WO2022199828A1

WO2022199828A1 - Nickel aluminium alloy compositions

Info

Publication number: WO2022199828A1
Application number: PCT/EP2021/057906
Authority: WO
Inventors: Christopher Harris
Original assignee: Jaguar Land Rover Limited
Priority date: 2021-03-26
Filing date: 2021-03-26
Publication date: 2022-09-29
Also published as: GB202315147D0; GB2620056A

Abstract

Aspects of the present invention relate to a composition for use in laser cladding a surface of a machined or cast aluminium part (100a), the composition comprising a matrix material and a hardener, wherein the hardener is present in an amount of at least 1wt% and at most about 20wt% and the balance of the composition comprising the matrix material, wherein the matrix material comprises nickel and aluminium, and wherein the hardener is chromium carbide.

Description

NICKEL ALUMINIUM ALLOY COMPOSITIONS

TECHNICAL FIELD The present disclosure relates to nickel aluminium alloy compositions. Aspects of the invention relate to nickel aluminium compositions for use in laser cladding and to processes for modifying a machined or cast aluminium part by laser cladding.

BACKGROUND It is known to provide cylinder heads for internal combustion engines having valve seats upon which the valve poppet rests when the valve is closed during engine operation. The cylinder head is typically formed of aluminium as it is lightweight and durable that can be easily cast and machined. Nonetheless, the valve seat is typically exposed to high temperatures and friction due to cyclic impact loading with the poppet valve and sliding wear caused by the deflection of the poppet valve head under cylinder pressure during engine operation. Thus the valve seat is required to exhibit greater wear resistance than other portions of the cylinder head. Traditionally and as described in US 3285235 A, the valve seat is provided with a cast valve seat insert to prevent excessive wear and breakage of the valve seat. The insertion method requires a valve seat to be driven into a pre-machined bore and held in place by means of a friction fit. However, such valve seat inserts impose constraints on cylinder head design due to the space requirements to accommodate the inserts and the material required behind the valve seat to maintain the structural integrity of the cylinder head. Port geometry, intake and exhaust port opening geometry in addition to combustion chamber layout are such design elements that are constrained by the application of valve seats of an insert type. Furthermore, securing the valve seat by means of friction fit through an insertion method creates air gaps between the valve seat insert and the mating surface of the cylinder head. This can create an insulation layer that increases the temperature of the valve seat, reducing thermal transmission and increasing the temperature in the region surrounding the valve seat and the poppet valve. In addition, patent application US 4723518 A describes laying a copper alloy upon the valve seat surface using a laser cladding technique.

It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION

Against this background, the invention resides in a first aspect a composition for use in laser cladding a surface of a machined or cast aluminium part, the composition comprising a matrix material and a hardener, wherein the hardener is present in an amount of at least 1wt% and at most about 20wt% and the balance of the composition comprising the matrix material, wherein the matrix material comprises nickel and aluminium, and wherein the hardener is chromium carbide.

In embodiments the composition further comprises and organic binder.

In another embodiment the composition is in particulate form. Typically, the particles have an average particle size in diameter of at least about 30 pm and at most about 150 pm.

In embodiments the composition is used in the manufacture of a valve seat surface within the cylinder head of an engine. Typically, the composition is applied to the surface of a valve seat, an intake port and/or an exhaust port via a laser cladding process.

A further embodiment resides in a cylinder head for use in an engine comprising: an exhaust valve having a valve seat defining a surface thereon, wherein the valve seat surface is modified by the application the composition.

Another embodiment resides in a cylinder head for use in an engine comprising: an intake port defining a surface thereon, wherein the intake port surface is modified by the application the composition.

In embodiments, the engine comprises an exhaust port defining a surface thereon, wherein the surface is modified by the application of the composition.

The invention resides in a second aspect in a process for modifying a surface of a machined or cast aluminium part, the process comprising: providing a particulate composition that comprises a matrix material and a hardener, wherein the hardener is present in an amount of at least 1 wt% and at most about 20wt% and the balance of the composition comprising the matrix material, wherein the matrix material comprises nickel and aluminium, and wherein the hardener is chromium carbide; and depositing the composition on to the substrate via a laser cladding procedure in order to modify the surface of the part with a cladding layer.

In embodiments the particulate composition further comprises and an organic binder.

