MORPHOLOGICAL-CHANGES AND HARDNESS EVOLUTION IN CU-30NI-5CR AND CU-45NI-15CR SPINODAL ALLOYS

The development of increased strength in Cu-Ni-Cr alloys, compared wit h binary Cu-Ni alloys, is dependent upon heat treatment. These alloys have compositions which permit them to be solution treated at elevated temperature and then aged at a lower temperature, in a two phase fiel d, to produce hardening. Decomposition into two phases may occur by nu cleation and growth or by a spinodal reaction, depending on alloy comp osition and heat treatment temperature. As part of a more extensive st udy of ternary Cu-Ni-Cr alloys, the decomposition of Cu-30Ni-5Cr and C u-45Ni-15Cr (wt-%) has been studied in the spinodal range. The evoluti on of microstructure has been determined together with the coarsening kinetics for the modulated spinodal decomposition products. Specimens rapid quenched from 1050-degrees-C, were aged in the temperature range 300-800-degrees-C. The progress of spinodal decomposition was followe d via hardness measurements, X-ray diffraction, and scanning and trans mission electron microscopy. Modulation wavelengths were measured from both X-ray diffraction patterns and electron micrographs. It was foun d that during the early stages of aging the modulation wavelength rema ined constant while the hardness increased continuously. After a certa in period of aging, the hardness remained constant at its peak value, while the modulation wavelength increased continuously. The results ar e consistent with current theories of spinodal decomposition and harde ning. (C) 1993 The Institute of Materials.