THE STRENGTH AND DUCTILITY OF ELECTRODEPOSITED METALS

96 Pages·02.509 MB·English

by  PRATER, THOMAS A

The Pennsylvania State College
The Graduate School
Department of Mineral Technology
Division of Metallurgy
The Strength and Ductility of Electrodeposited Metals
A Thesis
by
Thomas Allen Prater
Submitted in partial fulfillment
of the requirements
for the degree of
Doctor of Philosophy
August 1950
Approved:
;
■/ ~ /y/ rDiiitvn'i seii o/vnn rof Metallurgy
r? .
Chxef, Division of Metallurgy
TABLE OF CONTENTS
Page
introduction i
EXRSRTHENTAL PR0CEI1RE 9
Interpretation of Bulge ToFt Data in Terms
of Simple Tension 9
Testing Equipment and Testing Procedure 20
Specimen Preparation 26
EXPERIMENTAL RESULTS 31
Strain Distribution in the Bulge 31
Reproducibility Studies $0
Florr Curves 56
Thickness Effects 69
Effect of Basis Metal 81
CONCLUSIONS 86
BIFLIOGRAFHY 89
1
LIST OF FIGURES
la£e
Figure
1* Diagrammatic sketch shewing how a sheet specimen is
deformed in the bulge test. The specimen is shown
at the start of the test at left and partially de­
formed at right. 5
2. Typical curve of significant strain at the top of
the bulge vs. height of the bulge. 16
3, Typical working curve from which the radius of
curvature may be found for a given bulgeh eight. 15
U. Typical working curve from which the ratio of the
instantaneous thickness, t^, to the original thick­
ness, tc, may be determined for a given bulge height. 22
5. Photograph of the bulge test apparatus. The com­
ponents identified with letters are described in
the text. 2U
6. A plot of the distribution of strain in a
hydraulically formed bulge of .003 in. thick
annealed copper. 35
7• A plot of the distribution of strain in a
hydraulically formed bulge of .003 in. thick
annealed brass. 37
8. A plot showing significant strain at the top of
the bulge vs. height of the bulge for annealed
brass• Ul
9. A plot showing significant strain at tho top of
the bulge vs. height of the bulge for annealed
electroformed copper. U3
10. A plot showing significant strain at the top of
the bulge vs. height of the bulge for annealed
electroformed nickel. U5
11. A plot showing significant strain at the top of
the bulge vs. height of the bulge for stainless
steel #302. 1+7
12. Comparison of the relationsnip existing between
significant strain at the top of the bulge and
height of bulge for copper, trass, nickel, and
stainless steel. U9
LIS? OF FIGURES (Cent.)
Figure Page
13 • Average flour curves for annealed electrofcrmed
copper with thicknesses of 0.66 mil, 1.3 mils,
2.9 mils, and 3.6 mils. 58
ll*. Flow curves for two specimens of annealed electro-
formed copper 0.66 mil thick, showing typical
reproducibility. 60
15. Flow curves for two specimens of annealed electro-
formed copper 3.6 mils thick, showing maximum
deviation noted between any two duplicate tests. 62
16. Relationship between height of bulge and radius
of curvature of bulge for tester pictured in
Fig. 5. 65
17• Relationship existing between the ratio of
instantaneous thickness, t±, to the original
thickness, t0, and bulge height. 67
13. Variation of tensile strength of nickel deposits
with thickness of deposit from O.38 mil to 1.12
mil when tested in the stripped condition and as
composite specimens. 73
19. Variation of significant strain tc fracture of
nickel deposits with thickness nf deposit from
O.38 mil to 1.12 mil when tested in the stripped
condition and as composite specimens. 76
20. Variation of significant strain to fracture of
nickel deposits with thickness of basis metal for
two different thicknesses of deposits. 79
A C KN 0W1E DGl.E NT
The author wishes to express his appreciation to Lr. Harold J.
Read, under whose direction this research was conducted, for his
many helpful suggestions during the course of the investigation.
Appreciation is also extended to '/r. S. Skowronski of the
Raritan Copper Works, Perth Ai..boy, New Jersey, for supplying
electrofonred copper and to Dr. John R. Low, Jr. of the Knolls
Atomic Power Laboratory, Schenectady, New York, for supplying
stainless steel.
1
INTRODUCTION
Several recent publications^^,3,U,5,6) are indicative of the
current interest in the determination of the mechanical properties
of electrodeposited metals. It is rather remarkable how little is
known of these properties when one considers the long period of
time during which plated metallic coatings have been in common and
widespread use* Of the various mechanical properties which may be
determined for metals, tensile strength, ductility and hardness are,
