Articles having a continuous grain size radial gradient and methods for making the same

Abstract

An article is presented where the article comprises an alloy having a minor phase dispersed within a matrix phase and a plurality of substantially equiaxed grains. The article further comprises a continuous gradient in grain size from a first grain size at an outer surface of the article to a second grain size at an inner portion of the article, wherein the first grain size is less than the second grain size. Methods for forming the article using high deformation processing are also presented, where the processing includes extruding the feedstock material through a die having a twist channel configured to apply a torsional strain to the feedstock material as it passes through the die to form an extruded billet.

1 . A method for forming an article, the method comprising:
 providing a feedstock material comprising a first phase dispersed within a matrix phase; and   extruding the feedstock material through a die having a twist channel configured to apply a torsional strain to the feedstock material as it passes through the die to form an extruded billet, wherein the extruding step is performed using a predetermined combination of temperature, strain, and strain rate such that
 a. during the extrusion step, the temperature of the feedstock is maintained at below two thirds of the absolute melting temperature of the feedstock material, 
 b. the feedstock is plastically deformed without substantially damaging the die, 
 c. the feedstock material undergoes substantially no recrystallization during the extruding step, and 
 d. the feedstock material undergoes substantially no dynamic recovery during the extruding step. 
   
   
   
       2 . The method of  claim 1 , further comprising post-processing the extruded billet using at least one process selected from the group consisting of extrusion, rolling, forging, heat treating, and combinations thereof. 
   
   
       3 . The method of  claim 2 , wherein the post-processing causes recrystallization of grains within the extruded billet. 
   
   
       4 . The method of  claim 3 , wherein, after the post-processing, the grains have a median grain size less than about 10 micrometers. 
   
   
       5 . The method of  claim 1 , further comprising dissolving the first phase into the matrix to form a single phase material prior to extruding. 
   
   
       6 . The method of  claim 1 , wherein the grains are disposed within the extruded billet such that the extruded billet has a microstructure comprising a continuous size gradient from a first grain size at an outer surface of the extruded billet to a second grain size at an inner portion of the extruded billet. 
   
   
       7 . The method of  claim 6 , wherein the first grain size is less than the second grain size. 
   
   
       8 . The method of  claim 7 , wherein the first grain size is in the range from about 10 nanometers to about 1 micrometer. 
   
   
       9 . The method of  claim 7 , wherein the second grain size is in the range from about 1 micrometer to about 100 micrometers. 
   
   
       10 . The method of  claim 1 , wherein the feedstock material comprises at least one alloy selected from the group consisting of titanium alloys, superalloys, steels, aluminum alloys, copper alloys, magnesium alloys, refractory metal alloys, platinum-group metal alloys, and intermetallic alloys. 
   
   
       11 . The method of  claim 10 , wherein the feedstock material comprises a superalloy selected from the group consisting of nickel-based superalloys, cobalt-based superalloys, iron-based superalloys, and nickel-iron-based superalloys. 
   
   
       12 . The method of  claim 1 , wherein the feedstock material comprises Alloy 718. 
   
   
       13 . The method of  claim 1 , wherein the feedstock material comprises Ti-6% Al-4% V alloy. 
   
   
       14 . The method of  claim 1 , wherein the temperature of the feedstock material is less than about 725° C. 
   
   
       15 . The method of  claim 14 , wherein temperature of the feedstock material is less than about 625° C. 
   
   
       16 . The method of  claim 1 , wherein the strain, as measured by the strain at an outermost surface of the feedstock material, is greater than about 0.2. 
   
   
       17 . The method of  claim 16 , wherein the strain is greater than about 0.4. 
   
   
       18 . The method of  claim 1 , wherein the strain rate is in the range from about 0.1 sec −1  to about 0.5 sec −1 . 
   
   
       19 . A method for forming an article, the method comprising:
 providing a feedstock material comprising a nickel-based superalloy or a nickel-iron-based superalloy;   extruding the feedstock material through a die having a twist channel configured to apply a torsional strain to the feedstock material as it passes through the die to form an extruded billet, wherein the extruding step is performed using a predetermined combination of temperature, strain, and strain rate such that
 a. the temperature of the feedstock material is less than about 725° C., 
 b. the strain, as measured by the strain at an outermost surface of the feedstock material, is greater than about 0.2, and 
 c. the strain rate is in the range from about 0.1 sec −1  to about 0.5 sec −1 ; and 
   post-processing the extruded billet to cause recrystallization of grains within the extruded billet.   
   
   
       20 . A method for forming an article, the method comprising:
 providing a feedstock material comprising a titanium alloy;   extruding the feedstock material through a die having a twist channel configured to apply a torsional strain to the feedstock material as it passes through the die to form an extruded billet, wherein the extruding step is performed using a predetermined combination of temperature, strain, and strain rate such that
 a. the temperature of the feedstock material is less than about 625° C., 
 b. the strain, as measured by the strain at an outermost surface of the feedstock material, is greater than about 0.2, and 
 c. the strain rate is in the range from about 0.1 sec −1  to about 0.5 sec −1 ; and 
   post-processing the extruded billet to cause recrystallization of grains within the extruded billet.   
   
   
       21 . A method for forming an article, the method comprising:
 providing a feedstock material comprising a first phase dispersed within a matrix phase; and   extruding the feedstock material through a die having a twist channel configured to apply a torsional strain to the feedstock material as it passes through the die to form an extruded billet, wherein the extruding step is performed using a predetermined combination of temperature, strain, and strain rate such that
 a. during the extrusion step, the feedstock temperature is in a range from about two thirds of the melting temperature of the feedstock material to a solvus temperature of the first phase, 
 b. the feedstock is plastically deformed without substantially damaging the die, and 
 c. the feedstock material undergoes at least partial dynamic recrystallization during the extruding step. 
   
