Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
  • C23C8/10—Oxidising
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
  • C23C8/20—Carburising
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
  • C23C8/20—Carburising
  • C23C8/22—Carburising of ferrous surfaces
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
  • C23C8/24—Nitriding
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
  • C23C8/24—Nitriding
  • C23C8/26—Nitriding of ferrous surfaces
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C2204/00—End product comprising different layers, coatings or parts of cermet

Definitions

• the present invention is broadly concerned with cermets, particularly composition gradient cermets and reactive heat treatment process for preparing same.
• Erosion resistant materials find use in many applications wherein surfaces are subject to eroding forces.
• refinery process vessel internals exposed to aggressive fluids containing hard solid particles such as catalyst particles in various chemical and petroleum environments are subject to both erosion and corrosion.
• the protection of these vessel internals against erosion and corrosion induced material degradation especially at high temperatures is a technological challenge.
• Refractory liners are used currently for components requiring protection against the most severe erosion and corrosion such as the inside walls of cyclones such as the internal cyclones in fluid catalytic cracking units (FCCU).
• FCCU fluid catalytic cracking units
• the state-of-the-art in erosion resistant materials is chemically bonded castable alumina refractories. These castable alumina refractories are applied to the surfaces in need of protection and upon heat curing harden and adhere to the surface via metal-anchors or metal-reinforcements. It also readily bonds to other refractory surfaces.
• the typical chemical composition of one commercially available refractory is 80.0% A1 2 0 3 , 7.2% Si0 2 , 1.0% Fe 2 0 3 , 4.8% MgO/CaO, 4.5% P 2 0 5 in wt%.
• Ceramic-metal composites are called cermets.
• Cermets of adequate chemical stability can provide an order of magnitude higher erosion resistance over refractory materials known in the art. Cermets are generally produced using powder metallurgy techniques where metal and ceramic powders are mixed, pressed and sintered at high temperatures. Since powder metallurgically produced cermets usually have homogeneous microstructure and uniform composition, sophisticated attachment methods are needed to attach cermets onto the metallic surfaces wherein erosion resistance of the surface is desired.
• Composition gradient cermets are cermets wherein one surface of the cermet is ceramic-rich and the unexposed surface is metal-rich. In a typical composition gradient cermet there is a concentration gradient of the ceramic in the metal composition such that the concentration of the ceramic decreases with depth. These composition gradient cermets are desired and preferred for cost- effective attachment of cermets directly onto metal or alloy surfaces using methods such as welding due to the compatibility and ease of welding a substantially metallic object to another substantially metallic object. Furthermore, such composition gradient cermets can also exhibit superior durability particularly under conditions wherein thermal fluctuations are present. However, there is a need for effective processes to prepare composition gradient cermets.
• One object of the present invention is to provide a process for preparation of cermets, particularly composition gradient cermets via reactive heat treatment of a metal alloy.
• Another object of the present invention is to provide a composition gradient cermet product derived from the reactive heat treatment process.
• composition gradient cermet material comprising the steps of:
• Another embodiment is directed towards a composition gradient cermet product obtained from the disclosed reactive heat treatment process.
• Figure 1 depicts carbon activity of an environment based on the reaction CH 4 — > C + 2 H 2 compared to austenitic stainless steels (a c in equilibrium with Fe 3 C). Also marked are the carbon activity values of gas mixtures applicable to the instant invention.
• Figure 2 depicts the mass gain due to carbon ingression (a measure of cermet layer formation) of 304 stainless steel (74Fe:18Cr:8Ni in wt%) as a function of CH 4 content in H 2 at 1100°C for 3 hours.
• Figure 3 depicts the thickness variation of surface cermet structure on 304 stainless steel as a function of temperature in 37.3 vol% CH 4 :62.7 vol% H 2 environment for 3 hours.
• Figure 4 depicts the thickness variation of surface cermet formed on various Fe:Ni:Cr based high temperature alloys as a function of reaction times at 1100°C in 37.3 vol% CH 4 :62.7 vol H 2 environments.
