Mechanical testing and microstructural analysis of wire arc additively manufactured steels. (April 2022) - Huang, Cheng
Graphical abstract: Highlights: Results of tensile tests on WAAM normal- and high-strength steel coupons are presented. Influence of geometric variability and deposition strategy on the mechanical properties is investigated. Non-contact measurement methods are used to determine the specimen geometries and deformations. Slower cooling rates associated with the WAAM process result in lower mechanical strengths. Microstructural analysis reveals a weak crystallographic texture, explaining the mechanical properties being almost isotropic. Abstract: Wire arc additive manufacturing (WAAM) is a metal 3D printing method that allows the cost-effective and efficient production of large-scale elements, and has thus gained great interest from architects and structural engineers. Integration of this novel technology into the construction industry, however, requires the development of a clear understanding of the mechanical behaviour of WAAM materials. To this end, a comprehensive experimental study into the mechanical properties and microstructure of WAAM plates made of normal- and high-strength steels has been undertaken and is reported herein. A total of 137 as-built and machined tensile coupons were tested, extracted in various directions relative to the print layer orientation from WAAM plates of two nominal thicknesses, built using different deposition strategies. The influence of the geometric undulations inherent to the WAAM process and deposition strategy on the resulting mechanical properties was investigated. Microstructural characterisation was also performed by means of optical microscopy (OM) and electron backscatter diffraction (EBSD). The WAAM normal-strength steel plates exhibited a principally ferritic-pearlitic microstructure, while the WAAM high-strength steel plates displayed a mixed microstructure featuring ferrite, bainite and martensite. The EBSD analysis revealed a weak crystallographic texture, which explained the observed mechanical properties being almost isotropic. No significant differences in tensile properties were observed with the different deposition strategies, except for some variation in ductility. The geometric undulations of the as-built coupons resulted in some reduction in effective mechanical properties and a degree of anisotropy. Overall, the examined WAAM material exhibited consistent mechanical properties, a Young's modulus comparable to conventionally-produced steel plates, marginally lower strength, reflecting the slower cooling conditions than is customary, and good ductility.