Abstract
Residual stresses (RS) of great magnitude are usually present in parts produced by Laser Powder Bed Fusion (PBF-LB), mainly owing to the extreme temperature gradients and high cooling rates involved in the process. Those “hidden” stresses can be detrimental to a part’s mechanical properties and fatigue life; therefore, it is crucial to know their magnitude and orientation. The hole-drilling strain-gage method was used to determine the RS magnitude and direction-depth profiles. Cuboid specimens in the as-built state, and after standard solution annealing and ageing heat treatment conditions, were prepared to study the RS evolution throughout the heat treatment stages. Measurements were performed on the top and lateral surfaces. In the as-built specimens, tensile stresses of ~400 MPa on the top and above 600 MPa on the lateral surface were obtained. On the lateral surface, RS anisotropy was noticed, with the horizontally aligned stresses being three times lower than the vertically aligned. RS decreased markedly after the first heat treatment. On heat-treated specimens, magnitude oscillations were observed. By microstructure analysis, the presence of carbides was verified, which is a probable root for the oscillations. Furthermore, compressive stresses immediate to the surface were obtained in heat-treated specimens, which is not in agreement with the typical characteristics of parts fabricated by PBF-LB, i.e., tensile stresses at the surface and compressive stresses in the part’s core.
Highlights
Metals additive manufacturing (AM) is a flourishing technology, as it is growing rapidly and with great success
AM terminologies and general principles are standardized by the ISO/ASTM
Computer-aided design (CAD) model of the part to be built, which is sliced in several thin layers by a appropriate software [6]
Summary
Metals additive manufacturing (AM) is a flourishing technology, as it is growing rapidly and with great success. In the AM equipment, thin layers of material are selectively melted and joined on the top of each other progressively with the help of an energy source [6,7] This is a generic principle usually adopted for AM technology, among the different AM techniques it can be slightly distinct. Ison among the most properties compared properties with (good other corrosion alloys resistance and high strength) when com temperatures in environments, exhibiting exceptional known as superalloys, have been developed to work a large range of used superalloys ® 718for. Itwide has anumber wide number of alloying of alloying alloys, known as superalloys, developed to work on acurrently large range of metallic termetallic compounds and and inprocesses, isAM under ishave under research are just a been few of the metallic materials available for AM [7,14,15]. Fe,and is which strengthened isknown strengthened bysuperalloys, the precipitation bycompared the precipitation metastable of metastable resistance high strength) when with other alloysto[7,14].
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