Multi-scale and multi-phase dispersion strengthened iron-based alloy, and preparation and characterization methods thereof

Abstract

A multi-scale and multi-phase dispersion strengthened iron-based alloy, and preparation and characterization methods thereof are provided. The alloy contains a matrix and a strengthening phase. The strengthening phase includes at least two types of the strengthening phase particles with different sizes. A volume of the two types of the strengthening phase particles with different sizes having a particle size less than or equal to 50 nm accounts for 85-95% of a total volume of all the strengthening phase particles. The matrix is a Fe—Cr—W—Ti alloy. The strengthening phases include crystalline Y.sub.2O.sub.3 phase, Y—Ti—O phase, Y—Cr—O phase, and Y—W—O phase. The characterization method comprises electrolytically separating the strengthening phases in the alloy, and then characterizing by using an electron microscope. The tensile strength of the prepared alloy is more than 1600 MPa at room temperature, and is more than 600 MPa at 700° C.

Claims

1. A method for preparing a multi-scale and multi-phase dispersion strengthened iron-based alloy, comprising the following steps: Step 1: weighing a pre-alloyed iron-based powder and a rare earth oxide powder containing Y.sub.2O.sub.3, according to a mass ratio of the pre-alloyed iron-based powder:the rare earth oxide powder containing Y.sub.2O.sub.3=97-99.5:3-0.5; taking milling balls, according to a ratio of a total mass of the pre-alloyed iron-based powder and the rare earth oxide powder containing Y.sub.2O.sub.3 to a mass of the milling balls=1:10-20; and filling the pre-alloyed iron-based powder, the rare earth oxide powder containing Y.sub.2O.sub.3, and the milling balls into a milling can, and then closing the milling can, wherein the milling balls have diameters of 18-22 mm, 14-16 mm, 9-11 mm, 7-8.5 mm, 4.5-5.5 mm, and 2.5-3.5 mm according to a mass ratio of 1-2:1-2:1-2:1-2:1-2:1-2; Step 2: vacuuming the milling can, and then filling with an inert gas; Step 3: installing the milling can in Step 2 to a planetary ball milling machine, and then mechanical milling, wherein parameters of the mechanical milling include a milling time of 40-120 hrs, and a milling rotation speed of 300-380 r/min; Step 4: after the mechanical milling, sieving the powders under an inert gas atmosphere in a glove box to obtain an oxide dispersion strengthened iron-based alloy powder; and Step 5: sequentially subjecting the obtained oxide dispersion strengthened iron-based alloy powder to hot extrusion, hot rolling, and heat treatment to prepare the multi-scale and multi-phase dispersion strengthened iron-based alloy, wherein parameters of the hot extrusion include an extrusion temperature of 850-1100° C. and an extrusion ratio of 6-15:1, parameters of the hot rolling include a temperature of 850-1100° C., and a total deformation of 60-80%, parameters of the heat treatment include a temperature of 950-1200° C., holding 1-2 hrs, and air cooling to room temperature, wherein the multi-scale and multi-phase dispersion strengthened iron-based alloy comprises a matrix and a strengthening phase, wherein the strengthening phase comprises at least two types of strengthening phase particles with different sizes, the two types of the strengthening phase particles with different sizes are type A particle and type B particle, a size of the type A particle is less than or equal to 50 nm, and a size of the type B particle is larger than 50 nm and less than or equal to 200 nm, a volume of the type A particle accounts for 85% to 95% of a total volume of all the strengthening phase particles, and a content of the strengthening phase is 0.5 to 3.0 wt. %, the matrix is a Fe—Cr—W—Ti alloy, the strengthening phase comprises crystalline Y.sub.2O.sub.3 phase, Y—Ti—O phase, Y—Cr—O phase, and Y—W—O phase.

2. The method for preparing the multi-scale and multi-phase dispersion strengthened iron-based alloy according to claim 1, wherein a tensile strength of the fabricated multi-scale and multi-phase dispersion strengthened iron-based alloy is more than 1600 MPa at room temperature and more than 600 MPa at 700° C.