• Figure 5 depicts scanning electron micrographs showing (a) surface chromium carbide-metal cermet structure on 310 stainless steel (54Fe:21Ni:25Cr in wt%) after reactive heat treatment at 1100°C for 3 hours in 37.3 vol% CH 4 :62.7 vol% H 2 environment and (b) enlarged area on the surface revealing the Cr-rich carbide [(Cr 0 . 6 Feo. ) 7 C 3 ] and Cr-depleted steel (63Fe:31Ni:6Cr in wt%) to produce a composite ceramic-metal two-phase structure.
• the Cr-rich carbides appear dark gray and the metal appears recessed, because it has etched more deeply than the carbides.
• the first step of the process for preparing a composition gradient cermet material comprises heating a metal alloy containing at least one of chromium and titanium at a temperature in the range of about 600°C to about 1150°C to form a heated metal alloy.
• the metal alloy containing at least one of chromium and titanium comprises from about 12 to 60 wt% chromium, from 0 to 10 wt% titanium, and from 30 to 88 wt% of metals selected from the group consisting of iron, nickel, cobalt, silicon, aluminum, manganese, zirconium, hafnium, vanadium, niobium, tantalum, molybdenum, tungsten, and mixtures thereof.
• the major mass constituent of the alloy is iron.
• stainless steels such as type 304SS, 347SS, 321SS, 310SS and the like and iron-nickel based alloys such as Incoloy 800H are particularly suitable for the instant process.
• the second step of the process comprises exposing the heated metal alloy to a reactive environment selected from the group consisting essentially of reactive carbon, reactive nitrogen, reactive boron, reactive oxygen and mixtures thereof in the range of about 600°C to about 1150°C for a time period sufficient to provide a reacted alloy.
• a reactive environment selected from the group consisting essentially of reactive carbon, reactive nitrogen, reactive boron, reactive oxygen and mixtures thereof in the range of about 600°C to about 1150°C for a time period sufficient to provide a reacted alloy.
• a reactive carbon environment is defined as an environment in which the thermodynamic activity of carbon (a c ) in the environment is greater than that of the alloy.
• the reactive carbon environment suitable for the instant invention comprises at least one of CO, CH 4 , C 2 H 6 or C 3 H 8 .
• the reactive carbon environment may optionally include H 2 .
• the reactive carbon environment may further comprise 0 2 , C0 2 , and H 2 0.
• the following reactions [1], [2] and [3] shown below are some of the reactions that are believed to occur under the heat treatment conditions to provide the reactive carbon.
• the carbon reacts with the metal surface to form chromium-rich and titanium-rich carbide phases.
• the methane content in the gaseous mixture of methane and hydrogen can range from about 1 vol% to about 99 vol%, preferably about 2 vol% to about 45 vol%. This is depicted in Figure 2, where the mass gain due to carbon ingression (a measure of cermet layer formation) of 304 stainless steel (74Fe:18Cr:8Ni in wt%) at 1100°C exposed for 3 hours is plotted as a function of CH content in H 2 .
• the preferred methane content in the gaseous mixture of methane and hydrogen corresponds to the plateau region of the curve. In this range, the reaction times are shorter to obtain a specific thickness of cermet.
• Gas mixtures in which the methane content in the gaseous mixture of methane and hydrogen is greater than 45 vol% can also be used. However, in these ranges, solid carbon deposition on the alloy surface can be encountered as indicated by the rapid increase of mass gain in Figure 2.
• the CO content in the gaseous mixture of CO and hydrogen can range from about 0.1 vol% to about 5 vol%, preferably about 0.1 vol% to about 2 vol%.
• the reactive environment is a reactive nitrogen environment
• nitridation reactions are believed to occur. While not wishing to be bound to the mechanism of the reactive heat treatment process applicants believe that the nitridation process leads to precipitation of chromium-rich and titanium nitride phases for example Cr 2 N and TiN on the alloy surface and within the alloy matrix resulting in a cermet and particularly a composition gradient nitride cermet.
• a reactive nitrogen environment is defined as an environment in which the thermodynamic activity of nitrogen (a N ) in the environment is greater than that of the alloy.
• ammonia-bearing atmospheres are preferred.
• Ammonia is metastable and dissociates into molecular N 2 and molecular H 2 when heated to elevated temperatures.
• the preferred composition of the reactive nitrogen environment comprises at least one of air, ammonia and nitrogen.
• the composition can further comprise H 2 , He, and Ar. In such a reactive nitrogen environment at temperatures in the range of 600°C to 1150°C alloys containing elements such as Cr and Ti which have strong chemical affinities for nitrogen undergo rapid nitridation reactions.
