# Synthesis and Properties of Octet NiCr Alloy Lattices Obtained by the Pack Cementation Process
###### Abstract  
NiCr alloys with different components were obtained by pack chromatation and homogenization heat treatment of octet Ni lattice. The microstructure, alloy composition, microhardness and quasi-static compression properties of the NiCr lattice were tested. The results showed that after homogenization heat treatment, the NiCr alloy lattice had an austenitic structure with uniform composition. Compared with the pure nickel lattice, the microhardness, compressive strength, elastic modulus and energy absorption of the NiCr lattice increased with the increase of chromium content. The microhardness, specific strength, specific modulus and specific energy absorption of the Ni-45 Cr alloy were 363 HV, 11.1 MP/(g/cm\({}^{3}\)), 1169.1 MP/(g/cm\({}^{3}\)) and 10 1/g, respectively, which were attributed to the solid solution strengthening provided by chromium and the increase in density. NiCr alloy lattices have high strength and toughness and may have potential applications in high-temperature filters or heat exchangers. m chemical properties; nickel-based lattice; pack cementation; solution strengthening +
Footnote †: journal: Applied Sciences  
for hollow Ni lattice-embedded alloy elements, which further proved the feasibility of preparing Ni-based superalloy lattices by solid-powder embedding [24]. [PERSON] coated Cr, Al and Ti elements on the surface of a pure Ni microlattice via pack cementation and achieved, after homogenization and aging treatment, a uniform Ni-Cr-Al-Ti composition with a \(\gamma/\gamma^{\prime}\) superalloy microstructure. The compression properties of the lattices with different components were measured in air at 788 \({}^{\circ}\)C. After normalizing for density (\(\sigma/\rho\)), the specific strengths of single-phase and \(\gamma^{\prime}\) strengthened Ni-(10-14)Cr-3 Ti-1 Al (wt%) lattices reached 8.1 MPa/(g/cm\({}^{3}\)) and 4.8 MPa/(g/cm\({}^{3}\)). Compared to pure nickel lattices, they were about 3.7 times and 2.2 times higher, respectively. The high high-temperature compressive strength of Ni-Cr-Al-Ti resulted from the solution strengthening provided by Cr, Al and Ti (as well as from the fine \(\gamma^{\prime}\) precipitation that may be formed in aging), along with enhanced oxidation resistance provided by Cr and Al [25]. The octahedral lattice prepared by this method had high specific strength, but the actual strength was relatively low, and it could not withstand large loads due to its low relative density (less than 2%). In the study of multiple lattice materials, the octet structure has received extensive attention. The octet lattice consists of 36 rods of exactly the same length and diameter. Eight regular tetrahedrons are distributed on the surface surrounding the central regular octahedron (Figure 1). The Maxwell's criterion defines M = b - 3j + 6, b, where j represents the number of rods and nodes in the cell. If M \(\geq\) 0, the lattice structure is stretch-dominated, otherwise it is bend-dominated. Ideally, the relative modulus (relative strength) and relative density of the stretch-dominated structure satisfies E/Es \(\propto\rho/\rho_{\rm s}\), \(\sigma/\sigma\propto\rho/\rho_{\rm s}\), whereas the bend-dominated structure satisfies E/Es \(\propto(\rho/\rho_{\rm s})^{2}\), \(\sigma/\sigma\propto(\rho/\rho_{\rm s})^{1.5}\). E, \(\sigma\) and \(\rho\) represent the elastic modulus, yield strength and density of porous materials, and Es, \(\sigma_{\rm s}\), \(\rho_{\rm s}\) represent the elastic modulus, yield strength and density of solid materials. The closer the value of the power exponent is to 1, the slower the decrease in intensity and modulus as the density decreases. The structure of a nickel foam is disordered, similar to the Kelvin model, which is a curved-dominated porous material, while the octet lattice is a stretch-dominated material.