Ductile-brittle behavior at the (110)[001] crack in bcc iron crystals loaded in mode I

Fracture experiments performed at room temperature on four test samples made of Fe3wt.%Si single crystals with an edge crack (110)[001] (crack plane, crack front) showed approximately 45 degrees deflections of the crack from the initial crack plane (110). This behavior appeared to be independent on loading rate Fractographic analysis confirmed that the cracks were deviated along {100} planes and the fracture was accompanied by dislocation slip and by twinning. 3D simulations at 300 K by molecular dynamic technique in bcc iron with edge cracks of equivalent orientation indicated that the crack itself could contribute to understanding of this behavior by three processes: twinning on oblique {112} planes, which hindered growth of the original crack, and by emission of dislocations on oblique {011} and {123} planes. which led to separation of the {100} planes and might cause decohesion and subsequent cleavage fracture along the mentioned planes. (C) 2009 Elsevier Ltd. All rights reserved.