Unique Appearance of Lamellar Cleavage Patterns on Fracture Surfaces of Ti-Based Amorphous Matrix Composite
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RECENTLY, advances in bulk amorphous alloys have been remarkably made by developing amorphous alloys with high glass-forming ability,[1–7] but there are problems to be solved, typical one of which is brittle fracture.[8,9] In order to overcome this brittle fracture, development activities on composite-type alloys by homogeneously distributing ductile crystalline dendrites in Zr- or Ti-based amorphous matrix have been actively performed.[10–16] In order to systematically understand and improve mechanical properties of these amorphous matrix composites, fracture mechanisms should be verified in relation with composite microstructures basically composed of ductile dendrites and brittle amorphous matrix.[17–19] A simple way widely used to investigate fracture mechanisms is a phenomenal observation of fractured surfaces, the results of which have been mathematically quantified CHANGWOO JEON, Postdoctoral Researcher, and CHOONGNYUN PAUL KIM, Research Professor, are with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang 790-784, Korea. BYEONG-CHAN SUH, Postdoctoral Research Associate, is with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang 790-784, Korea. HYOUNG SEOP KIM and SUNGHAK LEE, Professors, are with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, and also with the Materials Science and Engineering, Pohang University of Science and Technology. Contact e-mail: [email protected] NACK J. KIM, Professor, is with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, and also with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology. Manuscript submitted October 18, 2014. Article published online March 18, 2015 2506—VOLUME 46A, JUNE 2015
to effectively describe mechanical properties. Studies on detailed fracture mechanisms such as direct observation of crack initiation and propagation processes[17–19] or deformed microstructures beneath fractured surfaces[19–22] have also been conducted. Lately, the scope of understanding of fracture mechanisms is extended as electron microscopes are more widely used.[23,24] In spite of these efforts, many difficulties still remain to be addressed to correlate microscopic fracture mechanisms with macroscopic mechanical properties and to systematically analyze and predict them. In many cases, microscopic fracture modes are occasionally varied with loading directions and modes of applied stresses or crack propagating rates,[25,26] and ductile-to-brittle transition phenomena can occur even in the same material or temperature,[27,28] but only limited information is available. In the present study, therefore, fracture modes of a Tibased amorphous matrix composite containing ductile dendrites and amorphous matrix were investigated in relation with stress intensity factor level and crack growth rate using an in situ loading stage installed inside a scanning electron microscope (SE
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