Microstructure and Mechanical Properties of Tungsten Zircaloy-4 Diffusion Welding Interface

Area of Science:

• Materials Science
• Surface Engineering
• Nuclear Engineering

Background:

• Tungsten is crucial for spallation neutron sources but suffers from poor corrosion resistance.
• Protective coatings are necessary to improve tungsten's durability in demanding applications.

Purpose of the Study:

• To investigate the feasibility of Zircaloy-4 coating on tungsten using hot isostatic pressure (HIP) diffusion welding.
• To analyze the interfacial microstructure, mechanical properties, and bonding strength of the coated tungsten.

Main Methods:

• Hot isostatic pressure (HIP) diffusion welding of Zircaloy-4 onto tungsten at temperatures from 900 °C to 1400 °C.
• Microstructural analysis using electron microscopy and phase structure analysis.
• Mechanical property testing including nanoindentation hardness and bonding strength measurements.

Main Results:

• A defect-free intermediate diffusion layer, primarily ZrW2, formed at the zirconium-tungsten interface.
• The diffusion layer thickness increased from 0.28 μm to 10.74 μm with increasing HIP temperature.
• The ZrW2 layer exhibited a high hardness of approximately 17.96 GPa, exceeding that of tungsten and Zircaloy-4.
• Maximum bonding strength of 83.9 MPa was achieved at a HIP temperature of 1000 °C.

Conclusions:

• Hot isostatic pressure diffusion welding is an effective method for coating tungsten with Zircaloy-4.
• The resulting ZrW2 diffusion layer significantly enhances the hardness and bonding strength of tungsten.
• Optimizing HIP temperature is critical for achieving superior bonding strength for spallation neutron source applications.