Heterogeneous Dislocation Nucleation Research Articles

Integrated experimental and computational study on the effect of hydrogen in mechanical responses of pure tungsten

Hydrogen irradiation profoundly changes the microstructure and morphological characteristics of tungsten, ultimately resulting in the modifications to its mechanical properties. Unfortunately, the specific mechanisms through which hydrogen irradiation influences the mechanical behavior of tungsten have not been clearly elucidated. Therefore, this study aims to further improve the understanding of the impact of hydrogen irradiation on the mechanical responses and its microstructure dependence in tungsten by employing two advanced techniques: nano-indentation experiments and Molecular dynamics (MD) simulations. The experimental findings revealed that deuterium (D) exposure decreased the maximum shear stress required for the incipient plasticity and led to the occurrence of multiple pop-ins. Particularly noteworthy was the most remarkable change in mechanical behaviors observed prominently in the recrystallized tungsten after D exposure. The microstructure dependence of irradiation-induced change in mechanical responses was investigated by two series of MD simulation, indentation and dislocation glide simulation, focusing on the independent effects of each irradiation-induced defect type (interstitial, substitutional, vacancy, vacancy-hydrogen (Vac-H) cluster, void-hydrogen (Vo-H) cluster) on dislocation activities. Based on the MD simulations, it was eventually revealed that Vo-H clusters were the most influential agent affecting dislocation activities. They not only lowered the pop-in stress by heterogeneous dislocation nucleation but also caused strain serration by a continuous pinning/unpinning process during dislocation glide. Consequently, we concluded that the dominant presence of D-induced Vo-H clusters facilitated the onset of plastic yielding and led to multiple pop-in phenomena in recrystallized tungsten, whereas inserted hydrogen caused minimal change in mechanical responses by interacting with pre-existing dislocation in cold-rolled tungsten.

Chemical complexity-changed deformation behavior of NiTi-based B2 low- to high-entropy intermetallic compounds: Atomistic simulations

Owing to the high chemical complexity and severe lattice distortion but still long-range ordered structure, the deformation behavior and defect activities of high-entropy intermetallic compounds are worth investigations. Hence in this study, the mechanical properties of NiTi-based low- to high-entropy intermetallic compounds were measured from different orientations at different temperatures simply by using nanoindentations, and compared with the structural evolution and defect activities suggested by molecular dynamics simulations. The deformation of the low-entropy intermetallic compound proceeded with regular martensitic transformation, followed by the heterogeneous nucleation of dislocations at the martensite/austenite interface and the subsequent long-distance gliding accompanied with sharp stress drops. With increasing temperature, a more intense shearing events and marked strength reduction were observed. In comparison, with the introduction of constitutional complexity, the martensitic transition was suppressed. Instead, the early homogeneous nucleation at a relatively small activation volume (acquired from indenting displacement bursts) and small-range activities of abundant defects mediated the smooth stress-strain response and uniform plastic deformation of the high-entropy intermetallic compound. At an elevated temperature, a similar deformation mechanism and the same level of strength were retained in the chemically complex alloy.

Effect of Al/Ti ratio on the microstructure, texture and incipient plasticity of (CoNiCr0.5)95AlxTiy high entropy alloys

To analyze the incipient plasticity and then optimize the micromechanical behavior of HEAs, the FCC (CoNiCr0.5)95AlxTiy (x = 1, 3, 4 and y = 4, 2,1 (at.%)) HEAs were selected and thermomechanical processed, and corresponding microstructure, mechanical property and incipient plasticity were investigated and discussed. As the Al/Ti ratio changes from 1/4 to 4/1, the average GND of HEAs decreases from 1.11 × 1014 m−2 to 1.05 × 1014 m−2, and the contents of the A {110} <111> and CopperTwin {552} <115> reach to 11% and 4.4%, respectively. Meanwhile, the ductility of HEA increases from 10.6% to 13.9% with the increased Al/Ti ratio, while the strength decreases from 1221.1 MPa to 910.3 MPa. Nanoindentation results show that the normalized maximum stress τmax/μ of the HEAs exhibit the value of (1/18–1/12)μ, and the average activation volume v∗are calculated to be 3.2–3.4 Ω. These indicate that the incipient plasticity of (CoNiCr0.5)95AlxTiy possesses heterogeneous dislocation nucleation triggered by cooperative migration of multiple atoms via vacancies.

