Color Changes and Mechanical Properties of Glass Fiber Reinforced Polycarbonate Composites after Thermal Aging

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.

Structure and Multistage Martensite Transformation in Nanocrystalline Ti-50.9Ni Alloy

An electron microscopic study of the evolution of the size, morphology, and spatial distribution of coherent Ti3Ni4 particles with a change in the aging temperature in a nanocrystalline (NC) Ti-50.9 at % Ni alloy with an inhomogeneous grain–subgrain B2-austenitic nanostructure has been carried out. It was found that with an increase in the aging temperature, along with a change in the size and shape of Ti3Ni4 nanoparticles, their spatial distribution changes from location at dislocations to precipitates at subboundaries. Research has shown that the presence of different types of internal interfaces in the nanostructure contributes to the heterogeneous distribution of coherent Ti3Ni4 nanoparticles in the volume of the B2 matrix, which is associated with the precipitation of particles in the region of low-angle subboundaries and the suppression of the Ti3Ni4 precipitation in nanograins with high-angle boundaries. The difference in the structural-phase state of nanograins and subgrains regions is the main reason for the implementation of the anomalous R-phase transformation effect in the sequence of multistage martensitic transformations B2↔R↔B19′.