Methanolic environments, stress

Titanium does not stress-crack in environments that cause stress-cracking in other metal alloys, eg, boiling 42% MgCl2, NaOH, sulfides, etc. Some of the aluminum-rich titanium alloys are susceptible to hot-salt stress-cracking. However, this is a laboratory observation and has not been confirmed in service. Titanium stress-cracks in methanol containing acid chlorides or sulfates, red Aiming nitric acid, nitrogen tetroxide, and trichloroethylene. 

For commercially pure titanium, the specific environments to be avoided are pure methanol and red, fuming nitric acid " , although in both environments the presence of 2% of water will inhibit cracking. On the other hand, the presence of either bromine or iodine in methanol aggravates the effect. When it does occur, stress-corrosion cracking of commercially pure titanium is usually intergranular in habit. 

The two principal forms of stress-corrosion failure are (a) hot salt cracking and (Z)) room-temperature cracking, the latter occurring in both aqueous and methanolic chloride environments, and in N2O4. In addition, environmental failures can occur in alloys in direct contact with some liquid and solid metals, and certain gases. 

Many titanium alloys are susceptible to stress-corrosion cracking in aqueous and methanolic chloride environments. 

An example of the growth behavior of crazes in a liquid environment is shown in Fig. 20 which is taken from the results of Williams and Marshall They measured the craze length versus loading time at different Kj-values in PMMA specimens immersed in methanol. The time-depettdent craze-behavior was interpreted in terms of a plasticisation mechanism incorporating the effect of the fluid Due to its porous nature the craze has a very high area to volume ratio so that penetration of the fluid by only a small distance leads to a complete plasticisation of the fibrils and a subsequent drop in the load carrying capacity (t of the fibrils the material effectively behaves as one with a lower craze stress oojc (a < 1). 

R.C. Newman, W. Zheng, R.P.M. Procter, Stress-corrosion cracking of carbon-manganese steeb in methanol-ammonia environments—II. Electrochemical and fractographic studies, Corros. Sci. 

Recently, Brown and Kramer have reported a study of the rise in stress after changing the environment of crazed polystyrene specimens under load from methanol, water or their mixtures to air [12]. They derived an equation relating the change in the surface component of the stress to the surface tension and the craze fibril geometry. 

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