The Formation of Two-Layer YSZ Ceramic Coatings Produced in Single Step PS-PVD Process

Abstract

Plasma Spray Physical Vapour Deposition (PS-PVD) is one of the promising methods considered as an alternative to Electron Beam Physical Vapour Deposition (EB-PVD) process used for production of ceramic columnar layer for turbine blades protection against high temperature. The PS-PVD method enables to control the coating structure. In presented article the dense to columnar structure was formed during single-step PS-PVD process using yttria stabilized zirconia oxide (YSZ). The ceramic coating was deposited using LPPS-Hybrid (Oerlikon-Metco) system at Rzeszow University of Technology. The IN 713 alloy with aluminide coating produced by CVD method was used as a base material. The inner zone of the ceramic coating was characterized by dense structure and the outer was characterized by columnar structure. The influence of power current, gas composition flow, powder feed rate and coating time on thickness of both zones was investigated using Scanning Electron Microscopy method. The relationship between process parameters and thermal conductivity was also investigated using Laser Flash Method (LFA). Conducted experimental process showed that using of 1800A power current higher Ar flow (80 NLPM) as well as powder feed rate (30 g/min) enables to obtain dense structure of coating. When higher energy of plasma (power current 2200 A, plasma gasses flow (Ar-35 NLPM, He-60 NLPM) and lower powder feed rate was used the columnar zone was formed. The thickness of obtained coating was in range 140-200 μm. The formation of thick dense layer increased the overall thermal conductivity of coating in comparison with conventional columnar ceramic layer. The combination of thin 20 μm dense-zone with thick (120 μm) columnar zone reduces thermal conductivity of whole coating.