First-principles calculations on Ni/W interfaces in Steel/Ni/W hot isostatic pressure diffusion bonding layer

In order to optimize the microstructure and improve the performance of Steel/Ni/W hot isostatic pressure (HIP) diffusion bonding joint, the interfacial structure, electron orbital hybridization, charge distribution, bonding characteristic and fracture process of Ni/W interface were investigated using first-principles density functional theory. The results indicate that, besides Ni (1 0 0)/W (1 0 0) interface, Ni (1 1 0)/W (1 1 0) interface and Ni (1 1 1)/W (1 1 1) interface, Bramfitt's lattice mismatches of the others Ni/W interfaces are all larger than 6%. Therefore, only those three interfaces can be considered as the typical Ni/W interfaces. For Ni (1 0 0) surface, W (1 0 0) surface, Ni (1 1 0) surface, W (1 1 0) surface, Ni (1 1 1) surface and W (1 1 1) surface, when the number of atomic layers are 5, 7, 7, 5, 5 and 5, their surface energies convergence to 2.24 J/m², 4.03 J/m², 2.18 J/m², 3.23 J/m², 1.92 J/m² and 3.56 J/m². At the three typical Ni/W interfaces, the chemical bonds between Ni slabs and W slabs are the typical metallic ones, but also show a certain degree of covalent characteristics and ionic characteristics. Moreover, the metallic bonding strength of Ni (1 1 1)/W (1 1 1) interface is larger than that of Ni (1 0 0)/W (1 0 0) interface and Ni (1 1 0)/W (1 1 0) interface, so are the covalent characteristics and ionic characteristics. The tensile fracture process shows that for Ni (1 0 0)/W (1 0 0) interface and Ni (1 1 0)/W (1 1 0) interface, when the large external strain is imposed, the inner strain of the interfacial structure is not equivalent but concentrates at layer 1′-1, which indicates that the layer 1′-1 (interface itself) is the weakness. However, for Ni (1 1 1)/W (1 1 1) interface, the concentrated strain is located at layer 2′-1′, which illustrates that the weakness is not the interface anymore but in Ni slab. Moreover, the sustainable imposed strain of Ni (1 1 1)/W (1 1 1) interface is ∼30%, much higher than that of Ni (1 0 0)/W (1 0 0) interface and Ni (1 1 0)/W (1 1 0) interface, which are ∼15% and ∼12%, respectively.