Mechanical Behavior and Applications of Plasma Arc Welded Ceramics

Zirconium diboride and zirconium carbide-based ceramics were joined by plasma arc welding to demonstrate the versatility of this technique. A parent material composition consisting of ZrB ₂ with 20 vol% ZrC was hot pressed to near full density, sectioned to produce specimens for welding, and welded together to produce billets for mechanical property studies. The four-point flexure strength of the parent material was~660 MPa, while the strength of the welded specimens ranged from~140 to~250 MPa. Microstructural analysis revealed that decreased strength in the welded specimens was caused by volume flaws, microcracking of large ZrB ₂ grains (up to 1 mm in length), and residual tensile stresses that developed at the surface of weld pools during cooling. The versatility of plasma arc welding was demonstrated by joining of ZrC-based ceramics and fabricating three ZrB ₂ -ZrC components for potential applications, including a high-temperature electrical contact, an ultra-high-temperature thermocouple, and a wedge that was a notional wing leading edge. These three applications demonstrated the ability to join ceramics to a refractory metal, fabricate a chemically inert high-temperature thermocouple, and produce complex shapes for aerospace applications.