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.

Titanium-based nitride physical vapour deposition (PVD) coatings, such as titanium nitride (TiN), are state-of-the-art solutions for surface modifications of CoCrMo-based implants for patients who are hypersensitive to metallic ions such as cobalt, chromium and nickel. Variations of the process parameters during the cathodic arc evaporation are known to exhibit an impact on the surface properties of coatings. The aim of this study was to characterise the effect of the substrate bias and the nitrogen pressure on the surface properties of TiNbN coatings deposited on CoCrMo alloys in a limited parameter set. Eighteen parameter sets were coated with TiNbN. The substrate bias (−100 to −200 V) and the nitrogen pressure (0.3–3.0 Pa) were selected following a randomised, multifactorial response surface test design. The coating thickness, roughness, hardness and scratch resistance were measured following standardised procedures. The structure of the coating was analysed by SEM and XRD. The substrate bias and the pressure exhibited a significant impact on the coating thickness and the surface roughness. The grain growth was predominantly impacted by the bias. The parameter variation did not show any significant impact on the XRD, hardness or scratch test results.