Microstructural evolution of a nickel-based single-crystal superalloy embrittled by molten Zn

The embrittlement treatment of Ni-based single-crystal superalloys in a Zn atmosphere causes the superalloys to break easily. This considerably increases the contact area in the dissolution process. Hence, this treatment has the potential for conveniently recovering rare precious metals from Ni-based superalloys. This study systematically examines the microstructures of Ni-based single-crystal superalloys after Zn embrittlement. Microstructural changes in the superalloy after reaction with Zn at 700, 900, 1100, and 1200 °C for 8 h were investigated and analyzed in detail via X-ray diffractometry, scanning electron microscopy, and electron probe microanalysis, using the phase and element composition as the evaluation indices. Results showed that the formation of the Ni5Zn21 intermetallic compound in the superalloys was the main reason. The formation of Ni5Zn21 disturbed the distribution balance and promoted the recombination of metallic elements, resulting in the embrittlement of the superalloys. The embrittlement mechanism involved a mutual diffusion reaction of Zn and Ni, but the degree of Zn diffusion was higher.