Impact of Scanning Speed on Microstructure and Mechanical and Thermal Expansion Properties of Fe-36Ni Alloy Fabricated by Selective Laser Melting

The Fe-36Ni alloy, with ultra-low thermal expansion and stable properties, is essential for aerospace remote sensors and aircraft load-bearing structures, widely used in aerospace. Additive Manufacturing, an emerging rapid prototyping technology with short cycles, high efficiency, and flexibility, addresses complex structural fabrication challenges. While selective laser melting (SLM) enables complex geometry fabrication, post-process treatments (e.g., annealing-induced homogenization, thermal aging for stress relief, surface polishing) remain critical for attaining metallurgical stability in as-built components. The impact of different laser scanning speeds (500 mm/s, 1000 mm/s, 1500 mm/s, 2000 mm/s) on the microstructure and mechanical and thermal expansion properties of the Fe-36Ni alloy fabricated by selective laser melting was studied. The results indicate that all Fe-36Ni alloys predominantly exhibit the γ-phase. Interestingly, a small amount of α precipitates was also observed, which is primarily attributed to the formation of a supercooled region. Notably, at a scanning speed of 1000 mm/s, the Fe-36Ni alloy samples exhibit optimal mechanical properties, with a tensile strength of 439 MPa and an elongation of 49.0%. This improvement is primarily attributed to the enhanced molding quality and grain refinement. The minimum coefficient of thermal expansion occurs at a scanning speed of 2000 mm/s, likely due to the elevated defect density.