Microstructure and High-temperature Mechanical Properties of Different Positions of Turbine Disc Forgings in GH4706 Superalloy

Abstract

In order to study the differences in microstructure and high temperature properties of different positions of turbine disc forging in GH4706 alloy， comparative analysis of mechanical properties at high temperature were carried out. Detailed experiments included high-temperature tensile property （conducted at the temperature of 400 ℃， 500 ℃， 600 ℃ and 650 ℃）， high-temperature low-cycle fatigue （conducted at the temperature of 400 ℃， 500 ℃ and 600 ℃） and high-temperature stress rupture life （conducted at the condition of 650 ℃/690 MPa and 600 ℃/700 MPa） based on typical service performance requirements. The test results showed that the grain sizes of the hub， spoke and rim varied significantly， with the hub grain size level 4 （average grain size 84 μm）， spoke grain size level 3 （average grain size 120 μm） and rim grain size level 2 （average grain size 183 μm）.The γ′-γ″ composite of the samples in different positions were dispersed in spherical shape. The η phase of hub and plate is in needle shape， with larger size， and distributed parallel to grain boundaries. The η phase of rim precipitates in the shape of short rods with smaller size and dispersed arrangement at grain boundaries. There was no significant difference in high-temperature tensile strength at different locations. However， the samples from hub had excellent low-cycle fatigue performance （4 363 cycle number）， while the tensile plasticity and stress rupture life of rim was the longest （1 259 h）. The study indicated that the variation of microstructure from different positions of turbine disc forging in GH4706 alloy had significant effects on mechanical properties.

Keywords

• gh4706 alloy； turbine disc； grain size； high-temperature mechanical properties