Influence of heat treatments on incipient melting structures of DD5 nickel-based single crystal superalloy

The evolution of microstructure and formation mechanism of incipient melting microstructure of DD5 single crystal superalloy during solution heat treatment were studied by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and energy dispersive spectroscopy (EDS). The solidus and liquidus of single crystal alloy were obtained by differential scanning calorimetry (DSC). Results show that the mosaic-like eutectic and fan-like eutectic are dissolved at first, and the coarse γ′ phase is dissolved later during the solution heat treatment of 1,390 °C/2 h+1,310 °C/4 h+1,320 °C/10 h + air cooling (AC). The composition segregations of Al, Ta, W and Re are 0.99, 0.96, 1.04 and 1.16, respectively, which close to 1. The incipient melting is caused by the low local temperature of the alloy, and the micropore region with a lower melting point is the preferred position for incipient melting.