High-velocity Impact Welding Research Articles

Standoff-free vaporizing foil actuator welding: Process principle, experimental validation, and mechanisms analysis

This paper introduces a novel high-velocity impact welding process: the standoff-free vaporizing foil actuator welding (standoff-free VFAW). This technique employs a new type of driving mechanism, overcoming the geometric placement constraints between the flyer plate and the target plate inherent in conventional impact welding processes. It enables welding without requiring an initial standoff distance between the two plates. The feasibility and general applicability of the proposed process were validated through experiments. The welding performance was evaluated using shear tests, peel tests, and microstructural analysis. The results indicate that the proposed process can successfully weld T2 copper to 304 stainless steel and AA5083-H112 to 304 stainless steel. Additionally, this study verified that the proposed process can achieve progressive welding, making it possible to utilize standoff-free VFAW for large-area metal welding. Furthermore, microanalysis revealed the presence of a typical wavy interface characteristic at the joint. Key parameters influencing the welding results were also explored through experiments and finite element modeling, which suggest that the boundary constraints of the workpiece play a key role in the success of standoff-free VFAW. This implies that the initiation of the small and dynamic gap between the flyer and target plates could be the potential mechanism for the proposed process. In summary, standoff-free VFAW presents simplicity and efficiency as its advantages. Moreover, the insights gained from this technique are not limited solely to vaporizing foil actuator welding (VFAW) but could also provide reference points for other high-velocity impact welding techniques.

Uncovering the influence of mechanical properties on wave formation during high-velocity impact welding by numerical simulation

The formation of wavy interface is one of the distinctive features of high-velocity impact welding. It is known that the geometric parameters of waves (amplitude a and length λ) depend not only on the impact conditions, but also on the mechanical properties of the materials being welded. However, until now, the impact of mechanical properties on the formation of waves has only been explored in a limited number of studies. To address this issue, in this paper, we use extensively a numerical simulation. First, we demonstrate that the numerical model, in conjunction with the smooth particle hydrodynamics (SPH) solver, effectively replicates the outcomes of a carefully controlled high-velocity impact welding experiment. Secondly, based on the validated model, we conducted a systematic study of the influence of strength on the wave formation process. Using numerical simulations with Johnson-Cook and ideal elastic-plastic strength models, we show that various characteristics of strength have a profound influence on the wave formation process. Furthermore, it is crucial to consider not only the yield strength of a material, but also factors such as strain and strain-rate hardening, along with thermal softening, to fully understand the wave formation during high-velocity impact welding.

Mechanical response and phase transformation characteristics of R-phase NiTi shape memory alloy under high strain rate compression

R-phase NiTi shape memory alloy (R-NiTi SMA) has many excellent properties, but there are application problems such as simple structure and high price. High velocity impact welding can effectively solve these problems, but the research on the mechanical response and phase transformation (PT) characteristics of R-NiTi SMA under dynamic deformation is lacking. Therefore, the quasi-static (0.001 s-1) and dynamic (500 s-1, 1000 s-1, 1500 s-1, 2000 s-1) compression experiments were conducted on R-NiTi SMA in this research. The results showed that the true stress-strain curves of R-NiTi SMA during deformation were characterized by three stages, including the superelastic, elastic, and plastic segments. The critical stress of austenite to R (A-R) and R to martensite (R-M) phase transformation increased with the increase of strain rate, and the phase transformation process gradually disappeared when the strain rate exceeded 1000 s-1, which was related to the velocities of A-R and R-M phase transformation. With the increase of strain rate, defects such as dislocations increased and hindered the phase transformation process during unloading, resulting in the increase of A-phase content. In addition, the enthalpy of the deformed samples decreased significantly and the temperature ranges of phase transformation increased slightly. This work deepens the understanding of the dynamic response of R-NiTi SMA and helps to expand the application of high strain rate processing technology in R-NiTi SMA.

