MXPA00002584A - Wear-resistant quasicystalline coating - Google Patents

Abstract

A thermally sprayed coating formed with a quasicrystal-containing alloy, the alloy consisting essentially of, by weight percent, 10 to 45 Cu, 7 to 22 Fe, 0 to 30 Cr, 0 to 30 Co, 0 to 20 Ni, 0 to 10 Mo, 0 to 7.5 W and balance aluminum with incidental impurities. The alloy contains at least 50 weight percent psi phase. The coating has a macrohardness of at least HR15N 75.

Description

QUASICRISTALI COATING NOT RESISTANT TO WEAR BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to quasi-crystalline alloys of aluminum-copper-iron and in particular to wear-resistant quasi-crystalline coatings exhibiting non-adhesive properties.

DESCRI PTION OF THE RELATIVE TECHNIQUE Quasi-crystals are materials whose structure can not be understood within the classical crystallographic methodology. These quasi-periodic structures have a long-range order of orientation, but lack transitional periodicity. The conventional crystals consist of repeated copies of a simple geometric atomic arrangement - a unit - cell stacked on them as partitions. The quasi-crystals, on the other hand, although they are also constructed from a simple type of atomic groups, differ in that the adjacent groups overlap, share atoms with their neighbors. When groups overlap by shared atoms (quasi-periodic packaging), they produce denser atomic arrays than conventional, periodic repeated packing patterns. The non-periodic structure of the quasi-crystals gives a wide range, which can not be obtained previously from physical properties incorporated within a simple material. The quasi-crystals exhibit poor thermal conductivity although they remain stable up to about 1, 100 ° C. Thus, a thin layer on a heat conducting surface will distribute the heat evenly by eliminating "hot spots". These hard coatings promote resistance to wear and scratching. In addition, due to their low coefficient of friction and electronic structure (low surface energy), they have non-adhesive properties. Finally, they offer resistance to both, corrosion and oxidation. Researchers have identified about eight hundred different alloys of quasi-crystals. Many of these alloys contain a combination of aluminum, copper and iron. These Al-Cu-Fe alloys give the specific icosahedral quasi-crystal identified in atomic percent as AI65Cu2oFe15. (This specification expresses all compositions in percent by weight, unless otherwise specifically noted). In addition, in some cases these alloys contain additional alloying elements such as chromium, cobalt and nickel. This allows the alloy to accommodate specific operating conditions. For example, DuBois et al., In the U.S. Patent. , No. 5,204, 191, describe various alloys of Al-Cu-Fe containing quasi-crystalline phases. Regardless of chemistry, however, quasi-crystals do not lend themselves to conventional manufacturing. They can not be formed or melted easily; however, they can be reduced to powder and thermally sprayed to form an adherent, useful coating. As far as is known, however, none of these alloys has established widespread commercial use. It is an object of this invention to produce an Al-Cu-Fe quasi-crystal alloy coating having increased hardness for improved wear resistance. It is a further object of this invention to produce an Al-Cu-Fe quasi-crystal alloy coating having non-adhesive properties and resistance to oxidation. It is a further object of this invention to produce an Al-Cu-Fe quasi-crystal alloy coating having a uniform high density surface.

BRIEF DESCRIPTION OF THE INVENTION A thermally sprayed coating formed with an alloy containing quasi-crystals, the alloy consisting essentially of, in percent by weight, 10 to 45 Cu, 7 to 22 Fe, 0 to 30 Cr, 0 to 30 of Co, 0 to 20 of Ni, 0 to 10 of Mo, 0 to 7.5 of W and the rest of aluminum with incidental impurities. The alloy contains at least 50 weight percent phase. The coating has a macrohardness of at least about H R 15N 75.

DESCRITION OF THE PREFERRED MODALITIES The coating consists of a wear-resistant Al-Cu-Fe alloy having at least about 50 weight percent phase? thermally sprayed at a fast enough rate to avoid harmful amounts of phase? Advantageously, this alloy contains at least about 60 weight percent phase. Typically, it contains approximately 60 to 90 weight percent phase. Most advantageously, the alloy contains at least 70 weight percent phase. The thermally sprayed coating has excellent hardness, density and surface uniformity. Advantageously, the coating has a roughness of less than about 240 Ra and a porosity of less than about 5 percent. In addition, this quasi-crystalline alloy advantageously contains chromium or cobalt for resistance to corrosion. The aluminum, copper, iron and chromium were fused with vacuum and atomized with inert gas. The powder analyzed, in percent by weight, 17.5 Cu, 13.3 Fe, 15.3 Cr and the rest of aluminum. This powder was completely spherical and free flowing. Table 1 lists the typical properties of AlCuFeCr quasi-crystals powder atomized with inert gas after sizing.

