Table 1.
The application and the biological and mechanical properties of mostly AM-fabricated metallic FGMs.
| Method | Material | Mechanical properties | Biological properties | Application | References |
|---|---|---|---|---|---|
| SLM | Ti6Al4V | Young's modulus in the range of cortical bone. The highest strength and toughness in honeycomb structures with supporting structure in the outer layer. | – | Orthopedic | Xiong et al., 2020 |
| SLM | Ti6Al4V | Mechanical properties in the range of cortical bone. Small pores with ~900 μm in core regions increase mechanical strength. | Large pores, about 1,100 μm in the outer surface, enhances cell penetration and proliferation. | Load-bearing implants | Onal et al., 2018 |
| SLM | Ti6Al4V | The variation in unit cell orientation affects the mechanical properties; this change is a function of the geometrical dimension of the unit cell size. There is a functional relationship between elastic modulus and compressive strength. | – | Bone implant | Weißmann et al., 2016 |
| SLM | Ti6Al4V | AM-produced porous FGM can decrease the elastic modulus up to 80% and enhance the biomechanical performance. | – | Bone scaffolds and orthopedic implants | Wang et al., 2017b |
| SLM | Ti6Al4V | Porosity variation strategy (diamond lattice structures) results in an elastic modulus of 3.7–5.7 GPa and yield strength of 27.1–84.7 MPa, which lie in the range of the corresponding mechanical properties of cancellous bone and cortical bone. | – | Bone scaffolds | Zhang X.-Y. et al., 2018 |
| SLM | Pure Ti | Diamond porous FGM scaffold production with a good geometric reproduction, possessing a wide range of graded volume fraction. The elastic modulus is comparable to cancellous bone and can be tailored by tuning the graded volume fraction. | – | Bone implant | Han et al., 2018a |
| SLM | CoCr | Pillar-octahedral-shape CoCr cellular structures with a porosity range of 41–67% indicate stiffness, strength, and energy absorption values that are similar to natural bone. | – | Metallic orthopedic implants | Limmahakhun et al., 2017 |
| SLM | CoCrMo | FGM design (square pore cellular structures) decrease the stiffness and weight up to 48% compared to the traditional fully dense stem. | – | Femoral stem implant | Hazlehurst et al., 2014a |
| SLM | CoCrMo | FGM structure (square pore) reduced the stress-shielding effect without compromising the bone strength. The most effective design is the full porous stems with an axially graded stiffness. | – | Hip implant | Hazlehurst et al., 2014b |
| EBM | Ti6Al4V | The deformation response of graded meshes is the weighted percentage of stress-strain response of each uniform mesh constituent. By tailoring the relative density and volume fraction, the graded meshes can achieve high strength and energy absorption values. | – | Implants that can withstand abrupt impact fractures. | Li et al., 2016 |
| EBM | Ti6Al4V | – | AM manufactured interconnected gradient porous architecture enhances cellular functions, including adhesion, proliferation, mineralization, and synthesis of actin and vinculin proteins. | Medication of segmental bone defects and bone remodeling | Nune et al., 2016 |
| EBM | Ti6Al4V | Aimed to inhibit the stress-shielding effect by decreasing the elastic modulus mismatch between the bone tissue and titanium alloy implant. | 3-D printed interconnected porous FGM is conducive to osteoblast cell functions, including proliferation, adhesion, calcium deposition, and synthesis of proteins, such as actin, vinculin, and fibronectin. | Bone implants | Nune et al., 2017 |
| EBM | Ti6Al4V | The weighted average gradient porosities of 65–21% show high compressive strength and hardness and suitable elastic modulus for bone implant application. | – | Treatment of segmental bone defect | Surmeneva et al., 2017 |
| EBM | Ti6Al4V | Regular diamond lattice indicates suitable compression strength and elastic modulus to implant application. Uniaxial compression behavior along the direction of gradation can be well-predicted by a simple rule of mixtures approach. | – | Orthopedic implant applications | van Grunsven et al., 2014 |
| EBM | Ti6Al4V | Periodic cellular structures with a 49%−70% porosity range with mechanical properties (effective stiffness, compressive strength values) suitable for loading conditions. | – | Hip and mandible implants | Parthasarathy et al., 2011 |
| EBM | Ti6Al4V | The porous FGM (open-cell cubic structure) has a compressive strength with a transition region between 4 and 8 mm and is superior to a sharp interface. | – | Biomedical implants | Wu et al., 2018 |
| SLM | 316L stainless steel | High density of subgrain boundaries and dislocations is responsible for good plasticity, and the considerable number of voids induces premature instability and fracture. | Higher biocompatibility and good biological performance. | Medical implant applications. | Kong et al., 2018 |
| Laser metal deposition | Stainless steel, HS6-5-2 | Low porosity and no delamination occurrence were seen. According to microhardness tests, gradient materials sintered in the N2-10% H2 atmosphere and reinforced with the VC carbide have the maximum hardness. | – | Possible biomedical application. | Matula and Dobrzański, 2006 |
| Laser cladding | Dissimilar stainless steel (SS)-zirconium (Zr) | Functionally graded deposition in dissimilar materials resulted in production of disintegrated structure and numerous longitudinal and horizontal cracks. Possibly micro-cracks are the result of large thermal stress build-up during the layer-by-layer AM process. | – | – | Khodabakhshi et al., 2019 |