Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/10—Alloys containing non-metals
• • 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
  • B22F7/00—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression
  • B22F7/02—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite layers
  • B22F7/04—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite layers with one or more layers not made from powder, e.g. made from solid metal
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B15/00—Layered products comprising a layer of metal
  • B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
  • B32B15/016—Layered products comprising a layer of metal all layers being exclusively metallic all layers being formed of aluminium or aluminium alloys
• • 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

• MMCs metal matrix composites
• the invention relates to methods for increasing the fracture toughness of metal matrix composites via the fabrication of discontinuously reinforced laminate structures.
• Metal matrix composites have received much attention as a means to produce products having improved properties. However, while significant gains may be made with respect to certain properties, sometimes these are obtained at the expense of other properties. For example, in the aluminum industry it is known that the yield strength and modulus of elasticity of an aluminum alloy can be increased through the use of discontinuous reinforcement additions to form discontinuously reinforced aluminum (DRA) materials. Nevertheless, commensurate improvement in fracture toughness is not obtained in such MMCs. For this reason the improvement in other properties may be unusable in components for which toughness is important.
• DRA discontinuously reinforced aluminum
• SUBSTITUTESHEET alloys if the yield strength, modulus of elasticity and fracture toughness can be improved together.
• the present invention permits these properties of a metal alloy to be enhanced. That is, the present invention provides MMCs having improvements in modulus of elasticity while maintaining or improving fracture toughness.
• the primary object of the present invention is to improve the toughness of a metal matrix composite.
• Another object of the present invention is to improve the fracture toughness of a metal matrix composite without significantly decreasing the yield strength or modulus of elasticity.
• Another object of the present invention is to improve the toughness of a metal matrix composite formed from alloys of aluminum, titanium, steel or combinations thereof.
• the metal matrix composite comprises a stack of alternate layers of unreinforced metal and discontinuously reinforced metal.
• the unreinforced metal is an aluminum alloy and the discontinuously reinforced metal is an aluminum alloy reinforced with silicon carbide particles.
• a second embodiment of the invention is a method for providing a metal matrix composite having improved fracture toughness. The method comprises the steps of: (a) providing a stack of layers of unreinforced metal and discontinuously reinforced metal; and (b) applying sufficient pressure to the stack to cause interlayer adhesion of the layers and thus form a laminated MMC.
• the stack of layers may be alternating layers of unreinforced metal and discontinuously reinforced metal. It is preferred that the unreinforced alloy forms the outer layers of the laminate.
• the method comprises the steps of: (a) providing a stack of alternating layers of an unreinforced aluminum alloy and aluminum alloy reinforced with silicon carbide particulates; (b) heating the stack and (c) applying sufficient pressure to the stack to cause interlayer adhesion. Afterwards, the stack may be solution heat treated and/or artificially aged. In a most preferred embodiment, metal foil is placed between the layers to enhance interlayer adhesion.
• Figure 1 is a photomicrograph of an aluminum alloy product made in accordance with the invention. The laminate has been tested and illustrates crack tip blunting and interface delam nation which resulted from impact testing.
• Figure 2 is an illustration of laminates of present invention in the crack divider and crack arrestor orientations.
• unreinforced metal is used herein to refer to metals and alloys containing less than 5 vol.% of non-metallic added reinforcement materials and preferably less than 1 vol.%. Examples of unreinforced metals
• SUBSTITUTE SHFET include aluminum, titanium, magnesium, iron, copper, zinc and alloys in which at least one of these metals is the largest single component.
• reinforcement metal and “reinforced alloy” are used interchangeably herein to refer to alloys containing more than 5 vol.% of non-metallic added reinforcement materials.
• reinforced metals include unreinforced metal to which fibers, whiskers, filaments, particles, ribbon, wire, flake, crystals, platelets and other non- metallic reinforcements are intentionally added.
• the term is not intended to include metals which contain only intermetallics except where the volume or type of such intermetallics provides significantly increased elastic modulus.
• discontinuously reinforced metal and specifically “discontinuously reinforced aluminum” (DRA) are used interchangeably herein to refer to metals and alloys in which the morphology of the reinforcement is discontinuous, most often with a ratio of largest to smallest dimension of less than about ten to one.
