WEAR RESISTANT COATING

Abstract

A method of forming a wear resistant and galling resistant coating for abrasive environments and a feed material for the method are disclosed. The feed material is for forming a wear resistant and galling resistant coating on a substrate by a welding process that heats the feed and the substrate. The feed material comprises 35 to 50 wt % titanium nitride particles and a balance of commercially pure titanium or titanium alloy particles and incidental impurities. The method involves delivering the feed material to a surface of a substrate and exposing the feed material and the substrate to sufficient energy to cause at least the commercially pure titanium or titanium alloy particles in the feed to melt and at least some of the titanium nitride particles in the feed to melt, thereby forming a melt pool. On solidification of the melt pool, at least some of the titanium nitride particles are embedded in a matrix formed from melt pool, thereby forming a wear resistant and galling resistant coating on the substrate. A wear resistant and galling resistant coating formed of the feed material is also disclosed.

Claims

1. A method of forming a coating on a substrate of titanium alloy, the coating being resistant to wear and galling in a corrosive and abrasive environment, the method comprising the steps of: (a) delivering a feed to a surface of a substrate by conveying the feed to the substrate in an inert conveying gas and controlling the flow of the conveying gas to control the feed rate of the feed, the feed consisting of: (i) 35 to 50 wt % titanium nitride particles; (ii) a balance of commercially pure titanium or titanium alloy particles with incidental impurities; (b) heating the feed and the substrate to cause at least the commercially pure titanium or titanium alloy particles, at least some of the titanium nitride particles and at least the exposed surface of the substrate to melt to form a melt pool; and (c) preheating the substrate and maintaining the substrate at the preheat temperature throughout steps (a) and (b); and whereby, on solidification of the melt pool, at least some of the titanium nitride particles are embedded in a matrix formed from melt pool, thereby forming a wear resistant and galling resistant coating on the substrate.

2. The method defined in claim 1, wherein the preheating temperature is selected to reduce or avoid cracking and porosity in the coating caused by forming excessive volumes of secondary nitrides.

3. The method as defined in claim 1, wherein the method includes preheating the substrate before steps (a) and (b) and maintaining the substrate temperature in a range of 50 C. to 100 C.

4. The method defined in claim 1, wherein the method includes controlling the hardness of the wear resistant coating by controlling the temperature of the molten material and the time during which the molten material remains molten.

5. The method defined in claim 1, wherein the method includes controlling the temperature of the molten material to be between the melting temperature of titanium nitride and the vaporisation temperature of titanium.

6. The method defined in claim 1, wherein the method includes controlling phases of titanium nitride formed upon solidification of the molten materials by controlling the time that the molten material remains molten.

7. The method defined in claim 1, wherein step (b) involves causing localized heating of the substrate and the feed by exposing the substrate and the feed to a targeted energy source.

8. The method defined in claim 6, wherein the heat input is controlled by adjusting (i) the intensity of the targeted energy source, (ii) the duration of exposure to the targeted energy source and (iii) the area of substrate exposed to the targeted energy source.

9. A titanium alloy autoclave or valve component having a coating that is resistant to wear and galling in a corrosive and abrasive environment, the wear and galling resistant coating comprises 35 to 50 wt % of titanium nitride particles dispersed in a matrix of commercially pure titanium or titanium alloy.

10. A titanium alloy autoclave or valve component having a wear resistant and galling resistant coating as defined in claim 9, wherein the titanium nitride particles comprise 35 to 45 wt % of the wear resistant coating.

11. A titanium alloy autoclave or valve component having a wear resistant and galling resistant coating as defined in claim 9, wherein the titanium nitride particles comprise 35 to 42 wt % of the wear resistant coating.

12. A titanium alloy autoclave or valve component having a wear resistant and galling resistant coating as defined in claim 9, wherein the matrix of titanium or titanium alloy comprises alloying elements with the balance being at least 50 wt % titanium and incidental impurities.

13. A titanium alloy autoclave or valve component having a wear resistant and galling resistant coating as defined in claims 9, wherein the wear resistant coating is formed to a thickness of greater than 0 and up to 10 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0052] FIG. 1 is a cross-section showing the microstructure of a TiO.sub.2 wear resistant coating.

[0053] FIG. 2 is a cross-section showing the microstructure of a TiN wear resistant coating.

[0054] FIG. 3 is a cross-section showing an embodiment of a microstructure of a TiN wear resistant coating formed according to the invention.

[0055] FIG. 4 is a perspective view of overlapping sections of the wear resistant coating in FIG. 3 formed on the surface of a titanium substrate.

[0056] FIG. 5 is a schematic representation of an apparatus for forming a wear resistant coating.

