The effect of shot peening on the corrosion behaviour of Ti-6Al-4V alloy made by DMLS

Abstract

Additive Manufacturing processes are being used increasingly in the scope of medicine and dentistry. As indicated by literature data, the durability and quality of medical implants is decisively influenced by surface modification. Insufficient quality of surface finishing leads, among others, to reduced service life of applied implants and to increased number of necessary revision surgeries. Furthermore, various types of finishing processes e.g. cleaning, shot peening or abrasive techniques are suggested by the manufacturers of products made by means of DMLS processes. Due to this fact, the analysis of proper formation of the surface layer of titanium products made by means of the method consisting in the direct laser sintering of metal powders (DMLS) was the subject matter of our research. Therefore, Ti-6Al-4V titanium alloy has been used for tests. The samples have been produced by means of EOSINT M280 system dedicated for laser sintering of metal powders. The surfaces of prepared samples have been subjected to shot peening process at three different values of working pressure (0.2, 0.3 and 0.4 MPa) by means of three different working media i.e. CrNi steel shot, crushed nut shells and ceramic balls. The characteristics of the materials used for shot peening process have been determined by means of Zeiss Ultra Plus scanning electron microscope. The samples have been subjected to profilometric measurements on Bruker Contour GT optical profilometer and the corrosion behaviour of Ti-6Al-4V titanium alloy in Ringer solution has been determined in electrode impedance spectroscopy (EIS) measurements by means of Atlas 0531 set dedicated for corrosion testing. The overall results of all tests indicate to favourable influence of the shot peening process on the corrosion behaviour of titanium alloy.

Changes of cytotoxicity of Ti-6Al-4V alloy made by DMLS technology as effect of the shot peening

“…Titanium alloys are protected as a result of thin passive layer spontaneously developing on their surface. The passive layer created on surgical Ti-6Al-4V alloys is stable in body fluids solution, and rich mainly in amorphous TiO 2 [4,29,37]. The thickness of such passive films is usually equal to a few nanometres, but they constitute a highly protective barrier between the metallic alloy surface and the aggressive environment of body fluids.…”

“…As a result of the shot peening process, a rough surface is created which is susceptible to corrosion in connection with destroyed areas of the passive film as a result of the shot impact [28,29]. However, Jelliti et al [4] observed the creation of a stable passive film, and the increase of electrochemical potential on titanium specimens subjected to the shot peening process.…”

“…The shot peening process was carried out under pressure of 0.4 MPa perpendicularly to the surface. According to previous publications [26,[28][29], the used treating parameters allowed to prepare material with the best mechanical properties and corrosion resistant. The principal parameters of materials used in the peening process are included in Table 1.…”

“…In accordance with research carried out by authors presented in earlier studies, as a result of shot peening, shot grains penetrate (drive) into subsurface layer and, with the exception of improvement of mechanical properties, may slightly deteriorate the corrosion resistance of the modified products. Furthermore, the residuals of shot peening medium in the surface layer may contribute to elements ions release to adjacent tissues, and consequently to toxicity [28,29].…”

How build angle and post-processing impact roughness and corrosion of additively manufactured 316L stainless steel

“…[68][69][70][71][72][73][74][75][76] • Mechanical surface finishing (planar polishing, tumble polishing, etc.) 20,33,35,40,43,44,[77][78][79][80][81][82] • Chemical polishing 83,84 • Investigating multiple techniques, separate and combined 78,85,86 All techniques showed reductions in surface roughness of the AM parts, yet an issue for many of them is their inability to effectively polish a complex shaped part. Electropolishing presents itself as a sound method to polish complex shapes, with current studies by Urlea et al on building customized cathodes adjacent to an AM part to improve polishing efficiency 64,65 .…”