Mechanical Behavior and Applications of Plasma Arc Welded Ceramics

Abstract

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 ZrB2 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 ZrB2 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 ZrB2–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.

Solidification of welded SiC–ZrB2–ZrC ceramics

“…Welding parameters were recorded and reported in Table . Initial parameters of 198 A current and 0.75 L/min plasma flow rate were selected based on welding parameters for ZrB 2 with 20 vol% ZrC . Based on similarities in the properties of TiB 2 and ZrB 2 as well as TiC and ZrC, it was hypothesized that a SiC–ZrB 2 –ZrC ternary eutectic was present in the system.…”

“…Initial parameters of 198 A current and 0.75 L/min plasma flow rate were selected based on welding parameters for ZrB 2 with 20 vol% ZrC. 22,23 Based on similarities in the properties of TiB 2 and ZrB 2 as well as TiC and ZrC, it was hypothesized that a SiC-ZrB 2 -ZrC ternary eutectic was present in the system. Furthermore, like the SiC-TiB 2 -TiC system, the ternary invariant temperature would be lower than any of the binary invariant temperatures.…”

“…Examination of the dual FZ microstructure was also undertaken in order to understand its formation, as a similar FZ microstructure has not been previously reported for arc welded ceramics. [19][20][21][22][23][24] Phase fraction analysis was performed on several cross-sections of different weldments. A light optical micrograph of part of the weldment 5 crosssection is presented in Figure 6.…”

“…Therefore, fusion joining technologies, such as laser or electron beam welding, could become attractive joining options . Previously, fusion welding of ultra‐high temperature ceramics has been demonstrated through the use of various arc welding techniques . It is noted that the fusion welding of a SiC f /SiC composite would not be possible, as pure SiC is known to dissociate, not melt; however, the melting of SiC can be facilitated through eutectic invariant reactions …”

“…[16][17][18] Previously, fusion welding of ultra-high temperature ceramics has been demonstrated through the use of various arc welding techniques. [19][20][21][22][23][24] It is noted that the fusion welding of a SiC f / SiC composite would not be possible, as pure SiC is known to dissociate, not melt 25 ; however, the melting of SiC can be facilitated through eutectic invariant reactions. 20,24 The purpose of this study is to demonstrate the ability to fusion weld a SiC-based ceramic via plasma arc welding (PAW).…”