Filters for filtering molten metals and alloys field

Abstract

A molten metal or molten metal alloy is filtered to remove contaminants. Filters may include imaging agents, especially those useful for N-ray radiography, X-ray analysis, and neutron activation. Currently preferred imaging agents include gadolinia and tungsten. Currently preferred refractory materials include yttria, zirconia, tantalum, tungsten and rhenium. A homogeneous distribution of refractory and imaging materials may be accomplished by vacuum impregnation, chemical vapor deposition, physical vapor deposition, chemical vapor infiltration, fusing, cocalcining, alloying, and physical mixing. Filters substantially resistant to chemical and mechanical degradation may be used. For example, filters may be constructed with at least an outer layer of the filter comprising yttria. Filters may define a porosity and mesh size for efficient filtration and to exclude the maximum allowed size of defects for the particular application. Castings may be analyzed for inclusions by X-ray analysis, neutron activation, and N-ray radiography. Preferred methods for filtering melts include providing a filter including an imaging agent and filtering the melt into a mold to cast a metal article. Filtration may include heating the filter during filtration. The melt may include any molten metal or metal alloy, particularly aluminum, steel, alloys of titanium, chromium, nickel, cobalt and alloys thereof.

We claim:  
     
         1 . A filter for filtering a molten metal or molten metal alloy, comprising an N-ray imaging agent other than borate or titanium boride.  
     
     
         2 . A filter for filtering a molten metal or molten metal alloy, comprising a refractory material and an N-ray imaging agent.  
     
     
         3 . The filter according to  claim 2 , where the refractory material comprises a refractory metal oxide.  
     
     
         4 . A filter for filtering a molten metal or molten metal alloy, comprising a refractory material and an imaging agent selected from the group consisting of dysprosium, erbium, europium, gadolinium, holmium, iridium, lutetium, neodymium, osmium, praseodymium, rhenium, samarium, tantalum, tungsten, ytterbium, isotopes thereof, physical mixtures thereof and chemical mixtures thereof.  
     
     
         5 . The filter according to  claim 4  where the imaging agent is a metal, a metal oxide, an intermetallic, a boride, a carbide, a nitride, metal halide, physical mixtures thereof or chemical mixtures thereof.  
     
     
         6 . The filter according to  claim 4  where the refractory material is a ceramic material, a refractory metal or combinations thereof.  
     
     
         7 . The filter according to  claim 6  where the ceramic material is a metal oxide.  
     
     
         8 . The filter according to  claim 4  where the refractory material is selected from the group consisting of yttria, zirconia, tantalum, tungsten, rhenium, physical mixtures thereof and chemical mixtures thereof.  
     
     
         9 . The filter according to  claim 4  where the imaging agent comprises gadolinia.  
     
     
         10 . The filter according to  claim 4  where the filter has a porosity of from about 10 to about 30 pores per inch.  
     
     
         11 . The filter according to  claim 4  where the filter defines apertures of a maximum dimension of from about 0.005 inches to about 0.05 inches.  
     
     
         12 . The filter according to  claim 4  where the filter defines apertures of a maximum dimension of from about 0.01 inches to about 0.03 inches.  
     
     
         13 . The filter according to  claim 4  having a first layer comprising the refractory material and a second layer comprising the imaging agent.  
     
     
         14 . The filter according to  claim 4  where the refractory material is substantially impregnated with the imaging agent.  
     
     
         15 . The filter according to  claim 4  where the refractory material and the imaging agent are mixed by chemical vapor deposition, physical vapor deposition, chemical vapor infiltration, fusing, cocalcining, alloying, and combinations thereof.  
     
     
         16 . The filter according to  claim 4  where the refractory material is mixed substantially homogeneously with the imaging agent.  
     
     
         17 . The filter of  claim 4  where the refractory material comprises yttria and zirconia.  
     
     
         18 . The filter of  claim 4  where the refractory material comprises yttria and zirconia and the imaging agent comprises gadolinia.  
     
     
         19 . The filter of  claim 13  where the second layer comprises yttria and gadolinia.  
     
     
         20 . A method for filtering molten metals or molten metal alloys, comprising: 
 providing a filter comprising a material selected from the group consisting of dysprosium, erbium, europium, gadolinium, holmium, iridium, lutetium, neodymium, osmium, praseodymium, rhenium, samarium, tantalum, tungsten, ytterbium, isotopes thereof, physical mixtures thereof, and chemical mixtures thereof;    providing a mold;    heating the filter; and    filtering a molten metal into the mold to cast a metal article.    
     
     
         21 . The method of  claim 20  where the molten metal comprises titanium or titanium alloys.  
     
