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G. Yao et al.
the extremely low solubility of chromium in copper at temperatures below 500 °C [2–
4]. Limited by the copper–chromium (Cu–Cr) phase diagram, the hardness/strength
of the Cu–Cr alloys by precipitation-hardening has reached a certain limit. Besides,
the softening of copper–chromium alloys at elevated temperatures due to the coarsening of precipitates and grains prevents them from being used in high-temperature
environments [5].
Dispersing nanoparticles into the alloys is promising to further enhance the
properties by multiple mechanisms including modifying aging behavior, refining
microstructures, and inducing Orowan strengthening. Positive results of nanoparticle
effects on precipitation formation have been reported for aluminum (Al) alloys [6, 7].
Incorporating titanium carbide (TiC) nanoparticles into a high-zinc Al–Zn–Mg–Cu
alloy enhanced the dissolution of the secondary phase by solution heat treatment
and increased the aging speed [8]. Besides, titanium carbide (TiC) nanoparticles led
to the higher hardness via natural aging and better machinability of Al–Zn–Mg–Cu
alloy [9]. Thus, incorporating suitable nanoparticles into copper–chromium (Cu–
Cr) alloys is expected to modify the aging behavior and further to enhance their
properties.
Fabrication of copper–chromium (Cu–Cr) matrix nanocomposites and the resultant property improvement by nanoparticles have been reported in the literature. Cu-2
at.% Cr-1 wt.% W nanocomposite was fabricated by high energy ball milling and
spark plasma sintering, with the hardness and wear resistance increased by 5 and 44%
from nanoscale tungsten (W) in the matrix [10]. Dispersed aluminum oxide (Al 2 O 3 )
nanoparticles in Cu-4.5 weight percent chromium (Cr) were achieved by mechanical alloying and high-pressure sintering, leading to increased microhardness [11].
Adding titanium diboride (TiB 2 ) to copper–chromium (Cu–Cr) during mechanical
alloying led to decreased grain sizes of copper (Cu) and chromium (Cr) that were
less than 50 nm [12]. However, little work was reported on the aging behavior of
Cu–Cr matrix nanocomposites.
Tungsten (W) has excellent mechanical properties (high hardness, strength, and
Young’s modulus) and thermal properties (high melting point, thermal stability,
thermal conductivity, and a low thermal expansion coefficient) [13]. Both tungsten
(W) and copper (Cu) do not form a solid solution or intermetallic compounds, which
otherwise would deteriorate the electrical conductivity or ductility of copper [14].
In fact, copper (Cu) strengthened by nano-tungsten (W) dispersions also exhibits a
good combination of high strength and high conductivity [15]. Moreover, tungsten
has a much higher electrical conductivity than common ceramic reinforcements for
metals such as titanium carbide (TiC) and titanium diboride (TiB 2 ). Thus, tungsten
(W) nanoparticles are considered a promising candidate to modify Cu–Cr alloys.
In this study, Cu-1.2Cr alloy nano-treated by 2 volume percent tungsten (W)
nanoparticles was cast. The microstructure and the improved aging behavior of Cu–
Cr/W nanocomposite were studied. The underlying mechanism of the enhanced
precipitation strengthening by W nanoparticles was discussed. This study provides
new insights into the design of high-strength high-conductivity copper–chromium
(Cu–Cr) alloys.
G. Yao et al.
the extremely low solubility of chromium in copper at temperatures below 500 °C [2–
4]. Limited by the copper–chromium (Cu–Cr) phase diagram, the hardness/strength
of the Cu–Cr alloys by precipitation-hardening has reached a certain limit. Besides,
the softening of copper–chromium alloys at elevated temperatures due to the coarsening of precipitates and grains prevents them from being used in high-temperature
environments [5].
Dispersing nanoparticles into the alloys is promising to further enhance the
properties by multiple mechanisms including modifying aging behavior, refining
microstructures, and inducing Orowan strengthening. Positive results of nanoparticle
effects on precipitation formation have been reported for aluminum (Al) alloys [6, 7].
Incorporating titanium carbide (TiC) nanoparticles into a high-zinc Al–Zn–Mg–Cu
alloy enhanced the dissolution of the secondary phase by solution heat treatment
and increased the aging speed [8]. Besides, titanium carbide (TiC) nanoparticles led
to the higher hardness via natural aging and better machinability of Al–Zn–Mg–Cu
alloy [9]. Thus, incorporating suitable nanoparticles into copper–chromium (Cu–
Cr) alloys is expected to modify the aging behavior and further to enhance their
properties.
Fabrication of copper–chromium (Cu–Cr) matrix nanocomposites and the resultant property improvement by nanoparticles have been reported in the literature. Cu-2
at.% Cr-1 wt.% W nanocomposite was fabricated by high energy ball milling and
spark plasma sintering, with the hardness and wear resistance increased by 5 and 44%
from nanoscale tungsten (W) in the matrix [10]. Dispersed aluminum oxide (Al 2 O 3 )
nanoparticles in Cu-4.5 weight percent chromium (Cr) were achieved by mechanical alloying and high-pressure sintering, leading to increased microhardness [11].
Adding titanium diboride (TiB 2 ) to copper–chromium (Cu–Cr) during mechanical
alloying led to decreased grain sizes of copper (Cu) and chromium (Cr) that were
less than 50 nm [12]. However, little work was reported on the aging behavior of
Cu–Cr matrix nanocomposites.
Tungsten (W) has excellent mechanical properties (high hardness, strength, and
Young’s modulus) and thermal properties (high melting point, thermal stability,
thermal conductivity, and a low thermal expansion coefficient) [13]. Both tungsten
(W) and copper (Cu) do not form a solid solution or intermetallic compounds, which
otherwise would deteriorate the electrical conductivity or ductility of copper [14].
In fact, copper (Cu) strengthened by nano-tungsten (W) dispersions also exhibits a
good combination of high strength and high conductivity [15]. Moreover, tungsten
has a much higher electrical conductivity than common ceramic reinforcements for
metals such as titanium carbide (TiC) and titanium diboride (TiB 2 ). Thus, tungsten
(W) nanoparticles are considered a promising candidate to modify Cu–Cr alloys.
In this study, Cu-1.2Cr alloy nano-treated by 2 volume percent tungsten (W)
nanoparticles was cast. The microstructure and the improved aging behavior of Cu–
Cr/W nanocomposite were studied. The underlying mechanism of the enhanced
precipitation strengthening by W nanoparticles was discussed. This study provides
new insights into the design of high-strength high-conductivity copper–chromium
(Cu–Cr) alloys.