Hardened surface manufacturing

Abstract

A method for forming a hardened surface on an article (10) includes providing an article to be treated. The article is exposed to an impactor (20) and tungsten carbide particles (22), the tungsten carbide particles being either free tungsten carbide particles or particles within the impactor. The impactor is a solid having an average diameter within the range of 0.1 to 10 mm. Preferably, the average diameter is within the range of 0.5 to 5 mm. A velocity difference (V) is created between the surface (12) of the article and the impactor. This creates an impact between the impactor and the surface of the article, resulting in a burnishing action. As a result, tungsten carbide particles are embedded in the surface of the article (14). At least 80% of the embedded tungsten carbide particles have a size within the range of 0.1 to 5 μm.

Description

[Technical Field]

[0001] The present technology relates to the formation of hardfacings on articles. [Background technology]

[0002] Metal matrix composites (MMCs) are metal alloys reinforced with fibers, particulates, whiskers, or wires. MMC materials are widely used to manufacture wear-resistant hardened surfaces. Tungsten carbide (WC) particles are the most commonly used reinforcement material in MMC hardened surfaces due to their extremely high hardness. See, for example, Grairia, A., Beliardouh, NE, Zahzouh, M., et al., "Dry sliding wear investigation on tungsten carbide particles reinforced iron matrix composites," in Materials Research Express, IOP Publishing Ltd, 5 (2018), pp. 116528.

[0003] Hard surfaces can be divided into thin and thick. Thin hard surfaces typically have thicknesses of 50 μm or less. Typical techniques for fabricating thin hard surfaces include physical vapor deposition (PVD), chemical vapor deposition (CVD), electroless / electroplating, chemical heat treatments such as carburizing, carbonitriding, nitriding, and boriding, and surface mechanical treatments. Thick hard surfaces, on the other hand, generally have thicknesses greater than 50 μm, up to several mm, or even more. Thick hard surfaces are typically fabricated by welding or brazing. Major techniques include laser hardening, plasma-transfer arc (PTA) welding, consumable and non-consumable electric arc welding, oxyacetylene flame welding and brazing, and furnace brazing. Thick hard surfaces are made of either homogeneous metals and alloys or MMCs with discrete hard phase particles as reinforcement. Tungsten carbide particle-reinforced MMCs can also be synthesized by powder metallurgy.

[0004] US Patent Application Publication No. 2018 / 178283 describes the use of tungsten carbide particles for hard surfacing.

[0005] U.S. Patent No. 4,192,984 describes embedding hard particles by softening the surface layer of the metal using eddy current technology. The main drawback of this method is that it affects the hardness of the metal. Particle bombardment can also be performed using cold gas dynamic spraying (CGDS).

[0006] EP 0 484 533 A1 proposes a method for coating metal articles using high-velocity impact of particles accelerated to velocities of 300-1,200 m / s in a gas stream.

[0007] There are also many thermal spray coating techniques, such as high velocity oxygen fuel (HVOF) thermal sprayed WC coatings, which are produced using conventional WC-Co feedstocks or suspended WC-Co feedstocks. For example, B. Heimann, RB, Lehmann, HD, “Recently Patented Work on Thermally Sprayed Coatings for Protection Against Wear and Corrosion of Engineered Structures”, in Recent Patents on Materials Science 1 (2008) 41-55, or Dong, SJ., Ye, J., Zhu, L. et al., “Thermal effect of high-velocity particle impingements on coating quality in cold gas spray dynamic operations” in J Mech Sci Technol 36, 3619-3629 (2022), or Ahmed, R., Vourlias, G., Algoburi, A., et al., “Comparative Study of Corrosion Performance of HVOF-Sprayed Coatings Produced Using Conventional and Suspension WC-Co Feedstock”, in Journal of Thermal Spray Technology. 27 (2018) 1579-1593, or Ali, O., Ahmed, R., Faisal, N., et al., “Influence of Post-treatment on the Microstructural and Tribomechanical Properties of Suspension Thermally Sprayed WC-12 wt%Co Nanocomposite Coatings”, in Tribology Letters. 65, 33 (2017).

[0008] Another technique suitable for producing WC coatings is laser cladding. In contrast to surface welding or thermal spraying, laser cladding allows for highly localized and highly complex coatings. However, because it is localized, it is more difficult to achieve a uniform coating. See, for example, Van Acker, K., Vanhoyweghen, D., Persoons, R., Vangrunderbeek, J., "Influence of tungsten carbide particle size and distribution on the wear resistance of laser clad WC / Ni coatings," in Wear. 258 (2005) 194-202.

[0009] Despite various approaches to providing MMCs based on hard particles such as WC, there remains a need for the development of methods that are easily applicable, particularly methods that are suitable for providing uniformly hardened surfaces on articles with complex geometries. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] US Patent Application Publication No. 2018 / 178283 [Patent Document 2] U.S. Patent No. 4,192,984 [Patent Document 3] European Patent Application Publication No. 0484533 [Non-patent literature]

[0011] [Non-Patent Document 1] B. Heimann, R.B., Lehmann, H.D., “Recently Patented Work on Thermally Sprayed Coatings for Protection Against Wear and Corrosion of Engineered Structures”, in Recent Patents on Materials Science 1 (2008) 41-55 [Non-Patent Document 2] Dong, SJ., Ye, J., Zhu, L. et al., “Thermal effect of high-velocity particle impingements on coating quality in cold gas dynamic spray operations” in J Mech Sci Technol 36, 3619-3629 (2022) [Non-Patent Document 3] Ahmed, R., Vourlias, G., Algoburi, A., et al., “Comparative Study of Corrosion Performance of HVOF-Sprayed Coatings Produced Using Conventional and Suspension WC-Co Feedstock”, in Journal of Thermal Spray Technology. 27 (2018) 1579-1593 [Non-Patent Document 4] Ali, O., Ahmed, R., Faisal, N., et al., “Influence of Post-treatment on the Microstructural and Tribomechanical Properties of Suspension Thermally Sprayed WC-12 wt%Co Nanocomposite Coatings”, in Tribology Letters. 65, 33 (2017) [Non-Patent Document 5] Van Acker, K., Vanhoyweghen, D., Persoons, R., Vangrunderbeek, J., “Influence of tungsten carbide particle size and distribution on the wear resistance of laser clad WC / Ni coatings”, in Wear. 258 (2005) 194-202 Summary of the Invention [Problem to be solved by the invention]

[0012] It is therefore a general object to provide an easily applicable method for producing hardened surfaces suitable for articles of complex shape. [Means for solving the problem]

[0013] The above object is achieved by the method according to the independent claims. Preferred embodiments are defined in the dependent claims.

