Effect of direct ageing treatment on stress-rupture properties of GH761 alloy

The effect of direct ageing treatment on microstructure and stress-rupture properties of GH761 alloy was studied. Phosphorus was added to the tested alloy for its beneficial effect on stress-rupture life. It was found that the grain size of the tested alloy became much finer after direct ageing treatment, in comparison with the commercial GH761 alloy under standard heat treatment condition. The optimum direct ageing treatment has been determined as follows: 830 degrees C x 4 h, air cooling+720 degrees C x 24 h, air cooling. After such treatment, the higher stress-rupture properties of the test alloy at 650 degrees C, 690 MPa were obtained. The role of phosphorus is still effective under the condition of direct ageing treatment.