The enhancement of the surface characteristics and corrosion resistance of cobalt alloys is under continuous examination for its biomedical applications. In this work, the investigation of corrosion performance of cobalt alloy coated with HA and HA/ZnO reinforced powders using plasma spray technique revealed that on the continuous increase of ZnO reinforcement the corrosion resistance improved progressively. The increment in surface hardness and drop in surface roughness was examined with the rise in ZnO content. Each coated sample exhibits a hydrophilic property. According to SEM and EDX investigations, homogeneous distribution of HA/ZnO coatings and intact reinforcement of ZnO in pure HA powder was noticed. All of the coated specimens maintain their morphological integrity, ensuring excellent protection of the prepared samples. The obtained outcomes denote HA/ZnO reinforced coatings on CoCr alloy as a suitable combination of enhanced surface properties and excellent corrosion resistance for future bone implant practices.

As a supersonic solid-state deposition process, Cold Spray (CS) has a unique role among other thermal spray techniques as it uses compressed and heated gas to accelerate particles to a critical velocity. CS can be an expensive process, especially when helium is used as a processing gas. In recent thermal spray developments, High-Velocity Air Fuel (HVAF) has taken a specific place in terms of providing dense and strong coatings similar to CS, but also coatings with less oxidation than High- Velocity Oxy-Fuel (HVOF). In contrast to these techniques, HVAF uses a mixture of fuel and air, instead of pure oxygen as in HVOF, to accelerate particles. Therefore, HVAF appears as a relatively cheaper and environmentally friendly alternative for the deposition of a wide variety of materials. The aim of this research is to produce fully dense copper coatings with limited oxidation using an inner diameter (ID) HVAF system and to compare the microstructure with CS copper coatings. Coating microstructures, surface roughness, and microhardness are studied using different characterization methods such as Scanning Electron Microscopy (SEM). Through this paper, the influence of both spray processes, CS and ID-HVAF, on the deposition of copper coatings is discussed. Cross-sectional studies of different coatings show a fairly dense microstructure for CS and ID-HVAF coatings. Moreover, it is discussed how the copper coating properties can change upon modifying the spray parameters.

Iron based coatings have recently gained much attention as they have favorable mechanical, frictional, and corrosion properties. The coatings possessed a high content of iron borides are particularly valuable for satisfying engineering needs. Boron and iron form two major boride phases, FeB and Fe2B, with different mechanical and thermal properties. Orthorhombic boride FeB is considered to be viable candidate to enhance the surface hardness and wear resistance of components, since it has high hardness. Producing of such coating by cold spray method is considered to be an alternative for boronizing method which is a conventional thermochemical surface hardening process. In this work, the crushed ferroboron (FeB) powders of Fe-17.9B-0.4C-1.6Si-0.3Al (wt. %) were deposited onto low carbon steel substrate by cold spraying. However, low and high pressure cold spraying allowed depositing very thin and single layer on the substrate, due to the intrinsic brittleness of the powder. Therefore, several contents of Al, Ni and Fe metallic powder and their combinations were added to FeB powder to obtain thick coating via cold spray processes. Post heat treated coatings at a temperature of 700 °C resulted in increase of the hardness, possibly the formation of hard phases such as intermetallic compound.

In this paper, as part of a systematic study on the rolling contact fatigue of HVOF-sprayed hardmetal coatings, the behavior of WC-17%Co coatings on hardened and nonhardened substrates is compared. To obtain a meaningful assessment, the coatings were applied to roller specimens made from soft as well as case-hardened MnCr steel. Two coating thicknesses were used with the expectation that maximum stress will occur in the substrate, in one case, and in the other case, in the coating. Test results show that the durability of HVOF-sprayed WC-Co is significantly better on nonhardened (soft) substrates and that the limiting factor for endurable Hertz pressure is the fatigue strength of the coating.