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This report WI. prepared by E. I. du Pont d. N.mourl.nd Company (Du Pond for the United Stltll Department of Energy under eontr.ct OE-AC08-78SROOOO1 and I, an account of work performed under that Contract. Nelth.r the United Stat ••• the United State. Department of Energy nor Du Pont, nor any of thalr employ"" • mekft .ny wan.nty. IXptltl or 'mpUed. or mumu any. ~, UIbUltv or relPOnsl• , bUllY for thl 8ccuracv. compl.t." .... or ullfulnen of any Info'rrnetlon. apparatus, product. or procel. disclosed h .... ln. or r,present. that itl use ""lit not)ntringe pdvately QWned right.. R.ference her.'n to eny JP8Clfic commerleal product, proc .... or service by trade nam •• mlrk, ",-nufacturer, or otherwise does not 'nflCllnarily constltut. or Imp'V endorsement. recommendadGn, or favoring of same by Du Pont or bV the United Stat •• Government or any agency thereof. The vleM and opinion. of authors expr.ued herein do not necessarily state or reflect those of the Unit~ States Government or any agency thereof.

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Work was continued to determine the mechanism of stress corrosion cracking of titanium alloys exposed to hot chloride salts.Metallographically polished strips of Ti-8Al-1Mo-lV alloy that were stressed to the yield point at 650°F cracked within 3-1/2 hours with a maximum depth of 0.022 inch after 14 days. A heavy oxide film appears to inhibit cracking.Additional evidence was obtained indicating that HCl gas and presumably NaOH are formed during dehydration of sea salt; either or both may be involved in the corrosion.Oxides formed at 900 and l100°F on 8-1-1 alloy are enriched with aluminum. Cracking may involve selective attack of this alloying element by NaOH or NaCl.Of the four principal chlorides in sea salt, NaCl and KCl used individually caused much more cracking than MgCl 2 or CaCl 2 • The difference may be related to the relative strengths of the hydroxides of the cations. Radiotracers 22 Na and 68 Cl in sea salt are being used to study the roles of sodium and chlorine in the corrosion reactions. Traces of both were detected on cracked samples.Transmission electron microscopy studies of the Ti-8Al-lMo-lV alloy were continued.-2 - CONTENTS

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