Advanced Materials Letters

Volume 10, Issue 3, Pages 189-192, March 2019

About Cover

The cover photo describes the scheme of the twin screw extruder for the preparation of thermoplastic starch (TPS).  As discussed by M. Paula Guarás, this screw extrusion process is very advantageous for the preparation of TPS films with improved mechanical and water vapor absorption properties in any industrial processing line for plastic packaging products. 

Fabrication of Y₂O₃ coatings by cold-spray

Lingyan Kong^1*, Rifei Han^{1, 2}, Yang Yang¹, Jiayi LI^{1, 2}, Tianying Xiong¹, Tiefan Li¹

¹Institute of Metal Research, Chinese Academy of Sciences

²School of Materials Science and Engineering, University of Science and Technology of China

Adv. Mater. Lett., 2019, 10 (3), pp 189-192

DOI: 10.5185/amlett.2019.2188

Publication Date (Web): Dec 31, 2018

Copyright © 2018 VBRI Press

E-mail: lykong@imr.ac.cn

Abstract

As a candidate material against plasma etching, yttrium oxide has been coated onto etching chamber by plasma spray technique. However, the plasma spray technique introduces undesirable coating properties such as porous structure and deleterious thermal effects. To reduce the disadvantage of thermal impact, cold spray was used as an alternative technology to deposit thick and dense yttrium oxide coatings.  Many studies have shown that the powders suitable for cold spray process should be with a size around 20μm. However, the Y₂O₃ are ceramics, it is difficult to form coatings by cold spray due to the lack of ductility when using the powders with a size about 20 μm. It is also difficult for nano-particles to get through the bow shock of cold spray process, which may cause deceleration or even deflection of lighter particles away from the surface, and therefore fail to be cold sprayed.  In this paper, we use Y₂O₃ with an original average size of 30 nm to form agglomerated Y₂O₃ particles by hydrothermal treatment. After the hydrothermal treatment, the nano-size Y₂O₃ agglomerated together to a size around 20 μm and then deposited by cold spray. Y₂O₃ coatings were forming in this way. In this research, Y₂O₃ nanoscale powder was tailored into a loose agglomerated structure by hydrothermal treatment, and it was found that the addition of inorganic salt promote the agglomeration process. Cold spray experiments verified the cold spray suitability of the as-modified particle. Gas temperature greatly affects the coating thickness and microstructure, and optimal spraying parameter was fixed at 600 °C. An excellent yttria coating was successfully fabricated on aluminum alloy 6061 with a maximum thickness of 200 µm and a low porosity less than 1% using compressed air as propellant gas. The loose aggregated feedstock fractured during impact instead of deformation. It is demonstrated that particle structure is key factor for ceramic deposition by cold spray technique. 

Keywords

Cold spray, ceramic coating, yttrium oxide (Y₂O₃).