Hybrid manufacturing for strength enhancement of selective laser melted (SLM) IN718 via pre-straining at the ambient temperature

The effects of room temperature compressive pre-straining on mechanical properties and microstructure of Selected Laser Melted (SLM) inconel 718 (IN718) is elucidated and compared with those of forged material. IN718 is a high strength material widely used in many industries for extreme working conditions. However, inferior mechanical properties of SLMed-IN718 confined its industrial applications. Room temperature pre-straining processes as a representative of cold-work manufacturing processes were therefore proposed for enhancement of mechanical properties. Comperehensive tensile and compression tests along with hardness and microstructural analysis were performed on the laboratory specimens. In SLMed specimens, the tensile yield and ultimate strength after 30 % pre-strain were increased by 31.8 % and 11.6 %, respectively. In forged specimens, the tensile yield and ultimate strength after 30 % pre-strained were increased by 18.8 % and 12.7 %, respectively. The compressive yield strength of SLMed-IN718 after 30 % pre-strain increased to 79.3 %. However, the corresponding value was 55.2 % in the forged specimen. The average grain size after 30 % pre-strain increased in SLMed specimens and decreased in forged specimens. Brinell hardness (BH) testing revealed that for 5 % and 15 % pre-straining condition, BH were lowered in pre-strained SLMed specimens compared with the as-received specimens. However, in forged specimens, the BH in 5 % pre-strained specimens was lower than that of as-received specimen and it was constant even with 15 % pre-straining. After 30 % pre-strain, the BH in SLMed and forged specimens were both higher than that of as-received specimen. The overall results show that pre-straining at room temperature enhances the compressive and tensile strength in all of specimens and it has a potential to combine with SLM for generating a hybrid manufacturing processes.