Micro-indentation and inverse analysis to characterize elastic–plastic graded materials

Properties of actual graded materials were characterized with a new procedure based on inverse analysis. This procedure utilizes indirect experimental records obtained from instrumented micro-indentation and extracts key properties of indented specimen through the Kalman filter technique. The graded material is composed of mixture of Yittria Partially Stabilized Zirconia (PSZ) and NiCrAlY and it possesses varying elastic–plastic properties through its thickness. This procedure enables determination of the compositional profile and the effective mechanical property without resorting to complex experimental measurements. It relies solely on the load–displacement records of instrumented spherical indentation and the inverse analysis during the post-processing. The graded specimens were fabricated by plasma spray deposition process under controlled feeding of PSZ and NiCrAlY powders. Prior to testing of the graded materials, single phased coatings were made with each component and analyzed. This process allows consistent material constants to be used in the graded material analysis. Here PSZ and NiCrAlY were assumed to be elastic and elastic–plastic, respectively. The elastic moduli of both materials were estimated with a common indentation method while the plastic properties of NiCrAlY were determined by modifying the inverse method proposed for the graded materials. The latter procedure represents a new indentation method for characterization of homogeneous elastic–plastic materials. Once the properties of constituents were identified, the properties of graded material were estimated with the Kalman filter technique. The indented load–displacement relations simulated from finite element analysis with the estimated properties and that of measured record showed excellent agreement, which assures a high degree of accuracy in the current measurement procedure.