Patent Publication Number: US-2007107809-A1

Title: Process for making corrosion-resistant amorphous-metal coatings from gas-atomized amorphous-metal powders having relatively high critical cooling rates through particle-size optimization (PSO) and variations thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of U.S. Provisional Patent Application No. 60/736,793 filed Nov. 14, 2005 and titled “Making Corrosion Resistant Amorphous Metal Using High Critical Cooling Rates.” U.S. Provisional Patent Application No. 60/736,793 filed Nov. 14, 2005 and titled “Making Corrosion Resistant Amorphous Metal Using High Critical Cooling Rates” is incorporated herein by this reference. 
    
    
      The United States Government has rights in this invention pursuant to Contract No. W-7405-ENG-48 between the United States Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory. 
    
    
     BACKGROUND  
      1. Field of Endeavor  
      The present invention relates to corrosion resistant materials and more particularly to forming corrosion resistant amorphous materials.  
      2. State of Technology  
      U.S. Pat. No. 4,880,482 issued Nov. 14, 1989 to Koji Hashimoto et al for highly corrosion-resistant amorphous alloy provides the following state of technology information, “It is generally known that a conventionally processed alloy has a crystalline structure in the solid state. However, an alloy having a specific composition becomes amorphous by prevention of the formation of long-range order structure during solidification through, for example, rapid solidification from the liquid state, sputter deposition or plating under the specific conditions; or by destruction of the long-range order structure of the solid alloy through ion implantation which is also effective for supersaturation with elements necessary for the formation of the amorphous structure.” 
      U.S. Pat. No. 6,767,419 issued Jul. 27, 2004 to Daniel Branagan for methods of forming hardened surfaces provides the following state of technology information, “Both microcrystalline grain internal structures and metallic glass internal structures can have properties which are desirable in particular applications for steel. In some applications, the amorphous character of metallic glass can provide desired properties. For instance, some glasses can have exceptionally high strength and hardness. In other applications, the particular properties of microcrystalline grain structures are preferred. Frequently, if the properties of a grain structure are preferred, such properties will be improved by decreasing the grain size. For instance, desired properties of microcrystalline grains (i.e., grains having a size on the order of 10 −6  meters) can frequently be improved by reducing the grain size to that of nanocrystalline grains (i.e., grains having a size on the order of 10 −9  meters). It is generally more problematic to form grains of nanocrystalline grain size than it is to form grains of microcrystalline grain size. Accordingly, it is desirable to develop improved methods for forming nanocrystalline grain size steel materials. Further, as it is frequently desired to have metallic glass structures, it is desirable to develop methods of forming metallic glasses.” 
      U.S. Patent Application No. 2003/0051781 by Daniel J. Branagan for hard metallic materials, hard metallic coatings, methods of processing metallic materials and methods of producing metallic coatings, published Mar. 20, 2003 provides the following state of technology information, “Both microcrystalline grain internal structures and metallic glass internal structures can have properties which are desirable in particular applications for steel. In some applications, the amorphous character of metallic glass can provide desired properties. For instance, some glasses can have exceptionally high strength and hardness. In other applications, the particular properties of microcrystalline grain structures are preferred. Frequently, if the properties of a grain structure are preferred, such properties will be improved by decreasing the grain size. For instance, desired properties of microcrystalline grains (i.e., grains having a size on the order of 10 −6  meters) can frequently be improved by reducing the grain size to that of nanocrystalline grains (i.e., grains having a size on the order of 10 −9  meters). It is generally more problematic, and not generally possible utilizing conventional approaches, to form grains of nanocrystalline grain size than it is to form grains of microcrystalline grain size.” 
     SUMMARY  
      Features and advantages of the present invention will become apparent from the following description. Applicants are providing this description, which includes drawings and examples of specific embodiments, to give a broad representation of the invention. Various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this description and by practice of the invention. The scope of the invention is not intended to be limited to the particular forms disclosed and the invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims.  
