Adhesion and cohesion of metals in ultrahigh vacuu

Ham, J. L.

English

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N.R.C. Project No. 42-1-121 
INVESTIGATION OF ADHESION 
AND COHEkION OF METALS 
I N  ULTRAHIGH VACUUM 
F i r s t  Quarterly Progress Report 
September 15, 1961 
John L. Ham 
Contract No. ~ ~ s r - 4 0  
Contract Period - June Pj9  1961 t o  June 30, 1962 
Approved by: 
Wamd H. Keller,  Director of 
Metals and Chemicals Programs 
Reviewed by: 
Office of Research Grants and Contracts 
Code BG9 NASA, 
Washington 25, D.C. 1 J hn V.E. Hansen 
C n t r ac t s  Manager W 
ABSTRACT 
Apparabis for the measurement of cohesion has been modif ied and cal ibrated i n  
preparation. f o r  i n i t i a l  tests on O.F.H.C.  copper by the fracture-rejoin method proposed. 
-1- 
INTRODUCTION 
This is  the first quarterly report  00 t h i s  project  and covers the period 
The preparatory work t o  be described is  based on 15 JuGe t o  15 Septezxiber 1961. 
Proposal No. Q42-1019 of March 2, 1961 with Scope amended by the revised Work State-  
ment i n  Proposal No. Q42-1065A of May 26, 1961. 
The or ig ina l  apparatus and tabular data on preliminary attempts t o  jo in  
specimens of copper were presented fn the proposal. 
h,reak or break and make hot cyl indrical  specimens end t o  end. Force i s  applied by 
heatiag or cooltng the legs  of the yoke; heat is provided by electron bombardment; 
and force neasured by e l e c t r i c a l  transducers. 
It was designed t o  make and 
PFOGRESS 
Apparatus designed for  the measurement of cohesion has been modified afid 
calibrated.  
!!?he trszsduzers used fo r  measuring the force a t  which specimens are  pushed 
kogether mid the force required t o  p u l l  them apart  consis t  of t h in  copper-beryl.iium 
a l loy  bushirrgs with resistance type s t r a i n  gauges glued on with epoxy. 
t i o n  consisted of put t ing four gauges on one bushing ( f u l l  bridge) and none on the 
other and of preloading the bushings with 2500 lbs .  compressive force. The calibra- 
tiori consisted of measuring bridge recorder deflection while loading the assembly 
with a standard t ens i l e  t e s t i n g  machine. 
"he nodifica- 
Sensi t ivi ty  and reproducibi l i ty  are very 
good. 
Molybd.emin aligning webs were instal led t o  maintain accurate alignment of the 
spec-n a f t e r  f rac ture  or  p r io r  t o  joining. 
- 2- 
The specillhen design was changed t o  permit break-make-break-make type operation 
ra ther  than make-break-mke-break. 
ra ther  than a pair ,  but  sharply notched to minimize d is tor t ion  p r io r  t o  f racture .  
such spechen  of O.F.H.C. copper is now i n  place. 
That is, the specimen is  or iginal ly  a s ingle  piece 
One 
The apparatus was set up, baked out, and pumped d a m  but had t o  be re-opened 
twice t o  r epa i r  e l e c t r i c a l  shorts  i n  the high voltage c i r c u i t  used t o  heating of the 
specben  by electron bombardment. The f i lauent  cathodes consis t  of thoriated tungsten 
wires passing through holes i n  the specimen. The shorts  were due t o  use of a ceramic 
insulated w i r e  ("Ceranatemp") which proved inadequate a t  the higher voltages. 
A l l  of the auxi l ia ry  tubes, valves and heaters required f o r  control l ing the 
force by d i f f e r e n t i a l  expansion and contraction of the long s t a in l e s s  s t e e l  tubes 
comprising the yoke a re  i n  place and have been tested.  
The new spechen  design is given i n  Figure 1. Thermocouples a re  spot welded 
t o  it, thoriated tungsten wires pass through the holes and alignment a f t e r  f rac ture  
is mintained by th in  close f i t t i n g  molybdenum webs clamped t.o the s ide  legs. 
The ca l ibra t ion  curves f o r  the force transducers a re  given i n  Figures 2 and 3. 