[0014] In general, in a first aspect, a method for forming a hardened surface on an article includes providing an article to be processed. The article is exposed to an impacting object and tungsten carbide particles. The tungsten carbide particles are provided as tungsten carbide particles contained in the impacting object and / or as tungsten carbide particles provided directly in a processing fluid as a dispersion. The impacting object is a solid having an average diameter in the range of 0.1 to 10 mm. Preferably, the average diameter is in the range of 0.5 to 5 mm. A velocity difference is created between the surface of the article and the impacting object. This creates an impact between the impacting object and the surface of the article, resulting in a burnishing action. At least 80% of the tungsten carbide particles have a diameter in the range of 0.1 to 5 μm. The tungsten carbide particles are embedded in the surface of the article, using the energy of the impact to drive the tungsten carbide particles into the article. [Effects of the Invention]

[0015] One advantage of the proposed technology is that it produces a wear-resistant, low-friction surface paved with embedded tungsten carbide particles regardless of the geometric macroscopic shape of the article being treated. Other advantages will become apparent upon reading the detailed description.

[0016] The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken together with the accompanying drawings, in which: [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a process flow diagram of one embodiment of a method for forming a hardened surface on an article. [Figure 2] FIG. 2 shows the hardness and use of different WC-Co materials. [Figure 3] FIG. 3 is an SEM image of the surface of one embodiment of the impactor. [Figure 4] Figure 4 is an SEM image of the WC-Co beads used as impactors. [Figure 5A] 5A-C are SEM images of steel surfaces treated by different embodiments of the method for forming a hardened surface on an article. [Figure 5B] 5A-C are SEM images of steel surfaces treated by different embodiments of the method for forming a hardened surface on an article. [Figure 5C] 5A-C are SEM images of steel surfaces treated by different embodiments of the method for forming a hardened surface on an article. [Figure 6] FIG. 6 shows the weight loss of the impacted object. [Figure 7] FIG. 7 is a schematic diagram of an impacting object approaching an article surface. [Figure 8A] 8A-C are schematic diagrams of different methods for creating a velocity difference. [Figure 8B] 8A-C are schematic diagrams of different methods for creating a velocity difference. [Figure 8C]8A-C are schematic diagrams of different methods for creating a velocity difference. [Figure 9] FIG. 9 is a schematic diagram of one embodiment of a vibrating barrel system. [Figure 10] FIG. 10 is a schematic diagram of one embodiment of a gravity-based stream completion system. [Figure 11A] 11A-B show measurements of the surface roughness of a piston before and after embedding WC particles. [Figure 11B] 11A-B show measurements of the surface roughness of a piston before and after embedding WC particles. [Figure 11C] FIG. 11C shows the W content on the surface of the treated piston. [Figure 12] FIG. 12 shows the coefficient of friction of the article before and after embedding of WC particles. [Figure 13] FIG. 13 shows the surface roughness parameters of the gear before and after the triboconditioning treatment. [Figure 14A] 14A-C are diagrams showing the surface characteristics of untreated pins. [Figure 14B] 14A-C are diagrams showing the surface characteristics of untreated pins. [Figure 14C] 14A-C are diagrams showing the surface characteristics of untreated pins. [Figure 15A] 15A-C are diagrams showing the surface characteristics of pins treated according to the triboconditioning treatment. [Figure 15B] 15A-C are diagrams showing the surface characteristics of pins treated according to the triboconditioning treatment. [Figure 15C] 15A-C are diagrams showing the surface characteristics of pins treated according to the triboconditioning treatment. DETAILED DESCRIPTION OF THE INVENTION

[0018] Throughout the drawings, the same reference numbers are used for similar or corresponding elements.

[0019] The phenomenon of abrasive particles becoming embedded in a workpiece during abrasive finishing is well-known but generally undesirable. The presence of embedded abrasive particles is usually detrimental to tribology, as it leads to reduced machining efficiency, increased friction, and faster wear. Therefore, specific measures are typically taken to avoid or minimize particle embedding, such as installing flushing nozzles at the grinding outlet, providing continuous coolant filtration, redesigning tool dressing, and using tougher or less friable abrasives. See, for example, Badger, JA, “How to avoid embedded particles,” in Cutting Tool Engineering, March 2020, https: / / www.ctemag.com / news / articles / how-avoid-embedded-particles.

[0020] Despite the knowledge that WC particles embed during polishing, this phenomenon does not appear to have been linked to improved tribological performance. At the same time, as shown in the background section, the use of WC particles on MMC hard surfaces has been shown to conversely lead to improved tribology. However, such methods require entirely different, generally complex and expensive, application methods.

[0021] After conducting screening tests of various mass-finishing media, it was unexpectedly discovered that the use of certain non-abrasive burnishing media—WC-Co cemented tungsten carbide beads—particularly those with a specific particle size distribution, resulted in unusually high levels of tungsten incorporation on the surface. SEM analysis of the treated surfaces revealed an unexpected high density of embedded WC particles, characteristic of MMC-type hardened surfaces. This result was completely unexpected, as the possibility of producing such MMC coatings using tribological processes was previously thought to be extremely low. Furthermore, it was discovered that MMC coatings produced using tribological processes do not require additional finishing processes because they are already "run-in" during production.

