INTRODUCTION 



Thick plate alloy titanium is being considered by the U.S. Navy 

 as potential material for the fabrication of pressure hulls for very 

 deep diving submersibles. Under the sponsorship of the Naval Ship 

 Systems Command and the Deep Submergence Systems Project Off-ice of 

 the U.S. Navy, the U.S. Naval Applied Science Laboratory is develop- 

 ing forming, welding and nondestructive testing techniques for the 

 fabrication of alloy titanium pressure hulls. 



The very large plate sizes that may be required for the fabrica- 

 tion of spherical hulls (150" or more in diameter and 4" or greater 

 in thickness) have yet to be produced and, in addition, approach the 

 limit of mill capacity in the United States for the production of 

 alloy titanium plate. 



In order to provide an alternative method for the production of 

 very large plates, a feasibility study was undertaken to determine 

 whether small plates, joined by welding to produce a large plate, 

 could be hot formed to produce a hemispheric head of the type that 

 might be required for the construction of a pressure hull. 



Earlier work at the Laboratory had shown that thick plate alloy 

 titanium could be welded, out -of- chamber, using gas metal arc weld- 

 ing techniques, both in the spray and short-circuit transfer modes, 

 with appropriate trailing and backing shields. The gas tungsten arc 

 technique had also been used at the Laboratory and by others^'^ for 

 welding thick titanium plate. All three welding techniques were 

 used in the work reported herein. 



MATERIAL 



Material for the study consisted of a rolled plate of Ti-721 

 alloy, 24" wide by 96" long by 3" thick, and 41 pounds of welding 

 wire of two sizes, 0.030 and 0.062 inch diameter, of similar compo- 

 sition to that of the plate. Ti-721 is a near alpha alloy of the 

 composition Ti-7Al-2Cb-lTa with superior fracture toughness (in 

 air) to that of any titanium alloy of comparable strength. Mechan- 

 ical properties of the plate and chemical composition of the plate 

 and welding wire are given in Tables 1 and 2. 



(1) Superscript numbers refer to references at end of report. 



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