• the term is not intended to include alloys reinforced with long fibers, ribbons, or whiskers with a ratio of largest to smallest dimension of more than about ten to one.
• composite is used herein to refer to a material in which two or more constituents are combined to result in a material which has properties significantly different from either consituent.
• Reinforced metal, reinforced alloy, discontinuously reinforced metal and discontinuously reinforced aluminum are examples of metal matrix composites.
• Typical composites are materials in which one of the components has very high strength, modulus or both and the other has high ductility. Some of their properties generally follow the rule of mixtures. For example, if elastic modulus is the property of interest, the elastic modulus of the composite is approximately the weighted sum of the elastic moduli of the constituents.
• intermetallic is used herein to refer to a phase formed in-situ as a result of chemical and thermodynamic interactions. Intermetallics may have a reinforcing effect. However as stated above, the term “reinforcing material” is not generally intended to include intermetallics.
• toughness and “fracture toughness” are used interchangeably herein to refer to the ability of a material to resist catastrophic growth of a crack.
• laminated is used herein to refer to a layered structure having at least two layers with dissimilar properties.
• Foil is used herein to refer to metal which has been formed into a layer having a thickness of less than about 0.15 mm (0.006 inches). Foil is commonly a rolled product having a rectangular cross section.
• sheet is used herein to refer to metal which has been formed into a layer having a thickness greater than about 0.15 mm (0.006 inches) and less than about 6.325 mm (0.249 inches) .
• Sheet is commonly a rolled product having a rectangular cross section.
• plate is used herein to refer to metal which has been formed into a layer having a thickness greater than about 6.325 mm (0.249 inches). Plate is commonly a
• ET rolled product having a rectangular cross section.
• FIG. 1 By reference to Figure 1, there is shown an enlarged cross-section of an aluminum alloy product produced in accordance with the present invention.
• a section of DRA (lighter color layer) is sandwiched between two layers of unreinforced alloy.
• the laminate alloy product of the invention has beneficial properties resulting from both types of layers.
• Powder metallurgy may be used to obtain the alloys laminated to form the composite structure of the present invention.
• the same alloy may be used in both the unreinforced and reinforced layers or one layer may be comprised of a different alloy, depending to some extent on the properties desired in the final product. It is preferred that in the reinforcement layers, the reinforcement material be uniformly distributed throughout the product in order to provide the opti um combination of strength, toughness and fatique resistance.
• a base aluminum powder alloy such as AA X2080, 6113 or X7093 is selected depending on the basic properties desired.
• powder metallurgy alloy X7093 exhibits higher levels of strength and toughness than conventional alloys such as 7075 and 7050.
• the base aluminum powder alloy can be selected to produce a fine grain structure.
• the base aluminum powder should have a particle size in the range of -200 to -325 mesh (Fisher sub-sieve sizing screen) .
• Unreinforced aluminum alloys have capability for good strength and fracture toughness but their elastic modulus is
• SUBSTITUTE SHEET considered to be less than desirable for stiffness critical applications.
• reinforcement materials such as particles of silicon carbide (SiC) to the alloy powder, serves to enhance the elastic modulus with respect to the unreinforced matrix alloy.
• the incorporation of reinforcement particles degrades fracture related properties such as ductility and fracture toughness.
• the combination of layers of unreinforced and reinforced layers produce a material having combined improvements in modulus of elasticity while maintaining improved toughness.
• the reinforcement material provides a mechanism for crack deflection.
• the fracture toughness of the laminate is increased through the mechanisms of crack blunting and crack front deflection. Crack blunting involves impeding crack growth. Crack front deflection increases the area in which fracture-related events occur and therefor increase the energy absorption capability of the material.
• the amount of reinforcement material can range from a very small amount to a rather significant amount if it is desired to greatly improve elastic modulus.
• the reinforced layers or regions are formed from a blend comprising at least 5 vol.% of the reinforcement constituent with preferred amounts being at least 10 to 30 vol.%. Normally, the blend should not comprise more than 55 vol.%.
• the base powder alloy and the reinforcement are mixed to provide a blend wherein the reinforcement material is
• the compact can be subjected to a vacuum preheat for purposes of degassing.
• the preheat is carried out at a temperature in the range of 800° to 1100°F. Thereafter, it may be hot pressed to provide up to 100% density.
