The Development of WC-Based Composite Tools for Friction Stir Welding of High-Softening-Temperature Materials

• Main Authors: Mohamed M. Z. Ahmed, Waheed S. Barakat, Abdelkarim Y. A. Mohamed, Naser A. Alsaleh, Omayma A. Elkady
• Format: Article
• Language: English
• Published: MDPI AG 2021-02-01
• Series: Metals
• Subjects: WC-based composites; powder metallurgy; consolidation; microstructure; fracture toughness; friction stir welding
• Online Access: https://www.mdpi.com/2075-4701/11/2/285

This work presents a detailed investigation for the effect of Y₂O₃ and Ni additions on the densification behavior, microstructural evolution and mechanical properties of a WC-Co-TaC-NbC composite. With the aim of obtaining WC-based composites with improved fracture toughness, to be used in severe conditions of high-temperature deformation, different concentrations of Y₂O₃ were incorporated with and without 5 wt% Ni addition. The consolidated composites were characterized using density measurement, XRD, SEM, hardness, fracture toughness, transverse rupture strength and compression testing. Fully dense composites were obtained through the applied consolidation regime of cold compaction and sintering at 1450 °C for 1.5 h under vacuum with a relative density up to 97%. The addition of 2.5 wt% Y₂O₃ to the base WC composite increased the relative density and then slightly decreased with the increase of the Y₂O₃ content. The addition of 5 wt% Ni to the base composites significantly increased the relative density to 97%. The XRD results indicated the existence of the Co₃W₃C η-phase after sintering, and the intensity of its peaks was reduced with the addition of 5 wt% Ni. The microstructure of the consolidated composites consisted of three phases: WC, Co₃W₃C and Y₂O₃. The area fraction of the Y₂O₃ phase increased as its weight fraction increased. In terms of the fracture toughness, the transverse-rupture strength (TRS) and the compressive strength were significantly improved by the addition of 5 wt% Ni with the 2.5 wt% Y₂O₃. Accordingly, this composition was used to manufacture the tools for the friction stir welding of the high-softening-temperature materials, which was successfully used for 25 plunges and about 500 cm of butt joints in nickel-based and carbon–steel alloys.