Analysis of influence of measurement conditions on repeatable results of thermal diffusivity of ceramic moulds designed for manufacturing the superalloys castings

Abstract

The article presents the study results concerning development of methodology for measuring thermal diffusivity with the laser-flash method with special attention being paid to their repeatability. The first stage involved the literature review of the problem determining an influence of variable measurement parameters including presence of graphite coating, error correction methods and laser power. The main part of the study includes evaluation of the sample structure influence. A real ceramic mould of specific porosity and green compacts made after its grinding were examined. Influence of sample thickness and interval between individual laser shots were also determined. The analysis was performed by using the Netzsch LFA 427 instrument designed for direct measurement of thermal diffusivity with the laser-flash method. The material analysed included different types of ceramic moulds designed for manufacturing the elements made of nickel based superalloys. The preliminary study performed showed that the main factor that has an influence on obtaining correct and repeatable results of thermal diffusivity study is proper preparation of samples i.e. using them in a form of directly cut out from the mould, selection of data acquisition time and interval between individual shots. It is especially important in the case of measurements taken at high temperature when radiation mechanism of heat transfer is of basic significance.