• molecular NH 3 is preferred to dissociate on the alloy surface, thus allowing dissociated atomic nitrogen to dissolve at the surface and diffuse into the bulk interior of the metal alloy. Similar to carburization process, nitridation can lead to the formation of surface nitrides, internal nitrides in the matrix and at grain boundaries near the alloy surface.
• the ammonia content in the gaseous mixture of ammonia and hydrogen can range from about 1 vol% to about 99 vol%, preferably about 2 vol% to about 70 vol%.
• the preferred temperature range for accomplishing the conversion of a metal alloy containing chromium, titanium and mixtures thereof to a nitride cermet is in the range of about 600°C to about 1150°C.
• the reactive environment comprises a mixture of reactive carbon and reactive nitrogen a mixed composition gradient cermet comprising carbide, nitride, carbonitride and mixtures thereof results.
• the reactive environment is a reactive carbon and nitrogen environment, carbonitridation reactions are believed to occur. While not wishing to be bound to the mechanism of the reactive heat treatment process applicants believe that the carbonitridation process leads to precipitation of chromium-rich and titanium carbonitride phases for example Cr 2 CN and TiCN on the alloy surface and within the alloy matrix resulting in a cermet and particularly a composition to gr- adient carbonitride cermet.
• a reactive carbon and nitrogen environment is defined as an environment in which the thermodynamic activity of carbon (a c ) and nitrogen (a N ) in the environment is greater than that of the alloy.
• the preferred composition of the reactive carbon and nitrogen environment comprises at least one of ammonia and nitrogen and at least one of CO, CH 4 , C 2 H 6 or C 3 H 8 .
• the composition can further comprise H , He, and Ar.
• a reactive carbon and nitrogen environment at temperatures in the range of 600°C to 1150°C alloys containing elements such as Cr and Ti which have strong chemical affinities for carbon and nitrogen undergo rapid carbonitridation reactions. Similar to carburization or nitridation process, carbonitridation can lead to the formation of surface carbonitride, internal carbonitride in the matrix and at grain boundaries near the alloy surface.
• the reactive environment is a reactive boron environment
• boridation reactions are believed to occur. While not wishing to be bound to the mechanism of the reactive heat treatment process applicants believe that the boridation process leads to precipitation of chromium-rich and titanium boride phases for example Cr 2 B and TiB 2 on the alloy surface and into the alloy matrix resulting in a cermet and particularly a composition gradient boride cermet.
• a reactive boron environment is defined as an environment in which the thermodynamic activity of boron (a B ) in the environment is greater than that of the alloy.
• the preferred composition of the reactive boron environment comprises for example at least one of diborane (B 2 H 6 ), BC1 3 , and BF 3 .
• the composition can further comprise H 2 , He, and Ar.
• a reactive boron environment at temperatures in the range of 600°C to 1150°C alloys containing elements such as Cr and Ti which have strong chemical affinities for boron undergo rapid boridation reactions. Similar to carburization or nitridation process, boridation can lead to the formation of surface borides, internal borides in the matrix and at grain boundaries near the alloy surface.
• the reactive environment is a reactive oxygen environment
• oxidation reactions are believed to occur. While not wishing to be bound to the mechanism of the reactive heat treatment process applicants believe that the oxidation process leads to precipitation of chromium-rich and titanium oxide phases for example (Cr,Fe) 2 0 3 , Cr 2 0 3 and Ti0 2 on the alloy surface and within the alloy matrix resulting in a cermet and particularly a composition gradient oxide cermet.
• a reactive oxygen environment is defined as an environment in which the oxygen potential in the environment is greater than the oxygen partial pressure in equilibrium with the oxide.
• the preferred composition of the reactive oxygen environment comprises at least one of air, oxygen and C0 2 .
• the composition can further comprise H 2 , He, and Ar.
• oxidation can lead to the formation of surface oxides, internal oxides in the matrix and at grain boundaries near the alloy surface.
• the third step of the process is cooling of the reacted alloy.
• the cooling step can include a variety of cooling rates and/or an intermediate temperature hold before cooling to below about 40°C.
• the cooling step comprises cooling the reacted alloy at a rate in the range of 0.5 °C per second to 25°C per second.
