Fig. 1. The ANN concept for predicting surface roughness of laser polishing SLMed Ti-6Al-4V alloy: (a) topological network structure with 3-7-1 architecture; (b) algorithms for optimization of the whole process; (c) MAE of 10-fold cross validation with 2000 epochs.

Fig. 2. Surface topography and nanoindentation analysis: (a) macroscopic image; (b) SEM morphology of as-received and laser polished surface; (c) 3D topographic image in polished surface; (d) cross-sectional microstructures after laser polishing including the microstructure of HAZ (d1) and the polished layer (d2); (e) nanoindentation load-displacement curves.

Fig. 3. EBSD analysis after laser polishing: (a) inverse pole figure (IPF) map; (b) phase distribution maps corresponding to (a); (c) pole figure of α′ martensite in polished layer; (d) the average lath width in as-received layer; (e) the average lath width in polished layer; (a-1) and (b-1) is the enlarged map in (a) and (b), respectively.

Fig. 4. Typical TEM observations of the laser polished layer: (a) ultrafine martensite contained in prior β grains, the grain boundary was marked by yellow dash line, and the corresponding SAED pattern recorded from the red circle; (b) high magnification TEM image of ultrafine martensite; (c) the detailed observations on α′ martensite lath boundaries; (d) indexed SAED pattern from red circle marked in (c); (e) nanotwins within α′ martensite lath and the corresponding SAED pattern; (f) inverse fast Fourier transformed (IFFT) image of Nanotwins and the corresponding FFT pattern; (g) typical bright-field image showing the presences of twins and stacking faults (SFs) within α′ martensite laths, and the corresponding SAED pattern recorded from the red circle; (h) HRTEM morphology of interactions of SFs-dislocations; (i) the IFFT image of the SFs and the corresponding FFT pattern, (g) the atomic structure of SFs interacted with partial dislocations.

Fig. 5. Analysis of deformation resistance by compression test: (a) SEM morphology of as-received sample; (b) SEM morphology of laser polished sample; (c) compression yield strength curve.