      Corrosion costs the nation billions of dollars every year. There is an immense quantity of material in various structures undergoing corrosion. For example, approximately 345 million square feet of structure aboard naval ships and crafts require costly corrosion control measures. In addition, fluid and seawater piping, ballast tanks, and propulsions systems require costly corrosion control measures. The use of advanced corrosion-resistant materials to prevent the continuous degradation of this massive surface area would be extremely beneficial.  
      Man-made materials with unusual service lives are needed for the construction of containers and associated structures for the long-term storage or disposal of spent nuclear fuel (SNF) and high-level waste (HLW) in underground repositories. Man has never designed and constructed any structure or system with the service life required by a SNF and HLW repository. Such systems will be required to contain these radioactive materials for a period as short as 10,000 years, and possibly as long as 300,000 years. The most robust engineering materials known are challenged by such long times. Thus, the ongoing investigation of newer, more advanced materials would be extremely beneficial.  
      The present invention provides a system for the deposition of full-density, pore-free, corrosion-resistant, thermal-spray amorphous-metal coatings for the protection of a less corrosion resistant substrate. The system comprises using particle-size optimization (PSO), and the integrated sensors and physical separation processes required to achieve PSO, to ensure that the amorphous metal particles are small enough to ensure that the critical cooling rate is achieved throughout the amorphous metal particles. The particle-size optimization system uses small enough amorphous metal powders in the mixed feed to ensure that the critical cooling rate is achieved throughout the amorphous metal particles, even in cases where the critical cooling rate may be relatively high (≧1000 K per second). In other embodiments materials with lower critical cooling rates are used (≦100 K per second).  
      There are many uses for the corrosion resistant amorphous metal coating of the present invention. For example, the coating has application on ships; oil, gas, and water drilling equipment; earth moving equipment; tunnel-boring machinery; pump impellers and shafts; containers for shipment, storage and disposal of spent nuclear fuel; pressurized water and boiling water nuclear reactors; breeder reactors with liquid metal coolant; metal-ceramic armor; projectiles; gun barrels; tank loader trays; rail guns; non-magnetic hulls; hatches; seals; propellers; rudders; planes; and any other use where corrosion resistance is needed.  
      Corrosion costs the nation billions of dollars every year, with an immense quantity of material in various structures undergoing corrosion. For example, in addition to fluid and seawater piping, ballast tanks, and propulsions systems, approximately 345 million square feet of structure aboard naval ships and crafts require costly corrosion control measures. The use of the corrosion resistant amorphous metal coating of the present invention to prevent the continuous degradation of this massive surface area would be extremely beneficial.  
      The corrosion resistant amorphous metal coating of the present invention could also be used to coat the entire outer surface of containers for the transportation and long-term storage of high-level radioactive waste (HLW) spent nuclear fuel (SNF), or to protect welds and heat affected zones, thereby preventing exposure to environments that might cause stress corrosion cracking. In the future, it may be possible to substitute such high-performance iron-based materials for more-expensive nickel-based alloys, thereby enabling cost savings in various industrial applications.  
      The invention is susceptible to modifications and alternative forms. Specific embodiments are shown by way of example. It is to be understood that the invention is not limited to the particular forms disclosed. The invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are incorporated into and constitute a part of the specification, illustrate specific embodiments of the invention and, together with the general description of the invention given above, and the detailed description of the specific embodiments, serve to explain the principles of the invention.  
       FIG. 1  illustrates one embodiment of a system incorporating the present invention.  
       FIG. 2  illustrates another embodiment of a system incorporating the present invention.  
       FIG. 3  illustrates yet another embodiment of a system incorporating the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to the drawings, to the following detailed description, and to incorporated materials, detailed information about the invention is provided including the description of specific embodiments. The detailed description serves to explain the principles of the invention. The invention is susceptible to modifications and alternative forms. The invention is not limited to the particular forms disclosed. The invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims.  
      Corrosion costs the Department of Defense billions of dollars every year, with an immense quantity of material in various structures undergoing corrosion. For example, in addition to fluid and seawater piping, ballast tanks, and propulsions systems, approximately 345 million square feet of structure aboard naval ships and crafts require costly corrosion control measures. The use of advanced corrosion-resistant materials to prevent the continuous degradation of this massive surface area would be extremely beneficial. The Fe-based corrosion-resistant, amorphous-metal coatings under development may prove of importance for applications on ships.  
