Classes of materials used in medicine - Biomedical Engineering Desk Reference - page 244

ASTM F136
This alloy is an alpha-beta alloy, the microstructure of
which depends upon heat treating and mechanical work-
ing. If the alloy is heated into the beta phase field (e.g.,
above 1000 C, the region where only BCC beta is ther-
modynamically stable) and then cooled slowly to room
temperature, a two-phase Widmanst¨tten structure is
produced ( Fig. 3.2.9-12 ). The HCP alpha phase (which is
rich in Al and depleted in V) precipitates out as plates or
needles having a specific crystallographic orientation
within grains of the beta (BCC) matrix. Alternatively, if
cooling from the beta phase field is very fast (as in oil
quenching), a ''basketweave'' microstructure will develop,
owing to martensitic or bainitic (nondiffusional shear)
solid-state transformations. Most commonly, the F136
alloy is heated and worked at temperatures near but not
exceeding the beta transus, and then annealed to give
a microstructure of fine-grained alpha with beta as isolated
particles at grain boundaries (mill annealed, Fig. 3.2.9-13 ).
Interestingly, all three of the just-noted microstruc-
tures in Ti-6Al-4V alloy lead to about the same yield and
ultimate tensile strengths, but the mill-annealed condi-
tion is superior in high-cycle fatigue ( Table 3.2.9-2 ),
which is a significant consideration.
Like the Co-based alloys, the above microstructural
aspects for the Ti systems need to be considered when

Table 3.2.9-5 Plane bending fatigue data for unnotched
1.0-mm-thick unalloyed titanium sheet, tested at 58 cycles/sec
in air (from Disegi, 1990)

Ultimate tensile
strength (MPa)

Sample
condition

Plane bending
fatigue strength
(MPa)

371 Annealed 246

402 Annealed 235

432 Annealed 284

468 Annealed 284

510 Cold rolled 265

667 Cold rolled 314

667 Cold rolled 343

745 Cold rolled 334

766 Cold rolled 343

772 Cold rolled 383

820 Cold rolled 383

Fig. 3.2.9-12 Widmanst ¨ tten structure in cast Ti d Al d 4V, ASTM F136. Note prior beta grains (three large grains are shown in
the photo) and platelet alpha structure within grains. (Photo courtesy of Zimmer USA, Warsaw, IN.)