     
         22 . The method of  claim 20  where the filter comprises a material selected from the group consisting of yttria, zirconia, tantalum, tungsten, rhenium, physical mixtures thereof and chemical mixtures thereof.  
     
     
         23 . The method of  claim 20  where the imaging agent comprises gadolinia.  
     
     
         24 . The method of  claim 20  where the filter has a porosity of from about 10 to about 30 pores per inch.  
     
     
         25 . The method of  claim 20  where the filter defines apertures of from about 0.005 to about 0.05 inches.  
     
     
         26 . The method of  claim 20  where the filter defines apertures of from about 0.01 to about 0.03 inches.  
     
     
         27 . The method of  claim 20  further comprising analyzing the metal article for inclusions by radiography.  
     
     
         28 . The method according to  claim 20  further comprising analyzing the metal article by X-ray analysis.  
     
     
         29 . The method according to  claim 20  further comprising analyzing the metal article by neutron activation.  
     
     
         30 . The method according to  claim 27  where analyzing the metal article comprises N-ray radiography.  
     
     
         31 . A method for filtering molten metals, comprising: 
 providing a filter comprising an N-ray imaging agent other than borate or titanium boride;    providing a mold; and    filtering a molten metal into the mold to cast a metal article.    
     
     
         32 . The method according to  claim 31 , further comprising heating the filter before filtering the molten metal.  
     
     
         33 . A method for filtering molten metals, comprising: 
 providing a filter comprising a refractory metal oxide and an N-ray imaging agent;    providing a mold; and    filtering a molten metal into the mold to cast a metal article.    
     
     
         34 . A method for filtering molten metals, comprising: 
 providing a filter comprising a first refractory material and a second imaging material, where the second imaging material comprises an imaging material selected from the group consisting of dysprosium, erbium, europium, gadolinium, holmium, iridium, lutetium, neodymium, osmium, praseodymium, rhenium, samarium, tantalum, tungsten, ytterbium, isotopes thereof, physical mixtures thereof, and chemical mixtures thereof;    providing a mold; and    filtering the molten metal into the mold to cast a metal article.    
     
     
         35 . The method of  claim 34 , where the molten metal comprises titanium or a titanium alloy.  
     
     
         36 . The method of  claim 34  where the filter comprises yttria and zirconia.  
     
     
         37 . The method of  claim 34  where the imaging material comprises gadolinia.  
     
     
         38 . The method of  claim 34  where the filter comprises yttria, zirconia, gadolinia, physical mixtures thereof and chemical mixtures thereof.  
     
     
         39 . The method according to  claim 34  further comprising analyzing the metal article for inclusions by radiography.  
     
     
         40 . The method according to  claim 34  further comprising analyzing the metal article by X-ray analysis.  
     
     
         41 . The method according to  claim 34  further comprising analyzing the metal article by neutron activation.  
     
     
         42 . The method according to  claim 39  where analyzing the metal article comprises N-ray radiography.  
     
     
         43 . A method for filtering molten metals, comprising: 
 providing a filter comprising a metal or metal alloy having a melting point substantially the same as or greater than the molten metal;    providing a mold;    heating the filter;    filtering molten metal through the filter; and    introducing the molten metal into the mold, thereby casting a metal article.    
     
     
         44 . The method according to  claim 43  where the filter comprises a metal selected from the group consisting of iridium, hafnium, osmium, rhenium, tantalum, tungsten, and alloys thereof.  
     
     
         45 . The method according to  claim 43  where the molten metal comprises titanium or a titanium alloy.  
     
     
         46 . The method according to  claim 43  where the molten metal is selected from the group consisting of aluminum, steel, nickel-based superalloys, cobalt-based superalloys and chromium-based superalloys.  
     
     
         47 . The method according to  claim 43  further comprising heating the filter to greater than about 2,400° F. (1,300° C.) before filtering molten metal.  
     
     
         48 . The method according to  claim 43  where the filter is heated by a method selected from the group consisting of resistive, conductive, inductive, convective, radiative heating and combinations thereof.  
     
     
         49 . The method according to  claim 43  where the filter is heated by striking an arc from the filter.  
     
     
         50 . The method according to  claim 43  further comprising analyzing the metal article for inclusions by radiography.  
     
     
         51 . The method according to  claim 43  further comprising providing the metal article to a third party to analyze the article for inclusions.  
     
     
         52 . The method according to  claim 43  further comprising analyzing the metal article for inclusions by X-ray analysis.  
     
     
         53 . The method according to  claim 43  further comprising analyzing the metal article for inclusions by neutron activation.  
     
     
         54 . The method according to  claim 50  where analyzing the metal article for inclusions comprises N-ray radiography.  
     
     
         55 . The method according to  claim 50  where analyzing the metal article for inclusions comprises producing a three-dimensional image of the article.  
     