[0022] Based on these surprising findings, the inventors gained the insight that it would be highly desirable to produce MMC-like coatings using conventional finishing processes, such as lapping and mass finishing. By finding the appropriate processing conditions, the previously deleterious particle embedding during abrasive finishing can instead be utilized to produce the desired MMC hardened surface and associated tribological benefits. Therefore, mass finishing processes have proven particularly important.

[0023] To better understand the proposed technology, it is useful to start with a brief overview of mass finishing.

[0024] The term "mass finishing" refers to a group of manufacturing processes that can finish large numbers of parts simultaneously. Two commonly used types of mass finishing are tumble finishing, also known as barrel finishing, and vibratory finishing.

[0025] Mass finishing uses abrasive contact between the workpiece and the finishing media surface to achieve the desired surface finish quality of the workpiece. Various types of finishing media can be used. Mass finishing can be done dry or wet. Wet methods use abrasives along with liquid lubricants, coolants, or cleaners. Cycle times can vary from minutes to hours, depending on the processing conditions, workpiece material, and finishing media used. The purpose of this type of finishing is to burnish, deburr, clean, radius, deflash, descale, remove rust, polish, brighten, harden surfaces, prepare for further finishing, or cut off die casting runners.

[0026] Mass finishing can be performed as a batch or continuous process and can involve sequentially passing workpieces through multiple different mass finishing steps. See, e.g., L.K. Gillespie, "Mass finishing handbook," Industrial Press, New York, 2007, pp. 781-784.

[0027] FIG. 1 is a flow diagram of steps in one embodiment of a method for forming a hardened surface on a product. In step S10, an article to be treated is provided. The article may have virtually any shape, including, for example, a convex and / or concave curved surface and / or a surface with a continuously and / or discontinuously varying curvature. In step S20, the article is exposed to impactors, e.g., bead-shaped impactors and tungsten carbide particles. Preferably, the article is subjected to impacts from impactors optionally wetted with a treatment fluid in which tungsten carbide particles are dispersed. As described further below, the tungsten carbide particles may be released by the impactors and / or provided separately. In other words, the tungsten carbide particles are provided as free tungsten carbide particles and / or tungsten carbide particles contained in the impactors. The impactors are solids having an average diameter in the range of 0.1 to 10 mm. Preferably, the average diameter is in the range of 0.5 to 5 mm. The size of the impactors is preferably selected to match the curvature of the article. In step S30, a velocity difference is created between the article surface and the impacting object. This velocity difference causes an impact between the impacting object and the article surface, resulting in a burnishing action. In step S40, tungsten carbide particles are embedded into the article surface using the energy of the impact. At least 80% of the tungsten carbide particles have a particle size within the range of 0.1 to 5 μm.

[0028] In a preferred embodiment, at least 80% of the tungsten carbide particles have a particle size with a maximum diameter in the range of 0.2 to 2 μm.

[0029] There are several types of tungsten carbide. Fused and crushed tungsten carbides (FTC) have a eutectic microstructure consisting of WC and WC. They are irregularly block-shaped and typically contain 3.5-4% carbon by mass. Spherical cast tungsten carbides (SCC) are made by spheroidizing melted and crushed carbides with a plasma torch. Like FTC carbides, SCC microstructures consist of a WC / WC eutectic phase. Macrocrystalline tungsten carbide, also known as monocrystalline carbide (MTC), consists of hexagonal WC carbides with an irregular block-like shape and typically contains 6.1% carbon. It has a higher melting point than the eutectic WC / WC carbide, making it thermodynamically more stable, and it has a lower density than the eutectic WC / WC carbide. Macrocrystalline WC carbide is less soluble than eutectic WC / WC carbide, resulting in a higher volume fraction of unmodified WC particles and superior wear resistance. Both types of tungsten carbide can be used to create hard surfaces on articles.

[0030] In one group of embodiments, the impactors include cemented tungsten carbide beads or balls.

[0031] By selecting the appropriate combination of hard phases, metallurgical binder phases, and processing parameters, a wide range of microstructural combinations with different mechanical properties can be achieved.

[0032] For example, a variety of binders are available, of which cobalt and nickel are the most common. WC-Ni cemented carbides offer high corrosion resistance but are generally softer than WC-Co cemented carbides. Thermally sprayed WC-Ni coatings are also characterized by high bond strengths, often exceeding 70 MPa, compared to 30-60 MPa for WC-Co coatings.

[0033] In one embodiment, the impacted object comprises at least one of Co cemented tungsten carbide and Ni cemented tungsten carbide. Preferably, the impacted object comprises Co cemented tungsten carbide.

[0034] The addition of other carbides such as TiC and / or nitrides such as TiN and Ti(C,N) allows for the creation of endless material combinations to fine-tune product properties. See for example Garcia, J., Cipres, VC, Blomqvist, A., Kaplan, B., “Cemented Carbide Microstructures: a Review”, in Int. J. Refractory Metals and Hard Materials, 80 (2019) 40-68.

[0035] To promote sufficient particle release and embedding, it is preferable to impact the WC-Co beads at an oblique angle against the workpiece surface. The momentum and energy of the impact should be high enough to provide a high probability of detaching WC particles from the impactor and driving them into the workpiece. At the same time, the momentum and energy should preferably not be too high to prevent surface damage, such as impact craters. For this purpose, hard WC-Co beads made by FTC with low adhesive strength are preferred.

