Introduction of Compressive Residual Stress by Means of Cavitation Peening into a Titanium Alloy Rod Used for Spinal Implants

Abstract

<p align="justify"> <span style="font-family:Verdana;">The introduction of compressive residual stress is an effective way to reduce fretting fatigue and fretting wear between a spinal implant rod and its holding fixture. The objective of this paper is to demonstrate that cavitation peening can introduce compressive residual stress into the surface of a spinal implant rod manufactured from medical grade tita</span><span style="font-family:Verdana;">nium</span><span> </span><span style="font-family:Verdana;">alloy Ti-6Al-4V, which has already been processed by glass shot peening. In order to apply the cavitation peening for the small rod, whose diameter is only 5.5 mm, the cavitating region was concentrated by increasing the ambient pressure. The depth profiles of the resulting residual stress were evaluated by X-ray diffraction following layer removal by electropolishing. The results show that cavitation peening creates compressive residual stress deeper into the rod, even though the stress value at the near surface is saturated due to initial processing using glass shot peening. The depth of the compressive residual stress continuously increases from 44 μm to 230 μm with an increase in the cavitation peen</span><span style="font-family:Verdana;">ing processing time. In addition, the full width at half maximum value of the X-ray diffraction profile, which is closely related to the micro-strain, decreases by up to 32% following the application of cavitation peening.</span><span></span> </p> <p> <span></span> </p

Using Cavitation Peening to Improve the Fatigue Life of Titanium Alloy Ti-6Al-4V Manufactured by Electron Beam Melting

“…Interestingly, cavitation peening decreases the FWHM as opposed to shot peening even though a compressive residual stress is also introduced. In past literature, it has been shown that cavitation peening can decrease the FWHM while also introducing compressive residual stresses in titanium alloy rods made of Ti-6Al-4V [23]. It is likely that the ultrasound produced by cavitation bubbles collapsing moves dislocations, which may be the source of the microstrain [24].…”

Experimental Investigation of Peening Cylindrical Workpieces Utilizing a Transducer with Ring Sonotrode

“…Water cavitation jet peening utilizes this deformation. A Ti-6Al-4V rod with a diameter of 5 mm was investigated using this process and it was found that the depth of the introduced compressive residual stress increased up to 230 µm at a processing time per unit length of 10 s/mm [10]. The laser peening process uses high-energy pulsed laser to generate shock waves on the surfaces of the treated surfaces [11].…”

Surface mechanics design by cavitation peening

“…However, impacts at cavitation bubble collapses can be utilised for mechanical surface treatment in the same way as shot peening. The peening method using cavitation impacts is called “cavitation shotless peening” [2–5] as shots are not required, or named simply “cavitation peening” [6–12]. The advantage of cavitation peening is that increase of surface roughness is less than that of conventional shot peening, as there is no solid collision [6].…”