Nucleation Of Partial Dislocations Research Articles

Nanoindentation responses of NiCoFe medium-entropy alloys from cryogenic to elevated temperatures

NiCoFe alloy, a medium-entropy alloy, shows potential for applications in extreme environments. However, there is a theoretical barrier concerning the unclear understanding of its high-temperature dislocation motion mechanism. The load response exhibits distinct signatures relevant to thermal activation, most notably a decrease in critical force (i.e., softening) from cryogenic to elevated temperatures, e.g., from 200 to 1000 K. The onset of plasticity is characterized by the nucleation of stacking faults and prismatic loops at low temperatures, whereas the surface nucleation of Shockley partial dislocations dominates plasticity at elevated temperatures. We show that thermal effects lead to non-uniform atom pile-ups and control the rate of phase transformation with increasing indentation depth. The findings in this work extend the understanding of the mechanical response of NiCoFe alloys under indentation at different temperatures, shedding light on the underlying dislocation motion mechanisms and surface deformation characteristics. The observed transformation-induced plasticity mechanism has implications for the properties of medium-entropy alloys and their potential applications in extreme environments.

Atomic mixing mechanisms in nanocrystalline Cu/Ni composites under continuous shear deformation and thermal annealing

Molecular dynamics (MD) simulations are used to reveal the mechanisms of defect substructure evolution and atomic mixing in nanocrystalline Cu/Ni composites under severe shear deformation and subsequent thermal annealing. A continuous shear scheme of MD simulation utilizing an on-the-fly periodic boundary adjustment approach enables it to reach any large shear strain. The comprehensive evaluation on the evolution of dislocation structures at various strain states indicates partial dislocation-mediated plastic deformation and triple junction slide via partial dislocation nucleation and emission from triple junctions and grain boundaries. The analysis of atomic structures in unique mixing regions suggests that triple junction sliding can result in a long-range region of atomic mixing facilitated by net dislocation flux, which is the key mechanism of atomic mixing in nanocrystalline Cu/Ni composite under severe shear, while dislocation emissions at interfaces result in short-range mixing. It is also found that thermal annealing causes the evolution of non-equilibrium defect substructures which assists atomic mixing.

Twin thickness-dependent tensile deformation mechanism on strengthening-softening of Si nanowires

Twin thickness-dependent deformation and the transition from strengthening to softening in twinned silicon nanowires are investigated using molecular dynamics simulations with cylindrical and hexagonal cross sections. The results show that the transition from strengthening to softening occurs at critical twin thicknesses of 8.1 nm (11.0 TB s) with cylindrical cross section and 11.0 nm (8 TBs) with hexagonal cross section with decreasing twin thickness, and that the strongest twin thickness originates from a transition in the initial plasticity mechanism from full dislocation nucleation and interaction with the TBs to partial dislocation nucleation and gliding parallel to the TBs. Moreover, it is found that the relationship between peak stress and twin thickness can be divided into two regions. Several full and partial dislocations are formed in the regions with strengthening twin thickness range. The accumulation and pile-up of these dislocations and their interaction with the TBs at high density cause the Hall-Petch strengthening behavior. In contrast, few full and partial dislocations are formed with softening twin thickness range. These dislocations are nucleated and propagate parallel to the TBs, resulting in TB migration that causes inverse Hall-Petch softening behavior. Our simulation results provide sufficient insight into the mechanical behavior of twinned silicon nanowires with cylindrical and hexagonal cross sections. The study will be helpful to the further understanding of CTB-related mechanical behaviors of non-metallic materials and non-metallic system.

Microstructural evolution and twins formation under tensile test of Ni-free Mn-N austenitic stainless steel using laser powder bed fusion method

At the initial uniaxial tensile stage, predominant planar dislocation slip occurs to generate dislocation pile-ups and dipole bundles. Low-energy Taylor lattice structure is then formed by co-planar slip bands along the primary slip system along [001]γ and [111]γ directions to form primary twins. Increasing the straining and generation of numerous micro-bands and crystallographic defects led to the strong restriction for dislocation motion, enhancing the formation of secondary twins with stacking fault near the deformation twin's energy. Decreasing the mean slip band and micoband spacing and configuration of complex dislocation arrangement would cause the dislocation slip, generating an extensive number of dislocation walls and cell blocks, resulting in forming a noncrystalline structure with multi-orientation. Molecular dynamics (MD) analyses revealed that deformation began by nucleation of Shockley partial dislocations with a burger vector of 1/6 〈112〉 from none-periodic boundaries. Afterwards, dislocations junctions created Hirth dislocations with a Burger vector of 1/3 〈100〉, which causes strain hardening in the system. At this point, Shockley dislocations nucleated from Hirth dislocations and strain hardening increases.

