Bradley Allison

Purdue University

Project Title: Effects of starting powder size on sintering of YSZ thermal barrier coatings
Advisor: Prof. Rodney Trice

Introduction

Thermal barrier coatings (TBCs) are ceramic coatings used to protect turbine blades in gas turbine engines. TBCs have a low thermal conductivity and reduce the temperature the blades are exposed to while in service. This allows the engines to be run at increased temperatures, which improve fuel efficiency. These coatings are plasma sprayed from Yttria stabilized Zirconia (YSZ) powder. YSZ coatings were studied to examine how the starting powder size affect the shrinkage that occurs after exposure to temperature up to 1400oC.

Project Objectives

  • Study the porosity of as sprayed and heat treated coatings
  • Study the lamella thickness that is experienced by varying the starting powder size
  • Study the shrinkage that occurs in coatings when exposed realistic service conditions
  • Study if the varying lamella size effects the phase change that occurs in YSZ

Approach

  • Examine the change in porosity using Archimedes density tests before and after heat treatment
  • Perform SEM on as-sprayed coatings to quantifying the difference in lamella size due to varied powder size
  • Examine shrinkage that occurs in cylindrical coatings using a dilatometer
  • Examine the phases present in coatings at each step of heat treatment using XRD

Findings

  • Larger starting powder size results in greater porosity in the coatings .
  • Phase changes in YSZ TBCs are affected by the lamella size which is directly determined by starting powder size.

Figure 1: Starting powder 350X magnification
Figure 2: TBC lamella 2000X magnification