Hydrogen-Induced Dislocation Nucleation and Plastic Deformation of 〈001〉 and 〈11¯0〉 Grain Boundaries in Nickel.

The grain boundary (GB) plays a crucial role in dominating hydrogen-induced plastic deformation and intergranular failure in polycrystal metals. In the present study, molecular dynamics simulations were employed to study the effects of hydrogen segregation on dislocation plasticity of a series of symmetrical tilt grain boundaries (STGBs) with various hydrogen concentrations. Our study shows that hydrogen both enhances and reduces dislocation nucleation events from STGBs, depending on different GB structures. Specifically, for STGBs, hydrogen does not affect the mode of heterogeneous dislocation nucleation (HDN), but facilitates nucleation events as a consequence of hydrogen disordering the GB structure. Conversely, hydrogen retards dislocation nucleation due to the fact that hydrogen segregation disrupts the transformation of boundary structure such as Σ9 () STGB. These results are helpful for deepening our understanding of GB-mediated hydrogen embrittlement (HE) mechanisms.

Short range ordering and strengthening in CoCrNi medium-entropy alloy

The CrCoNi medium-entropy alloy is found to exhibit higher incipient plastic strength by slow cooling after the homogenization treatment. Compared with water quenching, this strengthening originates from the inconsistency of the residual stress and short-range orderings (SROs). By deconvolution of the density distribution of the critical shear stress for the first pop-in, two peaks corresponding to homogeneous and heterogeneous dislocation nucleation, respectively, are suggested. Combining the mean, areal fraction, and activation volume of the two peaks, the roles of residual stress and SROs were quantified. Here, for SRO that increases the critical shear stress for heterogeneous and homogeneous nucleation by 22.4% and 39.9%, the residual stress is negligible for the 2.1% strengthening of both. As a result, slow cooling promotes the formation of SRO in CrCoNi, which is of immense benefit to elevate its properties.

Interstitial concentration effects on incipient plasticity and dislocation behaviors of face-centered cubic FeNiCr multicomponent alloys based on nanoindentation

• The interstitial concentration effects on dislocation behavior and incipient plasticity of a typical equiatomic FeNiCr multicomponent alloy are newly investigated via systematic nano-mechanical experimental study. • The dislocation nucleation of FeNiCr alloy processes in a manner of heterogenous nucleation mode with an activation volume exceeding one single principal atom, by the exchange between primary atoms and vacancies. • Interstitial-atom effects severely suppress the mobility of dislocations in the FeNiCr multicomponent alloys, which hinder the occurrence of pop-ins. • With increasing the concentration of interstitial atoms, both the critical shear stress and activation volume corresponding to the onset of incipient plasticity are enhanced. Interstitial atoms that commonly occupy the octahedral or tetrahedral interstices of face-centered cubic (FCC) lattice, can significantly affect the dislocation behaviors on deformation. Recently, interstitial doping has been applied to tune the mechanical properties of the emerging multicomponent, often termed high-entropy alloys (HEAs) or medium-entropy alloys (MEAs). However, the fundamental mechanisms of the dislocation nucleation and the onset of plasticity of interstitial multicomponent alloys governed by the concentration of interstitial atoms are still unclear. Therefore, in the present work, an instrumented nanoindentation was employed to investigate the interstitial concentration effects of carbon atoms on single FCC-phase equiatomic FeNiCr MEAs during loading. The results show that the pop-in events that denote the onset of incipient plasticity are triggered by the sudden heterogeneous dislocation nucleation via the primary atoms-vacancy exchange with the instant stress field, regardless of the interstitial concentration. Moreover, the measured activation volumes for dislocation nucleation of the FeNiCr MEAs are determined to be increased with the interstitial concentration, which definitely suggests the participation of interstitial atoms in the nucleation process. Besides, it is also found that the average value measured in statistics of the maximum shear stress corresponding to the first pop-in is enhanced with the interstitial concentration. Such scenario can be attributed to the improved local change transfer and lattice cohesion caused by the interstitial atoms with higher concentrations. Furthermore, the significant drag effect of interstitial carbon atoms hinders the mobile dislocations before exhaustion, which severely suppresses the subsequent occurrence of pop-in events in the carbon-doped specimens. The work gives a microscale view of interstitial effects on the mechanical properties of multicomponent alloys, which can further help to develop new interstitial strengthening strategies for structural materials with remarkable performance.

