MICROSTRUCTURE CHARACTERIZATION AND STABILITY OF RAPIDLY SOLIDIFIED NI-AU AND RH-CU ALLOYS

Alloys of Ni-Au and Rh-Cu were analyzed to determine the degree of extended solid solubility of the rapidly solidified structures. The rapidly solidified alloy of Ni58Au42 forms a one-phase extended solid solution, existing as featureless grains. During isothermal aging at 600°C, the rapidly solidified Ni-Au alloy transformed into a two-phase structure of nickle-rich and gold-rich phases. The Ni-Au rapidly solidified alloy was stable up to 350°C under continuous heating at 10°C min-1. The rapidly solidified alloy of Rh58Cu42 did not form a complete extended solid solution, but the rapid solidification did increase the solubility limits beyond the equilibrium phase boundaries. The microstructure appears as refined dendrites with less microsegration. During isothermal aging at 900°C, the rapidly solidified Rh-Cu alloy undergoes increased regregation to rhodium-rich and copper-rich phases. The rapidly solidified Rh-Cu alloy was stable up to 375°C under continuous heating at 10°C min-1. X-ray and electron diffraction and differential scanning calorimetry techniques were utilized to determine the microstructure, crystal structure and phase stability.