Fracture Toughness of Cold Sprayed Pure Metals

Cold spray ability to repair worn or damaged parts and structures is being extensively used in mission critical applications such as aerospace, power generation and medicine. The repair process consists of removing the damaged or worn area, cold spraying it with a new material and machining to the final shape. The fracture mechanical properties of the added material are very important as the cracks may initiate in this area and extend to the base material. The study of fracture toughness of pure Al, Cu, Ni and Ti deposited by cold spray was performed in order to gain fundamental understanding of the damage process and quantify the material performance. Bending specimens from self-standing deposits measuring 4x3x32 mm with fatigue pre-crack were tested in three- and four-point bending. The K_IC values were obtained from J-R curves as suggested by ASTM E1820 standard. The J-integral was evaluated from load-displacement record and also using the JMAN method from full field displacement obtained by digital image correlation (DIC). The crack length was measured also by DIC. The results correspond to crack growth curves observed for same materials in the previous studies, i.e. the K_IC are much lower than those expected for bulk materials.