Rolls-royce Corporation

Philip A Jennings

Neil John D'Souza

Keerthi Devendra

Previously a number of techniques have been used in order to form single crystal or pre-determined crystallography components and articles. Each one of these techniques has its own particular problems, including susceptibility to error. By utilization of a bi-crystal experiment to determine melt-back length LM and by consideration of the ingress distance d from potential initiation nucleation points on a perimeter of a seed crystal, it is possible to determine a maximum ingress length d. By ensuring that the maximum ingress length d is less than or equal to a seed crystal diameter R, it is possible to project locus from potential nucleation points C, Cin terms of potential radii for stray grain propagation. As the seed crystal will have a known crystalline orientation, it will be possible to consider two divergent growth curves of the crystal in terms of the stray grains propagating from the point C, C. In such circumstances, a connector channel can be provided with a radius r=R/4 in an area between the periphery of the seed and the locus of the stray grain maximum ingress distances d. In situations where it is found d exceeds the crystal radius R, it will be understood that the actual crystal diameter R used may be increased or adjustment made with regard to the melt-back length LM in order to alter the maximum ingress distance d.

Method and mould for casting articles with a pre-determined crystalline orientation

Previously a number of techniques have been used in order to form single crystal or pre-determined crystallography components and articles. Each one of these techniques has its own particular problems, including susceptibility to error. By utilisation of a bi-crystal experiment to determine melt-back length LM and by consideration of the ingress distance d from potential initiation nucleation points on a perimeter of a seed crystal, it is possible to determine a maximum ingress length d. By ensuring that the maximum ingress length d is less than or equal to a seed crystal diameter R, it is possible to project locus from potential nucleation points C, Cin terms of potential radii for stray grain propagation. As the seed crystal will have a known crystalline orientation, it will be possible to consider two divergent growth curves of the crystal in terms of the stray grains propagating from the point C, C. In such circumstances, a connector channel can be provided with a radius r=R/4 in an area between the periphery of the seed and the locus of the stray grain maximum ingress distances d. In situations where it is found d exceeds the crystal radius R, it will be understood that the actual crystal diameter R used may be increased or adjustment made with regard to the melt-back length LM in order to alter the maximum ingress distance d.

In order to more effectively utilise seed crystalsto achieve a single crystal grain orientation for a component without the problems of utilising a helix constriction previously necessary to avoid epitaxial grain competition and growth. The present invention creates a wax component pattern. This patterncomprises integral sections of wax for a mould component section and for a spacer section with the seed crystalor holder for that crystal therebetween. This patternis then utilised in order to form a final refractory mould within which the component is formed. By appropriate choice of the spacer section, an appropriate spacing between an upper surface of the seedwhich will be the initial interface with molten castable material to form the component and a chiller surface through which heat is transferred can be determined in order to achieve successful transfer of the seedorientation to the formed component.

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Bristol, United Kingdom

Philip A Jennings