Effect of Ni content and crystallographic orientation on mechanical properties of single-crystal (CoCr)100-x Ni x medium-entropy alloy

Nanoindentation analyses of (CoCr)100-x Ni x medium-entropy alloys with different Ni contents and crystal orientations were carried out by molecular dynamics simulations. Analyses show that the force-displacement curves during elastic deformation are in good accordance with the Hertz contact theory and the elastic modulus is closely related to the Ni contents and crystal orientations. The elastic-plastic transition point appears later in (CoCr)67Ni33 than in other alloys. The plastic deformation was studied by exploring the instantaneous microstructure, which was found to be dominated by homogeneous nucleation of Shockley partial dislocations and the accumulation of stacking faults, and different levels of dislocation density were produced in the alloys with different Ni contents and crystal orientations. By analyzing the evolution of dislocation density and hardness, a linear relationship between the square root of dislocation density and hardness can be revealed, which agrees well with the classical Taylor hardening model, and the empirical constant is found closely related to crystal orientations.

Crack mediated dislocation activities in Al/Ti nanolayered composites: an atomistic study

In this work, to understand crack propagation in Al/Ti nanolayered composites, a series of molecular dynamic simulations were performed with crack in different layers of the nanolayered composites and subjected to mode I loading. Nanolayered composite with a crack in Al layer, and monolithic Al show ductile fracture behavior that occurs by nucleation of Shockley partial dislocation at the crack tip. On the other hand, the fracture behavior in nanolayered composites with a crack in Ti shows crack bowing which is similar to the brittle fracture, and subsequent crack trapping at the interface. However, monolithic Ti shows typical cleavage fracture followed by activation of basal and pyramidal slip that blunts the crack leading to ductile fracture. When the crack is in the Ti layer, the other Ti layers in a nanolayered composite deform by prismatic and pyramidal slip. However, the Ti layer deforms only via slip on prismatic planes when the crack is in the Al layer. Critical strain energy release rate G c based continuum analysis predicts the fracture mode in monolithic Ti correctly, but it fails to predict the fracture mode in monolithic Al and nanolayered composites with crack in the Al layer. It is found that the G c determined based on external loading is marginally higher when the crack is in the Al layer as compared against the case when the crack is in the Ti layer. The G c value for the basal and pyramidal slip in Ti is higher than the G c value for cleavage. This poses an interesting phenomenon since the G c in monolithic Al is found to be much lower than that of monolithic Ti. The reason is attributed to the constrained plasticity in the presence of an Al/Ti interface.

Investigations on the interface-dominated deformation mechanisms of two-dimensional MAX-phase Ti3Al(Cu)C2 nanoflakes reinforced copper matrix composites

Two-dimensional (2D) materials showing the giant advantage over their bulk counterparts are believed to be the ideal reinforcement for metal matrix composites, whereas the deformation mechanism of which is currently unknown. Herein, we investigated the interface effect of 2D MAX phase Ti3Al(Cu)C2 nanoflakes (MAX NFs) obtained by a Cu-atoms-diffusion assisted exfoliation method on the plastic deformation process of Cu matrix. Tensile tests demonstrated a simultaneous enhancement in strength and fracture elongation with the increase of MAX NFs content. The composites exhibited a four-stage deformation process involving an extended “yield plateau” before obvious strain hardening stage. Microstructural examination revealed that the 2D nature of MAX NFs and the coherent interface structure facilitated the nucleation of partial dislocations, which coordinated the initial plastic deformation by gliding and interacting to form Lommer-Cottrel (LC) locks. At high strain levels, both LC locks and MAX NFs served as obstacles for dislocation cross-slip and thus achieved significant forest hardening (or latent hardening) effect, validated by EBSD texture from the in-situ tensile tests and visco-plastic self-consistent simulation. This sort of interface-induced microstructure evolution promoted tortuous micro-cracks along discontinuous slip bands and significant crack bridging and deflection extrinsic toughening mechanisms. The current findings provide a possible strategy of simultaneously enhancing strength and ductility through tailoring 2D geometric shape of reinforcements and their interface with the metal matrix.

