Tech Briefs

Preliminary results show promise for fabricating lightweight, strong structures.

An experimental study of vacuum brazing of titanium and of the effects of changes in brazing alloys and brazing process conditions has been performed. [As used here, “titanium” signifies both commercially pure titanium and an alloy nominally consisting of 90 weight percent of titanium, 6 weight percent of aluminum, and 4 weight percent of vanadium (commonly abbreviated “Ti-6Al-V”).] The knowledge gained in this study is intended to contribute to development of capabilities for fabricating titanium structures in circumstances in which welding — heretofore the typical method of joining titanium — cannot be performed because access is limited or adjacent nonmetallic components would be harmed. There is a particular need for such knowledge to enable fabrication of lightweight, durable titanium- based structures for armored vehicles. Examples of such structures include standard lightweight plate structures, titanium components encapsulating ceramics, and panels that comprise pyramidal frame cores sandwiched between face sheets.

This Sandwich Structure was fabricated by brazing a pyramidal frame core to face sheets. The face sheets and core were made of commercially pure titanium. The face sheets were 1.22 mm thick; the core members were fabricated from 0.61-mm-thick sheets. The brazing alloy was 37.5Ti-37.5Zr-15Cu-10Ni (proportions in weight percent).

The experiments performed in this study are summarized as follows:

  1. Blocks of Ti-6Al-4V having dimensions of 75 by 75 by 50 mm were joined by tungsten/ inert-gas welding around the edges, followed by hot isostatic pressing (HIP) in argon at a temperature of 900 °C and a pressure of 103 MPa.
  2. Blocks of Ti-6Al-4V were joined in a vacuum by diffusion bonding, using a foil of a brazing alloy comprising 70Ti- 15Cu-15Ni (proportions in weight percent) placed around the edges. In each case, the block-and-foil assembly was heated to a temperature of 1,000 °C under a deadweight equivalent to a pressure of about 15 kPa, followed by HIP as in experiment 1 described above.
  3. Blocks of Ti-6Al-4V were brazed and subjected to HIP as in experiment 2, except that prior to heating, the foil was placed over the entire Ti-6Al-4V bonding surface.
  4. Blocks of Ti-6Al-4V were brazed as in experiment 3, omitting the HIP step.
  5. Panels comprising commercially pure pyramidal frame cores sandwiched between commercially pure titanium face sheets (see figure) were fabricated in a process that included a multistep thorough cleaning, application of a zirconium- rich titanium-brazing paste/tape to the face sheets, stacking the face sheets to the cores (with the brazing paste/tape faces in contact with the cores) in the sandwich configuration, and heating in a vacuum furnace at about 900 °C under a deadweight equivalent to a pressure of 50 kPa.