3. The method for preparing the multi-scale and multi-phase dispersion strengthened iron-based alloy according to claim 1, wherein two gas valves are disposed on a lid of the milling can for vacuuming and filling with the inert gas as a protective gas after sealing, the protective gas is argon, the ball milling machine is a vertical planetary ball milling machine or an omni-directional planetary ball milling machine, and revolution and rotation directions are changed every 25-35 min during ball milling.

4. The method for preparing the multi-scale and multi-phase dispersion strengthened iron-based alloy according to claim 1, wherein a particle size of the rare earth oxide powder containing Y.sub.2O.sub.3 is 75 μm or less, and the pre-alloyed iron-based powder is Fe—Cr—W—Ti alloy powder with a particle size of 150 μm or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 presents a SEM image showing the microstructure of the ODS iron-based alloy in Example 1.

(2) FIG. 2 presents a TEM image showing the microstructure of the ODS iron-based alloy in Example 1.

(3) FIG. 3 presents a HRTEM image of a nano-strengthening phase in the ODS iron-based alloy in Example 1.

(4) FIG. 4 presents an OM image of the ODS iron-based alloy microstructure in Example 1 before electrolysis.

(5) FIG. 5 presents a SEM image showing the microstructure of the alloy electrolysis surface in Example 1 after electrolysis.

(6) FIG. 6 presents a TEM image showing the morphology of the nano-strengthening phase separated from the ODS iron-based alloy in Example 1.

(7) FIG. 7 presents a HRTEM image of the nano-strengthening phase separated from the ODS iron-based alloy in Example 1.

(8) FIG. 8 presents a TEM image of a strengthening phase obtained in Comparative Example 2.

(9) FIG. 1 shows that the ODS iron-based alloy prepared in Example 1 has a dense structure.

(10) FIG. 2 shows that in the ODS iron-based alloy prepared in Example 1, the strengthening phases are homogeneous distributed in the grains and the grain boundaries, and grain size of the alloy is fine.

(11) FIG. 3 shows that in the ODS iron-based alloy prepared in Example 1, the strengthening phase is in nano-scale which is less than 5 nm, but the image shows great interference. It is difficult to achieve high resolution image of this nano-scale oxide.

(12) FIG. 6 shows that the size of the strengthening phase separated from the ODS iron-based alloy prepared in Example 1 is less than 0.2 μm.

(13) FIG. 7 shows that a clear structure image of the strengthening phase separated from the ODS iron-based alloy prepared in Example 1 can be seen after the strengthening phase is magnified.

(14) As can be seen from FIG. 8, most of the strengthening phase is larger than 200 nm in size, and the maximum size of the strengthening phase is about 5 μm.

DETAILED DESCRIPTION

Example 1: Fe-14Cr-3W-0.4Ti-1.5Y.SUB.2.O.SUB.3 .(wt. %) Alloy

(15) Alloy Powder Preparation:

(16) Step 1: A total of 150 g of an atomized Fe-14Cr-3W-0.4Ti (wt. %) pre-alloyed iron-based powder and a Y.sub.2O.sub.3 power was weighed according to a mass ratio of 98.5:1.5, and then filled into a milling can. The pre-alloyed iron-based powder had a particle size of 150 μm or less, and the Y.sub.2O.sub.3 powder had a particle size of 45 μm or less. According to a ball-to-powder ratio of 10:1, 1500 g of milling balls respectively with diameters of 20 mm, 15 mm, 10 mm, 8 mm, 5 mm and 3 mm according to a mass ratio 1:1:1:1:1:1 was weighed and then filled into the milling can.

(17) Step 2: The milling can was sealed and vacuumed to a vacuum level of 0.1 Pa or less, and then filled with high-purity argon.

(18) Step 3: Installing the milling can to a vertical planetary ball milling machine and then mechanical milling. The parameters of the mechanical milling were set as follows: the rotating speed was 300 r/min, and the mechanical milling time was 60 h. The revolution and rotation directions were changed every 30 minutes during ball milling.

(19) Step 4: After the mechanical milling, the powders were sieved under an inert gas atmosphere in a glove box to obtain an oxide dispersion strengthened powder.

(20) Alloy Bulk Preparation:

(21) Step 1: The above prepared iron-based alloy powder was filled into a pure-iron can, and vacuumed to 0.1 Pa or less. The gas pipe was seal welded. Hot extrusion was performed at a temperature of 850° C., an extrusion speed of 15 mm/s, and an extrusion ratio of 10:1. Then the can was separated by wire cutting to obtain a hot formed ODS iron-based alloy.

