Melting Can Hinder Impact-Induced Adhesion

Abstract

Melting has long been used to join metallic materials, from welding to selective laser melting in additive manufacturing. In the same school of thought, localized melting has been generally perceived as an advantage, if not the main mechanism, for the adhesion of metallic microparticles to substrates during a supersonic impact. Here, we conduct the first in situ supersonic impact observations of individual metallic microparticles aimed at the explicit study of melting effects. Counterintuitively, we find that under at least some conditions melting is disadvantageous and hinders impact-induced adhesion. In the parameter space explored, i.e., ∼10 μm particle size and ∼1 km=s particle velocity, we argue that the solidification time is much longer than the residence time of the particle on the substrate, so that resolidification cannot be a significant factor in adhesion. DOI: 10.1103/PhysRevLett.119.175701 Understanding materials physics under impact has motivated extensive research in areas ranging from asteroid strikes [1] and ballistic deposition [2] to mechanochemical synthesis [3], materials failures [4,5], structural modification [6], and phase transformation [7]. Less conventionally, three decades ago, metallic powder particles were first observed to bond to metallic substrates under supersonicimpact conditions at low temperatures [8]. The notion of impact-induced adhesion, thereafter, has been implemented in powder processing through kinetic deposition or cold spray [9,10]. Kinetic deposition has proven successful in making coatings [11][12][13], in reclaiming damaged metallic surfaces [14], and in additively manufacturing bulk metallic materials [15].In this area of impact science, researchers have repeatedly observed a material-dependent critical velocity [16,17] [20] have been put forth to explain the underlying mechanism(s) of impact-induced adhesion, each of which enjoys partial support from observational data. For instance, sharp jumps observed in the temperature and strain in Lagrangian impact simulations have been used to support an argument for adiabatic shear localization [16,21]. Experimental measurements of reduced oxide content in cold spray coatings as compared to initial powder feedstock underpins an argument for oxide layer breakup [22]. Small spherical ejecta found in the coating [20] or intermetallic detected at the interface [23] suggest localized melting or interdiffusion.More consensus, however, has been attained around postmortem observations of material jets around the periphery of adhered particles [16,24,25]. We have recently, for the first time, conducted in situ observations of the impact behavior of individual supersonic metallic microparticles below and above the critical velocity and found that material ejection and jetting are crucial for adhesion [26,27]. We argued that neither shear localization nor melting are needed to account for material ejection. Rather, it can arise from the interaction of the impactinduced pressure wave with the contact periphery of the particle. A...

Melt-driven erosion in microparticle impact

“…1a , micron-sized particles are initially dispersed on a launching pad assembly, a stack comprising a glass substrate, a thin layer of gold, and a layer of elastomeric polyurea film. Microparticles are launched by focusing a laser excitation pulse, thereby ablating the gold film, and causing rapid expansion of the polyurea film 4 , 5 , 21 , 22 . The particle interaction with a substrate is recorded in real time using a high-frame-rate camera and a synchronized quasi-cw laser imaging pulse for illumination.…”

“…The exposure was set to be 5 ns for all frames, and the interframe time was adjusted depending on the impact velocity from 50 to 150 ns. Details regarding the launching pad preparation are described elsewhere 4 , 5 , 23 .

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“…The combination of high pressures, temperatures, and deformation rates that occur during an impact can evoke many unusual materials responses. These include crater formation 1 – 3 , solid state splashing 4 , impact bonding 5 , peculiar phase transformations 6 , nanocrystallization 7 , and chemical reactions 8 . Among the most extreme of such phenomena lies impact-induced erosion that often occurs at the micron scale whether in space 9 , on the ground 10 , or beneath 11 .…”

Laser-driven high-velocity microparticle launcher in atmosphere and under vacuum

“…), conductivity, dimensions, density, and shape, enabling systematic studies with many types of particles and substrates [14][15][16]. For instance, recent works from Hassani et al focused on metallic particle impacts on metallic substrates to investigate impact bonding and impact-induced erosion mechanisms [17][18][19]. In other works, Veysset et al and Hsieh et al studied the high strain rate response of hierarchical elastomers to supersonic microparticle impact in order to elucidate energy dissipation mechanisms in this class of materials [20,21].…”

Thermal Effects in Dissimilar Magnetic Pulse Welding

“…There are already thermal models existing for MPW [9,13,15,19] but they do not take the CoP into consideration as a heat source. The time for solidification has also been calculated in previous publications [9,20,21] but without considering dissimilar materials, the temperature distribution after the heating and not to mention the effect of phase transformations. For the prediction of the weld formation it is important to know the time dependent temperature in the joining zone.…”