The Secretary of State for Defence in Her Britannic Majesty's Government

Ic Gas International Limited

The Secretary of State for Defense in Her Britannic Majesty's Government

Cecil Hayman

James E Restall

Christine D Chalk

A halide based process for the removal of surface oxidation and corrosion contamination from metallic articles especially cracked superalloy turbine components, which utilizes a pulsed pressure cycle. Preferably the cycle is established by alternate evacuation and replenishment. A cycle operating at 150 torr or less and utilizing CHF.sub.3 hydrogen and inert gas as atmosphere is described. The evacuation phase of each cycle should preferably reach 20 torr or less. The process is also applicable to etching for detection of near-surface flaws.

Cleaning of metal articles

A process for producing a two element deposition coating on metals e.g. for oxidation/corrosion protection of superalloys, comprises halide transfer of the two elements in sequence from a reaction charge, the reaction charge including a significant excess of halide activator over the amount required for stoichiometric considerations. The transportation of the first element is terminated by reacting its source to exhaustion, in the course of the transport reaction or by evacuating from the reaction vessel. Preferred elements are aluminum with silicon and aluminum with chromium.

Process for diffusion coating metals

The material comprises at least one hydrated compound which undergoes reversible transformation to a less hydrated form and a fusion temperature-depressing salt, both dispersed and suspended throughout a water-swollen cross-linked polymer hydrogel (the hydrogel being as in European Pat. Nos. 99 and 11411). The improvement is that the fusion temperature-depressing salt is present in 50 to 75% of the eutectic amount; this substantially reduces thermal hysteresis. In a modification of the invention, water is present in excess of the amount required to fully hydrate the compound, in which case the amount of fusion temperature-depressing salt may be 50 to 90% by weight of the eutectic amount.

Heat storage materials

The heat storage material, which undergoes reproducible transition in the range 66.degree. to 74.degree. C., comprises sodium pyrophosphate decahydrate (Na.sub.4 P.sub.2 O.sub.7.10 H.sub.2 O) dispersed throughout an open cell polymeric matrix which is stable in an aqueous medium at 80.degree. C. In use (for example, for space heating) the material is alternately heated to above 80.degree. C. and cooled below its transition temperature with evolution of heat.

A process for coating an article such as a turbine blade composed of nickel-base alloy, comprises the steps of surrounding the article by a particulate pack in a chamber, the pack including coating material in elemental or chemically combined form, said coating material selected from the group comprising aluminium, chromium, titanium, zirconium tantalum, niobium, yttrium, rare earth metals, boron and silicon together with a halide activator, preferably of low volatility, and cyclically varying the pressure of an inert gas or a reducing gas or a mixture of said gases contained within said chamber, while maintaining the contents of the chamber at a temperature sufficient to transfer coating material onto the surface of the article and form a diffusion coating thereon.

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Rickmansworth, United Kingdom

Cecil Hayman