JOINING OF ULTRA-HIGH TEMPERATURE CERAMICS TO THE SAME AND REFRACTORY METALS VIA FUSION WELDING

<p>"This research focuses on the joining of ultra-high temperature ceramics to either themselves or refractory metals/alloys via fusion welding and the mechanical strength of produced joints. The ceramics studied consisted of compositions within a diboride-carbide-carbide ternary system while metals studied consisted of molybdenum and a molybdenum alloy. SiC-ZrB2-ZrC ceramics on a binary join between pure SiC and the ternary eutectic composition were found to be weldable when SiC content was below ~57.5 vol%. Compositions above 57.5 vol% SiC were unweldable based on pitting and off-gassing behavior. Welded strength of ceramics was ~180-300 MPa in the SiC-ZrB2-ZrC ternary eutectic composition, ~180-220 MPa in the SiC-ZrB2 binary eutectic composition, and ~130-180 MPa in a 60 vol% SiC – 40 vol% ZrB2 composition at room and elevated tempeatures. Welded strength was limited by pore size within the fusion zones. Thermal conductivity and electrical resistivity of parent materials in metal-ceramic welds were investigated to determine their effect on weldability. Welds were formed between molybdenum, or a molybdenum alloy, and ceramic compositions on a binary join between nominally pure ZrB2 and the SiC-ZrB2-ZrC ternary eutectic composition. Neither thermal conductivity nor electrical resistivity was found to affect weldability; however, melting temperature of ceramic coupons affected overall weld symmetry and penetration. Welded strength of joints between a molybdenum alloy and a 70 vol% ZrB2 – 19.5 vol% SiC – 10.5 vol% ZrC ceramic were ~10-100 MPa and failed due to the pores and cracks within produced samples. Removal of SiC from ceramics was found to reduce porosity and cracking in fusion zones"--Abstract, p. iv</p>

Name thesis:degree_name

Ph. D. in Ceramic Engineering

Grantor

Missouri University of Science and Technology

Author dc:creator

• Jarman, Jecee

• borides
• carbides
• fusion welding
• joining
• Ceramic Materials
• Engineering

Repository record dc:identifier

https://scholarsmine.mst.edu/doctoral_dissertations/3201

OAI identifier oai:identifier

oai:scholarsmine.mst.edu:doctoral_dissertations-4206