The Effect of Postprocessing on the Fatigue Properties of Ti-5Al-5Mo-5V-1Cr-1Fe Produced Using Electron Beam Melting

Abstract

Despite the significant potential advantages of processing Ti-5Al-5Mo-5V-1Cr-1Fe alloy (Ti-55511) using Electron Beam Melting (PBF-EB/M), when compared to conventional manufacturing technologies, the resulting internal defects are an important characteristic of such additive technologies and can highly decrease mechanical properties. One of the most dangerous defects formed during metal additive manufacturing processes are material discontinuities such as a lack of fusion. Defects of this type, due to their “flat” nature, are difficult to characterize. For cycle-loaded specimens, where the loading force acts perpendicular to the lack-of-fusion plane, defects of this type can significantly reduce fatigue properties. This paper presents the results of research aimed at improving the fatigue properties of Ti55511 alloy by reducing the influence of the lack-of-fusion defect on fatigue damage. The static and fatigue properties of specimens in the as-built state, as well as after hot isostatic pressing (HIP) treatment, were analyzed. The effect of HIP on both the reduction of pores and the degree of sphericity when using the X-ray computed tomography (XCT) system was presented. The change in the microstructure after HIP was analyzed in terms of the change in the size of individual phases, as well as the change in the phase ratio. This paper also contains a fractographic analysis of the samples after tensile and fatigue tests.

Speed function effects on properties of Ti-5Al-5Mo-5 V-1Cr-1Fe alloy manufactured by electron beam melting

“…These defects are difficult or impossible to remove by hot isostatic pressing, depending on their location [68,69]. Karoluk et al [70] conducted fatigue tests on PBF-EB-processed Ti-55511 with process parameters similar to use for manufacturing SF 86 samples. Despite relatively low porosity (0.06%) with mainly spherical pores, they observed that the main cause of fatigue cracks in the as-built specimens were lack of fusion defects.…”

“…This alloy category includes, amongst others (Ti-10 V-2Fe-3Al, Ti-5.8Al-4Sn-3.5Zr-0.7Nb-0.5Mo-0.35Si, Ti-5Al-2.5Sn, and Ti-5Al-5 V-5Mo-3Cr), the alloy Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511), also designated as VT22. It is characterised by its ability to operate short-term at temperatures of 750-800 °C, high strength (1080-1280 MPa), and high fracture toughness (66)(67)(68)(69)(70)(71)(72)(73)(74)(75)(76)(77) MPa-m 0.5 ) [12][13][14]. It can be heat treated and thermomechanically treated, thus affecting fatigue properties, tensile strength, and ductility [12,15,16] by obtaining a microstructure with a bimodal grain shape, an equiaxial grain shape, or the Widmanstätten structure with a lamellar grain shape [13,14,17].…”