[0036] In fact, the selection criteria are in some ways the opposite of those used for abrasive finishing. Abrasive grains that are easy to break are preferred. Impact damping can be further minimized by using a low-viscosity, low-lubricity coolant. This process can be performed under dry conditions, but this is undesirable due to excessive heat generation and dust generation. The presence of WC dust in the workplace air poses a significant health hazard. WC-Co beads with hardnesses of 750-2200 Hv, preferably 1600-2200 Hv, elastic moduli of 450-650 GPa, preferably 550-650 GPa, and compressive strengths of 3-9 GPa, preferably 6-9 GPa, have proven to be very usable. Furthermore, a polydisperse particle size distribution in the range of 0.1-2 μm, preferably 0.2-1 μm, and a cobalt content of 2-20%, preferably 5-15%, appear to be highly suitable for the currently presented method. Such impact materials provide a method for the production of MMC-like hardened surfaces by particle embedding. This includes WC-Co materials commonly used in wear parts, cutting tools, composite machining and wire drawing applications.

[0037] In other words, in one embodiment, the material of the impactor comprises 2-20% by mass Co, preferably 5-15% by mass Co, most preferably 5-10% by mass Co, and has a hardness of 750-2200 Hv, preferably 1600-2200 Hv, an elastic modulus of 450-650 GPa, preferably 550-650 GPa, and a compressive strength of 3-9 GPa, preferably 6-9 GPa.

[0038] The mechanical properties of WC-Co beads depend strongly on the size of the WC particles, with smaller particles resulting in improved hardness, wear resistance, compressive strength, and transverse fracture strength. According to the particle size classification by Fachverband Pulvermetallurgie (see, for example, Ortner, HM, Ettmayer, P., Kolaska, H., "The history of the technological progress of hardmetals," in International Journal of Refractory Metals and Hard Materials, 44 (2014) 148-159), the aforementioned preferred range of 0.2 to 1 um covers ultrafine, submicron, and fine particle sizes.

[0039] FIG. 2 is a diagram of various compositions of WC-Co materials of interest in this technology in terms of cobalt content and WC particle size. The solid lines represent the hardness of the material. The dotted areas indicate different typical application areas for WC-Co materials: area 100 represents resource extraction and construction, area 101 represents rolls, area 102 represents can-making tools, area 103 represents wear parts, area 104 represents metal cutting, area 105 represents composite machining, area 106 represents woodworking, and area 107 represents wire drawing. Area 110 represents the most favorable compositional options for the production of MMC-like hardened surfaces by particle embedding.

[0040] Polydispersity is also important because the larger particles attached to the WC-Co beads act as hammer faces to drive the loose smaller particles into the workpiece surface.

[0041] Figure 3 is a scanning electron microscope (SEM) image of the microstructure of the WC-Co material in the impactor used to fabricate an MMC-like hardened surface by particle embedding. Figure 4 is an SEM image of a whole WC-Co bead used as the impactor in the fabrication of an MMC-like hardened surface by particle embedding. Note the impact craters on the bead surface.

[0042] Many tests were conducted using different settings and treatment times. Figures 5A-C are SEM images of three treated surfaces. The microstructure of the MMC-like hardened surface on a steel surface produced using the method described above is shown. The bright areas indicate embedded WC particles. The chemical identity of the latter was also confirmed by EDX analysis. Figure 5A shows a surface treated in a centrifugal barrel finisher for 5 minutes, using 2 mm WC-Co beads in an oil-based treatment fluid as the impactor. Figure 5B shows a surface treated in a centrifugal barrel finisher for 15 minutes, using 2 mm WC-Co beads in an aqueous treatment fluid as the impactor. Figure 5C shows a surface treated in a vibratory tub finisher for 30 minutes, using a mix of 1 mm and 2 mm WC-Co beads in an oil-based treatment fluid as the impactor. Note that these images are only a sample of tests using different process parameters and material contents. From these SEM images, it can be concluded that embedded tungsten carbide particles are present in all cases, but in different amounts, which indicates that this method can be used with different finishing platforms and different process parameters.

[0043] The coverage of the embedded tungsten carbide varied but typically increased with time for each set of parameters. In Figure 5A-C, coverage ranged from 10 to 52%. However, improvements in tribological properties were already detected at relatively small coverages.

[0044] Thus far, WC particles have been described as being provided as a component in the impact material. However, alternatively or additionally, WC particles can be provided directly in the process fluid or coolant as a dispersion or slurry. In this case, other non-abrasive impact materials, such as steel or ceramic balls, can be used. Thus, in one embodiment, tungsten carbide particles are suspended in the process fluid. The impact material preferably comprises WC-Co, WC-Ni, steel, and / or ceramic materials.

[0045] When WC-Co impactors are used as a source of WC particles to be transferred to the workpiece, the impactors gradually wear down, losing weight. This is illustrated in Figure 6, which shows the weight loss of the impactor as a function of usage time. At some point, the impactor inevitably becomes too light to deliver sufficient impact energy and requires replacement. Furthermore, some impactors begin to disintegrate due to fatigue. To extend the service life of the media, as mentioned above, external WC particulate matter can be added to the system. This is advantageous because it offers greater flexibility and control over particle size. Furthermore, since friable abrasives are not required, the most wear-resistant WC-Co impactors can be used. Without external WC particle supply, media life may be limited to 100–200 hours in high-intensity centrifugal finishing processes, but with external WC particle supply, it can exceed 500 hours.

[0046] [Table 1]

[0047] Table 1. Sizes of WC-Co impactors useful for this technique.

[0048] The maximum number of parts that can be processed with a given volume of impactors can be easily estimated. Three practical sizes of WC-Co beads were considered: 1 mm, 2 mm, and 3 mm in diameter. Table 1 shows the size, number of impactors per volume, and total surface area of ​​the impactor volume.

[0049] 1dm 3 Removing 1 μm of material from impacted objects in a packed bed reduces the area of ​​the part by 1.4 to 4 m 2 It should be possible to cover the 1 dm with a micron-thick MMC layer. The impactor can be reduced in size by at least 10% without any significant change in processing performance. Therefore, even without an external particle supply, it is possible to reduce the size of the impactor by 1 dm 3 impact of at least 200m 2 The impact volume used in mass finishing machines can be several cm2 depending on the size of the machine.3 From several hundred dm 3 It can vary widely.

