Titanium stress corrosion cracking

King, E. J., Kappelt, G. F., and Field, C., "Titanium Stress Corrosion Crackings in N2O4, Presented at NACE Conference and 1966 Corrosion Show, Miami Beach, FL, April 1966. 

KE. Weber, J.S. Fritzer, D.S. Cow, and W.C. Gillchriest, Similarities in Titanium Stress-Corrosion Cracking Processes in Salt Water and in Carbon Tfetrachloride, in Accelerated Crack Propagation of Titanium by Methanol, Halogenated Hydrocarbons, and Other Solutions, DMIC Memorandum 228, Defense Metals Information Center, Battelle Memorial Institute, March 1967, p 39... 

Titanium is resistant to nitric acid from 65 to 90 wt % and ddute acid below 10 wt %. It is subject to stress—corrosion cracking for concentrations above 90 wt % and, because of the potential for a pyrophoric reaction, is not used in red filming acid service. Tantalum exhibits good corrosion resistance to nitric acid over a wide range of concentrations and temperatures. It is expensive and typically not used in conditions where other materials provide acceptable service. Tantalum is most commonly used in appHcations where the nitric acid is close to or above its normal boiling point. 

Steel is the most common constructional material, and is used wherever corrosion rates are acceptable and product contamination by iron pick-up is not important. For processes at low or high pH, where iron pick-up must be avoided or where corrosive species such as dissolved gases are present, stainless steels are often employed. Stainless steels suffer various forms of corrosion, as described in Section 53.5.2. As the corrosivity of the environment increases, the more alloyed grades of stainless steel can be selected. At temperatures in excess of 60°C, in the presence of chloride ions, stress corrosion cracking presents the most serious threat to austenitic stainless steels. Duplex stainless steels, ferritic stainless steels and nickel alloys are very resistant to this form of attack. For more corrosive environments, titanium and ultimately nickel-molybdenum alloys are used. 

Resistance to stress-corrosion cracking Commercially pure titanium is very resistant to stress-corrosion cracking in those aqueous environments that usually constitute a hazard for this form of failure, and with one or two exceptions, detailed below, the hazard only becomes significant when titanium is alloyed, for example, with aluminium. This latter aspect is discussed in Section 8.5 under titanium alloys. 

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 stress-corrosion cracking hazard for titanium alloys containing aluminium is significantly higher than that obtaining for commercially pure titanium, and in addition to stress-corrosion cracking in methanol and red... 

Sandoz, G., In Stress Corrosion Cracking in High Strength Steels and in Titanium and Aluminium Alloys, Ed. B.F. Brown, Naval Research Laboratory, Washington, pp. 79-145, (1972)... 

Stress-corrosion Cracking of Titanium, Magnesium and Aluminium Alloys... 

Stress-corrosion cracking occurs in titanium alloys in a number of environments, although the number of failures that have occurred under service conditions is very small. Because of the widespread use of titanium alloys in aeroplanes and space vehicles and their increasing use in marine applications it is important that the possibilities of service failures should be removed. As a result a considerable and increasing amount of work has been done on this subject over the last decade as indicated in a recent extensive survey. ... 

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

Stress Corrosion Cracking of Titanium, ASTM STP 397, ASTM, Philadelphia (1966)... 

In common with many of the alloy-environment systems described so far, if the alloy is not susceptible to stress-corrosion cracking under constant stress or stress intensity, then little or no effect of environment on fatigue crack growth is observed. In these cases, frequency, R ratio and potential within the passive or cathodically protected ranges for titanium have no effect on growth rates. 

Stress-corrosion cracking (Section 8.10) New metal/environment combinations which produce stress-corrosion cracking are continually being found. Combinations discovered in service in recent years include titanium in red fuming nitric acid carbon steel in liquid anhydrous ammonia and in... 

Titanium is immune to chloride induced stress-corrosion cracking but more expensive than type 300 series stainless steels. 

Titanium is resistant to nitric acid from 65 to 90 wt % and in dilute acid below 10 wt %. It is subject to stress-corrosion cracking above 90 wt %, and it is not used in red fuming acid service because of the potential for a pyrophoric reaction104. 

If chlorinated solvents are used with titanium surfaces, they must be completely removed prior to bonding. Chlorinated solvents give rise to stress corrosion cracking in the vicinity of welds. Welding of titanium often occurs in the same plant as adhesive bonding, and it is sometimes done on the same parts. So the best practice is to avoid the use of chlorinated solvents completely. Several airframe manufacturers that fabricate titanium alloys no longer permit the use of chlorinated solvents. 

Majority of titanium alloys are resistant to SCC stress-corrosion cracking has been observed in absolute methanol, red fuming nitric acid, nitrogen tetroxide, liquid, and metals of Cd and Hg and halide media67... 

The environments, along with the cracking modes of zirconium and titanium, are given in Table 4.88. It is obvious from the table that zirconium alloys are susceptible to stress-corrosion cracking in a variety of environments. It is necessary to subject the weld to heat treatment in order to lower the stress in the weld. The most serious problem encountered in the nuclear applications is delayed hydride cracking in addition to stress-corrosion cracking, particularly in Zr-2.5% Nb alloy. 

M.J. Blackburn, W.H. Smyrl, J.A. Feeney and B.F. Brown (eds.), Stress-Corrosion Cracking on High Strength Steel and in Titanium and Aluminum Alloys, Naval Research Laboratory, Washington, DC, 1972, pp. 245-363. 

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