Study on the effects of H on the plastic deformation behavior of grain boundaries in nickel by MD simulation

It is generally believed that the influence of hydrogen on plastic deformation of grain boundaries should be considered when analyzing hydrogen-induced intergranular fracture in polycrystalline metals. In this paper, the equilibrated H distribution around GBs was firstly investigated by employing the grand canonical Monte Carlo method. Then, MD simulations were performed to study the plastic response of GBs under uniaxial tensile loads in different directions, with various bulk H concentrations considered. The results indicate that the influence of H on dislocation nucleation from GB depends on both tensile directions and characteristics of GB structures. Specifically, two dislocation nucleation mechanisms, called dislocation dissociation nucleation (DDN) and heterogeneous dislocation nucleation (HDN), are identified. Careful analyses show that H segregation can increase the energy barrier of DDN, which results in H-inhibited dislocation nucleation. In contrast, the HDN mechanism involves H-enhanced or H-insensitive dislocation nucleation, which mainly depends on the influence of H on GB stress.

Atomistic interpretation of extra temperature and strain-rate sensitivity of heterogeneous dislocation nucleation in a multi-principal-element alloy

Incipient plasticity of crystals is usually initiated from versatile pre-existing crystalline defects of different geometries and length scales that formed during materials fabrication and processing, which is closely associated with the mechanical properties. Here we study the heterogeneous dislocation nucleation behaviors from an existing nanoscale void embedded in a prototypical multi-principal-element (MPE) NiCoCr alloy via atomistical exploration of possible minimum energy pathways and analyzes of the dislocation kinetics by a continuum-level mechanistic model, in comparison with the same plastic mechanism in an elemental face-centered cubic copper. It is found that the rough nucleation pathway of dislocation brings about extra thermal softening and strain-rate sensitivity for the critical nucleation stress of dislocation in the MPE alloy, which reproduces the experimental observations. The extra temperature softening is revealed to be associated with the high total entropy of the MPE alloy, in which the configurational entropy plays a dominating role rather than the vibrational counterpart. The extra strain rate sensitivity is caused by the relatively small activation volume in MPE alloy. Our strategy offers physical understanding of the experimental phenomena with atomistic details, which also emphasizes the critical role of configurational disorder in the dislocation accommodated plasticity in the generic complex concentrated alloys.

Probing hydrogen effect on nanomechanical properties of X65 pipeline steel using in-situ electrochemical nanoindentation

The hydrogen effect on a X65 carbon steel was investigated using in-situ electrochemical nanoindentation approach. The alterations in elastic behavior, pop-in load, and hardness under hydrogen-free and hydrogen-charged conditions in both ferrite and bainite were compared and discussed. The results demonstrated a non-affected elastic behavior by hydrogen in both microconstituents. The homogeneous and heterogeneous dislocation nucleation are proposed as the dominant mechanisms for pop-in behavior in ferrite and bainite, respectively. In addition, the reduction of pop-in load by hydrogen in both microconstituents indicates a hydrogen-enhanced dislocation nucleation in both homogenous and heterogeneous manners. Moreover, a hydrogen-induced hardness increment was detected in both microconstituents, which is related to the hydrogen-enhanced lattice friction on dislocations. Also, the more prominent hardness increment in bainite was caused by its significantly more trapping sites.

Atomistic insights into the deformation mechanism of a CoCrNi medium entropy alloy under nanoindentation

Understanding the fundamental of contact-induced behavior in metals is critical for the studies of associated mechanical properties. Although nanocontact plasticity in the conventional pure metals or solutions have been well established, such theoretical frameworks may break down in the recently emerging medium entropy alloys (MEAs), owing to their unique disordered feature and inevitable chemical fluctuations. Here combined with crystal defect theories, we investigate the nucleation and evolution of dislocations in CoCrNi MEA during nanoindentation. Molecular dynamics simulations of nanoindentation are carried out to analyze the effects of composition inhomogeneity and temperature on the defect behavior. In contrast to the usual homogeneous nucleation criterion in pure metals, heterogeneous dislocation nucleation is preferred to occur at Cr-rich clusters in CoCrNi MEA at a lower indentation depth. Although the local composition fluctuation can facilitate the nucleation of dislocations, these partials are pinned significantly by the local atomic sites with a high level of CoCr chemical short-range order. Moreover, nanotwin and phase-transformation are promoted at low temperature, due to the low stacking fault energy and enhanced glide resistance. In particular, the formation and evolution of the distorted prismatic dislocation loop are visualized at high temperature. The new phenomena reported herein could provide a basis for tuning local composition and atomic arrangement to obtain excellent mechanical properties in medium or even high entropy alloys.

