Mostafa Hassani

• Single crystal (SC) and polycrystalline Al microparticles were impacted on SC Al. • SC Al rebounds faster than polycrystalline Al at a same impact speed. • SC and polycrystalline Al show similar critical bonding conditions. • Both bonded Al particles exhibit similar interfacial microstructure. Extrinsic parameters such as particle size influence the impact-induced bonding behavior of metallic microparticles, with larger particles generally exhibiting lower critical velocities than smaller ones. However, the impact of intrinsic parameters such as particle grain size on impact and bonding behavior for a given particle size remains unclear. In this work, we study this effect using laser-induced microparticle impact tests (LIPIT), where similar-sized Al particles with two distinct initial grain sizes—single-crystal (SC) and polycrystalline (∼4.5 µm grain size)—were impacted onto a SC Al substrate. The results indicate that, although rebound mechanics at low velocities are influenced by the initial grain size, the critical conditions for bonding remain largely unaffected. This finding is counterintuitive, as variations in the initial grain size would be expected to alter material strength and, consequently, the extent of plastic deformation in both the particle and substrate. Instead, we find that extensive impact-induced microstructural evolution near the interface dominates the response, erasing the differences between the two initial states at the critical bonding velocity. This finding is confirmed by Transmission Electron Microscopy (TEM) and Transmission Kikuchi Diffraction (TKD) studies, which reveal similar bonding quality and comparable microstructural evolution near the bonded interfaces.

Supersonic impact of metallic microparticles onto metallic substrates generates extreme interfacial deformation and high contact pressures, enabling solid-state metallic bonding. Although higher impact velocities are generally believed to improve bond quality and mechanical properties in materials formed by supersonic impact deposition, here we report a peak in bond strength for single microparticle impact bonding, followed by a decline at higher impact velocities. Our in situ micromechanical measurements of interfacial strength for Al microparticles bonded to Al substrates reveal a three-fold increase from the critical bonding velocity (800 m/s) to a peak strength around 1,060 m/s. Interestingly, further increase in impact velocity results in a rapid decline in local interfacial strength. The decline continues up to the highest velocity studied, 1,337 m/s, which is well below the threshold required to induce melting or erosion. We show that a mechanistic transition from material strengthening to intensified elastic recovery is responsible for the peak strength in impact-induced bonding, with evidence linking the intensified elastic recovery to adiabatic softening at high impact velocities. Beyond 1,000 m/s for Al, interfacial damage induced by the intensified elastic recovery offsets the strength gain from higher impact velocities, resulting in a net decline in interfacial strength. This mechanistic understanding shall offer insights into the optimal design of processes that rely on impact bonding.

Dislocations are crucial to plastic deformation in crystals. At extreme strain rates, their motion shifts from thermally activated glide to ballistic transport, causing significant drag due to interactions with phonons, which can lead to embrittlement and failure in metals. The concept of dislons, quantized dislocations, has emerged to better understand these types of interactions. Similar to quantum treatment of dislocation-electron interactions, confining dislocations to nanometer scales, especially in nanocrystalline metals, could also yield unique mechanical behaviors different from bulk materials. Here, we present evidence showing that in Cu-3Ta, a thermo-mechanically stable nanocrystalline alloy, the phonon drag effect is entirely suppressed even at ultra-high strain rates (109 s−1). This is due to the stable confinement of dislocations within several-nanometer range, limiting their velocity and interaction with phonons. Our study indicates that in confined environments, the dislocation-phonon drag effect is minimal, potentially improving material performance under extreme conditions. Ballistic transport of dislocations and the resulting phonon drag are known to occur in crystalline metals under high strain rates, causing embrittlement. Here, we leverage dislocation confinement at the nanometer scale to entirely suppress the phonon drag regime, even at strain rates as high as 109 s−1.

Solid-state bonding can form when metallic microparticles impact metallic substrates at supersonic velocities. While the conditions necessary for impact-induced metallic bonding are relatively well understood, the properties emerging at the bonded interfaces remain elusive. Here, we use in situ microparticle impact experiments followed by site-specific micromechanical measurements to study the interfacial strength across bonded interfaces. We reveal a gradient of bond strength starting with a weak bonding near the impact center, followed by a rapid twofold rise to a peak strength significantly higher than the yield strength of the bulk material, and eventually, a plateau covering a large portion of the interface towards the periphery. We show that the form of the native oxide at the bonded interface—whether layers, particles, or debris—dictates the level of bond strength. We formulate a predictive framework for impact-induced bond strength based on the evolution of the contact pressure and surface exposure. In situ measurements reveal a significant strength gradient at interfaces formed by the supersonic impact of metallic microparticles on metallic surfaces, featuring weak central bonding and a rapid rise to a peak exceeding bulk material strength.