• the cooling step comprises cooling said reacted alloy to a temperature in the range of 500°C to 100°C, holding the temperature at any temperature in the range of 500°C to 100°C for a time period between 5 minutes to 10 hours and thereafter cooling at a rate in the range of 0.5°C per second to 25°C per second to below about 40°C. Applicants believe this preferred cooling profile has process and product advantages.
• the exposure time (the time period the heated alloy is exposed to the reactive environment) can vary in the range of about 1 hour to 800 hours to achieve various thickness of the carbide, nitride, carbonitride, boride or oxide cermet on the surface the metal alloy.
• An example for carbide cermet is depicted in Figure 4 where the thickness of the surface carbide cermet formed on various Fe:Ni:Cr high temperature alloys is plotted as a function of exposure time at conditions of 1100°C in 37.3 vol% CH :62.7 vol% H 2 environment.
• this example shows that the process of the instant invention can be used to obtain any thickness of carbide cermet resulting in a composition gradient carbide cermet.
• the process can also be used to completely convert the entire bulk of the chromium, titanium or mixture of chromium and titanium comprising alloy to a composition gradient cermet wherein the gradient traverses the entire thickness of the bulk alloy.
• the thickness of cermet layers can be controlled by the composition of the reactive environment, the temperature and the exposure time. Exposure times can be determined experimentally as depicted in Figure 4 for a carbide cermet. For thinner layers, the exposure time will be less, and for thicker layers the exposure time will be greater. Typical exposure times for a carbide cermet can range from about 1 hour to about 500 hours, preferably from about 5 hours to about 300 hours, and more preferably from about 10 hours to about 200 hours. Thus, the exposure time and temperature are two variables that can provide a desired thickness of cermet and a desired composition gradient cermet.
• typical exposure times can range from about 1 hour to about 800 hours, preferably from about 5 hours to about 500 hours, and more preferably from about 10 hours to about 300 hours.
• the exposure time and tempera- ture are two variables that can provide a desired thickness of nitride cermet and a desired composition gradient nitride cermet.
• Typical layer or cermet structure thickness can range from at least about 100 microns up to the thickness of the metal alloy being acted on, preferably from about 5 mm to about 30 mm, more preferably from about 5 mm to about 20 mm. Layer thickness can be determined by electron microscopy techniques known to one of ordinary skill in the art of electron microscopy.
• the instant invention is also applicable to an article consisting of an amount of chromium-rich or titanium-rich carbide, nitride, carbonitride, boride, and oxide in combination with a chromium and titanium containing metal alloy.
• the reactive heat treatment process of the instant invention results in a composition gradient cermet having erosion resistance superior to that of the untreated alloy containing chromium, titanium and mixtures thereof as shown in Example 4. This is because the erosion resistance of the alloy improves as the cermet layer develops and provides hardening.
• the amount of reactive carbon, reactive nitrogen, reactive boron, reactive oxygen diffusing into the metal alloy containing chromium, titanium and mixtures thereof from the respective reactive environment is utilized to produce the composition gradient cermet.
• the portion of the alloy containing chromium, titanium and mixtures thereof not converted to cermet, is unchanged and maintains the physical properties it possessed prior to treatment in accordance with the instant invention.
• composition gradient structure is particularly advantageous when one desires to use welding as an attachment method of the carbide cermet to a surface. Furthermore, a composition gradient cermet can have a superior thermal expansion match with the underlying metallic substrate with superior durability under thermal fluctuations. Thus, the cermet layer provides erosion resistance while retaining physical properties for the attachment and mechanical reliability of the alloy.
• composition gradient cermets produced by the process of instant invention can be used in the temperature range of 300°C to 800°C to protect any steel or any other alloy surface exposed to severe erosion and abrasion.
• Some non-limiting examples of these applications include protective linings, lining tiles for fluid-solids separation cyclones as in the cyclone of Fluid Catalytic Cracking Unit used in refining industry, wear plates, nozzle and grid hole inserts, turbine blades and components subject to erosion flow streams.
