Adiabatic Shear Instability Research Articles

Probing trade-off between critical size and velocity in cold-pray: An atomistic simulation

The detailed mechanism of bonding in the cold spray process has remained elusive for both experimental and theoretical parties. Adiabatic shear instability and hydrodynamic plasticity models have been so far the most popular explanations. Here, using molecular dynamics simulation, we investigate their validity at the nanoscale. The present study has potential applications in the fabrication of ultrathin layers in the electronics industry. For this aim, we considered Ti nanoparticles of different diameters and Si substrates of different orientations. It is shown that very high spray velocities are required for a jet to be observed at the nanoscale. We propose a method for thermostating the substrate that enables utilizing high spray velocities. For the first time, we demonstrate an oscillatory behavior in both the normal and radial stress components within the substrate that can propagate into the particle. We have shown that neither the adiabatic shear instability model nor the hydrodynamic plasticity model can be ignored at the nanoscale. In addition, the formation of a low-resistance titanium silicide proper for electronic application is illustrated.

Adiabatic Shear Localization in Metallic Materials: Review.

In advanced engineering applications, there has been an increasing demand for the service performance of materials under high-strain-rate conditions where a key phenomenon of adiabatic shear instability is inevitably involved. The presence of adiabatic shear instability is typically associated with large shear strains, high strain rates, and elevated temperatures. Significant plastic deformation that concentrates within a adiabatic shear band (ASB) often results in catastrophic failure, and it is necessary to avoid the occurrence of such a phenomenon in most areas. However, in certain areas, such as high-speed machining and self-sharpening projectile penetration, this phenomenon can be exploited. The thermal softening effect and microstructural softening effect are widely recognized as the foundational theories for the formation of ASB. Thus, elucidating various complex deformation mechanisms under thermomechanical coupling along with changes in temperatures in the shear instability process has become a focal point of research. This review highlights these two important aspects and examines the development of relevant theories and experimental results, identifying key challenges faced in this field of study. Furthermore, advancements in modern experimental characterization and computational technologies, which lead to a deeper understanding of the adiabatic shear instability phenomenon, have also been summarized.

Effect of Laser on the Interface and Thermal Conductivity of Metallized Diamond/Cu Composite Coatings Deposited by Supersonic Laser Deposition.

To achieve the rapid heat dissipation of components in the industrial field, the heat dissipation coating is prepared on the surface, which is conducive to improving the service life of the parts and greatly reducing the industrial costs. In this paper, metallized diamond/Cu composite coatings were fabricated on 1060Al substrate by supersonic laser deposition. The composite coatings were prepared at a nitrogen pressure of 3.0 MPa, a scanning speed of 10 mm/s, and a 1060 nm semiconductor coupled fiber laser with different laser power. The research results show that the laser power affects the interface bonding by affecting the temperature of adiabatic shear instability during particle impact. The metallized diamond forms a good bonding at the interface through the plastic deformation of the Cu matrix. Appropriate parameters ensure that the jet does not affect the subsequent particle deposition and build a good heat transfer bridge to elevate the heat transfer efficiency. The coating prepared at a laser power of 1000 W has the highest thermal diffusion coefficient of 89.3 mm2/s and thermal conductivity of 313.72 W/(m·K), which is 8.92% higher compared to the coating prepared without laser. Experiments with thermal imaging have also demonstrated that the coating at optimal parameter transferred heat faster. Our research provides a technical guidance for rapid preparation of high-quality heat dissipation coatings in industry.

Improving bond strength and deposition efficiency of ceramic coatings via low pressure cold spraying: A study on hydroxyapatite coatings with Cu-Zn blends

This study presents Low Pressure Cold Spraying (LPCS) method for ceramic coatings, aimed at enhancing efficiency and elucidating bonding mechanisms. It focuses on the deposition of ceramic coatings using LPCS, with hydroxyapatite (HA) on 316L stainless steel (SS) as an illustrative example. Despite the advantages of LPCS, retaining HA particles has proven challenging, resulting in thin coatings (11.09 ± 2.56 μm) with low bonding strength (1.80 ± 0.19 MPa). To address this issue, a composite coating strategy was developed by blending 20 wt% Cu and Zn powder with 80 wt% HA. This approach significantly improved coating properties, achieving enhanced bonding strength (33.70 ± 1.13 MPa), deposition efficiency (27 %), and hardness (136.30 ± 2.45 HV) compared to pure Cu-Zn coatings. Numerical simulations were conducted to interpret these experimental results, indicating that blending metal with HA improves deposition efficiency, bonding strength, and hardness. In HA coatings, particles fragment into submicron grains and embed into the substrate through mechanical interlocking (MI), with shockwave-induced bonding strengthening subsequent layers. For Cu-Zn coatings, bonding occurs through MI and adiabatic shear instability (ASI). In HA-Cu-Zn coatings, high-velocity HA particles and Zn particles enhance bonding further through in-situ tamping.

