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Abstract:
In this paper, mechanical properties of the as-received and aluminide layer coated MAR 247 nickel based superalloy were examined through creep and fatigue tests. The aluminide layer of 20 µm was obtained through the chemical vapor deposition (CVD) process in the hydrogen protective atmosphere for 8 h at the temperature of 1040 °C and internal pressure of 150 mbar. A microstructure of the layer was characterized using the scanning electron microscopy (SEM) and X-ray Energy Dispersive Spectroscopy (EDS). It was found that aluminide coating improve the high temperature fatigue performance of MAR247 nickel based superalloy at 900 °C significantly. The coated MAR 247 nickel based superalloy was characterized by the stress amplitude response ranging from 350 MPa to 520 MPa, which is twice as large as that for the uncoated alloy.

Keywords:
chemical vapor deposition, nickel alloys, aluminide coatings, high temperature fatigue, creep

Abstract:
The paper aims to investigate the nature of fracture behaviour through the microstructural and damage evolution analysis of a titanium alloy (Ti6Al4V) with tailored initial microstructures under FAST conditions. High-temperature uniaxial tensile tests with varying heating rates (4°C/s and 100°C/s) and temperatures (900 - 950°C) were conducted to study the effects of heating parameters on the formability and damage of the material. The microstructure and fracture morphology after high-temperature uniaxial tensile tests were characterised to reveal the evolution mechanisms of elongation and damage. It was found, that fast heating could restrain the phase transformation of α to β during the heating and therefore improve the formability of the Ti6Al4V titanium alloy under hot stamping condition.

Keywords:
Ti6Al4V, hot stamping, fracture behaviour, damage evolution