Supplementary Information
Controlling phase growth during solidification by nanoparticles
Lian-Yi Chen,a Jia-Quan Xu,b Xiao-Chun Lia*
a
Department of Mechanical and Aerospace Engineering, University of California at Los Angeles,
Los Angeles, California 90095, USA
b
Department of Materials Science and Engineering, University of California at Los Angeles, Los
Angeles, California 90095, USA
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Section 1. Experimental procedure
Melt preparation and nanoparticle dispersion: Sn-6.8Al alloy melt was prepared by melting
commercial pure tin (99.9%, Alfa Aesar) and aluminum (99.5%, AA1350) in an alumina crucible
using an electrical resistance furnace. TiC0.7N0.3 nanoparticles (shown in Fig. S1(b), with a
diameter of less than 150 nm and an average diameter of about 80 nm, from Sigma-Aldrich)
were fed and dispersed into the molten metal by an ultrasonic cavitation based method. Figure S2
(a) illustrates the schematic of the experimental setup for the melt preparation and ultrasonic
processing. The resistance heating furnace was used to heat Sn-6.8Al melt to designed
temperature (973 K) in an alumina crucible with a diameter of 36 mm. The inert gas protection
system was used to protect the melt and nanoparticles from oxidation by injecting argon through
two nozzles. The nanoparticle feeding system was used to feed nanoparticles into the melt. In
this study, a double-capsulate feeding method was used. Nanoparticles were wrapped with
0.0127 mm thin Al foil (alloy 1000), and then the Al foil was rolled into a rod shape with a
diameter of about 6 mm (making the first capsule). The Al foil rod, containing the nanoparticles,
was wrapped again with another thin Al foil (alloy 1100) with a dimension of 355.6 mm x 152.4
mm x 0.0254 mm (making the second capsule). The second Al foil would make the nanoparticles
discharge into the melt gradually, resulting from a gradual melting of the thicker wall of the
capsule. The ultrasonic processing system consists of an ultrasonic probe, booster, and transducer.
A ultrasonic probe made of niobium alloy C103 with a diameter of 12.7 mm and a length of 90
mm was attached to a booster (Sonicator 3000, Misonix Inc.), which was mounted in a
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transducer working under a frequency of 20 kHz and a maximum 600 W power output. When the
Sn-6.8Al alloy was melted in the alumina crucible, the tip of the niobium ultrasonic probe was
inserted about 6 mm in depth into the melt. Ultrasonic vibration with a frequency of 20 kHz and
a peak-to-peak amplitude of 50 um was generated from the transducer. Then the preheated
nanoparticles (at 423 K for one hour) were added into the melt with the double-capsulate feeding
method during ultrasonic processing. Each double-capsulate can carry about 1 vol.% of
nanoparticles into the melt. It took 15 minutes to disperse the nanoparticles released from one
capsulate by the ultrasonic processing. After feeding and dispersing nanoparticles at 973 K, the
ultrasonic probe was lifted out of the melt.
Solidification: After ultrasonic processing, the ultrasonic probe was lifted out of the melt.
Then the crucible was taken out of the furnace. The Sn-6.8Al melt with nanoparticles was cooled
down inside the crucible in air (as shown in Figure S2 (b)). For comparison, the pure Sn-6.8Al
alloy was also prepared under the same conditions (except no nanoparticles). We measured the
cooling rate by insert thermocouples inside the melt during cooling. The cooling rate before
solidification is about 1 K/s. To get various high cooling rates, we cast the melt into wedge
copper mold (as shown in Fig. S2 (c)). The cooling rates at different locations are calculated
from the thickness of the sample based on an empirical equation.
Structure characterization: After solidification, the morphology and size of the primary Al
phase was studied by FESEM (field-emission scanning electron microscopes, Zeiss LEO 1530)
by using SE2 detector. The structure of Al phase was studied by electron backscatter diffraction
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(EBSD). The nanoparticle distribution was investigated by FESEM by using in-lens detector. In
order to avoid the interference of the polishing powder on observation of the nanoparticles we
put in, the SEM sample for nanoparticle distribution study was cleaned by low angle ion milling
for 30 minutes with milling parameters of 4 kV voltage, 4 mA current, 15o milling angle, and
360o stage rocking angle. After ion milling, only embedded TiCN nanoparticles remain on the
sample, which was confirmed by electron energy-dispersive X-ray spectroscopy (EDS). To
reveal the dendrite structure more clearly, the samples are milled for 24 hours to preferentially
remove Sn matrix.
Section 2. Contribution of inoculation
In order to evaluate the contribution of inoculation on morphology modification of primary
Al phase, we investigated the Sn-6.8Al with low volume fraction of TiCN nanoparticles. For
inoculation, only small amount of nanoparticles is needed. Here we put 0.2 vol.% TiCN
nanoparticles into Sn-6.8Al alloy, which is enough for inoculation of primary Al phase. The SEM
image in Fig. S3(a) shows that the Al phase still forms dendrite structure during solidification in
pure Sn-6.8Al alloy. However, the size of dendrite structure is smaller than that observed in pure
Sn-6.8Al prepared under the same conditions. Zoom-in of the squared region in Fig. S3(a) is
shown in Fig. S3(b). TiCN nanoparticles in center of the dendrite structure were found, as shown
in Fig. S3(c). It is highly possible that these nanoparticles serve as nucleation agent during
solidification. After nucleation, the Al phase still grows to dendrite structure during further
cooling.
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A ssessed A l - Sn p h ase d i ag r am .
(a)
Al+L
Al+Sn
Sn6.8Al
(b)
1μm
Figure S1. Materials used for the study. (a) Phase diagram of Al-Sn alloy (ASM Handbook), the
selected composition is indicated by the blue line; (b) SEM image of TiC0.7N0.3 nanopartilces.
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In Al2O3 crucible in air (b)
(a)
Alloy
In Cu wedge mold
(c)
Figure S2. Schematic of the processing procedure. (a) Ultrasonic processing, (b) slow cooling in
crucible, and (c) fast cooling in copper wedge mold.
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(a)
(b)
(c)
d
10 µm
100 µm
1 µm
Figure S3. Morphology of primary Al phase and distribution of nanoparticles in Sn-6.8Al + 0.2
vol.% TiCN. (a), SEM image of Sn-6.8Al with 0.2 vol.% TiCN sample; (b), zoom-in of the
squared region in (a); (c), zoom-in of the squared region marked by c in (b). (a) and (b) are taken
by SE2 detector, (c) is taken by in-lens detector.
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