Effect of Electron Beam Remelting Treatments on the Microstructure and Properties of Atmospheric Plasma Sprayed Tungsten Coatings

Abstract

Atmospheric plasma-sprayed tungsten coating is one of the most prospective plasma-facing materials used in the first wall of nuclear fusion devices since its low tritium inventory, good compatibility, and cost-effective. However, there are still some issues need to be addressed for the atmospheric plasma-sprayed tungsten coatings, such as high porosity and low thermal diffusivity. In this study, electron beam remelting treatments (EBRTs) have been used to modify the surface microstructure of atmospheric plasma-sprayed tungsten coatings, and the properties of the coatings such as porosity, oxygen content, microhardness, wear, and corrosion resistance are characterized and studied systematically. The experimental results revealed that a compact remelted layer with a columnar crystal structure is formed on the surface of the tungsten coating by EBRTs, and the porosity and oxygen content have been significantly reduced. The microhardness of the tungsten coating has nearly doubled after EBRTs. Comparing with the assprayed tungsten coating, the wear and corrosion resistance of the electron beam treated tungsten coatings have been considerably improved. Moreover, the thermal diffusivity has also been significantly enhanced.

Effect of Varying Plasma Powers on High-Temperature Applications of Plasma-Sprayed Al0.5CoCrFeNi2Ti0.5 Coatings

“…Oxide stringers occur due to the high operating temperature of the APS process (>2000 °C), which causes powder particles to melt and oxidize during the spraying process. Studies have shown that the oxidation of the heated powder particles keeps occurring until the molten particles impact on the substrate, forming lamellar structures with dispersed oxides [ 12 ]. The interlamellar cracks, oxide phases and pores decreased as the plasma power was increased, which was attributed to increased spraying power.…”

“…In the thermal spray process, the feedstock material, which could be in form of powders, wires, rods or suspension, is fed into a spray torch and then heated to a molten or near-molten state before being propelled to form a coating on a substrate base material. The classification of thermal spray-coating processes is based on three factors; (1) the combustion heat source, such as high-velocity oxygen fuel spray (HVOF) or a detonation gun; (2) plasma or arc formation using electrical energy, for example an atmospheric plasma spray (APS); (3) low-temperature processes, which utilize energy developed from gas expansion, for instance cold-spray (CS) process [ 11 , 12 ]. The APS process is a versatile process performed under ambient conditions, which makes it economically viable and therefore well established in the surface coatings industry.…”

Advancements and Perspectives in Additive Manufacturing of Tungsten Alloys and Composites: Challenges and Solutions

“…With appropriate preheating, EBM can address cracking issues in AM for W materials [51,80,81], with many promising results from EBM-fabricated W being reported [51,79,80]. EBM has also been adapted for W surface treatment to enhance quality, due to its controlled beam size and thermal influence [88]. Despite the advantages of EBM, challenges in its use that include complexities associated with electron focusing and the need for maintaining a high vacuum remain [51].…”

“…Over the past decade, extensive research has been undertaken on the AM of unalloyed and alloyed W, as well as W-matrix composites [43,44]. Most studies on unalloyed W have utilized laser powder bed fusion through selective laser melting (LPBF-SLM) [32,[36][37][38]40,43,, and electron beam melting (EBM) [52,53,66,[78][79][80][81][82][83][84][85][86][87][88] of W. Other notable methods employed include laser-direct energy deposition (L-DED) [26,53,66,[78][79][80]89], wire arc additive manufacturing (WAAM) [90], the emerging laser melting deposition [91][92][93][94][95][96][97], and the binder jetting additive manufacturing (BJAM), which shows immense promise for W-based materials [98][99][100][101][102]. Other novel methods such as ultrashort-time liquid phase sintering (LPS) [103], and bound metal deposition (BMD) have also been introduced …”

A comprehensive study on the microstructure of plasma spraying coatings after electron beam remelting

“…Liao et al [3] presented the results of electron beam (EB) remelting of the tungsten coating. A compact remelted layer with a columnar crystal structure was formed.…”