Evolution of the interfacial microstructure in 316L/AlxCoCrFeNi composite material induced by high-velocity impact welding

AlxCoCrFeNi high entropy alloy with various Al contents has been successfully joined to 316L steel. The effect of mechanical properties of AlxCoCrFeNi induced by Al content on the interfacial microstructure in the 316L/ AlxCoCrFeNi has been investigated. All the 316L/AlxCoCrFeNi composite plates showed the typical interfacial microstructure of the high-velocity impact welding—periodic wavy interface. Four areas of the straight smooth area, the small wave area, the wave area, and the large wave area were along the radial direction in the interface orderly. The differences in wavelength, amplitude, ratios of the length in each area to the overall length, and the evolution of interfacial microstructure were discussed. The analysis of grain orientation, grain boundary, recrystallization, and orientation difference in the wave area showed that interfacial differences were caused by the difference in deformation mechanism of AlxCoCrFeNi matrix with different Al content. The deformation mechanism was closely related to the elongation and hardness in the macroscopic mechanical properties, which represented the ability to deformation and resist deformation, respectively. Consequently, the effect of Al content on the evolution of interface morphology was essentially the effect of hardness and elongation of AlxCoCrFeNi matrix. Additionally, all the wavy interfaces of 316L/AlxCoCrFeNi had good bonding strength in the wave area.

Acceleration of metal plates by hybridization of electrical and chemical energy for potential application in high-velocity impact welding

Vaporizing foil actuator welding is employed to connect dissimilar metals by utilizing the energy of an electrical explosion as the driving force for flyer plate acceleration. Herein, the electrical and chemical energies of explosives were combined to increase flyer plate velocity. A metal foil or wire mesh was used as an actuator, and a small amount of explosives was placed on the foil. Uniform acceleration of the flyer plate on the actuator was recorded using a high-speed video camera. The electrical energy applied to the actuator was measured synchronously by filming. The explosion of chemical explosives was successfully initiated owing to the electrical explosion of the actuator. In all experiments, the combination of the electrical explosion and chemical reaction improved the acceleration of the samples, facilitating higher velocities. The impact of the actuator type (mesh or foil) and the electric discharge parameters on the performance was studied. While foil actuators were more efficient in experiments on electric explosions alone, mesh actuators were superior when the chemical explosive was added. Explosions of the mesh actuator could initiate low density pentaerythritol tetranitrate (PETN) (the space-filling rate of PETN was approximately 30%). An explosive force of 0.3 g of PETN was converted into a driving force, imparting the flying plate with a velocity greater than 210 m/s. Electrical energy consumption for PETN initiation may be assumed to have an insignificant impact on flyer plate acceleration. In future, the proposed method may be used to connect heavier and thicker materials without expensive high-performance capacitors.

Microstructure and mechanical properties investigation of explosively welded titanium/copper/steel trimetallic plate

In this work, a systematic investigation of microstructure and mechanical properties of explosively welded Ti/Cu/Fe trimetallic plate is presented. Smoothed particles hydrodynamics (SPH) methods is applied to simulate the high-velocity oblique impact welding process. The simulation results reproduce the formation of the wave boundary, vortex zones, and jetting, supporting and extending the presented experimental results. Combined with the SEM, EBSD, TEM and XRD examinations, Cu4Ti intermetallics are identified in the vortices and solid-solid bonded regions at Ti/Cu interface, while ultra-fine Cu grains are formed along the entire Cu/Fe interface. During explosive welding, heat transfer between the vortex zones and severely deformed layers of the parent plates induces the formation of above microstructures. Microhardness contours depict well the characterized hardness distribution across the entire Ti/Cu/Fe joints. The nanoindentation tests reveals the individual properties of the typical phases formed, i.e., Cu4Ti ∼ 11.8 GPa, ultra-fine Cu grians∼3.9 GPa. The Ti/Cu/Fe trimetallic plates show the average tensile strength of 366 MPa, with brittle fracture observed at Ti/Cu interface region.

Weldability Window for High-Velocity Impact Welding of Al and Ti Plates Obtained by Numerical Simulation

In this study, the process of high-velocity impact welding of commercially pure Al and Ti plates was simulated using smoothed particle hydrodynamics (SPH) method. The paper aimed to determine by numerical simulation the range of collision parameters suitable for Al and Ti welding, and to compare the results obtained with the known semi-empirical models used to construct the "weldability window". For this, a set of simulations with different collision point velocity and collision angle was carried out. From the data obtained, it follows that SPH simulation reproduces well the shape of the interface, typical for high-velocity impact welding, and provides better understanding of material flow and related phenomena. This method allows one to select the collision parameters that are optimal for a high-quality joint.