Figure 2 shows the curve without preloading A force of f 5 lbs. i s  eas i ly  readable. 
and Figure 3 shows the preloaded curve t o  be used. 
assembly . 
Figure 4 is a sketch of the 
PROCEDUFES 
!l%e following ten ta t ive  procedure has been l a i d  out f o r  the first test: 
Have heaters ready i n  side legs. 
te&qerature  without reading force and compensating, if necessary). 
Have a h -  and water ready f o r  middle  leg but no water i n  it. 
1. (Never l e t  the legs or  specimen change 
2. 
-3- 
3. 
4. 
5 .  
6 .  
7- 
8. 
9- 
10 0 
With filaments cold, gradually r a i se  high voltage t o  1500 vo l t s  t o  check 
insulation. Be sure filament is negative with respect t o  ground. 
With 1500 -Jolts on the cathodes, ra i se  current i n  filaments slowly enough t o  
keep pressure below lom6 mm. 
When =.a. meter starts t o  move, ra i se  current i n  top filament u n t i l  10 n. a. 
is obtained, keeping voltage a t  1500. 
Then raise the current i n  the bottom filament u n t i l  20 IG. a. is  obtained. 
Occasionally check that the m. a .  i s  the same f o r  each filament by cooling 
one u n t i l  it no longer e f f ec t s  the t o t a l  m. a. and seeing t h a t  the drop is 
5 6 .  
-6 
Raise the t o t a l  m. a,  as necessary t o  reach 500°C without exceeding 10 mm 
pressure, while heating s i d e  legs  a s  necessary t o  keep the force a t  zero. 
After obtaining the best possible vacuum w i t h  the specimen a t  500°C (may take 
a day o r  two) cool it t o  4OO0C, keeping force a t  zero and the voltage a t  1500. 
Run a i r  through the middle l eg  u n t i l  it is  below 100°C, then water if necessary, 
L77tching t& fayr cps+&pJ7 sz6 +h-o+$ +hS windcx for frac*4?-2. 
If no f rac ture  occurs, heat the side legs  u n t i l  it does. 
Note the  exact time of f rac ture  and immediately blow the water out of middle  
leg, put  a heater i n  it and turn it on f u l l ,  then p u l l  the beaters out of the 
s ide l egs  and put a i r  through them u n t i l  they reach 100°C (then water if 
necessary) b a t  do not l e t  the force exceed that  which was required f o r  f racture .  
When t h i s  force is reached, immediately cool the s i d e  legs  u n t i l  the  force is 
exact ly  one-half of the fracture  force. 
hours, taking frequent readings of all variables. 
first compression) 
Try t o  hold th i s  condition f o r  two 
(Note the exact time of 
-4- 
11. 
12 0 
13 
After two hours repeat the procedure, s t a r t i ng  with i t e m  (g), t o  measure the 
force of cohesion, if  any. Note the exact t h e  of f rac ture  and r e jo in  speci- 
mens immediately by procedure (10) and adjust  compressive force t o  same value 
a s  before, but... 
If cohesive force was high, drop the specben  temperature 50°C. 
(or zero) r a i se  specimen temperature 50°C a s  quickly a s  possible a f t e r  noting 
the cohesive force. 
Hold this condition f o r  two hours,then repeat ,s tar t ing with i t e m  ( 9 ) .  
If it was low 
-5 - 
Figure 1. COHESION TEST SPECIMEN OF THE "BREAK-MAKE" TYPE 
. . I_ , 
. . . . . . - 
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0 
A- cu 
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0 
3 
0 co 0 
I 
I 
I 
cu' 
d 
F 
... . . 
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--- 
0 
;t 
0 0 
=t 
0 co 
0 
n 
[P 
5 
v 
a, 
0 
E 
z 
8 
0 
4 
I 
8 
8 
I 
R 
i3 
3 
&= Expansiorr Members 
(Hollow Legs) 
Negative H i g h  Vcltage 
Thoriated Tuzigsten 
W i r e s  
. _ ~ _  . 
CU-Be Force Balancing 
Bushing 
.. . -. ~ . 
(. . . . . - . 
I 
~ - . - -- __  ~ -~ 
I 
4 
I 
1' 
-. ... 
- .. . . 
._. . 
! 
Figare 4. SCHEMATIC DRAWING OF COHESION !PEST ASSEMBLY 


INVESTIGATION OF ADHESION AND COHESION OF METALS IN ULTRAHIGH VACUUM.

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