A unified statistical model for indentation pop-in: Effects of indenter radius and microstructure density on the transition from homogeneous nucleation to heterogeneous nucleation to bulk plasticity

Indentation pop-in, i.e. a sudden displacement burst on the measured load-penetration depth curves, has been known as the onset of elastic-plastic deformation for crystalline materials. Depending on the indenter radius or density of pre-existing dislocation nucleation sources, the evolution of pop-in shear stress can generally be categorized into three deformation stages, i.e. the homogeneous dislocation nucleation stage, heterogeneous dislocation nucleation stage and bulk plasticity stage. For the former, the fluctuation of pop-in stress is dominated by the thermally activated nucleation process. For the middle, a size-dependent pop-in behavior with stress fluctuation is informed over a wide range of indenter radius and microstructure density. For the later, the materials strength is determined by the critical resolved shear stress for the motion of existing dislocations. Here, we find two additional transition stages between the adjacent deformation stages that can be effectively addressed by a novel competition mechanism, and the transition points are affected by the density of dislocation nucleation sites. All these critical features are well characterized by a unified statistical model proposed in this work. Moreover, a mechanistic model with closed-form formulas is developed for the size-dependent pop-in behavior during the heterogeneous dislocation nucleation stage. By comparing both the calibrated and predicted theoretical results with different sets of experimental data, good agreements are achieved that can rationally verify the proposed model. This work presents a theoretical framework to characterize the fundamental pop-in mechanisms, and provides an avenue towards the prediction of transition points distinguishing different plasticity deformation regimes.

Crystal orientation and grain boundary effects on plastic deformation of FCC particles under high velocity impacts

Material plastic behavior during deformation is affected by several parameters such as atomic structure, crystalline orientation, grain boundaries, impurities etc. In this study, molecular dynamic simulations were performed to provide a detailed understanding of the effects of grain orientation and grain boundaries on plastic deformation of FCC particles under high velocity impacts. Two single-crystal particles with different crystalline orientations, two simple polycrystal particles (bicrystal, and tricrystal) with inner walls parallel and perpendicular to the shock wave, and a polycrystal particle with 64 random grains were modeled. The results showed that the deformation behavior and microstructural evolution depended directly on their initial microstructure of the particles, whereas the resulting shear strain pattern was the same for all the particles. Phenomena such as recovery, crystallization, recrystallization, grain growth, twining, and grain rotation were observed during the deformation of the particles. In addition, it was shown that heterogeneous nucleation of Shockley partial dislocations was the main mechanism at the onset of the deformation. Another important deformation mechanism was solid-state amorphization due to the densification of the dislocation network in certain regions of the particles, also associated with thermal softening effects.

Bimodality of incipient plastic strength in face-centered cubic high-entropy alloys

ABSTRACT Spherical tip nanoindentation experiments on two typical face-centered cubic high-entropy alloys (HEAs), CoCrFeNi and CoCrFeMnNi in as-solutionized and aged conditions were performed using tips of two different radii. Large datasets of the strength at the first pop-in were obtained and their statistical nature were analyzed to gain insights into the micromechanisms responsible for the onset of incipient plasticity in HEAs that are notionally monophasic. In all the cases examined, the probability density distributions were bimodal in nature. The deconvoluted distributions were utilized to estimate the activation volumes of the underlying deformation mechanisms. They show that when the probed material's volume is relatively small, heterogeneous dislocation nucleation aided by monovacancies occurs at lower indentation stresses; this followed by homogeneous dislocation nucleation at high loads, resulting in strengths corresponding to the theoretical strengths. When a substantially larger volume is sampled, by using a larger radius tip, either the preexisting dislocation mediated ones at low stresses or vacancy cluster /grain boundary aided heterogeneous dislocations nucleation at higher stresses become dominant. Increasing the chemical short-range order in the alloy via high temperature aging leads to overall strengthening of the alloy by enhancing stress required for the homogeneous dislocation nucleation. Implications of such plurality of mechanisms with overlapping strength distributions at HEA's disposal in imparting high strength-ductility combinations are discussed.

