LASER PROCESSING OF ORTHOPEDIC BIOMATERIALS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 300

TABLE 9.2. Hardness and Initial Mean Hertzian Contact Stresses (p m ) for Ti - 6Al - 4V ELI and
TNZT 2 B

Alloy Hardness (VHN) p m (GPa) for Si 3 N 4 balls p m (GPa) for SS 440 C balls

Ti - 6Al - 4V
ELI

320 0.95 0.90

TNZT 2B 375 1.01 0.95

TABLE 9.3. Heat Treatment Conditions for Ti - 6Al - 4V ELI and TNZT 2 B for Wear Testing

Alloy Heat treatment

Ti - 6Al - 4V ELI As deposited

Ti - 6Al - 4V ELI 600 ° C/10 hours/FC/Oxide Layer

Ti - 6Al - 4V ELI 600 ° C/10 hours/FC/Oxide Layer removed

TNZT 2B As deposited

TNZT 2B 600 ° C/10 hours/FC/Oxide Layer

TNZT 2B 600 ° C/10 hours/FC/Oxide Layer removed

Zr + 5 wt% Ta + 2 wt% B. The total weight of pre - blended powders per depos-
it was

300 gm. The processing conditions used were similar to those discussed
previously for the Ti - Nb - Zr - Ta alloys. The as - deposited specimens were sub-
sequently characterized using SEM, OIM, and, TEM. Post-wear testing, the SEM
studies of the worn and unworn surfaces were carried out in a FEI Sirion SEM
equipped with an EDS detector. Their indentation hardness (VHN) values for
these samples are listed in Table 9.2. Friction and wear behavior of TNZT + 2B
and Ti-6Al-4V ELI were determined using a Falex (Implant Sciences) ISC-200
Tribometer. This tribometer is a pin-on-disk type confi guration which measures
the sliding friction coeffi cients on planar surfaces. The details of the wear tests
are discussed elsewhere [44]. Also, some of the polished samples were subjected
to separate heat treatments in air before testing, shown in Table 9.3. The heat-
treatments carried out on the TNZT + 2B and Ti-6Al-4V ELI samples had a two-
fold objective, namely to study the infl uence of

∼

precipitates and the surface
oxide layer, formed as a result of the heat treatment on the resulting friction and
wear behavior.
The microstructure of the LENS ™ - deposited TNZT + 2B alloy at different
magnifi cations is shown in the backscatter SEM images in Figure 9.19 [44]. Figure
9.19a shows a low magnifi cation backscattered image of the boride composite
while Figure 9.19b shows a higher magnifi cation view of the microstructure con-
sisting of the coarser primary boride precipitates and the fi ner scale eutectic
boride precipitates dispersed in a matrix. Furthermore, while the fi ner scale eutec-
tic borides exhibit a uniform contrast in the backscatter SEM images, the coarser
primary boride precipitates exhibit strong contrast variations within the same
precipitate suggesting a possibility of compositional variation within the same

α