DETAILED DESCRIPTION

[0057] The description that follows is in the context of applying a wear resistant coating to a substrate of titanium alloy. It is important to appreciate, however, that the wear resistant coating may be applied to other materials that can be directly welded with titanium and other alloys by use of a suitable butter layer.

[0058] An apparatus 1 for forming a wear resistant coating on a substrate 10 is shown in FIG. 5.

[0059] The apparatus 1 comprises a spray nozzle 20 having an elongate body. The spray nozzle 20 includes a laser generator 22 that generates a laser 40. The laser generator 22 is aligned along a central longitudinal axis of the elongate body. A sleeve surrounds the laser generator 22 to form an annular feed flow chamber 24.

[0060] The laser generator is linked to a power source 26 to generate the laser 40 with sufficient energy to melt small particles of titanium in the range of 20 to 170 m. The chamber 24 is linked via a conduit to a reservoir 28 of feed particles for forming the wear resistant coating. The reservoir 28 is supplied with argon gas from a gas source 30 to fluidize the particles and convey the entrained particles through the conduit and chamber 24 and then onto the substrate 10.

[0061] The flow of particles and gas from the chamber 24 is controlled to converge from the annular opening surrounding the laser generator 22 in a flow stream (denoted by an arrow marked 50 in FIG. 5) that intersects the laser 40 at the surface of the substrate 10. Accordingly, the feed particles are subject to high temperatures at the surface of the substrate 10.

[0062] The feed particles comprise a blend of titanium alloy particles and titanium nitride particles. The titanium nitride particles comprise 35 to 50 wt % of the blend. Both the titanium particles and the titanium nitride particles have a size in the range of 20 to 170 m.

[0063] It will be appreciated that alternative configurations for supplying feed particles to the surface of the substrate 10 may be adopted. For example, the titanium alloy particles and the titanium nitride particles may be supplied from separate reservoirs and combined together in the chamber 24 so that a blend of feed particles is formed in the chamber 24 and is supplied as described above to the surface of the substrate 10.

[0064] Alternatively, the blend of particles may be formed at the surface of the substrate 10 by supplying the titanium alloy particles and the titanium nitride particles through separate nozzles that direct the particles to the point on the surface of the substrate 10 that is irradiated by the laser.

[0065] The applicant has observed that, although the laser melts the titanium alloy particles, the titanium nitride particles generally remain in a solid state and become embedded in the wear resistant coating by being surrounded in a matrix of titanium alloy dispersed with secondary titanium nitrides.

[0066] The applicant has also observed that because the laser energy is selected to melt the titanium alloy particles only, a weld pool generated by the laser quenches so rapidly under the argon shield gas (powder gas) that oxygen is unable to react with the molten titanium. This results in a wear resistant coating that is generally free of oxygen.

[0067] Substrate: Titanium grade 12

[0068] Substrate thickness: >25 mm

[0069] Preheat: >50 C./<150 C.

[0070] Ti particles: Amperit 155.093

[0071] Ti particle size/density: 90 to 125 m/4.51 g/cm.sup.3

[0072] Ti particle weight %: 58

[0073] TiN particles: Amperit K80

[0074] TiN particle size/density: 40 to 145 m/5.22 g/cm.sup.3

[0075] TiN particle weight %: 42

[0076] Substrate pre-cleaning: acetone wash

[0077] Conveying gas and flow rate: Argon at 10 l/min

[0078] Shielding gas & flow rate: Argon at 23 l/min

[0079] Ti/TiN particle feed rate: 18 g/min

[0080] Laser: Laserline LDF 6,000-100

[0081] Spot size: 8.5 mm

[0082] An example of a microstructure for a wear resistant coating formed in accordance with these conditions is shown in FIG. 3. Discrete particles of titanium nitride are shown dispersed generally homogenously in a generally continuous matrix of titanium alloy with secondary precipitates of titanium nitrides. These secondary precipitates add both wear & galling resistance. The titanium alloy of the substrate is metallurgically bonded with the wear resistant coating. A wear resistant coating formed by a series of side-by-side laser passes is shown in FIG. 4. The feed rate of particles identified above produces a wear resistant coating thickness of 1.0 mm. However, it is possible with this process to build up the thickness of the coating by running subsequent laser passes and feed particles over already formed coating. In this manner, it is possible to build up the coating to any desired depth, but it is expected that thicknesses of up to 10 mm will be suitable for a wide variety of applications. For example, the wear resistant coating may be applied to agitator blades for autoclaves, diffuser cones, wear plates and valve components.

[0083] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word comprise or variations such as comprises or comprising is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

[0084] It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention.

[0085] It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

[0086] In addition, the foregoing describes only some embodiments of the invention(s), and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.

[0087] Furthermore, invention(s) have been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention(s). Also, the various embodiments described above may be implemented in conjunction with other embodiments, for example, aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments.