Piston dilatometry applied to aluminium and nickel alloys.

The use of piston dilatometry is described for the measurement of the melting behaviour for metals and alloys. In this technique, a cylindrical sample of the test alloy is held between ceramic pistons within a ceramic cylinder, and treated as a thermal expansion test-piece. The technique has been applied to a series of Al-Si alloys, with a good match being found between theoretical and experimental liquidus temperatures, widths of solid/liquid phase region (so-called ‘mushy’ zone), and liquid phase volumetric expansion coefficients. The technique has also been used successfully on a variety of other alloys, including nickel-base superalloys. In some cases, the technique fails because of reactions between the ceramic and metal, or because of leakage of molten metal down the narrow gap between piston and containing cylinder wall.