Room- and elevated-temperature nano-scaled mechanical properties of low-density Ti-based medium entropy alloy

The incipient plasticity and creep behavior of body-centered cubic (BCC) Ti65(AlCrNb)35 medium entropy alloy (MEA) were investigated via nanoindentation. The elastic modulus and hardness obtained from different methods were compared. The activation volume for plastic deformation was calculated to be 11 b3, indicating a larger-scaled Peierls deformation mechanism typical for BCC metals. The orientation effect on incipient plasticity was studied on (100), (110) and (111) orientations at room temperature. The orientation difference is attributed to the different Schmid factors for different planes. The activation volume and activation energy of dislocation nucleation on Ti65(AlCrNb)35 was estimated as 0.8–0.9 b3 and 0.43 eV, which suggests that the mechanism of incipient plasticity is heterogeneous dislocation nucleation assisted by pre-exist defects, with a very localized activated volume. Also, the activation volume and energy of Ti65(AlCrNb)35 are higher than those of conventional metals (Ni, Pt, Cr and Mg) and lower than those of high entropy alloys (HEAs), which suggests that the dislocation nucleation in Ti65(AlCrNb)35 is more difficult than that in metals but easier than that in HEAs. Creep responses of the (100), (110) and (111) grains at 500–600 °C were found to be all dominated by the power-law dislocation creep mechanism (stress exponent n ~ 5) with the activation energy ~130 kJ/mol. The high stress applied by the indenter tip led to the stress-induced pipe diffusion, assisting the dislocation climb and lowering the activation energy. The activation volume was measured as 3–6 b3, related to dislocation climb and atom diffusion at elevated temperatures. The creep displacements and creep rates for the (100), (110) and (111) planes are quite similar, probably resulting from (i) complex slip systems in BCC structure underneath the indenter tip, (ii) a complex strain field produced by concentrated solute atoms, and (iii) the stress-induced pipe diffusion.

The effect of grain boundary on the local incipient plastic deformation of fcc metals during nanoindentation

The effect of grain boundaries (GBs) on deformation mechanisms becomes increasingly important as the volume of deformation reaches the submicrometer and nanoscale. The current work investigates the impact of grain boundaries on the incipient plasticity of small-scale deformations of fcc metals. For this purpose, the behavior of single and bi-crystal Au thin films during nanoindentation are studied, using large-scale atomistic simulations. Various symmetric ⟨110⟩ tilt GBs with a wide range of misorientation angles are included to analyze the effect of GB geometry on the nanoscale plasticity mechanisms. Potentially, GBs can act as a source, sink, or obstacle for lattice dislocation, depending on their geometry, energy level, and distance from the deformation zone. The role of the heterogeneous nucleation and emission of dislocations from GBs on the plasticity and hardness of bicrystals is analyzed. According to our results, the intrinsic free volume involved in the GB region is associated with dislocation nucleation at the GB. The volume of the plastic zone generated beneath the tip and the way it grows is strongly dependent on the GB structure. Dislocation nucleation occurs predominantly in the early stages of indentation at GBs with a dissociated interface structural unit, before the interaction of lattice dislocation and GB. Coherent twin boundaries display the lowest effect on the hardness. Based on our results, there is a strong correlation between the interfacial boundary energy and its effect on the bicrystal hardness. GBs with lower interfacial energy offer a higher barrier against slip transmission and nucleation at the GB.

Lattice distortion effect on incipient behavior of Ti-based multi-principal element alloys

In this work, we studied the influence of lattice distortion on the initiation of plasticity in Ti-based (multi-principal element alloy) MPEAs at a loading rate of 500 μN/s. The surface dependence was observed in Ti20Al20Cr20V20Nb20 (Ti20) MPEA, where the lowest first burst load was determined in (110) oriented grain, which is the same as that in Ti60Al10Cr10V10Nb10 (Ti60). This implies this kind of crystallographic dependence is the intrinsic feature of present studied alloys and it is not covered by the lattice distortion effect. In spite of similar orientation dependence, a much higher load at first burst was identified in Ti20 compared with Ti60, which is attributed to the fact that the more severe lattice distortion causes a larger critical resolved shear stress (CRSS) to nucleate the dislocation and a greater lattice friction to overcome during dislocation multiplication and emission process. In addition, based on the activation volume value, the mechanism in Ti20 is regarded as the same as that in Ti60, inferring that altering the lattice distortion does not change the pop-in mechanism in MPEAs. Lastly, the lattice distortion influence on the homogeneous dislocation nucleation process was investigated and compared with the heterogeneous dislocation nucleation event.