Phase Volume Fraction-Dependent Strengthening in a Nano-Laminated Dual-Phase High-Entropy Alloy.

A recently synthesized FCC/HCP nano-laminated dual-phase (NLDP) CoCrFeMnNi high entropy alloy (HEA) exhibits excellent strength–ductility synergy. However, the underlying strengthening mechanisms of such a novel material is far from being understood. In this work, large-scale atomistic simulations of in-plane tension of the NLDP HEA are carried out in order to explore the HCP phase volume fraction-dependent strengthening. It is found that the dual-phase (DP) structure can significantly enhance the strength of the material, and the strength shows apparent phase volume fraction dependence. The yield stress increases monotonously with the increase of phase volume fraction, resulting from the increased inhibition effect of interphase boundary (IPB) on the nucleation of partial dislocations in the FCC lamella. There exists a critical phase volume fraction, where the flow stress is the largest. The mechanisms for the volume fraction-dependent flow stress include volume fraction-dependent phase strengthening effect, volume fraction-dependent IPB strengthening effect, and volume fraction-dependent IPB softening effect, that is, IPB migration and dislocation nucleation from the dislocation–IPB reaction sites. This work can provide a fundamental understanding for the physical mechanisms of strengthening effects in face-centered cubic HEAs with a nanoscale NLDP structure.

Slip transmutation between basal [formula omitted] dislocation and [formula omitted] twinning across [formula omitted] twin boundary in titanium

Molecular dynamics simulations reveal slip transmutation mechanisms between basal 〈a〉 dislocations and {112¯1} twinning in titanium. When a co-planar pileup of basal 〈a〉 dislocations approaches (112¯4) coherent twin boundary (CTB), the 1st dislocation transmutes into a four-layer (112¯1) twin in the (112¯4) twin, forming a (112¯4)−(112¯1) double twin, and the 2nd and 3rd dislocations climb along the (112¯4) CTB and then transmute into twinning dislocations, thickening the (112¯1) secondary twin. When the (112¯1) secondary twin propagates and encounters the other (112¯4) CTB, a reverse transmutation happens associated with the nucleation and emission of partial dislocations.

Deformation of Copper Nanowire under Coupled Tension-Torsion Loading.

Metallic nanowires (NWs) are essential building blocks for flexible electronics, and experience different deformation modes due to external mechanical loading. Using atomistic simulations, this work investigated the deformation behavior of copper nanowire under coupled tension–torsion loading. A transition in both yielding pattern and dislocation pattern were observed with varying torsion/tension strain ratios. Specifically, increasing the torsion/tension strain ratio (with larger torsional strain) triggered the nucleation of different partial dislocations in the slip system. At low torsion/tension strain ratios, plastic deformation of the nanowire was dominated by stacking faults with trailing partial dislocations pinned at the surface, shifting to two partial dislocations with stacking faults as the strain ratio increases. More interestingly, the NW under tension-dominated loading exhibited a stacking fault structure after yielding, whereas torsion-dominated loading resulted in a three-dimensional dislocation network within the structure. This work thus suggests that the deformation behavior of the NW varies depending on the coupled mechanical loading, which could be beneficial for various engineering applications.

Effects of cross-sectional area and aspect ratio coupled with orientation on mechanical properties and deformation behavior of Cu nanowires

Metal nanomaterials exhibit excellent mechanical properties compared with corresponding bulk materials and have potential applications in various areas. Despite a number of studies of the size effect on Cu nanowires mechanical properties with square cross-sectional, investigations of them in rectangular cross-sectional with various sizes at constant volume are rare, and lack of multifactor coupling effect on mechanical properties and quantitative investigation. In this work, the dependence of mechanical properties and deformation mechanisms of Cu nanowires/nanoplates under tension on cross-sessional area, aspect ratio of cross-sectional coupled with orientation were investigated using molecular dynamics simulations and the semi-empirical expressions related to mechanical properties were proposed. The simulation results show that the Young’s modulus and the yield stress sharply increase with the aspect ratio except for the 〈110〉{110}{001} Cu nanowires/nanoplates at the same cross-sectional area. And the Young’s modulus increases while the yield stress decreases with the cross-sectional area of Cu nanowires. However, both of them increase with the cross-sectional area of Cu nanoplates. Besides, the Young’s modulus increases with the cross-sectional area at all the orientations. The yield stress shows a mildly downward trend except for the 〈111〉 Cu nanowires with increased cross-sectional area. For the Cu nanowires with a small cross-sectional area, the surface force increases with the aspect ratio. In contrast, it decreases with the aspect ratio increase at a large cross-sectional area. At the cross-sectional area of 13.068 nm2, the surface force decreases with the aspect ratio of the 〈110〉 Cu nanowires while it increases at other orientations. The surface force is a linearly decreasing function of the cross-sectional area at different orientations. Quantitative studies show that Young’s modulus and yield stress to the aspect ratio of the Cu nanowires satisfy exponent relationship. In addition, the main deformation mechanism of Cu nanowires is the nucleation and propagation of partial dislocations while it is the twinning-dominated reorientation for Cu nanoplates.

