Hydrogen in hot-salt stress corrosion cracking of titanium-aluminum alloys
- PDF / 1,415,011 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 100 Downloads / 266 Views
T h i s p a p e r d i s c u s s e s one a s p e c t of t h i s m e c h a n i s m : the e x p e r i m e n t a l d e t e c t i o n of h y d r o g e n , and i t s e f f e c t s a s a h o t - s a l t c o r r o s i o n p r o d u c t that u l t i m a t e l y c a u s e s c r a c k i n g of t i t a n i u m a l l o y s . A d s o r p t i o n of h y d r o g e n w a s d e m o n s t r a t e d to affect c h a r a c t e r i s t i c s of f r a c t u r e s u r f a c e s . F u r t h e r m o r e , i n j e c t i o n of h y d r o g e n into s t r e s s e d t i t a n i u m a l l o y s by ion b o m b a r d m e n t was shown to c a u s e s i m i l a r c r a c k s by i t s e l f . The a m o u n t of h y d r o g e n r e q u i r e d to i n i t i a t e and p r o p a g a t e t h e s e c r a c k s was e s t i m a t e d f r o m t h e s e t e s t s . DETERMINATION OF H2 AS A CORROSION PRODUCT The volatile corrosion products evolved in heating machined chips of Ti-8AI-IMo-lVor Ti-5AI-2.5Sn alloys coated with a halide salt were analyzed with a Consolidated Engineering Corp. Model 21-103 mass spectrometer. Salt solutions were evaporated to dryness on the c h i p s a t r o o m t e m p e r a t u r e ; s o m e of the s a l t - c o a t e d c h i p s w e r e then h e a t e d to 350~ for 89h r to r e m o v e m o i s t u r e f r o m the s a l t . S a m p l e s of the c h i p s w e r e p l a c e d in a r e a c t i o n v e s s e l , F i g . 1. P r e -
pie Well Cooling Water Mass Spectrometer
Cooling Water
Quartz Crucible
I00 mm
Borosilicate Gloss
30mm Fig. 1--Reaction vessel. VOLUME 1,NOVEMBER 1970-3031
I0
I
I
I
I
Hydrogen Peak
I
400~ (750~
o~ (D
1,0
-
I
NaF 20 M.I HzO
|
NaCI I0/.~1 H20
t
P)
~
o
NaBr 25/J.I H20
C(,500'~
o.J
rY
Nal
I0 ~I H20
c-
=? 0,01
,, q 25
L 50 75 I00 Time, minutes
125
Fig. 3--Hydrogen produced by reaction of hot-salt and titanium.
Fig. 2--Evolution of hydrogen in hot-salt (NaC1) corrosion of Ti-SAI-IMo-IV.
determined amounts of water were added to the s a m ples of specially dried chips but not to the unheated ones. The vessel was partially evacuated so that, at the test temperature with no reaction, the pressure would be one atmosphere. After the reaction vessel was attached to the m a s s spectrometer, the vessel was heated to the test temperature. About 2 pct of the gas in the reaction vessel was removed each time a sample was taken. Both H2 and HCI ~ were identified by m a s s spectrometry as corrosion products in the hot-salt stress corrosion cracking of Ti-AI alloys. The increase with heating time in the concentration of hydrogen in the reaction vessel for two different temperatures is shown in Fig. 2. The hydrogen must have c o m e from a chemical reaction of moist salt with the metal and not from the m e t a l itself. Heating Ti-A1 a l l o y s in a i r at these t e m p e r a t u r e s did not d r i v e off the s m a l l a m o u n t (50 ppm) of H2 c o n t a i n e d in these a l l o y s . M o r e o v e r the total a m o u n t of hydrogen would be only about 0.1 mole pct, Fig. 2. To p r o v e
Data Loading...
