Grain refinement in a single titanium powder particle impacted at high velocity

Mechanical behavior of Ti cold spray coatings determined by a multi-scale indentation method

“…While no direct comparison for H o can be made for the feedstock powders, the comparison to the Ti plate, which had similar hardness to the powders at a load of 1 mN, provides evidence that the cold sprayed particles become harder upon impact. Higher hardness measurements in the cold spray coatings is likely a result of high impact stresses and strain induced by the cold spray deposition process, but perhaps also grain refinement as previously reported by Kim et al [22,37]. Trends for the true hardness, H o , versus deposition velocity for both the spherical and non-spherical coatings were found to be rather weak.…”

“…This version of the indentation size effect becomes less pronounced at higher indentation loads and the nanohardness eventually converged to a constant hardness value, H o , which is independent of the indentation depth. This parameter, H o , is the "true" material hardness, which is dependent on the statistically stored dislocation density in the material and could be also tied to the material grain size, work hardening and recrystallization linked to cold spray deposition process [22,24,29,37,44].In a fully dense material, H o should correlate well with indentation at higher loads and greater indentation depth (e.g. the microhardness measured here).…”

“…The powders impact onto a substrate and build up a coating. Many complex phenomena take place during deposition, including: work hardening, formation of adiabatic shear instabilities and recrystallization [21][22][23][24]. The plastic deformation and formation of the adiabatic shear instability are believed to contribute to the bonding [25][26][27][28] for both particle to substrate (i.e.…”

“…coating cohesion). Also, cold sprayed coatings demonstrate regions of high dislocation density and grain refinement [22] and have varying amounts of large scale defects such as porosity and particle boundaries [29,30]. The extent and character of the defects within cold sprayed materials is very dependent on the processing conditions and will not necessarily be constant within a given coating.…”

Formation of an Intermediate Layer Between Grains in Nickel-Based Superalloy Turbine Blades

“…After cross-sectioning, a TEM sample was fabricated by an in situ FIB lift-out technique. [14,15] However, as it was difficult to preserve the interface between two grains without critical damage during FIB cutting and thinning because the interested region was not flat (see Figures 2 through 4, and 6), a simple technique using the rotation of a thin lamellae was used as shown in Figure 1. A region of interest was selected, and a platinum layer was deposited on it for protection during FIB sampling.…”