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.

Hard Quasicrystalline Coatings Deposited by HVOF Thermal Spray to Reduce Ice Accretion in Aero-Structures Components

Weather hazards, in particular icing conditions, are an important contributing factor in aviation accidents and incidents worldwide. Many different anti-icing strategies are currently being explored to find suitable long-lasting solutions, such as surface engineering, which can contribute to reduce ice accumulation. Quasicrystals (QCs) are metallic materials, but with similar properties to those of ceramic materials, such as low thermal and electrical conductivities, and high hardness. In particular, QCs that have low surface energy are commercially used as coatings to replace polytetrafluoroethylene (PTFE), also known as Teflon, on frying pans, as they do not scratch easily. PTFE exhibits excellent anti-wetting and anti-icing properties and therefore QCs appear as good candidates to be employed as ice-phobic coatings. Al-based QCs have been applied by High Velocity Oxyfuel (HVOF) thermal spray on typically used aeronautic materials, such as Ti and Al alloys, as well as steels. The coatings have been characterized and evaluated, including the measurement of hardness, roughness, wetting properties, ice accretion behavior in an icing wind tunnel (IWT), and ice adhesion by a double lap shear test. The coatings were studied, both as-deposited, as well as after grinding, in order to study the effect of the surface roughness and morphology on the ice accretion and adhesion properties. The QC coating was compared with PTFE and two polyurethane (PU)-based commercial paints, one of them known to have anti-icing properties, and the results indicate an ice accretion reduction relative to these two materials, and ice adhesion lower than bare AA6061-T6, or the PU paint in the ground version of one of the two QCs. Since the QC coatings are hard (GPa Vickers hardness > 5), a durable behavior is expected.

KETAHANAN MULUR BAJA SUS 304 HASIL PELAPISAN METAL MATRIX COMPOSITE NiCr+ Cr3C2 DENGAN METODA HVOF

KETAHANAN MULUR DAN OKSIDASI SIKLIK BAJA SUS 304 HASIL PELAPISAN METAL MATRIX COMPOSITE NiCr+Cr3C2 DENGAN METODA HVOF. Telah dilakukan proses deposisi Metal Matrix Composite coating 60% NiCr + 30% Cr3C2+ 10% Al2O3 dan 60% NiCr + 40% Cr3C2 dengan menggunakan teknik High Velocity Oxygen Fuel (HVOF) Thermal Spray Coating, pada permukaan baja SUS 304. Tujuan pelapisan untuk meningkatkan ketahanan mulur dan oksidasi siklik dalam aplikasi pipa boiler tubes PLTU. Pengujian creep telah dilakukan pada temperatur 550oC dengan pembebanan sebesar 0.4 σy dan 0.6 σy (yield strength) selama 30240 menit (21 hari). Pengujian oksidasi siklik dengan variasi temperatur 600oC, 700oC dan 800oC selama 1 jam dalam tubes furnace dan pendinginan diluar selama 15 menit dalam 1 siklus dan di lakukan sebanyak 5 siklus. Spesimen coating Metal Matrix Composite (MMC) 3 komponen merupakan coating yang rekomendasikan dalam aplikasi pipa boiler tubes PLTU merupakan laju mulur yang paling rendah sebesar 0.000148917%/jam. Spesimen coating MMC 3 komponen pada temperatur 600oC memiliki perubahan berat oksida, ketebalan coating, dan senyawa oksida yang terbentuk paling rendah.Kata kunci: SUS 304, HVOF Thermal Spray Coating, Metal Matrix Composite, ketahanan mulur, oksidasi siklik.