(22) Step 2: The ODS iron-based alloy formed by hot extrusion was hot rolled at a temperature of 850° C., a rolling speed of 0.36 m/s, and a total deformation of 80%.

(23) Step 3: The hot-rolled ODS iron-based alloy was heat treated at a temperature of 950° C. for 1 h and air cooling, to obtain a multi-scale and multi-phase dispersion strengthened iron-based alloy.

(24) Alloy Microstructure Characterization:

(25) Before the strengthening phases were electrolytically separated from the Fe-14Cr-3W-0.4Ti-1.5Y.sub.2O.sub.3 alloy, microstructure of the alloy was characterized by OM, then characterized by electron microscope according to the following steps:

(26) Step 1: The Fe-14Cr-3W-0.4Ti-1.5Y.sub.2O.sub.3 alloy sample was used as the anode and a stainless steel cylinder was used as the cathode. The strengthening phases in the Fe-14Cr-3W-0.4Ti-1.5Y.sub.2O.sub.3 alloy were electrolytically separated from the matrix in an electrolytic solution, to obtain an electrolytic solution containing the strengthening phases. Where the electrolytic solution was composed of 2 wt. % of tetramethylammonium chloride, 15 wt. % of acetylacetone, and 3 wt. % of glycerol, with the balance being ethanol. The electrolysis parameters included a voltage of 6V, and an electrolysis time of 10 min.

(27) Step 2: The electrolytic solution containing the strengthening phases prepared by electrolysis was extracted, and then diluted with ethanol by a factor of 5, to obtain a suspension containing the strengthening phases with nanometer to micron size.

(28) Step 3: The suspension containing the strengthening phases prepared in Step 2 was dispersed by ultrasonic for 10 min, to obtain a solution containing the strengthening phases with nanometer to micron size for use;

(29) Step 4: The solution obtained by ultrasonic dispersion in Step 3 was dripped onto an ultra-thin carbon support film for 3 times, and dried to obtain a sample for electron microscope.

(30) Step 5: The microstructure of reaction surface after electrolysis was observed by SEM; and the strengthening phases in the sample prepared in Step 4 were characterized by transmission electron microscope.

(31) The ODS iron-based alloy obtained in this example has a strengthening phase with a size of 2 nm to 200 nm, a tensile strength of up to 1680 MPa and an elongation of 10.85% at room temperature. The tensile strength of the alloy is 620 MPa at 700° C.

(32) FIG. 1 is a SEM image showing the microstructure of an ODS iron-based alloy in Example 1. FIG. 2 is a TEM image showing the microstructure of the ODS iron-based alloy in Example 1. The alloy has a fine grain structure and the strengthening phases are homogeneous distributed in the matrix (the grain and grain boundary). FIG. 3 is a HRTEM image of a nano-strengthening phase in the ODS iron-based alloy in Example 1. The size of the strengthening phase is less than 5 nm, and the interference is very large as seen from FIG. 3. After finished the observation shown in FIGS. 2 and 3, the TEM device needs to be undergone astigmatism of the objective lens at different magnifications. The electron beam status and beam condition need to be readjusted.

(33) FIG. 4 is an OM image showing the microstructure of the ODS iron-based alloy in Example 1 before electrolysis. FIG. 5 is a SEM image showing the electrolysis surface microstructure of the alloy after electrolysis. The pits left on the reaction surface of the alloy after the strengthening phase separated from the alloy matrix by the electrolytic reaction can be observed through comparison of FIGS. 4 and 5. FIG. 6 is a TEM image showing the nano-strengthening phase microstructure in Example 1. As can be seen from FIG. 6, the size of the nano-strengthening particles is totally distributed in the range of 2-20 nm, and some strengthening phase has a size larger than 50 nm; but the size of all strengthening phase is less than 200 nm. Comprehensive statistics of 5 TEM images of this sample show that the volume of particles with a size of 50 nm or less accounts for about 86% of the total volume of all particles in the strengthening phase.

