Effect of solution aggressiveness on the crack - growth resistance and cracking mechanism of AA2024-T3

Aluminium alloy 2024-T3 was examined – using a range of microscopy techniques – at the early stages of corrosion attack to investigate the corrosion-induced cracking mechanism. Two different corrosive environments, exfoliation corrosion (EXCO) and 3.5 % wt. NaCl, were used for the exposure of tensile and pre-notched compact-tension C(T) specimens of AA2024-T3. Different embrittlement mechanisms are noticed for the two investigated corrosive environments. Significant intergranular corrosion (IGC) and grain boundary embrittlement is evident in the specimens exposed to EXCO solution, while this was not the case for the milder solution; comprising of 3.5 % wt. NaCl. With regards to the milder solution, corrosion attack is not restricted to the grain boundary, but evolves transgranularly to the neighbouring grains of the IGC attacked region and, consequently, the grain boundary strength in the direct vicinity is not notably affected. The extent of secondary cracks – after the exposure of C(T) specimens to EXCO solution and the subsequent crack-growth resistance evaluation – were found to correlate with the diameter of the plastically affected zone (≈ 3.78 ± 0.04 mm). Additionally, the depth of these cracks was found to correlate well with the thickness of the intergranular fracture surface, giving evidence that the secondary cracks form due to grain boundary embrittlement; probably attributed to hydrogen embrittlement phenomena.

Research Progress of the Effects of Trace S Element on the Microstructure of Cast Nickel-base Superalloys

In the process of alloy melting and vacuum pouring, the impurity S element will inevitably be introduced into the nickel-base superalloys, which will cause adverse effects on the microstructure and properties of the cast nickel-base superalloys. In this paper, the research progress of S element in cast nickel-base superalloys is summarized. The effects of S element on the microstructure are described in detail from experimental researches and first-principles. The reasons for the grain boundary embrittlement caused by S atom are discussed, and the authors wish to provide some references for the better development of cast nickel-base superalloys.

Understanding solute effect on grain boundary strength based on atomic size and electronic interaction

Solute segregating to grain boundary can stabilize the microstructure of nanocrystalline materials, but a lot of solutes also cause embrittlement effect on interfacial strength. Therefore, uncovering the solute effect on grain boundary strength is very important for nanocrystalline alloys design. In this work, we have systematically studied the effects of various solutes on the strength of a Σ5 (310) grain boundary in Cu by first-principle calculations. The solute effects are closely related to the atomic radius of solutes and electronic interactions between solutes and Cu. The solute with a larger atomic radius is easier to segregate the grain boundary but causes more significant grain boundary embrittlement. The weak electronic interactions between the s- and p-block solutes and Cu play a very limited role in enhancing grain boundary strength. While the strong d-states electronic interactions between transition metallic solutes and Cu can counteract embrittlement caused by size mismatch and significantly improve the grain boundary strength. This work deepens our understanding of solute effects on grain boundary strength based on atomic size and electronic interactions.

Effect of Rolling Strain on the Mechanical and Tribological Properties of 316 L Stainless Steel

The mechanical and tribological performances of 316 L stainless steel subjected to different cold rolling (CR) strains were investigated. The microhardness and strength of 316 L stainless steel were improved attributed to the formation of high-density defects, such as dislocations and parallel lamellar structures. Furthermore, the tribology tests were conducted under dry sliding at room temperature. With the increase in rolling strain, the wear rate of 316 L stainless steel gradually decreased due to the improvements in microhardness and strength. For the as-received specimen, the strong adhesive wear leads to the maximum wear rate compared with the cold rolled specimens. Under higher rolling strain conditions, the grain boundary embrittlement caused by oxygen reaction leads to the formation of oxidative abrasive under dry sliding conditions, and then the oxidative abrasive could serve as the third body at the siding interface. Consequently, there is a transition phase where the wear mechanism gradually shifts from adhesive to abrasive wear.