Under strong fluid scour in special service environment, the film-substrate system is prone to weaken its mechanical properties due to the additional shear stress by fluid, resulting in film debonding. The present study establishes a mechanical model incorporating the fluid shear stress for a film-substrate system with partial debonding. The debonding length, scour strength and thermal mismatch are considered in the model, respectively. Fluid induces compressive stress on inflow side and tensile stress on outflow side. Potential debonding behavior of film by the additional shear stress is qualitatively analyzed. Results show that the compressive stress by fluid releases part of the tensile stress of thermal mismatch, may mitigate surface cracking of film. The surface scour effect is amplified by the partial debonding, and is further enhanced with the increase of debonding length. The unevenness of stress distribution at the interface is intensified by the debonding and fluid scouring. The fluid scour poses a potential threat to the film-substrate system

The copper (Cu)-beryllium (Be) alloy is a critical material for high-performance photomultiplier cathodes. The microstructure evolution of the beta phase in the Cu-2.8Be alloy subjected to cooling rate ranging from 0.5 to 80 C-degrees/ s after heat treatment. The non-isothermal phase transformation kinetics equation of the alloy was derived. At a cooling rate of 0.5 C-degrees/s, the beta phase completely transformed into the alpha phase and gamma phase through a eutectoid reaction (beta -> alpha + gamma). The gamma phase preferentially precipitates at locations with higher free energy, such as grain boundaries and defects in the parent phase. The orientation relationship between the alpha phase and the gamma phase follows the Kurdjumov-Sachs (K-S) relationship ([110](alpha) [111](gamma); (111)(alpha) (011)(gamma)), and the alpha phase nucleates and grows with a twin relationship to the Cu matrix. As the cooling rate increases, the transformation fraction of the beta phase decreases. The critical cooling rate at which the beta phase eutectoid reaction is completely suppressed is 80( degrees)C/s. A non-isothermal phase transformation kinetics equation for the beta phase eutectoid transformation was {established: f(r) = 1 - exp - {34.703r(- 1.062)[exp(- 0.9107r) - 0.3575]}(2.2)}, elucidating the relationship between the phase transformation fraction and the cooling rate, which provides a theoretical basis for controlling the microstructure of Cu-Be alloy through heat treatment. Validated by the Cu-3.3Be alloy, this equation demonstrates excellent universality.

Indentation size effect (ISE), in general, is observed in shallow indentation tests, which is manifested as an increase (NISE) or decrease (RISE) in hardness with penetration depth decreases. The complicated origin of ISE is dependent on multiple factors, which can be divided into two types, both strain gradient and external factors. It's very difficult to judge which factor is the source for a certain ISE phenomenon. Further, studies on ISE phenomena under the joint of multiple factors are fewer. To date, the classical Nix-Gao model based on strain gradient has been widely recognized, but it's sometimes not suited for all ISE. And most current analytical models on ISE are not yet mature. Therefore, more mechanistic models on ISE are required, especially for RISE. Herein, we critically reviewed several mechanistic models on ISE, focusing on the exploration of RISE, and developed an analytical model incorporating external factors, i.e. surface undulation and indenter tip irregularity, to account for NISE and RISE. We examined the two external factors on the origin responsible for ISE in light of 3D numerical simulations and experimental observations, meanwhile, the combined effect of both factors on ISE was also considered. The effect of both external factors on ISE can be equivalent to a depth deviation δ. The corresponding hardness deviation caused by δ can be theoretically eliminated through correcting the depth deviation. More importantly, only after eliminating the effect of external factors on ISE, one can determine whether the ISE results from strain gradient plasticity. Finally, this paper was summarized and outlooked.

Corrosion morphology is a key factor that influences the reliability and service life of a structure. As most structures service under stress corrosion, there is a great need to understand the effect of stress on the formation conditions of different morphologies. This paper introduces a numerical method to simulate the evolution of surface morphologies. The results indicate that a corroded surface will become rougher and sharper with an increase in stress, and as a consequence, the corrosion morphology will transfer from a flatter surface to a pit and then a crevice. The critical stress values for different morphologies (crevice, pit, and a flatter surface) were captured. Among the three morphologies, the flatter surface and pit maintain a fixed shape, also known as stable morphology. As stress exceeds a critical value, crevices are generated, and the morphology evolution becomes unstable. On the basis of the simulation results, the influence of morphology on the service life of the structure was evaluated. The corrosion velocity of a rough surface exceeds that of a flat surface, and this reduces the service life of the structure more significantly. With a rise in applied stress, the acceleration of corrosion presents a quadratically increasing relationship with applied stress.