HIGH-TEMPERATURE OXIDATION BEHAVIOR OF AN N5 NANOCRYSTALLINE COATING DEPOSITED BY ESD ON A NI-BASED SINGLE-CRYSTAL SUPERALLOY

An N5 nanocrystalline coating was prepared on a Ni-based single-crystal superalloy by electrospark deposition. The morphologies, chemical composition, and phase constitution of the coating were analyzed by scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and X-ray diffraction (XRD), respectively. The high-temperature oxidation resistance of the substrate and coating at 1100℃ was tested in a static isothermal oxidation experiment. The results show that the electrospark deposition coating with columnar crystal structure is composed of nanocrystalline; there is no elemental interdiffusion between the substrate and the coating, which effectively avoids decreasing the mechanical properties of the substrate alloy due to the interdiffusion. Migration and aggregation of a reactive element, Ta, in the nanocrystalline coating substantially improves oxide film adhesion

New HfNbTaTiZr High-Entropy Alloy Coatings Produced by Electrospark Deposition with High Corrosion Resistance

The aim of the present paper is to investigate an innovative high corrosion resistance coating realized by electrospark deposition. The coating material was fabricated from HfNbTaTiZr high-entropy alloy. HEA was produced by the mechanical alloying of Hf, Nb, Ta, Ti, and Zr high-purity powders in a planetary ball mill, achieving a good homogenization and a high alloying degree, followed by spark plasma sintering consolidation. The electrodes for electrospark deposition were cut and machined from the bulk material. Stainless steel specimens were coated and electrochemically tested for corrosion resistance in a 3.5% NaCl saline solution.

Obtaining of Coatings from Ni-Al by Electro Spark Deposition and Surface Smoothing by Ultrasonic Plastic Deformation

The article presents the research results on obtaining coatings on steels 1030 and AISI 420 by the method of electrospark deposition and subsequent smoothing by means of ultrasonic surface plastic deformation (USPD). Intermetallic alloys consisting mainly of NiAl and Ni3Al phases were used as materials for obtaining coatings. It was found that the coatings consist of columnar crystallites of complex composition and have high plastic properties. To ensure the minimum parameters of the surface roughness of the obtained coatings, it is necessary to carry out 3-6 times of ultrasonic surface treatment.

Parametric Study of Automated Electrospark Deposition for Ni-Based Superalloys

Conventional electrospark deposition (ESD) processes used in industry are well suited to the coating and repair of small areas for the purpose of hardfacing, corrosion resistance, or dimensional restoration. Although significant advances have been made in the range of materials that can be processed, the comparatively slow deposition rate limits the potential applications of a traditional manually operated ESD process. In this study, an automated ESD system was demonstrated for the application of Ni-based superalloy (Inconel 718) coatings on Ni- and Fe-based substrates. A preliminary study was used to determine the influence of process parameters on an automated system, with capacitance, voltage, electrode force, and electrode travel speed parameters chosen to provide higher deposition rates while maintaining high deposition quality. A comparison of Inconel 718 and 316L stainless steel substrates found that the influence of substrate composition on coating hardness and coating composition was limited to the first 40um. These results pave the way for ESD of larger-area coatings and longer-duration repairs without the need for human operators.

Microstructure Peculiarities of Intermetallic and Composite Coatings

Coatings were obtained by the method of electrospark deposition (ESD), using Ni-Al intermetallic alloys, steel having been used as cathodes. The structure of samples preliminarily, coated with nickel aluminides of various phase compositions (NiAl, Ni3Al), was investigated. In addition to the indicated anode materials, a complex alloyed metal matrix alloy obtained by the method of self-propagating high-temperature synthesis, was used. It was established that the coating microstructure consisted of columnar crystallites, vertically oriented to the cathode surface. X-ray microanalysis of the transverse sections showed a change in the composition of crystallites along their height. It was found that the content of the cathode components decreased from the surface of the sample to the upper part of its coating, however, the content of the anode components increased. The revealed regularities indicate the fact that the coating structure obtained at ESD, was formed through the stage of liquid-phase mixing, which explained high coating adheasion. The mechanisms of structure formation of both single-layer and two-layer coatings proved to be identical.