Method of manufacture of a thixotropic deposit

Claim 1

A method of making a thixotropic deposit on a collector comprising the steps of atomising a stream of molten metal or metal alloy by subjecting the stream of molten metal or metal alloy to relatively cold gas directed at the stream, thereby forming a spray of metal or metal alloy droplets, directing the resultant spray of droplets at the collector, modifying the spray by rapidly extracting heat at a controlled rate from the droplets in flight to form a spray predominantly comprising semi-liquid/semi-solid particles with dendritic solidification of the particles having been initiated, depositing the particles onto the collector with sufficient velocity to fragment dendrites formed during flight into dendrite nuclei, the nuclei being interdispersed in a deposit surface comprising a thin film of semi-liquid/semi-solid metal, rapidly growing the dendrite nuclei by passing the relatively cold atomising gas over the surface of the growing deposit to form substantially spherical nodules of rapidly solidified metal within a network of segregated liquid phase metal, and slowly cooling the segregated liquid by conduction to produce a network of segregated solid metal around the rapidly solidified metal modules which has a melting point less than the melting point of the nodules.

Claim 2

A method of making a thixotropic deposit on a collector comprising the steps of atomising a stream of molten metal or metal alloy by subjecting the stream of molten metal or metal alloy to relatively cold gas directed at the stream, thereby forming a spray of metal or metal alloy droplets, directing the resultant spray of droplets at the collector, modifying the spray by rapidly extracting heat at a controlled rate from the droplets in flight to form a spray predominantly comprising semi-liquid/semi-solid particles with dendritic solidification of the particles having been initiated, depositing the particles onto the collector with sufficient velocity to fragment dendrites formed during flight into dendrite nuclei, the nuclei being interdispersed in a deposit surface comprising a thin film of semi-liquid/semi-solid metal, rapidly growing the dendrite nuclei by passing the relatively cold atomising gas over the surface of the growing deposit to form substantially spherical nodules of rapidly solidified metal within a network of segregated liquid phase metal, and slowly cooling the segregated liquid by conduction to produce a network of segregated solid metal around the rapidly solidified metal modules which has a melting point less than the melting point of the nodules.

Claim 6

A method of making a thixotropic deposit comprising the steps of: atomising a stream of molten metal or metal alloy by subjecting the stream of molten metal or metal alloy to relatively cold gas directed at the stream, directing the resultant spray of metal droplets at a collector, rapidly extracting heat from the metal droplets in flight by means of the relatively cold atomising gas to initiate dendritic solidification of the metal droplets to form semi-liquid/semi-solid particles, depositing the particles onto the collector in a condition such that the growing deposit includes a surface zone comprising solid phase fragmented dendrite nodules in a residual liquid phase, the residual liquid phase bieng sufficient such that the identity of new arriving semi-liquid/semi-solid particles is lost on deposition, rapidly extracting further heat on deposition as the relatively cold atomising gas passes over the surface of the growing deposit so as to rapidly solidify liquid metal about said nodules, and cooling the residual liquid phase about said nodules more slowly by conduction to the underlying solidified portions of the deposit whereby the deposit consists of a non-dendritic rheocast-type microstructure in which the more slowly cooled residual liquid phase consists of a fine network of microsegregate about the rapidly soldified metal nodules which is molten at a lower temperature than the rapidly solidified metal nodules so that the deposit as a whole may exhibit thixotropic properties while retaining the property of being self-supporting.

Claim 7

A method of making a thixotropic deposit comprising the steps of: atomising a stream of molten metal or metal alloy by subjecting the stream of molten metal or metal alloy to relatively cold gas directed at the stream, directing the resultant spray of metal droplets at a collector, rapidly extracting heat from the metal droplets in flight by means of the relatively cold atomising gas to initiate dendritic solidification of the metal droplets to form semi-liquid/semi-solid particles, depositing the particles onto the collector in a condition such that the growing deposit includes a surface zone comprising solid phase fragmented dendrite nodules in a residual liquid phase, the residual liquid phase bieng sufficient such that the identity of new arriving semi-liquid/semi-solid particles is lost on deposition, rapidly extracting further heat on deposition as the relatively cold atomising gas passes over the surface of the growing deposit so as to rapidly solidify liquid metal about said nodules, and cooling the residual liquid phase about said nodules more slowly by conduction to the underlying solidified portions of the deposit whereby the deposit consists of a non-dendritic rheocast-type microstructure in which the more slowly cooled residual liquid phase consists of a fine network of microsegregate about the rapidly soldified metal nodules which is molten at a lower temperature than the rapidly solidified metal nodules so that the deposit as a whole may exhibit thixotropic properties while retaining the property of being self-supporting.