Oxide dispersion-strengthened iron-based alloy powder and characterization method thereof

Abstract

An oxide dispersion-strengthened (ODS) iron-based alloy powder and a characterization method thereof are provided. The alloy powder comprises a matrix and strengthening phases. The strengthening phases include at least two types of strengthening phase particles with different sizes, wherein a volume of the particles with a particle size of 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 characterization method of the ODS iron-based alloy powder comprises separating the strengthening phases from the powder matrix through electrolysis, and analyzing and characterizing the strengthening phases using an electron microscope.

Claims

1. A method for preparing a ODS iron-based alloy powder, comprising: 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 to 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 powder materials 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 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 and are matched according to a mass ratio of 1-2:1-2:1-2:1-2:1-2:1-2; Step 2: vacuuming the milling can to create a vacuum environment within the milling can, and then filling with an inert gas to create an inert gas atmosphere in the milling can; Step 3: installing the vacuumed and filled milling can resulting from step 2 to a planetary ball milling machine, and mechanical milling, wherein parameters of the mechanical milling include a milling time of 40-120 hrs, and a milling rotating speed of 300-380 r/min; and Step 4: after the mechanical milling, sieving the powder under an inert gas atmosphere in a glovebox to obtain the ODS powder, wherein the ODS iron-based alloy powder comprises a matrix and strengthening phases; the strengthening phases comprise at least two types of strengthening phase particles with different sizes; the two types of the strengthening phase particles with different sizes are particle A and particle B, a size of the particle A is less than or equal to 50 nm, and a size of the particle B is larger than 50 nm and less than or equal to 200 nm, a volume of the particle A accounts for 85-95% of a total volume of all the strengthening phase particles, and a content of the strengthening phases is 0.5-3.0 wt. %, wherein the matrix is a Fe—Cr—W—Ti alloy, wherein the strengthening phases comprise crystalline Y.sub.2O.sub.3, amorphous Y.sub.2O.sub.3, Y—Ti—O, Y—Cr—O and Y—W—O.

2. The method of preparing the ODS iron-based alloy powder according to claim 1, wherein two gas nozzles are disposed on a lid of the milling can for vacuuming and filling with the inert gas after closing; the inert 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 once per 25-35 min during ball milling.

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

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 presents a SEM image showing the microstructure of gas-atomized pre-alloyed powder used in Example 1 of the present disclosure.

(2) FIG. 2 presents a SEM image showing the microstructure of mechanical milled powder obtained in Example 1 of the present disclosure.

(3) FIG. 3 presents a TEM image of a nanometer strengthening phase of the mechanical milled powder obtained in Example 1 of the present disclosure.

(4) FIG. 4 presents a HRTEM image of the nanometer strengthening phase of the mechanical milled powder obtained in Example 1 of the present disclosure.

(5) FIG. 5 presents a particle size distribution curve of mechanical milled powder obtained in Example 2 of the present disclosure.

(6) FIG. 6 presents a TEM image of a strengthening phase of the mechanical milled powder obtained in Example 2 of the present disclosure.

(7) FIG. 7 presents a HRTEM image of a nanometer strengthening phase of the mechanical milled powder obtained in Example 2 of the present disclosure.

(8) FIG. 8 presents a phase XRD analysis result of the mechanical milled powder obtained in Example 2 of the present disclosure. The result shows that the as-milled alloy powder without Y.sub.2O.sub.3 diffraction peak means that the Y.sub.2O.sub.3 is amorphized.

DETAILED DESCRIPTION OF THE EMBODIMENTS

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

(9) Powder Preparation:

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

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

(12) 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: a rotating speed of 300 r/min, and a mechanical milling time of 60 hrs. The revolution and rotation directions were changed once per 30 min during ball milling.

(13) Step 4: After the mechanical milling, the powder was sieved under an inert gas atmosphere in a glovebox to obtain the ODS powder.

(14) Powder Characterization:

(15) Step A: The prepared alloy powder and foam nickel (the pore diameter of the foam nickel is less than 200 μm) were soak into absolute ethanol, then dispersed by ultrasonic for 3 min to obtain foam nickel filled with the ferromagnetic ODS iron-based alloy powder.

(16) Step B: The foam nickel filled with the ODS iron-based alloy powder was soaked into an electrolyte for electrolysis, to separate the strengthening phases from the iron-based alloy matrix, and magnetic separation was conducted by magnets to obtain an electrolyte containing the strengthening phase particles. The electrolyte for electrolysis was composed of the following components in percentage by mass: 2% of tetramethylammonium chloride, 15% of acetylacetone, 3% of glycerol, and the rest being absolute ethanol.

