Thermal spray technologies such as the cold spray process can be used for various applications such as applying metal layers to non-metallic substrates to make metal layer-containing composite articles, applying metal outer layers to substrates of a different material, for example to obtain corrosion benefits of the outer layer metal with the processability of the substrate metal, field repair of metal components, and various other additive manufacturing technology applications.
Titanium and titanium alloys are widely used for various applications such as aircraft, motor vehicles, and countless other applications, where they provide beneficial properties including but not limited to strength, strength:weight ratio, corrosion resistance, high specific heat, and tolerance of extreme temperatures. However, the use of titanium alloys as metal powder used in the cold spray process has been limited by factors such as degradation of the nozzles used in the cold gas spray process and a tendency of the titanium alloys to clog nozzles used in the cold spray process. Conventional approaches for dealing with such nozzle problems typically involve the use of exotic (and expensive) materials such as quartz for the cold spray nozzles, or modification of cold spray process parameters to lower temperatures or other process modifications that can cause adverse impacts to the properties of cold spray-applied material.
According the invention, there is a method of applying a metal comprising titanium to a substrate. The method comprises nitriding the surface of metal powder particles comprising titanium by contacting the particles with a first gas comprising nitrogen in a fluidized bed reactor, and depositing the nitrided metal powder particles onto the substrate with cold spray deposition using a second gas.
In some aspects of the invention, the metal powder particles comprise titanium or titanium alloys Ti—6Al—4V, Ti—3Al—2.5V, Ti—5Al—2.5Sn, Ti—8Al—1Mo—1V, Ti—6Al—2Sn—4Zr—2Mo, α+β Ti—6Al—4V, or near β Ti—10V—2Fe—3Al.
In some aspects of the invention, the metal powder particles comprises titanium or titanium alloy grades 5 (Ti—6Al—4V) or 23 (Ti—6Al—4V) according to ASTM B861-10.
In some aspects of the invention, the metal powder particles after nitriding comprise elemental nitrogen at the particle surface and also comprise an internal particle portion that is free of elemental nitrogen.
In some aspects of the invention, the metal powder particles after nitriding have a surface nitrogen content ranging from 5.96 wt. % to 12.22 wt. % as determined by x-ray photoelectron spectroscopy.
In some aspects of the invention, the metal powder particles after nitriding have a nitrogen:oxygen surface wt. % ratio of from 5.96:26.20 to 12.22:16.75 as determined by x-ray photoelectron spectroscopy.
In some aspects of the invention, the first gas comprises at least 1 vol. % nitrogen.
In some aspects of the invention, the first gas consists essentially of nitrogen.
In some aspects of the invention, the fluidized bed reactor is operated at a temperature of 500° C. to 850° C.
In some aspects of the invention, the first gas is at a pressure of 0.11 to 0.12 MPa.
In some aspects of the invention, the space velocity of the first gas in the fluidized bed reactor is from 1 min−1 to 30 min−1.
In some aspects of the invention, the metal powder particles are contacted with the first gas in the fluidized bed reactor for at least 1 minute.
In some aspects of the invention, the second gas comprises helium or argon.
In some aspects of the invention, the second gas comprises helium or argon and nitrogen.
In some aspects of the invention, the second gas consists essentially of helium or argon.
In some aspects of the invention, the second gas is at a temperature of 20° C. to 850° C.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying figures, in which:
An exemplary fluidized bed reactor assembly for nitriding titanium alloys is depicted in
In operation, a gas comprising nitrogen from gas source 24 is fed through feed line 22, with the flow rate and gas pressure controlled by mass flow controller 26 and pressure regulating valve 28. The nitrogen-containing gas enters the outer tubing 18 through inlet 20. The gas is heated as it passes through the space between fluidized bed 12 and outer tubing 18 to enter the fluidized bed reactor 12 through inlet 14. The fluidized bed reactor 12 has metal particles 46 comprising titanium disposed therein, and the upward gas flow rate through the reactor applies sufficient upward force to the particles 46 to counteract the force of gravity acting on the particles so that they are suspended in a fluid configuration in the reactor space. The gas flow is generally maintained below levels that would carry entrained particles out of the reactor 16 through outlet 16, and outlet 16 can also be fitted with a filter or screen to further assist in keeping metal powder particles 46 from exiting the reactor 12. Nitrogen-containing gas exits the reactor 12 through outlet 16 and flows via outlet line 36 to the bubbler 38, from which it is exhausted to the atmosphere through exhaust port 44.
The invention can utilize any titanium metal or titanium metal alloy, including any of the grades of titanium alloys specified in ASTM B861-10. Alpha titanium alloys, near-alpha titanium alloys, alpha-beta titanium alloys, and beta titanium alloys. In some embodiments, the titanium alloy comprises from 0 to 10 wt. % aluminum and from 0 to 10 wt. % vanadium. In some embodiments, the titanium alloy is an alpha-beta titanium alloy such as Ti—6Al—4V (e.g., grades 5 or 23 according to ASTM B861-10), Ti—Al—Sn, Ti—Al—V—Sn, Ti—Al—Mo, Ti—Al—Nb, Ti—V—Fe—Al, Ti—8Al—1Mo—1V, Ti—6Al—2Sn—4Zr—2Mo, α+β Ti—6Al—4V or near β Ti—10V—2Fe—3Al. In some embodiments, the titanium alloy is a Ti—6Al—4V alloy such as grade 5 or grade 23 according to ASTM B861-10.
