Nanostructured ferritic alloy and method of forming

Abstract

An alloy and method of forming the alloy are provided. The alloy includes a matrix phase, and a multimodally distributed population of particulate phases dispersed within the matrix. The matrix includes iron and chromium, and the population includes a first subpopulation of particulate phases and a second subpopulation of particulate phases. The first subpopulation of particulate phases include a complex oxide, having a median size less than about 15 nm, and present in the alloy in a concentration from about 0.1 volume percent to about 5 volume percent. The second subpopulation of particulate phases have a median size in a range from about 25 nm to about 10 microns, and present in the alloy in a concentration from about 0.1 volume percent to about 15 volume percent. Further embodiments include articles, such as turbomachinery components and fasteners, for example, that include the above alloy, and methods for making the alloy.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application is a continuation-in part of application Ser. No. 13 / 931,108, filed 28 Jun. 2013.BACKGROUND[0002]The invention relates generally to a nanostructured ferritic alloy. More particularly the invention relates to a nanostructured ferritic alloy having multimodal scale dispersions.[0003]Gas turbines operate in extreme environments, exposing the turbine components, especially those in the turbine hot section, to high operating temperatures and stresses. In order for the turbine components to endure these conditions, they are manufactured from a material capable of withstanding these severe conditions. As material limits are reached, one of two approaches is conventionally used in order to maintain the mechanical integrity of hot section components. In one approach, cooling air is used to reduce the part's effective temperature. In a second approach, the component size is increased to reduce the stresses. However, these approaches...

AI Technical Summary

Benefits of technology

[0007]In one embodiment, an alloy is provided. The alloy includes a matrix phase, and a multimodally distributed population of particulate phases dispersed within the matrix. The matrix includes iron and chromium, and the population includes a first subpopulation of particulate phases and a second subpopulation of particulate phases. The first subpopulation of particulate phases include a complex oxide, having a median size less than about 15 nm, and present in the alloy in a concentration from about 0.1 volume percent to about 5 volume percent. The second subpopulation of particulate phases have a median size in a range from about 25 nm to about 10 microns, and present in the alloy in a concentration from about 0.1 volume percent to about 15 volume percent. Further embodiments include articles, such as turbomachinery components and fasteners, for example, that include the above alloy.

[0008]In one embodiment, an article is provided. The article includes an alloy that includes a matrix phase and a population of particulate phases dispersed within the matrix. The matrix includes iron and chromium, and the population includes a first subpopulation of particulate phases and a second subpopulation of particulate phases. The first subpopulation of particulate phases includes a complex oxide that includes yttrium and titanium, and having a median size less than about 10 nm, and present in the alloy in a concentration from about 0.1 volume percent to about 5 volume percent. The second subpopulation of particulate phases include precipitated Laves phase, have a median size in a range from about 50 nm to about 3 microns, and present in the alloy in a concentration from about 1 volume percent to about 6 volume percent.

[0009]Another embodiment is an article. The article includes an alloy that includes a matrix phase and an alloy comprising a matrix phase and a multimodally distributed population of particulate phases dispersed within the matrix. The matrix includes iron and chromium, and the population includes first and second subpopulations of particulate phases. The first subpopulation includes a complex oxide including yttrium and titanium, has a median size less than about 15 nm, and is present in the alloy in a concentration from about 0.1 volume percent to about 5 volume percent. The second subpopulation includes an oxide, has a median size in a range from about 25 nm to about 100 nm, and is present in the alloy in a concentration from about 0.1 volume percent to about 5 volume percent.

[0010]In one embodiment, a method of forming an alloy is provided. The method includes melting starting materials comprising iron and chromium; atomizing the melt to form an alloy powder; milling the alloy powder in the presence of an oxide until the oxide is at least partially dissolved into the alloy powder, thus forming a milled alloy powder; consolidating the milled alloy powder at a first temperature; precipitating a first subpopulation of particulate phases comprising a complex oxide having a median size less than about 15 nm; and establishing a second subpopulation of particulate phases having a median size in a range from about 25 nm to about 10 microns.

[0011]In one embodiment, a method of forming an alloy is provided. The method includes the steps of forming a milled alloy powder, consolidating the milled alloy powder at a first temperature, precipitating a first subpopulation of particulate phases including a complex oxide comprising yttrium and titanium, and establishing a second subpopulation of particulate phases by an in-situ precipitation of a Laves phase. Forming a milled alloy powder includes melting starting materials having iron and chromium through a vacuum induction melting process; atomizing the melt to form an alloy powder; and milling the alloy powder in the presence of an oxide to dissolve oxide into the alloy powder. The first subpopulation of particulate phases have a median size less than about 15 nm, in a concentration from about 0.1 volume percent to about 5 volume percent of the alloy. Establishing a second subpopulation of particulate phases by an in-situ precipitation of a Laves phase may include hot-working the consolidated, milled alloy powder, and heat-treating the hot-worked, consolidated, milled alloy powder at a second temperature. The Laves phase has a median size in a range from about 30 nm to about 10 microns, in a concentration from about 1 volume percent to about 4 volume percent of the alloy.

[0012]In one embodiment, another method of forming an alloy is provided. The method includes the steps of forming a milled alloy powder, adding a particulate phase comprising an oxide, boride, or a combination of an oxide and boride, mixing the added particulate phase, consolidating the milled and mixed alloy powder at a first temperature, precipitating a first subpopulation of particulate phases including a complex oxide comprising yttrium and titanium, and establishing a second subpopulation of particulate phases resulting from the added particulate phases. Forming a milled alloy powder includes melting starting materials having iron and chromium through a vacuum induction melting process; atomizing the melt to form an alloy powder; and milling the alloy powder in the presence of an oxide to dissolve oxide into the alloy powder. The first subpopulation of particulate phases have a median size less than about 20 nm, in a concentration from about 0.1 volume percent to about 5 volume percent of the alloy. The second subpopulation of particulate phases have a median size in a range from about 30 nm to about 10 microns, in a concentration from about 1 volume percent to about 4 volume percent of the alloy.

Problems solved by technology

Gas turbines operate in extreme environments, exposing the turbine components, especially those in the turbine hot section, to high operating temperatures and stresses.

However, these approaches can reduce the efficiency of the turbine and increase the cost.

However, conventional steels cannot currently be used in high temperature and high stress applications because they do not meet the necessary mechanical property requirements.