In another embodiment the particles have an average particle size diameter of at least about 30 pm and at most about 150 pm. In embodiments the depth of the cladding layer is at least about 1000 microns and at most about 2000 microns.

In a further embodiment the composition is deposited upon the surface at a temperature of at least about 1200 °C and at most about 1500 °C.

In another embodiment the surface is comprised within a valve seat, and/or the exhaust port, and/or the intake port. In embodiments an engine comprises the cylinder head.

In a further embodiment a vehicle comprises the engine.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a schematic representation of a (A) a cross section of a valve seat having a laser cladded surface and (B) cross section of a traditional cylinder valve seat; and Figure 2 shows electron microscope images of laser cladded substrates.

DETAILED DESCRIPTION

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Prior to setting forth the invention, a number of definitions are provided that will assist in the understanding of the invention. As used herein, the term "comprising" means any of the recited elements are necessarily included and other elements may optionally be included as well. "Consisting essentially of means any recited elements are necessarily included, elements that would materially affect the basic and novel characteristics of the listed elements are excluded, and other elements may optionally be included. "Consisting of means that all elements other than those listed are excluded. Embodiments defined by each of these terms are within the scope of this invention.

The term “alloy” is used herein to denote a metallic composition comprising a mixture of a predominating metallic element and other elements, including impurities.

As used herein, the term “balance”, when used in reference to a particular element, is used to describe that the remainder of the composition (in wt%) excluding any alloying additions is comprised of the designated element. Hence, the total composition including the “balance” element in combination with other stated alloying elements is equal to 100 wt% of the alloy composition. The term “impurity” refers to a metallic or non-metallic element that is present in an alloy but which is not added intentionally. In embodiments of the present invention where only specific component elements are specified, the balance of the alloy may comprise aluminium, nickel or aluminium/nickel matrix.

“Casting” is a manufacturing process that can produce metal components through the use of moulds. In some instances the mould may be sacrificial, as in the case of gravity casting where a sand-mould is used, or the mould may take the form of a reusable die, such as may be used in high pressure die casting processes. The casting process involves a furnace, metal and the mould. Alternatively, a casting machine may also be used to apply pressure to the mould or die during the casting process. The metal, is first melted in the furnace and then poured or injected, optionally under pressure, into the mould. Once the casting has cooled and has set the part can be subjected to additional tooling or trimmed and finished. The cutting of the cast metal product is also known as machining. Casting processes can produce large and small component parts, with geometrically complex shapes. The cast parts are typically of high strength and can be subjected to considerable loads when in use. The process supports a reasonably high rate of production and is favoured producing consistent parts with good surface finish.

“Machining” is a manufacturing process that can produce metal components. Machining involves various processes by which a raw material, typically metal material, is cut into a desired shape. Machining may comprise any process that removes material in a controlled manner from a work piece (subtractive manufacturing). Traditionally there are three main machining processes, namely: turning (rotation of the work piece against a cutting tool), drilling (production of holes by bringing a rotating cutter in contact with the work piece) and milling (rotation of the cutting toll to bring the cutting edges to bear against the work piece).

“Laser cladding” (after casting) is a process that allows for the deposition of material onto a substrate. More specifically, the cladding is applied by the melting of a metallic powder by a laser beam that is focussed upon a target area for where the cladding is to be applied. The laser beam slightly melts the surface of the target area creating a weld pool. Powder is applied through a coaxial or lateral nozzle partly carried by a shielding gas. Once the powder mixes with the melt pool it is melted under the heat of the laser beam. As the laser traverses along the workpiece the cladding solidifies, cooling rapidly forming a hard facing layer on the surface of the workpiece. In order to produce the coating either the nozzle/laser assembly or substrate may be moved in X, Y and Z direction.

As used herein, the term “vehicle” is used to denote any means in or by which people, animals or goods are transported or conveyed. Typically, vehicles may include road transport motor vehicles as well as rail locomotives. Watercraft may include marine vessels, such as boats, ships, submarines and hovercraft. Aircraft may include fixed wing or non-fixed wing aircraft, as well as spacecraft.

The term “composition” as used herein, refers to a composition predominantly comprising metals suitable for use in laser cladding. The composition may be a composite material, preferably a composite powder.

As used herein, the term “hardener” refers to any material or element that improves the strength (hardness) of the overall composition, typically the cladding material. Engine tests will typically determine if the cladding material is hard enough.

