Thermal aging of polymer matrix composites exert significant influence on their properties and applications. This paper studied the color changes and mechanical properties of glass fiber reinforced polycarbonate (GF-PC) composites after aging at different temperatures, and the correlation between the trend of color changes and mechanical properties after aging was discussed. The GF-PC composites were aged at 85 °C, 100 °C, 115 °C, 130 °C and 145 °C, respectively. Thereafter, CIELAB colors were used to characterize the color changes of the composites after aging. Tensile and three-point bending tests were carried out to determine the mechanical properties of the composites. According to the values of CIELAB color, the color changes and the color difference (ΔE) of the GF-PC composites after aging were calculated, which showed that color of the GF-PC composite aged at 100 °C changed the most. The color changes of the composites after aging mainly comes from the change of brightness (L value), which was 25.067 for the Raw GF-PC composite. When the aging temperature increased from 85 °C to 100 °C, the brightness of the composites also increased, but decreased when the aging temperature is above 100 °C and continues to rise. Coincidentally, the trend of the mechanical properties of GF-PC composites is closely associated with color changes in the aging temperature range of 85 °C to 145 °C. The tensile and flexural strength of the composites reached the maximum value 72 MPa and 131 MPa, respectively, after aged at 100 °C. It can be speculated that the brightness of the GF-PC composites correlates with trends observed in its tensile strength and bending strength.

Film bulk acoustic resonators (FBARs) based on aluminum nitride (AlN) and scandium-doped aluminum nitride (AlScN) exhibit tremendous application aspects in the radio frequency front-end due to achievable high-frequency characteristics, superior thermal performances and compatibility with harsh environments. Delicately controlling the resonant frequency (f_s) of FBAR is essential for integrating filters or modules. In this work, we provide a practical feasibility in adjusting f_s of AlN and AlScN FBAR using external direct current electric bias (E_DC). When applying a negative E_DC (the direction along the reversed c-axis), f_s shifts to a lower frequency, whereas a positive E_DC brings a higher f_s. In order to extract the equivalent values of the stiffness coefficient (c₃₃), piezoelectric coefficient (e₃₃) and dielectric constant (ε_zz) of AlN and AlScN piezoelectric materials, we adopted the electromechanical equivalent Mason model. The results show that the equivalent values of c₃₃ increase with the change of E_DC from negative to positive, and, on the other hand, those of e₃₃ and ε_zz decrease. Our work provides a systematic investigation on the electric field-influenced stiffening effect of AlN and AlScN piezoelectric films and opens a feasibility for frequency-tunable resonators.

By modifying the accumulative roll-bonding (ARB) procedures, accumulative roll-bonding (ARB) processing up to 30 cycles (N) with a 50% thickness reduction per cycle (equivalent strain = 24) at room temperature was conducted on pure copper. The bonding condition, microhardness and electrical conductivity of the ARBed Cu were studied. Results showed that good bonding condition of the samples was achieved. As N increases, the microhardness of ARBed Cu increases, reaching ~2.9 times that of annealed Cu for N = 30. The electrical conductivity of ARBed Cu decreases slightly but with periodic fluctuations for N > 10, with a minimum of 90.4% IACS for N = 30. Our study indicated that ARB can be an effective way to produce high-hardness and high-conductivity pure copper better than or comparable to Cu alloys and Cu based composites as reported.

The properties of nanoporous gold (NPG) were known to be dependent on the microstructure of NPG. In this study, the effects of cold rolling and annealing of the original Ag_0.7Au_0.3 alloy on the microstructure of NPG produced by dealloying under free corrosion condition were investigated. Ag_0.7Au_0.3 alloy samples were cold-rolled to different strain levels/thickness reductions up to 98% and annealed at 900 °C for 3 h before dealloying. It was found that cold rolling and annealing of the original alloy can lead to reduced ligament and pore sizes of NPG. Moreover, post-deformation annealing of the original alloy was found to facilitate the formation of a homogeneous and continuous NPG structure. The minima of pore and ligament sizes (both being ~8 nm) with uniform distribution were obtained in the annealed sample with a thickness reduction of 60% for a dealloying time of 7 h. The present study indicated the significant effect of a pre-dealloying treatment of the original alloy (by plastic deformation and annealing) on the formation and optimization of the NPG microstructure produced by dealloying.