      Such materials could also be used to coat the entire outer surface of containers for the transportation and long-term storage of high-level radioactive waste (HLW) spent nuclear fuel (SNF), or to protect welds and heat affected zones, thereby preventing exposure to environments that might cause stress corrosion cracking. In the future, it may be possible to substitute such high-performance iron-based materials for more-expensive nickel-based alloys, thereby enabling cost savings in various industrial applications.  
      New and innovative tools and devices will be enabled specifically by this invention, which is a novel composite material or coating with exceptional corrosion resistance, wear resistance, and damage tolerance. Those devices and tools enabled by this material may include: metal-ceramic armor, projectiles, oil and water drilling equipment, earth moving equipment, and tunnel-boring machinery. Such inventions include, but are not limited to: any modified disc cutter for a tunnel boring machine; any modified bit for an “Alpine Pick” using either amorphous metal coatings, bulk amorphous metals, or derivatives thereof, showing advantages over conventional technology.  
      Referring now to the drawings and in particular to  FIG. 1 , one embodiment of a system incorporating the present invention is illustrated. This embodiment is designated generally by the reference numeral  100 . First, raw materials are induction melted and introduced into a gas atomization process. This gas atomization process in turn produces amorphous metal powders  105  with relatively high critical cooling rate (CCR) and a broad distribution of particle sizes. In the fully automated version of this process, these powders are then pneumatically conveyed pass a particle size sensing module which communicates with the particle size controller. The controller can then activate the physical separation process  101 . The physical separation process  101  separates the amorphous metal powders  105  into an optimum size fraction  102 , and a non-optimum size fraction. The optimum size fraction  102  has a size distribution that enables the CCR to be maintained across the entire diameter of each particle or molten droplet, as those particles or droplets undergoes thermal spraying in process  103 , thereby enabling the amorphous nature of the particle to be preserved as it is incorporated into the corrosion and wear resistant amorphous metal coating  104 .  
      The non-optimum size fraction is then conveyed to a process element for reforming and remelting, thereby achieving recycle and high overall product yield. These integrated process steps avoid the incorporation of devitrified particles into the thermal spray coating  104 , thereby compromising coating performance. The coating  104  has many uses, for example, the coating  104  has application on ships; oil, gas, and water drilling equipment; earth moving equipment; tunnel-boring machinery; pump impellers and shafts; containers for shipment, storage and disposal of spent nuclear fuel; pressurized water and boiling water nuclear reactors; breeder reactors with liquid metal coolant; metal-ceramic armor; projectiles; gun barrels; tank loader trays; rail guns; non-magnetic hulls; hatches; seals; propellers; rudders; planes; and any other use where corrosion resistance is needed.  
      Referring now to  FIG. 2 , another embodiment illustrates the present invention in greater detail. This embodiment is designated generally by the reference numeral  200 . First, raw materials  201  are induction melted and introduced into the gas atomization process  202 . This gas atomization process in turn produces amorphous metal powders  202  with relatively high critical cooling rate (CCR) and a broad distribution of particle sizes.  
      In a fully automated version of this process, these powders are then pneumatically conveyed pass the particle size sensing module  204   a  which communicates with the particle size controller  204   b . The controller can then activate the physical separation process  205 . The physical separation process  205  separates the amorphous metal powders  203  into an optimum size fraction  206 , and a non-optimum size fraction  209 . The optimum size fraction  206  has a size distribution than enables the CCR to be maintained across the entire diameter of each particle or molten droplet, as those particles or droplets undergoes thermal spraying in process  207 , thereby enabling the amorphous nature of the particle to be preserved as it is incorporated into the corrosion and wear resistant amorphous metal coating  208 .  
      The non-optimum size fraction  209  is then conveyed to process element  210  for reforming and remelting, thereby achieving recycle and high overall product yield. These integrated process steps avoid the incorporation of devitrified particles into the thermal spray coating  210 , thereby compromising coating performance.  
