Cold spray additive manufacturing of Invar 36 alloy: microstructure, thermal expansion and mechanical properties

In this work, the Invar 36 alloys were manufactured using cold spray (CS) additive manufacturing technique. The systematic investigations were made on the microstructural evolution, thermal expansion and mechanical properties under as-sprayed (AS) and heat-treated (HT) conditions. XRD (X-ray diffraction) and ICP-AES (inductively coupled plasma atomic emission spectroscopy) analyses show that no phase transformation, oxidation, nor element content change have occurred. The X-ray computed tomography (XCT) exhibited a near fully dense structure with a porosity of 0.025% in the helium-produced sample under as-sprayed condition, whereas the nitrogen-produced samples produced at 5 MPa and 800 degrees C show more irregular pore defects. He-AS sample shows a more prominent grain refinement than that of nitrogen samples due to the more extensive plastic deformation. The post heat-treatment exhibited a promoted grain growth, inter-particle diffusion, as well as the formation of annealing twins. Between 25 degrees C and 200 degrees C, the nitrogen samples possessed lower CTE (coefficient of thermal expansion) values (1.53 x 10(-6)/degrees C) compared with those produced by casting and laser additive manufacturing. The He-AS samples exhibited a noticeable negative CTE value between 25 degrees C and 200 degrees C, which may due to the significant compressive residual stress (-272 MPa) compensating its displacement with temperature increase during CTE test. The N2-HT and He-HT Invar 36 samples present a notable balance between strength and ductility. In conclusion, the CS technique can be considered as a potential method to produce the Invar 36 component with high thermal and mechanical performance. (C) 2021 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.