## 3 Composite Matrices and Applications
### Metals
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Composites** & **Formulation** & **Output** \\ \hline AlCTS01 & 100\% Al (aluminum) & Baseline mechanical properties, wear rate \(\sim\)0.038 mm\({}^{3}\)/km at 40 N load \\ \hline AlCTS02 & 99 wt\% Al + 0.5 wt\% CNT + 0.5 wt\% TiC & Few CNT/TiC particles, minor improvement in tensile strength \\ \hline AlCTS03 & 98.5 wt\% Al + 0.5 wt\% CNT + 1 wt\% TiC & Moderate improvement in wear resistance \\ \hline AlCTS04 & 98 wt\% Al + 0.5 wt\% CNT + 1.5 wt\% TiC & Significant wear resistance improvement \\ \hline AlCTS05 & 97.5 wt\% Al + 0.5 wt\% CNT + 2 wt\% TiC & Maximum wear resistance, wear rate \(\sim\)0.006 mm\({}^{3}\)/km (84.21\% reduction) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Aluminum–CNT composites with TIC reinforcement. (Summary of the study of [PERSON] et al. [113]). \begin{table}
\begin{tabular}{l l l} \hline \hline
**Composites** & **Formulation** & **Output** \\ \hline AZ61 & AZ61 alloy (6.5 wt\% Al, 1 wt\% Zn, and 0.1 wt\% Mn) & Baseline corrosion rate: 0.0336 mm/yr \\ \hline AZ61-CNT 0.1 & AZ61 alloy + 0.1 wt\% CNT & Decreased compression strength, corrosion rate: 0.0388 mm/yr \\ \hline AZ61-CNT 0.2 & AZ61 alloy + 0.2 wt\% CNT & Best corrosion resistance, corrosion rate: 0.0324 mm/yr \\ \hline AZ61-CNT 0.5 & AZ61 alloy + 0.5 wt\% CNT & Increased porosity, lower ductility, corrosion rate: 0.0678 mm/yr \\ \hline AZ91 & AZ91 alloy (8.5 wt\% Al, 0.8 wt\% Zn, and 0.25 wt\% Mn) & Baseline corrosion rate: 0.0396 mm/yr \\ \hline AZ91-CNT 0.1 & AZ91 alloy + 0.1 wt\% CNT & Improved corrosion resistance, corrosion rate: 0.0267 mm/yr \\ \hline AZ91-CNT 0.2 & AZ91 alloy + 0.2 wt\% CNT & Optimal balance, corrosion rate: 0.0178 mm/yr \\ \hline AZ91-CNT 0.5 & AZ91 alloy + 0.5 wt\% CNT & Reduced ductility, corrosion rate: 0.0718 mm/yr \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Magnesium alloy composites with CNT reinforcement. (Summary of the study of [PERSON] et al. [114]). \begin{table}
\begin{tabular}{l l l} \hline \hline
**Composites** & **Formulation** & **Output** \\ \hline HEA (AlCoFeMnNi) & Spark plasma sintering (SPS) at 850 \({}^{\circ}\)C & Baseline hardness \(\sim\)500 VHN, crystallite size \(\sim\)40 nm \\ \hline HEA-CNT 1\% & Mechanical alloying + SPS at 850 \({}^{\circ}\)C & Hardness improved to \(\sim\)650 VHN, crystallite size reduced to \(\sim\)10 nm \\ \hline HEA-CNT 1\% Higher & Mechanical alloying + SPS at 950 \({}^{\circ}\)C & Further hardness increase to \(\sim\)670 VHN, reduced porosity \\ \hline \hline \end{tabular}
\end{table} 
Table 8: High entropy alloy (HEA)/CNT nanocomposites. (Summary of the study of [PERSON] et al. [115]). tures and reinforcements such as fibers or nanoparticles. These composites are designed to exhibit tailored properties that meet specific performance criteria, which ordinary concrete may not offer [116, 117]. Cement composites consist of a binder, usually Portland cement, supplemented by various additives, like fly ash, slag, and silica fume, which enhance the material properties through pozzolanic reactions [116]. The binder is mixed with water, initiating hydration that results in the hardening of the composite. Aggregates, both fine (sand) and coarse (gravel), are added to provide volume and strength. Advanced cement composites may also include high-performance admixtures, such as superplasticizers for workability, retarders for controlling the setting time, and accelerators for early strength gain [116, 118, 119]. Due to their wide application in building insulation, significant research has been undertaken on improving the quality and performance of cementitious composites. Reinforcements in cement composites can vary from macroscopic reinforcements (e.g., steel bars) to CNTs, graphene/graphene oxide, and polymer microfibers. These reinforcements are introduced to improve the tensile strength, ductility, and toughness of the material, properties that pure cementitious materials lack.