To fully understand particle interactions with both substrate and neighboring particles in cold spray, ultrasound wave generation and ultrasonic monitoring of particle impacts were studied. The multi–channel ultrasonic system works in pulse– echo and passive modes. In pauses between pulse–echo data acquisition frames the system is in the passive mode receiving the signals generated by the particle impacts. The particles being deposited generate the ultrasonic signals in a very wideband frequency range at more than 40 dB signal-to-noise ratio. The particle impact signals are considered as a sum of the background wideband noise and the sparse strong pulses observed when the nozzle passes over the location of the transducer. It was shown that these components of the particle impact signal can be separated by threshold processing. The results of the passive monitoring are confirmed by the ultrasonic pulse–echo and direct measurements of a deposited coating geometry.

The study of corrosion protection of magnesium and aluminum becomes increasingly important as the use of these alloys increases rapidly in the automotive and aerospace industries due to their advantages of light-weight, adequate mechanical properties and moderate cost. Corrosion, however, limits the application of magnesium and aluminum alloys. Fasteners, spot welds of dissimilar materials and their galvanic corrosion is of major concern in automotive applications. The paper presents first results of Low Pressure Cold Spray (LPCS) of Al based coatings for corrosion protection. The corrosion protection provided by these coatings was evaluated by electrochemical measurements in 1M NaCl electrolyte. The microstructures and electrochemical behavior of the coated joints were investigated. The electrochemical corrosion mechanisms of the coatings and microstructure were discussed.

To fully understand particle interactions with both substrate and neighboring particles in Cold Spray (CS), ultrasonic monitoring and acoustic emission of particle agglomerate impact were studied. The results obtained show the influence of particle agglomeration density on stress and strain distribution in the particles and at the particle interfaces. The results are compared with metallographic structures of real coatings. The development of monitoring procedure is made using acoustic methods, specifically testing during the actual spray process itself. It is shown that the final thickness as well as the dynamics of buildup can be evaluated. Cross sections of the coating thickness are also easy to obtain and show true profiles of the coating. Comparisons of real thickness and acoustically estimated thickness show a close linear relationship.

The FeAl intermetallic compound offers a combination of attractive properties such as thermal barrier, good strength at intermediate temperatures and an excellent corrosion resistance at elevated temperatures under oxidizing, carburizing and sulfidizing atmospheres. So they have attracted considerable attention as potential candidates for structural and coatings applications at elevated temperatures. However, the application of these intermetallics has been limited due to lack of deposition techniques and their low ductility at room temperature. To overcome the drawbacks we apply Low Pressure Cold Spray (LPCS) with following sintering for improving coating ductility and structure. The aim of this paper is to present the first results of FeAl intermetallic compound synthesis with this technique. A CS deposit is built up by the successive impact of individual powder particles that are the ‘‘building blocks’’ of the deposit. Sintering is applied to utilize reactions between the particles and obtain complex intermetallic compound. The microstructures and properties of the coatings were characterized by SEM, EDX and thermal diffusivity tests to define the structure formation mechanisms.

Supersonically Induced Mechanical Alloy Technology (SIMAT™) also known as gas-dynamic spraying is under development for corrosion protection and material repair for aluminum airframe structures. This technology enables material powder consolidation that is not possible using other spray technologies. Similar to cold spray but based on compact spray head with nozzle powder feed, SIMAT™ is a low temperature process and does not create the high-temperature environment that affects both the substrate (especially thermally non-stable substrates) and the deposited coating. The emerging SIMAT™ technology, now in development, has the potential for coating, repairing, joining and rapid prototyping powder based materials. The SIMAT™ method adds new flexibility to powder material deposition producing thin to very thick deposits of various metals and metal-ceramic mixtures based on a cold spray particle kinetic approach inducing impact fusion. Solid particles in the size range of 10 to 100 microns are accelerated into a supersonic stream (ranging from 300 to 1200 m/s) using compressed air. These high velocity cold particles are projected on to a work piece. There is no heat discharge in the spray device itself, thus the powder material retains original characteristics. This spraying technique can generate a wide range of deposited layers with thickness ranging from tens of microns up to as much as centimeters. The process extends beyond the concept of “coatings” and includes the capability for in-situ material build-up and consolidation to three-dimensional structures and joining of the components. The deposition and consolidation can be performed from a range of hybrid powders consisting of metals, alloys, ceramics and glasses. Sample tests demonstrate examples of the process on typical aircraft components for new or restored corrosion protection and demonstrate damage repair for potential service life extension of the aircraft structure.

Gas Dynamic Spray (GDS) is a high rate, direct material-deposition process that utilizes the kinetic energy of particles sprayed at supersonic velocities to cause bonding through the particle plastic deformation on impact. GDS seems to be similar to the powder shock consolidation process, which is governed by dynamic regimes of granular material deformation under impulse loading. These regimes are characterized by adiabatic shear band (ASB) formation. This paper describes the preliminary analysis of ASB formation during GDS on the basis of a combination of the Johnson-Cook and shock wave consolidation models. The dependence of the ASB width on different parameters, including initial powder porosity, average impact stress, shear strain, initial temperature, and contact time was determined. The ASB width was found to vary in the range of 0.5–15 μm, which reveals the great localization of particle deformation in the GDS process.