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V. Ya. Podhurska et al.
is also caused by a pulsed electric arc that occurs due to insufficient contact between
the insert and the wires of a catenary. As a result, hardened metal alloys appear on
the surface of the insert, which intensifies the wear of contacting components during
friction [2].
The aim of this work is to study composites based on the MAX phases of Ti–
Al–C system as promising materials for the pantograph inserts in the public vehicles
from the point of view of the microstructure and phase composition effects on their
physical and mechanical properties.
2 Materials and Methods
Previous composites based on MAX phase were obtained using two-step technology,
which consisted of synthesis in a vacuum (1350 °C) and hot pressing in the air
(1350 °C, 30–35 MPa) [10]. However, such technology involves the use of a complex
incorporating expensive equipment for high-temperature synthesis in vacuum, which
is a disadvantage in industrial applications. Therefore, it is necessary to study the
properties of such materials obtained by one-step technology, which is only hot
pressing. We investigated titanium composites based on 312 (Ti 3 AlC 2 ) and 211
(Ti 2 AlC) MAX phases of structural modifications made using the following one-step
technology, which consisted of hot pressing at pressures of 15 and 30 MPa at 1350 °C
for 30 min of powders TiH 2 , TiC, and Al. These powders were mixed and milled in a
planetary MPF-1 activator in argon environment and then compacted at a pressure of
30 MPa. The phase composition of the obtained materials is shown in Table 1 (variants
1–6). These composite materials were compared with the optimum material obtained
previously by two-step technology (variant 7) and with the aluminum alloy of the
Al–Fe–Cu–Si system (variant 8) used for the production of tram pantograph inserts
[10]. To determine the microhardness of the materials a PMT-3 M device with a load
of 200 g (HV200) was used.
A series of prismatic specimens of 4 × 5 × 40 mm in size were subjected. The
strength of the composite materials in the initial state (σ f ) was determined by the
three-point bend test of the specimens in the air at 20 °C. The wear resistance of the
materials was evaluated by the weight loss (m) of the body 1 (composite materials)
and the counterbody 2 (M1 copper) under non-lubricating slip conditions (Fig. 1a).
Taking into account the operating conditions of the friction pair, a specific contact
load of 0.25 MPa and a running distance of 5 km were selected. The specific electrical
conductivity of the composite material was determined in the air at 20 °C using a
four-point scheme. The resistance of materials to the action of an electric arc was
determined, whose power was regulated by the capacitance (300–600 μF) of the
discharge capacitor (W = CU
2 /2, where C is the capacitor capacitance and U is
the maximum voltage in the capacitor discharge). To estimate the damage degree
to the surface of specimens, the diameter (d) and depth (h) of the crater were used
(Fig. 1b). These parameters were determined using the interference profilograph [10].
V. Ya. Podhurska et al.
is also caused by a pulsed electric arc that occurs due to insufficient contact between
the insert and the wires of a catenary. As a result, hardened metal alloys appear on
the surface of the insert, which intensifies the wear of contacting components during
friction [2].
The aim of this work is to study composites based on the MAX phases of Ti–
Al–C system as promising materials for the pantograph inserts in the public vehicles
from the point of view of the microstructure and phase composition effects on their
physical and mechanical properties.
2 Materials and Methods
Previous composites based on MAX phase were obtained using two-step technology,
which consisted of synthesis in a vacuum (1350 °C) and hot pressing in the air
(1350 °C, 30–35 MPa) [10]. However, such technology involves the use of a complex
incorporating expensive equipment for high-temperature synthesis in vacuum, which
is a disadvantage in industrial applications. Therefore, it is necessary to study the
properties of such materials obtained by one-step technology, which is only hot
pressing. We investigated titanium composites based on 312 (Ti 3 AlC 2 ) and 211
(Ti 2 AlC) MAX phases of structural modifications made using the following one-step
technology, which consisted of hot pressing at pressures of 15 and 30 MPa at 1350 °C
for 30 min of powders TiH 2 , TiC, and Al. These powders were mixed and milled in a
planetary MPF-1 activator in argon environment and then compacted at a pressure of
30 MPa. The phase composition of the obtained materials is shown in Table 1 (variants
1–6). These composite materials were compared with the optimum material obtained
previously by two-step technology (variant 7) and with the aluminum alloy of the
Al–Fe–Cu–Si system (variant 8) used for the production of tram pantograph inserts
[10]. To determine the microhardness of the materials a PMT-3 M device with a load
of 200 g (HV200) was used.
A series of prismatic specimens of 4 × 5 × 40 mm in size were subjected. The
strength of the composite materials in the initial state (σ f ) was determined by the
three-point bend test of the specimens in the air at 20 °C. The wear resistance of the
materials was evaluated by the weight loss (m) of the body 1 (composite materials)
and the counterbody 2 (M1 copper) under non-lubricating slip conditions (Fig. 1a).
Taking into account the operating conditions of the friction pair, a specific contact
load of 0.25 MPa and a running distance of 5 km were selected. The specific electrical
conductivity of the composite material was determined in the air at 20 °C using a
four-point scheme. The resistance of materials to the action of an electric arc was
determined, whose power was regulated by the capacitance (300–600 μF) of the
discharge capacitor (W = CU
2 /2, where C is the capacitor capacitance and U is
the maximum voltage in the capacitor discharge). To estimate the damage degree
to the surface of specimens, the diameter (d) and depth (h) of the crater were used
(Fig. 1b). These parameters were determined using the interference profilograph [10].