Iron-Based Alloy Strengthened by Intermetallic Compound Phase-Coated Nano-Oxide Phase and Preparation Method Thereof

Abstract

Disclosed are an iron-based alloy strengthened by an intermetallic compound (IMC) phase-coated nano-rare earth oxide phase and a preparation method thereof. The preparation method includes the following steps: step S1, preparation of a pre-alloyed powder; step S2, first mechanical alloying; step S3, mixing by ball milling; step S4, second mechanical alloying; step S5, thermomechanical densification; and step S6, solid solution heat treatment and aging heat treatment.

What is claimed is: 
     
         1 . A method for preparing an iron-based alloy strengthened by an intermetallic compound (IMC) phase-coated rare earth element oxide (REEO) nano-phase, comprising:
 step S1, preparation of a pre-alloyed powder: preparing the pre-alloyed powder of the iron-based alloy by vacuum melting and gas atomization;   step S2, first mechanical alloying: subjecting a raw material powder for forming an IMC to high-energy ball milling according to a stoichiometric ratio of the IMC to obtain an IMC mechanically-alloyed powder;   step S3, mixing by ball milling: mixing the pre-alloyed powder of the iron-based alloy obtained in step S1, the IMC mechanically-alloyed powder obtained in step S2, and a rare earth element-containing powder in a high-speed oscillating ball mill thoroughly under a first inert gas protection to obtain a mixed powder;   step S4, second mechanical alloying: subjecting the mixed powder obtained in step S3 to mechanical alloying ball milling under a second inert gas protection to obtain a supersaturated solid solution mechanical alloying powder;   step S5, thermomechanical densification: charging the supersaturated solid solution mechanical alloying powder obtained in step S4 into a can, vacuumizing, and conducting thermomechanical densification by hot extrusion/hot isostatic pressing/spark plasma sintering to obtain an iron-based alloy bulk, wherein a large amount of dispersed REEO nano-phase precipitates inside grains and at grain boundaries of an iron-based alloy matrix during the thermomechanical densification; and   step S6, solid solution heat treatment and aging heat treatment: subjecting the iron-based alloy bulk to a solid solution heat treatment and an aging heat treatment to obtain the iron-based alloy strengthened by the IMC phase-coated REEO nano-phase, wherein during the solid solution heat treatment and the aging heat treatment, the REEO nano-phase further precipitates, and the REEO nano-phase has a particle size of 2 nm to 30 nm and a number density of 1022-1024 particles/m 3 ; an IMC phase preferentially precipitates with a phase interface of the REEO nano-phase as a heterogeneous nucleation site, and then almost all of the REEO nano-phase is gradually wrapped, thereby forming a nano-particle with a core-shell structure with a REEO nano-phase having three or more elements as a core and the IMC phase as a shell; and a small amount of single-phase nano-particles of the IMC phase are also separately precipitated;   wherein, the obtained iron-based alloy strengthened by the IMC phase-coated REEO nano-phase features heat resistance; since almost all of the REEO nano-phase is wrapped, the nano-particles with the core-shell structure have a total precipitation number density of 1022-1024 particles/m 3  and maintains a high degree of coherency and a high thermal stability in the iron-based alloy matrix.   
     
     
         2 . The method of  claim 1 , wherein the iron-based alloy is one selected from the group consisting of a Cr-containing full ferrite alloy and a Cr-containing ferrite/martensite alloy. 
     
     
         3 . The method of  claim 1 , wherein the IMC phase comprises the IMC in step S2 alone; alternatively, the IMC phase comprises the IMC in step S2 and an alloying element in the iron-based alloy. 
     
     
         4 . The method of  claim 1 , wherein the IMC in step S2 is one or more selected from the group consisting of Ni—Al series, Ti—Al series, Fe—Al series, Ti—Si series, Ni—Si series, Ni—Ti series, Nb—Al series, Ru—Al series, Mo—Si series, and Nb—Si series. 
     
     
         5 . The method of  claim 1 , wherein the REEO nano-phase exhibits a high thermal stability. 
     