(34) FIG. 7 is a HRTEM image of the nano-strengthening phase of Example 1. In FIG. 7, the nano-strengthening phase has a size of about 15 nm, and a clear structure of the nano-strengthening phase can be observed.

Example 2: Fe-14Cr-3W-0.4Ti-1.0Y.SUB.2.O.SUB.3 .(wt. %) Alloy

(35) Alloy Powder Preparation:

(36) Step 1: A total of 150 g of an atomized Fe-14Cr-3W-0.4Ti (wt. %) pre-alloyed iron-based powder and a Y.sub.2O.sub.3 power was weighed according to a mass ratio of 99:1, and then filled into a milling can. The pre-alloyed iron-based powder had a particle size of 150 μm or less, and the Y.sub.2O.sub.3 powder had a particle size of 75 μm or less. According to a ball-to-material ratio of 10:1, 1500 g of milling balls respectively with diameters of 20 mm, 15 mm, 10 mm, 8 mm, 5 mm and 3 mm according to a mass ratio 1:1:1:1:1:1 was weighed and filled into the milling can.

(37) Step 2: The milling can was sealed and vacuumed to a vacuum level of 0.1 Pa or less, and then filled with high-purity argon.

(38) Step 3: Installing the milling can to a vertical planetary ball milling machine and then mechanical milling. The parameters of the mechanical milling were set as follows: the rotating speed of 320 r/min, and the mechanical milling time of 120 h. The revolution and rotation directions were changed every 30 minutes during mechanical milling.

(39) Step 4: After the mechanical milling, the powders were sieved under an inert gas atmosphere in a glove box to obtain an oxide dispersion strengthened powder.

(40) Alloy Bulk Preparation:

(41) Step 1: The above prepared iron-based alloy powder was filled into a pure-iron can, and vacuumed to 0.1 Pa or less. The gas pipe was seal welded. Hot extrusion was performed at a temperature of 950° C., an extrusion speed of 25 mm/s, and an extrusion ratio of 11:1. Then the can was separated by wire cutting to obtain a hot formed ODS iron-based alloy.

(42) Step 2: The ODS iron-based alloy formed by hot extrusion was hot rolled at a temperature of 950° C., a rolling speed of 0.36 m/s, and a total deformation of 90%.

(43) Step 3: The hot-rolled ODS iron-based alloy was heat treated at a temperature of 1050° C. for 1 hr, and air cooling, to obtain a multi-scale and multi-phase dispersion strengthened iron-based alloy.

(44) Alloy microstructure characterization: The characterization method in this example was the same as that in Example 1.

(45) The ODS iron-based alloy obtained in this example has a strengthening phase with a size of 5 nm to 500 nm, a tensile strength of up to 1620 MPa, and an elongation of 10.13% at room temperature. The tensile strength of the alloy is 605 MPa at 700° C.

Example 3: Fe-14Cr-3W-0.4Ti-2.0Y.SUB.2.O.SUB.3 .(wt. %) Alloy

(46) Alloy Powder Preparation:

(47) Step 1: A total of 150 g of an atomized Fe-14Cr-3W-0.4Ti (wt. %) pre-alloyed iron-based powder and a Y.sub.2O.sub.3 power was weighed according to a mass ratio of 98:2, and filled into a milling can. The pre-alloyed iron-based powder had a particle size of 150 μm or less, and the Y.sub.2O.sub.3 powder had a particle size of 45 μm or less. According to a ball-to-material ratio of 10:1, 1500 g of milling balls respectively with diameters of 20 mm, 15 mm, 10 mm, 8 mm, 5 mm and 3 mm according to mass ratio 1:1:1:1:1:1 was weighed and filled into the milling can.

(48) Step 2: The milling can was sealed and vacuumed to a vacuum level of 0.1 Pa or less, and then filled with high-purity argon.

(49) Step 3: The milling can was installed to a vertical planetary ball milling machine and mechanical milling. The parameters of the mechanical milling were set as follows: the rotating speed of 300 r/min, and the mechanical milling time of 60 h. The revolution and rotation directions were changed every 30 minutes during mechanical ball milling.

(50) Step 4: After the mechanical milling, the powders were sieved under an inert gas atmosphere in a glove box to obtain an oxide dispersion strengthened powder.

