Precipitation Hardening of the HVOF Sprayed Single-Phase High-Entropy Alloy CrFeCoNi

The application of high-entropy alloys (HEA) in surface technology has great potential due to the high corrosion and wear resistance. A further improvement can be achieved by applying thermochemical treatments. Powder-pack boriding enables the formation of a protective precipitation layer. This process has already been applied for cast HEAs causing the formation of a diffusion-enriched surface layer and a distinct increase in wear resistance. In the current investigations, the alloy CrFeCoNi with a single-phase face-centred cubic (fcc) structure is considered. An efficient application can be achieved by limiting the material usage of HEAs to the surface. Therefore, the high-velocity-oxygen-fuel (HVOF) thermal spray process is applied. Boriding was conducted with an adapted powder-pack routine. Furthermore, borided bulk HEAs were considered as a reference. The influence of the production route and boriding treatment on the microstructure, phase formation, and properties was investigated in detail. For the coating and the cast HEA, a precipitation layer is formed. Hence, the hardness and wear resistance are significantly increased. The current study proves the suitability of the investigated process combination.

Stellite Superalloy Powder Deposition on 7075 Aluminum Alloy

Several types of powders can be deposited on metal alloys for property improvement using thermal spray processes. Aircraft grade 7075 aluminum alloy possesses good mechanical properties but poor wear and corrosion resistance. Thermal spray coatings can improve the poor wear performance of 7075 so that it is suitable for use in severe conditions by depositing a hard, wear-resisting layer over the base material. This can be done by a simple production process while maintaining the base material properties. Among the available coatings, cobalt-base superalloys, such as Stellites, provides excellent protection against corrosion and wear. However, the treatment must not deteriorate the substrate hardness. In the High Velocity Oxygen Fuel (HVOF) thermal spray process, the short resident time of the powder in the flame results in a relatively small temperature increase, which in turn results in a lower substrate temperature during the coating deposition. In the present work, HVOF thermal spray process was used to coat 7075-T3 aluminum alloy samples with Stellite 6 superalloy. This treatment resulted in layers of high hardness and improved wear performance while keeping the base material properties unchanged.

HVOF Thermal Spray Alternative for Hard Chrome Plating Process

Hard chrome plating is a process that has been in commercial production for over 50 years and which is a critical process associated with manufacturing and maintenance of parts in the industries. The paper presents aspects regarding the use of HVOF thermal spray process as an alternative for hard chrome plating.