Advanced alloy surface modification using ultrasonic pulsed waterjets**

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Surface modification of metallic alloys is an important method for improving properties such as fatigue, wear resistance, and even the corrosion susceptibility. Traditionally, this can be achieved by shot peening or grit blasting, while laser shock peening techniques are also now available. Recently, a novel ultrasonic pulsed waterjet manufacturing technique has been developed by VLN Advanced Technologies (Ottawa, ON). This method allows precision metal cutting and controlled removal of surface coatings (e.g., hard chromium plating). However, it has also been demonstrated that surface peening may be possible, with the waterjet technique being much more environmentally friendly, and physically cleaner, than conventional shot peening. The proposed research, in collaboration with both VLN and GKN Sinter Metals (St. Thomas, ON), will investigate the fundamental physical mechanisms operating during ultrasonic waterjet peening, particularly in terms of potential cavitation phenomena, and the associated materials interactions. The effects of waterjet peening will be investigated for various aluminium, iron and titanium alloys, fabricated using either powder metallurgy or additive manufacturing, and compared to conventional wrought alloy variants. These materials are of great importance to the aerospace and automotive industries within Canada. The degree and depth of residual surface stress generated following peening will be quantified through X-ray diffraction, and the effects on a variety of physical and chemical properties will be investigated. Surface characterisation will be conducted using several profilometry and microscopy techniques. The pre- and post-peened fatigue response will be assessed. The wear and corrosion response of the peened materials will be investigated, as both are sensitive to the metallurgical surface condition, which will be strongly affected through peening treatments. The recrystallization response will also be assessed, using differential scanning calorimetry and electron back scatter diffraction. Successful completion of this multi-disciplinary project will provide a scientific and engineering validation of the technique, and an international competitive advantage for both VLN and GKN.