Abstract
For decades Ti-6Al-4V has been the workhorse alloy for aerospace sheet applications due to its good balance of properties and the known ability to hot roll it with relative ease. Sheet of Ti-6Al-4V is made by hot pack rolling, which is a costly and time consuming process, due to the alloy having insufficient room-temperature workability to support significant cold reduction or forming. Consequentially, Ti-6Al-4V is not typically offered in foil gauges, since the direct product of hot pack rolling contains an undesirable surface finish and insufficient gauge control. Hot pack rolling also limits the maximum sheet size and annual capacity. As a world leader in advanced sheet alloys of titanium, nickel, cobalt, and specialty stainless steels, ATI is developing new titanium alloys with improved strength compared to Ti-6Al-4V that take advantage of a recent understanding of cold workability in high-strength alpha-beta titanium. These α+β alloys exceed Ti-6Al-4V strength while being highly cold formable. Cold rolling via coil processing also enables longer lengths of sheet with significantly improved gauge control and surface finish. Results from pilot scale ingots will be presented upon, including final properties of these unique alloys and microstructure-property correlations developed through modelling.
Highlights
Alpha-beta titanium alloys represent the largest segment of alloyed titanium used in the aerospace industry
This results from the lower alloy content and price associated with these alloys over beta-titanium alloys, as well as the balance of properties they generally offer
These alloys do demonstrate a higher strength in the transverse direction, they demonstrate equivalent or better elongations and work hardening in that direction. While this is not typical for titanium sheet produced by hot pack rolling, it is more common in aerospace aluminium alloys that are produced on coils, rather than individual sheets
Summary
Alpha-beta titanium alloys represent the largest segment of alloyed titanium used in the aerospace industry. In addition to titanium alloys, ATI produces sheet in nickel, cobalt, and stainless steels using hot strip rolling and cold rolling processes. In addition to obvious performance goals, the use of cold rolling equipment enables greater gauge control, which can benefit design weight, and significantly increased manufacturing capacity over pack-rolling processes. For these reasons, ATI has continued to develop cold rollable, high strength titanium alloys; three of which will be described . Mechanical testing of the alloys consisted of tensile testing in the as-worked material at slab, plate, and sheet conditions, as well as following several heat treatments in laboratory furnaces. Samples were universally mounted in conductive phenolic compound, polished through colloidal silica, and imaged in an un-etched condition
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