Effects of laser cladding on fatigue performance of AISI 4340 steel in the as-clad and machine treated conditions

Abstract

Laser clad specimens were fabricated to characterize the axial fatigue failure behavior of laser clad 4340 steel in the as-clad condition and for specifically designed clad specimens with pre-clad machining and post-clad surface grinding processes. Three types of laser clad fatigue test specimens (Type I, II and III) were tested to study fatigue failure behavior and were compared to the unclad 4340 steel substrate specimen. Type I specimen investigates fatigue failure behavior from the clad toe region of as-clad specimens. Type II specimen evaluates fatigue strength enhancement effects by pre-clad machining of a groove for depositing a clad layer with post-clad surface grinding to process the added clad layer in the groove to be flush with the substrate material. Type III specimen studies clad specimens with extended clad area and surface grinding to promote fatigue failure within the clad region. The fatigue S-N curve for Type I, II and III clad specimens were compared to the S-N curve for the substrate specimens to show the reduction in fatigue strength for as-clad Type I specimens, and machining methods to improve fatigue strength for Type II and Type III specimens. The fatigue strength of all laser-clad specimens was observed to be lower as compared to that of the unclad substrate specimen.