The Effect of the Static Load in the UNSM Process on the Corrosion Properties of Alloy 600

Abstract

To suppress stress corrosion-cracking, compressive residual stresses, such as shot peening, laser peening, water jet peening, ultrasonic peening, and ultrasonic nanocrystal surface modification (UNSM) are utilized. However, among the numerous techniques, there is little research about the corrosion effect of detailed conditions, such as static load or amplitude in UNSM. A study on UNSM among various techniques of adding compressive residual stress to Alloy 600 was conducted. The focus of this study was on the effect of the static load in UNSM on the corrosion properties of Alloy 600. Microstructure analysis was conducted using an optical microscope (OM), a scanning electron microscope (SEM), and electron backscattering diffraction (EBSD), while compressive residual stress was measured using a nano-indentation technique. A cyclic polarization test and the AC (Alternating Current)-impedance measurement were both used to analyze the corrosion properties. An increase in static load under critical static load enhanced the grain boundary diffusion, consequently strengthened the passive film, and facilitated the surface diffusion, thereby improving the passivation of Alloy 600. However, higher static loads over the critical value can lead to an increase in the friction between the striking tip and the surface, thereby creating an overlapped wave, which reduces the corrosion properties.

Method of ultrasonic nano-crystal surface modification for improvement of surface characteristics of AISI D2 heat-treated with different tempering conditions

“…An excessive load increases the friction between the ball tip and material. It appears that such an increase in friction causes excessive plastic deformation [30] and decreases the roughness improvement rate. On the other hand, with low loads applied to D2-H55, as shown in Fig.…”

“…It is estimated that the roughness improvement rate is reduced when a load of 50 N is applied to D2-H40 owing to the generation of these wave patterns and cracks. In addition, these features may act as starting points for corrosion, thereby reducing the corrosion resistance [30]. In the case of D2-H55, however, the top surface was leveled through the ball tip, unlike D2-H40, as shown in Fig.…”

“…These results indicate that the roughness improvement increases as the inter-pass interval decreases regardless of the initial hardness of the base metal but that the static load effectively improves the roughness only when it lies within the critical range. An increase in the static load (within the critical range) may increase the dislocation density by leveling the surface, thereby improving the corrosion resistance [30].…”

Effects of Ultrasonic Nanocrystal Surface Modification on Mechanical and Corrosion Behavior of LZ91 Mg–Li Alloy

“…Recently, Hou et al 26) utilized UNSM technology to process AZ31B Mg alloy, the results showed that UNSM could significantly improve the mechanical properties of Mg alloys without compromising their corrosion rate. Kim et al 27) focus on the effect of the static load in UNSM on the corrosion properties of Alloy 600, they found that an increase in static load under critical static load improved corrosion performance.…”

Effect of Processing Route on Microstructure and Mechanical Properties in Single-Roll Angular-Rolling

“…Heterostructured materials are a new class of materials with artificial microstructural heterogeneities, and their unique strengthening mechanisms effectively contribute to strength-ductility synergy. Accordingly, microstructural approaches using SPD have been shifted to tailoring the heterogeneous microstructure by partial grain refinement, such as plastic flow machining [11] and ultrasonic nanocrystalline surface modification [12,13].…”