Development of Tests to Simulate Use Conditions and Fabrication of Additively Manufactured Ceramic Nozzles

Abstract

Additive manufacturing (AM) allows for the rapid production of a desired shape, and enables the ability to modify the design before it is produced again. This can be a valuable tool in industry as a method for manufacturing prototypes, and larger runs of the same part, to an extent. There is a cost/benefit tipping point that is influenced by the complexity of the part, number of parts needed, frequency and value of design modifications, quality of parts produced, turnaround time, skill level of labor, infrastructure, profit margin for product, and other factors. AM of ceramics has lagged behind polymers and metals, as ceramic fabrication includes issues of shrinkage, distortion, and strength limiting process flaws. This AM alumina work was stimulated by a need in aerospace applications for a ceramic nozzle to replace a machined high temperature precious metal. This nozzles is an excellent test case for the rapid response of AM to develop a high value ceramic part.

Technical ceramics can have superior characteristics, such as the ability to withstand high temperatures and high compressive forces, compared to other materials. Lithography-based Ceramic Manufacturing (LCM) is one of the current techniques that can be used for AM of ceramics. This work focused on producing nozzles out of Al2O3by means of LCM, and then subjecting the printed parts to internal pressure and thermal shock tests. To conduct pressure tests on the samples a custom apparatus had to be designed and produced to hold the sample while allowing the freedom to select the pressure that was applied. The testing jig was electronically controlled and allowed for a max pressure of 6.9 MPa (1,000 psi) to be tested. The printed Al2O3 parts were thermally shocked once to four different ΔT's; 300°C, 500°C, 700°C, 900°C. Each ΔT were then rapidly internally pressurized up to 205 times to two different pressures; 3.4 MPa (500psi), 6.9 MPa (1,000 psi). The ΔT's of 300°C and 500°C showed they could survive being thermally shocked and survive 6.9 MPa (1,000 psi). Whereas samples that had a ΔT of 700°C and 900°C received critical damage from being thermally shocked and could not handle any pressure.