SUMMARY

Water cavitation peening is a surface treatment process used to generate beneficial compressive residual stresses while being environmentally sustainable. Compressive residual stresses generated by the collapse of the cavitation cloud at the workpiece surface result in enhanced high cycle fatigue and wear performance. Co-flow water cavitation peening, a variant of cavitation peening involves injection of a high-speed jet into a low-speed jet of water, which makes the process amenable to automation and imparts the variant with the ability to process large structural components. Ultrasonic cavitation peening, another variant of cavitation peening, is used for peening small areas. However, an increase in cavitation intensity is needed to reduce the processing time for practical applications and to enhance process capabilities for a wide range of materials in both these variants. An experimental investigation along with numerical modelling is presented to demonstrate cavitation intensity enhancement through suitable modifications to the inner jet nozzle design in co-flow water cavitation peening. Particularly, the effects of upstream inner-jet organ pipe nozzle geometry, inner-jet nozzle orifice conicity, and inner-jet nozzle orifice length are studied to show enhanced cavitation intensity, measured via extended mass loss tests, strip curvature and residual stress measurements, high speed videography, and impulse pressure measurements. Numerical modeling using computational fluid dynamics (CFD) is presented to explain and provide insights into the experimental findings. A study of the addition of water-soluble polyethylene oxide polymer additives to enhance cavitation intensity in ultrasonic cavitation peening is also presented. Greater cavitation activity by addition of polymer additives is shown through high-speed videography and impulse force measurements. Greater pitting and surface roughness are observed with polymer additives indicating the potential for favorable surface modification.