Ac. Hollis et Jc. Scully, THE STRESS-CORROSION CRACKING AND HYDROGEN EMBRITTLEMENT OF TITANIUM IN METHANOL HYDROCHLORIC-ACID SOLUTIONS, Corrosion science, 34(5), 1993, pp. 821-835
Pre-exposure tests on unstressed specimens of IMI 125 (low-oxygen, com
mercially pure titanium) in MeOH/HCI solutions revealed that intergran
ular anodic dissolution was occurring. In addition it was also observe
d that for pre-exposure times of 25 h or more, absorbed hydrogen was r
esponsible for an intergranular strain-rate dependent embrittlement wh
en specimens were tested in air, in the strain rate range 5.56 x 10(-4
)-5.56 x 10(-6) s-1 immediately upon removal from the test environment
. If an ageing period of 20 h at 150-degrees-C was inserted in between
removing the specimens from the environment and testing, then the emb
rittlement effect could be eliminated. Constant crosshead speed stress
corrosion tests were also performed in MeOH/HCI in the range of cross
head speeds 166.67 mum s-1 to 1.67 nm s-1. The mode of cracking was ob
served to be predominantly intergranular, with small regions of transg
ranular cleavage evident. Crack velocities of in excess of 1.2 mm h-1
were observed for the intergranular SCC. Additions of selenium, a cath
odic poison, to the test environment produced a significant increase i
n the observed crack velocity, whilst additions of platinum were obser
ved significantly to reduce crack propagation rates and, in some insta
nces, cause complete crack arrest. Significantly less intergranular fr
acture was evident in specimens tested in platinum-containing solution
s compared with those tested in platinum-free solutions. The above obs
ervations supported the argument that hydrogen embrittlement is the me
chanism responsible for the intergranular SCC of titanium in MeOH/HCI
solutions.