Assessment of Metallographic Preparation Techniques for

Bi2Sr2CaCu2O8+x (Bi-2212) Superconducting WiresSarah Sortedahl, James McFarlane, Mahira Araujo, Joseph Christian, Gavriel DePrenger-Gottfried,

Dr. Amir Kajbafvala, and Dr. Matthew JewellMaterials Science Center ���� University of Wisconsin – Eau Claire

Celebration of Excellence in Research and Creative Activity (CERCA) April 29 – 30, 2015

The authors thank our fellow UWEC students for the printing of this poster via differential tuition (Blugold Commitment).

Experimental Procedure

AcknowledgementsThis project is funded by the U.S. Department of Energy, Office of High Energy Physics grant no.

DE-FG02-13ER42036 and the National Science Foundation MRI award DMR-1428875. The authors

would like to thank the University of Wisconsin-Eau Claire, Material Science Center for the use of

experimental facilities and staff support.

Confocal Microscope

Summary

Introduction Results

Cutting

#1 #2 #3

Mounting

�Bi-2212 composite wires were cut, mounted, ground, and polished.

�We have developed a novel attack polish technique that yields a scratch-free

sample surface.

�To study details of Bi-2212 filament structures, we used a deep etching method

along with SEM and confocal microscope imaging.

�The combination of these sample preparations techniques allow us to assess

the effects of mechanical strain on the Bi-2212 filaments structure

Polishing

Automatic polisherManual polisher

� Bi2Sr2CaCu2O8+x (Bi-2212) is a high-temperature superconductor that can be formed into a round wire

for high field magnets applications.

� A good polishing technique is critical for further microstructural analysis of Bi-2212.

� The brittle Bi-2212 filaments are embedded in a soft Ag matrix. The extreme differences in the hardness

of these two materials makes creating a well-polished specimen difficult.

� Having a smooth sample surface is necessary for visual analysis and to observe various phases, voids,

and cracks inside the material.

� Here, we have developed an effective sample preparation technique to reveal the complex microstructure

of Bi-2212 wire and to efficiently correlate the electrical and mechanical behavior of the material.

Grinding and Polishing

Grinding using SiC Paper�Machines: manual, automatic

�Lubricants: water, dry, ethanol based lubricant

Polishing

�Machines: manual, automatic, vibratory

polisher

�Diamond Suspensions: 9, 6, 3 micron diamond

suspensions; water and ethanol based

�Alumina Suspensions: 1, 0.3, 0.05 micron

alumina suspensions; water and ethanol based

600 grit

SiC papers

800 grit 1200 grit

Bright field

Bright field Dark field

Dark field

Attack Polish

1200 grit800 grit600 grit

Grinding

Manual method using SiC papers

For the grinding steps, it was found that manually grinding, with no lubricant,

and with a paper towel cushion yielded the cleanest, most evenly polished

sample surface.

Alumina Polishing

SEM images showing the Bi-2212 wire surface after polishing with

1 µm alumina suspension in ethanol for 15 minutes

SEM images of a Bi-2212 wire low magnification (left) and high

magnification (right) with almost all of the Ag matrix etched away to reveal

the delicate Bi-2212 filaments.

An attack polish composed of a silver etchant and polishing suspension was

utilized. The silver etchant consisted of H2O2 and NH4OH. This silver etchant

was added to a 0.05 micron alumina 15 weight percent ethanol based

suspension. The ratio of the H2O2: NH4OH: 0.05 micron alumina suspension

was 1:1:50.

The scanning laser confocal microscope is used to assess the 3D morphology of the

composite Bi-2212 filamentary structure and identify the microstructural origin of electric

current-degrading fracture events.

Here, a quantitative height map

is used to evaluate matrix

etching, which is used to reveal

sub-surface crack initiation sites

in the Bi-2212 superconducting

filaments.

Image Analysis

SEM Micrographs of Deep Etched Samples

Vibratory polisher

Optical images showing the polishing quality for an attacked polished

sample in bright field (left) and dark field (right)

SEM images showing a final attack polished sample