Non-destructive measurement of elastic properties of structural metals and ceramics at high temperature

The elastic modulus of metals and ceramics is important in the design of many high temperature components. Mechanical integrity and creep induced failure of metals subjected to high temperatures and pressures in steam and power generation applications are of broad interest because of the potential for lifetime limiting premature failures. In these types of applications components are subjected to temperatures greater than 500 deg C and stresses of the order of 40-60 MPa. The temperature dependence of the mechanical properties and creep behaviour are crucial in the design, selection and monitoring of structural high temperature materials. This is especially true of 2.25Cr-1Mo steels that are widely used in large pressure vessels such as super heater headers with maximum application temperature of 540 deg C. Likewise, advanced structural ceramics are also used in high-temperature applications such as automotive valves, heat exchangers and gas turbines by virtue of their excellent strength, toughness and creep resistance. Such applications require load-bearing ceramic components to be subjected to temperatures greater than 1000 deg C. In both cases the elastic modulus is a key parameter in strength and toughness relations. Accordingly, access to basic elastic property data at high temperature, especially Young's modulus, is crucial for modelling purposes and assessing the performance of these materials in service. Typically the method for measuring elastic modulus at temperature is from the stress-strain relation obtained from a tensile test. The accuracy of this technique is limited by rate of loading, deformation effects such as creep, and the stress level at which the elastic properties are determined. Further, the complexity of the experimental arrangement leads to difficulties in measuring the strain on the material. In the case of ceramics it is also extremely costly to machine tensile specimens. An alternative yet simpler method is the impulse excitation technique (IET). It is a dynamic method of measuring elastic properties based on the analysis of a transient vibration of the test specimen resulting from a mechanical impact. The result is a precise measure of the fundamental natural frequency of vibration. This information, together with the mass and dimensions of the specimen permits the calculation of Young's modulus. The method is relatively simple to perform and minimal specimen preparation is required, yielding accurate and precise data. We have developed a measurement apparatus to non-destructively determine Young's modulus of materials in-situ at high temperature. Here we report on the Young's modulus response of a 2.25Cr-1Mo steel and various advanced ceramic materials at temperatures ranging from 20 deg C to 1500 deg C