Combined Effects of TiB Volume Fraction and Orientation on Four-Point Bending Fatigue Properties of TiB-Reinforced Ti–3Al–2.5V Composite

Abstract

TiB-reinforced Ti–3Al–2.5V, in which the TiB whiskers are oriented parallel to the direction of heat extrusion, was fabricated via powder metallurgy. To investigate the effects of TiB whisker volume fraction on fatigue properties in Ti–3Al–2.5V, four-point bending fatigue tests were conducted on plate-type specimens having TiB whiskers of varying volume fraction and orientation. The fatigue limit and fatigue life of Ti–3Al–2.5V having TiB whiskers that are oriented parallel to the loading direction tended to be increase with increasing TiB volume fraction, whereas the fatigue limit and fatigue life of specimens having TiB whiskers oriented along the short transverse direction did not depend on the TiB volume fraction. The fatigue limit of specimens with TiB whiskers oriented along the long transverse direction tended to decrease with increasing TiB volume fraction, because fatigue cracks were initiated and propagated along the TiB whiskers. Thus, the resistances of fatigue crack initiation and propagation behavior in Ti–3Al–2.5V changed with both the TiB volume fraction and orientation.

Fig. 9 (a) Optical micrograph, (b) boron map obtained by EPMA analysis, and (c) SEM micrograph of the surface of a 10.0 vol% TiB-reinforced T-type specimen tested at σ_a = 370 MPa near the crack initiation site (N_f = 7.3 × 10³ cycles). White arrows represent the crack initiation site and red arrows represent the crack path.