ENCYCLOPÉDIE DE LA RECHERCHE SUR L’ALUMINIUM AU QUÉBEC 2013 | Page 59

NOUVEAUX PRODUITS ET MATÉRIAUX À BASE D'ALUMINIUM

OnThermal-Stability of Al-B4C ALUMINIUM Alloyed
NEW Composites BASED PRODUCTS AND MATERIALS
with Sc and Zr at Elevated Temperatures

57

STABILITÉ THERMIQUE DES COMPOSITES Al-B C

4
Stabilité Thermique des composites Al-B4C combinés Zr À TEMPERATURE ÉLEVÉE
COMBINÉS AVEC Sc ET
avec Sc et Zr à Temperature élevée

ON THE THERMAL-STABILITY OF Al-B4C COMPOSITES
ALLOYED WITH Sc AND Zr AT ELEVATED TEMPERATURES

Jian Qin, Zhan Zhang, X.-Grant Chen
NSERC/Rio Tinto Alcan Industrial Research Chair in Metallurgy of Aluminium Transformation,
Université du Québec à Chicoutimi

Introduction
Al-B4C composites as neutron absorber materials have been widely used for the transport and storage of spent nuclear fuels
in the nuclear industry. The storage materials are required to maintain stable mechanical properties at elevated temperatures
for a quite long time. Sc and Zr have been introduced into the Al‒B4C composite to form Al3Sc and Al3(ScxZr1-x)
precipitates which offer significant strengthening effect and good thermal stability of mechanical properties at elevated
temperature. In this study, the microstructure and mechanical properties after long-term exposed at elevated temperature
were examined in order to understand the thermal stability of the composites.

Objective
Evaluate the mechanical properties of Al‒B4C
composites with Sc and Zr addition after long term
exposing at elevated temperatures.
Study the strength mechanism of the composites at
elevated temperature.

Results

Experimental

b

a

a

1. Sample Preparation:

Cast ingots of two Al-B4C composites, S40 (Al-15vol.%B4C with
0.4wt.% Sc) and SZ40 (Al-15vol.%B4C with 0.4wt.% Sc and
0.24wt.% Zr) were prepared.

Figure 3 Microstructure of the composites
exposed at elevated temperature

The heat treatment was carried out as the following conditions:
Step
Solution
Aging

T(ºC)
S40
SZ40
S40
SZ40

Time(hour)
24

640
250
300
350

500

1000

c

water

96
24

a. OM image of S40
exposed at 300ºC for 2016h

Cooling

2000

b. TEM image of interface,
S40 exposed at 300ºC for 2016h

d

c. EBSD images of
SZ40 exposed at 300ºC for 24h

air

b

d. Grain size of S40 and SZ40 before and after
long term exposed at 300ºC

2.Mechanical Properties
The compression tests were carried out at 250ºC, 250ºC, 300ºC and
350ºC on Gleeble 3800 thermome-chanical testing machine. Cylinder
samples with 15 mm length and 10 mm diameter were prepared. The
total deformation was 0.3 and stain rate was fixed to 10-3 s-1.

a

a

b
Figure 4 TEM dark-field images

b

showing the nano-scale precipitates
which were taken utilizing (100) superlattice reflections near [011] zone axis.

c

PRIX // AWARD

a. S40 aged at 300ºC for 24 hours
b. b.S40 aged at 300ºC for 2000 hours
c. SZ40 aged at 300ºC for 24 hours
d. SZ40 aged at 300ºC for 2000 hours

Figure 1 Compression test
a. Gleeble testing machine b. Compression sample with extensometer
Hardness tests were carried out at ambient temperature. According to
the ASTM standard E92‒82, the load of test was fixed to be 25 g and an
indentation time 15 s. A minimum of 20 measurements were performed
on the matrix of each sample.

3. Microstructure Observation

The size of grain and precipitates of the S40 and SZ40 composites
before and after long-term exposed at elevated temperature were
examined by optical and electron microscopes in order to understand
the microstructure evolution and coarsening rate of the precipitates
during hot deformation.

c

d

Figure 2 Mechanical properties of S40 and SZ40 at elevated
temperature during long term heating.
a. Yield strength of S40 as a function of exposed time
b. Yield strength of SZ40 as a function of exposed time
c. Hardness of S40 and SZ40, exposed at 300ºC tested at
ambient temperature, as a function of exposed time

Analysis
a.
b.
c.

With more than 500 hours exposing time at 300ºC, the the yield strength of S40 at 300ºC was higher than that of SZ40,but the hardness of the former is less than that of the
latter at ambient temperature.
After long term exposed at elevated temperature, the interfaces of the composites did not have significant change.
Base on the EBSD images that the grain of composites had barely grown during the long term exposed at elevated temperature.

d.
During the long term heating, the coarsening of Al3Sc precipitate was obvious. The Al3(ScxZr1-x) precipitate are slowly but progressively coarsening and some of the precipitates grow up faster
than the others.
It was found that the yield strength of the composites increases with increasing radius of the precipitates. This would be attributed to the dislocation movement and the changes of the misfit between
precipitate particles and matrix. [1,2,3].
[1] E.A. Marquis, D.C. Dunand, Scr. Mater., 47 (2002) 503-508.
[2] C.B. Fuller