Investigation into the effects of laser shock peening as a post treatment to laser impact welding

In this work, laser shock peening (or simply laser peening) is investigated for the first time as a post welding treatment for dissimilar foils joined via the fully-mechanical, high-velocity laser impact welding technique. Single and double laser peening shots were applied to laser-impact-welded foils using three different metallic material combinations. Subsequent lap shear testing showed that single-shot laser peening increased the average weld strength by 12% to 25%, depending on the flyer and target material combination. In contrast, with double-shot laser peening, the average weld strength decreased regardless of the flyer and target materials involved. Scanning electron microscope images revealed wavy weld interfaces and increased interlocking between the foils for the single-shot laser peening treatments as compared to the initial “flat” weld interface geometry, thereby leading to greater flyer/target weld strength. In the double-shot laser peening treatments, however, separations and melting were observed along the weld interface due to rebounding and excessive plastic heat dissipation of the foils. The findings of this study reveal the first insights and effects regarding the application of laser shock peening as a post-welding treatment beyond conventional fusion-based welding to high-velocity impact welding methods.

Microstructure and mechanical properties of laser high-velocity impact welded Ta/Cu joints

In this study, a laser high-velocity impact welding of Ta/Cu metal foil was successfully realized under different laser energies and flight distances. The morphology, microstructure, and mechanical properties of welded specimens were investigated via systematic experiments. Results indicated that the plastic deformation of the welded specimens was further pronounced with the increase in laser energy or flight distance. The welding area was ring-shaped, and the variation laws of the effective welding area under different laser energies and flight distances were summarized. The transition of the interface waveform was different when changing the laser energy and flight distance. Energy dispersive spectroscopy results showed that a trace element diffusion formed at the welding interface and intermetallic compounds were absent. Nanoindentation hardness tests showed that the hardness value increased with the decrease in distance from the welding interface. Two main failure modes of the Ta/Cu welding specimens occurred in the tensile shear tests, and the trend of the maximum tensile force under different process parameters was concluded.

Interface Kinematics of Laser Impact Welding of Ni and SS304 Based on Jet Indentation Mechanism

With the application of high-velocity impact welding (HVIW) technology, the research on the mechanism of the formation and evolution of interface waveforms has become an important research direction in HVIW. Understanding the mechanism of interface motion can help control and improve HVIW. Laser impact welding (LIW), a branch of HVIW, lacks research on the formation and evolution of interface waveforms. Therefore, LIW experiments of Ni and SS304 are carried out. The jet indentation mechanism and the smoothed particle hydrodynamics method are used to simulate and analyze the formation and evolution of the LIW interface waveform. Results show that the interface materials exhibit fluid behavior during LIW. The jet indentation mechanism can explain the formation and evolution of waveforms in LIW. Jet velocity, normal stress, and flyer horizontal welding speed are the main factors affecting the variation of the interface waveform size in LIW. At the collision point, the smaller the horizontal welding speed of the flyer, the larger the wavelength; the smaller the jet velocity, the smaller the amplitude. In addition, the propagation of the normal stress deviating from each other at the welding interface along the welding direction is the fundamental cause of springback and cracking.

SPH simulation of plastic deformation in high velocity impact welding process of 6061-T6 alloy plates

In this study, the plastic deformation process of two plates of aluminum alloy 6061-T6 was simulated at different collision point velocities using the method of smoothed-particle hydrodynamics (SPH). The results of numerical simulation were compared with the results obtained in experimental and theoretical studies of other authors. The data obtained indicate that the SPH method reproduces the wavy interface between the plates, which was previously observed in numerous experiments. In addition, SPH simulation allows one to study in better detail the features of plastic deformation occurring near the interlayer boundaries, in particular at the vortex zones.

