Fatigue crack growth in a particulate TiB2-reinforced powder metallurgy iron-based composite

Abstract

Fatigue crack growth behavior has been examined in a particulate titanium diboride (TiB 2 )-reinforced iron-based composite that had been produced via a mechanical alloying process. Comparison with equivalent unreinforced material indicated that fatigue crack growth resistance in the composite was superior to monolithic matrix material in the near-threshold regime. The composite exhibited relatively low crack closure levels at threshold, indicative of a high intrinsic (effective) threshold growth resistance compared to the unreinforced iron. The lower closure levels of the composite were consistent with reduced fracture surface asperity sizes, attributable to the reinforcement particles limiting the effective slip distance for stage I-type facet formation. The observed shielding behavior was rationalized in terms of recent finite-element analysis of crack closure in relation to the size of crack wake asperities and the crack-tip plastic zone. The different intrinsic fatigue thresholds of the composite and unreinforced iron were closely consistent with the influences of stiffness and yield strength on cyclic crack-tip opening displacements. Cracks in the composite were generally seen to avoid direct crack-tip-particle interaction.

Fatigue and fracture of a 316 stainless steel metal matrix composite reinforced with 25% titanium diboride

“…The production of a planar crack is in agreement with other literature on similar iron-based systems [31]. This is unlike many of the aluminium-based MMC systems, where the crack tortuosity is enhanced in the composite compared to their parent alloy, promoting roughness induced closure resulting in superior threshold growth rates [22].…”

Effect of (Ti:B) atomic ratio on mechanical properties of TiB2–Fe composites “in situ” fabricated via Self-propagating High-temperature Synthesis

“…Similar observations for TiB 2 -reinforced Fe-based composites in a fatigue test were reported by Yang and Sinclair [30].…”

“…MPa [4] can be reached for nearly monophasic TiB 2 material, while the same properties for unreinforced Fe are E= 210GPa and σ 0.2 = 135MPa, respectively [30]. The broken pieces after the compression test revealed cracks propagated in a plane oriented at 45° to the loading direction.…”

Microstructure refinement for high modulus in-situ metal matrix composite steels via controlled solidification of the system Fe–TiB2

“…The tensile elongation was for instance found to be almost halved by the incorporation of just 10 vol.% TiB 2 with a morphology and dispersion comparable to our VIM and ARC experiments [25]. While the exact interaction between soft and ductile metallic matrix and the hard and stiff ceramic particles during co-deformation is complex and still not fully understood [31,32,42,43], the unfavourable ductility can be assumed to be mainly caused by the irregular dispersion of comparatively large and sharp-edged particles acting as stress concentrators. This is corroborated by results from powder metallurgy experiments, where the dispersion of particles is easily controlled, but their morphology and size and thus the bulk materialś ductility are nevertheless not satisfactory [44].…”