Notas / Notes - Active Congress.......

MARTES / TUESDAY
16
The results presented show that the hand polished CoCrMo
alloy caused the higher UHMWPE wear of the acetabular
cups, when tested with the HJS. The CoCrMo coating causes
the least UHMWPE wear, while the mass finished CoCrMo
alloy causes an intermediate UHMWPE wear.
The wear zones were observed at high magnifications with
a SEM to observe the very fine microstructure remaining
after the wear tests. The SEM observation was focused in
Table 1. Chemical composition of the forged CoCrMo alloy (%)
the formation of UHMWPE particles that detach from the
worn surface producing wear debris. The border zones in
all cups have a similar ripple-like microstructure; there is
almost no UHMWPE particle formation in this wear zone.
For all the cups observed, the microstructure of the polar
zones appears likely to be ripple-like but less accentuate
than in the border zone. On the other hand, the UHMWPE
particle formation could not be seen.
Element Cr Mo Mn Ni Si Fe C N
Balance 26-30 5-7 max 1 max 1 max 1 max 0.7 max 0.35 max 0.25
Table 2. Roughness and hardness of each material tested
Material Roughness Ra Hardness
(µm) (HVN)
Hand-polished 0.03±0.01 673±21
Mass-finished 0.05±0.01 840±62
CoCrMo coating 0.10±0.01 884±28
Table 3. Test conditions of the HJS wear tests
Test parameter Value
Type of motion Multidirectional (BRM)
Contact geometry Real (as in a hip joint replacement)
Frequency 1.23 Hz (810 ms/cycle)
Contact area Real, as in hip prostheses
Load applied 1000 N (102 Kg)
Test length 3 million cycles (at intervals of
333,333)
Lubricant 30 mg/ml initial protein content
Temperature Room
Acetabular UHMWPE GUR1020
component (cup)
Femoral CoCrMo forged (hand polished)
component (head) CoCrMo forged (mass finished)
CoCrMo forged with a CoCrMo coating
Table 4. HJS wear tests: UHMWPE cups wear rates.
Wear rate R 2
(mm 3 /106 cycles)
Hand polished 90 0.998
Mass finished 68 0.993
CoCrMo coating 44 0.998
Figure 1. Motion/loading configuration of the HJS wear test machine.
Figure 2. Average wear losses of the UHMWPE cups in the HJS wear
tests.