      The coating  208  has many uses, for example, the coating  208  has application on ships; oil, gas, and water drilling equipment; earth moving equipment; tunnel-boring machinery; pump impellers and shafts; containers for shipment, storage and disposal of spent nuclear fuel; pressurized water and boiling water nuclear reactors; breeder reactors with liquid metal coolant; metal-ceramic armor; projectiles; gun barrels; tank loader trays; rail guns; non-magnetic hulls; hatches; seals; propellers; rudders; planes; and any other use where corrosion resistance is needed.  
      Referring now to  FIG. 3  another embodiment of the present invention is illustrated. This embodiment of the present invention is designated generally by the reference numeral  300 . The system  300  provides deposition of amorphous-metal coatings. In step  301  particle-size optimization (PSO) is used to produce an amorphous-metal. In step  302 , critical cooling rate is achieved throughout the amorphous metal particles. In step  303  the amorphous metal is used in a spray process. In step  305  the spray process produces the coating.  
      Corrosion costs the nation billions of dollars every year, with an immense quantity of material in various structures undergoing corrosion. For example, in addition to fluid and seawater piping, ballast tanks, and propulsions systems, approximately  345  million square feet of structure aboard naval ships and crafts require costly corrosion control measures. The use of the corrosion resistant amorphous metal coating of the present invention to prevent the continuous degradation of this massive surface area would be extremely beneficial.  
      The corrosion resistant amorphous metal coating of the present invention can also be used to coat the entire outer surface of containers for the transportation and long-term storage of high-level radioactive waste (HLW) spent nuclear fuel (SNF), or to protect welds and heat affected zones, thereby preventing exposure to environments that might cause stress corrosion cracking. In the future, it may be possible to substitute such high-performance iron-based materials for more-expensive nickel-based alloys, thereby enabling cost savings in various industrial applications.  
      The coating  104  is formed by spray processing  103  as illustrated in  FIG. 1 . The spray processing  103  can be thermal spray processing or cold spray processing. The coating  104  is produced using particle-size optimization to ensure that the amorphous metal particles are small enough to ensure that the critical cooling rate is achieved throughout the amorphous metal particles. The particle-size optimization method uses small enough amorphous metal powders in the mixed feed to ensure that the critical cooling rate is achieved throughout the amorphous metal particles, even in cases where the critical cooling rate may be relatively high (≧1000 K per second).  
      In cases where materials with lower critical cooling rates can be used (≦100 K per second), it may be possible to achieve similar results without application of PSO.  
      Predictive computational codes (design tool) used for the prediction of the optimum particle size for producing thermal spray coatings from amorphous metals without devitrification. These codes are based upon the simultaneous solution of differential equations that: (1) quantify the devitrification kinetics within amorphous metal particles of various sizes, based upon kinetic measurements from wedge casting, differential scanning calorimetry, and differential thermal analysis; (2) quantify the temperature history within amorphous particles of various sizes, based upon transient heat transfer calculations within the spray gun, sub-sonic or hypersonic spray, and at the surface being sprayed; (3) quantify softening within the sprayed particles, and account for the deformation and flow of particles at the surface being sprayed.  
      Extension of the predictive computational design tool for PSO described in item (2) to metal composites involving amorphous metal particles, other metal, glass and ceramic particles where phase transformations can occur. Ceramics may include compatible metal oxides, carbides, nitrides and other materials.  
      Any full-density, pore-free, corrosion-resistant, thermal-spray or cold-spray amorphous-metal protective coating where post-spray high-density infrared fusing (HDIF) to achieve lower porosity and higher density than otherwise possible, thereby enhancing corrosion resistance and damage tolerance of the metal-ceramic composite coating.  
