Effect of gas nitriding on 316 L stainless steel lattice manufactured via selective laser melting

Nitriding is well-known as a surface treatment method to improve the wear and fatigue properties. This work demonstrates the capability of nitriding in improving the overall mechanical performance of the open cellular structure, by taking the 316 L stainless steel lattice structure fabricated by additive manufacturing as an example. The microstructure, composition distribution, and compressive properties of the obtained structure were analyzed. It is found that the effective elastic modulus, compressive proof strength, and energy absorption capacity of the lattice were improved after conventional gas nitriding. A nitrided layer with a thickness of about 60 um was formed on the surface of the nitrided parts, including an outer layer of chromium nitrides and an inner layer containing expanded austenite. The nitrided lattices with thinner struts were strengthened more due to the higher proportion of the nitrided layer. Meanwhile, the lattices were embrittled after nitriding. However, the toughness of the lattice can be compensated by adjusting the lattice structure, such as changing the angle between the strut and the compression direction so that a lattice with good strength and toughness can be obtained.