Effect of W addition on the microstructure and properties of Ni-W substrates for coated conductors

We fabricated Ni and Ni-W alloys for use as substrates in YBCO coated conductor applications and evaluated the effects of the W addition on the texture, microstructure, and mechanical and magnetic properties of the substrate. Pure Ni and Ni-W (2, 3, and 5 at.%) alloys were prepared by plasma arc melting and then cold rolled and annealed in the temperature range of 600-1300°C. The texture of the substrates was evaluated by pole-figure and orientation distribution function (ODF) analysis. The magnetic properties were also evaluated using the physical property measurement system (PPMS). It was observed that the Ni-W substrates had a stronger cube texture and a wider annealing temperature range in which the cube texture became stable than those of the pure Ni substrate. The full-width at half-maximums (FWHMs) of in-plane texture for the Ni-W substrate were 4.42°-5.57° at an annealing temperature of 800°C-1300°C, while that of pure Ni was 9.5° at 800°C. Therefore, it is considered that the addition of W enhances the formation of the cube texture and improves the texture stability at higher annealing temperatures. In addition, the Ni-W substrates had a smaller grain size and higher mechanical strength and hardness, as compared to those of the pure Ni substrate. These improvements are probably due to various strengthening mechanisms, such as solid solution hardening and/or grain size strengthening. PPMS analysis showed that the addition of W effectively reduced the saturation magnetization in an applied magnetic field, as well as the Curie temperature.