      Any full-density, pore-free, corrosion-resistant, thermal-spray or cold-spray amorphous-metal protective coating where post-spray high-density infrared fusing (HDIF) to achieve lower porosity and higher density to achieve enhanced metallurgical bonding, and to control damage tolerance through controlled devitrification of the amorphous metal matrix. Predictive computational codes (design tool) used for the prediction of the optimum light flux for producing thermal spray coatings from amorphous metals without devitrification, or with controlled levels of devitrification for achieving desired mechanical properties. These codes are based upon the simultaneous solution of equations that: (1) quantify the reflection, scattering and absorption of the incident light flux, as a function of source wavelength, polarization and intensity, and as a function of amorphous-metal coating composition, microstructure, and surface roughness; (2) quantify the devitrification kinetics within deposited amorphous metal particles, based upon kinetic measurements from wedge casting, differential scanning calorimetry, and differential thermal analysis; (3) quantify the temperature history within the amorphous-metal coating, based upon transient heat transfer calculations within the coating and substrate; and (4) quantify softening, melting and flow of the deposited amorphous metal.  
      Extension of the predictive computational design tool for HDIF described in item (6) to metal-ceramic composites involving amorphous metal particles, other metal, glass and ceramic particles where phase transformations can occur. Ceramics may include compatible metal oxides, carbides, nitrides and other materials.  
      Enabling amorphous metal atomization processes, where the yield of optimally sized particles is substantially enhanced with feedback control. The process will use real-time measurements of atomized particle size distribution, measured with optical single particle analyzers, or multi-color laser Doppler velocimetry, to precisely control operating parameters that include, but are not limited to: temperature of the molten metal and coolant gas, differential nozzle pressure, and mass flow rates.  
      Enabling particle-size classification processes for separation of optimally sized amorphous metal particles from a broader particle size distribution. Such processes will separate amorphous-metal particles based upon their differences in aerodynamic drag, which are size dependent. Differential motion can be induced in amorphous metal particles that are suspended in an inert gas atmosphere by first imparting an electrostatic charge to the particles, and then subjecting them to an electrostatic force. Capture of desired particle sizes can be triggered with optical sensors based upon optical single particle analyzers or multi-color laser Doppler velocimetry.  
      Enabling particle-size classification processes for separation of optimally sized amorphous metal particles from a broader particle size distribution. Such processes will separate amorphous-metal particles based upon the size-dependent differences aerodynamic drag in a cyclonic flow field. Differential motion can be induced in amorphous metal particles by entraining them in a cyclonic separator. The capture of desired particle sizes can be triggered with optical sensors based upon either optical single particle analyzers or multi-color laser Doppler velocimetry.  
      Enabling particle-size classification processes for separation of optimally sized amorphous metal particles from a broader particle size distribution. Such processes will separate amorphous-metal particles based upon the differences in magnetic properties of fully amorphous and completely, or partially devitrified iron-based amorphous metal particles, and the application of an external magnetic field. Differential motion can be induced in amorphous metal particles by entraining them in a magnetic separator. The capture of desired particle sizes can be triggered with optical sensors based upon magnetic sensors, optical single particle analyzers or multi-color laser Doppler velocimetry.  
      A novel induction-heated spray process for producing full-density, pore-free, corrosion-resistant, thermal-spray amorphous-metal coatings for the protection of a less corrosion resistant substrate. In this process, ambient-temperature particles entrained in an ambient-temperature flowing gas, and then passed coaxially through an induction coil, where the oscillating electric field (frequency of 1 to 100 kHz) couples directly to the amorphous metal particles, without direct heating of the carrier gas. This particle-specific heating allows more rapid cooling of the amorphous metal particles than possible in processes where the gas is used to heat the particles. The same processing can be applied to ceramic particles, provided that a higher frequency is used (1 to 10 GHz).  
      Any new and innovative tools and devices enabled specifically by the aforementioned metal-ceramic composite materials and coatings, which have exceptional corrosion resistance, wear resistance, and damage tolerance. Such devices and tools may include, but are not limited to: containers for the shipment, long-term storage, and disposal of spent nuclear fuel (SNF) and high-level radioactive waste (HLW); ground support systems for underground tunnels; pressure vessels, piping and heat exchangers for the chemical process industry, fossil power plants, and nuclear power plants; pump shafts and impellers; valve seats; propellers, rudders, shafts and bearings for marine applications; non-sparking trays and racks for munitions; gun barrels; projectiles; armor; rail guns; etc.  
      While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.