• composition gradient cermets prepared by the process of the instant invention offer a combination of erosion resistance and toughness as well as an optimization of thermal stresses within the component. Compared to conventional cermets prepared via powder metallurgy method, it affords attachment via conventional welding techniques and a better matching of thermal expansion to the base steel. It also could provide a superior method of protecting turbine blades from both oxidation and erosion.
• composition gradient cermet product prepared by the process comprising:
• the process of the instant invention can be applied to any surface.
• the internal surface of any chemical or petroleum processing reactor comprised of a metal selected from the group consisting essentially of chromium, titanium and mixtures thereof at a temperature can be heated to a temperature in the range of about 600°C to about 1150°C and then exposed to a reactive environment selected from the group consisting essentially of reactive carbon, reactive nitrogen, reactive boron, reactive oxygen and mixtures thereof in the range of about 600°C to about 1150°C for a time period sufficient to provide a reacted internal surface.
• a composition gradient cermet material is formed on the internal surface of the reactor.
• the internal surface of the rector comprising the composition gradient cermet can exhibit enhanced erosion resistance.
• One non-limiting illustrative example of this use is the cyclone separator of a Fluid Catalyst Cracking Unit in oil refining.
• the surface of any object for example the blades of a turbine, can be made of a metal selected from the group consisting essentially of chromium, titanium and mixtures thereof at a temperature, heated to a temperature in the range of about 600°C to about 1150°C and then exposed to a reactive environment selected from the group consisting essentially of reactive carbon, reactive nitrogen, reactive boron, reactive oxygen and mixtures thereof in the range of about 600°C to about 1150°C for a time period sufficient to provide a heat treated object.
• a composition gradient cermet material is formed on the surface of the object exposed to the reactive environment.
• the cermet compositions prepared by the process of the instant invention possess enhanced erosion and corrosion properties.
• the erosion rates were determined by the Hot Erosion and Attrition Test (HEAT) as described in the examples section of the disclosure.
• the erosion rate of the gradient cermets prepared by the process of the instant invention is less than l.OxlO "6 cc/gram of SiC erodant.
• the corrosion rates were determined by thermogravimetric (TGA) analyses as described in the examples section of the disclosure.
• the corrosion rate of the gradient cermets prepared by the process of the instant invention is less than lxlO "10 g 2 /cm 4 sec.
• the cermet compositions prepared by the process of the instant invention possess fracture toughness of greater than about 3 MPa-m 1/2 , preferably greater than about 5 MPa-m , and more preferably greater than about 10 MPa-m 1/2 .
• Fracture toughness is the ability to resist crack propagation in a material under monotonic loading conditions. Fracture toughness is defined as the critical stress intensity factor at which a crack propagates in an unstable manner in the material. Loading in three-point bend geometry with the pre- crack in the tension side of the bend sample is preferably used to measure the fracture toughness with fracture mechanics theory.
• the cermets of the instant invention can be affixed to metal surfaces by mechanical means or by welding.
• the samples had rectangular geometry with dimensions of about 1.25 cm x 1.25 cm x 1 cm.
• the sample surfaces were ground to a 600 grit SiC finish and cleaned ultrasonically in acetone.
• the procedure used in the invention was to establish the kinetics of carburization of the selected alloys in a purely carburizing environment (CH 4 -H 2 ), which was determined thermogravimetric- ally in a Cahn 1000 thermogravimetric unit.
• the investigations were carried out in the temperature range, 800°C to about 1160°C.
• a coupon was heated to a temperature of 1100°C in a hydrogen environment in a vertical quartz reactor tube and held at that temperature for approximately 5 minutes.
• FIG. 5 a reveals that a chromium carbide-metal cermet layer of 400 micron thickness has formed on 310 stainless steel (54Fe:21Ni:25Cr in wt%) surface after reactive heat treatment at 1100°C for 3 hours in 37.3 vol% CH 4 :62.7 vol% H 2 environment.
• FIG. 5b A magnified view of cermet microstructure, revealing the Cr-rich carbide [(Cr 6 Fe 0 . ) 7 C 3 ] and Cr-depleted steel (63Fe:31Ni:6Cr in wt%) to produce a composite ceramic-metal two-phase structure, is depicted in Figure 5b.
• Cr-rich is meant that the metal Cr is of a higher proportion on a weight basis than the other constituent metals comprising M, where M is 54Fe:21Ni:25Cr in wt%.
• the Cr-rich carbides appear dark gray and the metal appears recessed, because it has etched more deeply than the carbides.
