A persistent purpose for self-powered and wearable electronic devices is the fabrication of graphene-PVDF piezoelectric nanogenerators with various co-solvents that could provide enhanced levels of durability and stability while generating a higher output. This study resulted in a piezoelectric nanogenerator based on a composite film composed of graphene, and poly (vinylidene fluoride) (PVDF) as a flexible polymer matrix that delivers high performance, flexibility, and cost-effectiveness. By adjusting the co-solvent in the solution, a graphene-PVDF piezoelectric nanogenerator can be created (acetone, THF, water, and EtOH). The solution becomes less viscous and is more diluted the more significant the concentration of co-solvents, such as acetone, THF, and EtOH. Additionally, when the density is low, the thickness will be thinner. The final film thickness for all is ~25 µm. Furthermore, the- crystal phase becomes more apparent when graphene is added and combined with the four co-solvents. Based on the XRD results, the peak changes to the right, which can be inferred to be more dominant with the β-phase. THF is the co-solvent with the highest piezoelectric output among other co-solvents. Most of the output voltages produced are 0.071 V and are more significant than the rest.

Bioactive hydroxyapatite (HA) coating is applied on a commercially pure Ti by electrophoretic deposition (EPD). Optimizing the coating structure is necessary to obtain a stable layer and the best corrosion protection. The EPD was conducted at a constant voltage of 20, 30, and 40 V for 30 min in a HA/DMF (dimethylformamide) suspension. Uniform HA layers with a Ca/P ratio of 1.82 were successfully deposited on the Ti surface. The layers, which consisted of HA grains with the size of 1–5 μm, exhibited a gradual increase in thickness of 32, 50, and 60 μm with formation voltage. For the biomedical application, the suitable coating thickness was at least 50 μm. The high compaction of HA grains deposited at 30 V led to an order magnitude higher polarization resistance and ten times lower corrosion current density relative to the other specimens. The porous HA layer formed at 20 V, and the presence of cracks in the 40 V-coating led to a lower corrosion resistance relative to the 30-V coating. The 20 V- and 30 V-coatings remained intact and triggered the deposition of HA during immersion in simulated body fluid for 28 days, while the 40 V-coating dissolved into the solution. The optimum EPD voltage for depositing a stable HA coating with reasonable coating thickness and the best corrosion resistance was 30 V.

The mechanical properties of high strength aluminum alloy AA7075 were greatly affected by heat treatment. This paper was intended to clarify the effect of heat treatment on the microstructure and the mechanical hardness of commercial alloy AA7075-T651. Heat treatment was performed at a variation temperature of 300, 400, 500, and 600°C for 1 h in a vacuum furnace followed by a water quench. The surface observation was done by using optical and electron microscopy and the mechanical hardness was measured by the Vickers Hardness test. The XRD result on as-received alloy revealed the precipitates in the alloy was MgZn₂, Al₇Cu₂Fe, and Al₂CuMg. The average hardness of the as-received alloy was 136 HV. The hardness became significantly lower (78.5 HV) after heat treatment at 400°C while heat treatment at others temperature gave hardness in the range 116-122 HV. Heat treatment induced grain growth and dissolution of metastable precipitates. Reduction in the number of MgZn₂ and Fe-rich phase decreased the hardness significantly. Heat treatment above 400°C promoted segregation of fresh precipitates which enhanced the metal hardness again. The metallic grain size increased with heat treatment temperature. At 600°C, most of the precipitates were segregated along the equiaxed grain boundaries.