Electron microscope study of boron-doped titanium carbide sample

Venables, J. D.

English

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SOLID STATE STUDIES I N  CERAMIC ALLOYS 
Quarterly Progress Report No. 2 
Contract NASw-lL?9O 
December 1, 1963 - February 28, 1966 
National Aerc@autics and Space Administration 
Washington, D. C. 20546 
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It w a s  suggested i n  the  last report  t h a t  t h e  faults observed i n  
TiC containing 100 p.p.m. of boron probably serve as nucleation sites f o r  
the  "Mondrian" prec ip i ta te  observed by W i l l i a m s  (J. Appl. Phys. 32, 552 
(1961)) i n  more heavily doped (- 0.1% boron) material .  
these precipitates,  and t o  determine what re la t ionship exists between the 
f a u l t s  and precipitates,  m electron microscope invest igat ion has been made 
on samples containing approximately O.l$ boron. 
I n  order t o  iden t i fy  
The thinning techniques which were employed f o r  the pure and l i g h t l y  
doped specimens would not suf f ice  f o r  the heavily doped material, 
t he  samples are thinned by electropolishing i n  a mixed acids  so lu t ion  after 
a dish-shaped cavi ty  has been introduced by j e t  etching. 
doped material, however, the eleczropolishing operation p re fe ren t i a l ly  r e  - 
moved the prec ip i ta tes  f r o m  the thinned sections.  I n  view of th i s ,  a non- 
p r e f e r e n t i a l  methcd of thinning w a s  developed which allowed re ten t ion  of 
the pa r t i c l e s .  
f i l m  w a s  first formed on the sample by anodizing i n  an appropriate solu- 
t ion .  
process was then repeated u n t i l  breakthrough occurred. 
Ordinar i ly  
I n  the  heavily 
Thinning was car r ied  out i n  a two-step process. An oxide 
The film w a s  then removed i n  concentrated hydrofluoric acid.  This 
Tie examination of heavily doped mater ia l  has revealed t h a t  the 
p rec ip i t a t e s  are indeed related t o  the  faults. It is  infer red  from the  
observations that the  growth o r  thickening of the p rec ip i t a t e  p l a t e l e t s  
i s  accomplished by n e w  faults being formed repeatedly on planes p a r a l l e l  
i 
I 
-1 
- 2  - 
t 
and adjacent t o  the o r ig ina l  fau l t s .  Thus it is observed t h a t  the precipi-  
t a t e s  are  bounded by many p a r t i a l  dislocations -- each p a r t i a l  bounding a 
fau l ted  region. 
It w a s  possible t o  obtain a selected area d i f f rac t ion  pa t te rn  from 
one of the precipi ta tes .  
than spots)  as would be expected from a p l a t e l e t  approximately 5 0 A  i n  thick-  
ness. 
the posi t ion of spots that would be produced by the compound TiB2. 
tion, the or ientat ion of the s t reak  pa t te rn  with respect t o  the  matrix pa t te rn  
suggests a very simple ep i t ax ia l  re la t ionship between the TiB2 and T i c  as 
follows: 
The pattern consis ts  of a se r i e s  of st reaks ( ra ther  
0 
The center  of gravi ty  of the s t reaks  however corresponds exact ly  t o  
I n  addi- 
and 
This study indicates t ha t  T i B  prec ip i ta tes  do form i n  boron doped 2 
T i c  and, s ignif icant ly ,  t h a t  nucleation occurs at  dissociated dislocations 
wIu ullc;I=:I~rt. r~ec.erugeneous. The number oT' p rec ip i ta tes  should therefore 
depend upon the or ig ina l  dislocation density.  
2 -  L L - - - - ~  ___- l - . ~  
- - - - - - - - - -  
Erratum: I n  the f i rs t  report it was s t a t ed  t h a t  tk f a u l t s  observed 
i n  T i c  were i n t r i n s i c  i n  nature. Th i s  statement i s  i n  e r r o r ,  A subsequent 
r. 
6 - 3 -  
review of the d i f f rac t ion  dsta indicates that the faults are ac tua l ly  ex- 
t r i n s i c ,  and are  probably formed by the  reaction 
ra ther  than tha t  suggested i n  the report .  
i n  the manuscript sent t o  physica s ta tus  so l id i .  
This e r r o r  has been corrected 


Solid state studies in ceramic alloys Quarterly progress report no. 2, 1 Dec. 1965 - 28 Feb. 1966

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