uniaxial and biaxial tensile experiments at room temperature and 400 °C. The mechanical behavior is interpreted based on micro-texture and dominant slip system activity. Thermal activation of basal systems is found as a key mechanism affecting mechanical behavior across the temperature range. The biaxial stress states produce resolved shear stresses contrasting to uniaxial stress states. Mechanical testing and implications for reactor pellet-cladding mechanical interaction stress conditions are discussed.

From anti-Arrhenius to Arrhenius behavior in a dislocation-obstacle bypass: Atomistic simulations and theoretical investigation

Dislocations are the primary carriers of plasticity in metallic materials. Understanding the basic mechanisms for dislocation movement is paramount to predicting the material mechanical response. Relying on atomistic simulations, we observe a transition from non-Arrhenius to Arrhenius behavior in the rate of an edge dislocation overcoming the long-range elastic interaction with a prismatic loop in tungsten. Close to the critical resolved shear stress, the process shows a non-Arrhenius behavior at low temperatures. However, as the temperature increases, the activation entropy starts to dominate, leading to a traditional Arrhenius-like behavior. We have computed the activation entropy analytically along the minimum energy path following Schoeck’s method [1], which captures the cross-over between anti-Arrhenius and Arrhenius domains. Also, the Projected Average Force Integrator (PAFI) [2], another simulation method to compute free energies along an initial transition path, exhibits considerable concurrence with Schoeck’s formalism. We conclude that entropic effects need to be considered to understand processes involving dislocations bypassing elastic barriers close to the critical resolved shear stress. More work needs to be performed to fully understand the discrepancies between Schoeck’s and PAFI compared to molecular dynamics.

Molecular dynamics simulation study of void collapse mechanisms in cubic metals under shock compression

Molecular dynamics simulations have revealed the collapse mechanism of a void in cubic metals under shock compression along [100] direction. The results show that the void collapse is caused by emitting dislocations from its surface. The type of cubic metal plays a decisive role in the subsequent microstructural evolution around the void. Void in face-centered-cubic metals collapses by emitting Shockley dislocations from its surface when piston velocity exceeds the threshold; while void in body-centered-cubic metals collapses by emitting prismatic dislocation loops, which are formed by the reaction of edge dislocations. Simulation results also reveal that the type of dislocation that induces void collapse is independent of void size. Finally, based on the elastic theory, we find that the maximum resolved shear stress along the slip direction determines the types of dislocation emitted from the voids.

Microstructural characteristics and recrystallization mechanism of Ti-6.5Al–2Zr–1Mo–1V alloy during two-stage hot deformation

In this study, we investigated the two-stage deformation behavior of near α Ti-6.5Al–2Zr–1Mo–1V alloy at various temperatures (915 °C, 950 °C, 1020 °C) and strain rates (0.01 s−1, 0.1 s−1). The alloy underwent differing holding periods (500s, 1000s) between deformation stages. The results demonstrated an increase in flow stress with decreasing deformation temperature and increasing strain rate. Work hardening of flow stress was observed during the two-stage thermomechanical processing within the α+β two-phase region. Microstructural evolution was characterized by the formation of α lamellar kink bands, the separation and migration of grain boundaries, and grain spheroidization. An increase in deformation temperature and a decrease in strain rate enhanced grain refinement, accelerated structural evolution, and intensified the degree of spheroidization. Dynamic recrystallization (DRX) was more prevalent at higher temperatures and lower strain rates, as the critical nucleation rate for DRX was more readily achieved. The increased interval between thermomechanical processing stages led to a transition from low-angle to high-angle grain boundaries, and a reduction in dislocation density due to static recovery occurred during the holding period. At 915 °C, hot deformation induced the formation of {10-10} twinning, altering grain orientation and reducing stress. The Schmid factor for {10-10}<1120> slip was higher at lower temperatures, which reduced the critical resolved shear stress necessary for yielding in the α phase of the Ti-6.5Al–2Zr–1Mo–1V alloy, thereby facilitating further plastic deformation.

Deformation mechanisms in the α phase of the Ti-6Al-2Sn-4Zr-2Mo titanium alloy: In situ experiments and simulations

