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The microstructure evolution and mechanical behavior of an Fe-33Mn-4Si alloy steel under low-cycle fatigue deformation were investigated by using the X-ray diffraction and electron backscatter diffraction techniques.Results show that the experimental steel has an initial microstructure consisting of austenite and thermally induced ε-martensite. The initial microstructure remarkably affects the low-cycle fatigue property of the experimental steel through influencing the ε-martensitic transformation during deformation. At the early stage of fatigue deformation (first 100 deformation cycles), with increasing deformation cycles, a rapid increase in the volume fraction of ε-martensite and the frequency of the intersection of ε-martensite with different variants result in a quick rise in cyclic average peak stress and work hardening degree. With the continuation of cyclic deformation up to fatigue fracture, the ε-martensite becomes the dominant constituent phase in the deformation microstructure, and the volume fraction of ε-martensite and the frequency of the intersection of ε-martensite increase at an appreciably slower rate, thereafter significantly slowing the increase in cyclic average peak stress and work hardening degree.

Laser cladding provides a cost-effective and high-quality solution for repairing aircraft engines. A finite element model was developed in this study to simulate and analyze the stress distribution during the cladding of a complex curved groove structure made of Ti6Al4V. The mechanism underlying the microstructure at the interface was revealed. The stress concentration locations in the curved groove structure are located at the intersection of the cladding layer and sidewall, as well as at both ends of the cladding layer and the groove bottom. By applying reverse swing scanning, a more consistent distribution of stress fields can be obtained. Optimizing the scanning strategy reduced the maximum stress in the repair layer from 717 MPa to 711 MPa. The experimental stress distribution data are in good agreement with the computational results. The cladding layer undergoes changes in heat cycling and nucleation conditions, leading to the formation of alternating columnar and equiaxed grain morphologies. [ABSTRACT FROM AUTHOR]