Ceramic Shell Moulds Research Articles

Examination of defects in gamma titanium aluminide investment castings

Induction skull melting (ISM) and vacuum induction rollover (VIR) furnaces have been used to melt a γ-TiAl alloy prior to casting into ceramic shell moulds. Castings produced by ISM contained only a slightly higher oxygen content than the charge material, but the melt was cast at a relatively low superheat resulting in numerous turbulence-induced gas bubbles in the castings. Although higher superheat could be achieved by VIR, the use of refractory crucibles resulted in castings with a high oxygen content. Castings poured turbulently under an argon atmosphere were liable to misrun and contained gas bubble defects. These defects were eliminated by pouring the melt into the moulds in a quiescent manner. Casting in a vacuum helped to reduce misrun even when the mould was filled quickly in a turbulent manner. Zirconia cannot be used as a crucible material for melting γ-TiAl alloys, whereas high purity (>98%) calcia is more suitable.

Microstructure and Phase Stability Studies on Heusler Phase Ni2AlHf and G-phase Ni16Hf6Si7in Directionally Solidified NiAl–Cr(Mo) Eutectic Alloyed with Hf

Small additions of Hf to directionally solidified NiAl–Cr(Mo) eutectic resulted in precipitation of a high density of Heusler phase Ni2AlHf along with fine G-phase Ni16Hf6Si7. The Heusler phase was mainly located on the grain boundary region. The fine G-phase formed in the presence of Si, which was a contamination resulting from contact with ceramic shell molds during directional solidification of the alloy. These fine G-phases were cuboidal in shape and coherent with the NiAl matrix. After hot isostatic pressing and aging treatment, the fine G-phases completely disappeared. The density of the Heusler phase was partially reduced, and the Heusler particles precipitated preferentially on the NiAl/Cr(Mo) interfaces and grain boundaries of the NiAl matrix. Some Heusler particles precipitated locally within the NiAl matrix, and small amounts of them precipitated within the Cr(Mo) phase. The structures of the NiAl/Ni2AlHf and NiAl/Ni16Hf6Si7interfaces were investigated by high-resolution electron microscopy. The habit plane of the fine G-phase was {001}NiAl. This result was in good agreement with calculation based on the linear elastic theory. The misfit dislocation network on the NiAl/Ni2AlHf (110) interface was calculated from the O-lattice model and compared with the observation, which showed good agreement.

Ceramic innovations in the 20th century

Ceramic innovations in the 20th century

Growth of nickel-base superalloy bicrystals by the seeding technique with a modified Bridgman method

Abstract A process for consistently growing large bicrystals (16 × 63 × 100 mm) of a NiCrFe ternary alloy in ceramic-shell molds by a modified Bridgman method was established. A pair of single-crystal seeds, oriented along the [0 0 1] direction, was used to grow each bicrystal with a prescribed tilt-boundary orientation. Initial processing parameters were established by using a commercial single-crystal casting (PWA-1480) superalloy. It was found that, to be successful, adequate superheating of the molten tip of the seed crystals is required prior to alloy casting in addition to the usual considerations of melt superheat, thermal gradient, and withdrawal rate. The development of this process and the specific process parameters are reviewed. General guidelines derived from this study are presented and discussed.

Crystallography of the NiHfSi phase in a NiAl (0.5 Hf) single-crystal alloy

Small additions of Hf to conventionally processed NiAl single crystals result in the precipitation of a high density of cuboidal G-phase along with a newly identified silicide phase. Both of these phases form in the presence of Si which is not an intentional alloying addition but is a contaminant resulting from contact with the ceramic shell molds during directional solidification of the single-crystal ingots. The morphology, crystal structure and orientation relationship (O.R.) of the silicide phase in a NiAl (0.5 at. %Hf) single-crystal alloy have been determined using transmission electron microscopy, electron microdiffraction and energy dispersive X-ray spectroscopy. Qualitative elemental analysis and indexing of the electron microdiffraction patterns from the new phase indicate that it is an orthorhombic NiHfSi phase with unit cell parameters, a = 0.639 nm, b = 0.389 nm and c = 0.72 nm, and space group Pnma. The NiHfSi phase forms as thin rectangular plates on {111}NiAl planes with an O.R. that is given by (100)NiHfSi|(111)NiAl and [010]NiHfSi|[1¯01]NiAl. Twelve variants of the NiHfSi phase were observed in the alloy and the number of variants and rectangular morphology of NiHfSi plates are consistent with symmetry requirements. Quenching experiments indicate that nucleation of the NiHfSi phase in NiAl(Hf) alloys is aided by the formation of 〈111〉NiAl vacancy loops that form on the {111}NiAl planes.

