Unique Appearance of Lamellar Cleavage Patterns on Fracture Surfaces of Ti-Based Amorphous Matrix Composite

Abstract

In order to improve mechanical properties of Ti-based amorphous matrix composites basically composed of ductile b-Ti dendrites and brittle amorphous matrix by overcoming their inherent brittle nature, their fracture mechanisms should be verified in relation with microstructure, stress intensity factor level, and crack growth rate. In this study, thus, detailed fractographic observations including the unique appearance of lamellar cleavage patterns, which has not been reported in previous studies on conventional metals and alloys, were conducted. According to fractographic results, lamellar cleavage patterns were formed by repeated interruptions of crack propagation on {100} cleavage planes by difference between dendrite orientation and loading direction. Ductile-to-brittle transition phenomenon (ductile dimpled fracture fi lamellar cleavage fracture fi ordinary cleavage fracture in dendrite areas, and vein pattern fi smooth pattern in amorphous matrix areas) occurred with increasing crack growth rate was also plausibly explained by the concept of time required for crack growth as well as dendrite orientation.

Effects of Effective Dendrite Size on Dynamic Tensile Properties of Ti-Based Amorphous Matrix Composites

“…These are called 'lamellar cleavage patterns' in previous studies on Ti-based amorphous composites. [34] Lamellar cleavage patterns originate from dendritic areas, while vein and smooth patterns originate from amorphous matrix regions. [34] The spacing of lamellar cleavage patterns is about 1 lm.…”

“…[34] Lamellar cleavage patterns originate from dendritic areas, while vein and smooth patterns originate from amorphous matrix regions. [34] The spacing of lamellar cleavage patterns is about 1 lm. Lamellar cleavage patterns are parallel inside some dendrites, and the other lamellar patterns are vertically formed.…”

“…According to Jeon et al, [34] the lamellar cleavage fracture is a kind of cleavage fracture modes occurring in bcc materials, and lamellar patterns are spaced in an almost same interval. The orientation difference of dendrites or effective dendrite size importantly influences the appearance of ductile dimpled fracture or lamellar cleavage fracture, and consequently leads to the ductile to brittle transition (ductile dimpled fracture fi lamellar cleavage fracture fi ordinary cleavage fracture) in dendrite areas.…”