     
         56 . The method according to  claim 50  where analyzing the metal article comprises analyzing the article in real time.  
     
     
         57 . A method for making a filter for filtering molten metals, comprising: 
 providing a filter pattern; and    applying an aqueous or non-aqueous slurry comprising an N-ray imaging agent other than borate or titanium boride to the filter pattern.    
     
     
         58 . A method for making a filter for filtering molten metals, comprising: 
 providing a filter pattern; and    applying an aqueous or non-aqueous slurry comprising a refractory metal oxide and an N-ray imaging agent to the filter pattern.    
     
     
         59 . A method for making a filter for filtering molten metals, comprising: 
 providing a filter pattern comprising a ceramic material;    providing an aqueous or non-aqueous slurry comprising an imaging agent where the imaging agent is selected from the group consisting of dysprosium, erbium, europium, gadolinium, holmium, iridium, lutetium, neodymium, osmium, praseodymium, rhenium, samarium, tantalum, tungsten, ytterbium, isotopes thereof, physical mixtures thereof, and chemical mixtures thereof;    applying the slurry to the filter pattern; and    firing the filter pattern at a temperature sufficient to sinter the imaging agent and the ceramic material.    
     
     
         60 . The method according to  claim 59  where firing the filter pattern comprises firing at a temperature of greater than about 2,000° F.  
     
     
         61 . The method according to  claim 59  where applying the slurry to the filter comprises depositing the imaging agent in a quantity sufficient for detection of inclusions.  
     
     
         62 . The method according to  claim 59  where the imaging agent is deposited substantially homogeneously in at least an outer layer on the filter.  
     
     
         63 . The method according to  claim 59  where the filter pattern comprises partially stabilized zirconia.  
     
     
         64 . The method according to  claim 59  where applying the slurry comprises vacuum impregnating the filter pattern.  
     
     
         65 . The method according to  claim 59  where the slurry comprises yttria.  
     
     
         66 . The method according to  claim 59  where the slurry comprises yttria and gadolinia.  
     
     
         67 . A system for filtering and casting molten metals, comprising: 
 a crucible for pouring molten metal;    a filter comprising an N-ray imaging agent other than borate or titanium boride positioned in a flow path of the molten metal; and    a mold positioned to receive filtered molten metal.    
     
     
         68 . The system according to  claim 67  further comprising heating means for heating the filter.  
     
     
         69 . A system for filtering and casting molten metals, comprising: 
 a crucible for pouring molten metal;    a filter comprising a refractory metal oxide and an N-ray imaging agent positioned in a flow path of the molten metal; and    a mold positioned to receive filtered molten metal.    
     
     
         70 . The system according to  claim 69  further comprising heating means for heating the filter.  
     
     
         71 . A system for filtering and casting molten metals, comprising: 
 a crucible for pouring molten metal;    a filter comprising an imaging agent selected from the group consisting of dysprosium, erbium, europium, gadolinium, holmium, iridium, lutetium, neodymium, osmium, praseodymium, rhenium, samarium, tantalum, tungsten, ytterbium, physical mixtures thereof and chemical mixtures thereof positioned in a flow path of the molten metal; and    a mold positioned to receive filtered molten metal.    
     
     
         72 . The system according to  claim 71  where the filter is heated with a heater.  
     
     
         73 . The system according to  claim 72  where the filter is connected to the heater.  
     
     
         74 . A filter for filtering a molten metal or molten metal alloy, comprising a refractory material with at least an outer layer that includes yttria.  
     
     
         75 . The filter of  claim 74 , where the filter comprises an inner layer comprising zirconia.  
     
     
         76 . A metal alloy comprising titanium and an N-ray imaging agent selected from the group consisting of gadolinium, samarium, europium, and mixtures thereof.  
     
     
         77 . The metal alloy of  claim 76  where the N-ray imaging agent comprises less than ten percent gadolinium.  
     
     
         78 . The metal alloy of  claim 76  comprising about 6% by weight gadolinium.  
     
     
         79 . A method for filtering a first metal or metal alloy comprising a solid fraction that includes an imaging agent, comprising: 
 forming a mixture comprising a metal or a first metal alloy and a second imaging alloy comprising titanium and an N-ray imaging agent selected from the group consisting of gadolinium, samarium, europium, and mixtures thereof;    providing a filter; and    providing a molten material comprising the metal or first metal alloy and a solid fraction comprising the second imaging alloy; and    filtering the molten material comprising the solid fraction.    
     
     
         80 . The method according to  claim 79  further comprising determining if the metal alloy is retained on the filter by N-ray radiography.  
     
     
         81 . The method according to  claim 79  and further comprising: 
 forming a cast article from the molten material after filtering; and  
 determining whether the article has inclusions by at least N-ray radiography.