(51) Alloy Bulk Preparation:

(52) Step 1: The above prepared iron-based alloy powder was filled into a pure-iron can, and vacuumed to 0.1 Pa or less. The gas pipe was seal welded. Hot extrusion was performed at a temperature of 950° C., an extrusion speed of 15 mm/s, and an extrusion ratio of 12:1. Then the can was separated by wire cutting to obtain a hot formed ODS iron-based alloy.

(53) Step 2: The ODS iron-based alloy formed by hot extrusion was hot rolled at a temperature of 950° C., a rolling speed of 0.36 m/s, and a total deformation of 80%.

(54) Step 3: The hot-rolled ODS iron-based alloy was heat treated at a temperature of 1050° C. for 1 hr, and air cooling, to obtain a multi-scale and multi-phase dispersion strengthened iron-based alloy.

(55) Alloy microstructure characterization: The characterization method in this example was the same as that in Example 1.

(56) The ODS iron-based alloy obtained in this example has a strengthening phase with a size of 2 nm to 500 nm, a tensile strength of up to 1690 MPa, and an elongation of 10.05% at room temperature. The tensile strength of the alloy is 638 MPa at 700° C.

Example 4: Fe-14Cr-3W-0.4Ti-0.5Y.SUB.2.O.SUB.3 .(wt. %)

(57) Alloy Powder Preparation:

(58) Step 1: A total of 150 g of an atomized Fe-14Cr-3W-0.4Ti (wt. %) pre-alloyed iron-based powder and a Y.sub.2O.sub.3 power was weighed according to a mass ratio of 99.5:0.5, and then filled into a milling can. The pre-alloyed iron-based powder had a particle size of 150 μm or less, and the Y.sub.2O.sub.3 powder had a particle size of 75 μm or less. According to a ball-to-material ratio of 10:1, 1500 g of milling balls respectively with diameters of 20 mm, 15 mm, 10 mm, 8 mm, 5 mm and 3 mm according to a mass ratio 1:1:1:1:1:1 was weighed and filled into the milling can.

(59) Step 2: The milling can was sealed and vacuumed to a vacuum level of 0.1 Pa or less, and then filled with high-purity argon.

(60) Step 3: Installing the milling can to a vertical planetary ball milling machine and then mechanical milling. The parameters of the mechanical milling were set as follows: the rotating speed was 300 r/min, and the milling time was 120 h. The revolution and rotation directions were changed every 30 minutes during mechanical milling.

(61) Step 4: After the mechanical milling, the powders were sieved under an inert gas atmosphere in a glove box to obtain an oxide dispersion strengthened powder.

(62) Alloy Bulk Preparation:

(63) Step 1: The above prepared iron-based alloy powder was filled into a pure-iron can, and vacuumed to 0.1 Pa or less. The gas pipe was seal welded. Hot extrusion was performed at a temperature of 950° C., an extrusion speed of 15 mm/s, and an extrusion ratio of 8:1. Then the can was separated by wire cutting to obtain a hot formed ODS iron-based alloy.

(64) Step 2: The ODS iron-based alloy formed by hot extrusion was hot rolled at a temperature of 950° C., a rolling speed of 0.36 m/s, and a total deformation of 90%.

(65) Step 3: The hot-rolled ODS iron-based alloy was heat treated at a temperature of 1050° C. for 1 h, and air cooling, to obtain a multi-scale and multi-phase dispersion strengthened iron-based alloy.

(66) Alloy microstructure characterization: The characterization method in this example was the same as that in Example 1.

(67) The ODS iron-based alloy obtained in this example has a strengthening phase with a size of 2 nm to 500 nm, a tensile strength at room temperature of up to 1608 MPa, and an elongation at room temperature of 11.35%. The tensile strength of the alloy is 605 MPa at 700° C.

Comparative Example 1: Fe-14Cr-3W-0.4Ti-1.0Y.SUB.2.O.SUB.3 .(wt. %) Alloy

(68) Alloy Powder Preparation:

(69) Step 1: A total of 150 g of an atomized Fe-14Cr-3W-0.4Ti (wt. %) pre-alloyed iron-based powder and a Y.sub.2O.sub.3 power was weighed according to a mass ratio of 99:1, and then filled into a milling can. The pre-alloyed iron-based powder had a particle size of 150 μm or less, and the Y.sub.2O.sub.3 powder had a particle size of less than 150 μm. According to a ball-to-material ratio of 10:1, 1500 g of milling balls respectively with diameters of 20 mm, 15 mm, 10 mm, 8 mm, 5 mm and 3 mm according to a mass ratio 1:1:1:1:1:1 was weighed and filled into the milling can.