Atomic-scale understanding of the reversible HCP↔FCC phase transition mechanisms at [formula omitted] twin tip in pure titanium

In this paper, by using high-resolution transmission electron microscopy (HRTEM) observations and molecular dynamics (MD) simulations, the mechanisms of hexagonal close-packed (HCP) structure to face-centered cubic (FCC) structure transition and its inverse transition at the {101¯1} twin tip in pure titanium were investigated. The HCP→FCC phase transition at the {101¯1} twin tip in cold-rolled pure Ti was experimentally observed for the first time. On the other hand, under electron beam irradiation, the FCC lamella shrank gradually and eventually recovered to the HCP structure. After the HCP↔FCC phase transformations, the interfacial structures of the twin tip changed from the (101¯0)T//(101¯3)M facets to a common Basal-Pyramidal (BPy) facets. MD simulations indicated that the reversible HCP↔FCC phase transitions were caused by successive slip of Shockley partial dislocations on {0001}HCPand{111}FCC planes, respectively. The nucleation of Shockley partial dislocations stemmed from the dissociation of twinning dislocation (TD) with the Burgers vector of b⇀4 = 4γ2−93+4γ2<101¯2¯> at the twin tip. The Shockley partial dislocations could be absorbed by twin tip boundaries through reacting with the residual dislocations to form new TDs b⇀4 during the FCC→HCP phase transition. The periodic serrated feature of the (101¯0)T//(101¯3)M facets of the twin tip boundaries in pure Ti was discovered via atomistic simulations. The interfacial structure evolution of the twin tip was caused by a series of dislocation reactions and generation of phase transformation at the twin tip. The transformation from the HCP structure to the FCC structures was due to the stress concentration caused by the plugging of the periodically distributed TDs b⇀4 at the twin tips in the case of external loading. The shrinkage of FCC lamella was caused by the relaxation of internal stress at the twin tip during the thermal relaxation by electron beam.

Atomistic study of coreshell and functionally graded nanospheres under compressive loading

Functionally grading and coreshell are two interesting engineering modifications to nanomaterials structure for tailored applications in electronics, energy conversion devices and so on. Understanding the mechanical response of these nanostructures are of particular importance to ensure the reliability of these devices under service conditions. In this paper, functionally graded and coreshell Silver–Gold (Ag–Au) nanospheres are studied under compression load using molecular dynamics simulation. The fracture and deformation mechanism along with the incipient plasticity through dislocation nucleation and propagation has been studied for both functionally graded and coreshell structure for different percentages of Ag and Au of the nanosphere. Our results indicate that plastic deformation is dictated by the partial dislocation nucleation and propagation from the contact surface which varies as the alloying percentages of the coreshell and functionally graded nanosphere. An inverse size effect is observed for the mechanical properties which also affects the deformation mechanism of the nanosphere by forming stacking fault tetrahedra for both the nanostructures. For a range of Ag percentages in Au, the coreshell nanospheres showed higher compressive strength compared to functionally graded nanospheres. As coreshell and functionally grading are two promising nanoscale materials design, current work will inspire developing new metal nanospheres to harness the materials potential for different engineering applications.

Unraveling the effects of interface orientation and crystallography on the deformation mechanisms of accumulative roll-bonded Cu-Nb-multilayered nanocomposites using molecular dynamics.