Welding Window: Comparison of Deribas’ and Wittman’s Approaches and SPH Simulation Results

A welding window is one of the key concepts used to select optimal regimes for high-velocity impact welding. In a number of recent studies, the method of smoothed particle hydrodynamics (SPH) was used to find the welding window. In this paper, an attempt is made to compare the results of SPH simulation and classical approaches to find the boundaries of a welding window. The experimental data on the welding of 6061-T6 alloy obtained by Wittman were used to verify the simulation results. Numerical simulation of high-velocity impact accompanied by deformation and heating was carried out by the SPH method in Ansys Autodyn software. To analyze the cooling process, the heat equation was solved using the finite difference method. Numerical simulation reproduced most of the explosion welding phenomena, in particular, the formation of waves, vortices, and jets. The left, right, and lower boundaries found using numerical simulations were in good agreement with those found using Wittman’s and Deribas’s approaches. At the same time, significant differences were found in the position of the upper limit. The results of this study improve understanding of the mechanism of joint formation during high-velocity impact welding.

Investigation of melting phenomena in solid-state welding processes

High-velocity impact welding has usually been presumed as a solid-state manufacturing process. In this study, by integrating meshfree numerical simulations, advanced interfacial characterizations, and diffusion calculations, the relationships between the formation of microstructural defects within the bonding area and melting phenomena were determined. It was also inferred that the emergence of significant grain refinement in the vicinity of the weld interface could be associated to melting and subsequent recrystallization due to the ultra-fast heating and cooling rate of the high pressure impact process. The new results challenge the prevailing belief regarding the solid-state nature of the impact-based welding processes.

High-Velocity Impact Welding Process: A Review

High-velocity impact welding is a kind of solid-state welding process that is one of the solutions for the joining of dissimilar materials that avoids intermetallics. Five main methods have been developed to date. These are gas gun welding (GGW), explosive welding (EXW), magnetic pulse welding (MPW), vaporizing foil actuator welding (VFAW), and laser impact welding (LIW). They all share a similar welding mechanism, but they also have different energy sources and different applications. This review mainly focuses on research related to the experimental setups of various welding methods, jet phenomenon, welding interface characteristics, and welding parameters. The introduction states the importance of high-velocity impact welding in the joining of dissimilar materials. The review of experimental setups provides the current situation and limitations of various welding processes. Jet phenomenon, welding interface characteristics, and welding parameters are all related to the welding mechanism. The conclusion and future work are summarized.

Numerical Study on High Velocity Impact Welding Using a Modified SPH Method

High velocity impact welding (HVIW) involves processes like the impact of metal structures and strong fluid-structure interactions with complex phenomena such as interfacial waves and jet generation. It is very difficult to model the HVIW process with typical physics well captured due to the large deformation and moving interfaces, while the associated mechanisms inherent in HVIW are also not well understood. In this paper, the HVIW process is simulated using a modified smoothed particle hydrodynamics (SPH) model, in which the kernel gradient correction is used to improve computational accuracy and an artificial stress term is used to ease stress instability during the welding process. The mechanisms in HVIW are investigated, and typical phenomena including the wavy interface, jet formation, interfacial temperature and pressure distribution are captured. It is demonstrated that with proper impact welding velocity and initial welding angle, the modified SPH method can well reproduce the morphology evolution of the welding interface from straight to wavy and further to wavy interface with vortex shedding. Based on comprehensive numerical data from SPH simulations, the weldability windows for the HVIW are obtained and are compared with experimental and theoretical results. Welding limits for HVIW are also discussed in detail.

Depiction of interfacial morphology in impact welded Ti/Cu bimetallic systems using smoothed particle hydrodynamics

Numerical simulations of high-velocity impact welding are extremely challenging due to the coupled physics and highly dynamic nature of the process. Thus, conventional mesh-based numerical methodologies are not able to accurately model the process owing to the excessive mesh distortion close to the interface of two welded materials. A simulation platform was developed using smoothed particle hydrodynamics, implemented in a parallel architecture on a supercomputer. Then, the numerical simulations were compared to experimental tests conducted by vaporizing foil actuator welding. The close correspondence of the experiment and modeling in terms of interface characteristics allows the prediction of local temperature and strain distributions, which are not easily measured.

