Joining Tungsten (W) to Tungsten Carbide (WC) by Spark Plasma Welding (SPW) and Examining the Effect of Temperature and Heating Rate on the Mechanical Properties of the Joint

In this study, tungsten (W) was successfully joint to tungsten carbide (WC) using spark plasma welding (SPW). In this study, the effect of two key parameters, joining temperature and heating rate, was investigated on the mechanical properties of the joint. Qualitatively, reduction of the heating rate to 50°C/min resulted in the formation of a continuous and gap-free joint, while higher rates (100°C/min and 200°C/min) led to the formation of gaps and discontinuities in the joint owing to the creation of a strong temperature gradient and thermal stresses. Further, the formation of a uniform and deep penetration zone in the joint, which is essential for lowering stress concentration and increasing bond strength, was only possible at low heating rates and optimal temperatures. Quantitatively, the specimen bonded at 1250°C and a heating rate of 50°C/min attained the best mechanical properties, including a flexural strength of 665 MPa and a tensile strength of 267 MPa. Under these conditions, the hardness rose from 289 to 357 Vickers in the tungsten region and from 1910 to 2180 Vickers in the tungsten carbide region. In contrast, elevation of the temperature to 1350°C, while augmenting the density and reducing the porosity, diminished the flexural strength to 580 MPa and the tensile strength to 191 MPa due to grain growth and the formation of a brittle tungsten carbide (W₂C) phase. The specimens bonded at a high heating rate (200°C/min) also revealed a very low flexural strength of about 104 MPa owing to high porosity and weak bonding. Microstructural and phase analyses confirmed that the formation of a diffusion zone with a gradual chemical composition gradient without the formation of thick and brittle intermetallic layers is the key to achieving a strong and reliable bond between these two refractory materials.