Low-cycle Fatigue Behavior of Ni-based Superalloy GH586 with Laser Shock Processing

Low-cycle fatigue behavior of Ni-based superalloy GH586 with laser shock processing（LSP） was investigated. The residual stress of the specimens treated with LSP was assessed by X-ray diffraction method. The microstructure and fracture morphology were characterized by using an optical microscope（OM）, a scanning electron microscope（SEM）, and a transmission electron microscope（TEM）. The results indicated that the maximum residual compressive stress was at about 1 mm from the shocking spot center, where the residual compressive stress was slightly lower. High density tangling dislocations, dislocation walls, and dislocation cells in the microstructure of the specimens treated with LSP effectively prevented fatigue cracks propagation. The fatigue life was roughly twice as long as that of the specimens without LSP. The fatigue crack initiation（FCI） in specimens treated with LSP was observed in the lateral section and the subsurface simultaneously. The fatigue striation in the fracture treated with LSP was narrower than that in the untreated specimens. Moreover, dimples with tear ridges were found in the fatigued zones of the LSP treated specimens, which would be caused by severe plastic deformation.

Effects of processing parameters on fatigue properties of LY2 Al alloy subjected to laser shock processing

We address the effects of processing parameters on residual stresses and fatigue properties of LY2 Al alloy by laser shock processing （LSP）. Results show that compressive residual stresses are generated near the surface of samples due to LSP. The maximum compressive residual stress at the surface by two LSP impacts on one side is higher than that by one LSP impact. The maximum value of tensile residual stress is found at the mid-plane of samples subjected to two-sided LSP. Compared with fatigue lives of samples treated by single-sided LSP, lives of those treated by two-sided LSP are lower. However, these are higher than untreated ones.

Corrosion fatigue behavior of friction stir processed interstitial free steel

In this study, interstitial free （IF） steel plates were subjected to double-sided friction stir processing （FSP）. The fine-grained structure with an average grain size of about 12 μm was obtained in tbe processed zone （PZ）with a thickness of about 2.5mm. The yield strength （325 MPa） and ultimate tensile strength （451 MPa） of FSP IF steel were significantly higher than those of base material （BM） （192 and 314 MPa）, while the elongation （67.5%） almost remained unchanged compared with the BM （66.2%）. The average microhardness value of the PZ was about 130 HV, 1.3 times bigher than that of the BM. In addition, the FSP IF steel showed a more positive corrosion potential and lower corrosion current density than the BM, exhibiting lower corrosion tendency and corrosion rates in a 3.5 wt% NaCl solution. Furtbernlore, FSP IF steel exhibited higher fatigue life than the BM both in air and NaCl solution. Corrosion fatigue fracture surfaces of FSP IF steel mainly exhihited a typical transgranular fracture with fatigue striations, while the BM predominantly presented an intergranular fracture. Enhanced corrosion fatigue performance was mainly attributed to the increased resistance of nucleation and growth of fatigue cracks. The corrosion fatigue mechanism was primarily controlled by anodic dissolution under the combined effect of cyclic stress and corrosive solution.

Comparing the Fatigue and Corrosion Behavior of Nanograin and Coarse-Grain IF Steels

In the present work,a nanograin layer of about 150 μm thick was formed on the surface of an interstitial-free（IF） steel via friction stir processing.Then,the fatigue and corrosion behaviors of IF steel with nanograin layer were compared with that of coarse-structure counterpart.More than threefold increase in the hardness was observed due to the formation of nanograin layer.The size of nanograms in the stir zone was within 30-150 nm.This resulted in 50%increase in the fatigue strength of nanostructured specimen.Furthermore,the fracture surfaces were characterized using field emission scanning electron microscopy and scanning electron microscopy.As for the fatigue behavior of nanograin IF steel,the fracture surface was characterized by the formation of nanospacing striations and nanodimples.Besides,the nanograin structure pronounced the passivity and exhibited higher corrosion resistance.

What is going on in magnesium alloys？

China has been developed into one of the most active regions in terms of both fundamental and applied research on magnesium （Mg） and its alloys in the world from a solid base laid by its prominent metallurgist and materials scientists over the past decades. Nowadays, a large number of young-generation researchers have been inspired by their predecessors and become the key participants in the fields of Mg alloys, which consequently led to the establishment of China Youth Scholar Society for Magnesium Alloys Research in 2015. Since then, the first two China Youth Scholars Symposiums on Mg Alloys Research had been held at Harbin （2015） and Chongqing （2016） China, respectively. A number of crucial research inter- ests related to fundamental and applied Mg research were discussed at the conferences and summarized in this short perspective, aiming to boost far-reaching initiatives for development of new Mg-based materials to satisfy the requirements for a broad range of industrial employments. Herein, four main aspects are included as follows： i） Plastic deformation mechanism and strengthening strategy, ii） Design and development of new Mg-based materials, iii） Key service properties, and iv） New processing technologies.