The nitrogen-containing gas can contain from 1 vol. % to 100 vol. % nitrogen, more specifically from 5 vol. % to 100 vol. % nitrogen, and more specifically from 25 vol. % to 75 vol. % nitrogen. In some embodiments, the nitrogen-containing gas consists essentially of nitrogen, and in some embodiments the nitrogen-containing gas is pure. The nitriding reaction conducted in the fluidized bed reactor is typically conducted at elevated temperature, compared to ambient conditions. The reaction temperature in the reactor can range from 500° C. to 800° C., more specifically from 600° C. to 750° C., and even more specifically from 600° C. to 700° C. Pressures in the reactor can range from 0.11 MPa to 0.13 MPa, more specifically from 0.11 MPa to 0.12 MPa, and even more specifically from 0.11 MPa to 0.115 MPa. The flow rate of nitrogen to the reactor can vary based on factors such as reactor dimension, with exemplary flow rates of 0.0069 m/min to 0.013 m/min, more specifically from 0.0097 m/min to 0.011 m/min, and even more specifically from 0.010 m/min to 0.0105 m/min. The metal powder particles can be nitrided for periods (i.e., contact time with the nitrogen-containing gas) of at least 1 minute, for example, time periods ranging from 1 minute to 30 minutes, more specifically from 1 minute to 10 minutes, and even more specifically from 1 minute to 5 minutes. In batch mode, such as depicted in the reaction scheme shown in
After processing the titanium-containing metal particles in the nitrogen-containing fluidized bed reactor, the particles can have a surface nitrogen content ranging from 5.96 wt. % to 12.22 wt. %, more specifically from 5.96 wt. % to 7.90 wt. %, or from 7.90 wt. % to 9.77 wt. %, or from 9.77 wt. % to 12.22 wt. %, as determined by x-ray photoelectron spectroscopy. As used herein, x-ray photoelectron spectroscopy and the values specified herein are according to the protocols of according to ASTM E2735-14, Standard
Guide for Selection of Calibrations Needed for X-ray Photoelectron Spectroscopy (XPS) Experiments, ASTM International, West Conshohocken, Pa., 2014. Surface nitrogen on titanium or titanium alloy metal particles can bond with titanium or other metals in the alloy such as aluminum, and in doing so can displace oxygen from metal oxide at the particle surface, thus reducing the material's oxygen content at the surface. In some embodiments, after nitriding the metal powder particles can have a nitrogen:oxygen surface wt. % ratio of from 5.96:26.20 to 7.90:21.83 as determined by x-ray photoelectron spectroscopy, and more specifically can have a nitrogen:oxygen surface wt. % ratio of from 9.77:19.99 to 12.22:16.75. The use of pure titanium nitride as a cold spray applied metal can result in undesirable porosity levels in the applied material. Accordingly, in some embodiments, the nitriding reaction is conducted under conditions (e.g., contact time, temperature, space velocity) so that nitriding occurs on the surface of the metal particles but not throughout the interior of the particles, resulting in particles with a surface layer comprising nitrogen and at least a portion of the particles' interior being free of nitrogen.
As mentioned above, the nitride titanium or titanium alloy metal powder is applied to a substrate with a cold spray deposition process. In a cold spray process, unmelted metal particles are introduced into a high velocity gas stream being projected out of a high velocity (e.g., supersonic) nozzle toward the coating substrate target. The particles' kinetic energy provides sufficient heat on impact with the coating substrate such that the particles plastically deform and fuse with the substrate and surrounding deposited metal material. As the particles impact the substrate, they rapidly cool even as the particles are deforming. The particles change shape dramatically from relatively round to very thin flat splats on the surface.
An exemplary system is depicted in
The invention is further described in the following Examples.
Ti—6Al—4V alloy powder materials were nitrided in a fluidized bed reactor as shown in
After the target temperature was reached using an argon gas flow in the reactor, the gas flow was switched to nitrogen (Matheson) and the temperature was held for the times indicated in Table 1. After treating the powder samples in nitrogen at the designated temperature and time, the gas flow was switched to argon and the reactor was allowed to cool down. This was done primarily to isolate the soak time and to prevent any further nitridation that might occur at the higher temperatures during the slow cooling process. Once the powder temperature reached a low enough temperature (about 300° C.), the gas flow was switched again, back to nitrogen and the furnace continued to cool down to ambient temperature. The resulting metal powders, along with samples of the untreated powder, were characterized using scanning electron microscopy (SEM) and energy dispersive X-ray micro-analysis (EDX). Identification of bulk phase structures and the extent of nitridation were conducted by X-ray diffraction (XRD) using Rigaku and JADE software from MDI. Surface elemental composition was determined by X-ray photoelectron spectroscopy (XPS) using a PHI VersaProbe. Elemental surface analysis was conducted by x-ray photoelectron spectroscopy, the results of which are shown in
The metal powders were used in a system as shown in
As used herein: The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. “Or” means “and/or.” The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity). The terms “front”, “back”, “bottom”, and/or “top” are used herein, unless otherwise noted, merely for convenience of description, and are not limited to any one position or spatial orientation. The terms “first”, “second”, “third”, and so on are used herein, unless otherwise noted, merely for convenience of description, and are not limited to any one ordering or order of preference. The endpoints of all ranges directed to the same component or property are inclusive and independently combinable (e.g., ranges of “less than or equal to 25 wt %, or 5 wt % to 20 wt %,” is inclusive of the endpoints and all intermediate values of the ranges of “5 wt % to 25 wt %,” etc.). The suffix “(s)” is intended to include both the singular and the plural of the term that it modifies, thereby including at least one of that term (e.g., the colorant(s) includes at least one colorants). “Optional” or “optionally” means that the subsequently described event or circumstance can or can not occur, and that the description includes instances where the event occurs and instances where it does not. Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this invention belongs.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
Filing Document | Filing Date | Country | Kind |
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PCT/US2016/013995 | 1/20/2016 | WO | 00 |
Number | Date | Country | |
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62106140 | Jan 2015 | US |