[0050] The preferred impact size range, which is practical for wet processes using neat oil or aqueous processing fluids, is 0.5 to 5 mm. The smallest impact size is determined by the fluid velocity. Since G-forces are countered by viscous drag, the following scaling relationship is preferred:

number

[0051] In the formula, G is the acceleration due to centrifugal action or vibration, and r is the radius of the impact object.

[0052] Therefore, the maximum impact velocity of the impacting object is

number

[0053] Therefore, the impact energy decreases rapidly as the impact size decreases. The practical viscosity range of the processing fluid used in this process is 1 to 10 cP, and it is difficult to achieve sufficient impact energy for impact size less than 0.5 mm in diameter when using a standard mass finishing platform. In other words, in one embodiment, the processing fluid containing the impactor has a viscosity of 1 to 10 cP at room temperature.

[0054] In FIG. 7, a workpiece or article 10 having a processing surface 12 is illustrated together with an impact object 20. The impact object 20 is wetted with a processing fluid 24, and the impact object 20 incorporates tungsten carbide particles 22. When the impact object 20 collides with the surface 12 at a velocity V, the tungsten carbide particles 22 may be released from the impact object 20 and become embedded tungsten carbide particles 14. As shown, the size of the largest impact object 20 defined by the radius r, with respect to the workpiece 10, should not exceed the minimum radius of curvature min(Rc) of the concave portion of the surface 12, and r < min(Rc) is preferred. Otherwise, portions of the surface 12 with a smaller radius of curvature will become inaccessible due to the impact of the impact object. This means that the selection of the impact object may depend on the workpiece, and a general upper limit cannot be set based on such considerations.

[0055] Another limit on size is due to excessive edge erosion by heavy impact objects. Thus, using WC-Co impact objects having a diameter exceeding 5 mm is typically impractical. Preferably, the impact object should be 3 mm or less.

[0056] Conveniently, various non-abrasive impact object shapes can also be used. A spherical shape such as a bead is useful for most applications. However, as non-exclusive examples, other shapes such as tubes, parallelepipeds, pyramids, etc. can also be used. When using impact objects with a high aspect ratio, rotation may also affect the impact energy.

[0057] In other words, in one embodiment, the impact object has an average diameter within the range of 0.5 to 5 mm, preferably within the range of 1 to 3 mm.

[0058] Various mass finishing platforms use different methods to create relative motion between the impactor and the article being treated. The article may be fixed, such as attached to a fixture, or free-standing, such as embedded within the bulk of the impactor. For most finishing platforms, it has been found that the velocity differential is preferably in the range of 0.5-5 m / s to achieve good embedding action.

[0059] Vibratory finishers utilize cyclic mechanical motion of an impact object 20 and a container containing the article 10. The principle is shown diagrammatically in Figure 8A. The G-force is controlled by the amplitude and frequency of the vibration.

[0060] There are many different designs for vibratory finishers. One of the simplest designs, shown schematically in FIG. 9, uses a bowl 30 attached to a shaft 33 with an eccentric weight 34 driven by a motor 32. The impacting object 20, article 10, and treatment fluid 24 are placed inside the bowl 30. The bowl 30 is supported by a spring 36, and the inertia of the eccentric weight 34 generates vibration of the impacting object 20. See, for example, Zhang, C., Liu, W., Wang, S., et al., “Dynamic modeling and trajectory measurement on vibratory finishing,” in The International Journal of Advanced Manufacturing Technology 106 (2020) 253-263.

[0061] The dynamics of the process depend on the dimensions of the bowl and the amplitude and frequency of the vibration. As a result, the velocity of the impacting object is proportional to the product of the amplitude and frequency, and the force is proportional to the product of the amplitude and frequency. 2The vibration amplitude depends on the eccentricity, i.e., the distance between the center of mass of the eccentric weight and the shaft, and the weight ratio (eccentric weight / bowl weight) (including the impacting object, fluid, and item). Friction between the impacting object, item, and bowl acts as a damping factor. The energy supplied to the system is mostly dissipated as frictional heat. The vibration amplitude can vary from a few millimeters to several centimeters. The speed range of a typical impacting object is typically 0.1 to 1 m / s. Using a vibratory finisher with a frequency of 50 Hz and an amplitude of 5 mm and 2 mm WC-Co beads, an MMC-like hardened surface can be formed within 1 to 2 hours. High-intensity vibratory finishing processes can deliver the same impact energy as low-intensity stream finishing processes. See, for example, Kacaras, A., Gibmeier, J., Zanger, F., and Schulze, V., “Influence of rotational speed on surface states after stream finishing,” in Proc. CIRP 71 (2018) 221-226.

[0062] Stream finishing and drag finishing differ primarily in what is moving: the impactor or the article. In stream finishing, the impactor 20 moves relative to a fixed, or possibly rotated, article 10, as shown diagrammatically in FIG. 8B. In drag finishing, the article 10 is dragged across the floor of the stationary impactor 20. The article 10 must be attached to a holder, which can ultimately be rotated or tilted to prioritize the treatment of certain areas.

[0063] Stream finishing operations are typically performed using a media velocity of 0.1 to 5 m / s. See, for example, Kacaras, A., Gibmeier, J., Zanger, F., Schulze, V., “Influence of rotational speed on surface states after stream finishing,” in Proc. CIRP 71 (2018) 221-226. When using WC-Co beads as a finishing impactor, a range of 0.5 to 5 m / s is currently considered more appropriate to promote sufficient particle embedding while simultaneously avoiding damage to the article. The smaller the bead size, the higher the velocity required to achieve the desired effect. This velocity range can be easily covered by a free-fall impactor. The drop height is determined by ignoring air resistance and V 2 The force is determined as / 2g, where V is the velocity of the impacting object when it impacts the item, and g is the acceleration due to gravity. This results in a typical drop height range of 0.01 to 1.2 m. The simplest design concept for implementing this technique is shown in Figure 10. A conveyor belt 38 transports the impacting object 20 from a barrel 37 containing the impacting object 20 and drops it onto the item 10.