(17) Step C: The electrolyte containing the strengthening phase particles prepared by electrolyzing was extracted and diluted with absolute ethanol by a factor of 5 to obtain a diluted suspension.

(18) Step D: The diluted suspension was dispersed by ultrasonic for 3 min to obtain a solution containing nano-scale to submicron-scale strengthening phase particles for use.

(19) Step E: The solution containing the nano-scale to submicron-scale strengthening phase particles for use was dripped onto an ultrathin carbon support film for 3 times, and dried to obtain an electron microscope test sample.

(20) Step F: The powders before and after ball milling were observed by SEM; and the strengthening phase particles were characterized by using a TEM/HRTEM.

(21) FIG. 1 presents a SEM image of the gas-atomized pre-alloyed powder used in Example 1. It shows that the sphericity of the powder is good, and a small amount of special-shaped powder and some satellite powder appear.

(22) FIG. 2 presents a SEM image showing the microstructure of mechanical milled powder of Example 1. It shows that the powder changes to a flat shape after mechanical milling, and a large number of defects exist on the surface, which provides an effective structural basis for the formation of multi-scale oxides.

(23) FIG. 3 presents a TEM image of a nanometer strengthening phase particles in Example 1, where the volume of particles A with a size of less than 50 nm accounts for 50% of the total volume of strengthening phase particles in the whole view. According to statistics of a large amount of TEM data in Example 1, the volume of strengthening phases with a size of less than 50 nm accounts for about 88% of the total volume of strengthening phases of the alloy powder.

(24) FIG. 4 presents a HRTEM image of a nanometer strengthening phase in Example 1. It shows that the size of nanometer strengthening phases is 15 nm, and a typical nano-scale structure is also shown.

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

(25) Powder Preparation:

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

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

(28) 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: a rotating speed of 320 r/min, and a mechanical milling time of 60 hrs. The revolution and rotation directions were changed once per 30 min during ball milling.

(29) Step 4: After the mechanical milling, the powder was sieved under an inert gas atmosphere in a glovebox to obtain the ODS powder.

(30) Powder Characterization:

(31) Step A: The prepared alloy powder and foam nickel (the pore diameter of the foam nickel is less than 200 μm) were soaked into absolute ethanol, then dispersed by ultrasonic for 5 min to obtain foam nickel filled with the ferromagnetic ODS iron-based alloy powder.

(32) Step B: The foam nickel filled with the ODS iron-based alloy powder was soaked into an electrolyte for electrolysis, to separate the strengthening phases from the iron-based alloy matrix, and magnetic separation was conducted by magnets to obtain an electrolyte containing the strengthening phase particles. Electrolyzing was carried out by applying a constant-voltage of 6 V at room temperature for 10 min. The electrolyte for electrolysis was composed of the following components in percentage by mass: 2% of tetramethylammonium chloride, 15% of acetylacetone, 5% of glycerol, and the rest being absolute ethanol.

(33) Step C: The electrolyte containing the strengthening phase particles prepared by electrolyzing was extracted and diluted with absolute ethanol by a factor of 5 to obtain a diluted suspension.

(34) Step D: The diluted suspension was dispersed by ultrasonic for 5 min to obtain a solution containing nano-scale to submicron-scale strengthening phase particles for use.

(35) Step E: The solution containing the nano-scale to submicron-scale strengthening phase particles for use was dripped onto an ultrathin carbon support film for 3 times, and dried to obtain an electron microscope test sample.

(36) Step F: The powders before and after ball milling were observed by SEM; and the strengthening phases were characterized using a TEM/HRTEM.

(37) FIG. 5 presents a particle size distribution curve of mechanical milled powder in Example 2, where the particle size of the powder is concentrative distribution, and the Dv(50)=46.3 μm.

(38) FIG. 6 presents a TEM image of a strengthening phase in Example 2. In FIG. 6, the size distribution of the strengthening phase particles is 2-50 nm, where the volume of particles A with a size of less than 50 nm accounts for 70% of the total volume of strengthening phase particles in the whole view. According to statistics of a large amount of TEM data in Example 2, the volume of particles A with a size of less than 50 nm accounts for about 92% of the total volume of strengthening phases of the alloy powder.

(39) FIG. 7 presents a HRTEM image of a nanometer strengthening phase in Example 2. In FIG. 7, the size of nanometer strengthening phase particles is 20 nm, and a typical nano-scale structure is also shown.