     
         6 . The method of  claim 5 , wherein the REEO nano-phase comprises one type of a complex oxide phase having three or more elements; alternatively, the REEO nano-phase comprises multiple types of complex oxide phases having three or more elements. 
     
     
         7 . The method of  claim 1 , wherein the rare earth element-containing powder is one selected from the group consisting of a rare earth element oxide powder and a rare earth element hydride powder. 
     
     
         8 . The method of  claim 1 , wherein the first mechanical alloying and the second mechanical alloying each are conducted using an omnidirectional planetary ball mill at a disk speed of 200 rpm to 400 rpm, a longitudinal speed of 10 rpm to 20 rpm, and a ball-to-material mass ratio of 5:1 to 10:1 for 5 h to 15 h; and the omnidirectional planetary ball mill is stopped for 5 min to 10 min and then changes a rotational direction every 15 min to 30 min of ball milling. 
     
     
         9 . The method of  claim 1 , wherein in step S6, the solid solution heat treatment is conducted at a temperature of 800° C. to 1100° C. for 1 h to 3 h with a cooling process of water cooling, and the aging heat treatment is conducted at a temperature of 500° C. to 650° C. for 1 h to 3 h with a cooling process of water cooling. 
     
     
         10 . An iron-based alloy strengthened by an IMC phase-coated REEO nano-phase prepared by the method of  claim 1 . 
     
     
         11 . The iron-based alloy strengthened by an IMC phase-coated REEO nano-phase of  claim 10 , wherein the iron-based alloy is one selected from the group consisting of a Cr-containing full ferrite alloy and a Cr-containing ferrite/martensite alloy. 
     
     
         12 . The iron-based alloy strengthened by an IMC phase-coated REEO nano-phase of  claim 10 , wherein the IMC phase comprises the IMC in step S2 alone; alternatively, the IMC phase comprises the IMC in step S2 and an alloying element in the iron-based alloy. 
     
     
         13 . The iron-based alloy strengthened by an IMC phase-coated REEO nano-phase of  claim 10 , wherein the IMC in step S2 is one or more selected from the group consisting of Ni—Al series, Ti—Al series, Fe—Al series, Ti—Si series, Ni—Si series, Ni—Ti series, Nb—Al series, Ru—Al series, Mo—Si series, and Nb—Si series. 
     
     
         14 . The iron-based alloy strengthened by an IMC phase-coated REEO nano-phase of  claim 10 , wherein the REEO nano-phase exhibits a high thermal stability. 
     
     
         15 . The iron-based alloy strengthened by an IMC phase-coated REEO nano-phase of  claim 14 , wherein the REEO nano-phase comprises one type of a complex oxide phase having three or more elements; alternatively, the REEO nano-phase comprises multiple types of complex oxide phases having three or more elements. 
     
     
         16 . The iron-based alloy strengthened by an IMC phase-coated REEO nano-phase of  claim 10 , wherein the rare earth element-containing powder is one selected from the group consisting of a rare earth element oxide powder and a rare earth element hydride powder. 
     
     
         17 . The iron-based alloy strengthened by an IMC phase-coated REEO nano-phase of  claim 10 , wherein the first mechanical alloying and the second mechanical alloying each are conducted using an omnidirectional planetary ball mill at a disk speed of 200 rpm to 400 rpm, a longitudinal speed of 10 rpm to 20 rpm, and a ball-to-material mass ratio of 5:1 to 10:1 for 5 h to 15 h; and the omnidirectional planetary ball mill is stopped for 5 min to 10 min and then changes a rotational direction every 15 min to 30 min of ball milling. 
     
     
         18 . The iron-based alloy strengthened by an IMC phase-coated REEO nano-phase of  claim 10 , wherein in step S6, the solid solution heat treatment is conducted at a temperature of 800° C. to 1100° C. for 1 h to 3 h with a cooling process of water cooling, and the aging heat treatment is conducted at a temperature of 500° C. to 650° C. for 1 h to 3 h with a cooling process of water cooling.