Fatigue performance and cyclic deformation behaviour of titanium TI-6AL-4V additively manufactured by wire + ARC directed energy deposition

icaf2023 Tracking Number 111

icaf2023 poster

NEWAM (NEw Wire Additive Manufacturing) is a 5 year research programme focused on the process, material and structural integrity of wire based directed energy deposition AM (w-DEDAM) processes. Four universities (Cranfield, Manchester, Strathclyde and Coventry) are combined in a research programme with UK EPSRC funding and industry support from AM equipment supply chain, service providers and industry end users. Project partners include aerospace OEMs who are interested in the future potential of this manufacturing method for increased material buy-to-fly ratio, manufacturing lead time reduction and weight reduction. Coventry University are leading the “Material Performance and Structural Integrity” of NEWAM, determining structural integrity through fatigue initiation, fatigue fracture, and residual stress research. Hottinger Bruel & Kjaer are working with Coventry researchers and contributing strain-life fatigue testing and material characterization services at their Advanced Materials Characterization & Test (AMCT) Facility. This presentation will describe this fatigue initiation research and findings for as-deposited wire + arc additive manufactured high strength titanium Ti-6Al-4V alloy. Two walls were manufactured with an oscillatory torch and wire path. Cylindrical blanks were extracted from these walls in horizontal and vertical orientations with respect to the deposited layers. Fatigue test specimens were manufactured and tested according to ASTM E606 standard. Fully reversed strain-controlled fatigue testing were performed for 50 fatigue test specimens to investigate material deformation behaviour and fatigue performance from low cycle fatigue (LCF) through high cycle fatigue (HCF) regimes. X-ray computed tomography was used to detect defects in the test samples, and microstructure and fractography were performed to understand the role of microstructure on crack initiation and fracture. Fatigue testing and investigations revealed no porosity defects in the material, crack initiation was from microstructure features. Fatigue characterisation showed marginal difference in fatigue performance with build layer orientation (anisotropy) in LCF at high applied strain, with no significant difference (isotropy) in HCF at low applied strain.