Microstructural evolution and dynamic mechanical behavior of PM 2195 Al-Li alloy with resistance to shear instability in high strain rate deformation

The risk of adiabatic shear instability is common in traditional alloys covering high-strength steels, copper alloys and aluminum alloys during high strain rate deformation. However, the research on shear instability of 2195 Al-Li alloy prepared by powder metallurgy (PM) at high strain rates is still blank. The purpose is to explore its microstructure evolution and dynamic compression behavior. In this work, the 2195 Al-Li alloy prepared by PM amazingly demonstrates excellent resistance to shear instability at high strain rates during Split-Hopkinson pressure bar (SHPB) experiment. The microstructural evolution of grains and T1 (Al2CuLi) precipitate phase, and dynamic compression behavior of PM 2195 Al-Li alloy at various strain rates from 3000 s−1 to 9000 s−1 are investigated in detail employing correlative electron-backscatter diffraction (EBSD) and transmission electron microscopy (TEM). During high strain rate deformation, the alloy undergoes grain fragmentation and rotation, increasing dislocation density around the grains. When the strain rate is from 3000 s−1 to 7500 s−1, the Kernel Average Misorientation (KAM) value increases, indicating intensified localized strain. At a strain rate of 9000 s−1, a small number of grains are surrounded by nanocrystals (around 200 nm) that undergo stress release, while the average size of micrometer-sized grains is 0.81 μm. As the strain rate increases, the T1 phases in the alloy extends, vibrates, and fractures before dissolving in the matrix, while high-rate deformation promotes dislocation entanglement and defects, leading to the decomposition or ordering of precipitated phases through rapid plastic deformation. By virtue of energy dissipation strategy via the formation of nanocrystallines and dislocation behavior induced by the dissolution of T1 phases, the "positive-positive" effect is observed. The PM 2195 Al-Li alloy undergoes no shear failure even at the strain rate of 9000 s−1, showing great prospects in future applications in dynamic-loading conditions.

Multiple Deformation Mechanisms in Adiabatic Shear Bands of a Titanium Alloy during High Strain Rate Deformation.

The occurrence of adiabatic shear bands, as an instability phenomenon, is viewed as a precursor to failure caused by instability at high strain rates. Metastable β titanium alloys are extensively utilized due to their excellent mechanical properties, which are often subjected to high strain rate loads in service conditions. Understanding and studying their adiabatic shear instability behavior is thus crucial for preventing catastrophic failure and enhancing material performance. In this study via detailed microstructural analyses in the adiabatic shear region of a Ti-10V-2Fe-3Al alloy subjected to high strain rates, it was observed that α″ martensitic transformation and nano-twinning plus β-to-α phase transformation with α″ martensite as an intermediate phase occurred, in addition to substantial fine grains. The grain refinement mechanisms were mainly related to dynamic recovery dominated by dislocation migration alongside severe plastic deformation.

Microstructural Study of Cold-Sprayed CoCrFeNiMn High Entropy Alloy

The rapid development of cold spraying technology for additive manufacturing of engineering components has made it a viable option for developing thick deposits from high-entropy alloys (HEAs). The microstructure of cold-sprayed CoCrFeNiMn deposit was investigated in this study using electron backscattered diffraction, scanning electron microscopy, and finite element analysis (FEA). The limited studies on the impact deformation behavior of the HEA during cold spraying, limiting our understanding of impact phenomena, and interactions between the HEA particles under ultra-high strain rate deformation motivated this study. From the microstructural characterization, heterogeneous microstructure appears to be formed in the cold-sprayed HEA deposit, comprising of equiaxed ultrafine grains at the particle–particle interfacial regions and coarse grains at the particle interiors. The FEA reveals large strain (> 250%) and temperature (> 90% of the alloy solidus temperature), mainly at the splat’s interfaces. Adiabatic shear instability and rotational dynamic recrystallization resulting from heat accumulation and high strain are believed to be responsible for these observations during the ultra-high strain rate deformation of the HEA. The large deformation and grain refinement experienced by the HEA resulted in greater deposit hardness when compared with the sprayed powder, with the nanohardness increasing from 1.16 GPa in the powder to 5.14 GPa in the deposit. This study explores and provides an understanding of the deformation behavior of the HEA and the resulting microstructure during cold spraying.