(70) Step 2: The milling can was sealed and vacuumed to a vacuum level of 0.1 Pa or less, and then filled with high-purity argon.

(71) Step 3: Installing the milling can to a vertical planetary ball milling machine and then mechanical milling. The parameters of the mechanical ball milling were set as follows: the rotating speed was 300 r/min, and the mechanical ball milling time was 40 h. The revolution and rotation directions were changed every 30 minutes during mechanical ball milling.

(72) Step 4: After the mechanical milling, the powders were sieved under an inert gas atmosphere in a glove box to obtain an oxide dispersion strengthened powder.

(73) Alloy Bulk Preparation:

(74) Step 1: The above prepared iron-based alloy powder was filled into a pure-iron can, and vacuumed to 0.1 Pa or less. The gas pipe was seal welded. Hot extrusion was performed at a temperature of 1200° C., an extrusion speed of 15 mm/s, and an extrusion ratio of 8:1. Then the can was separated by wire cutting to obtain a hot formed ODS iron-based alloy.

(75) Step 2: The ODS iron-based alloy formed by hot extrusion was hot rolled at a temperature of 950° C., a rolling speed of 0.36 m/s, and a total deformation of 80%.

(76) Step 3: The hot-rolled ODS iron-based alloy was heat treated at a temperature of 1050° C. for 1 h, and air cooling, to obtain a multi-scale and multi-phase dispersion strengthened iron-based alloy.

(77) Alloy microstructure characterization: The characterization method in this comparative example was the same as that in Example 1.

(78) The ODS iron-based alloy obtained in this comparative example has a strengthening phase with a size of greater than 0.5 μm, a tensile strength of 1293 MPa, and an elongation of 6.23% at room temperature. The tensile strength of the alloy is 425 MPa at 700° C.

Comparative Example 2: Fe-14Cr-3W-0.4Ti-1.0Y.SUB.2.O.SUB.3 .(wt. %) Alloy

(79) Preparation of Alloy Powder:

(80) Step 1: A total of 150 g of an atomized Fe-14Cr-3W-0.4Ti (wt. %) pre-alloyed iron-based powder and a Y.sub.2O.sub.3 power was weighed according to a mass ratio of 99:1, and then filled into a milling can. The pre-alloyed iron-based powder had a particle size of 150 μm or less, and the Y.sub.2O.sub.3 powder had a particle size of 75 μm or less. According to a ball-to-material ratio of 10:1, 1500 g of milling balls respectively with diameters of 20 mm, 10 mm, and 5 mm according to a mass ratio 1:1:1 was weighed and filled into the milling can.

(81) Step 2: The milling can was sealed and vacuumed to a vacuum level of 0.1 Pa or less, and then filled with high-purity argon.

(82) Step 3: Installing the milling can to a vertical planetary ball milling machine and then mechanical milling. The parameters of the mechanical milling were set as follows: the rotating speed was 300 r/min, and the milling time was 60 h. The revolution and rotation directions were changed every 30 minutes during mechanical milling.

(83) Step 4: After the mechanical milling, the powders were sieved under an inert gas atmosphere in a glove box to obtain an oxide dispersion strengthened powder.

(84) Alloy bulk preparation: The alloy preparation method in this comparative example was the same as that in Comparative Example 1.

(85) Alloy microstructure characterization: The alloy characterization method in this comparative example was the same as that in Example 1.

(86) The ODS iron-based alloy obtained in this comparative example has a strengthening phase with a size of greater than 0.8 μm, a tensile strength of 1025 MPa, and an elongation of 5.10% at room temperature. The tensile strength of the alloy is 367 MPa at 700° C.

(87) FIG. 8 is a TEM image of a strengthening phase in the ODS iron-based alloy obtained in Comparative Example 2. It can be seen that the size of the strengthening phase is larger than 200 nm, and the maximum size of the strengthening phase is about 5 μm.