Microstructure, mechanical properties, and fracture mechanism of As-cast (Ti0.5Cu0.25Ni0.15Sn0.05Zr0.05)100−x Mo x composites

Abstract

Copper mold cast cylinders of (Ti 0.5 Cu 0.25 Ni 0.15 Sn 0.05 Zr 0.05 ) 100-x Mo x composites are prepared. Addition of Mo in the bulk glass-forming alloy induces the formation of a dendrite/matrix composite. For 3-mm-diameter cylinders, the matrix exhibits a homogenous ultrafine microstructure for Mo content of 2.5 at. pct, and a fine eutectic microstructure for 5 at. pct Mo. For 5-mm-diameter cylinders, the matrix exhibits a dendritic microstructure for 2.5 at. pct Mo, and exhibits a coarser eutectic microstructure for 5 at. pct Mo. Despite the formation of a dendrite/nanostructured matrix composite in the cylinders, the quenched surface layer with a nanoscale grain size dominates the deformation and fracture of the 3-mm-diameter cylinders. More than 56 vol pct quenched layer leads to a distensile fracture mode and the samples exhibit high fracture strength and high Young's modulus but low ductility. For 5-mm-diameter cylinders, the composite microstructure becomes dominant due to its more than 64 vol pct volume fraction leading to a cone-shaped fracture surface. The samples exhibit lower yield strength and lower Young's modulus but better ductility compared to the 3-mm-diameter cylinders. The mechanical behavior of the Mo-bearing composites strongly depends on the microstructural homogeneity and casting defects formed upon solidification.

Effect of Nb content on the microstructure and mechanical properties of Zr–Cu–Ni–Al–Nb glass forming alloys

“…Therefore, the higher the volume fraction of the dendrite phase, the larger is the plastic strain. However, the plasticity does not occur for this alloy [19]. The embitterment of the as-cast alloys might be caused by the microstructure difference between the center part and the peripheral part of the materials.…”

Brittleness of Zr-based bulk metallic glass matrix composites containing ductile dendritic phase

“…From the general profile of the fractured sample shown in Fig. 9(a), the materials exhibits basically brittle fracture features and seems to follow a distensile mode by which the samples break or form multiple fracture surfaces [18][19][20]. In the central region of the fracture plane shown in Fig.…”

Effect of Sn on microstructure and mechanical properties of Ti-base dendrite/ultrafine-structured multicomponent alloys

“…[21] Since no dendrites exist in the quenched layer, the ultrafine structure in the layer dominates the fracture process and exhibits brittle fracture features without plasticity. For the present alloy A, the as-cast 3-mm-diameter samples exhibit a shear fracture mode with about 2 pct plasticity, revealing the significant enhancement of the plasticity by the dendritic phase dispersed throughout the entire microstructure ( Figure 1).…”