• the compact can be hot pressed at a temperature in the range of 800° to 1100°F., and pressing can be carried out at pressures in the range of 30,000 to 90,000 psi.
• the alloy be prepared according to specific method steps in order to provide the most desirable characteristics.
• the alloy described herein can be provided as an ingot or billet for fabrication into a suitable wrought product by techniques currently employed in the art.
• the ingot or billet may be preliminarily worked or shaped to provide suitable stock for subsequent working operations.
• the reinforced metal can be rolled or extruded or otherwise subjected to working operations to produce stock such as sheet, plate or extrusions or other stock suitable for shaping into the end product.
• extruding for example, of the hot pressed compact, should be performed at a temperature in the range of 550° to 900°F. depending on the composition of the alloy.
• the reinforced metal sheet or plate is then stacked in alternating layers with unreinforced metal.
• a layer of metallic foil may be placed between the layers to increase the interlayer adherence.
• the stack is then roll bonded to produce a unreinforced laminate having alternating layers or strata of unreinforced and reinforced material.
• the resulting laminate can then be formed or worked to the desired product, various thermal operations may be required to obtain the proper metallurgical condition in the metal.
• a solution heat treatment is used to substantially dissolve soluble elements.
• the solution heat treatment is preferably accomplished at a temperature in the range of 800 to 1100°F. and typically at about 900°F. for about 1 hour.
• Solution heat treatments can range from several minutes to about 2 hours or more at the solution heat treating temperature. Extend ⁇ ing the solution heat treatment time beyond about 2 hours generally does not provide further improvements in final properties.
• alloys which are solution heat treated should be rapidly quenched to prevent or minimize uncontrolled precipita ⁇ tion of various phases which, when improperly formed, can degrade properties.
• a cold water quench is preferred.
• the quenching rate be at least 10°F./sec with a preferred quench rate being at least 100°F./sec.
• the product can be artificially aged. This may be accomplished by subjecting the product to a temperature in the range of about 200° to 400°F. for a sufficient period of time to provide the desired yield strength. The period for artificial aging can run from several minutes to many hours. For some alloys such as 7XXX series alloys, artificial aging is accomplished by subjecting the product to a temperature in the range of 250° to 325°F. for a period of at least 16 hours.
• Example 1 (Prior Art) A batch of powdered aluminum alloy, X7093 was cold isostatically compacted into a cylindrical mold to 70-80 % of theoretical density. The cylindrical mold was sealed,
• Example 2 (Prior Art) A batch of the powdered aluminum alloy used in Example 1 is mixed with 15 vol.% silicon carbide particles to produce a uniform blend. The blend was then processed as in Example 1. The elastic modulus, yield strength (YS) and strain at failure were then measured and recorded on Table 1. As can be seen in Table 1, the reinforced material of Example 2 exhibited a 52% increase in modulus of elasticity over the material of Example 1 and the yield strength remained about the same (7% increase) .
• Example 3 Material from Examples 1 and 2 were each rolled to a plate thickness of approximately 0.5 inches and trimmed.
• a three layer laminate formed from two layers of the unreinforced material of Example 1 surrounding the reinforced material of Example 2 were produced by first etching the surfaces with a solution of sodium hydroxide and mechanically abrading the bonding surfaces. The layers were then stacked, held together with a spot weld and preheated to approximately 850°F. The heated stack was then passed through the nip of rollers and reduced approximately 15% per pass for three passes to form the laminate.
• Example 4 The procedure of Example 3 was repeated except that a layer of aluminum foil (A 1100 alloy) was placed between the unreinforced and reinforced alloys. The elastic modulus, yield strength (YS) and strain at failure were then measured and recorded on Table 1. As can
• Example 4 B T TESHEET be seen in Table 1, the laminated material of Example 4 exhibited a 22% increase in modulus of elasticity over the material of Example 1.
• Table 3 illustrates that the drop in toughness or impact energy (reported as total energy) of the unnotched laminate of Example 4 was significantly less than the reinforced material of Example 2.
• the toughness of the unnotched material of Example 4 was over 600% higher than the reinforced material of Example 2 in both the crack arrestor and crack divider orientations.
