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In this study, melt pool radiation monitoring and signal denoising in laser powder bed fusion (LPBF) is carried out. Photodiodes and semiconductor cameras are used to capture coaxial radiation signals and images of melt pools. The temperature of the melt pool rises as laser input energy increases, and the fluctuation of radiation signals caused by spatter intensifies. Furthermore, variational mode decomposition (VMD) method is used to obtain radiation signal components related to the melt pool region or nonmelt pool region. The radiation of the nonmolten pool region (i.e., noise) contains fundamental frequencies and related harmonics that can be decomposed into a low-frequency mode with a center frequency of $\sim $ 110 Hz. By comparing the correlation and the center frequency, the noise component is confirmed, and the original signal is modified accordingly. In this way, melt pool temperature accuracy is improved, enhancing melt pool behavior features.

It has always been challenging work to reconcile the contradiction between the strength and plasticity of titanium materials. Laser powder bed fusion (LPBF) is a convenient method to fabricate innovative composites including those inspired by gradient layered materials. In this work, we used LPBF to selectively prepare TiN/Ti gradient layered structure (GLSTi) composites by using different N2–Ar ratios during the LPBF process. We systematically investigated the mechanisms of in-situsynthesis TiN, high strength and ductility of GLSTi composites using microscopic analysis, TEM characterization, and tensile testing with digital image correlation. Besides, a digital correspondence was established between the N2concentration and the volume fraction of LPBF in-situsynthesized TiN. Our results show that the GLSTi composites exhibit superior mechanical properties compared to pure titanium fabricated by LPBF under pure Ar. Specifically, the tensile strength of GLSTi was more than 1.5 times higher than that of LPBF-formed pure titanium, reaching up to 1100 MPa, while maintaining a high elongation at fracture of 17%. GLSTi breaks the bottleneck of high strength but low ductility exhibited by conventional nanoceramic particle-strengthened titanium matrix composites, and the hetero-deformation induced strengthening effect formed by the TiN/Ti layered structure explained its strength-plasticity balanced principle. The microhardness exhibits a jagged variation of the relatively low hardness of 245 HV0.2 for the pure titanium layer and a high hardness of 408 HV0.2 for the N2in-situsynthesis layer. Our study provides a new concept for the structure-performance digital customization of 3D-printed Ti-based composites.