Search Results (3)

Additive manufacturing (AM) or 3D printing of metals is gaining popularity due to its flexibility when fabricating parts with highly complex designs, as well as when simplifying manufacturing steps and optimizing process times. In this investigation, 17-4 PH stainless steel was additively manufactured using Laser Powder Bed Fusion (L-PBF), followed by functionalization through a DUPLEX treatment. This treatment involved a plasma-assisted nitriding process, followed by the deposition of an arc-PVD c-Al_0.7Cr_0.3N hard coating. The microstructural modifications resulting from plasma nitriding (such as the formation of Fe_2,3N and Fe₄N and the αN or expanded martensite phases) and the surface improvements with the c-Al_0.7Cr_0.3N coating on the 3D-printed 17-4 PH steel are evaluated in comparison to conventionally manufactured 17-4 PH steel. These microstructural characteristics are correlated with the mechanical response of the treated surfaces. As a result of the plasma nitriding process, the hardness of the 3D-printed 17-4 PH SS increased by approximately 260%. The wear, measured through dynamic and static scratch testing, was reduced by approximately 31%. This improvement was attributed to the modification of adhesive failure mechanisms, leading to a reduction in wear volume, improved coating adhesion, and enhanced scratch resistance. Full article

Elemental Cr/C/Al multilayers (stoichiometric ratio: 2:1:1) with and without a Cr overlayer have been synthesized on Zircaloy-4 substrates by magnetron sputtering. The effects of annealing temperatures (400 and 550 °C) on phase/microstructure formation, mechanical properties, and oxidation/corrosion performance have been comparatively studied. Annealing of the multilayers at 400 °C led to the formation of nanocrystalline composite consisting of intermetallic and binary carbide phases. Single-phase Cr₂AlC was obtained after 550 °C annealing, but with microcracking of the coatings. Both annealed coatings displayed similar mechanical properties, high-temperature oxidation, and hydrothermal corrosion mechanisms. The composite coatings annealed at 400 °C significantly enhance the high-temperature oxidation resistance (α-Al₂O₃ scale growth) and hydrothermal corrosion (Cr₂O₃ passivation layer formation) of a Zircaloy-4 substrate without coating microcracking and delamination. Nanocomposite CrCAl-based coatings are promising candidates for coated ATF applications with acceptable processing temperatures and excellent oxidation/corrosion resistances for a zirconium alloy substrate. Full article

In this study, AlCrN coatings were deposited using modulated pulsed power magnetron sputtering (MPPMS) with different power pulse parameters by varying modulated pulsed power (MPP) charge voltages (350 to 550 V). The influence of power pulse parameters on the microstructure, mechanical properties and thermal stability of the coatings was investigated. The results indicated that all the AlCrN coatings exhibited a dense columnar microstructure. Higher charge voltage could facilitate a denser coating microstructure. As the charge voltage increased up to 450 V or higher, the microvoids along the column boundaries disappeared and the coatings became fully dense. The main phase in the AlCrN coatings was the c-(Al, Cr)N solid solution phase with NaCl-type phase structure. A diffraction peak of the h-AlN phase was detected at a 2θ of around 33°, when the charge voltage was higher than 500 V. The hardness of the AlCrN coatings varied as a function of charge voltage. The maximum value of the hardness (30.8 GPa) was obtained at 450 V. All the coatings showed good thermal stability and maintained their structure and mechanical properties unchanged up to 800 °C during vacuum annealing. However, further increasing the annealing temperature to 1000 °C resulted in apparent change in the microstructure and decrease in the hardness. The charge voltages also showed a significant influence on the high-temperature tribological behavior of the coatings. The coating deposited at the charge voltage of 550 V exhibited excellent tribological properties with a low friction coefficient. Full article