• the combination of high modulus of elasticity and high toughness (in arrestor orientation) of the laminated material of Example 4 is unexpected and will be more useful in aircraft applications such as wings, fuselage and tail sections than either the reinforced or unreinforced X7093 alone.
• Example 5 The procedure of Example 3 was repeated except that the laminate was adhesively bonded instead of roll bonded. The adhesive bonding was accomplished by applying a layer of
• TITUTE SHEET epoxy to the bonding surfaces after etching.
• AF1632K epoxy which is commerically available from 3M corporation is suitable for use as an adhesive.
• the stack is formed as in Example 3. The stack is held at approximately 70 psi and 250°F. for one hour to cure the epoxy.
• Table 3 illustrates that the drop in toughness or impact energy (reported as total energy) of the unnotched laminate of Example 5 was significantly less than the reinforced material of Example 2.
• the toughness of the unnotched material of Example 3 was over 450% higher than the reinforced material of Example 2 in the crack arrestor orientation.
• the combination of high modulus of elasticity and high toughness (in arrestor orientation) of the laminated material of Example 5 is unexpected and will be more useful in aircraft applications such as wings, fuselage and tail sections than either the reinforced or unreinforced X7093
• each layer of material to be used in the laminate may be formed from spray forming or plasma spraying technique in which the amount of the reinforcement is varied as the metal product is being deposited.
• the volume percent of reinforcement material may be varied across the thickness of the reinforcement layer. This variation in volume percent may be abrupt or gradual depending on the desired outcome.
• the entire laminate may be formed by changing the alternating the volume percent of particulate material from below 5 vol.% to above 5 vol.% and thereby form the dual structure (unreinforced and reinforced layers) with a single spraying.
• the composition of the alloy that is being deposited may be varied within each layer or the entire structure.
• each layer need not extend the entire length or width of the product.
• the present invention will also be valuable producing laminated composites made of other aluminum alloys containing about 80 percent or more by weight of aluminum and one or more alloying elements.
• suitable alloying elements is at least one element selected from the group of essentially character forming alloying elements and consisting of manganese, zinc, beryllium, lithium, copper, silicon and magnesium. I term these alloying elements as essentially character forming for the reason that the contemplated alloys containing one or more of them essentially derive their characteristic properties from such elements.
• the amounts of each of the elements which impart such characteristics are, as to each of magnesium and copper, about 0.5 to about
• the elements iron and silicon while perhaps not entirely or always accurately classifiable as essentially character forming alloy elements, are often present in aluminum alloy in appreciable quantities and can have a marked effect upon the derived characteristic properties of certain alloys containing the same.
• Iron for example, which if often present and considered as an undesired impurity, is oftentimes desirably present and adjusted in amounts of about 0.3 to 2.0 wt.% of the total alloy to perform specific functions.
• Silicon may also be so considered, and while found in a range varying from about 0.25 to as much as 15%, is more often desirably found in the range of about 0.3 to 1.5% to perform specific functions.
• the elements iron and silicon may, at least when desirably present in character affecting amounts in certain alloys, be properly also considered as character forming alloying ingredients.
• Such aluminum and aluminum alloys which may contain one or more of these essential elements
• SUBSTITU character forming elements may contain, either with or without the aforementioned character forming elements, quantities of certain well known ancillary alloying elements for the purpose of enhancing particular properties.
• ancillary elements are usually chromium, nickel, zirconium, vanadium, titanium, boron, lead, cadmium, bismuth, and occasionally silicon and iron.
• lithium is listed above an essential character forming element, it may in some instances occur in an alloy as an ancillary element in an amount within the range outlined above.
• the cast alloys treatable by the present invention include most preferably the cast aluminum alloys, such as those designated 222, 242, 295, 296, 319, 336, 355, 356, and 712. These cast alloys generally have the generic designation 200 series alloys, 600 series alloys and 700 series alloys.

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• 1993
  • 1993-10-28 JP JP6511323A patent/JPH08503023A/ja active Pending
  • 1993-10-28 CA CA 2148251 patent/CA2148251A1/en not_active Abandoned
  • 1993-10-28 EP EP93925104A patent/EP0668936A4/de not_active Withdrawn
  • 1993-10-28 WO PCT/US1993/010360 patent/WO1994010351A1/en not_active Application Discontinuation

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