Table 1 Due to the non-periodic honeycomb structure of the alloy, X-ray diffraction (XRD) identified the quasi-crystals. The positions of the quasi-crystal or phase (of icosahedron (?)) Are in round numbers in 23, 25, 41, 44, 62.5, and 75 - an icosahedron is a polygon that has 20 faces and a decagon is a polygon that has 10 angles and 10 faces. As atomized, the sized powder showed only a minor amount of phase? Rather, a decagonal phase (d) predominated. The presence of two (2) phases was attributed to the cooling regime experienced when going from liquid to solid. The rate of cooling, and solidification of subsequent dust particles, greatly affected the resulting phase equilibrium. At very fast regimes is the? metastable; If the solidification becomes slow, phase d or its next ones are formed. The differential thermal analysis performed on the powder indicated a melting temperature of about 1.044 ° C. When reduced to powder, these quasi-crystals facilitate thermal spraying with various types of equipment. This includes plasma, HVOF, detonation and other types of thermal spray equipment. However, for this example plasma was selected as the only means of application. The equipment used to apply the coatings was the Praxair SG-100 plasma gun. The gun was mounted on an ABB IRB 2,400 robot arm to facilitate automatic spraying and to ensure consistency. A "hard" coating, one that is adherent and dense, was applied using the SG-100 in the Match 1 mode with argon and helium as the plasma-forming gases. The starting parameters of Table 2 consisted of those established for pure quasi-crystals of aluminum-copper-iron.

Table 2 Eleven parametric variables are listed. Four are active and not controllable. These include anode, cathode, gas injector and powder size. Two, carrier gas voltage and flow are active and controllable; however, the former was regulated through the secondary gas flow while the latter was allowed to remain fixed. There were five active and controllable parameters: amperage, primary and secondary gas flows, dust feed regime and dew distance. Since these parameters were insufficient to optimize the hardness of the coating, a transverse piston regime or amount deposited per pass was added. The Mach 1 coatings were applied at a thickness of 0.51 to 0.74 mm. Among the coating attributes evaluated were the micro- (DPH3oo) and macrohardness (HR15N) tests; the microstructure, including density and oxide content as determined using image analysis; surface roughness; XRD for phase distribution; and tension / union test. Based on the results of macrohardness alone, a set of optimized spray parameters was derived. Together with the transverse pistol regime, the six active and controllable parameters were given in high and low ranges. Table 3 illustrates the controlled parameters.

Table 3 Table 4 below shows the results of these tests in a three-level orthogonal arrangement with the Rockwell 15N hardness reported for each spray run and the resulting surface roughness or texture.

Table 4 Inserted in a Taguchi L27, the high, medium and low levels of each parametric variable of the three-level orthogonal arrangement were evaluated, with particular attention to their interaction among them. The Table and parameter response calculations used to predict the hardness of the coating are shown in Tables 5 and 6. Table 5 illustrates a response table containing the average hardness calculated for the active-controllable parameters at three levels.

Table 5 Table 6 shows calculations for high hardness (μ) based on the results in Table 5.

Table 6 Referring to the response table and selecting the highest hardness values for a given parameter that fixes the optimal values, to deposit a coating with a typical hardness of H R15N of 79.06, they are presented in Table 7.

Table 7 Table 8 Table 8 represents the average coating properties derived from the optimized parameters of Table 7. From the response tables, those parameters considered the most likely to produce a hard, dense, well-bonded quasi-crystalline coating high in the phase icosahedral (?), are presented in Table 8.

The baseline coating contained approximately 70 weight percent phase? (icosahedral) with phase ß (cubic) and phases d (decagonal). The width of the peaks suggested that the coating was very fine grain (<1 μm). The baseline coating contained porosity and fine trans-punched fracture. The optimized coating, which was thought to be in a non-equilibrium state, contained 70 percent by weight of phase? and phase ß. Some phase d was noted on the left side of the highest intensity peak. The optimized parameters improved the density, but the trans-splashed break remained. AlCuFeCr alloy powder atomized with inert, spherical, free-flowing gas does not contain a high percentage of the non-periodic (?) Phase, icosahedral, that is, quasi-crystalline in three (3) directions. Rather, due to its cooling regime, it is constituted by substantial quantities of a decagonal phase (d) and a cubic phase (ß). Although these are quasi-crystalline phases, they do not cover the non-periodic lamination of the phase? However, when plasma is sprayed, under the appropriate conditions, can they be coated to the phase? - the electronic structure of the phase? it contributes to a low surface energy and therefore to good release properties. Table 9 below provides "approximately" the composition of the thermally sprayed coating, in percent by weight.

Table 9 more incidental impurities * Cr + Co is at least 10.

