Laser surface engineering to improve wear resistance of austempered ductile iron

In the present study, an attempt has been made to evaluate the scope of enh ancing wear resistance of austempered ductile iron (ADI) by laser surface m elting (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 surf ace region and a predominantly austenitic microstructure in the laser melte d zone. On the other hand, LSH, compared to LSM, results into a higher and more uniform microhardness profile due to a primarily fine martensitic micr ostructure in the laser hardened zone. Careful X-ray diffraction analyses c oupled with microstructural studies reveal that diffusion of carbon from gr aphite is responsible for a higher volume fraction of retained austenite an d lower hardness in the laser irradiated zone following LSM than those afte r LSH. Furthermore, LSH develops residual compressive stress, while LSM pro duces residual tensile stress on the surface. Finally, adhesive wear tests with a pin-on-disc machine and subsequent microstructural analyses show tha t LSH is more appropriate than LSM to enhance adhesive wear resistance of A DI. (C) 2001 Elsevier Science B.V. All rights reserved.