Sample 1：

                                           Sample 1: 40X After Corrosion -1                                                                      Sample 1: 40X After Corrosion -2

                                              Sample 1: 200X After Corrosion -1                                                                     Sample 1: 200X After Corrosion -2

   Sample 2：

                                           Sample 2: 40X After Corrosion -1                                                                        Sample 2: 40X After Corrosion -2

                                            Sample 2: 200X After Corrosion -1                                                                     Sample 2: 200X After Corrosion -2

   Sample 3：

                                          Sample 3: 100X After Corrosion -1                                                                       Sample 3:100X After Corrosion -2

                                           Sample 3: 100X After Corrosion -1                                                                         Sample 3:100X After Corrosion -2

• Metallographic conclusion:
  1. Sample 1 has a small amount of pores evenly distributed inside, and the pores are spherical, indicating that the printed powder has been fully melted, and the pores are caused by the gas that has not overflowed in time. The sample is accompanied by cracks, indicating that the uneven heat conduction of the molten pool leads to large thermal stress, causing through cracks. The photos after corrosion show that the internal structure is uniform, the printing lines are clear and regular, and there are obvious fine and broken structures in the edge area. The grains are small, which should be caused by the fast cooling rate.
  2. Sample 2 has more pores inside, and the pore shape is irregular, indicating that the powder particles of the raw material have not been fully melted. The local melting may not achieve the optimal arrangement of the particles, resulting in loose internal structure. The sample is accompanied by cracks inside, and the phenomenon of particle tearing occurs, which should be caused by thermal stress. In addition, there is a significant difference in density between the left and right sides of the sample. Is it caused by uneven feeding? Clear printing lines were found in the structure after corrosion.
  3. Sample 3 is relatively dense inside, with no obvious defects in the core and a small number of continuous pores on the surface. The voids are round, which are caused by closed gas after melting. The structure is uniform and stable after corrosion.

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