Residual Stresses Development during Cold Spraying of Ti-6Al-4V Combined with In Situ Shot Peening

As a new member of the additive manufacturing family, cold spray provides various benefits such as a limited oxidation during deposition. Titanium alloys, being oxidation-sensitive materials, could thus benefit from this processing route. However, the high strength of these alloys implies that dense deposition is a significant challenge. Two pathways were explored to reduce porosity. The sensitivity to the different deposition parameters was first investigated. Further improvements were then obtained using in situ shot peening. Another major issue regarding the material performance is the presence of residual stresses. Usually, cold spray induces compressive residual stresses in the resulting deposits because of the shot peening effect of the solid-state particles. In contrast, the prevailing stresses are in tension in cold sprayed Ti-6Al-4V. An improved understanding of this feature, which stems from the contribution of different physical phenomena to the final stress state, would provide insights into a reduction of residual stress. This is crucial to maintain structural integrity and, in turn, consider cold spray as a viable additive manufacturing process. The in situ coating properties device allowed to measure the evolution of the residual stresses during and after deposition and to identify most influent operating parameters. The purpose of this study is to provide guidelines to control porosity and residual stresses in order to produce dense and thick Ti-6Al-4V coatings with good structural integrity.

Automated summary

Cold spray as a new additive manufacturing process provides benefits for oxidation-sensitive materials like titanium alloys, but the challenge lies in achieving dense deposition due to high alloy strength. This study explores the sensitivity of deposition parameters and the application of in situ shot peening to reduce porosity. The presence of residual stresses is also addressed, aiming to provide guidelines for controlling porosity and residual stresses to produce dense and thick Ti-6Al-4V coatings with good structural integrity.