• the chromium containing alloys listed above were reactively heat treated in a tube furnace for 24 hours at 1100°C in 10 vol% CH 4 :90 vol% H 2 environment. Samples were heated to a temperature of 1100°C in a hydrogen environment and held at that temperature for approximately 5 minutes. After 24 hours of exposure, the alloy samples were cooled down. After the samples reached room temperature (25°C), the surface microstructure and the thickness of cermet layer formed on various alloy surfaces were investigated by cross sectional scanning electron microscopy. Chemical compositions of M 7 C 3 carbide phase and Cr-depleted binder phase were investigated by semi- quantitative energy dispersive x-ray spectroscopy.
• the tendencies of Fe and Ni to partition between the metal matrix and the carbide precipitates are expected to be different.
• the thickness of cermet layers, Cr and Fe contents in M 7 C 3 carbide phase and composition of Cr-depleted metal matrix phase within cermet layers are summarized below.
• Alloys containing different concentrations of Fe, Ni, Cr and Ti were prepared by arc melting.
• the arc-melted alloy buttons were annealed at 1100°C overnight in inert argon atmosphere and furnace-cooled to room temperature. Cubical samples of about 1.25 cm x 1.25 cm x 0.75 cm were cut from the buttons.
• the sample faces were polished to 600-grit finish and cleaned in acetone.
• the specimens were exposed to a 10 vol% CH :90 vol% H 2 gaseous environment at 1100°C for 24 hours.
• An alloy of composition 60Fe:25Cr: 10Ni:5Ti (in wt%) generates cermet structure with mixed TiC and M 7 C 3 carbide and metal phase.
• the thickness of cermet layers, Cr and Fe contents in M 7 C 3 carbide phase and compositions of Cr-depleted metal matrix phase within cermet layers are summarized in Table 3.
• the reactive heat treatments were conducted on commercial 31 OSS to prepare samples for Hot Erosion and Attrition Test (HEAT).
• the 310SS samples had rectangular geometry with dimensions of about 2.0 inch x 2.0 inch x 0.5 inch.
• One sample was reactively heat treated in a tube furnace for 138 hours at 1100°C in 10 vol% CH 4 :90 vol% H 2 environment and named as C310SS1100.
• the other sample was reactively heat treated in a tube furnace for 96 hours at 1150°C in 10 vol% CH 4 :90 vol% H 2 environment and named as C310SS1150.
• Erosion Rate was measured as the volume of cermet, refractory, or comparative material removed per unit mass of erodant particles of a defined average size and shape entrained in a gas stream, and had units of cc/gram (e.g., ⁇ 0.001 cc/1000 gram of SiC).
• Key defined erosion test conditions are erodant material and size distribution, velocity, mass flux, angle of impact of the erodant as well as erosion test temperature and chemical environment.
• HEAT Hot Erosion and Attrition Test
• the 58 ⁇ m angular SiC particles used as the erodant were 220 grit #1 Grade Black Silicon Carbide (UK Abrasives, Inc., Northbrook, IL).
• the erodant velocity impinging on cermet targets was 45.7 m/sec (150 ft/sec) and the impingement angle of the gas-erodant stream on the target was 45° ⁇ 5°, preferably 45° ⁇ 2° between the main axis of the riser tube and the surface of the specimen disk.
• the carrier gas was air for all tests.
• the erosion tests in the HEAT unit were performed at 732°C (1350°F) for 7 hours. After testing the cermet specimen were again weighed to an accuracy of ⁇ 0.01 mg, to determine the weight loss.
• the erosion rate was equal to the volume of material removed per unit mass of erodant particles entrained in the gas stream, and has units of cc/gram. Improvement in Table 4 is the reduction of weight loss due to erosion compared to a value of 1.0 for the standard RESCOBONDTM AA-22S (Resco Products, Inc., Pittsburgh, PA). AA-22S typically comprises at least 80.0% A1 2 0 3 , 7.2% Si0 2 , 1.0% Fe 2 0 3 , 4.8% MgO/CaO, 4.5% P 2 0 5 in wt%. Micrographs of the eroded surface were electron microscopically taken to determine damage mechanisms. Table 4 summarizes the erosion loss of selected cermets as measured by the HEAT
• FCCU catalysts are based on alumina silicates which are typically softer than aluminas which are typically much softer than SiC.
• a specimen cermet of about 10 mm square and about 1 mm thick was polished to 600 grit diamond finish and cleaned in acetone.
• Step (2) was conducted for 65 hrs at 800°C.
• Thickness of oxide scale was determined by cross sectional microscopy examination of the corrosion surface.
• the thickness of oxide scale was ranging about 0.5 ⁇ m to about 1.5 ⁇ m.
• the cermet compositions exhibited a corrosion rate less than about lxlO "11 g /cm -s or an average oxide scale of less than 30 ⁇ m thickness when subject to 100 cc/min air at 800°C for at least 65 hours. These represent superior corrosion resistance.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
• Powder Metallurgy (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)

