Crack Orientation Dependence of Fatigue Behavior in Titanium Single Crystals by Thin Sheet Plain Bending

Tensile and fatigue crack growth behavior of commercially pure titanium produced by laser powder bed fusion additive manufacturing

“…The higher threshold for the L-T orientation is attributed to the strong texture and difficulty of slip or twining. found that the unfavorable slip plane orientation instead favors crack growth by deformation twinning and separation of the basal planes, giving higher fatigue crack growth resistance [33,36,37]. Further evidence for this crack growth mechanism is seen in Figure 13 where a faceted mode of fatigue crack propagation is seen for the L-T samples.…”

“…Grain size, grain morphology, and crystallographic texture can greatly affect the mechanical and physical properties of titanium and its alloys , and fatigue performance is a property of particular importance for biomedical implants made from titanium [1]. In the case of conventionally manufactured cast or wrought CP-Ti, there has been previous work devoted to understanding how these microstructural factors affect the fatigue performance [32][33][34][35][36][37][38][39][40][41].…”

“…When considering grain orientation, fatigue crack initiation in CP-Ti tends to occur mostly on the active basal or prismatic slip planes [41], although under some test conditions crack initiation on twin planes [41] or at grain boundaries [40] has been observed. Regarding fatigue crack growth, studies of single crystal CP-Ti have shown that when the crystal is oriented for easy prismatic slip (i.e., soft orientation), the crack will grow either by alternating shear on prismatic and pyramidal slip systems or on two sets of pyramidal slip systems depending on the crack growth direction [33,36,37]. In contrast, for loading along the c-axis (i.e., hard orientation) cracks grow by deformation twinning which gives rise to much higher fatigue crack growth resistance [33,36,37].…”

“…Regarding fatigue crack growth, studies of single crystal CP-Ti have shown that when the crystal is oriented for easy prismatic slip (i.e., soft orientation), the crack will grow either by alternating shear on prismatic and pyramidal slip systems or on two sets of pyramidal slip systems depending on the crack growth direction [33,36,37]. In contrast, for loading along the c-axis (i.e., hard orientation) cracks grow by deformation twinning which gives rise to much higher fatigue crack growth resistance [33,36,37]. In this case, crack growth occurs by separation of the basal planes, and in polycrystals this mechanism is observed when the loading axis is within 50° of the caxis of each grain [35].…”

“…In this case, crack growth occurs by separation of the basal planes, and in polycrystals this mechanism is observed when the loading axis is within 50° of the caxis of each grain [35]. Accordingly, fatigue life tends to improve when loading is along or near the alpha phase c-axis of strongly textured titanium alloys since this orientation impedes both crack initiation and propagation [17,21,30,31,37].…”