Superplastic Behavior of ATI 718Plus Superalloy

摘要

Complex shaped, ultra thin-walled parts can be manufactured using superplastic forming. Hot working temperature for the production of fine-grained billets (d=5-15 μm) out of ATI Allvac 718Plus~R superalloy is in the range of 982-1038°C. An ultrafine-grained structure (d=0.3 μm) was produced by multi-axial forging with a gradual decrease of the forging temperature from 950 to 700°C. Superplastic properties of the alloy were carried out in the temperature interval of 700-950°C. It has been revealed that the fine-grained alloy provided superplastic elongations about 300% at 950°C and strain rate of 10~(-4) s~(-1). The highest elongation of ultrafine-grained alloy was about 1450% and very low flow stresses were reached at 900°C and strain rate of 3×10~(-4) s~(- 1). The ultrafine-grained alloy showed superplastic properties also at 700°C (0.62T_m). The microstructure and superplastic properties of the alloys 718 and 718Plus are compared.