As used herein, the term “matrix material” refers to the material, typically metal in which the hardener is embedded. Typically the matrix material is the predominant material in the composition. The matrix material may be nickel/aluminium.

The wording “particulate form” refers to a material or composition being in the form of particles such as powders or any other granular materials. Particles are typically considered small localised object having physical or chemical properties such as volume, density or mass.

The wording “machined or cast part” as used herein refers to any part produced by the processes described above i.e. machining and casting. The wording “depth of the cladding layer” as used herein refers to the thickness of the cladding layer which has been deposited onto a substrate comprised within a work piece. This “depth” encompasses the thickness of a heat affected layer within the body of the substrate, the thickness of the layer below the surface of the work piece and the thickness of any deposition above the surface of the work piece.

Turning now to the composition of a specific embodiment of the invention for use in laser cladding of a machined or cast aluminium part that comprises: a matrix material and a hardener, wherein the hardener is present in an amount of at least 1 wt% and at most about 20wt% and the balance of the composition comprising the matrix material, wherein the matrix material comprises nickel and aluminium, and wherein the hardener is chromium carbide, tungsten carbide and silicon carbide. Typically, the hardener is chromium carbide.

The hardener is present in the composition of the herein presented invention at an amount of at least about 3wt%, or suitably about 5wt%, or typically about 7.5wt%; and suitably at most about 10wt%, or typically about 15wt%, or optionally up to about 20wt%.

The hardener of present composition is able to increase the hardness of the composition once deposited via a laser cladding process onto a substrate. The substrate may be an aluminium substrate or work piece, and is typically a valve seat and/or exhaust port and/or intake surface. It is important to achieve a sufficiently hard cladding layer in order to reduce the amount of friction abrasion whilst providing for a part that is still can be machined and falls within the hardness allowed for machining. Advantageously, the present composition provides for such a composition.

The matrix is present in the composition of the herein presented invention at an amount of at least about 80wt%, or suitably about 85wt%, or typically about 90wt%; and suitably at most about 92wt%, or typically about 95wt%, or optionally up to about 97wt%. The matrix material may comprise: nickel coated aluminium; aluminium coated nickel; mixtures of aluminium and nickel; or combinations thereof. The matrix material may be in particulate form.

The matrix material may predominately comprise nickel. The matrix material may comprise at least about 80wt% nickel, typically at least about 90wt% nickel. The matrix material may comprise at most about 98wt% nickel, typically about 95wt% nickel. Suitably the matrix material comprises about 93 wt% nickel.

The matrix material may also comprise aluminium. The matrix material may comprise at least about 1wt% aluminium, typically at least about 1wt% aluminium. The matrix material may comprise at most about 10 wt% aluminium, typically about 5wt% aluminium. Suitably the matrix material comprises about 4 wt% aluminium.

The matrix material may be used as a first phase which is then supplemented by a second phase comprising a hardening material (hardener). Such a hardener may be chromium carbide, tungsten carbide, silicon carbide or mixtures thereof. The hardener may be added in an amount of about 40wt%, about 25wt% or about 10wt%. Preferably the hardener may be present in an amount of about 5wt% or about 7.5wt%. A skilled person will appreciate that composition has to comprise an adequate level of porosity and hardness whilst avoiding delamination.

The composition may comprise an organic binder in the amount of at least about 0.1 wt% and at most about 1 5wt%. Typically, the organic binder may be present in about 0.5 wt%.

The depth of the cladding layer applied to the valve seat may be at least about 500 microns or suitably about 750 microns, or typically about 1000 microns and suitably at most about 1500 microns, or typically about 2000 microns or optionally up to about 2500 microns. The depth of the cladding layer that extends above the surface of the work piece prior to applying the cladding may be at least about 50 microns, or suitably about 100 microns, or typically about 150 microns and suitably at most about 200 microns, or typically about 250 microns or optionally up to about 300 microns. Hence, in embodiments of the invention the cladding layer applied to the valve seat surface integrates into the body of the valve seat as well as extending slightly proud of the surface. This ensures that the poppet maintains a suitable seal about the entire periphery of the clad valve seat surface when the valve is closed. In addition, this further ensures that the cladding layer is not simply applied superficially to the surface of the valve seat such that no integration into the material of the work piece is attained. In this latter instance the cladding layer has a tendency to degrade and flake leading to valve seat failure.

