93
Protection and Restoration
improvement to functionality of material structures can be achieved through hybrid
or multi-process 3D printing (Liu et al., 2021). However, additive manufacturing
of pure metals is difficult since they exhibit relatively poor mechanical properties
(Cooke et al., 2020).
According to Sanchez et al. (2020), plastics and polymer materials are a key area
in the field of AM, by far the most used material type. They include thermoplastics,
thermosets, elastomers, hydrogels, functional polymers, polymer blends, composites, and biological systems. Most amorphous, thermoplastic materials are processed
by material extrusion methods, with fused filament fabrication (FFF) and fused
deposition modeling (FDM) being the most popular techniques. In these techniques,
polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) are among the most
widely used materials, but general polymers that can be melted at an adequate temperature without degradation can be processed with material extrusion systems.
Technical requirements of materials include interfacial adhesion and undisturbed
polymer entanglement to allow for manufacture of nonporous objects with mechanical properties similar to products made by conventional techniques. In particular,
rheology, thermal, and mechanical properties need to be characterized to validate
a candidate material for this application, such as geometric characteristics, tensile,
fatigue, flexion, etc. (Sanchez et al., 2020).
Cooke et al. (2020) point out that the metal AM industry has seen a surge in 3D
printer technology with highly advanced devices and methods, but the number of
metal alloys that can be reliably printed is minimal. A vast majority of metal alloys
used in conventional processes are unable to produce adequate parts in AM. Among
metallic materials that can be used in AM techniques are steels, aluminum (Al) and
magnesium (Mg) alloys, titanium (Ti) and its alloys, and Ni/Co-based alloys. Kumar
and Sathiya (2021) provided their short review as follows.
Only a tiny fraction of available Fe alloys can be processed with AM methods.
Different steel materials such as stainless steel (SS), austenitic stainless steel, maraging steel, and tool steel are generally used in both general and tooling applications
where high hardness and strength are required. Some steels, e.g., hardenable SS
and austenitic steels, are sensitive to parameters of AM techniques. For machine
elements, fasteners, and tools, 34CrNiMo6 steel with high strength, toughness, and
hardness is used. However, when this material is processed with a laser, significant
changes in its microstructure and mechanical properties take place. After processing 300 M steel by laser solid forming (LSF), as-deposited martensite and coarse
bainite turn out to be uniform during heat treatment. Uniform transition of tempered
martensite and bainite retains a small amount of austenite. These microstructural
changes may cause fatigue crack to grow.
Al and its alloys are very attractive for aerospace engineering due to their light
weight and appreciable mechanical properties. They are available at low cost and,
having high thermal conductivity, they enable quick fabrication with reduced thermal
stresses compared to other metallic materials. However, high-performance Al alloys
have poor weldability and are highly reflective in the range of laser wavelengths,
which pose some limitations to their applications. Among the commonly used Al
alloys are AlSi10 and AlSi12. The Al alloy with added scandium fabricated with the
Protection and Restoration
improvement to functionality of material structures can be achieved through hybrid
or multi-process 3D printing (Liu et al., 2021). However, additive manufacturing
of pure metals is difficult since they exhibit relatively poor mechanical properties
(Cooke et al., 2020).
According to Sanchez et al. (2020), plastics and polymer materials are a key area
in the field of AM, by far the most used material type. They include thermoplastics,
thermosets, elastomers, hydrogels, functional polymers, polymer blends, composites, and biological systems. Most amorphous, thermoplastic materials are processed
by material extrusion methods, with fused filament fabrication (FFF) and fused
deposition modeling (FDM) being the most popular techniques. In these techniques,
polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) are among the most
widely used materials, but general polymers that can be melted at an adequate temperature without degradation can be processed with material extrusion systems.
Technical requirements of materials include interfacial adhesion and undisturbed
polymer entanglement to allow for manufacture of nonporous objects with mechanical properties similar to products made by conventional techniques. In particular,
rheology, thermal, and mechanical properties need to be characterized to validate
a candidate material for this application, such as geometric characteristics, tensile,
fatigue, flexion, etc. (Sanchez et al., 2020).
Cooke et al. (2020) point out that the metal AM industry has seen a surge in 3D
printer technology with highly advanced devices and methods, but the number of
metal alloys that can be reliably printed is minimal. A vast majority of metal alloys
used in conventional processes are unable to produce adequate parts in AM. Among
metallic materials that can be used in AM techniques are steels, aluminum (Al) and
magnesium (Mg) alloys, titanium (Ti) and its alloys, and Ni/Co-based alloys. Kumar
and Sathiya (2021) provided their short review as follows.
Only a tiny fraction of available Fe alloys can be processed with AM methods.
Different steel materials such as stainless steel (SS), austenitic stainless steel, maraging steel, and tool steel are generally used in both general and tooling applications
where high hardness and strength are required. Some steels, e.g., hardenable SS
and austenitic steels, are sensitive to parameters of AM techniques. For machine
elements, fasteners, and tools, 34CrNiMo6 steel with high strength, toughness, and
hardness is used. However, when this material is processed with a laser, significant
changes in its microstructure and mechanical properties take place. After processing 300 M steel by laser solid forming (LSF), as-deposited martensite and coarse
bainite turn out to be uniform during heat treatment. Uniform transition of tempered
martensite and bainite retains a small amount of austenite. These microstructural
changes may cause fatigue crack to grow.
Al and its alloys are very attractive for aerospace engineering due to their light
weight and appreciable mechanical properties. They are available at low cost and,
having high thermal conductivity, they enable quick fabrication with reduced thermal
stresses compared to other metallic materials. However, high-performance Al alloys
have poor weldability and are highly reflective in the range of laser wavelengths,
which pose some limitations to their applications. Among the commonly used Al
alloys are AlSi10 and AlSi12. The Al alloy with added scandium fabricated with the