Numerical studies on high-velocity impact welding: smoothed particle hydrodynamics (SPH) and arbitrary Lagrangian–Eulerian (ALE)

The manufacturing industry often relies on numerical simulations to reduce the number of trial-and-error iterations required during the process development to reduce costs. However, this can be difficult in high strain rate manufacturing processes. For instance, in high-velocity impact welding, extremely high plastic strain regions develop. Thus, a traditional pure Lagrangian analysis is not able to accurately model the process due to excessive element distortion near the contact zone. In this paper, numerical simulations were conducted using smoothed particle hydrodynamics (SPH) and arbitrary Lagrangian–Eulerian (ALE) methods to investigate a high-velocity oblique impact between two metal plates. While the preliminary results show that the two methods were capable of modeling the process, a trade-off between the computational cost and full prediction of the critical process parameters should be considered for industrial applications.

Shear instability of plastically-deforming metals in high-velocity impact welding

High-speed oblique impact of two metal plates results in the development of an intense shear region at their interface leading to interfacial profile distortion and interatomic bonding. If the relative velocity is sufficient, a distinct wavy morphology with a well-defined amplitude and wavelength is observed. Emergence of this morphology below the melting point of the metal plates is usually taken as evidence of a successful weld. Amongvarious proposed mechanisms, instability owing to large tangential velocity variations near the interface has received significant attention. With one exception, the few quantitative stability analyses of this proposed mechanism have treated an anti-symmetric/shear-layer base profile (i.e., a Kelvin-Helmholtz configuration) and employed an inviscid or Newtonian viscous fluid constitutive relation. The former stipulation implies the energy source for the instability is the presumed relative shearing motion of the two plates, while the latter is appropriate only if melting occurs locally near the interface. In this study, these restrictions, which are at odds with the conditions realized in high-velocity impact welding, are relaxed. A quantitative temporal linear stability analysis is performed to investigate whether the interfacial wave morphology could be the signature of a shear-driven high strain-rate instability of a perfectly plastic material undergoing a jet-like deformation near the interface. The resulting partial differential eigenvalue problem is solved numerically using a spectral collocation method in which customized boundary conditions near the interface are implemented to properly treat the singularity arising from the vanishing of the base flow strain-rate at the symmetry plane of the jet. The solution of the eigenvalue problem yields the wavelength and growth rate of the dominant wave-like disturbances along the interface and confirms that a shear instability of a plastically-deforming material is compatible with the emergent wavy interfacial morphology.

Arbitrary Lagrangian–Eulerian finite element simulation and experimental investigation of wavy interfacial morphology during high velocity impact welding

Finite element simulations of high strain rate forming processes are of significant interest to industry, but are challenging due to the coupled physics and dynamic nature of the processes. For instance, in high velocity impact welding, extremely high plastic strain regions develop. Thus, a traditional pure Lagrangian analysis is not able to accurately model the process due to excessive element distortion near the contact zone. In this study, the Arbitrary Lagrangian–Eulerian method (ALE) was used to simulate an impact welding process for two Al6061-T6 plates. The ALE method was able to numerically predict the temperature at the interface as well as the necessary process parameters to achieve a wavy morphology at the interface of the materials which is assumed to be a characteristic of a quality impact weld. This allowed the prediction of a weldability window, including separate regions for melting and purely solid state welds. To validate the proposed numerical model and wavy morphology regions, experimental tests with a Vaporizing Foil Actuator Welding (VFAW) process were conducted including Photon Doppler Velocimetry (PDV) measurements of the impact velocity. The numerical results were in good agreement with the experimental tests including the temperature prediction and interfacial melting observed through microstructural analyses.

Characteristics of the wavy interface and the mechanism of its formation in high-velocity impact welding

The known similarity between the wavy weld interface observed in high-velocity impact welding of metals and the wakes behind an obstacle in a uniform stream was analyzed. The wavelength, the wave size, and the wave shape were established in terms of semi-empirical relationships. The energy consumed in the formation of the interface wave was found to be over 90% of the collision energy for copper to steel welds. The Mathieu function was found to provide a very good approximation to the wave shape. The analysis was based on applying Birkhoff’s model of the swinging Foppl wake behind an obstacle as an analogy to determine the shape and size of the developed waves.