A B S T R A C T This paper presents an experimental investigation of the fracture and fatigue crack growth properties of Ti-6Al-4V produced by the Wire + Arc Additive Manufacture (WAAM®) process. First, fracture toughness was measured for two different orientations with respect to the build direction; the effect of wire oxygen content and build strategy were also evaluated in the light of microstructure examination. Second, fatigue crack growth rates were measured for fully additive manufactured samples, as well as for samples containing an interface between WAAM® and wrought materials. The latter category covers five different scenarios of crack location and orientation with respect to the interface. Fatigue crack growth rates are compared with that of the wrought or WAAM® alone conditions. Crack growth trajectory of these tests is discussed in relation to the microstructure characteristics.Keywords fatigue crack growth; fracture toughness; microstructure; titanium; wire + arc additive manufacture. N O M E N C L A T U R Ea = Crack length B = Compact tension specimen thickness K IC = Plane-strain fracture toughness K Q = Conditional fracture toughness value P max = Applied load at fracture P Q = Conditional load value at fracture determined by ASTM Standard W = Compact tension specimen width σ ys = Material yield strength under tension load I N T R O D U C T I O NTitanium alloy Ti-6Al-4V (Ti64) has been used in the aerospace and other industries owing to its high specific strength, excellent resistance to fatigue and corrosion, and good performance at elevated temperature. With the increasing use of carbon fibre polymer composites in the airframes, titanium will be increasingly used because of its good compatibility with this material. However, titanium alloys are extremely expensive and very difficult to machine, if compared with other aerospace alloys such as aluminium. Therefore, using the Additive Manufacture (AM) technology to build titanium parts has become very attractive owing to the significant reduction in material waste, machining and tooling cost, manufacturing energy and time to market. Conventional powder bed AM also makes it possible to easily produce complicated parts. However, the cost of material powder is usually particularly high, which affects the overall cost of the process. This drawback is counterbalanced by the reduced material waste. Studies have shown that AM can be an economically and environmentally superior option to the traditional methods of machining from cast or forged billets for production in small batches.

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