Assessing critical process condition for bonding in cold spraying

Cold spray bonding mechanism is often correlated with adiabatic shear instability and jetting at inter-splat boundaries. In this work, the role of in-flight temperature on the deposition characteristics is synergistically addressed with the in-flight velocity of the impacting powders. The fraction of inter-splat bonding and the properties of the coatings are correlated as a function of total energy of the powder upon impact rather than in-flight velocity alone. Fraction of inter-splat bonding is used to obtain normalised electrical conductivity and normalised elastic modulus for variety of materials ranging from low melting point zinc (Zn) to high melting point tungsten (W). Onset of deposition is characterized with the dimension less parameter estimated by normalising the total energy of the impacting powder with the Ebond (critical energy). The data is correlated with the experimental results. For instance, the critical velocity (VCr) and critical energy (Ebond) for bonding of copper are estimated to be 451 m/s and 27.25 μJ respectively. One can tailor the process condition to deposit the metallic powder in cold spraying by selecting either in-flight velocity or in-flight temperature. The synergistic effect of velocity and temperature can be corroborated with the bonding state in cold sprayed coatings.

On adiabatic shear instability in impacts of micron-scale Al-6061 particles with sapphire and Al-6061 substrates

Impact mechanics of micron-scale, Al-6061 particles on sapphire and Al-6061 substrates were investigated experimentally and through simulations. Particle impact experiments were carried out by using the laser induced projectile impact test (LIPIT) and the coefficient of restitution was evaluated for impact velocities in the range of 50–950 m/s. Bonding was observed only in Al-on-Al impacts with impact velocities over 810 m/s. A continuum model of the impacts was implemented by using commercially available finite element software. The bilinear Johnson–Cook model was implemented to model the material flow effects in the ultra-high strain rate (UHSR) regime. A cohesive zone model was used for the bonding along the particle–substrate contact interface. Heat generation due to plasticity and friction, and material damage were also included in the simulations. A quantitative measure of adiabatic shear instability (ASI) was implemented into the modeling framework to search for material points that experience drop of strength during loading. A small volume of the material internal to the particle was found to experience ASI in Al-on-sapphire impacts, but this was not observed in Al-on-Al impacts. However, if the flow rule is switched to one that neglects the effects of the UHSR-regime, ASI can be predicted in regions of the particle where the finite element mesh deforms excessively. It is recommended that any study searching for ASI in high-velocity impact simulations should assess the mesh distortion carefully and use a flow rule that includes UHSR effects.

Atomistic characterization of impact bonding in cold spray deposition of copper

We investigate the cold-spray additive manufacturing process of nanometric copper particles impacting a copper substrate using molecular dynamics (MD) and focus on the interplay between particle size (2–32 nm), particle velocity (100–2800 m/s), ensuing particle penetration depth and the impact bonding energy (IBE) binding the impinging particle with the substrate. It is observed, based on trends in the IBE, that even at low particle velocities (∼100 m/s) smaller sized particles (<8 nm) bind to the substrate, while there is a size-dependent critical velocity (≥200 m/s) for binding of larger particles (≥8 nm). At velocities near and above 500 m/s, material jetting and significant increase in particle penetration into the substrate are observed for larger particles. Rapid temperature increase, accompanied by adiabatic shear banding and instability (ASI), is observed, especially at the particle-substrate interface, resulting in particle-cratering at higher velocities in the range studied. Further, while jetting and ASI are observed together at high impact velocities, simulations show that ASI is not essential for jetting, consistent with recent investigations. In addition, both ASI and jetting are not prerequisites for particle binding to the substrate. A significant observation involves self-similar variations in particle penetration depth and IBE with particle kinetic energy across all particle sizes, which is captured by a quantitative constitutive relationship governing the particle's kinetic energy, penetration depth, and IBE.

