Patent ID: 12250753

DETAILED DESCRIPTION

Referring toFIG.1there is illustrated a blend (10), for cold spray or solid-state deposition, produced by mixing i) at least one ductile or malleable metal (18), typically as particles, with ii) particles (20) comprising a) one or more metals (12) and/or metalloids (14) together with compounds or salts thereof (16) or b) one or more metal or metalloid compounds or salts (16).

The blends (10) may be pre-mixed and introduced into a cold spay or other solid-state deposition apparatus for use in the method of the invention or may be introduced separately and mixed in situ.

Referring toFIG.2, the blend (10) may be fed into a cold spray apparatus (50) such that blend particles (22) pass into a heated (52), compressed (54), supersonic gas jet (56) where they are accelerated through a nozzle (58) at a temperature (T) and pressure (P) to the surface (42) of a substrate (40) which is positioned a distance (D) from the nozzle such that the blend particles (22) adhere to the surface (42) forming a coating (30).

The result is a coating (30), seeFIG.3, in which the i) at least one ductile or malleable metal (18) serves to “bond” ii) particles (20) comprising a) one or more metals (12) and/or metalloids (14) together with compounds or salts thereof (16) or b) one or more metal or metalloid compounds or salts (16) to the surface (42) of the substrate (40).

The cold spray coatings of the invention can be distinguished from those produced by thermal spray techniques, which melt the particles being deposited, by a person skilled in the art. Cold sprayed coatings exhibit less heterogeneity and porosity than those that are thermally sprayed.

Thermal spraying with HVOF, using highly ductile materials can achieve high density deposition with low porosity when operated at particularly high temperatures and velocities using very ductile components alone. However, the majority of thermal deposition techniques (such as flame spraying) or compositions sprayed result in very variable levels of density (in the range of between 50%-85%) (i.e. porosity levels of 15%-50%). Generally, the denser levels are achieved in regions (or in total coatings) where the level of ductile materials is particularly high, and the lower density (higher porosity) levels are achieved in areas where the (brittle) ceramic component(s) are more prominent.

In contrast, the levels of density achieved by cold spraying of the current ductile metals with brittle ceramic type components gives rise to overall levels of >90% density (<10% porosity).

Indeed, the porosity of the coatings of the invention may be less than 10%, through 8%, 6%, 4% to as little at 3%, 2% or 1%.

This is illustrated by a comparison ofFIGS.4a-c(a thermally sprayed coating) andFIG.5acold spray coating of the invention.

FIG.4ashows the complex micro-structure of a flame-sprayed mixed metal/metal oxide deposit. There is a random distribution & separation of the different phases post thermal spraying. The metal particles (18), because of their higher back-scattered light reflectance, show as white. The mixed metal oxides (20) appear in grey tones, whilst the blacker regions are voids, or ‘hollows’, which give rise to the high overall porosity of these coatings.

The high (but variable) degree of distortion of the metal particles experienced during molten phase application becomes more apparent at higher magnifications. The particles range from being totally ‘splatted’ (by being exposed to higher temperature zones within the flame and/or shorter flight paths, with less opportunity to cool before impact), through differing degrees of deformation, to some that remain almost spherical. The most distorted species will have also undergone varying degrees of oxidation, reacting with the available ambient oxygen gas present in the flame, to also develop highly complex micro-structures both in and around the ‘splats’.

FIG.4billustrates the surface fromFIG.4aat an increased magnification factor of ×2.5. The highly complex microstructures are more apparent within the metallic (lighter) zones (18) and the metal oxide (greyer) zones (20). The voids still show as darker areas.

FIG.4cillustrates the coating at a ×5 magnification. The metallic region (18) shows porosity and is surrounded by a metal oxide shell region (20). Elemental mapping of region (18) shows high levels of nickel metal with the presence of embedded oxide particles, but which contain higher concentrations of iron & chrome oxides, both of which would be expected to react preferentially with the available oxygen present in the flame during the molten phase flight. Similarly, the high presence of small metallic particles, within the broken outer shell of the metal oxide phase, is to be noted. This clearly illustrates the complexity and the resulting heterogeneity of thermally sprayed deposits.

These can be contrasted with the considerably less heterogeneous structures which result from using cold-spray application processes, which occur as solid state deposition processes, typified by theFIG.5illustration in which the metal oxide (20) particles are embedded in the ductile metal (18).

Whilst still heterogeneous in distribution, the constituent zones (i.e. electrically conductive, ductile metal zone & the electrically non-conductive, brittle metal oxide or metal salts zone) have not undergone any molten phase transition and have not accordingly chemically modified their respective compositions. The challenge in making such coatings is to carefully control the physical application conditions of the cold spray unit used, so as not to simply ‘grit blast’ away the substrate being coated and/or any material already deposited. This arises from the very nature of the brittleness of the metal oxides/metal salts, which are usually used as grit blasting powders to clean the surface of substrates when depositing 100% ductile metals.

