TECHNICAL NOTE NO. 320 - UNASSIGNED

Library, N.W

SEP 2 9 1965

^ecknical ^iote ^Ho. 321

SPARK PLANING DAMAGE IN COPPER

JOHN J. GNIEWEK, ALAN F. CLARK,

AND

JOHN C. MOULDER

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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technical ^©te 321

ISSUED September 6, 1965

SPARK PLANING DAMAGE IN COPPER

John J.Gniewek, Alan F.Clark, and John C. Moulder

Cryogenics Division - NBS Institute for Materials Research

National Bureau of Standards

Boulder, Colorado

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

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SPARK PLANING DAMAGE IN COPPER

John J. Gniewek, Alan F. Clark, and John C. Moulder

ABSTRACT

The damage to copper crystals, produced by spark planing

operations, has been measured using a dislocation etch pit technique,

The tabulated results show the depth of damage to vary from 0. 7 -

1. 1 mm on the coarsest planing range used, to 0. 2 - 0. 3 mm on the

finest range. Two photomicrographs showing the etch pit density

increase near the spark planed surface are included.

Key Words: copper, damage, dislocations, spark-erosion

in

SPARK PLANING DAMAGE IN COPPER

John J„ Gniewek, Alan F. Clark, and John C. Moulder

In connection with a project to measure the magnetoresistance of

low-resistivity copper, it is necessary to prepare single crystal samples

cut along each of the three major crystallographic directions. A commercial spark cutting machine-:' is used to first cut the three samples from

the same single crystal ingot and then plane the samples to the correct

orientation. To insure that these samples have electrical properties

representative of the bulk material, it is necessary to know the extent of

damage introduced by the spark machining operations and to remove this

amount of material by chemical etching. This note describes the results

of spark cutter damage studies on copper as revealed by dislocation etch

pits.

The method of cutting is spark erosion, caused by a rapid series of

spark discharges between the cutting tool and the work piece. This operation has often been referred to as relatively strain-free machining;

however, very little quantitative data are available defining the extent to

which physical damage is introduced. Cole, Bucklow, and Grigson , using x-ray diffraction and reflection electron microscopy, stated that

their preliminary results on copper and aluminum indicated the damaged

layer to be on the order of a few microns deep. Dislocation etch pitting,

a more direct and more sensitive method for measuring depth of damage,

[2]

was used by Palatnik, et al. in their studies on bismuth, antimony,

and zinc. Their results indicated that the damaged layer, surrounding a

single crater formed by spark discharge, extended to a depth on the order

[3,4]

of a few tenths of a millimeter. Other workers have published

damage values for 3-l/4% Si-Fe and 70:30 brass.

*Servomet Type SMD; Metals Research Ltd. , Cambridge, England

The dislocation etch pit method was used in our work with copper.

An annealed single crystal was first oriented using back- reflection Laue

photographs and then planed with the spark machine to a (111) surface.

The crystal was then etched in dilute HNO for a time sufficient to remove

all traces of damage. The etching time was determined by dislocation

counts at intermediate stages of the nitric acid etch. Etching was terminated when no further reduction in dislocation density was observed.

After etching in nitric acid, the sample was chemically polished for 1-3

minutes in a solution of 40ml HNO , 50ml HC H O and 110ml H PO at

60-70°C. The dislocation etchant (lMFeCl -6H O, 12MHC1, 0. 25 MHBr)

[5]

3 2

was that developed by Young for use on (111) surfaces. The resulting

6 2

background dislocation density was determined to be about 5x10 /cm . The crystal was then spark-planed with the gap voltage set at 180

volts on a plane perpendicular to the (111) plane. Damage from this operation is revealed by an increasing dislocation density approaching the

newly planed surface which appears as the edge in Figs. 1 and 2. The defined depth of damage is arbitrary since the dislocation density increase

is gradual from the crystal interior. It is defined here as the depth at

which the density of dislocation etch pits has increased to the point of

7, 2

being unresolved. This corresponds to a density of about 5x10 /cm . For comparison purposes, an area is marked in Fig. 2 where the average

6, 2

dislocation density was determined to be approximately 5x10 /cm . As

is seen in Fig. 1, the depth of damage is not constant along the length of

the crystal. The damage depths tabulated in Table 1 show a spread corresponding to this variation. The values presented here are in good agree'

[6] ment with unpublished work of Hazzledine who measured the damage in

copper, as revealed by dislocation etch pits, produced by planing on two

ranges (3 and 7) of the same model spark cutter.

Table I

Spark Cutter Damage

Cutting Range Capacitor in Discharge Circuit Depth of Damage (mm)

4 . Z5|x£ 0.7 - 1. 1

5 o 05(if 0.4 - 0. 6

6 . 01f*£ 0.3 - 0.4

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REFERENCES

[1] M. Cole, I. A. Bucklow, C. W. B. Grigson, Brit. J. Appl. Phys.

YL> 296 (1961).

[2] L. S. Palatnik, A. A. Levchenko, V. M. Kosevich, Soviet Phys.

Doklady, _6, 418 (1961).

[3] A. Szirmae, R. M. Fisher, ASTM STP 372, 3 (1964).

[4] L. E. Samuels, J. Inst. Metals 9j_» 191 (1963).

[5] F. W. Young, Jr., J. Appl. Phys. 3_2, 192(1961).

[ 6] P. Hazzledine, private communication.

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