[0064] A variety of commercially available stream finishing systems are available to accommodate high density media types. Typical processing times range from 1 to 30 minutes when using 2mm WC-Co beads.

[0065] In drag finishing, the impactor and processing fluid are typically placed in a bowl. The article is attached to a holder, submerged in the impactor bed, and dragged at a constant speed. When using WC-Co beads as the finishing medium, a speed in the range of 0.5 to 5 m / s, the same as for stream finishing, is typically appropriate to ensure sufficient particle embedding while simultaneously avoiding damage to the article. When using 2 mm WC-Co beads, typical processing times range from a few minutes to 30 minutes.

[0066] In centrifugal barrel finishing, turret rotation is used to control G-forces. The local conditions are similar to those in drag finishing (Figure 8C), but the article follows a rotational path. In a typical application, the article is placed in a barrel along with the impactor and processing fluid. The total fill rate of the impactor and fluid inside the barrel is typically 50-90%, of which the impactor fill rate is typically 20-80%, but preferably 40-60%. The barrel is mounted in a cradle attached to the turret. The turret rotates around a horizontal axis, creating a Ferris wheel-like motion with a 1:1 ratio of barrel rotation to turret rotation. Inside the barrel, the rotational motion induces collisions between the impactor and article, altering the surface finish of the article and embedding tungsten carbide particles. The processing dynamics depend on the dimensions of the barrel and turret. For a 20 cm diameter barrel and a 60 cm diameter turret, the turret typically rotates at 150-220 rpm. The optimum window is found to be 160-180 rpm. Speed ​​is the ratio of diameter to rpm. 2 Scale up with dimensions to keep constant. Processing times can vary from a few minutes to an hour, with 10-30 minute intervals often being targeted.

[0067] Many hybrid solutions also exist, for example, by selecting the appropriate vibration mode, it is possible to both secure the article and direct the media flow in a vibratory finisher.

[0068] Besides mechanical action, the impacted object can also be forced into motion using gravity (as mentioned above), fluid flow, magnetic fields, etc. For the treatment to be successful, the appropriate impact energy must be achieved: too high an energy will lead to damage to the article and excessive wear of the impacted object; too low an energy will not achieve the required particle embedding.

[0069] Shot peening and abrasive flow machining (AFM) systems are also suitable for the purposes of the present invention, with AFM technology being suitable for treating internal cavities. In shot peening, the impactor is accelerated using compressed air. In abrasive flow machining, the impactor is set in motion by hydrodynamic forces. However, the impactor speed of 10-100 m / s, which can be considered the standard speed in conventional shot peening, may be too high, at least when using high-density media. In such cases, it is preferable to use lower-density media or a lower speed.

[0070] In one embodiment of the method for forming a hardened surface on an article, the step of creating a velocity differential is accomplished using a centrifugal barrel finishing, a vibratory finishing, a stream finishing, or a drag finishing as a platform.

[0071] Unlike traditional abrasive finishing, where particle embedding is a priority, the presence of a certain amount of WC particles in the processing fluid is beneficial. However, if the particle concentration becomes too high, the fluid's rheology changes significantly. The fluid begins to resemble a slurry, damping the impact of the impacting object. Furthermore, the particle composition can change over time as metal particles from the processed parts accumulate in the machine.

[0072] Various fluid management systems can be used to ensure process stability. The simplest is a cascade system comprised of a settling tank or multi-weir system supplemented with cyclones and magnetic separators. Such systems are effective at removing excess WC and magnetic metal particles from the process fluid. After the process fluid reaches its end of life, the burnishing media is reconditioned and cleaned, and new fluid is filled into the unit. The latter operation is scheduled as planned maintenance.

[0073] Particle embedding can also be achieved under dry conditions without the use of treatment fluids, but this is undesirable due to excessive dusting, and airborne WC dispersion poses a significant health and safety hazard.

[0074] Generally, two types of treatment fluids are most suitable for use with this technology: neat oil and water-based synthetic fluids. The following examples show two possible formulations:

[0075] Neat oil Naphtha (Exxol D100, ExxonMobil) 96% by mass Sulfurized olefin (Additin RC 2540, Rhein Chemie) 2% by mass Zinc dialkyldithiophosphate (Lubrizol 1371, Lubrizol) 2% by mass Antioxidant (Rianox 1135, Rianlon) 500ppm Antifoaming agent (Viscoplex 14-520, Evonik) 200 ppm The kinematic viscosity of this composition at 25°C is 2.4 cSt and the specific gravity is 0.82 g / cm 3 , and the flash point is 90°C.

[0076] Water-based synthetic fluid Water 60% by mass Propylene glycol 30% by mass Water-soluble polyalkylene glycol (Breox 50 A 20, BASF) 5% by mass Corrosion inhibitor (SR1, Chemworld) 5% by mass Antifoaming agent (DOWSIL™ AFE-1267, Dow) 500 ppm

[0077] This composition has a kinematic viscosity of 1.7 cSt at 25°C and a specific gravity of 1.0 g / cm 3 is.

[0078] Similar mass finishing equipment has also been found to be useful in carrying out the mechanochemical surface finishing process known as Triboconditioning®, based on patent application PCT / SE2022 / 050859. By replacing fixed tooling with a swarm of non-abrasive dispersed impactors such as cemented carbide balls, ceramic beads, aluminum oxide beads, zirconium oxide beads, etc., this process overcomes particular difficulties associated with processing parts with complex geometries or dissimilar parts within the same batch.

