Volume 6, Issue 2 (February 2009)
Dilatometric Analysis for Investigating Age Hardening in a Commercial Precious Metal Dental Alloy
Age hardening in a commercial precious metal dental alloy based on the Au–Cu–Ag system with platinum addition was investigated by light optical microscope, scanning electron microscope, energy dispersion x-ray system microanalysis, image analysis, hardness measurements, and dilatometric tests. Dilatometric tests are known to give important information for optimizing the heat treatment parameters of metallic materials but are seldom used in studying the hardening of precious alloys. Nonisothermal dilatometric tests were used to point out the temperature range within which the microstructural hardening transformations occur, while isothermal tests were adopted to study the kinetics of each transformation. The macrohardness and microhardness measurements contributed to the understanding of the nature of the observed transformations, together with the microstructural analysis. We concluded that hardening is mainly due to order-disorder transformations taking place in the matrix. The identified optimal parameters were used for the heat treatment of a lost wax casting alloy prepared according to the traditional procedures for prosthesis manufacturing.