22
S. Gupta
20 MPa, respectively [49]. The addition of 30 vol% Ti 3 SiC 2 particles in the Bi-matrix
improved the strength of Bi from ~42 to ~71 MPa. In Ag-based MRMs, the addition of
20 vol% Ti 3 SiC 2 increased the yield strength to ~164 MPa as compared to ~47 MPa
in Ag. However, the addition of 30 vol% Ti 3 SiC 2 decreased the yield strength to
~117 MPa [57]. Fuka and co-workers [62] also observed mild enhancement in yield
strength of ~498 MPa of Ni-10%MoAlB (1550 °C) (porosity: ~17%) as compared
to ~467.5 MPa in Ni (165 MPa) (porosity: 18%) (please refer to this reference for
details about the processing conditions). Comparatively, in Ni-Ti 3 SiC 2 composites,
Ni-5%312Si had yield strength of ~592 MPa, and it decreased to ~465 MPa and
~227 MPa in Ni-20%312Si, and Ni-30%312Si, respectively [63]. The yield strength
of Zn, Zn-5%Ti 3 SiC 2 , Zn-10%Ti 3 SiC 2 was 139 ± 4 MPa, 120 ± 26 MPa and 132 ±
19 MPa, 147 ± 22 MPa, respectively [71]. By analyzing the results, we can conclude
that the yield strength of MRMs is dependent on the metal/alloy composition, and
processing conditions which control reaction kinetics and porosity of the composites.
More studies are needed to understand the interaction of MAX phase particles with
dislocation movement in these metals. These composites also showed triboactive
behavior where the presence of MAX phases enhanced the wear resistance and
lowered the friction coefficient.
Liu and co-workers [58] also observed enhancement in tensile strength in
Ag/Ti 3 AlC 2 composites which were fabricated by vacuum hot-pressing at 800 °C
for 120 min by applying a stress of 30 MPa (Fig. 2a). They proposed that due to
the synergistic effect of high hardness of Ti 3 AlC 2 and interfacial region composed
of strengthened Ag (Al) solid solution interfacial zone was responsible was for the
enhancement in tensile strength. The authors also reported that the optimum composition of Ag/5 vol% Ti 3 AlC 2 had a high electrical conductivity of (2.90 ± 0.01) μ cm
which corresponds to 59.5% IACS (the international annealed copper standard).
Zhai and co-workers [61] designed novel self-lubricating composites of Ni 3 AlTi 3 SiC 2 -TiC-C (NMC) by Spark Plasma Sintering (SPS) at 1150 °C for 5 min under
a pressure of 40 MPa by using Ar as shielding gas. They observed that the additions 15 weight % Ti 3 SiC 2 lubricant was able to impart triboactive behavior (lowfriction coefficients of 0.17–0.58 and wear rates of 0.31–4.2 × 10
−5 mm
3 /Nm in the
temperature range of 25–800 °C) to these composites.
Xu and co-workers [66] reported that the addition 12 weight % Ti 3 SiC 2 or
12 weight % Ag or 12 weight % Ag and 12 weight % Ti 3 SiC 2 in the TiAl matrix
can enhance the triboactive behavior of these solids. They did not report any reaction
between different constituents. They reported that due to the synergistic effect of Ag
and Ti 3 SiC 2 , the TiAl matrix composites reinforced with Ag and Ti 3 SiC 2 showed
“lower friction coefficients (0.32–0.43) and less wear rates (1.23–4.13 × 10
−4 mm
3
N
−1 m
−1 )”, in the temperature range of RT to 800 °C.