Influence of cutting parameters on cutting specific energy of Inconel718 based on strain gradient

In this paper, the Johnson-Cook constitutive model is modified by considering the influence of hard point such as TiC and NbC in the matrix of Inconel718 on the deformation stress. The theoretical model of cutting specific energy in the main deformation zone of Inconel718 is modified based on the new constitutive model by combining the strain gradient theory. The effect of different cutting parameters on cutting specific energy is studied, and the effect of cutting specific energy on cutting deformation and the resulting dimensional effect are also analyzed. The research results show that cutting specific energy increases with the increase of cutting speed. With the increase of cutting thickness, the cutting specific energy reduced, and the trend is non-linear. The change of undeformed chip thickness will cause size effect. The cutting specific energy increases with the reduction of the thickness of undeformed chip, and the impact of the thickness of undeformed chip on the cutting specific energy becomes smaller and smaller as the speed increases. The existence of hard points makes the main deformation zone generate a large amount of heat energy and deformation energy, which leads to dimensional effects and makes the material be more prone to adiabatic shear instability, then leads to the increase of cutting specific energy. With the increase of cutting specific energy, the width of adiabatic shear band is narrowed, the degree of serration is aggravated, and the chip morphology is closer to the experimental results.

Adiabatic shear instability in a titanium alloy: Extreme deformation-induced phase transformation, nanotwinning, and grain refinement

Increasingly harsh service conditions place higher requirements for the high strain-rate performance of titanium alloys. Adiabatic shear band (ASB), a phenomenon prone to dynamic loading, is often accompanied by catastrophic damage. Yet, it is unclear how the internal nanostructures are related to shear instability. Here we report detailed microstructural evolution in the ASB of a titanium alloy via in-depth focused ion beam (FIB), transmission Kikuchi diffraction (TKD), and high-resolution transmission electron microscope (HRTEM) analyses, with the deformation instability phenomenon discussed from the energy perspective. The ASB interior undergoes multifaceted changes, namely deformation-induced beta-to-alpha transformation and deformation-induced martensitic transformation to form substantially refined and heterogeneous structures. Meanwhile, two types of extremely fine twins are identified to occur within both nano-sized martensite and alpha phase. The critical plastic work representing the onset of adiabatic shear instability and dynamic equilibrium is observed to be constant for a specific structure in the same deformation mode. The energy analysis could be extended to other materials subjected to high strain-rate dynamic deformation.

Mechanistic Study of Rail Gouging during Hypersonic Rocket Sled Tests

Gouging—an obstacle to the development of hypersonic rocket sled test techniques—was mechanistically investigated through experimental and theoretical analyses. Typical gouges were analyzed using macroscopic and microscopic experiments to investigate the evolution of gouging. Quasistatic compression and Hopkinson bar experiments were performed to systematically study the thermoviscoplastic properties of U71Mn rail steel under wide ranges of the strain rate and temperature. The critical condition for gouging was derived based on a thermoviscoplastic constitutive model supplemented by a three-variable criterion for an adiabatic shear instability. The results showed the following. (1) Adiabatic shear bands (ASBs) form when stress reduction under the combined action of frictional heating and high-speed deformation exceeds the strain-hardening effect of the rail material. (2) The nonuniform deformation of the edges of ASBs leads to the generation of cracks that split the rail surface. As the ASBs expand, the cracks grow and coalesce, eventually causing the material to peel off, forming gouges. (3) The relationships among the temperature, strain rate, and strain at the onset of gouging can be determined based on the critical condition for the formation of ASBs in rail steel.

Microstructure and mechanical performance of nickel coating on copper sheet via laser shock processing

A novel technique of laser shock processing (LSP) was proposed to consolidate Ni powder into coating at room temperature to protect Cu substrate. This is a combined process of shock compaction of powder, shock micro-welding of particle/particle and particle/substrate. The required pressures of each process were calculated and the effect of laser energy on the aspect of microstructure, surface morphology, and mechanical properties of coatings were investigated. Experimental results showed that a fully dense (relative density 99.81%), smooth and uniform Ni coating without oxidation was fabricated due to the high-speed, high-pressure, and cold processing characteristic of LSP. The coating/substrate interface presented curved convex feature by mechanical locking and a 1.2 μm thick atomic diffusion layer by metallic bonding under adiabatic shear instability. The relative density and mechanical performance of coating was improved with a proper increase of laser energy. The maximum hardness of coating reached 332 HV, presenting approximately three times increment of substrate. The wear rate of coating decreased sharply with increasing laser energy, with the minimum value being 20.7% of substrate. The improvement of mechanical properties was attributed to the coupled effect of void collapse by high-speed plastic or viscoplastic deformation and the shockwave-induced microstructure refinement.

