Measurement of Thermal Expansion at High Temperature by a Transient Interferometric Technique

A transient interferometric technique to measure the thermal expansion of pure metals and alloys during rapid heating is presented. The metallic specimen is resistively heated from room temperature to a high temperature close to melting within approximately 500 ms by the passage of a high electrical current pulse. The temperature of the specimen is measured and time resolved by a fast pyrometer; the thermal expansion is obtained by a high-speed laser-interferometer. The device used is a modified polarized-beam Michelson-type interferometer with a phase-quadrature detector that distinguishes between expansion and contraction. Details of its principle, the construction, adjustment, and operation are described. In addition, thermal expansion measurements performed on molybdenum and tungsten standard reference materials (SRMs) are presented and compared with results obtained by other researchers.