CAREER: High Temperature Deformation of Stand-Alone Plasma-Sprayed Yttria-doped Zirconia Coatings

Purdue University, West Lafayette IN

Investigators

Abstract

Thermal barrier coatings of plasma-sprayed 7 wt.% Y2O3-ZrO2 (YSZ) are to be extensively studied at representative use temperatures (800 degrees C-1400 degrees C) using a modified compression test for stand-alone coatings. For the test, the YSZ coating is removed from the substrate to isolate its behavior, and creep testing, stress relaxation, and fast fracture experiments will be performed. In addition to mechanical testing, we will use the following characterization methods for the proposed work: dilatometry, transmission electron microscopy, X-ray diffraction, Raman Spectroscopy, and laser flash (to measure thermal conductivity). Each method listed will provide the necessary information to interpret the mechanical testing results. Thus, the principal output of this research will be structure-property relationships of plasma-sprayed YSZ in simulated operating environments. This will involve establishing deformation mechanisms as a function of temperature, stress, time, and sample microstructure (i.e. porosity and lamella size). This program will also establish a foundation for a lifetime of educational excellence through curriculum development, outreach, and mentoring. To increase non-majors participation in materials classes at Purdue, web-based modules will be designed that directly relate materials science applications to each of the engineering majors, and then incorporated into the introductory materials course. Beyond the activities at Purdue, an outreach program for science students at Jefferson High School (JHS) in Lafayette, Indiana will be established. In this program, high school juniors will spend 8 weeks of the summer with our research group, then continue their research in the fall and spring of their senior year through an established research based science class at JHS. There will also be a significant undergraduate mentoring component in the proposed work through support of a Purdue MSE undergraduate student every fall and spring semester of the program, as well as a Research Experience for Undergraduates (REU) student every summer. Virtually every commercial and military aircraft flying today uses thermal barrier coatings (TBCs) to protect the metallic structure of its gas turbine engine(s) from temperature extremes and/or to allow the engine to be operated at higher, more efficient temperatures. In addition to the transportation sector, the energy sector also relies on the efficiency boosts TBCs provide industrial gas turbines (IGTs) as they produce electricity. While the benefits of TBCs result in significant cost savings in these and other sectors, there are still many aspects of TBCs we don't understand. For example, they often shrink, crack and even detach from the underlying metallic structure during elevated temperature service. Thus, basic research into their high temperature mechanical properties will allow us to fully utilize the benefits of using these coatings. At its most fundamental level, then, this proposal focuses on determining the material properties that govern how well TBCs "work" while they are in service and will serve as a basis for designing next-generation TBCs.