A sustainable ecofriendly additive manufacturing approach of repairing and coating on the substrate: cold spray

ABSTRACT In this study, surface modification and deformation behaviour of different engineering materials were microscopically examined by an approach called cold spray additive manufacturing (CSAM). The CSAM is a layer-by-layer deposition technique for repairing and coating the deteriorated or dimensionally unstable surface. Furthermore, in this study, both the experimental and numerical investigation have been carried to understand the surface modification approach. In the experimental procedure, the de Laval nozzle accelerates the microsize particle at a high velocity on the substrate to obtain the uniform surface coating. Engineering materials like copper, aluminium, titanium and mild steel were probed with different ranges of velocities. Additionally, an explicit/Abaqus finite element approach was used to investigate the bonding between particle and substrate by using the high velocity of particles. At the interface, refining meshing size reduces the beginning velocity for adiabatic shear instability (ASI). For the different combinations of particles and substrates like copper/copper, aluminium/aluminium, titanium/aluminium, aluminium/ titanium, and copper/mild steel at perpendicular impact, the adiabatic shear instability was numerically estimated. Deformation behaviour for multi-impact has also been seen with different particle diameter sizes to determine coating phenomenon. Furthermore, the characterisation technique called scanning electron microscopy (SEM) also showed the uniform coating on the substrate.

Cold spray deposition characteristic and bonding of CrMnCoFeNi high entropy alloy

Particle bonding physics remains an important area of study in cold spray (CS) deposition. It has been argued that for pure metals, large interfacial strains in particles triggered either by adiabatic shear instability (ASI) or hydrostatic plasticity promote bonding while the bonding mechanisms of high entropy alloys (HEA) have not been explored. HEAs are an emerging class of materials that have superior work-hardening ability and are usually resistant to softening, a behavior that is different from pure elements and conventional alloys. In this study, equiatomic CrMnCoFeNi HEA feedstock powder is produced and CS experiments are conducted to explore the deformation evolution of these HEA particles and their bonding characteristics. The shear localization strain of the HEA is theoretically estimated and compared to conventional alloys and elements to explain the deposition behavior of the HEA. Results show that the particle impact morphology is strain rate dependent in addition to being material and microstructure dependent. Electron channelling contrast imaging reveals severe plastic deformation at the lower half of the particles due to the dynamic inertia effect. Deformation nano-twins with a thickness of about 200 nm were observed. HEA/HEA pair has a higher critical velocity compared to HEA/Nickel, HEA/Inconel625 and HEA/Stainless steel 304 pairs. This is attributed to the excellent strain hardening and intermediate softening of the HEA alloy used, which potentially postpones shear localization and impedes bonding, requiring a higher deposition velocity. Finally, it is shown that the ASI based criterion for bonding can predict the deposition mechanism of HEAs more inclusively.

Advances in formation mechanisms and multiscale simulations of adiabatic shear bands in metallic materials

