Rapid Fabrication of Ceramic Molds with Integral Core/shell Structures for the Investment Casting of Advanced Turbine Blades
MIAO K. 1, LU Z. 1, LI S. 1, WU L. 1, LIU T. 1, SUN C. 1
1 Xi'an Jiaotong University, Xi‘an, China
Turbine blades are the key components in gas turbines. Based on the additive manufacturing technique and gelcasting process, we proposed a rapid fabrication process of alumina ceramic molds with integral core/shell structures. Combined with the precision casting technology, this process has been expected to realize the fabrication of advanced turbine blades rapidly.
A resin prototype that exactly matched the final metal casting was produced by the stereolithography. The duplication of tiny structures inside the resin prototype were realized by gelcasting. The closest packing formula for the multi-level gradations by using irregular alumina particles was deduced. A ceramic slurry with a low viscosity and high solid loading were prepared by a tetramodal system. The maximum solid loading was 62vol%, and the viscosity was only 0.29Pa.s.
The control methods of structural integrity of ceramic cores during pre-sintering were put forward. The mechanical properties in pre-sintering were improved after adding polydimethylsiloxane (PDMS), which had a low pyrolysis rate during heating. The bending strength at 500°C of cermamic molds with PDMS was greatly improved form 0 to 1.037MPa, when 4wt% PDMS was added. The structural integrity was maintained after pre-sintering.
The high-temperature strengths of ceramic molds were increased, and the sintering shinkages were controlled. The formation mechanisms of high-temperature enhanced phases were investigated. The high-temperature strengths could be adjusted between 18.5 and 34.9MPa at 1500°C by controlling the content of mullite.
A pioneering approach is developed to achieve zero shrinkage of the cerami molds during multistep sintering, using a combination of active fillers: ZrAl3 and Al75Si25. The response surface method is used to optimize the material compositions and sintering process, achieving shrinkages of less than 0.05% for the entire process. The combination of ZrAl3 and Al75Si25 can help realize the continuous expansion of the matrix in a wide temperature range of 600–1400 ?. Owing to shrinkage suppression, the profile deviation of the samples is less than 0.1 mm, and the proportion of microcracks is reduced by 97.8%.
Finally, fabrications of advanced turbine blades were realized by the aboved mentioned ceramic molds.