Abstract
The notch sensitivity of additively manufactured IN 625 superalloy produces by laser powder bed fusion (LPBF) has been investigated by tensile testing of cylindrical test pieces. Smooth and V-notched test pieces with four different radii were tested both in as-built state and after a stress relief heat treatment for 1 h at 900 °C. Regardless of the notch root radius, the investigated alloy exhibits notch strength ratios higher than unity in both as-built and in stress-relieved states, showing that the additive manufactured IN 625 alloy is not prone to brittleness induced by the presence of V-notches. Higher values of notch strength ratios were recorded for the as-built material as a result of the higher internal stress level induced by the manufacturing process. Due to the higher triaxiality of stresses induced by notches, for both as-built and stress-relieved states, the proof strength of the notched test pieces is even higher than the tensile strength of the smooth test pieces tested in the same conditions. SEM fractographic analysis revealed a mixed mode of ductile and brittle fracture morphology of the V-notched specimens regardless the notch root radius. A more dominant ductile mode of fracture was encountered for stress-relieved test pieces than in the case of the as-built state. However, future research is needed to better understand the influence of notches on additive manufactured IN 625 alloy behaviour under more complex stresses.
Highlights
Material failure is considered an important task during material selection and in the designing phase of a new product
For the purpose of this study, IN 625 superalloy coupons were manufactured by selective laser melting using as feedstock IN 625 metal powder produced by vacuum induction melting inert gas atomization (particle size range 15–45 μm and cumulative distribution by mass recommended by the machine manufacturer Q3 (d) [%]: d10 = 20 ± 2 μm, d50 = 30 ± 5 μm, d90 = 45 ± 5 μm) supplied by LPW Technology Ltd. (Runcorn, UK, subsidiary of Carpenter Technology Corporation)
The additively manufactured IN 625 superalloy is not sensitive to tensile brittleness induced by the presence of V-notches
Summary
Material failure is considered an important task during material selection and in the designing phase of a new product. Many studies have been conducted over the years regarding the characterization of material properties and failure modes. It is known that materials fail when they are subjected to loads beyond their limit, but sometimes material discontinuities are responsible for material failure. Material discontinuities such as cracks or notches are considered to be stress concentrators and they can be located externally (on a material’s surface) or internally (in a material’s mass). The assessment of notch influence on tensile properties is significant for material sensitivity determination [1]. In the last few decades, different methods have been applied to study the influence of notches in several metallic, ceramic and composite materials and various analysis methods have been used such as share sliding theory, finite element analysis etc. In the last few decades, different methods have been applied to study the influence of notches in several metallic, ceramic and composite materials and various analysis methods have been used such as share sliding theory, finite element analysis etc. [1,4,5,6,7,8]
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