Laser surface engineering to improve wear resistance of austempered ductile iron

Abstract

In the present study, an attempt has been made to evaluate the scope of enhancing wear resistance of austempered ductile iron (ADI) by laser surface melting (LSM) and laser surface hardening (LSH). A detailed study concerning microstructural evolution and mechanical properties following LSM and LSH indicates that LSM develops a relatively low microhardness at the near surface region and a predominantly austenitic microstructure in the laser melted zone. On the other hand, LSH, compared to LSM, results into a higher and more uniform microhardness profile due to a primarily fine martensitic microstructure in the laser hardened zone. Careful X-ray diffraction analyses coupled with microstructural studies reveal that diffusion of carbon from graphite is responsible for a higher volume fraction of retained austenite and lower hardness in the laser irradiated zone following LSM than those after LSH. Furthermore, LSH develops residual compressive stress, while LSM produces residual tensile stress on the surface. Finally, adhesive wear tests with a pin-on-disc machine and subsequent microstructural analyses show that LSH is more appropriate than LSM to enhance adhesive wear resistance of ADI.