Yesheng Zhong

Microstructural evolution of ultrafine-grained NiCrCoAl foil after heat treatment at 1000°C

Abstract This research investigated the microstructural evolution of Ni–23·5Cr–2·66Co–1·44Al superalloy foil fabricated by electron-beam physical vapour deposition and annealed at 1000°C. The results showed that the deposited alloy mainly consisted of the γ-phase. After annealing at 1000°C, the peak moved to a lower 2θ degree on the deposited side and to a higher 2θ degree on the substrate side, which indicated that uniform strain existed at the deposited state and recovery occurred during annealing. With an increase in the annealing time, the (220) diffraction peak increased significantly. The average size of the grains increased and showed zigzag structures after being etched by a mixture of HNO3, HCl and HF etchant. After being annealed at 1000°C for 4 hours, the ultimate tensile strength of the Ni–23·5Cr–2·66Co–1·44Al superalloy foil was improved from 641 to 800 MPa.

Study of pack cementation aluminising at 630°C on Ni–Fe–Cr–Al alloy sheet produced by EB-PVD

Abstract This paper reports the Ni-based alloy sheets which were produced by electron-beam physical vapour deposition and further aluminisation. The microstructures of the as-deposited and aluminised sheets were characterised by scanning electron microscope, X-ray diffraction, and so on. It is found that the as-deposited Ni-base alloy sheets present a Ni-based solid solution structure, and the microcrystal grain was compact, uniform and no precipitation. When the alloy sheets have been aluminised at 630°C, the phase structure changed from Al3Ni to Al3Ni2 during heat treatment period. The thickness of every layer was no more than 10 µm. The coating was compact and a small amount of aluminium-rich region appeared in a small area. The interface between coating and substrate was clear and smooth, and macro-defect-free.

Cyclic oxidation behaviour of the Al2TiO5/TiO2/ZrO2 composite coating on Ti–6Al–4V alloy with plasma electrolytic oxidation

Abstract Al2TiO5/TiO2/ZrO2 plasma electrolytic oxidation coating deposited on the surface of Ti–6Al–4V alloy was prepared in NaAlO2–NaH2PO2–NaOH electrolytes system, which was doped with ZrO2 micro-particles by a kind of pulsed bipolar plasma electrolytic oxidation. The microstructure, surface morphology and phase composition of the Al2TiO5/TiO2/ZrO2 coatings were studied by SEM and XRD, respectively. Its cyclic oxidation behaviour was studied over the temperature of 1000°C for 100 hours in dry air. After high-temperature oxidation, the original crater eruption topography of plasma electrolytic oxidation coating has disappeared and it obviously took a decreasing tendency of both pore numbers and their diameters. The scales of original plasma electrolytic oxidation coating consisted mostly of Al2TiO5, R-TiO2 and α-Al2O3intermixed with small amounts of ZrO2 particles. They were transferred into R-TiO2, α-Al2O3 and ZrO2 with small amounts of Al2TiO5 after high-temperature oxidation procedure. The weight gains of plasma electrolytic oxidation composite coating increased linearly with the extended oxidation cycles.