Effect of zirconia content and particle size on the properties of 3D‐printed alumina‐based ceramic cores

Abstract

Ceramics usually have high hardness which is difficult to achieve, especially for complex parts with fine structures. [1][2][3][4] Considering the requirements of ceramic cores with rather intricate structures and requiring high precision, it is essential to develop fast, low cost, and high-precision ceramic-forming techniques. 5,6 Ceramic cores are applied in the form of internal passages for high-temperature hollow blades, a key factor to determine the quality of hollow blades. 7 Traditional preparation of ceramic cores is not only time consuming but also expensive, thus hindering the development of aircraft engines. 8 Fortunately, the emergence of 3D printing technology has changed the traditional production. In this method, parts are fabricated based on a layer-by-layer forming mode, significantly saving the raw materials. 9 Among various 3D printing technologies, printed parts obtained using stereolithography technique have the highest accuracy. 10 Thus, stereolithography-based 3D printing technology provides the possibility to fabricate ceramics parts in a highly efficient manner. [11][12][13][14] Alumina-based ceramic cores could resist a high operating temperature of 1520-1875°C and exhibit excellent high-temperature stability, exhibiting obvious advantages compared to the currently most used silica-based ceramic cores. 15,16 However, the binding force between alumina grains is weak when the sintering temperature is relatively low; therefore, second-phase zirconia is added to the alumina-based ceramic cores to guarantee good connections between the ceramic grains. [17][18][19] Several studies have focused on alumina-zirconia composite ceramics. Zhu et al. 20 studied the ballistic impact performance of nanocrystalline zirconia-toughened alumina (nZTA) and alumina ceramics; the fracture toughness of nZTA was found to be about 1.3 times than that of alumina, indicating that the toughness of alumina ceramics increased by adding zirconia. To lower the manufacturing costs and development time for complex parts, Pappas et al. 21 found that

Influence of sodium hydroxide on phase transformation of gamma alumina to alpha alumina

“…observed through X‐ray photoelectron spectrometer (XPS) measurements that Fe 2 O 3 additions resulted in a higher ratio of O:Al, suggesting that doping with Fe 2 O 3 increased the surface adsorption of oxygen molecules or atoms and lowered the onset temperature of transformation. Although it is well‐reported that certain cations, such as Ca 2+ , Zr 4+ , Fe 3+ , and Ti 4+ , accelerated structural changes, other cations like Ba 2+ , La 3+ , and Si 4+ delayed them 43,49,50 . Several groups have also suggested that the pH of starting Al(OH) 3 powder suspensions influenced the final particle size and shape, 30 which affected the onset temperature of α‐Al 2 O 3 formation, as well as the transformation sequence leading to α‐Al 2 O 3 51,52 …”

“…Although it is well-reported that certain cations, such as Ca 2+ , Zr 4+ , Fe 3+ , and Ti 4+ , accelerated structural changes, other cations like Ba 2+ , La 3+ , and Si 4+ delayed them. 43,49,50 Several groups have also suggested that the pH of starting Al(OH) 3 powder suspensions influenced the final particle size and shape, 30 which affected the onset temperature of α-Al 2 O 3 formation, as well as the transformation sequence leading to α-Al 2 O 3 . 51,52 Although significant progress has been made to understand the effect of sodium on properties of alumina, its influence on transformation of γ-Al 2 O 3 remains incomplete.…”

Enhanced 3D printed alumina ceramic cores via impregnation

“…Alumina ceramic cores are ceramic parts with especially fine and complex structures, serving as a medium for the formation of the internal structure of high‐temperature metallic hollow turbine blades, used in aircraft engines 7 , 8. Indeed, the characteristics of the alumina ceramic cores determine the precision and quality of the blades 9 .…”