3D printing externally reinforced layers for high-speed railway brake discs: Adaptability of SLM processes for manufacturing gradient materials

Abstract

In this paper, the quasi-continuous ratio gradient alloy steel for the high-speed railway brake disc is prepared by selective laser melting (SLM). While maintaining the strength of the 24CrNiMo alloy steel at the core, it significantly improves the external wear and corrosion resistance of the material. The composition of the designed gradient alloy steel is x% 24CrNiMo + (1-x)% wear-corrosion resistant stainless steel (x is 100, 65, 35 and 0). Through the 20 groups of processes, the optimal process parameters of each gradient are summarized. Besides, the density, surface roughness and residual stress of the material are systematically characterized. The scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) are used to study the types of defects and formation mechanisms in the SLM process. The results show that the optimal laser energy density (LED) range for gradient alloy steel is 56 J mm−3 to 47.8 J mm−3. With the increase of LED, the density of the alloy first increases then decreases, and the type of defects changes from spheroidization defects to cracking. The sample with the best process parameter has a good metallurgical bonding between the gradients, which lays a good foundation for the subsequent analysis of wear resistance and corrosion resistance.