Impact Strength of the Ni-P Coated Spring Steel with Varied Phosphate Content and Notch Orientation

Spring steel is a prominent piece of material in the automotive, aerospace and marine engineering applications. The existence of crack like flaws cannot be precluded in any engineering structures. During the course of manufacturing or under service conditions, corner cracks are formed. In the present experimental investigation, the impact toughness of spring steel with flat and corner notches has been analyzed. Also, the surface roughness and micro hardness studies have been carried out. The samples were coated with electroless Ni-P coating with varied phosphate content from 5 to 15%. The specimen preparation and the experimentations have been carried out according to the ASTM standards. Low velocity pendulum impact testing has been adopted for the experimentation with the corner notched specimen placed diagonally in the anvil. Results have revealed that the face notched sample has lower impact toughness compared to the corner notched one. The micromechanism study has shown that, even though the impact toughness of the corner notched samples is high, their failure behavior is more dangerous and unpredictable. The Ni-P coating with 10 % phosphate showed high impact toughness and delayed fracture.