Abstract
TiB-reinforced Ti-3Al-2.5V matrix composites, in which TiB whiskers are oriented parallel to the direction of heat extrusion, were fabricated via mechanical alloying and hot isostatic pressing (HIP). To investigate the near-threshold fatigue crack propagation in TiB-reinforced Ti-3Al-2.5V matrix composites, stress intensity factor K-decreasing tests were conducted for disk-shaped compact specimens having two different orientations of TiB whiskers at force ratios from 0.1 to 0.8 under ambient conditions. The crack growth rates, da/dN, for the composites incorporating TiB whiskers oriented perpendicular to the direction of crack growth were constantly lower than those obtained in the case where the orientation was parallel at the same stress intensity range ΔK, while the threshold stress intensity range, ΔKth, was higher. This effect can be explained by the increase in the degree of roughness-induced crack closure resulting from the perpendicular TiB, because fatigue cracks preferentially propagated across the boundaries between the matrix and the TiB in certain regions. In contrast, the effective threshold stress intensity range, ΔKeff,th, for composites was unaffected by the TiB orientation at low force ratios.
Highlights
As a result of their high heat resistance and superior specific strength, titanium alloys are frequently employed in aerospace components
The ΔKth values of the LT series are always greater than those of the TL series. These findings indicate that fatigue crack propagation in titanium boride (TiB)/Ti3Al-2.5V composites under near-threshold conditions is affected by both the force ratio and the TiB
The values of da/dN acquired using the LT specimens are always lower than the values observed cracking due to mechanical fatigue and sustained load at high force ratios
Summary
As a result of their high heat resistance and superior specific strength, titanium alloys are frequently employed in aerospace components. The microstructure of a metal typically determines its mechanical properties, and so modifying this microstructure could effectively improve the characteristics of materials based on titanium. Such modifications can be achieved using a variety of methods, including the generation of surface topography [1], the insertion of additional elements in an alloy [2,3,4,5,6,7,8,9,10,11], and grain refinement [11,12,13,14]. Hyman et al [31] and Li et al [32] have
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