It is well known that chemical strengthening of glass brings the benefit of increased fracture strength . Despite extensive research on processing and mechanics at the macroscale , the effectiveness of chemical strengthening on glass elements with all three dimensions in the micrometer regime remains largely unexplored. Here, we develop a novel process for chemical strengthening of micrometer-sized spherical glass powder particles and study the fracture behavior of these particles with in-situ particle compression tests inside a scanning electron microscope . Cross-sectional microscopy and energy dispersive spectroscopy measurements confirm ion exchange and show an increase in diffusion depth with an increase in processing time and temperature. We report a higher fracture strength for chemically strengthened powder particles compared with the as-received ones. We show that the increase in fracture strength is associated to the compressive residual stress resulting from ion exchange during chemical strengthening.

The Z-axis lifting height is significant in layer-by-layer fabrication using laser directed energy deposition (L-DED). In this paper, we have deeply examined the porosity and grain morphologies in the double layers of AlSi10Mg by blue laser directed energy deposition (BL-DED). After the deposition of a single track, the depositional head was raised by a certain Z-axis lifting height and then a second layer was deposited. As the Z-axis lifting height increases, the quantity density of pores in the second layer increases, leading to higher porosity. Especially, the boundary of the overlapping area exhibits the highest porosity, measuring 0.84%. The Z-axis lifting height can be set lower than the height of a single track, while maintaining high dimensional accuracy and surface quality.

Abstract The deformation behavior of particles plays a significant role in achieving adhesion during cold spray. The deformation behavior of the particles is associated with the fracture of the oxide layer and recrystallization, which are the key elements of the quality of cold spray. Studies of particle compression have been made to understand the deformation behavior of a particle. However, the deformation behavior of particle under controlled load and precise and high strain rate is yet to be studied. Here, we show the oxide layer fracture pattern and recrystallization regime under controlled load with a precise and high strain rate. We found that the cracks in the oxide layer initially appeared on the equator of the particle and propagated towards the edge of the top surface. Meanwhile, on the top surface, the circumferential crack was developed. On the other hand, the nanoindentation result showed that the compressed particle under a high strain rate has an unusual load-displacement behavior. Our results demonstrate that the oxide layer fracture behavior corresponds to the adhesion mechanism suggested by previous studies. Our study also revealed that recrystallization takes place within the particle under a high strain rate. We anticipate this finding to give a general insight into the deformation behavior of particles during cold spray. For instance, since the recrystallization behavior at a given strain rate can be predicted through this study, the resultant grain size and shape, which is associated with mechanical properties, can also be predicted. Furthermore, the amount of strain and strain rate to form optimal adhesion can be evaluated.

Impact-induced bonding of individual powder particles in solid state is the unit process of the material buildup in cold spray. In this chapter, we discuss the conditions and mechanisms of impact bonding from a physics and materials perspective. We start with the physics of plate impact and the role of shocks in explosive welding to then discuss how this understanding can be applied to the case of cold spray particle impacts. We highlight the role of impact-induced jetting for bonding and discuss adiabatic heating and shear localization upon impact. We close the chapter with a discussion on the effects of particle/substrate characteristics on impact bonding.

Surface oxide layer fracture and the subsequent exposure of clean metallic surfaces are critical in various solid-state processes for powder consolidation and additive manufacturing. We resolve this process in-situ by deforming individual spherical powder particles inside a scanning electron microscope. We reveal three fracture modalities, i.e., meridian, radial, and circumferential cracking that sequentially activate with particle flattening. Real time measurements of load and displacement upon particle flattening also reveal a significant strengthening effect by surface oxide. We attribute the strengthening to two mechanisms: the composite strengthening and the strain gradient strengthening.

In this research, according to the high amount of sludge in a petrochemical company, an iron package type of drying sludge bed was made/designed with carbon steel. Then, the drying sludge pond was filled with layers of sand with different mesh sizes. The excess sludge from the sedimentation pond was passed over this bed, and the amount of sludge removed by the bed was obtained at %96. The values of heavy metal and microbial forms were determined usingthe proposed method based on activated sludge after was tewater treatment. For the validation process, 10 mL of deionized water (DW) was mixed with 1.0 g of dried sludge with pure nitric acid (2%HNO3), and then the solid phase was filtered with the Whatman filter(WF). The concentration of heavy metals (As, Cd, Cu, Pb, Hg, Mo,Ni, Co, Se, Zn) in the remaining solution of sludge (mg kg-1) and was tewater (μg L-1) was extracted/ separated based on sulfur-dopedgraphene oxide adsorbent (SDGO) by solid-phase microextraction procedure (SPME) before being determined by the flame and hydride generation atomic absorption spectrometry (F-AAS; HG-AAS) which had similar range to the polarography analysis. The limit of detection(LOD), linear range (LR) and preconcentration factor (PF) for (As,Hg) and (Cd, Cu, Pb, Mo, Ni, Co, Se, Zn) were obtained (0.016μgL-1;3.3μg L-1), (0.05-10μg L-1;10-1000μg L-1), and 10.0 by HG-AAS and F-AAS, respectively.