4
A. Patil et al.
Introduction
Metal matrix composites (MMCs) are advanced materials reinforced with rigid
ceramics reinforcements exhibiting excellent mechanical strength as well as tribological behavior are embedded in a ductile metal matrix to overcome the limitations
of metals and alloys in providing both stiffness and strength to the structure while
retaining the ductility of base metal [1]. Metal matrix composites exhibit attractive
physical as well as mechanical properties due to a combination of metallic properties
such as high strength and high modulus as well as ceramic properties such as high
hardness and wear resistance [2, 3]. These excellent properties, various processing
routes, and the feasibility of tailoring the properties by altering the nominal composition make it a promising material for automotive, aerospace, and structural, and
surface engineering applications [1–4]. Factors such as size and the volume fraction
of the reinforcement precipitates, and its dispersion within the metal matrix affect the
mechanical properties of metal matrix composites [4, 5]. The mechanical properties
of metal matrix composites are governed not only by the size and volume fraction of reinforcement but also dependent on the nature of the matrix-reinforcement
interface [6, 7]. The uniform dispersion of fine thermodynamically stable ceramic
reinforcement particulates within the metal matrix is desirable for achieving optimum
mechanical properties of metal matrix composites.
Depending on the reinforcement formation process, metal matrix composite is
classified as ex situ and in situ MMCs. Ex situ MMCs uses a conventional technique of
composite fabrication in which reinforcement is added externally to the metal matrix.
Whereas, in in situ MMCs, the reinforcement is formed within the metal matrix due
to chemical reaction. Ex situ MMCs possess disadvantages as compared to in situ
MMCs such as poor interfacial bonding, size restriction of the reinforcement, and
poor wettability, affecting the distribution of the reinforcement particulates. Surface
contamination and particulate agglomeration can also be seen in particulate reinforced ex situ MMCs. Homogeneous dispersion of nanosized, thermally stable reinforcement in the metal matrix and stable interfacial bonding between the metal matrix
and ceramic reinforcement is desirable to achieve optimal mechanical properties and
enhanced mechanical performance of the metal matrix nanocomposites. By using
the in situ technique of processing, the reinforcements are synthesized in the metal
matrix during the fabrication process due to exothermic chemical reaction between
the constituents, thus resulting in a strong and clean interfacial bonding between
the metal matrix and fine-scale nanosized reinforcement precipitates [8–10]. Therefore, remarkably improved mechanical properties are achieved due to homogeneous
dispersion of particles within the metal matrix, good wettability of the reinforcement particulates with the metal matrix, and excellent interfacial bonding between
metal matrix and ceramic reinforcement. Thus, in situ processing route is preferable
over ex situ for the fabrication of MMCs due to several shortcomings. Previously,
several researchers conducted research on the in situ formation of titanium carbide
reinforcement precipitates within the metal matrix to achieve enhanced mechanical
and tribological properties [11–14]. However, there is a necessity to investigate the
A. Patil et al.
Introduction
Metal matrix composites (MMCs) are advanced materials reinforced with rigid
ceramics reinforcements exhibiting excellent mechanical strength as well as tribological behavior are embedded in a ductile metal matrix to overcome the limitations
of metals and alloys in providing both stiffness and strength to the structure while
retaining the ductility of base metal [1]. Metal matrix composites exhibit attractive
physical as well as mechanical properties due to a combination of metallic properties
such as high strength and high modulus as well as ceramic properties such as high
hardness and wear resistance [2, 3]. These excellent properties, various processing
routes, and the feasibility of tailoring the properties by altering the nominal composition make it a promising material for automotive, aerospace, and structural, and
surface engineering applications [1–4]. Factors such as size and the volume fraction
of the reinforcement precipitates, and its dispersion within the metal matrix affect the
mechanical properties of metal matrix composites [4, 5]. The mechanical properties
of metal matrix composites are governed not only by the size and volume fraction of reinforcement but also dependent on the nature of the matrix-reinforcement
interface [6, 7]. The uniform dispersion of fine thermodynamically stable ceramic
reinforcement particulates within the metal matrix is desirable for achieving optimum
mechanical properties of metal matrix composites.
Depending on the reinforcement formation process, metal matrix composite is
classified as ex situ and in situ MMCs. Ex situ MMCs uses a conventional technique of
composite fabrication in which reinforcement is added externally to the metal matrix.
Whereas, in in situ MMCs, the reinforcement is formed within the metal matrix due
to chemical reaction. Ex situ MMCs possess disadvantages as compared to in situ
MMCs such as poor interfacial bonding, size restriction of the reinforcement, and
poor wettability, affecting the distribution of the reinforcement particulates. Surface
contamination and particulate agglomeration can also be seen in particulate reinforced ex situ MMCs. Homogeneous dispersion of nanosized, thermally stable reinforcement in the metal matrix and stable interfacial bonding between the metal matrix
and ceramic reinforcement is desirable to achieve optimal mechanical properties and
enhanced mechanical performance of the metal matrix nanocomposites. By using
the in situ technique of processing, the reinforcements are synthesized in the metal
matrix during the fabrication process due to exothermic chemical reaction between
the constituents, thus resulting in a strong and clean interfacial bonding between
the metal matrix and fine-scale nanosized reinforcement precipitates [8–10]. Therefore, remarkably improved mechanical properties are achieved due to homogeneous
dispersion of particles within the metal matrix, good wettability of the reinforcement particulates with the metal matrix, and excellent interfacial bonding between
metal matrix and ceramic reinforcement. Thus, in situ processing route is preferable
over ex situ for the fabrication of MMCs due to several shortcomings. Previously,
several researchers conducted research on the in situ formation of titanium carbide
reinforcement precipitates within the metal matrix to achieve enhanced mechanical
and tribological properties [11–14]. However, there is a necessity to investigate the