Titanium alloys are widely employed in aerospace applications due to an outstanding combination of properties. The variety of loading conditions and microstructures encountered in industrial components is urging the development of microstructure sensitive modeling capabilities. In particular, reliable predictions require a good knowledge of operating deformation mechanisms. The present study aims at providing a thorough characterization of deformation mechanisms in the near-α Ti-6Al-2Sn-4Zr-2Mo alloy using experiments and simulations. The sequential activation of deformation mechanisms in the α phase was monitored in situ during a tensile test carried out in a scanning electron microscope using a combination of slip traces analysis and electron back-scattered diffraction. Basal slip is activated first, and prismatic slip activity, which proceeds at a higher macroscopic stress level, is needed for a significant creep/relaxation to occur. While little evidence of 〈a〉-type pyramidal slip was found, 〈c + a〉 pyramidal slip involved first-order pyramidal planes and operates at stress levels near or above the 0.2% proof stress. Atomic force microscopy characterization of the features of the different slip modes revealed that 〈a〉 slip is coarser and wavier than 〈c + a〉 slip. Twinning, which is usually neglected in such alloys within this strain regime, was observed to be slip stimulated at a plastic strain as low as 0.5%. Crystal plasticity parameters leading to an accurate simulation of the activation sequence of deformation mechanisms were then determined. For this purpose, critical resolved shear stress values were derived for the different slip and twinning modes using specific approaches and subsequently validated using crystal plasticity simulations based on fast-Fourier transforms.

Effect of deformation mode on martensitic transformation in medium Mn steel

In the present work, we have investigated the effect of deformation modes namely uniaxial loading and plane strain loading on martensite transformation in medium Mn TRIP steels, since it plays an important role in influencing formability. Interrupted deformation experiments showed that the martensitic transformation proceeds continuously with plastic strain and is influenced by the specific deformation mode applied. Uniaxially loaded samples underwent a complete austenite to martensite transformation. On the other hand, under plane strain loading, only 70 % of the austenite transformed into martensite, even after fracture had occurred. Through synchrotron and EBSD experiments, we observed that under uniaxial loading, the transformation sequence followed the γ-ε-α′ pathway, whereas, under plane strain, a direct γ-α′ transformation was observed. The intermediate ε-martensite phase is known to facilitate the transformation from austenite to martensite. Consequently, the presence of ε-martensite resulted in a higher degree of austenite transformation in the uniaxial samples. We rationalize the difference in transformation sequences based on resolved shear stress calculations for the two deformation modes.

Moment tensor potential for static and dynamic investigations of screw dislocations in bcc Nb

A new machine-learning interatomic potential, specifically a moment tensor potential (MTP), is developed for the study of screw-dislocation properties in body-centered-cubic (bcc) Nb in the thermally- and stress-assisted temperature regime. Importantly, configurations with straight screw dislocations and with kink pairs are included in the training set. The resulting MTP reproduces with near density-functional theory (DFT) accuracy a broad range of physical properties of bcc Nb, in particular, the Peierls barrier and the compact screw-dislocation core structure. Moreover, it accurately reproduces the energy of the easy core and the twinning-anti-twinning asymmetry of the critical resolved shear stress (CRSS). Thereby, the developed MTP enables large-scale molecular dynamics simulations with near DFT accuracy of properties such as for example the Peierls stress, the critical waiting time for the onset of screw dislocation movement, atomic trajectories of screw dislocation migration, as well as the temperature dependence of the CRSS. A critical assessment of previous results obtained with classical embedded atom method potentials thus becomes possible.

Microstructure and mechanical properties of laser welded and post-weld heat-treated K439B superalloy

Laser welding of the new nickel-based alloy K439B applied for engine turbine was carried out. The effects of post-welding heat treatment (PWHT) on the microstructure and mechanical properties of the joints were investigated. Semi-quantitative statistical results show that after PWHT, γ’ phases in the whole joint grow up, and the radii of the primary and secondary γ’ phases are about 25 and 150 nm, respectively. The results of mechanical properties show that PWHT improves the microhardness in the weld by about HV 100, and the critical resolved shear stress provided by γ’ phases increases from 4.8 to 92 MPa. The tensile strength and yield strength of the heat-treated joint are comparable to those of the base metal. The presence of a large amount of carbides is the reason for the preferential fracture of the base metal during the tensile process.

Evolutionary mechanisms in the plastic deformation of γ'-Ni3(Al, Ti)-strengthened additively manufactured nickel-based 939 superalloys at intermediate temperatures

Tensile interruption experiments with different strains were conducted on additively fabricated nickel-based Inconel 939 superalloys at 700 ℃ to investigate the evolution of multiple deformation mechanisms. The microstructures of different strain groups captured by transmission electron microscopy (TEM) were analyzed, and it was concluded that a total of four various deformation mechanisms were identified, of which the first to be activated was the Orowan loop bypassing γ', and a tendency of transition from double to single loop was observed. Anti-phase boundary (APB) shearing was subsequently initiated, with a needed critical resolved shear stress level of approximately 195.82 MPa. Stacking faults (SFs) and deformation twinnings (DTs) were observed at higher stress, accompanied by the dissociation of dislocations. In addition, the magnitude of the stacking fault energy of AM 939 superalloys at intermediate temperature was calculated and estimated by matching the experimental phenomena with the critical shear stress.