Third Day Poster Session, 17 June 2010 - NanoTR-VI

P
P,P
P*P
Poster Session, Thursday, June 17
Theme F686 - N1123
Tribological Properties of Al/AlR2ROR3R Nano-composite Surface Layer on Al-based Substrate
1
1
1
Aziz Shafiei ZarghaniP
PSeyed Farshid Kashani-BozorgP
Pand Abbas Zareie-HanzakiP
1
PSchool of Metallurgy and Materials Engineering, University of Tehran, Tehran, Iran
Abstract-Friction stir processing technique was employed for the production of Al/AlR2ROR3R nano-composite surface layer on Al-based substrate;
Nano-size AlR2ROR3R particulates were introduced into the stir zone and dispersed uniformly within it by optimizing the process parameters. Micro
hardness value and wear resistance of the fabricated layer and the untreated substrate were evaluated. The micro hardness value of the surface
nano-composite layer was found to be improved by almost three times of that of the as-received Al alloy. Also, significant improvement in wear
resistance was exhibited by surface nano-composite layer as compared to the as-received substrate. The improved wear resistance of surface
nano-composite layer is attributed to its greater micro hardness value (due to grain refinement of the Al matrix and uniform dispersion of nanosize
AlR2ROR3R particulates).
Metal matrix composites reinforced with hard ceramic
particulates can offer relatively higher strength, stiffness, and
superior wear resistance than those of the un-reinforced matrix
material. Surface modification processes can provide hard
surface with enhanced wear properties while the material
retains its internal ductility and toughness. Friction stir
processing (FSP) is a solid state processing technique to obtain
surface modified/composite layers with fine-grained
microstructure [1-2]. The aim of the present investigation was
evaluation of wear performance of surface nano-composite
layer produced using FSP.
An A6082 aluminium substrate with a thickness of 7 mm
was used. A groove was machined through the center of the
substrate. Nano-size AlR2ROR3R powder with an average particle
size of ~50nm was filled in groove. The FSP unit was a
modified form of a conventional miller machine. A hardened
H-13 tool steel pin was used. A tool rotation rate of 1250 rpm
was used, and the rotating tool was traversed at a speed of 135
mm/min along the long axis of the work piece. Samples were
subjected to various numbers of FSP passes from one to four.
Fig. 1 shows that uniform dispersion of AlR2ROR3R was achieved
using four FSP passes. The dark regions in images are AlR2ROR3R
Figure 1. Secondary electron image of the surface nanocomposite
layer fabricated using four FSP passes at fixed tool
rotation rate and travel speed.
particles which have been verified using energy dispersive
spectroscopy, and the white particles are strengthening
precipitates of A6082 alloy which are dispersed in the Al
matrix. The grain size of Al matrix was refined by the FSP. It
seems that the grain refinement was caused due to dynamic
recrystallization during the FSP. However, the FSP with the
nano-size AlR2ROR3R particles more effectively reduced the grain
size of the A6082 alloy matrix. For example, some matrix
grains of the surface nano-composite layer produced by four
FSP passes were less than 300 nm while the grain size of
A6082 extruded bar was 120m. The surface nano-composite
layer produced using four FSP passes exhibited almost a three
times increment of the hardness value of the parent Al alloy
(312 compared to 110 Hv).
Figure 2. The wear loss weight of the as-received substrate and
surface nano-composite layer fabricated using four FSP passes
as a function of sliding distance.
The wear loss of as-received Al and surface nano-composite
layer fabricated using four FSP passes were measured by a
pin-on-disc wear testing machine against hardened GCr15
steel disc with hardness of about 60 HRC under 40N applied
load. It may be noted that wear loss is considerably reduced
(to almost two or three orders of magnitude) due to FSP
composite surfacing (Fig. 2). The superior wear behavior is
attributed to improved micro hardness in the surface layer
because of the presence of hard ceramic particles and grain
refinement.
In this investigation, Al/AlR2ROR3R surface nano-composite
layer was successfully fabricated by the FSP and tribological
behavior was studied. Hardness and wear resistance of the
surface nano-composite layer produced by four passes is
superior to those of the matrix alloy; this is attributed to
improved micro hardness in the surface layer because of the
presence of hard ceramic particles and grain refinement.
*Corresponding author: fkashani@ut.ac.ir
[1] R.S. Mishra and Z.Y. Ma, Mat. Sci. and Engine. R 50, 1(2005).
[2] R.S. Mishra et al. Mat. Sci. and Engine. A 341, 307 (2003).
[3] Y. Morisada et al. Mat. Sci. and Engine. A 419, 344 (2006).
[4] A. Shafiei-Zarghani et al. Mat. Sci. and Engine. A 500, (2009).
6th Nanoscience and Nanotechnology Conference, zmir, 2010 747