Microstructural evolution and strength variability in microwires

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 652; pp. 239 - 249
• Main Authors: Agepati, S., Ghosh, P., Chokshi, A.H.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.01.2016
• Subjects: Fracture; Fracture mechanics; Grains; Microstructure; Microwires; Shear; Shear band; Slip bands; Strength; Weibull; Weibull modulus; Wire; Microwires; Fracture; Weibull; Shear band; Strength
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2015.11.086

Tensile experiments on cold-drawn Ni microwires with diameters from ~115 to 50µm revealed high strengths, with significant strength variability for finer wires with diameters less than ~50µm. The wires showed pronounced necking at fracture. The coarser wires with diameters >50µm exhibited conventional ductile cup-cone fracture, with dimples in the central zone and peripheral shear lips, whereas finer wires failed by shear with knife or chisel-edge fractures. Shear bands were observed in all samples. Further, through- section microscopy of selected fractured samples revealed that the shear bands did not go across the enitre specimen for the coarser wires. The shear bands led to grain fragmention, with a reduction in grain aspect ratio as well as rotations away from the initial orientations. The strength data were analysed based on a Weibull approach. The data could be rationalized in terms of failure from volume defects in coarser wires, with a high Weibull modulus, and from surface defects in finer wires, with a low Weibull modulus and greater variability.