Any particle size of material that is suitable for laser cladding is considered to be encompassed by the invention. Specifically, the maximum average particle size may be at most 500 pm. More suitably, the maximum average particle size may be at most 300pm, 250pm, 200pm, 150pm, or 100pm. Most suitably, the maximum average particle size may be at most 50pm, 40pm, 30pm, 20pm, 10pm, or 5pm. The minimum average particle size may be 0.01 pm, 0.1 pm, 0.5pm, 1 pm, 2pm, or 5pm.

An alternative measure of particle size is to quote a maximum particle size and a percentage value or “d” value for the proportion of the sample that falls below that particle size. Most suitably the particle size of the matrix material may be at most 500pm. More suitably, the maximum particle size may be at most 300pm, 250pm, 200pm, 150pm, or 100pm. Most suitably, the maximum particle size may be at most 50pm, 40pm, 30pm, 20pm, 10pm, or 5pm. The minimum particle size may be 0.01 pm, 0.1 pm, 0.5pm, 1 pm, 2pm, or 5pm. Any “d” value may be associated with these particle sizes. Suitably, the “d” value associated with any of the above maximum particle sizes may be d99, d98, d95, d90, d80, d70, d60, or d50.

The surface of the machined part may be a machined profile of a radius of at least about 2 mm and at most about 4 mm, typically 3 mm.

The composition is used in the manufacture of a valve seat surface and/or exhaust port surface and/or intake port surface within the cylinder head of an engine. Typically the composition is applied to the surface of a profile machined on to the intake port and/or exhaust port openings and/or the valve seat via a laser cladding process. Any composition or process described herein is applicable to the surface of a valve seat and/or intake port opening and/or exhaust port opening of a cylinder.

A cross section of a cylinder head having valve seat 100a with a laser cladded surface 104a in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figure 1 A. Figure 1 B shows a cross section of a cylinder head having a traditional valve seat 100b with a valve seat insert 104b.

When the valve for example a poppet valve is closed during the engine operation cycle in an internal combustion engine the valve seat 102a, 102b as part of the cylinder head 100a, 100b provides for a surface against which the exhaust valve poppet 108a, 108b rests. Therefore, it is highly desirable for the valve seat surface to be abrasion and heat resistant. Traditionally so- called valve seat inserts 104b have been deployed via push fit into a recess formed in the cylinder head to address this problem (Figure 1 B). However, valve seat inserts 104b occupy a lot of space around the port opening 106b in the cylinder 100b and therefore restrict available design space for optimisation of cooling. According to the present invention the valve seat insert 104b is replaced by a laser clad valve seat surface 104a. As a result, the distance between the valve centres is reduced allowing for larger valve heads 108a. In addition, the cooling jacket area as well as the port geometry 106a is suitably enlarged for optimised air flow. The overall reduction in mass around the cylinder head is highly advantageous resulting in improved cooling as well as contributing to a lighter engine block. This in turn leads to consequent improvements in operational and manufacturing efficiency for engines and vehicles that comprise the embodiments of the invention.

With reference to Figure 1A, there is shown a cross sectional view of an engine cylinder head as a whole 100a. The cylinder head is typically integrated into a cylinder block to define a combustion chamber which is not shown. In the centre of the cylinder head 100a there is provided a valve which may be a poppet valve (not shown) having a valve head 108a. Circumferentially around the valve head 108 a there is air passage leading to the port opening 106a. The internal walls of the cylinder head 100a are substantially tapered towards the port opening 106a. In close proximity of the port opening 106 there is provided a valve seat 102a upon which the valve head 108a rests when the poppet valve is closed. The valve seat 102 according to the present invention is provided with a nickel aluminium cladding layer 104a. Accordingly, the cylinder head is provided with an integral valve seat surface without the need for a valve seat insert part.

With reference to Figure 1 B, there is shown the same cylinder head as described above in relation to Figure 1A. However, instead of a cladded valve seat 102a, 104a there is shown a valve seat insert 104b which has traditionally been deployed in for example the automotive industry.

