Nanotechnologies / Materials
Electronic devices, Electric vehicles

Advanced copper sintered composites strengthened byoxide nano-particles
Joining and Welding Research Institute

Professor Katsuyoshi Kondoh

Researchmap https://researchmap.jp/kondoh

Assistant Professor Abdollah Bahador

Researchmap https://researchmap.jp/Abdollah_Bahador

Nanotechnologies / Materials

Abstract
The trade-off between strength and ductility has been a dilemmain copper (Cu) matrix composites. In this work, we introduce a wayof strengthening copper matrix composites containing TiO2 nanoparticles with remarkable ductility. The Cu–8wt%TiO2 composites
were fabricated using the powder metallurgy route with spark plasma sintering (SPS) for different holding times incorporating hot extrusion. The sintered composites for longer holding times showed
an inhomogeneous distribution of large dispersed particles locatedmostly along the grain boundaries. However, tensile strength wasimproved compared with pure copper while ductility was reduced.
In contrast, after hot extrusion, a homogeneous distribution of reinforcement particles and grain refinement concurrently triggered
strong strengthening and enhanced ductility. The contribution ofsynergistic strengthening mechanisms, i.e. Hall–Petch strengthening, Orowan pinning, dislocation density and load transfer effect,
was studied and the key strengthening mechanisms were elucidated. It was found that composite yielding was strongly affected bysintering time, particulate size and interparticle spacing so that thecomposite via SPS for 30min. presented the excellent yield strengthof 290 MPa, about 72% above pure copper.

▍ Significance of the research and Future perspective
An improved strength-ductility balance is significantly effective
for both weight reduction and high reliability of electronic components made by Cu alloys, which mainly used in automotive andaircrafts. In particular electric vehicles are equipped with a lot ofCu material parts. In the near future, we will start a cooperation
with the industrial companies for practical use of this advanced Cucomposites.

▍ Background & Results
The superior electrical and thermal conductivity of copper has
triggered this metal to become a promising choice to be utilized in
an extremely wide range of applications such as heat exchangers,
combustion chamber liners, rocket nozzles, high voltage switches
and the electrode for resistance welding. However, the low intrinsic
strength of copper and its alloys limits their use in applications that
require high mechanical properties. In this regard, researchers
have recently striven to come up with ways to enhance the strengthof copper while retaining its unique properties. There are two common strengthening routes to obtain high-performance copper composite: precipitation-hardening and ceramic particulate-reinforced
composites such as oxide or boride fine particles. Both methods
are effective to enhance the strength improvement of Cu alloys, butthe elongation remarkably decreases at the same time. That is, theconventional materials design is limited in their trade-off balance
between strength and ductility. To achieve the main objective in thisstudy meaning the interface bonding improvement between oxide
nano-particle reinforcement and Cu matrix for high strength andenough elongation, the solid-state sintering process was employed
to fabricate Cu-TiO2 composite alloys via powder metallurgy route.
The strengthening and deformation mechanism was clarified by theexperiment using in-situ SEM tensile test and theoretical analysis,in particular grain refinement, dislocation hardening and Orowan
looping effects were dominant in the remarkable strength improvement.

P a t e n t
Bahador, Abdollah; Umeda, Junko; Kondoh, Katsuyoshi et al. Synergistic strengthening mechanisms of copper matrix composites with TiO2 nanoparticles.
Materials Science & Engineering A. 2020; 772: 138797. doi: 10.1016/j.msea.2019.138797.
Bahador, Abdollah; Umeda, Junko; Kondoh, Katsuyoshi et al. Deformation mechanism and enhanced properties of Cu-TiB2 composites evaluated by thein-situ tensile test and microstructure characterization. Journal of Alloys and Compounds. 2020; 847: 156555. doi: 10.1016/j.jallcom.2020.156555.
UR
L http://www.jwri.osaka-u.ac.jp/~dpt6/index_en.html
K e y w o r d copper alloys, powder metallurgy, nanocomposites, mechanical property

Tr e a t i s e