Micro-Forging and Peening Aging Produced by Ultra-High-Temperature and Pressure Cavitation

From microstructural examination of specimen surfaces or sides and from the mechanical properties resulting from compressive residual stress using Cr-Mo steel (SCM435), Ni-Cr-Mo steel (SNCM630), Ti-6aAl-4V, and Inconel (UNSN06601) processed by WJC and UTPC (micro-forging), the microstructure of the WJC-processed specimen revealed that voids and cracks tended to occur in the depth region of 0.5-1 mm from the topmost surface. The microstructure of the UTPC-processed specimen showed the spheroidization of cementite observed in the depth region of 0.5-1 mm from the topmost surface. In addition, voids and cracks were not observed in the specimen bulk. The Charpy impact energy of UTPC had the highest value of 101 J because ductile layers were formed by UTPC processing. Stress relaxation behavior of various processed materials at a temperature of 500°C was investigated. Compressive residual stress of more than 100 MPa was retained after annealing both the WJC- and UTPC-processed specimens for 5 hours. After stress relaxation testing, cracks owing to thermal stress do not occur at the grain boundary in the UTPC material having a tenacious tough layer inside. Micro-forging (UTPC) is promising for high-temperature oxidation of low-alloy steel, Ti alloy, and Inconel. Moreover, low-temperature and low-pressure cavitation (LTPC) is applied to age hardening of aluminum alloy Al-Mg-Si (AC4CH).