By careful control of powder mixing and feeding through the cold-spray gun with defined ratios, applicant is able to achieve reproducible compositions with uniformity of heating performance.

In an exemplary method the blend (10) may be as illustrated in any of Examples 1 to 7.

Particles having a mean diameter of 5 to 35 microns are heated in a gas stream of air, to a temperature of below 600 C, and at a pressure of about 5 Atm where they leave the apparatus and travel a distance of between 8 mm-300 mm where they are deposited on a ceramic surface (42) where they form a coating (30) in a layer (32) with a thickness of about 45 microns.

The coating (30) may be deposited in a controlled manner forming a track or tracks (44) which may form, for example, a functional component. Thus, as illustrated inFIG.6, a heating device (60) comprises a steel substrate (40) with a ceramic surface (42) onto which has been deposited, in a tracked manner, a heating element (62) comprising, for example, a coating (30) comprising nickel oxide and zinc. A pair of electrical contacts (64;66) is provided which can be connected to a power source (68) such that the heating device can be heated.

Alternatively, the arrangement may comprise a plurality of heating elements sharing a common feed terminal (64) and having independent return terminals (66).

The power source is preferably a low voltage supply of less than 30 V.

The heating device may be used in many different applications, but two particularly favoured applications are in vehicles such as, but not limited to, cars, lorries, trains, boats and airplanes and in buildings such as, but not limited to: houses, offices, hospitals, and warehousing.

To further exemplify the invention(s) there follow some exemplary blends, and details of their deposition onto substrates to form heating elements.

Example 1

A blend (10) of zinc metal powder (18), nickel metal powder (12) and alumina (16) powder in a mix, by weight, of 75:23:2 and with a particle size range of between 15 and 30 μm was deposited using a cold spray or solid state apparatus, at 10 mm separation onto a vitreous enamelled (42) steel substrate (40), using compressed air at 5.6 bar as the carrier gas, heated at ˜600° C., as deposited parallel element tracks of some 0.45 cm width with a spray speed of 4 cm/sec. When a 20V AC power supply was connected across the length of the deposited element track, the latter heated to 120° C., drawing 4 amps of current.

Example 2

The same blend of zinc powder, nickel powder, and alumina, as used in Example 1, was blended 1:1 with a thermally pre-oxidised Inconel 600 alloy (to around 10% overall oxidation level and 45 μm to dust) at 5.6 bar pressure and was deposited using a 12 mm separation and 4 cps spraying speed onto a plasma sprayed alumina steel substrate, using compressed air as the carrier gas, heated at ˜600° C., as deposited adjacent tracks to a total width of ˜4.5 cm. When a 10V AC power supply was connected across the length of the deposited element track, the latter heated to 60° C., drawing 3 amps of current.

Example 3

A blend as per Example 2 was sprayed at 400° C. onto a toughened glass substrate using a 10 cm separation and an 8 cps traverse speed and deposited as parallel elements of some 0.45 cm width.

Example 4

A blend as in Example 2 was sprayed onto a SiN ceramic block at 600° C. and 5.6 bar pressure, using an 8 cm separation and 4 cps traverse speed, producing adjacent tracks to a total width of ˜4.5 cm.

Example 5

A 4:1 blend of nickel oxide powder (16) (15□m) with zinc metal powder (18) at 600° C. and 4.4 bar pressure, using an 8 cm separation and 8 cps traverse speed, was sprayed onto a ceramic coated steel architectural panel, depositing parallel element tracks some 0.45 cm wide.

Example 6

A blend of zinc metal powder (18), nickel metal powder (12) and thermally pre-oxidised Inconel 600 alloy (16) as used in Example 2 was sprayed onto a ceramic coated steel architectural panel at 400° C. and 5.6 bar pressure, using an 8 cm separation and 12 cps traverse speed, depositing parallel element tracks some 0.45 cm wide. When a 40V DC power supply was connected across the length of the deposited element track, the latter heated to 110° C., drawing 2 amps of current.

Example 7

A 6:1 blend of a thermally pre-oxidised Inconel 600 alloy (16) as used in Example 2 and zinc metal powder (18) was sprayed onto a ceramic coated steel architectural panel at 570° C. and 5.6 bar pressure, using an 8 cm separation and 4 cps traverse speed, depositing parallel element tracks some 0.45 cm wide. When a 240V AC mains power supply was connected across the length of the deposited track, the latter heated to 250° C., drawing 0.9 amps of current.