Abstract
Solar concentrators increase the amount of usable energy available in solar collection systems by focusing energy through an aperture to which energy is magnified within the area of its trajectory. Design challenges of a solar concentrators for space applications are to make them more lightweight, compact, and exhibit a smooth and consistent reflective surface curvature for optimal performance. Shape memory alloys (SMAs) offer an effective and compact solution to engineering needs, such as solar reflectors, to reduce weight and improve overall energy collection and concentration performance. The one-way shape memory effect can be used for this application, where the SMA is heat treated in a strained designed curvature by forcing the austenite microstructure to “remember” the original shape even after deformation. SMAs are capable of actuating from the stow configuration and into the designed shape after the solar energy exposure induces a phase transformation. In this study, NiTi and NiTiCu SMAs were thermomechanically processed into plates and cut into three sizes of triangular chips for use as reflector components. Standard binary NiTi SMAs was modified with the substitution of Cu for Ni to achieve a narrower hysteresis and better thermomechanical cycling stability. The SMAs were produced from commercially available NiTi SM495 plates by ATI Specialty Alloys and Components (Albany, OR) and custom-melted NiTiCu buttons. Each processing step was comprehensively characterized to monitor microstructural and thermomechanical property changes using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and Vickers hardness (HV). The NiTi and NiTiCu triangular chips were shape-set utilizing a custom-made apparatus to attain the intended curved surface with specific dimensions for a reflector component within a solar concentrator.
