Malko Gindrat

The 2016 Thermal Spray Roadmap

Considerable progress has been made over the last decades in thermal spray technologies, practices and applications. However, like other technologies, they have to continuously evolve to meet new problems and market requirements. This article aims to identify the current challenges limiting the evolution of these technologies and to propose research directions and priorities to meet these challenges. It was prepared on the basis of a collection of short articles written by experts in thermal spray who were asked to present a snapshot of the current state of their specific field, give their views on current challenges faced by the field and provide some guidance as to the R&D required to meet these challenges. The article is divided in three sections that deal with the emerging thermal spray processes, coating properties and function, and biomedical, electronic, aerospace and energy generation applications.

Vapor Phase Deposition Using a Plasma Spray Process

Plasma spray - physical vapor deposition (PS-PVD) is a low pressure plasma spray technology recently developed by Sulzer Metco AG (Switzerland) to deposit coatings out of the vapor phase. PS-PVD is developed on the basis of the well established low pressure plasma spraying (LPPS) technology. In comparison to conventional vacuum plasma spraying (VPS) and low pressure plasma spraying (LPPS), these new process use a high energy plasma gun operated at a work pressure below 2 mbar. This leads to unconventional plasma jet characteristics which can be used to obtain specific and unique coatings. An important new feature of PS-PVD is the possibility to deposit a coating not only by melting the feed stock material which builds up a layer from liquid splats but also by vaporizing the injected material. Therefore, the PS-PVD process fills the gap between the conventional physical vapor deposition (PVD) technologies and standard thermal spray processes. The possibility to vaporize feedstock material and to produce layers out of the vapor phase results in new and unique coating microstructures. The properties of such coatings are superior to those of thermal spray and electron beam - physical vapor deposition (EB-PVD) coatings. In contrast to EB-PVD, PS-PVD incorporates the vaporized coating material into a supersonic plasma plume. Due to the forced gas stream of the plasma jet, complex shaped parts like multi-airfoil turbine vanes can be coated with columnar thermal barrier coatings using PS-PVD. Even shadowed areas and areas which are not in the line of sight to the coating source can be coated homogeneously. This paper reports on the progress made by Sulzer Metco to develop a thermal spray process to produce coatings out of the vapor phase. Columnar thermal barrier coatings made of Yttria stabilized Zircona (YSZ) are optimized to serve in a turbine engine. This includes coating properties like strain tolerance and erosion resistance but also the coverage of multiple air foils.© 2010 ASME

Plasma Jet-Substrate Interaction in Low Pressure Plasma Spray-CVD Processes

Conventional equipment for plasma spraying can be adapted for operation at low pressure so that PECVD-like processing can be performed. The plasma jet generated by the torch is characterized by a high convective velocity and a high gas temperature. The influence of these properties on a deposition process are investigated in the framework of simple theoretical considerations and illustrated by various experimental results obtained with SiOx deposition. A conclusion of this study is that the deposition process is dominated by diffusion effects on the substrate surface: the deposition profiles and the deposition rates are determined by the precursor density and by the gas temperature on the substrate surface. The high velocity of the jet does not play a direct role in the deposition mechanism. On the other hand it strongly increases the precursor density available for the deposition since it efficiently transports the precursor up to the substrate.

Advanced TBC Systems by Vapor Deposition Using LPPS Thin Film

LPPS-Thin Film is a vacuum plasma spray technology recently developed by Sulzer Metco. In comparison to conventional Vacuum Plasma Spraying (VPS) or Low Pressure Plasma Spraying (LPPS), LPPS-Thin Film uses a working pressure below 2 mbar and a high energy plasma gun. This leads to unconventional plasma jet characteristics which can be used to obtain specific and unique coatings. An additional new feature of LPPS-Thin Film is the possibility to deposit a coating not only from liquid splats by melting the feed stock material but also from gas phase by vaporizing the injected material. The coatings produced from vapor phase show similar structures to EB-PVD layers. The coating thickness can vary from only a few microns up to more than 300 μm. The LPPS-Thin Film process fills the gap between conventional PVD/CVD technologies (≤ 1–5 μm) and standard thermal spray processes (≥ 50 μm). However the concept of “Thin-Film” not only refers to the thickness of the coating. In particular the vaporizing of ceramic coating material also enables new layer properties in a domain between thermal spray and EB-PVD. Yttria Stabilized Zirconia (YSZ) can be deposited with a columnar microstructure. Lab investigations show that these coatings have potential for lower thermal conductivity and higher thermal stress tolerance compared to standard EB-PVD layers.Copyright