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Abstract:
Although intensively researched in the last decade, additive manufacturing techniques are still subject to certain shortcomings, such as internal porosity or anisotropy of properties. In this work, we investigate the effects of postprocessing via hot isostatic pressing (HIP) on the properties of the titanium alloy Ti6Al4V produced via two various additive manufacturing methods: laser powder bed fusion (LPBF) and cold spray (CS). The LPBF produced a microstructure composed of a mixture of hcp-structured α(Ti) and α’(Ti), whereas α(Ti) and bcc-structured β(Ti) were recognized in the CS-ed materials. The subsequent HIP treatment did not cause reformation of the LPBF microstructure. This process had a significant effect on the densification of the CS-ed samples. To study the anisotropy of the material properties, the tensile and compressive strengths of the materials were determined in the planes parallel and perpendicular to the building (LPBF) and spraying (CS) directions. The LPBF materials exhibited significantly better mechanical properties stemming from the typical α/α’ martensitic microstructure, whereas the CS-ed materials presented a high number of pores and smooth and textured regions composed of recrystallized grains and grains with a high number of dislocations, respectively. The HIP treatment led to a reduction in porosity, causing a significant increase in the mechanical properties (UTS by 132%) and a reduction in the UTS anisotropy in the CS-ed materials

Keywords:
Ti6Al4V, Laser powder bed fusion, Cold spray, Hot isostatic pressing, Mechanical properties

Abstract:
Additive manufacturing (AM) has seen remarkable development in recent years due to relatively high efficiency of the process. Cold spraying (CS) is a particular method of AM, in which titanium and titanium alloy powders are used. CS is a very competitive technology enabling the deposition of coatings, repairing machine parts, and manufacturing new components. For specific applications, the surface of cold-sprayed materials may require further processing. This paper reports an attempt to employ laser surface treatment (LST) of cold-sprayed coatings on an aluminium alloy substrate. The influence of laser beam interaction time on the coatings’ properties was analysed. The microstructure was investigated and observed employing scanning electron microscopy (SEM). To evaluate residual stress after CS and LST, the sin2ψ technique was used. Investigations were also performed on Vickers hardness, contact angle, and surface roughness. Significant changes in the surface morphology of the coatings and elevated residual stress levels dependent on the laser beam interaction time were observed. Increased Vickers hardness was recorded for titanium alloy Ti6Al4V. LST also led to increased surface hydrophilicity of the modified materials Ti and Ti6Al4V.

Keywords:
cold spray, laser surface treatment, titanium coating, Ti6Al4V, residual stresses