Medium-entropy alloy having excellent cryogenic properties

Abstract

Disclosed is a medium-entropy alloy, which is further improved in cryogenic mechanical properties of an existing FCC-based high-entropy alloy and is capable of ensuring price competitiveness, the medium-entropy alloy including 6 to 15 at % of Cr, 50 to 64 at % of Fe, 13 to 25 at % of Co, 13 to 25 at % of Ni, and the remainder of inevitable impurities, wherein the medium-entropy alloy includes a metastable FCC phase, whereby deformation-induced phase transformation from an FCC phase into a BCC phase occurs upon plastic deformation of the alloy, thus manifesting excellent cryogenic mechanical properties.

1 . A medium-entropy alloy, comprising 6 to 15 at % of Cr, 50 to 64 at % of Fe, 13 to 25 at % of Co, 13 to 25 at % of Ni, and a remainder of inevitable impurities, wherein deformation-induced phase transformation from a face-centered cubic (FCC) phase into a body-centered cubic (BCC) phase occurs upon plastic deformation. 
     
     
         2 . The medium-entropy alloy of  claim 1 , wherein the deformation-induced phase transformation occurs in a metastable FCC phase. 
     
     
         3 . The medium-entropy alloy of  claim 1 , wherein an amount of the Cr is 7.5 to 12.5 at %. 
     
     
         4 . The medium-entropy alloy of  claim 3 , wherein an amount of the Fe is 57.5% to 62.5 at %. 
     
     
         5 . The medium-entropy alloy of  claim 1 , wherein the Co is substitutable with at least one selected from among Mo and Al. 
     
     
         6 . The medium-entropy alloy of  claim 1 , wherein the Ni is substitutable with Mn. 
     
     
         7 . The medium-entropy alloy of  claim 1 , wherein at least one of C and N is included in an amount of less than 1 at % based on a total at % of the medium-entropy alloy. 
     
     
         8 . The medium-entropy alloy of  claim 6 , wherein at least one of C and N is included in an amount of less than 1 at % based on a total at % of the medium-entropy alloy. 
     
     
         9 . The medium-entropy alloy of  claim 1 , wherein the deformation occurs at a temperature equal to or lower than room temperature (298 K). 
     
     
         10 . The medium-entropy alloy of  claim 2 , wherein a fraction of the metastable FCC phase is 50% or more. 
     
     
         11 . The medium-entropy alloy of  claim 1 , wherein the medium-entropy alloy is composed of a combination of a BCC phase and a metastable FCC phase, or is composed of a metastable FCC phase alone. 
     
     
         12 . The medium-entropy alloy of  claim 1 , wherein the medium-entropy alloy has a tensile strength of 226 MPa or more and an elongation of 67% or more at room temperature (298 K). 
     
     
         13 . The medium-entropy alloy of  claim 1 , wherein the medium-entropy alloy has a tensile strength of 1024 MPa or more and an elongation of 47% or more at a cryogenic temperature (77 K).