Platinum Metals Rev., 1963, 7, (2), 53
High Temperature Strain Gauges
Tungsten-Platinum Alloy Wires
Nickel-chromium alloy wires are invariably used for strain gauges operated at temperatures above 250°C. Above 340°C, however, order-disorder reactions affect the electrical resistivity and make gauge readings unreliable. The demand for reliable strain measurements extending for long periods on such parts as turbine blades or on heated structures such as steam piping has thus encouraged search for a more stable wire material.
In reporting the results of experiments at the Central Electricity Research Laboratories, Leatherhead, K. E. Easterling points out (Brit. J. Appl. Phys., 1963, 14, 79-84) that the need is for a strong oxidation resistant alloy of high electrical resistivity which, since it must not undergo structural changes, should be of the solid-solution type. It should also have a low temperature coefficient of resistance.
By far the most satisfactory materials tested were the tungsten-platinum alloys with 5 to 9 per cent of tungsten, the 8 per cent alloy being preferred. Gauges made from this had a gauge factor of 4.45, appeared unaffected by cold work, and showed outstanding stability up to 800°C.