Abstract :
In the present work, we demonstrate the
use of equal channel angular extrusion (ECAE) for the
consolidation of metallic nanoparticles at room temperature
as a bottom up approach to fabricating
nanocrystalline (NC) metals. Three different initial
average particle sizes of pure copper were used: –325
mesh micron size particles, 130 nm and 100 nm nanoparticles.
The processing work was divided into three
major stages (Stages I–III), depending on the powder
filling procedure used prior to ECAE, to investigate
the effect of processing parameters such as extrusion
rate and ECAE route, powder filling environment, and
hydrostatic pressure on the final performance of the
consolidates. Microstructure of the consolidates and
monotonic mechanical behavior were determined at
room temperature. The Stage I experiments revealed
what can materials, ECAE routes and range of
extrusion rates to use for achieving near full density
consolidates. In Stages II and III, the effect of initial
compact density on the resulting mechanical behavior
was investigated. It was found that the prior compaction
is helpful in breaking down the initial nanoparticle
agglomerates and achieving high tensile strength and
ductility levels in the ECAE consolidates. Tensile
strength as high as 800 MPa and tensile ductility as
high as 7% were achieved in 100 nm Cu particle
consolidates, which were more than 1.5 cm in diameter
and 10 cm in length, with a bimodal grain size
distribution in the range of 50–100 nm and 300 nm–
600 nm. ECAE was also used to consolidate 316 L
stainless steel nanoparticles resulting in bulk samples
with tensile strength of 1180 MPa and 4% ductility.
The present study shows that ECAE can be a feasible
method for fabricating bulk NC materials with all
dimensions in the centimeter range. Future work is
needed to further optimize the processing parameters
for improving the ductility level further and controlling
the grain size distribution
