This article investigated the microstructure of Ti6Al4V that was fabricated via selective laser melting; specifically, the mechanism of martensitic transformation and relationship among parent β phase, martensite (α’) and newly generated β phase that formed in the present experiments were elucidated. The primary X-ray diffraction (XRD), transmission electron microscopy (TEM) and tensile test were combined to discuss the relationship between α’, β phase and mechanical properties. The average width of each coarse β columnar grain is 80–160 μm, which is in agreement with the width of a laser scanning track. The result revealed a further relationship between β columnar grain and laser scanning track. Additionally, the high dislocation density, stacking faults and the typical ( $10\overline{1}1$ ) twinning were identified in the as-built sample. The twinning was filled with many dislocation lines that exhibited apparent slip systems of climbing and cross-slip. Moreover, the α + β phase with fine dislocation lines and residual twinning were observed in the stress relieving sample. Furthermore, both as-built and stress-relieved samples had a better homogeneous density and finer grains in the center area than in the edge area, displaying good mechanical properties by Feature-Scan. The α’ phase resulted in the improvement of tensile strength and hardness and decrease of plasticity, while the newly generated β phase resulted in a decrease of strength and enhancement of plasticity. The poor plasticity was ascribed to the different print mode, remained support structures and large thermal stresses.

Graphene nanoplatelets/aluminum (GNPs/Al) nanocomposites were fabricated using a novel two-step method. High resolution transmission electron microscope (HRTEM), Raman, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), EDS mapping, and mechanical testing system (MTS) were applied to characterize the microstructure and mechanical properties of the GNPs/Al nanocomposites. The GNPs were homogeneously dispersed in GNPs/Al nanocomposites, and presented a fine interface behavior and microstructure characteristics. A harmful phase, aluminum carbide (Al4C3), was not observed in significant quantities in the nanocomposite. Compared with pure aluminum, the mechanical properties of the GNPs/Al nanocomposites containing a low volume fraction of GNPs were sharply improved. When 0.5 vol.%, 1.0 vol.%, and 2.0 vol.% GNPs were added to the aluminum matrix, the average compressive strength of GNPs/Al nanocomposites was 297, 345, and 527 MPa, respectively, which remarkably increased the strength over the original aluminum by 330% to 586%.

To further improve the electrochemical performance of electrode materials for supercapacitors, we have achieved a significant increase of the micropore volume of a MnO₂ hybrid film on IrO₂ nano-wedges grown on a pre-treated Ti plate by the co-doping of vanadium and iron (V+Fe). X-ray diffraction and microstructural analyses demonstrate that the V+Fe co-doped MnO₂ hybrid films consist of the lamellar structure that is composed of γ-MnO₂ nanocrystallites jointed by disordered interface. Nitrogen sorption analysis confirms that the pore characteristics of the MnO₂ film change from mesopore-dominant to micropore-dominant after the co-doping, accompanied by increases in the pore volume and specific surface area. The specific capacitance of the V+Fe co-doped MnO₂ hybrid film electrode declines from 426 F g⁻¹ to 314 F g⁻¹ with a relatively limited loss of 26% when the galvanostatic (GV) charging-discharging rate is increased from 0.2 to 5 A g⁻¹. In particular, the doped MnO₂ film electrode has a loss of only 6% in the specific capacitance after 9000 cycles at a charge-discharge current density of 10 A g⁻¹.

Pore defects have an important effect on the mechanical properties of graphene reinforced aluminum nanocomposites. The simulation study found that the pores affect the stress distribution in the matrix of the composite. Along the stretching direction, the larger stress appears on both sides of the pore, which is the source of potential cracks. It results in a sharp decrease in the mechanical properties of the composite. The higher the porosity, the greater the tendency of pore aggregation, and the risk of material failure is higher. The stress distribution in the matrix becomes more uneven as the pore size increases, and the large strain area around the pores also increases. Composites with circular pores have a higher strength than other irregularly shaped pores. The failure mode might be pore cracking, while composites with other shape pores are more prone to interface detachment. The simulation value of the stress-strain of the composite material is in good agreement with the experimental value, but the finite element simulation value is larger than the experimental value.