[0079] Centrifugal barrel finishing, stream finishing, and vibratory finishing equipment have also proven suitable for performing triboconditioning processes using small balls / beads made of cemented carbide, nitride, zirconium oxide, or ceramic. The preferred ball size is 1–5 mm. When processing concave surfaces, for example, large diametral pitch gears, smaller ball sizes are required to access the tooth flanks and bottom lands. Wet finishing methods, in which the finishing media is used in conjunction with a reactive fluid that acts as a reagent for the tribochemical reaction, are preferred. In contrast to the well-known chemical mechanical polishing (CMP) process used in the semiconductor industry, the reactive fluid used in the triboconditioning process has a completely different function and composition. Unlike CMP fluids, triboconditioning fluids are not expected to chemically etch the surface to speed up the process. Their primary role is to provide the chemical reaction required to generate the tribofilm, as well as the corrosion protection and cleaning functions required for process stability.

[0080] This version of the triboconditioning process relies on the ability of the treatment to modify the article surface in the desired manner. The article's macrogeometry is maintained within applicable specifications. The surface roughness profile (according to ISO 1302) is modified by obtaining a negative skewness Rsk = -0.5 to -3, decreasing amplitude roughness, especially decreasing peak height and core roughness (Rpk and Rk), and slope roughness, which can be expressed as the root-mean-square slope Rdq or, when using angle-resolved light scattering (ARLS) techniques, as the variance Aq of the angular distribution of scattered light. A low-friction solid lubricant tribofilm is generated during treatment by tribochemical reactions with the processing fluid. A compressive stress, i.e., negative residual stress, is generated below the surface.

[0081] The fluid formulations used in the triboconditioning process can also be used in the particle embedding method of the present invention. Priming the tribofilm typically requires a different additive strategy. In particular, the triboconditioning process preferably uses high levels of extreme pressure and antiwear additives in the fluid. However, these additives tend to increase fluid costs and can have detrimental effects on the health, safety, and environmental profile of the fluid. Alternatively, it is certainly possible to combine the two approaches: triboconditioning and particle embedding.

[0082] Thus, in one embodiment, in a method for forming a hardened surface on an article, the processing fluid is a chemically reactive processing fluid comprising a solvent and a solid lubricant precursor additive. The solvent is a low-volatility, high-flash solvent. The solid lubricant precursor additive is a surface-reactive compound as a carrier of at least one of S, P, and B, and a surface-reactive compound as a carrier of at least one refractory metal and / or oil-soluble metal carboxylate, in combination with a sulfurized additive. The method includes the further step of forming a solid lubricant material on the article surface in the presence of the chemically reactive processing fluid by a chemical reaction involving the solid lubricant precursor induced by the energy of the impact. The chemical reaction occurs simultaneously on the surface of the workpiece in which the tungsten carbide particles are embedded. [Example]

[0083] Example 1: Treatment of pistons for radial piston pumps Hydraulic pistons made from 1020 steel were finished according to this technique using a centrifugal barrel finishing platform. A number of randomly selected parts were inspected before and after processing.

[0084] Figure 11A shows the Ra, as defined in accordance with ISO 1302, of 19 randomly selected parts before treatment as curve 120 and after treatment as curve 121. Similarly, Figure 11B shows the Rpk, as defined in accordance with ISO 1302, of 19 randomly selected parts before treatment as curve 122 and after treatment as curve 123. It is readily apparent that there is a distinct change in the surface roughness parameters of the pistons treated in accordance with the disclosed method. Thus, it is clear that a finishing action occurred during exposure to the impact.

[0085] Figure 11C shows the measurement of tungsten on the surface of the treated piston. Analysis was performed by XRF analysis. The absence of tungsten carbide on the majority of the piston is evidence that the established finish involves embedding tungsten carbide into the surface.

[0086] The treated parts were then subjected to tribological testing. Improved tribological performance was demonstrated. Both the starting friction torque and wear of the pump were significantly reduced.

[0087] Example 2: Powder Metallurgy Sintered Pin The 10mm diameter powder metallurgy sintered pins were made from Astaloy CrA (Fe-1.8%Cr). They were sintered and low-pressure carburized to a density of 7.2g / cm. 3 , hardness 760HV 0.1 Metal pins were finished according to this method on a centrifugal barrel finishing platform equipped with 1 mm WC-Co impactors. The processing time was 15 minutes at 165 rpm.

[0088] The surface roughness parameters Ra, Rpk, Rk, Rvk, and Rsk defined in ISO 1302 were measured before and after treatment, and the results are shown in Table 2.

[0089] [Table 2]

[0090] Table 2. Variation of surface roughness parameters of powder metallurgy pins processed according to the disclosed method.

[0091] XRF measurements also confirmed that the treated pins were characterized by an MMC-like layer due to embedded WC particles.

[0092] Tribological tests were also performed before and after treatment. Figure 12 shows the friction coefficient of lubricated metal-to-metal contact for the powder metallurgy pins as a function of time. Cross-cylinder friction and wear tests were performed at a load of 5 N. Curve 126 corresponds to the untreated pin, and curve 127 corresponds to the treated pin. As can be seen, the treatment significantly improved the tribological performance in both friction and wear.

[0093] Example 3: Gears A set of bevel gears made of 16MnCr5 gear steel with a hardness of 64HRC was finished using a centrifugal barrel finishing platform with 2mm WC-Co beads as finishing impacts. Table 3 shows the evolution of the surface roughness parameters defined according to ISO 1302.

[0094] [Table 3]

[0095] Table 3. Changes in surface roughness parameters of gears before and after treatment.

[0096] The formation of an MMC-like surface coating was confirmed by scanning electron microscope imaging and SEM-EDX elemental analysis. Based on X-ray diffraction (XRD) analysis, the compressive residual stress in the outermost material layer increased from 900 MPa to 1400 MPa.

[0097] This parameter is shown in the diagram of FIG. 13, where box 128 represents the surface roughness parameter of a reference ground gear and box 129 represents the surface roughness parameter of a gear processed according to the above principles.

[0098] Gear sets finished in accordance with the present invention demonstrated improved NVH behavior, with operating sound pressure levels reduced from 68 dB to 63 dB, reduced wear and improved pitting resistance.

