Grain Boundary Precipitates and Mechanical Properties of Alloy 706

Abstract

Effects of cooling rate from solution treatment temperature on mechanical properties and microstructures of a large Alloy 706 disk forging has been invest i gated. The precipitation of delta and eta phases occured at the grain boundaries with a increase of cooling rate from solution treatment temperature. The morphology changes of from globular type to cellular type and coarsening of precipitates were observed with decresing the cooling rate, The mechanical properties at room temperature such as yield strength, tensile strength, elongation, reduction in area and absorbed energy increased with increasing the cooling rate from solution treatment temperature. Same tendency was observed in the yield and tensile strength at elevated temperatures, although ductilities at 650 "C slightly decreased with incresing the cool ing rate. Creep rupture time at 650 "C under 690 MPa extended with increasing the cooling rate from solution treatment, while creep rupture ductility decreased with increasing cooling rate. These results were closely associated with the precipitation behavior of delta and eta phases at grain boundaries.