The Effect of Fused Silica Crystallization on Flexural Strength and Shrinkage of Ceramic Cores for Investment Casting

Abstract

Complex designed silica-based ceramic cores were fabricated by ceramic injection molding. Slow heating rate (0.2K/min) for debinding restrained bloating on the surface of ceramic cores. To investigate effect of sintering conditions on mechanical properties of ceramic cores, green bodies were sintered at temperatures in a range from 1150°C to 1400°C for various dwelling times (6 h to 48 h). Sintering above 1300°C for 12 h and dwelling time over 24 h at 1200°C reduce the flexural strength and increase the linear shrinkage of ceramic cores. Cristobalite, formed by high sintering temperature or long dwelling time, induces reduction of mechanical properties due to its phase transformation, which is accompanied by volume contraction and microcracking. Ceramic core sintered at 1200°C for 12 h endured wax patterning and shell molding, and was manufactured successfully.

Effect of silica fiber on the mechanical and chemical behavior of alumina-based ceramic core material

“…The amount of phase transformation of amorphous phase to beta-crystobalite is increased with increasing of the sintering temperature. In turn, during the cooling process after sintering the beta-cristobalite will transform to alpha-cristobatite, and this transformation will give rise to the micro-crack [14][15][16] due to the volume difference of alpha-crisobalite and beta-cristobalite. It is worthy to note that the number and length of the micro crack increase with the sintering temperature increasing in silica fibers (Fig.…”

Hot ceramic lithography of silica-based ceramic cores: The effect of process temperature on vat-photopolymierisation

“…The fundamental restrictions and key requirements for ceramic cores according to previous studies [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. heating cover unit was designed by mounting three constant temperature PTC electric fan heaters (12 V, 150 W) onto a hood to cover the 3D printer, controlled by a temperature controller (Inkbird ITC-308S, Shenzhen, Guangdong).…”

“…Therefore, as nucleation and the grain of the powder mixture began to grow at 1300 • C according to the TGA-DSC analysis in Fig. 2, and previous study outcomes [57], the optimum sintering temperature range was selected and further studied between 1150 and 1300 • C (Section 3.6). The intensity of the cristobalite diffraction peaks on raw material was analysed through XRD analysis, and there were no apparent cristobalite diffraction peaks in the XRD pattern (Fig.…”

“…Besides, high flexural strength is required for the ceramic cores to survive high pressure wax injection process. Hence, the key characteristics of ceramic cores are summarised in Table 1, summarizing the previous studies [4][5][6][7][8][9][10][11][12][13][14][15][16][17] and the general practices in this industry. Despite a high requirement for mechanical properties at high temperature as well as creep resistance of ceramic cores, the main difficulty in 3D printing complex ceramic cores lies in controlling the dimensional accuracy of the prints, cracking and delimitations in the printing and post-printing (sintering) processes.…”

Leaching improvement of ceramic cores for hollow turbine blades based on additive manufacturing

“…The reason for this is that the presence of a few low-meltingpoint phases in SiO 2 can help to reduce the high-temperature strength, accelerate the creep, and promote the sintering, leading to an increased sintering shrinkage rate. Simultaneously, SiO 2 transformed into cristobalite during the sintering process [19], which severely shrank when cooled to 180-270°C. The shrinkage could easily produce microcracks, thus damaging the high-temperature strength and improving the sintering shrinkage rate.…”