Priority Applications (6)

Applications Claiming Priority (4)

Publications (2)

Family

ID=33479307

Family Applications (1)

Country Status (9)

Cited By (5)

Families Citing this family (4)

Citations (7)

Family Cites Families (7)

• 2004
  • 2004-05-18 AU AU2004242136A patent/AU2004242136A1/en not_active Abandoned
  • 2004-05-18 WO PCT/US2004/015552 patent/WO2004104245A2/en active Application Filing
  • 2004-05-18 JP JP2006533184A patent/JP2007516348A/ja not_active Withdrawn
  • 2004-05-18 EP EP04752548A patent/EP1644549A2/en not_active Withdrawn
  • 2004-05-18 KR KR1020057022108A patent/KR20060004696A/ko not_active Application Discontinuation
  • 2004-05-18 BR BRPI0410402-1A patent/BRPI0410402A/pt not_active IP Right Cessation
  • 2004-05-18 MX MXPA05011135A patent/MXPA05011135A/es unknown
  • 2004-05-18 RU RU2005136134/02A patent/RU2005136134A/ru not_active Application Discontinuation
  • 2004-05-18 CA CA002523587A patent/CA2523587A1/en not_active Abandoned

Patent Citations (7)

Non-Patent Citations (8)

Also Published As

Similar Documents

Legal Events