Both as bulk material and coatings, cemented carbides currently occupy very well-established market niches and exhibit a promising future thanks to the development of compositions and manufacturing parameters. Direct comparisons of the properties of both are found only very rarely in the literature, very likely because the fields of application are complementary to each other but keep mostly separated. The current work is intended to evaluate similarities and differences in terms of microstructure and properties for two submicron WC-12 wt.%Co coatings obtained by High Velocity Air Fuel (HVAF) and Cold Gas Spray (CGS), together with a conventional sintered part. Microstructural features are discussed according to the inherent characteristics of each processing method. This covers a wide range in terms of the mechanical and thermal stresses acting on the material. While in CGS, the impacting particles do not melt, but experience extremely high plastic strain rates, the cobalt matrix is fully molten in the conventional sintering process, allowing time enough for diffusion processes. HVAF is to be placed in between, since the deposition process is characterized by a moderate heat input, leading to partial and/or full melting of cobalt, followed by rapid cooling. The microstructure and phases of the deposited coatings and bulk are characterized by using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Electron Backscattered Diffraction (EBSD) investigations enable local phase distribution of Co and WC in the samples. The hardness of the alloy processed by the three different routes is investigated as well. Additionally, electrochemical corrosion measurements in NaCl media are presented to evaluate the facility for electrolyte penetration and how the degradation of the material is affected by its inherent microstructure.

Assemblies containing fiber-reinforced plastic (FRP) and metal parts are typically fastened together via mechanical joining or adhesive bonding. Mechanical joining processes tend to weaken FRP parts by cutting fibers, while adhesives require long cures and often lead to inseparable material compounds. This paper evaluates a new joining method in which plastic parts are laser treated, then metallized via wire-arc spraying, and finally soldered to mating metal parts using a low-temperature process. Due to the effective increase in interface area resulting from laser structuring, bond strengths of up to 15.5 MPa can be achieved.

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.

Due to its low weight and excellent dimensional stability, carbon fibre-reinforced carbon (C/C) gains more and more importance as construction material for light-weight charging racks in industrial furnaces. However, for high-temperature applications above 1,000 °C, C/C has to be protected with a diffusion-inhibiting coating in order to avoid an undesired carburization of components which are in contact with the charging rack. In the present work, coatings were produced by means of atmospheric plasma spraying (APS) and powder flame spraying (PFS). The ceramic powders Al 2 O 3 , Al 2 O 3 /Cr 2 O 3 , Al 2 O 3 /TiO 2 and yttria stabilized zirconia (YSZ) were used as coating materials, while molybdenum and silicon carbide served as adhesion-promoting intermediate layers. In order to reduce the residual stresses in the ceramic coatings, specimens with a defined segmented surface structure were compared with conventional closed coatings. Long-term high-temperature tests in several atmospheres were conducted on laboratory scale as well as in industrial practice.

Cermets like WC/Co or Cr 3 C 2 /Ni20Cr are well-established materials for thermally sprayed wear protection coatings. However, their high price and the adverse health effects of nickel and cobalt cause the motivation for the development of novel materials with excellent wear resistance. Within the AiF/DFG research cluster “Thermal Spraying”, a multi-institutional cooperation of various German research centres, the focus is put on particle-reinforced iron-based composite alloys. High-alloyed steels serve as matrix materials into which hard CrB 2 particles are incorporated by means of high-energy ball milling (HEM). By adjusting appropriate milling parameters, the microstructure of the powder and its level of amorphisation can be influenced effectively. The high-velocity oxygen fuel process (HVOF) allows a transfer of the desired nanocrystalline structure from the particles to the coatings. The deposited coatings exhibit low porosity and high microhardness values of more than 1000 HV0.3. The wear resistance of the coatings was determined by means of Miller test (ASTM G75-01) and compared with conventional wear protection materials and coatings produced with agglomerated and sintered powders. The obtained outstanding results qualify particle-reinforced iron-based materials as a promising alternative for a wide range of applications.