   
   
       22 . The method of  claim 21 , further comprising post-processing the extruded billet using at least one process selected from the group consisting of extrusion, rolling, forging, heat treating, and combinations thereof. 
   
   
       23 . The method of  claim 22 , wherein the post-processing causes recrystallization of grains within the extruded billet. 
   
   
       24 . The method of  claim 22 , wherein, after the post-processing, the grains have a median grain size less than about 10 micrometers. 
   
   
       25 . The method of  claim 23 , wherein the grains are disposed within the extruded billet such that the extruded billet has a microstructure comprising a continuous size gradient from a first grain size at an outer surface of the extruded billet to a second grain size at a center portion of the extruded billet. 
   
   
       26 . The method of  claim 25  wherein the first grain size is less than the second grain size. 
   
   
       27 . The method of  claim 26  wherein the first grain size is in the range from about 10 nanometers to about 1 micrometer. 
   
   
       28 . The method of  claim 26  wherein the first grain size is in the range from about 1 micrometer to about 100 micrometers. 
   
   
       29 . The method of  claim 21  wherein the feedstock material comprises at least one alloy selected from the group consisting of titanium alloys, superalloys, steels, aluminum alloys, copper alloys, magnesium alloys, refractory metal alloys, platinum-group metal alloys, and intermetallic alloys. 
   
   
       30 . The method of  claim 29 , wherein the feedstock material comprises a superalloy selected from the group consisting of nickel-based superalloys, cobalt-based superalloys, iron-based superalloys, and nickel-iron-based superalloys. 
   
   
       31 . The method of  claim 21 , wherein the feedstock material comprises Alloy 718. 
   
   
       32 . The method of  claim 21 , wherein the feedstock material comprises Ti-6% Al-4% V alloy. 
   
   
       33 . The method of  claim 21 , wherein the temperature of the feedstock material is at least about 725° C. 
   
   
       34 . The method of  claim 21 , wherein temperature of the feedstock material is at least about 625° C. 
   
   
       35 . The method of  claim 21 , wherein the strain, as measured by the strain at an outermost surface of the feedstock material, is at least about 0.2. 
   
   
       36 . The method of  claim 35 , wherein the strain is at least about 0.4. 
   
   
       37 . The method of  claim 21 , wherein the strain rate is in the range from about 10 −4  sec −1  to about 10 −2  sec 1 . 
   
   
       38 . A method for forming an article, the method comprising:
 providing a feedstock material comprising a nickel-based superalloy or a nickel-iron-based superalloy;   extruding the feedstock material through a die having a twist channel configured to apply a torsional strain to the feedstock material as it passes through the die to form an extruded billet, wherein the extruding step is performed using a predetermined combination of temperature, strain, and strain rate such that
 a. the temperature of the feedstock material is in the range from about 725° C. to about 1000° C., 
 b. the strain, as measured by the strain at an outermost surface of the feedstock material, is at least about 0.2, and 
 c. the strain rate is at least about 10 −2  sec −1 ; and 
   post-processing the extruded billet to cause recrystallization of grains within the extruded billet.   
   
   
       39 . A method for forming an article, the method comprising:
 providing a feedstock material comprising a titanium alloy;   extruding the feedstock material through a die having a twist channel configured to apply a torsional strain to the feedstock material as it passes through the die to form an extruded billet, wherein the extruding step is performed using a predetermined combination of temperature, strain, and strain rate such that
 a. the temperature of the feedstock material is in the range from about 625° C. to about 1000° C., 
 b. the strain, as measured by the strain at an outermost surface of the feedstock material, is at least about 0.2, and 
 c. the strain rate is at least about 10 −2  sec −1 ; and 
   post-processing the extruded billet to cause recrystallization of grains within the extruded billet.   
   
   
       40 . An article comprising:
 an alloy comprising a first phase dispersed within a matrix phase;   a plurality of substantially equiaxed grains; and   a continuous gradient in grain size from a first grain size at an outer surface of the article to a second grain size at an inner portion of the article, wherein the first grain size is less than the second grain size.   
   
   
       41 . The article of  claim 40 , wherein the first phase is substantially uniformly dispersed within the matrix phase. 
   
   
       42 . The article of  claim 40 , wherein the first grain size is in the range from about 10 nanometers to about 1 micrometer. 
   
   
       43 . The article of  claim 40 , wherein the second grain size is in the range from about 1 micrometer to about 100 micrometers. 
   
   
       44 . The article of  claim 40 , wherein the alloy comprises at least one selected from the group consisting of titanium alloys, superalloys, steels, aluminum alloys, copper alloys, magnesium alloys, refractory metal alloys, platinum-group metal alloys, and intermetallic alloys. 
   
   
       45 . The article of  claim 44 , wherein the alloy comprises a superalloy selected from the group consisting of nickel-based superalloys, cobalt-based superalloys, iron-based superalloys, and nickel-iron-based superalloys. 
   
   
       46 . The article of  claim 45 , wherein the alloy comprises Alloy 718. 
   
   
       47 . The article of  claim 44 , wherein the alloy comprises Ti-6% Al-4% V alloy. 
   
   
       48 . The article of  claim 40 , wherein the article comprises a component of a turbine assembly. 
   
   
       49 . The article of  claim 48 , wherein the component is selected from the group consisting of a fan blade, a fan disk, a compressor blade, a compressor disk, a turbine airfoil, a disk, a duct, a frame, a casing, and a hot gas path component. 
   
   
       50 . The article of  claim 50 , wherein the article comprises a shaft or a gear.