[0099] When using the methods presented above to fabricate MMC-like hardened surfaces, it is important to pay attention to geometric dimensions and tolerances, for example, according to ISO 1101:2017, ASME Y14.5-2018, or other applicable standards. In general, the microgeometry of parts processed according to this technique should always be established during prior polishing processes, such as turning and grinding. Under most conditions suitable for this method, the tungsten carbide embedding process typically only affects the surface roughness profile. However, the tungsten carbide embedding process can be preceded by a dedicated polishing media finishing step to control surface waviness as well as to create a specific surface roughness profile. For example, an initial polishing finish can be used to "prime" the surface by cutting deeper grooves, followed by a tungsten carbide embedding process with a specific finish to flatten the surface peaks and create an MMC-like hardened surface. This two-stage process layout can push the boundaries of tribological performance.

[0100] Figures 14A-C show the surface characteristics of an untreated pin as a reference measurement. Figure 14A shows the surface roughness profile 130. Figure 14B shows the material ratio 131 and amplitude density curve 132. Figure 14C shows the Fourier transform 133 of the roughness profile. The total height of the profile Wt = 0.45 μm.

[0101] Figures 15A-C show the surface characteristics of a pin processed according to the principles described above. Figure 15A shows the surface roughness profile 134. Figure 14B shows the material ratio 135 and amplitude density curve 136. Figure 14C shows the Fourier transform 137 of the roughness profile. The total height of the profile Wt = 0.17 um.

[0102] The proposed tungsten carbide embedding process significantly improves the surface roughness of the treated object. Despite the embedding of tungsten carbide particles, a smoother surface is obtained. Thus, improved wear resistance as well as low friction are achieved.

[0103] In conclusion, a method for forming a hardened surface on an article involves exposing the article to an impactor, either directly or in the presence of free tungsten carbide particles dispersed in a treatment fluid. The impactor can be a solid, such as a tungsten carbide bead or ball, with a diameter ranging from 0.1 to 10 mm. Preferably, the average diameter should be within the range of 0.5 to 5 mm. A velocity difference is created between the surface of the article and the impactor. This results in an impact between the impactor and the article surface, resulting in a burnishing action. If the impactor is made of tungsten carbide, it will release tungsten carbide particles upon impact. If dispersed tungsten carbide particles are present in the treatment fluid, other non-abrasive impactors, such as steel or ceramic balls, can be used. As a result, the tungsten carbide particles become embedded in the surface of the article. At least 80% of the embedded tungsten carbide particles have a size ranging from 0.1 to 5 μm.

[0104] The above-described embodiments should be understood as a few illustrative examples of the present invention. It will be understood by those skilled in the art that various modifications, combinations, and changes can be made to the embodiments without departing from the scope of the present invention. In particular, different part solutions in different embodiments can be combined in other configurations, where technically possible. However, the scope of the present invention is defined by the appended claims.

Claims

1. A method for forming a hardened surface on an article (10), comprising: a step (S10) of supplying an article (10) to be treated; A step (S20) of exposing the article (10) to an impact object (20) and tungsten carbide particles (22), The tungsten carbide particles (22) are provided as at least one of tungsten carbide particles contained in the impact object and tungsten carbide particles (22) supplied directly to the treatment fluid (24) as a dispersion; the impactor (20) is a solid having an average diameter in the range of 0.1 to 10 mm, preferably 0.5 to 5 mm, A step (S30) of generating a speed difference between the surface (12) of the article (10) and the impacting object (20), thereby generating an impact between the impacting object (20) and the surface (12) of the article (10) and providing a burnishing effect, at least 80% of the tungsten carbide particles (22) have a particle size in the range of 0.1 to 5 μm; and a step (S40) of embedding tungsten carbide particles (14) into the surface (12) of the article (10) and driving the tungsten carbide particles (14) into the article (10) using the energy of the impact; A method comprising:

2. 2. The method of claim 1, wherein the step (S20) of exposing the article (10) comprises exposing the article (10) to the treatment fluid (24) to which the impactor (20) and the tungsten carbide particles (22) are supplied.

3. 3. The method of claim 2, wherein the treatment fluid (24) with the impact object (20) has a viscosity of 1 to 10 cP at room temperature.

4. 4. The method of claim 2 or 3, characterized in that the treatment fluid (24) comprises one of neat oil and water-based synthetic fluid.

5. The method according to any one of claims 1 to 4, characterized in that at least 80% of the tungsten carbide particles (22) have a particle size in the range of 0.2 to 2 μm.

6. A method according to any one of claims 1 to 5, characterized in that the impactors (20) comprise the tungsten carbide particles (22).

7. 7. The method of claim 6, wherein the impactor (20) is made of Co-hard alloy tungsten carbide.

8. 8. The method according to claim 7, characterized in that the impactor (20) comprises 2-20 wt. % Co, preferably 5-15 wt. % Co, most preferably 5-10 wt. % Co, and has a hardness of 750-2200 Hv, preferably 1600-2200 Hv, a modulus of elasticity of 450-650 GPa, preferably 550-650 GPa, and a compressive strength of 3-9 GPa, preferably 6-9 GPa.

9. The tungsten carbide particles (22) are suspended in the treatment fluid (24), and the impactor (20) W.C.-Co, WC-Ni, Steel, and ceramic objects The method according to any one of claims 2 to 5, characterized in that it comprises at least one of the following.

10. A method according to any one of the preceding claims, characterized in that the impactors (20) have an average diameter in the range of 0.5 to 5 mm, preferably in the range of 1 to 3 mm.

11. The step (S30) of generating a speed difference includes the following platforms: Centrifugal barrel finishing, Vibratory finishing, Stream Finish, Drag finish, and Shot peening 11. The method according to claim 1, wherein the method is carried out using one of the following:

12. 12. The method according to any one of claims 1 to 11, characterized in that the velocity difference is in the range of 0.5 to 5 m / s.

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