The effect of annealing an as-cast nickel-chromium base denture alloy (Ticonium Premium 100) on its microstructure, tensile properties, hardness and fracture behavior was studied by light microscopy and scanning electron microscopy. The as-cast alloy exhibited an inhomogeneous dendritic structure consisting of fcc #gamma# phase dendrites with an inhomogeneous distribution of #gamma#' precipitates and an interdendritic eutectic mixture of fcc #gamma# phase and NiBe. This structure had a yield strength of 760 MPa, a tensile strength of 825 MPa, a percent elongation of 3.4 percent and hardness of 348 HV. Annealing at 600 deg C for various times up to 10 hours resulted in little change in microstructure and mechanical properties. Annealing at 750 deg C resulted in precipitate formation in the center of the dendrites, a small increase in strength and hardness and no change in ductility. Annealing at 900 deg C resulted in a coarsening of the as-cast precipitate structure, a decrease in the strength and hardness and an increase in the ductility. Annealing at 1,050 deg C resulted in the dissolution of the as-cast precipitate structure, a large decrease in strength and hardness and a large increase in ductility. The fracture surfaces of the as-cast alloy and alloy annealed at 600 deg C and 750 deg C exhibited brittle features such as cleavage through intermetallic particles. Alloy annealed at 900 deg C and 1,050 deg C exhibited ductile dimple rupture. Annealing the as-cast alloy for 1 hour at 1,050 deg C, quenching and then aging at 750 deg C for 1 hour, resulted in a fine distribution of precipitates in the dendrites, higher strength and hardness that the as-cast alloy, but much improved ductility.
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