The present work summarizes the most important results of a research project dealing with the comprehensive!! investigation of the bonding mechanisms between cold sprayed Al coatings and various poly- and monocrystalline ceramic substrates (Al 2 O 3 , AlN, Si 3 N 4 , SiC, MgF 2 ). Due to their exceptional combination of properties, metallized ceramics are gaining more and more importance for a wide variety of applications, especially in electronic engineering. Cold spraying provides a quick, flexible and cost-effective one-step process to apply metallic coatings on ceramic surfaces. However, since most of the existing cold spray-related publications focus on metallic substrates, only very little is known about the bonding mechanisms acting between cold sprayed metals and ceramic substrates. In this paper, the essential factors influencing the bonding strength in such composites are identified. Besides mechanical tensile strength testing, a thorough analysis of the coatings and especially the metal/ceramic interfaces was conducted by means of HRTEM, FFT, STEM, EDX, EELS, XRD and EBSD. The influence of substrate material, substrate temperature and particle size is evaluated with regard to the observed bonding behavior. The results suggest that, apart from mechanical interlocking, the adhesion of cold sprayed metallic coatings on ceramics is based on a complex interplay of different mechanisms such as quasi-adiabatic shearing, static recrystallization as well as heteroepitaxial growth.

The present work builds on investigations of cold gas-sprayed Al coatings on Al 2 O 3 , which strongly indicated that heteroepitaxial growth is a possible mechanism supporting the adhesion between metal and ceramic at their interface. The present study was focused on the deposition of Al on further ceramic substrates (AlN, Si 3 N 4 and SiC). In particular, it should be clarified whether the different ionicity of the chemical bonding in these substrate materials influences the interface formation or not. Aluminum coatings were deposited alternatively by using cold-gas spraying (CGS) and magnetron sputtering. In CGS coatings, the effect of substrate roughness, substrate temperature and powder fraction on the adhesion of the coating was investigated. The magnetron-deposited coatings were used to evaluate the role of the heteroepitaxy in the interface formation and to identify microstructure defects in the metal/ceramic interface, which are caused solely by the lattice misfit between the counterparts and not by the impact-induced deformation that is typical for cold gas-sprayed coatings. Interface characterization was conducted by scanning electron and high resolution transmission electron microscopies combined with XRD.

This work investigates the adhesion mechanisms associated with cold gas sprayed metallic coatings on ceramic substrates. Aluminum layers were deposited on sintered corundum plates and single-crystalline sapphire substrates with different lattice orientations. Examination of the interface region showed that adhesion was the result of recrystallisation and heteroepitaxial growth. Cold spray aluminum coatings were also deposited on Al 2 O 3 , AlN, Si 3 N 4 , and SiC substrates to determine if ionic bonding plays a role in interface formation. For comparison, aluminum coatings produced by physical vapor deposition were also examined.

In this study, aluminum is deposited by cold gas spraying on smooth and rough alumina substrates. SEM examination of single particle splats on polycrystalline Al 2 O 3 suggests that mechanical interlocking is the primary bonding mechanism for cold gas sprayed metals on rough ceramic surfaces. Coating cross-sections on monocrystalline, atomically smooth sapphire substrates were examined by means of high-resolution TEM, revealing nanosized Al grains close to the interface, which could be an indicator of recrystallisation induced by local heating and the deformation energy stored in the particle during impact.