Glassy Phase in Alumina–Silica Ceramic Shell Molds

Variation of the amount and the composition of the glassy phase in high‐purity Al2O3‐SiO2 shell molds and the crystallization of the glassy phase have been studied. The results indicate that the two main modes of transformation from a glassy phase to a crystalline phase during firing are (1) formation of mullite through a chemical reaction and (2) devitrification of the glassy phase that comes from the original materials. The transformation is mainly influenced by the S/(A + S) value (A and S are the weight percentages of Al2O3 and SiO2, respectively), the Na2O content, and the firing temperature. Low S/(A+S), low Na2O, and high firing temperature are favorable to the transformation.

Relation between the Characteristics of the Hydrolyzed Solution of Ethyl Silicate 40 and the Strengh of the Ceramic Shell Mold Bonded with the Solution

Relation between the Characteristics of the Hydrolyzed Solution of Ethyl Silicate 40 and the Strengh of the Ceramic Shell Mold Bonded with the Solution

Reaction between Ni-Base Superalloy Melt for Single Crystal Castings and Ceramic Shell Molds of Mullite-Alumina System

Reaction between Ni-Base Superalloy Melt for Single Crystal Castings and Ceramic Shell Molds of Mullite-Alumina System

Method of casting metal matrix composite in ceramic shell mold: (Nusbaum, H.J., Wilmington, DE, USA) US Pat 4 476 916 (16 October 1984)

Method of casting metal matrix composite in ceramic shell mold: (Nusbaum, H.J., Wilmington, DE, USA) US Pat 4 476 916 (16 October 1984)

Study on the Binders for Ceramic Shell Molds

Study on the Binders for Ceramic Shell Molds

The replicast CS (Ceramic Shell) process

The Replicast CS process developed at the Steel Castings Research and Trade Association, Sheffield, England, uses disposable, high quality, expanded polystyrene patterns to facilitate the manufacture of exceptionally thin, highly refractory ceramic shell moulds without parting lines or cores. With suitable support, these high quality moulds can be used to produce relatively large components with excellent ‘as-cast’ integrity and surface finish. Combined with zero draft and high dimensional accuracy, these features offer substantial benefits to customers and foundries alike.

Effects of Padding and Chilling on Sound Zones of Ceramic Shell Mold Castings

Effects of Padding and Chilling on Sound Zones of Ceramic Shell Mold Castings

Effects of Casting Variables on Structures and Mechanical Properties of Ceramic Shell Mold Castings

Effects of Casting Variables on Structures and Mechanical Properties of Ceramic Shell Mold Castings

Effects of Mold-to-Mold Radiation on Sound Zone of Ceramic Shell Mold Stainless Steel Castings

Effects of Mold-to-Mold Radiation on Sound Zone of Ceramic Shell Mold Stainless Steel Castings

Metal Sculpture: Polystyrene Patterns in Ceramic Shell Molds

Sculptors and craftsmen have been fascinated for thousands of years with the possibilities and the enduring qualities of castable metals such as bronze and so am I. Since my earliest experiences with art, I have maintained an interest in the process of metal casting as a way of producing art objects. The two main concerns of a craftsman working with the process are the type of pattern and the kind of mold to be selected. For lack of a better material, patterns have been made of wax for at least 3000 years. The material for molds, however, has varied considerably, since sculptors relentlessly search for a better refractory material. The purpose of this report is to present the results of my experiences in using a plastic for patterns and a ceramic shell for molds. Ceramic shell, a relatively new type of mold-making material, provides significant advantages to sculptors. Compared with other types of investment molds, the ceramic shell mold is superior for producing small details and for its reliability in casting relatively small objects. On the other hand, the initial financial outlay for equipment and the need to give special attention to certain steps of the technique are much greater than for solid investment molds. After I had tried using many types of molds, I decided that ceramic shell molds are the most suitable for my purposes and I have used them exclusively during the past five years. Having made this decision, I turned to the problem of materials for patterns, which still concerns me. Incidentally, the process for constructing ceramic shell molds, which involves the application of several layers of silica (sand) with a liquid binder to a pattern, is described in Ref. 1.