PRECISE PEENING OF NI-CR-MO STEEL BY ENERGY-INTENSIVE MULTIFUNCTION CAVITATION IN CONJUNCTION WITH POSITRON IRRADIATION

The peening characteristics of Ni-Cr-Mo steel were investigated using energy-intensive multifunction cavitation using positron irradiation (PMEI-MFC). It was found that PMEI-MFC in a high magnetic field, multifunction cavitation in a high magnetic field (MEI-MFC), laser irradiation ultrasonic cavitation (LMEI-UC), and a combination of positron and laser irradiation ultrasonic cavitation in a high magnetic field (PLMEI-UC) could reduce the surface roughness of unprocessed metal specimens by approximately one-fourth. Furthermore, the PMEI-MFC method greatly improved the residual stress at the metal surface by up to 1155 MPa. Each of these technologies was found to increase the surface hardness although the PLM-WJC and PMEI-MFC processes, which generated high temperatures, produced smaller increases than were obtained using the LMEI-MFC technique. This difference is attributed to recrystallization, which eliminated work hardening at the outermost metal surface during processing using positrons. The data also indicate that the PMEI-MFC method was able to both smooth and flatten the metal surface. This research demonstrates an approach to precision peening that can reduce surface roughness while imparting high compressive residual stress.