Here, we report a novel highly sensitive wearable strain sensor based on a highly stretchable multi-walled carbon nanotube (MWCNT)/Thermoplastic Polyurethane (TPU) fiber obtained via a wet spinning process. The MWCNT/TPU fiber showed the highest tensile strength and ultra-high sensitivity with a gauge factor (GF) of approximately 2800 in the strain range of 5–100%. Due to its high strain sensitivity of conductivity, this CNT-reinforced composite fiber was able to be used to monitor the weight and shape of an object based on the 2D mapping of resistance changes. Moreover, the composite fiber was able to be stitched onto a highly stretchable elastic bandage using a sewing machine to produce a wearable strain sensor for the detection of diverse human motions. We also demonstrated the detection of finger motion by fabricating a smart glove at the joints. Due to its scalable production process, high stretchability and ultrasensitivity, the MWCNT/TPU fiber may open a new avenue for the fabrication of next-generation stretchable textile-based strain sensors.

In this study, to fabricate neutron shielding material, boron carbide (B₄C)-reinforced aluminum (Al) alloy composites were successfully fabricated by stir casting followed by a hot rolling process. Microstructural analysis of B₄C/Al6061 composites with different volume fractions (5, 10, 20, 25, and 30%) revealed that the composites had volume ratios similar to the target volume ratios of B₄C. Furthermore, B₄C reinforcements were uniformly dispersed in the Al matrix, forming multi-interfacial layers of Al₄C₃/(Ti,Cr)B₂. The interfacial layer generated during stir casting maintained its own structure after the hot rolling process, indicating strong interfacial bonding strength. The tensile strengths of the B₄C/Al6061 composites increased to 20 vol.% and stayed above the value for Al6061, even reaching 30 vol.%. The measured thermal neutron shielding rate increased with increasing B₄C content, and the highest thermal neutron shielding rate was observed at 30 vol.% composite, which corresponds to 95.6% neutron shielding at 0.158-cm thickness.

In this study, high volume fraction B₄C reinforced Al matrix composites were fabricated with a liquid pressing process. Microstructural analysis by scanning electron microscope and a transmission electron microscopy shows a uniform distribution of the B₄C reinforcement in the matrix, without any defects such as pore and unwanted reaction products. The compressive strength and wear properties of the Al7075 matrix and the composite were compared at room temperature, 100, 200, and 300 °C, respectively. The B₄C reinforced composite showed a very high ultimate compression strength (UCS) over 1.4 GPa at room temperature. The UCS gradually decreased as the temperature was increased, and the UCS of the composite at 300 °C was about one third of the UCS of the composite at room temperature. The fractography of the compressive test specimen revealed that the fracture mechanism of the composites was the brittle fracture mode at room temperature during the compression test. However, at the elevated temperature, AMCs had a mixed mode of a brittle and ductile fracture mechanism under the compressive load. The composite produced by a liquid pressing process also showed superior wear resistance compared with the Al matrix. The result of the wear test indicates that the wear loss of the Al matrix at 300 °C was two times higher than that of the AMCs, which is attributed to the formation of a mechanically mixed layer (MML) in the composites at the high temperature.

Aluminum alloy (Al7075) composites reinforced with a high volume fraction of silicon carbide (SiC) were produced by a liquid-pressing process. The characterization of their microstructure showed that SiC particles corresponding to a volume fraction greater than 60% were uniformly distributed in the composite, and Mg₂Si precipitates were present at the interface between the matrix and the reinforcement. A superior compressive strength (1130 MPa) was obtained by an effective load transfer to the hard ceramic particles. After solution heat treatment and artificial aging, the Mg₂Si precipitates decomposed from rod-shaped large particles to smaller spherical particles, which led to an increase of the compressive strength by more than 200 MPa. The strengthening mechanism is discussed on the basis of the observed microstructural evolution.

In this study, to evaluate the effect of boron carbide (B₄C) addition on the wear performance of aluminum (Al), Al6061 and 5, 10, and 20 vol.% B₄C/Al6061 composites were manufactured using the stir casting and hot rolling processes. B₄C particles were randomly dispersed during the stir casting process; then, B₄C particles were arranged in the rolling direction using a hot rolling process to further improve the B₄C dispersion and wear resistance of the composites. Furthermore, a continuous interfacial layer between B₄C and the Al6061 matrix was generated by diffusion of titanium (Ti) and chromium (Cr) atoms contained in the Al6061 alloy. Wear depth and width of the composites decreased with increasing B₄C content. Furthermore, with B₄C addition, coefficient of friction (COF) improved as compared with that of Al6061. The results indicate that interface-controlled, well-aligned B₄C particles in the friction direction can effectively increase the wear properties of Al alloys and improve their hardness.

This study was conducted on titanium diboride (TiB₂) reinforced Al metal matrix composites (MMCs) with improved properties using a TiB₂ and aluminum (Al) 1050 alloy. Al composites reinforced with fine TiB₂ at volume ratios of more than 60% were successfully fabricated via the liquid pressing infiltration (LPI) process, which can be used to apply gas pressure at a high temperature. The microstructure of the TiB₂–Al composite fabricated at 1000 °C with pressurization of 10 bar for 1 h showed that molten Al effectively infiltrated into the high volume-fraction TiB₂ preform due to the improved wettability and external gas pressurization. In addition, the interface of TiB₂ and Al not only had no cracks or pores but also had no brittle intermetallic compounds. In conclusion, TiB₂–Al composite, which has a sound microstructure without defects, has improved mechanical properties, such as hardness and strength, due to effective load transfer from the Al matrix to the fine TiB₂ reinforcement.