Epitaxy of tungsten on polycrystalline molybdenum using chemical vapor transport deposition technology

Polycrystalline tungsten (W) coatings were deposited on molybdenum (Mo) polycrystalline substrates via chemical vapor transport deposition (CVTD). The structural characterization of the samples indicates an epitaxial relationship between W and Mo; however, there are voids at the W–Mo interface, and the number of voids increases as the temperature decreases. Further, the deposition rate of W coatings decreases with decreasing temperature and pressure. The grains of the coatings deposited at 1420–1590 K have diverse orientations when the pressure is 250 Pa; however, the [1 0 0]-oriented grains are the majority. When the temperature reaches 1590 K, penetration twins form inside the coatings as the pressure decreases from 250 to 50 Pa. Further, the coating grains have no obvious preferred orientation with decreasing pressure. Compositional penetration was discovered at the W–Mo interface, and the penetration depth of Mo into W decreased with decreasing temperature. This study analyzes the competitive growth of W grains and the formation of penetration twins according to influence of the environment on the growth process. The voids and compositional penetration at the W–Mo interface are caused by the diffusion at the defects; thus, the distribution of the diffusion sites can demonstrate the perfection of the epitaxial W–Mo coherent interface. This study contributes to the structural regulation of epitaxial W on Mo.