<p indent=0mm>Adiabatic shear bands (ASBs) become an important failure mechanism when the ductile metallic materials are loaded under the dynamic impact. This thermoplastic instability behavior occurring in such a narrow band under the coupling actions of force and thermal effect easily causes a rapid propagation of crack inside the ASB or along its boundary, subsequently leading to a sudden failure. The extremely small scale of adiabatic shear bands in space and time has brought great challenges to experimental investigations. For this reason, scholars have not obtained a comprehensive understanding of this unique mechanical behavior, but a lot of research work has already been done and many breakthroughs have been made in this research field. In the experimental studies, the applications of high-speed and high-resolution testing techniques make people observe the whole process of initiation and propagation of the ASBs more clearly, and further recognize the role of different influencing factors in the emergence of ASBs, more specifically, the causal relationship between the adiabatic temperature rising and plastic localization. Based on a large number of experimental results, scholars have summarized a variety of mechanical explanations in recent years to reveal the formation mechanism of adiabatic shear instability behavior. Moreover, in the aspect of numerical analysis, the scholars have already put forward many kinds of modelling and simulation methods to help discern the formation process of ASB. In addition to the modelling method at a macro scale, multiscale simulation methods consider different kinds of microscopic mechanisms in their constitutive relations. As such, the influences of different microscopic variables on the dynamic mechanical behavior can be analyzed independently via multiscale simulations, which can greatly promote the comprehension of formation mechanisms of adiabatic shear bands. In this review, the latest investigation advances on adiabatic shear instability behavior of the research group from impact dynamics and engineering application laboratory in Northwestern Polytechnical University, as well as a number of published results of other scholars, focusing on the formation mechanisms of ASBs in the metallic materials with different microscopic characteristics, are summarized. Firstly, the most classical thermal softening theory is discussed, and the latest measurement results revisiting the causal relationship between adiabatic temperature rise and localized deformation are reviewed. Then we briefly introduce some other softening mechanisms proposed based on the microstructure characteristics of metallic materials, including the geometric softening theory and dynamic recrystallization softening mechanism. Based on these above instability mechanisms, many simulation models are constructed to reproduce the formation process of ASBs. Therefore, we also systematically elaborate on the simulation studies on adiabatic shear instability behavior via multiscale simulation methods and track their respective progress. Besides the traditional modelling and finite element method at the macro scale, more simulations carried out at the meso/micro scales to reveal the physical essence of this behavior in recent years are stated, such as the crystal plasticity finite element method, phase filed simulation, discrete dislocation dynamics method and even atomistic simulations. Finally, we discuss the problems existing in this research field and future research focuses for the adiabatic shearing localizations.

HVAF deposition mechanism of γ-TiAl-based coating containing β phase

The Ti-45Al-7Nb-4V, Ti-45Al-7Nb-4Cr, Ti-45Al-7Nb-2V-2Cr alloy coatings were prepared on the surface of the aluminum alloy by high-velocity-air-fuel (HVAF). The surface and cross-section of three kinds of titanium aluminum alloy coatings and the micromorphology of the bonding interface between the coating and substrate were observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). The deformation behavior of titanium aluminum alloy particles and the phase composition of the titanium aluminum alloy coating were analyzed by X-Ray Diffraction (XRD) and energy dispersive x-ray analysis (EDAX). The results show that the coordinated deformation between TiAl particles and Al alloy matrix is a necessary condition for the deposition of the first layer of titanium‑aluminum alloy particles. The bonding mechanism of the TiAl coating and the matrix is mechanical bonding, and there are both mechanical bonding and metallurgical bonding between spraying particles. In the process of coating deposition and formation, the β phase grains undergo coordinated deformation to form typical structures such as striped grains and circular columnar crystals. The deformation mechanism of the titanium aluminum alloy particles is the slip and kink mechanism in the grains, and the sliding and rotation mechanism of the grain boundary and the phase boundary. Adiabatic shear instability and dynamic recrystallization occurred during the formation of titanium aluminum alloy coating.

Deposition of Titanium Dioxide Coating by the Cold-Spray Process on Annealed Stainless Steel Substrate

The surface of most metals is covered with thin native oxide films. It has generally been believed that to achieve bonding, the oxide covering the surface of metallic particles or metal substrates must be broken and removed by adiabatic shear instability (ASI), whether induced at the particle–substrate interface or at the particle–particle interface. The aim of the present research is to investigate the correlation between the remaining oxide amorphous layer and substrate-deformation with the adhesion strength of cold-sprayed TiO2 coatings towards the bonding mechanism involved. Relevant experiments were executed using stainless steel (SUS 304), subjected to various annealing temperatures and cold-sprayed with TiO2 powder. The results indicate an increasing trend of coating adhesion strength with increasing annealed substrate temperature. The influence of substrate plastic deformation and atomic intermixing at the remaining amorphous oxide layer is discussed as the factors contributing to the increasing adhesion strength of cold-sprayed TiO2 coatings.

First-Principle Calculation on Critical Velocity for Cu and Al Cold-Spray Bonding

The first-principles calculation with a newly developed high-efficient computing method was firstly applied to prediction of critical velocity for Cu/Al cold-spray bonding without any empirical parameters. An excellent agreement between predicted values and experimental values was obtained. The bonding mechanism of cold-spray was clarified by analyzing the atomic response in displacement during cold-spray process. A mixed bonding mechanism of adiabatic shear instability and pressure-release was confirmed. The computing method could be popularized to extensive applications in critical velocity prediction.