Brittle Fracture of Iridium. How This Plastic Metal Cleaves?

Abstract

The refractory platinum group metal iridium is the unique material, insomuch as it exhibits simultaneously two controversial mechanical properties such as the high plasticity and the inclination to the brittle transcrystalline fracture. Although iridium has the face-centered cubic lattice, it meets some empirical cleavage criteria despite considerable plasticity. This is the so called "iridium problem" and it is not solved until now. The review is aimed to the discussion of the experimental data concerning the deformation behavior of iridium and the crack growth in iridium single crystals on the microscopic (in the single crystalline samples stretched on air) and nano-(in the thin foils for transmission electron microscopy) levels. It is shown that cracks in iridium thin foils grow like a crack in such ductile metals as aluminum, copper, and nickel. Cracks in the bulk iridium single crystals behave like either a brittle trancrystalline crack, when the resource of crystal plasticity has been exhausted, or a notch in ductile metal, when the plastic deformation of the sample is possible.

Some Features of Cleavage Cracks in Rocks and Metals

“…6f and Ref. [11]). Moreover, the cleavage cracks in iridium single crystal with abraded surface after elongation of 10-18% (Fig.…”

“…The refractory FCC-metal iridium cleaves under tensile stress at room temperature after considerable elongation or macroscopic plasticity [11]. Therefore, the cleavage crack morphology in iridium single crystals under , c -crack in silicon thin foil for TEM at temperature higher than brittle to ductile transition temperature [9]; d -crack in MgO thin foil for TEM [10].…”

“…Examination of the dangerous crack in thin foils of iridium and aluminum under in situ tension in TEM has shown that both cleavable iridium and ductile aluminum show the same fracture mode in thin foil (Fig. 14), namely, the dragon teeth that is intrinsic fracture mode of ductile metals [11]. This finding allowed concluding that the inclination of iridium to the transgranular cleavage is the property of bulk samples of this refractory FCC-metal, while its thin foils for TEM behave like usual FCCmetal.…”