Mechanical Properties & Origin of Corrosion in Electrodeposited Nanocrystalline Materials

ChEMS Seminar

Featuring Dr. Indranil Roy
Wireline Services Engineer, Schlumberger
Liberal, Kansas

Location: Engineering Tower, Room 204
Free and open to the public
Refreshments will be provided

Abstract:
The mechanisms of deformation and fracture evolution in fully dense bulk Ni specimens as a function of its grain size, micro to nanocrystalline (nc) were determined from results of uniaxial tensile tests. The effect of strain rate on strength and ductility, corresponding strain rate sensitivity and activation volume were determined from strain jump tests conducted selectively at 393 and 413 K. Transmission electron micrographs of fractured gauge sections of tensile specimens indicated that the deformation mechanism in specimens having an average grain size of 20 nm to be generally dictated by nanovoid formation at grain boundaries (GBs), collective motion of grains, grain rotation, and some twinning. With increase in the grain size the primary mechanism of fracture changed to twinning deformation and some dislocation activity, subsequently to a complete dislocation accommodated deformation in microcrystalline specimens.

Strengthening materials through grain refinement often results in reduced ductility necessitating means to augment their elongation to failure. An approach to simultaneously enhance both strength and ductility by engineering its grains through introduction of annealing twins and increasing the volume fraction of coherent low sigma boundaries was invented.

Corrosion resistance has been demonstrated to be significantly superior in several ED nc-metals and alloys as compared to their coarse grained counterparts. Based on orientation imaging microscopy (OIM) performed to produce electron backscatter diffraction (EBSD) maps, it was observed that GBs in ED nc-Ni are predominantly 3s. The superior corrosion resistance of ED nc-Ni is attributed to this large volume fraction of naturally occurring coherent low sigma coincidence site lattice (CSL) boundaries.

Commercialization of nanocrystalline materials is slowly being initiated in not only engineering but also different other industrial segments. Potential applications in oil and gas, specifically for developing / designing state of the art tools to investigate well bore structure, lithology, (nuclear / sonic) porosity, formation mechanical properties etc. will be discussed.

Applications range from developing cables, coatings, and electronics for wireline and related segments.

Dr. Roy received his Ph.D. degree in materials science engineering from the UC Irvine in 2006.