Effects of Ultrasonic Impact Treatment on the Stress-Controlled Fatigue Performance of Additively Manufactured DMLS Ti-6Al-4V Alloy

Abstract

Additive manufacturing (AM) offers many advantages for the mechanical design of metal components. However, the benefits of AM are offset to a certain extent by the poor surface finish and high residual stresses resulting from the printing process, which consequently compromise the mechanical properties of the parts, particularly their fatigue performance. Ultrasonic impact treatment (UIT) is a surface modification process which is often used to increase the fatigue life of welds in ship hulls and steel bridges. This paper studies the effect of UIT on the fatigue life of Ti-6Al-4V manufactured by Direct Metal Laser Sintering (DMLS). The surface properties before and after the UIT are characterized by surface porosity, roughness, hardness and residual stresses. Results show that UIT enhances the fatigue life of DMLS Ti-6Al-4V parts by suppressing the surface defects originating from the DMLS process and inducing compressive residual stresses at the surface. At the adopted UIT application parameters, the treatment improved the fatigue performance by 200%, significantly decreased surface porosity, reduced the surface roughness by 69%, and imposed a compressive hydrostatic stress of 1644 MPa at the surface. methodology, P.W., S.M., E.T. and S.N.; software, E.T.; validation, E.T., P.W.; formal analysis, E.T. and P.W.; investigation, P.W., S.M., E.T. and S.N.; resources, M.S.A.E.; data curation, E.T, P.W.; writing-original draft preparation, E.T., P.W. and S.N.; writing-review and editing, P.W. and M.S.A.E.; visualization, E.T., P.W. and S.N.; supervision, M.S.A.E.; project administration, M.S.A.E.; funding acquisition, M.S.A.E.

Enhanced cooling rates in laser directed energy deposition with interlayer peening

“…A more recent trend in the hybrid AM field is the application of peening processes during the intermediate build phases. Surface modification processes such as peening [for example, shot peening (SP), hammer peening (HP), laser shock peening (LSP)] have been applied as a post processing step for AM components (Hönnige et al , 2017; Hackel et al , 2018; Maamoun et al , 2018; Walker et al , 2019; Xing et al , 2019; Gatto et al , 2020; Jin et al , 2020; Soyama and Takeo, 2020; Lesyk et al , 2021; Walczak and Szala, 2021; Aguado-Montero et al , 2022). More recently, they have been hybridized with AM processes such that they are applied to intermediate build layers (Gale and Achuhan, 2017; Kalentics et al , 2017a, 2017b, 2018, 2019, 2020; Sealy et al , 2021; Zhang et al , 2021b).…”

Effect of Post-Processing Treatment on Fatigue Performance of Ti6Al4V Alloy Manufactured by Laser Powder Bed Fusion

“…They indicated that the disadvantage of ultrasonic nanocrystal surface modification is that it is not applicable to complex geometries. The experiments conducted by [24] showed that the ultrasonic impact treatment distributes residual stresses and generates a hardened surface. Additionally, it is able to close surface porosity and reduce roughness.…”

Transformations of the Microstructure and Phase Compositions of Titanium Alloys during Ultrasonic Impact Treatment Part II: Ti-6Al-4V Titanium Alloy

“…The effect of strain-induced phase transformations on the mechanical behavior of the highly stable Ti-6Al-4V alloy is also negligible. UIT provides benefits only for weld joints of Ti-6Al-4V, since it induces compressive stress improving their fatigue properties [5][6][7]. Moreover, the combination of UIT and Wire Arc Additive Manufacturing (WAAM) was recently proposed to improve the mechanical properties of Ti-6Al-4V parts [8].…”

“…The interstitials affect the electron structure of titanium causing its lattice transformation. However, the microstructural investigations of titanium alloys subjected to UIT are often focused on the evolution of dislocation density and grain structure [6,7], although the study of the strain-induced phase transformations should also yield both theoretical insight and practical results.…”