This work elucidates the effect of interface orientation, loading mode, and crystallography on the deformation mechanisms of Cu-Nb-multilayered nanocomposites. Molecular dynamics simulations of deformation behavior of accumulative roll-bonded Cu-Nb-multilayered nanocomposites (MNCs) were performed at room temperature conditions and at a constant strain rate under iso-stress and iso-strain conditions. Interface deformation mechanisms involving nucleation of partial dislocation at the interface and gliding in the Cu layer were observed under iso-stress and iso-strain conditions. Uniaxial stress-strain curves were analyzed for tension and compression under iso-stress and iso-strain loading conditions. The stress-strain plots were explored to understand the elastic, yield, and post-yielding behavior of Cu-Nb MNCs. Under compression with interface orientation normal to the loading direction, twin nucleated via gliding of partial dislocations. Under tension in the iso-stress case, only slip-assisted deformation was observed. Conversely, the deformation behavior under compression and tension was via slip and twinning, respectively, for iso-strain conditions.

Nanotwin-induced ductile mechanism in thermoelectric semiconductor PbTe

•Pb-CTBs weaken ionic Pb-Te bonds to generate an easy dislocation source at CTBs •Twinning partial dislocations glide on (111) twin planes, leading to CTB migration •“Catching bond” induces high ductility and maintains integrity for nanotwinned PbTe Coherent twin boundaries (CTBs) with the lowest interfacial energy provide a strong phonon-CTB scattering source to suppress the lattice thermal conductivity needed for thermoelectric properties, but the impact on mechanical properties of PbTe remains unexplored. We construct nanotwinned structures with Pb- or Te-terminated CTB (Pb- or Te-CTB) along (111) plane and employ molecular dynamics simulations to examine structural evolution. We find that Pb-CTBs weaken ionic Pb-Te bonds to generate an easy dislocation source at CTBs. Due to nucleation and motion of partial dislocations on each Pb-CTB plane driven by shear load, Pb-CTBs gradually migrate to Te-CTBs, which is accompanied by breaking and re-forming of Pb-Te bonds. This “catching bond” maintains structural integrity while dramatically enhancing deformability of nanotwinned PbTe. Dislocations move from Te-CTBs toward twin lamellae, resulting in the structural slippage and fracture. These findings provide a theoretical strategy to improve the ductility of PbTe-based semiconductors through TB engineering. Coherent twin boundaries (CTBs) with the lowest interfacial energy provide a strong phonon-CTB scattering source to suppress the lattice thermal conductivity needed for thermoelectric properties, but the impact on mechanical properties of PbTe remains unexplored. We construct nanotwinned structures with Pb- or Te-terminated CTB (Pb- or Te-CTB) along (111) plane and employ molecular dynamics simulations to examine structural evolution. We find that Pb-CTBs weaken ionic Pb-Te bonds to generate an easy dislocation source at CTBs. Due to nucleation and motion of partial dislocations on each Pb-CTB plane driven by shear load, Pb-CTBs gradually migrate to Te-CTBs, which is accompanied by breaking and re-forming of Pb-Te bonds. This “catching bond” maintains structural integrity while dramatically enhancing deformability of nanotwinned PbTe. Dislocations move from Te-CTBs toward twin lamellae, resulting in the structural slippage and fracture. These findings provide a theoretical strategy to improve the ductility of PbTe-based semiconductors through TB engineering.

Shear strain-induced structure relaxation of Ni Σ17 [110](223) grain boundary: A molecular dynamics simulation

The stabilization of grain boundaries (GBs) is beneficial for improving the stability and mechanical properties of nanocrystalline (NC) metals. Molecular dynamics (MD) calculations were performed to investigate the shear response of Ni [Formula: see text]17 [110](223) symmetrical tilt GB. It was found that under the action of shear, the nucleation and evolution of the GB source Shockley partial dislocations ultimately result in the low-energy-state transformation of the GB structure units (SUs). However, the Ag atom contained in the GB increases the shear stress and strain required for the GB relaxation, and the strain range for the GB relaxation is expanded, indicating the inhibitory effect of the Ag atom on the structural relaxation of Ni [Formula: see text]17 [110](223) GB. As the temperature increases from 10 K to 250 K, the structural relaxation of Ni [Formula: see text]17 [110](223) GB becomes easier to proceed. In addition to segregation-induced GB stabilization, strain-induced GB relaxation and the roles of foreign atom and temperature clarified in this work could provide several new entry points for stabilizing high-energy GBs.

