Microstructural stability and tensile properties of a Ti-containing single-crystal Co-Ni-Al-W-base alloy

Microstructural stability and tensile properties of a Ti-containing single-crystal Co-Ni-Al-W-alloy with low tungsten content have been investigated. The alloy possesses relatively lower density and higher gamma' solvus temperature compared to some high-tungsten-content Co-Al-W-base alloys. After aging at 900-1000 degrees C for 400 h, the alloy maintains the stable gamma/gamma' two-phase microstructure without the presence of secondary phases. In the low and medium temperature range (R.T.-800 degrees C), the alloy exhibits superior tensile strength compared to the reported single-crystal Co-Al-W-base alloys, while above 800 degrees C, the yield stress decreases rapidly with temperature increasing. The major deformation mechanisms of the alloy consist of shearing of the gamma' precipitates by pairs of a/2 < 110 >-type dislocations from room temperature to 800 degrees C and bypassing of the gamma' precipitates by a/2 < 110 >-type matrix dislocations above 900 degrees C. At 900 degrees C, it shows a transition from the gamma' shearing to bypassing. (C) 2015 Elsevier B.V. All rights reserved.