Parametric manipulation can also alter the atomic structure of the alloy. However, from the information herein, it is apparent that as both thermal and kinetic energies are varied, the cooling rates are altered and the coatings produced accordingly reflect those changes. In addition, those properties initially intended for modification were modified appreciably. For example, the hardness improved to a level of at least H R15N 75. Most advantageously, the alloy has a hardness of at least H R15N 78. In addition, by spraying in Mach 1 high speed mode, the powder heated up and cooled sufficiently to transform the decagonal phase of the icosahedral phase,? low friction Referring to the metallography of the coating, the extensive fracture within individual spatters was not anticipated. Although Quasi-crystals icosahedral are brittle at room temperature, plastically deformed at higher temperatures. A) Yes, it was not recognized that the individual splashes would comply formatively with the rough substrate sharing and fracturing rather than a ductile type molding. It was believed that the droplets in flight were hot enough to conform easily to the contour of the substrate - this was not the case. The quasi-crystals have very poor thermal conductivity and therefore, any level of thermal energy contributed when sprayed should be considered. This can be important when several high-speed devices are used as the main application devices. Potential uses of quasi-crystal coatings include: non-stick surfaces for cookware; steam irons only; underlying thermal barrier; lubrication and bearing surfaces; non-sticky paper and glass making rolls; piston rings; anti-abrasive protection for aerodynamic dovetails; sliding wear applications such as valves and gates; clutch plates; and "oscillating" compressor plates for air conditioning. These coatings facilitate the spraying of both metallic and non-metallic substrates. Wherever a substitute is required for a highly lubricated surface or a long-life Teflon (Teflon is a DuPont trademark for fluorinated ethylene propylene) it presents opportunities for quasi-crystalline coatings. These coatings can be further improved by the addition of hard particles such as carbides, metals, nanocarbons, nitrides, oxides and intermetallic compounds. Specific examples include: alumina, chromia, molybdenum, and tungsten, chromium, titanium and vanadium carbides. The coating has a hardness of at least HR15N 75 for excellent wear resistance. In addition, the quasi-crystalline alloy contains at least 50 weight percent phase? for excellent non-adhesive properties. Finally, the coating forms a smooth surface of less than 240 Ra and has a porosity of less than 5 percent. The combined properties of the coating are useful for a variety of applications for wear resistance. Although the invention has been described in detail with reference to a certain preferred embodiment, those skilled in the art will recognize that there are other embodiments of the invention within the spirit and scope of the claims.

Claims (10)

1. REVIVAL NAMES 1. A thermally sprayed coating formed with an alloy containing quasi-crystals, the alloy consisting essentially of, in percent by weight, about 10 to 45 Cu, about 7 to 22 Fe, about 0 to 30 Cr, about 0 to about 30 of Co, about 0 to 20 of Ni, about 0 to 10 of Mo, about 0 to 7.5 of W and the rest of aluminum with incidental impurities and having at least about 50 weight percent of phase? and the coating having a macrohardness of at least about HR15N 75.
2. 2. The coating of claim 1 wherein the coating has a porosity of at least about 5 percent and a roughness of less than about 240 Ra.
3. 3. The coating of claim 1 wherein the alloy contains at least about 60 weight percent phase.
4. 4. The coating of claim 1 wherein the coating contains hard particles selected from the group consisting of carbides, metals, nanocarbons, nitrides, oxides and intermetallic compounds.
5. 5. A thermally sprayed coating formed with an alloy containing quasi-crystals, the alloy consisting essentially of, in percent by weight, about 12 to 24 Cu, about 10 to 20 Fe, about 5 to 25 Cr, about 0 to 20 of Co, at least approximately 10 of Cr and total Co, approximately 10 to 15 of Ni, approximately 0 to 7.5 of Mo, approximately 0 to 6 of W and the rest of aluminum with incidental impurities and which has less about 50 percent by weight of phase? and the coating having a macrohardness of at least about H R15N 78. The coating of claim 5 wherein the coating has a porosity of less than about 5 percent and a roughness of less than about 240 Ra and the alloy contains at least about 60 weight percent phase? The coating of claim 5 wherein the coating contains hard particles selected from the group consisting of carbides, metals, nanocarbons, nitrides, oxides and intermetallic compounds. 8. A thermally sprayed coating formed with an alloy containing quasi-crystals, the alloy consisting essentially of, in percent by weight, about 15 to 20 Cu, about 10 to 16 Fe, about 10 to 20 Cr, about 0 to 10 of Co, about 0 to 10 of Ni, about 0 to 5 of Mo, about 0 to 5 of W and the rest of aluminum with incidental impurities and at least about 50 weight percent of phase? and the coating having a macrohardness of at least about H R15N 78. 9. The coating of claim 8 wherein the coating has a porosity of less than about 5 percent and a roughness of less than about 240 Ra and the alloy Does it contain at least about 70 percent by weight of phase? The coating of claim 9 wherein the coating contains hard particles selected from the group consisting of carbides, metals, nanocarbons, nitrides, oxides and intermetallic compounds.