perhaps, the most useful from the engineering viewpoint* The hard­
ness of electro deposits exceeding a few mils in thickness may be
measured quite easily with equipment which is readily available, and
the determination of this property is not so badly in need of attention
as are methods for measuring strength and ductility*
Such measurements of strength and ductility as are presently to be
found in the literature have been made on sheet tensile specimens or
tubes which were pulled in simple tension* Almost without exception
the deposits have been much thicker than those commonly used for
decorative or protective coatings or both* There are serious ob­
jections in many cases to the use of thick deposits since it is
well known that the character of the deposit, particularly with re­
spect to grain size and structure, varies markedly with increase in
thickness. There is, therefore, no assurance that measurements on
a thick deposit will be even approximately valid for thin deposits.
The work of Brenner and Jennings(3), for instance, indicates that
thickness has a profound effect on the properties of electrodeposited
nickel. It is not even desirable to use thick deposits to compare
2 •
several deposits on a qualitative basis since the variations caused
by thickness may not be comparable in the specimens.
At once the inquiry arises, why not use thinner specimens? The
answer is simply that it is not very practical to use ordinary sheet
tensile testing methods on specimens which range from a fraction of
a mil to only a few mils in thickness. Some of the difficulties are
set forth in the following paragraphs.
(a) Specimen Preparation — The usual Bheet tensile specimens
must be cut or machined to rather accurate dimensions. Although this
operation can be carried out on very thin materials either by stamp­
ing with a die (such as is used in preparing rubber tensile speci­
mens) or by machining the specimens while they are clamped between
heavy supporting durriy blocks, special equipment or expensive
labor or both are required.
(b) Specimen Grips - The grips available for standard testing
machines are not adapted to the holding of very thin specimens.
Special grips which will hold the specimens can and have been
designed, but they are eo bulky and unwieldy that it is difficult
to mount the specimens in them without distortion.
(c) Alignment - In order to obtain satisfactory results in the
tensile test, particularly with brittle materials (and many electro-
deposits fall in this category), axiality of loading is highly im­
portant. The author is not familiar with any method of checking
axiality of loading which could be applied to specimens even as
thick as £ mils, much less thinner specimens.
(d) Measurement of Elongation and Reduction of Area - The two
criteria of ductility which are normally measured in the tensile test
3.
are percent elongation and percent reduction in area, and of these,
reduction in area is generally accepted as being the more important*
Elongation is measured after fitting together the broken pieces of
the specimen after fracture* The execution of this operation on
material irhich is a mil or a fraction thereof in thickness presents
a well-nigh insuperable problem in technique* The author is not
familiar with any means by which reduction in area can be accurately
and conveniently measured, or for that matter, even closely approxi­
mated.
These matters are sufficient to show that the simple tensile test
is fraught with difficulties so far as thin materials are concerned.
Doubtless many of them could be overcome if necessary, but fortu­
nately there is another test which will yield the desired information.
This is the hydraulic bulge test*
In 1930 Jovignot(7) in an effort to improve the bulge test as
a means of measuring the ductility of sheet metal, proposed that
the hemispherical plunger of the familiar Erichsen cup tester be
replaced by oil under hydraulic pressure* This arrangement, shown
diagramatically in Fig, 1, permits the uniform application of pressure
to all parts of the bulge (which is not possible with a solid,
metallic plunger), and allows the application of well-known equations
relating to the strength of thin shells. It is known^®^ that for
bulges which have a spherical surface
where T is the tensile strength, P the pressure at the moment of
fracture, R the radius of curvature of the bulge, and t the thickness

u.
Fig. 1* Diagrammatic sketch showing how a sheet specimen is deformed
in the bulge test. The specimen is shown at the start of the
test at left and partially deformed at right.