The surface of most metals is covered with thin native oxide films. It has generally been believed that to achieve bonding, the oxide covering the surface of metallic particles or metal substrates must be broken and removed by adiabatic shear instability (ASI), whether induced at the particle–substrate interface or at the particle–particle interface. The aim of the present research is to investigate the correlation between the remaining oxide amorphous layer and substrate-deformation with the adhesion strength of cold-sprayed TiO₂ coatings towards the bonding mechanism involved. Relevant experiments were executed using stainless steel (SUS 304), subjected to various annealing temperatures and cold-sprayed with TiO₂ powder. The results indicate an increasing trend of coating adhesion strength with increasing annealed substrate temperature. The influence of substrate plastic deformation and atomic intermixing at the remaining amorphous oxide layer is discussed as the factors contributing to the increasing adhesion strength of cold-sprayed TiO₂ coatings.

The cold spraying of ceramic materials is widely acknowledged as a difficult process because it necessitates the feedstock powder particles experiencing a plastic deformation for deposition on a substrate. The problem arises due to the brittle properties of ceramic powder feedstock such as titanium dioxide (TiO₂), combined with a lack of understanding of the bonding mechanisms. In this study, TiO₂ coatings were deposited onto copper and aluminum substrates and the adhesion strength was evaluated to investigate the bonding mechanism. The influence of substrate hardness and remaining surface oxide layer was investigated by annealing the substrates with various temperatures. The results showed that the adhesion strength of the coatings on the aluminum substrate was higher than the copper substrate. Furthermore, the adhesion strength was decreased with increasing the annealing temperature on both substrate materials. These results indicate that a softer aluminum substrate was advantageous for adhesion. Annealing led to thermal softening the substrate; however, the thickness of the surface oxide layer was increased. Therefore, bonding occurred between the cold-sprayed TiO₂ particle and newly deform substrate surface, which yielded the higher adhesion strength. The main bonding mechanism is metallurgical, similarly to the cold-sprayed metallic coatings.

Titanium alloys, especially Ti6Al4V, have an excellent combination of properties. However, in many cases their application is limited because of poor wear and corrosion properties. In this research, a surface modification (duplex coating) has been carried out to improve the surface properties of Ti6Al4V. The duplex coating of the Ti6Al4V alloy was conducted with the aim of improving the corrosion resistance and mechanical properties of the alloy. In this study, plasma nitriding of Ti6Al4V was performed using a microwave plasma technique at a temperature 600°C for 1 and 3 h, followed by deposition of TiAlBN coating on plasma-nitrided samples for duplex coating purposes. Microstructural measurement revealed that the duplex coating process produces a relatively smooth and crack-free modified surface layer which is believed able to inhibit the occurrence of corrosion process. The electrochemical behaviour of duplex coating samples and untreated Ti6Al4V was evaluated using the Tafel Extrapolation method and it was found that the duplex coating significantly increased the corrosion protection property. In addition, the duplex surface obtained in this study has a superior surface hardness property compared to untreated Ti6Al4V, especially for samples with the longer nitriding time.

The cold spray or Supersonic Particle Deposition technique has great potential for producing ceramic nanostructured coatings. This technique operates at a processing temperature that is low enough to preserve the initial feedstock materials’ microstructure. Nevertheless, depositing ceramic powders using a cold spray can be challenging because of the materials’ brittle nature. The interaction between substrate and particles is significantly influenced by substrate attributes, including hardness, material nature, degree of oxidation and temperature. In this study, the effect of the substrate’s remaining oxide composition on the adhesion strength of an agglomerated nano-TiO₂ coating was investigated. The results showed that the coating adhesion strength increased for hard materials such as stainless steel and pure chromium as the annealed substrate temperature also increased from room temperature to 700 °C, indicating thicker oxide on the substrate surface. TiO₂ particles mainly bond with SUS304 substrates through oxide bonding, which results from a chemical reaction involving TiO₂-OH⁻. Chromium oxide (Cr₂O₃) is thermodynamically preferred in SUS304 and provides the OH⁻ component required for the reaction. SUS304 shows a thermodynamic preference for chromium oxide (Cr₂O₃), and this enables Cr₂O₃ to provide the necessary OH⁻ component for the reaction.

Unmanned Aerial Vehicles or UAVs were pilotless aircraft or aircraft with minimum human interaction. UAVs material and structure were critical aspects to consider throughout the development phase. UAVs were utilized in both the military and the civilian sector. However, because of this diversity of uses, their materials and structure differed due to the requirements and resilience needed for those uses. Due to the different materials used in the other development of UAVs, this study aimed to study the appropriate structure material for the development of UAVs. Moreover, this study investigated the process of preparing the body structure of the selected material from developed UAVs particularly for military specifications. Additionally, this study analyzed the best approach that was used to reduce the maximum take-off weight. This study focused on the best structure from the successful product of UAVs from the selected company. This case study was performed to investigate what had been practiced and for further analysis while analytical hierarchy process (AHP) and quality function deployment (QFD) were used as research methods to perform the multi-criteria decision analysis. Carbon fiber was selected as suitable material for wing and propellor while fiberglass composite was identified as suitable material for tail and body of UAVs. This study provided a strong basis for future UAV development, this all-encompassing strategy sought to create an organized framework for decision-making that synchronized technical specifications with operational and customer objectives.