Wang and co-workers [67] showed that the pre-oxidation can also improve the
tribological performance of Ti 2 AlN/TiAl composites. This group reported that preoxidation helps in protecting the substrate by decreasing abrasive wear and resisting
plastic deformation. Xu and co-workers [68] designed TiAl composites by adding
15 weight % Ti 3 SiC 2 . They observed that the oxide-rich tribofilms (mainly Al-TiSi-Fe oxides) formed during tribological studies at ambient temperature has a vital
S. Gupta
20 MPa, respectively [49]. The addition of 30 vol% Ti 3 SiC 2 particles in the Bi-matrix
improved the strength of Bi from ~42 to ~71 MPa. In Ag-based MRMs, the addition of
20 vol% Ti 3 SiC 2 increased the yield strength to ~164 MPa as compared to ~47 MPa
in Ag. However, the addition of 30 vol% Ti 3 SiC 2 decreased the yield strength to
~117 MPa [57]. Fuka and co-workers [62] also observed mild enhancement in yield
strength of ~498 MPa of Ni-10%MoAlB (1550 °C) (porosity: ~17%) as compared
to ~467.5 MPa in Ni (165 MPa) (porosity: 18%) (please refer to this reference for
details about the processing conditions). Comparatively, in Ni-Ti 3 SiC 2 composites,
Ni-5%312Si had yield strength of ~592 MPa, and it decreased to ~465 MPa and
~227 MPa in Ni-20%312Si, and Ni-30%312Si, respectively [63]. The yield strength
of Zn, Zn-5%Ti 3 SiC 2 , Zn-10%Ti 3 SiC 2 was 139 ± 4 MPa, 120 ± 26 MPa and 132 ±
19 MPa, 147 ± 22 MPa, respectively [71]. By analyzing the results, we can conclude
that the yield strength of MRMs is dependent on the metal/alloy composition, and
processing conditions which control reaction kinetics and porosity of the composites.
More studies are needed to understand the interaction of MAX phase particles with
dislocation movement in these metals. These composites also showed triboactive
behavior where the presence of MAX phases enhanced the wear resistance and
lowered the friction coefficient.
Liu and co-workers [58] also observed enhancement in tensile strength in
Ag/Ti 3 AlC 2 composites which were fabricated by vacuum hot-pressing at 800 °C
for 120 min by applying a stress of 30 MPa (Fig. 2a). They proposed that due to
the synergistic effect of high hardness of Ti 3 AlC 2 and interfacial region composed
of strengthened Ag (Al) solid solution interfacial zone was responsible was for the
enhancement in tensile strength. The authors also reported that the optimum composition of Ag/5 vol% Ti 3 AlC 2 had a high electrical conductivity of (2.90 ± 0.01) μ cm
which corresponds to 59.5% IACS (the international annealed copper standard).
Zhai and co-workers [61] designed novel self-lubricating composites of Ni 3 AlTi 3 SiC 2 -TiC-C (NMC) by Spark Plasma Sintering (SPS) at 1150 °C for 5 min under
a pressure of 40 MPa by using Ar as shielding gas. They observed that the additions 15 weight % Ti 3 SiC 2 lubricant was able to impart triboactive behavior (lowfriction coefficients of 0.17–0.58 and wear rates of 0.31–4.2 × 10
−5 mm
3 /Nm in the
temperature range of 25–800 °C) to these composites.
Xu and co-workers [66] reported that the addition 12 weight % Ti 3 SiC 2 or
12 weight % Ag or 12 weight % Ag and 12 weight % Ti 3 SiC 2 in the TiAl matrix
can enhance the triboactive behavior of these solids. They did not report any reaction
between different constituents. They reported that due to the synergistic effect of Ag
and Ti 3 SiC 2 , the TiAl matrix composites reinforced with Ag and Ti 3 SiC 2 showed
“lower friction coefficients (0.32–0.43) and less wear rates (1.23–4.13 × 10
−4 mm
3
N
−1 m
−1 )”, in the temperature range of RT to 800 °C.
Wang and co-workers [67] showed that the pre-oxidation can also improve the
tribological performance of Ti 2 AlN/TiAl composites. This group reported that preoxidation helps in protecting the substrate by decreasing abrasive wear and resisting
plastic deformation. Xu and co-workers [68] designed TiAl composites by adding
15 weight % Ti 3 SiC 2 . They observed that the oxide-rich tribofilms (mainly Al-TiSi-Fe oxides) formed during tribological studies at ambient temperature has a vital