With reference to Figure 2, there is shown electron microscope images of nickel aluminium cladding compositions 202b, 202c deposited onto aluminium substrates 208b, 208c using different beam radii and traverse speeds during the laser cladding process. The beam radius and traverse speeds used during the laser cladding process can have an effect on the number of voids, the porosity and level of oxidation in the cladding layer. For simplicity each electron microscope image B and C is additionally provided below with a schematic drawing illustrating the layers visible in the electron microscope image namely: the ‘cladding layer below the valve seat surface’ 204b, 204c sandwiched between the ‘heat affected zone (HAZ)’ 206b, 206c as the bottom layer and the ‘cladding layer above the valve seat surface’ 202b, 202c as the top layer. Without wishing to be bound by theory, it is understood that deposition of the molten particulate laser cladding composition onto the substrate 208b, 208c e.g. aluminium exposes the substrate surface to heat which results in a change of material properties of the substrate surface. This heat affected substrate surface is termed heat affected zone (HAZ) 204b, 204c.

It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

The invention is further illustrated by the following non-limiting examples.

Example 1

A variety of hardeners in particulate form, namely: chromium carbide, tungsten carbide and silicon carbide have been added in an amount of 10 wt%, 25 wt% and 40 wt% to nickel aluminium matrix material in particulate form. Experimental details of the laser cladding process parameters are provided in table 1 below.

Table 1 - Overview of hard phase methodology

The peak hardness determined by the Vickers Hardness Test in Micro Hv has been measured for every composition. It was found that silicon carbide compositions lead to delamination of silicon carbide cladding. Although not showing delamination, tungsten carbide compositions suffered from large amounts of porosity especially for higher hardener loadings (25 wt% and 40 wt%). Similarly chromium carbide compositions having a 40wt% hardener loading showed delamination. However, the inventors of the present disclosure have surprisingly found that chromium carbide compositions at loadings of 10wt% and 25 wt% showed sufficient hardness whilst not causing delamination.

Although particular embodiments of the invention have been disclosed herein in detail, this has been done by way of example and for the purposes of illustration only. The aforementioned embodiments are not intended to be limiting with respect to the scope of the appended claims, which follow. It is contemplated by the inventors that various substitutions, alterations, and modifications may be made to the invention without departing from the spirit and scope of the invention as defined by the claims.

Claims

1 . A composition for use in laser cladding a surface of a machined or cast aluminium part, the composition comprising a matrix material and a hardener, wherein the hardener is present in an amount of at least 1wt% and at most about 20wt% and the balance of the composition comprising the matrix material, wherein the matrix material comprises nickel and aluminium, and wherein the hardener is chromium carbide.

2. The composition of claim 1 , wherein the composition further comprises an organic binder.

3. The composition of claim 1 or 2 wherein the composition is in particulate form.

4. The composition of claim 3, wherein the particles have an average particle size in diameter of at least about 30 pm and at most about 150 pm.

5. The use of the composition as described in any one of claims 1 to 4 in the manufacture of at least one of: a valve seat surface; an intake port; and an exhaust port, within the cylinder head of an engine.

6. The use of claim 5 wherein the composition is applied to at least one of: the surface of the valve seat:, the intake port; and the exhaust port, via a laser cladding process.

7. A cylinder head for use in an engine comprising an exhaust valve having a valve seat defining a surface thereon, wherein the valve seat surface is modified by the application of a composition as defined in any one of claims 1 to 4.

8. A process for modifying a surface of a machined or cast aluminium part, the process comprising: providing a particulate composition that comprises a matrix material and a hardener, wherein the hardener is present in an amount of at least 1 wt% and at most about 20wt% and the balance of the composition comprising the matrix material, wherein the matrix material comprises nickel and aluminium, and wherein the hardener is chromium carbide; and depositing the composition on to the substrate via a laser cladding procedure in order to modify the surface of the part with a cladding layer.

9. The process for manufacturing the cladding layer of claim 8, wherein the particulate composition further comprises an organic binder.

10. The process of claims 8 or 9, wherein the particles have an average particle size diameter of at least about 30 pm and at most about 150 pm.

11. The process of any one of claims 8 to 10, wherein the depth of the cladding layer is at least about 500 microns and at most about 2000 microns.

12. The process of any one of claims 8 to 11 , wherein the composition is deposited upon the surface at a temperature of at least about 1200 °C and at most about 1500 °C.

13. The process of any one of claims 8 to 12, wherein the surface is comprised within a valve seat, intake port and/or exhaust port.

14. An engine comprising a cylinder head as defined within claim 7.

15. A vehicle comprising the engine of claim 14.