Abstract: A substrate such as a single crystal gas turbine blade is given a protective coating by composite electrodeposition of a metal matrix M.sub.1 containing particles of CrAlM.sub.2, where M.sub.1 is Ni or Co or Fe and M.sub.2 is Y, Si, Ti, or a rare earth element. The preferred matrix is Ni or Co or NiCo and the preferred particles are CrAlY. The particle size is important and preferably 75% by weight are between 3.9 and 10.5 .mu.m. The coating is heat treated to produce interdiffusion between the constituents of the matrix and the particles.

Abstract: 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.

Abstract: 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.

Abstract: An alloy having the nominal composition Ni--30/40 wt % Cr--1/5 wt % Ti--2/8 wt % Al is used for coating gas turbine components to give protection against oxidation--and sulphidation--corrosion. A specific alloy having the composition Ni--37 Cr--3 Ti--2Al is applied to a blade fabricated from a nickel superalloy by sputter ion plating to give an overlay coating up to 100 .mu.m thick. Preferably a platinum intermediate layer is flashed on to the substrate before coating. The coating alloy can additionally include rare earths, hafnium or silicon.

Abstract: A metallic or ceramic layer is deposited on a component by plasma spraying. This produces a rough, still porous, coating which is poorly bonded at the interface with the substrate. Aluminium or chromium is vapor deposited under pulsating pressure to react with the substrate to form an oxidation resistant coating of Ni Al (intermetallic) or Ni Cr (solid solution) which may include ceramic particles and is aerodynamically smooth.

Abstract: 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.