Study On Heat Treatment Process Of Spray Formed GH742y Ni-Base Super Alloy

The main characteristics of spray formed alloys are very fine microstructures, the extension of solid solutions compared to the conventional techniques such as ingot metallurgical. It is necessary that the heat treatments process of spray formed alloys should be influenced by these features. To future enhance the mechanical properties of the spray formed alloys, it is important to study deeply the heat treatment procedures of these alloys.The heat treatment processes of the hot isostatic pressing (HIP) spray formed GH742y alloy was studied in the paper. Theγ′phase of alloy heat treated was observed by using optical microscope and scanning electron microscope (SEM), and preliminary optimize the heat treatment process. The validity of the optimum heat treatment process was proved by analyzing the solution aging hardness curves and mechanical properties. The results shown the microstructure of the spray formed alloy is fine equiaxed grains with about 50μm, and density of 95.5% for as-deposited alloy. The grains size did not grow significantly after HIPing consolidated treatment, but the density of as-deposited alloy up to 99.6%. The fine and uniformγ′phase was obtained at 1140℃solution for 6h, air cooling. After various aging treatments, the peak aging hardness value reached at 780℃/8h, AC, according to the aging hardness curves. Two heat treatment procedures are determined according to solution and ageing treatment tests. In the first treatment, the alloy was solutionized at 1140℃for 6h and air cooled. In the second treatment, aging at 780℃for 8h and air cooling was added on the basis of the first treatment. The mechanical properties of the heat treated the spray formed alloy were studied. The results show that mechanical properties of the spray formed alloy treated by two heat treatment procedures respectively, are better than those of the alloy treated by conventional heat treatment. But the most mechanical properties is obtained by the second treatment procedure, which is attributed to cooperation among the primary and secondaryγ′phases. The fracture surfaces are characterized by dimple aggregation. The optimum heat treatment procedure is determined as 1140℃/6h, AC +780℃/8h, AC.