Microstructure and properties of intermetallic compounds of W/Ni/Ta diffusion couple

The addition of tantalum (Ta) to W-Ni-Fe alloys is a new direction to improve the performance of tungsten (W) alloys. However, the diffusion-reaction between Ni and Ta generates a variety of intermetallic compounds (IMCs) during the high-temperature sintering stage, which seriously affects the organization and properties of the tungsten alloy. This study held the W/Ni/Ta solid diffusion experiments at 1000-1400 degrees C for 1-h. Results showed that the diffusivity of the Ta-Ni couple was much stronger than that of W-Ni at the same temperature. However, it was difficult to form an effective bond between Ni and Ta when the temperature was below 1200 degrees C, and Ni/Ta interface would generate layered NiTa2, NiTa, Ni2Ta, and Ni3Ta phases under 1300 degrees C. When the holding temperature increases to 1400 degrees C, a violent liquid phase diffusion occurs between Ni and Ta, generating a large amount of NiTa and Ni2Ta phases. The average hardness and modulus of the NiTa phase are 14.51 GPa and 300.93 GPa, respectively. The appearance of the NiTa phase in tungsten alloy will seriously damage the toughness and increase the risk of brittle fracture of the alloy.