(40) FIG. 8 presents a phase XRD analysis result of the mechanical milled powder obtained in Example 2. The result shows that the as-milled alloy powder without Y.sub.2O.sub.3 diffraction peak means that the Y.sub.2O.sub.3 is amorphized.

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

(41) Powder Preparation:

(42) Step 1: The alloy powder had the same components as Example 1. Fe powder, Cr powder, W powder, Ti powder and Y.sub.2O.sub.3 powder with particle sizes of 4 μm, 63 μm, 10 μm, 45 μm and 45 μm respectively, were selected as raw materials. A total of 150 g of the raw materials was weighed and filled into a milling can; and 1500 g of milling balls with a diameter of 10 mm respectively was weighed according to a ball-to-material ratio of 10:1, and filled into the milling can.

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

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

(45) Step 4: After the mechanical milling, the powder was sieved under an inert gas atmosphere in a glovebox to obtain the ODS powder.

(46) Powder characterization: The characterization method is the same as Example 1.

(47) The result shows that a large amount of agglomerated powder with inhomogeneous element distribution appears in the mechanical alloyed powder, and even some non-alloyed powder appears.

(48) The result shows that the volume of strengthening phases with a size of less than 50 nm in the powder accounts for about 20% of the total volume of strengthening phases of the alloy powder.

Example 3

(49) The ODS iron-based alloy powder prepared in Example 1 was sequentially subjected to hot extrusion, hot rolling and heat treatment to prepare a multi-scale and multi-phase dispersion-strengthened iron-based alloy.

(50) Alloy Bulk Preparation:

(51) Step 1: The above ODS iron-based alloy powder prepared in Example 1 was filled into a pure-iron can, and vacuumed to 0.1 Pa or less. The gas pipe was seal welded. Hot extrusion was conducted 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-electrode cutting to obtain as-extruded ODS iron-based alloy.

(52) Step 2: The as-extruded ODS iron-based alloy was hot rolled at a temperature of 850° C., and a total deformation of 80%.

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

(54) The tensile strength of the alloy was 1680 MPa at room temperature and 620 MPa at 700° C., and the elongation was 10.85% at room temperature.

(55) The inventor has also tried experiments using other sizes combinations of milling ball; however, mechanical properties of all products obtained by sequentially conducting hot extrusion, hot rolling and heat treatment of the fabricated powder (condition parameters are the same as those in Example 3) are obviously lower than that of Example 3.

Example 4

(56) The ODS iron-based alloy powder prepared in Example 2 was sequentially subjected to hot extrusion, hot rolling and heat treatment to prepare a multi-scale and multi-phase dispersion-strengthened iron-based alloy.

(57) Alloy Bulk Preparation:

(58) Step 1: The above ODS iron-based alloy powder prepared in Example 2 was filled into a pure-iron can, and vacuumed to 0.1 Pa or less. The gas pipe was seal welded. Hot extrusion was conducted 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-electrode cutting to obtain as-extruded ODS iron-based alloy.

(59) Step 2: The as-extruded ODS iron-based alloy was hot rolled at a temperature of 950° C., and a total deformation of 90%.

(60) 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 room temperature, to obtain a multi-scale and multi-phase dispersion-strengthened iron-based alloy.

(61) The tensile strength of the alloy was 1620 MPa at room temperature, and 605 MPa at 700° C., and the elongation was 10.13% at room temperature.

Comparative Example 2

(62) The other conditions in Comparative Example 2 were the same as those in Example 2, except that milling balls with diameters of 20 mm, 10 mm and 5 mm were matched according to a mass ratio of 1:1:1, to obtain iron-based alloy powder.

(63) Alloy Bulk Preparation:

(64) Step 1: The above ODS iron-based alloy powder prepared in Comparative Example 2 was filled into a pure-iron can, and vacuumed to 0.1 Pa or less. The gas pipe was seal welded. Hot extrusion was conducted 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-electrode cutting to obtain as-extruded ODS iron-based alloy.

(65) Step 2: The as-extruded ODS iron-based alloy was hot rolled to obtain a hot-rolled ODS iron-based alloy at a temperature of 950° C., a rolling speed of 0.36 m/s, and a total deformation of 80%.

(66) 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 room temperature, to obtain a multi-scale and multi-phase dispersion-strengthened iron-based alloy.

(67) The size of strengthening phases of the alloy was 0.8-5 μm, the tensile strength was 1025 MPa at room temperature and 367 MPa at 700° C., and the elongation was 5.10% at room temperature.