R TCP - Washington State Universityday.mme.wsu.edu/day2014/posters/SFB 2014 Poster...Tribofilm...
of 1
/1
Embed Size (px)
Transcript of R TCP - Washington State Universityday.mme.wsu.edu/day2014/posters/SFB 2014 Poster...Tribofilm...
-
Γ (1
11
)
HA
P
HA
P
HA
P
HA
P
Γ (2
20
)
Γ (2
00
)
ε (1
01
)
CoCrMo-0%CaP
CoCrMo-3%CaP
R TCP
Laser Processed CoCrMo-Calcium Phosphate Composites for Articulating Surfaces Himanshu Sahasrabudhe, Thomas Gualtieri, Susmita Bose and Amit Bandyopadhyay
W. M. Keck Biomedical Materials Research Laboratory, School of Mechanical and Materials Engineering
Washington State University, Pullman, WA 99164 USA. E-mail: [email protected]
Laser Engineered Net Shaping
Laser Engineered Net Shaping (LENSTM) is a additive manufacturing technique in
which a powdered material is simultaneously melted and deposited by a high power
Nd:YAG laser. The powder is carried through Argon carried gas. Successive layer wise
deposition of the material finally yields a complete 3D part. The design is specified through
a CAD software.
CoCrMo is a widely used material for implants. CoCrMo is hard and shows good wear and corrosion resistance. However, release of Co and Cr ions in vivo is a serious concern. Various attempts have been
made to reduce metal ion release from CoCrMo. In this research, we have used Laser Engineered Net Shaping (LENSTM) to form a meal-ceramic composite layer by the addition of calcium phosphate to
CoCrMo. The objective of our study is to measure the effect of CaP on the tribological properties of CoCrMo. Our hypothesis is that CaP will act as a solid lubricant and reduce metal ion release from CoCrMo
during articulation. If successful, these composites hold the potential to considerably improve the life of metal-on-metal implants without altering the material significantly.
Acknowledgement
References
Authors would like to acknowledge the financial support from the Life Sciences Discovery
Fund (LSDF) Authority, Washington.
Processing of CoCrMo-CaP by LENSTM
Three different compositions: CoCrMo-0%, 1% & 3% by weight of Hydroxyapatite was
premixed.
Processed at a power of 425W on SS410 base plate
Each sample was ~15mm thick with layers each 0.15mm thick
Cross section SEM and top surface XRD analysis was done to verify phases.
50 µm 50 µm
CoCrMo-3%CaP structure appears more discontinuous as compared to the CoCrMo-0%CaP
structure. Structure of CoCrM-0% shows more equiaxed grained with random orientation.
Both 1% and 3% composites do not show CaP particles.
50 µm
Addition of CaP to
CoCrMo alloy stabilizes
the ε phase.
Γphase of CoCrMo is lost
after CaP addition and
LENSTM processing.
HAP though not seen from
SEM images, is prominent
in the diffraction pattern.
XRD Analysis of CoCrMo-CaP Composites
Hardness Testing of CoCrMo-CaP Composites
Sample Vickers Hardness
(HV0.1)
CoCrMo-0%CaP 564±10
CoCrMo-1%CaP 568±7
CoCrMo-3%CaP 570±8
Addition of CaP to
CoCrMo does not
change the hardness of
the CoCrMo alloy.
Wear Testing of CoCrMo-CaP Composites
Linear Reciprocating Wear Tests performed in DI Water Medium
Short distance wear test for 1km and long distance wear test for 3km
Constant Load of 5N, constant speed of 1200mm/min and 10mm long wear track
CoCrMo-0%CaP CoCrMo-3%CaP
500 µm 500 µm
Wear Track
Wear track in DI medium for CoCrMo-3%CaP sample is not as wide and as deep
as the wear track for CoCrMo-0%CaP tested under the same conditions.
Wear track is difficult to locate on SEM because of its small depth and width.
Sample Wear Rate x 10-5
(mm3/Nm)
CoCrMo-0%CaP 3.02±0.32
CoCrMo-1%CaP 1.71±0.29
CoCrMo-3%CaP 1.02±0.37
Wear rate decreases by
almost 3 times by the
addition of 3%CaP to
CoCrMo alloy and LENSTM
processing.
Addition of CaP to CoCrMo alloy
does not reduce the coefficient of
friction; it slightly increases it.
All samples achieve a steady state
at a distance of ~100m, after which
the COF is more or less the same.
CaP does not reduce friction but
reduces surface wear.
CoCrMo-3%CaP CoCrMo-0%CaP
Formation of Tribofilm During Wear
High magnification SEM reveals the formation of a tribofilm in the CoCrMo alloy samples’
wear tracks with CaP addition. It was not seen on the wear track of CoCrMo-0%CaP.
50 µm
Tribofilm
CoCrMo alloy underneath
Tribofilm was discontinuous for
1km wear track of CoCrMo-3%CaP
samples.
It was relatively more continuous
towards the center of the wear track
than towards the edges.
CoCrMo-3%CaP- 1km Wear Distance
20 µm
CoCrMo-3%CaP- 3km Wear Distance
There was full coverage of the tribofilm after
longer wear distance of 3000m.
Development of tribofilm during wear is time
dependent. It may be absent or highly scattered
during initial phases of wear. It becomes more
continuous with time. Thus wear rate reduces with
distance.
Tribofilm After Etching The Wear Tracks
50 µm 40 µm
Partially Etched Wear Track Deep Etched Wear Track
Partial etching of the
wear track removed
some of the tribofilm
from the surface.
Complete etching
shows the
microstructure of the
wear track, completely
etching out the
tribofilm.
Summary
1. Addition of CaP to CoCrMo alloy has found to reduce the wear in DI medium.
2. Addition of CaP does not however decrease the coefficient of friction of CoCrMo alloy. CaP
seems to be the preferentially wearing phase that prevents the wear of the alloy.
3. A distinct tribofilm forms during wear. It is discontinuous in shorter distances of wear and
more continuous for longer distances of wear.
1. R. Pourzal et al., Wear (2011), 271-9-10, pp 1658-1666.
2. S.A. Dittrick et al., MSE ‘C’(2011), 31-4, pp 809-814.
2014 Annual Meeting
in Denver, CO.
mailto:[email protected]