Dislocation nucleation in CoNiCrFeMn high entropy alloy

In this work, the homogeneous and heterogeneous nucleation of dislocations in a representative face-centered-cubic high entropy alloy (HEA) CoNiCrFeMn is studied by combining molecular dynamics simulations and continuum mechanics modeling. It is found that as compared to conventional metals such as Cu, HEAs have relatively low activation energy but require high athermal stress for dislocation nucleation. This seemingly odd behavior originates from the uniquely low (even negative) stacking fault energy in HEAs that leads to low critical nucleation radius and low activation volume for dislocation nucleation.

Novel atomic-scale mechanism of incipient plasticity in a chemically complex CrCoNi medium-entropy alloy associated with inhomogeneity in local chemical environment

Understanding the incipient plastic mechanism in metals is critical for their associated mechanical properties. While heterogeneous dislocation nucleation from pre-existing defects constitutes the most prevalent onset mechanism of plasticity in the conventional solutions, such a scenario may break down in the recently emerging chemically-disordered high/medium entropy alloys (HEAs/MEAs), owing to their unique multiple-component feature and the inevitable inhomogeneity in local atomic environments. Here, classical molecular dynamics simulations and first-principles density functional theory calculations are carried out to study the atomic-scale mechanisms governing the incipient plasticity in a prototypical chemically complex face-centered cubic (fcc) CrCoNi MEA. Dislocation nucleation is found to occur preferentially at an energetically unstable defect cluster with body-centered cubic like (bcc-like) atomic environment as a precursor, after certain deformation before plasticity, which is in contrast with the usual mechanism of heterogeneous dislocation nucleation in the conventional solute solution metals. The minimum energy pathway of dislocation nucleation from a bcc precursor is discussed to rationalize the usual phenomenon. First-principles athermal quasi-static compression test validates the mechanism suggested by atomistic simulations. Further electronic structure analysis suggests that the local bcc-like defect cluster is related to the localized electronic behaviors of Cr atoms and the weak Cr-Cr bonding, which promote the dislocation nucleation and therefore the incipient plasticity of CrCoNi MEA. The atomic and electronic insights reported here highlight the significant role of local chemical order in determining the mechanical property, and shed light on the strategy of optimizing mechanical performance via tailoring composition and local atomic arrangement in the generic highly concentrated solutions.

Unraveling the Role of Interfaces on the Spall Failure of Cu/Ta Multilayered Systems

Molecular dynamics (MD) simulations are carried out to investigate the effects of the type and spacing of FCC/BCC interfaces on the deformation and spall behavior. The simulations are carried out using model Cu/Ta multilayers with six different types of interfaces. The results suggest that interface type can significantly affect the structure and intensity of the incoming shock wave, change the activated slip systems, alter dislocation slip and twinning behavior, affect where and how voids are nucleated during spallation and the resulting spall strength. Moreover, the above aspects are significantly affected by the interface spacing. A transition from homogeneous to heterogeneous dislocation nucleation occurs as the interface spacing is decreased to 6 nm. Depending on interface type and spacing, damage (voids) nucleation and spall failure is observed to occur not only at the Cu/Ta interfaces, but also in the weaker Cu layer interior, or even in the stronger Ta layer interior, although different mechanisms underlie each of these three distinct failure modes. These findings point to the fact that, depending on the combination of interface type and spacing, interfaces can lead to both strengthening and weakening of the Cu/Ta multilayered microstructures.

Deformation of copper particles upon impact: A molecular dynamics study of cold spray

In this work, Molecular Dynamics simulations were performed to predict and provide detailed understanding of the deformation behavior of solid copper particles accelerated against a copper substrate. Simulations were carried out at an initial particle/substrate temperature of 300 K. The particles were assigned an initial velocity of 1000 m/s normal to the substrate surface, oriented in the [1 1 1] direction. The particles diameter was varied from 5 to 40 nm in order to assess changes in the deformation behavior due to size effects. For particles with diameters larger than 10 nm, the results showed well-defined patterns of dislocation activity associated with three distinct stages of deformation. The onset of plastic strain was localized at the flattened particles bottom, in the region of contact with the substrate, and characterized by the heterogeneous nucleation of Shockley partial dislocations. In the subsequent stage, a dense dislocation network was formed in the lower half of the particles, while the top of the particles remained undeformed. The plastic deformation of the top of the particles completed the process, resulting in the final flattened splat shape. High temperatures (above 1000 K) were observed at the particle-substrate interface, where fluid-like flow contributed to the formation of material jetting.