The aim of this study is to clarify the factors that control the macroscale strength of cold spray coatings by evaluating local strength at the microscale. Using pure copper powder and high-pressure cold spray equipment, thick (15 mm) copper layers were deposited on aluminum substrates. The coatings were evaluated by SEM and EBSD analysis, then freestanding Cu specimens were fabricated in a FIB system, where in-situ micro tensile tests were carried out. The results are presented and discussed along with the role of microvoids.

Thermally grown oxide (TGO) grows at the top / bond coating interface of the thermal barrier coating (TBC) in service. It is supposed that the failures of the TBC occur due to thermal stress and the decrease of adhesive strength caused by the TGO growth. Recently, large local stress has been found to change both the diffusion constant of oxygen through an existing oxide and the rate of chemical reaction at the oxide / oxidized material interface. Since high thermal stress occurs in the TBC, the volume expansion of the newly grown oxide, and centrifugal force, the growth rate of the TGO may change depending on not only temperature but also the stress. The aim of this study is to make clear the influence of stress on the growth rate of the TGO quantitatively. As a result, the thickness of the TGO clearly increases with increase of the amplitude of the applied stress and temperature. The increase rate of the TGO thickness is approximately 23% when the applied stress is increased from 0 to 205 MPa at 900 °C, and approximately 29 % when the stress is increased from 0 to 150 MPa at 950 °C.