tensile rest was carried out at different temperature starting from room temperature to 850°C. it is observed that yield strength and ultimate tensile strength remain unaffected until 650°C but ductility starts increasing after 550°C and maximum at 650°C and thereafter decreases. YS unaffected could be due to kear wilsdrop lock. similarly the ultimate tensile strength may be due to work hardening of the material. After 650°C, it is decreased due to onset of dynamic recovery.
A possible explanation is that for nickel superalloys, precipitation hardening is characteristic at aging in the region of 700°C due to the precipitation of the gamma-prime phase. At 650°C there is still no hardening, so the maximum ductility is measured.
You can test this hypothesis by holding the samples for a long time (more than 24 hours) at 720°C before measuring the strength. If the hypothesis is correct, then the anomalous plasticity at 650°C should disappear.
The standard heat treatment for this alloy appears to be aimed at increased creep resistance and elevated temperature service rather than conventional lower temperature tensile strength. • The standard heat treatment as utilized on the as received material has a high-temperature solution cycle aimed at setting the grain size and partially dissolving the prior particle boundaries. • Slow cooling is employed to allow large section sizes to be processed with reduced risk of quench cracking. • A slow or interrupted cooling rate through the gamma prime precipitation and growth range was used to set the large gamma-prime size and distribution. • The ageing cycle used for this material is believed to stabilize the gamma-prime and secondary carbide phases for optimum high-temperature performance.
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