Improvement of the Fatigue Behavior of Stainless Steel Substrates by Low Pressure Fluidized Bed Peening (FBP)

Abstract

This study investigates the effectiveness of fluidized bed peening (FBP) to improve the fatigue behavior of axial-symmetric stainless steel substrates. The substrates were rotated at moderate speed inside a fluidized bed of stainless steel media. Their fatigue failure was determined by rotating bending testing procedure. The number of cycles to fracture was plotted versus the maximum amplitude of alternating stress for fluidized bed peened and unpeened substrates. The effect of peening time was also looked into. FBP was found to definitely improve the number of cycles to fracture. Fatigue life was normally increased of four to five times, although improvements up to an order of magnitude were detected. Hardness measurements, profilometry, scanning electron microscopy, and X-ray diffractometry allowed interpreting the improvement of the fatigue behavior of the peened substrates. After FBP, the substrates surface was characterized by a higher hardness, a smoother and less defective morphology, as well as a beneficial compressive residual stress. Therefore, the improvement in surface and microstructural properties of the peened substrates induced a related increase in their fatigue life. Peening time was also found to influence the fatigue behavior of the substrates, although the sharpest variations in the number of cycles to fracture were observed at the beginning of the fluidized bed process. Based on the previous experimental findings, approximate analytical models, very useful for automation and process control, were proposed, thus providing to the practitioners first hints on how to best set FBP process parameters.