Effect of surface roughness on fatigue performance of additive manufactured Ti–6Al–4V

Abstract

Additive manufacturing is increasingly considered for production of high quality, metallic, aerospace parts. Despite the high potential of this manufacturing process to reduce weight and lead time, the fundamental understanding of additive manufactured Ti–6Al–4V material is still at an early stage, especially in the area of fatigue and damage tolerance. This paper covers the effects of inherent surface roughness on the fatigue life. In the as built condition, metallic parts have a poor surface texture, which is generally removed in fatigue critical areas. It is shown that the fatigue properties of Ti–6Al–4V samples, produced by direct metal laser sintering and electron beam melting, are dominated by surface roughness effects. A simple model based on an equivalent initial flaw size is formulated

Influence of surface pre-treatments on the high-cycle fatigue behavior of Ti–6Al–4V – From anodizing to laser-assisted techniques

“…Especially due to the letter aspect specimens treated by parameter set 3 show inferior properties. Focusing on the local timetemperature path during laser treatment, rapid heating and cooling of the specimen surfaces play a dominant role in microstructure evolution, as has been documented for laser-based processes in general [20,21,24,[30][31][32][33]. The key to improved resistance to short crack advance in the laser treated specimens in the current work seems to be the combination of the ultrafine-grained martensitic microstructure and the residual stress profile in the subsurface region.…”

“…At high stress amplitudes, crack 20 initiation is primarily triggered by the local inhomogeneity of the brittle nanostructured layer, which is more pronounced upon NaTESi treatment. Evolution of residual stresses and subsurface microstructural changes are hardly seen and, thus, fatigue properties are very similar to the non-treated reference condition.…”

“…Numerous factors have been shown to affect the fatigue behavior of metallic specimens and components, as discussed in [14][15][16][17][18][19][20][21]. In addition to microstructural features such as grain size, grain morphology, precipitates and phase fractions, geometrical factors such as specimen volume and shape have a strong impact.…”

Part orientation optimisation for the additive layer manufacture of metal components

“…The surface roughness creates multiple stress concentrations which can have a negative effect on the fatigue performance of the component [6]. Research in this area indicates that post processing is necessary to increase fatigue life, particularly for titanium alloys.…”

Effect of corrosion and fatigue on the remaining life of structures and its implication to additive manufacturing

“…This is particularly true for cracks in aircraft applications where, as detailed in MIL-STD 1530 [32], the design and certification approval require analytical tools that are capable of capturing crack growth and the role of testing is to validate or correct the damage tolerance analysis. Berto et al [33][34][35][36], Kahlin, Ansell and Moverare [37,38], Greitemeier et al [39], Chan [40] and Leuders et al [41] each revealed that the rough surfaces associated with as additively manufactured parts significantly degrade the fatigue performance of AM structures. The sentence used in [37] was: "The surface roughness is the single most severe factor for fatigue for additive manufactured materials".…”