Generalized stacking fault energy surface mismatch and dislocation transformation

Even though the fundamental rules governing dislocation activities have been well established in the past century, we report a phenomenon, dislocation transformation, governed by the generalized-stacking-fault energy surface mismatch (GSF mismatch for short) between two co-existing phases. By carrying out ab-initio-informed microscopic phase-field simulations, we demonstrate that the GSF mismatch between a high symmetry matrix phase and a low symmetry precipitate phase can transform an array of identical full dislocations in the matrix into an array of two different types of full dislocations when they shear through the precipitates. The precipitates serve as a passive Shockley partial source, creating new Shockley partial dislocations that are neither the ones from the dissociation of the full dislocation. This phenomenon enriches our fundamental understanding of partial dislocation nucleation and dislocation-precipitate interactions, offering additional opportunities to tailor work-hardening and twinning processes in alloys strengthened by low-symmetry precipitate phases.

Atomistic simulation of nanoindentation response of dual-phase nanocrystalline CoCrFeMnNi high-entropy alloy

In this study, molecular dynamics (MD) simulation is adopted to explore the mechanical properties and microstructure evolution of a dual-phase CoCrFeMnNi high-entropy alloy during nanoindentation. The influence of the volume fraction of the hexagonal closed-packed (hcp) phase is considered, and the P–h curves are plotted, where the indentation depths of curves initially into the plastic stage and the maximum indentation force for each curve are significantly different. At the elastic stage, the results from MD simulations are in agreement with those of the Hertz contact theory. However, the fitting coefficient k is remarkably influenced by the hcp phase volume fraction. The correlating P–h curves of plastic deformation are investigated by analyzing the instantaneous defect structures dominated by the nucleation of Shockley partial dislocations or the movements of stacking faults. Furthermore, the microstructure evolution with the increment in indentation depth is demonstrated, and it revealed that the plastic deformation is affected by the phase structure indenter that initially contacts. Unlike the slipping process for the face-centered-cube phase, a new hcp structure grain is created through dynamic recrystallization if the hcp phase is the first phase that the indenter touches.

Temperature-Dependent Superplasticity and Strengthening in CoNiCrFeMn High Entropy Alloy Nanowires Using Atomistic Simulations.

High strength and ductility, often mutually exclusive properties of a structural material, are also responsible for damage tolerance. At low temperatures, due to high surface energy, single element metallic nanowires such as Ag usually transform into a more preferred phase via nucleation and propagation of partial dislocation through the nanowire, enabling superplasticity. In high entropy alloy (HEA) CoNiCrFeMn nanowires, the motion of the partial dislocation is hindered by the friction due to difference in the lattice parameter of the constituent atoms which is responsible for the hardening and lowering the ductility. In this study, we have examined the temperature-dependent superplasticity of single component Ag and multicomponent CoNiCrFeMn HEA nanowires using molecular dynamics simulations. The results demonstrate that Ag nanowires exhibit apparent temperature-dependent superplasticity at cryogenic temperature due to (110) to (100) cross-section reorientation behavior. Interestingly, HEA nanowires can perform exceptional strength-ductility trade-offs at cryogenic temperatures. Even at high temperatures, HEA nanowires can still maintain good flow stress and ductility prior to failure. Mechanical properties of HEA nanowires are better than Ag nanowires due to synergistic interactions of deformation twinning, FCC-HCP phase transformation, and the special reorientation of the cross-section. Further examination reveals that simultaneous activation of twining induced plasticity and transformation induced plasticity are responsible for the plasticity at different stages and temperatures. These findings could be very useful for designing nanowires at different temperatures with high stability and superior mechanical properties in the semiconductor industry.

In-situ TEM investigation of unfaulting behavior of Frank loops in FCC Pd during H2+ & He+dual-beam irradiation

A faulted Frank dislocation loop (FDL) can transform into an unfaulted perfect dislocation loop (PDL) under plastic deformation, quenching or particle irradiation. Here, we report our direct observation of the unfaulting processes of FDLs in palladium (Pd) by in-situ ion irradiation in transmission electron microscopy. Results indicate that the FDL unfaulting is a combination of three processes involving the interaction between adjacent FDLs, the interaction between FDL and PDL, and the nucleation and growth of Shockley partial dislocations within FDL. Meanwhile, bubbles tend to nucleate within dislocation loops, and the PDLs capture more He/H2 over FDLs, which confirms for the first time that the irradiation-induced loops play an important role in the aging of Pd and the unfaulting strengthens this process.