# Synthesis and Properties of Octet NiCr Alloy Lattices Obtained by the Pack Cementation Process
## 3 Results and Discussion  
### Microstructure Characterization  
Figure 2a shows the local topography of a hollow nickel lattice sample after annealing. As can be seen in the figure, a periodic hollow tube array was obtained by sintering removal of the polymer and a high-temperature reduction treatment, and its basic unit was the octet structure. The hollow nickel lattice surface was highly dense, and there were no obvious  
holes and cracks. As can be seen in Figure 2a,d, the Ni lattice had straight grain boundaries after heat treatment, and the shape of the grains was regularly polygonal. Figure 2c shows the size distribution of pure Ni lattice grains, with an average particle size of 11 \(\upmu\)m. The grain size was mainly concentrated in the range of 5\(\sim\)15 \(\upmu\)m, which accounted for 80% of the total number of grains. Figure 2d shows the XRD patterns of Ni lattices. It can be seen that there were significant diffraction peaks at 44.51\({}^{\circ}\), 51.9\({}^{\circ}\) and 76\({}^{\circ}\). They corresponded to the (111), (200) and (220) crystal faces of Ni and were consistent with the nickel powder peaks on the diffraction standard card JCPDS: 04-085. The surface morphology of NiCr alloy lattices with different compositions was basically similar. Figure 3a shows the macroscopic morphology of the NiCr lattice, Figure 3d presents the outer surface morphology of the hollow rod and Figure 3b,e the morphology of the inner surface of the rod. As can be seen in the Figures, the hollow rod cross sections were circular and elliptical, and there were no obvious distortion and deformation in the lattice rod. The NiCr alloy lattice maintained the original macro-structure of the octet hollow Ni lattice. This showed that the Ni lattice was not seriously damaged by the high-temperature heat treatment process, and the NiCr alloy still had the excellent structural properties of the octet. Compared with the initial Ni lattice surface topography (Figure 2a), the surface roughness of the alloy lattice increased, which could be due to vapor deposition on both the inner and the outer surfaces during the packaging chromation and vapor-phase diffusion coating processes. The roughness of the outer surface was greater than that of the lattice rod, which could be caused by the combination of electrodeposition and packaging chromation. The few white bright spots on the rod surface in the Figure were Al\({}_{2}\)O\({}_{3}\) particles (used as the filler powder). They were attached to the inner and outer surfaces of the NiCr lattice during the packaging chromation process [11]. Figure 2: Characterizing the basic properties of pure nickel lattices: (**a**) SEM micrographs; (**b**) optical micrographs of the etched cross section of a lattice strut; (**c**) grain size distribution; (**d**) XRD diffraction spectrum. Figure 3c shows the typical metallographic structure of the Ni-23 Cr lattice material after homogenization. It can be seen that there was no obvious alloy layer in the NiCr alloy structure after homogenization. The microstructure of NiCr was a homogeneous (Ni, Cr) austenite structure with distinct grain boundaries [10,25]. Compared with the grain size of the heat-treated Ni lattice, the grains of the lattice alloy had grown after homogenization, and the size was about 40-80 \(\upmu\)m, so that 1-2 grains could span the entire lattice wall. Figure 3f shows the XRD diffraction spectrum of the NiCr lattice. It can be seen that the homogenized lattice NiCr alloy surface did not present a pure Ni phase or Cr phase, but only a single Ni solid-solution phase existed. We speculate that this was because the atomic radii of Ni and Cr (0.162 nm and 0.185 nm, respectively) and the lattice constants (0.353 nm and 0.289 nm, respectively) were very close. In a high-temperature environment at 1200 \({}^{\circ}\)C, the two elements Ni and Cr would diffuse toward each other: Cr atoms from the surface inward, and Ni atoms from the inside to the outside, to form an FCC (Ni, Cr) solid solution [11,29].