METHOD FOR IMPROVING CORROSION RESISTANCE OF NEODYMIUM-IRON-BORON MATERIALS BY LOW-TEMPERATURE OXIDATION AND/OR NITRIDATION TREATMENT

Abstract

A method for improving the corrosion resistance of NdFeB materials is provided. The method includes in-situ growing a layer of oxide, nitride, or oxynitride on the surface of NdFeB magnet correspondingly by performing at least one of an oxidation treatment and a nitridation treatment at low temperature in a range of 200˜400° C., thereby significantly improving the corrosion resistance of the magnet. The method is simple to operate, low-cost, green, safe, and efficient. Depending on the parameters of the low-temperature oxidation and/or nitridation treatment, the thickness of the oxide, nitride, or oxynitride layer is adjustable from 10 nm to 100 μm, which can improve the corrosion resistance of the magnet while maintaining excellent magnetic properties. Moreover, the thin surface layer is in-situ grown on the NdFeB substrate, which is strong and stable over a long service period and can be applied for mass production.

Claims

1. A method for improving corrosion resistance of neodymium-iron-boron (NdFeB) materials, comprising: in-situ growing at least one selected from a group consisting of an oxide layer, a nitride layer and an oxynitride layer on a surface of a NdFeB magnet by correspondingly performing at least one of low-temperature oxidation treatment and low-temperature nitridation treatment.

2. The method according to claim 1, wherein the performing at least one of the low-temperature oxidation treatment and the low-temperature nitridation treatment comprises: vacuumizing to 10.sup.2˜10.sup.4 pascals (Pa) in a tube furnace or an atmosphere furnace, then introducing gas with a flow rate in a range of 15˜5000 milliliters per minute (mL/min); wherein the gas is at least one selected a group consisting of oxygen (O.sub.2), nitrogen (N.sub.2), ammonia gas (NH.sub.3) and water vapor, a temperature of the at least one of the low-temperature oxidation treatment and the low-temperature nitridation treatment is controlled in a range of 200˜400 degrees Celsius (° C.), and a reaction time is controlled in a range of 0.5˜24 hours.

3. The method according to claim 1, wherein a thickness of the at least one selected from the group consisting of the oxide, the nitride and the oxynitride layer is adjustable in a range from 10 nanometers (nm) to 100 micrometers (μm).

4. The method according to claim 1, wherein components of the NdFeB magnet, in atomic percent, are (RE.sub.aRE′.sub.1-a).sub.x(Fe.sub.bM.sub.1-b).sub.100-xy-z, where RE is at least one of lanthanide elements except lanthanum (La), cerium (Ce) and yttrium (Y); RE′ is at least one selected from a group consisting of La, Ce and Y; Fe is iron; M is one or two of cobalt (Co) and nickel (Ni); M′ is at least one selected from a group consisting of niobium (Nb), zirconium (Zr), tantalum (Ta), vanadium (V), aluminum (Al), copper (Cu), gallium (Ga), titanium (Ti), chromium (Cr), molybdenum (Mo), manganese (Mn), argentum (Ag), aurum (Au), plumbum (Pb) and silicon (Si); B is boron; and a, b, x, y, and z respectively satisfy conditions comprising: 0.55≤a≤1, 0.8≤b≤1, 12≤x≤18, 0≤y≤2, and 5.5≤z≤6.5.

5. A method for improving corrosion resistance of neodymium-iron-boron (NdFeB) materials, comprising: in-situ growing at least one selected from a group consisting of an oxide layer, a nitride layer and an oxynitride layer on a surface of a NdFeB magnet at a low-temperature in a range of 200˜400 degrees Celsius (° C.) by correspondingly performing at least one of an oxidation treatment and a nitridation treatment; wherein components of the NdFeB magnet, in atomic percent, are (RE.sub.aRE′.sub.1-a).sub.x(Fe.sub.bM.sub.1-b).sub.100-xy-zM′.sub.yB.sub.z, where RE is at least one of lanthanide elements except lanthanum (La), cerium (Ce) and yttrium (Y); RE′ is at least one selected from a group consisting of La, Ce and Y; Fe is iron; M is one or two of cobalt (Co) and nickel (Ni); M′ is at least one selected from a group consisting of niobium (Nb), zirconium (Zr), tantalum (Ta), vanadium (V), aluminum (Al), copper (Cu), gallium (Ga), titanium (Ti), chromium (Cr), molybdenum (Mo), manganese (Mn), argentum (Ag), aurum (Au), plumbum (Pb) and silicon (Si); B is boron; and a, b, x, y, and z respectively satisfy conditions comprising: 0.55≤a≤1, 0.8≤b≤1, 12≤x≤18, 0≤y≤2, and 5.5≤z≤6.5.

Description

DETAILED DESCRIPTION OF EMBODIMENTS

[0015] The disclosure is further described below in relation to specific embodiments, but the disclosure is not limited to the following embodiments.

Embodiment 1

[0016] Components of neodymium-iron-boron (NdFeB) magnet, in terms of atomic percent, are (Pr.sub.0.2Nd.sub.0.8).sub.14Fe.sub.78.95(Cu.sub.0.5Al.sub.02Ga.sub.0.2Zr.sub.0.1).sub.1B.sub.0.65. After vacuumizing to 2×10.sup.−2Pascals (Pa) in a tube furnace, oxygen (O.sub.2) is introduced with a flow rate of 800 milliliters per minute (mL/min), a temperature of low-temperature oxidation is controlled at 350 degrees Celsius (° C.), and a reaction time is controlled at 3 hours. A thickness of an oxide thin layer in-situ grown on the magnet surface is 1 micrometer (μm). Test results of AMT-4 permanent magnet characteristic measuring instrument show that the remanence of the magnet after surface oxidation treatment is 14.0 kilogauss (kG) and the coercivity is 14.8 kilo-oersted (kOe). Test results of AMETEK electrochemical workstation show that corrosion current of the magnet in 3.5% sodium chloride (NaCl) solution after surface oxidation treatment is 5 microamperes per square centimeter (μA/cm.sup.2).

Comparative Embodiment 1

[0017] The difference with the embodiment 1 is that the magnet is not treated with low-temperature oxidation. Test results of AMT-4 permanent magnet characteristic measuring instrument show that the remanence of the magnet is 14.0 kG and the coercivity is 14.9 kOe, which are similar to the embodiment 1. Test results of AMETEK electrochemical workstation show that the corrosion current of the magnet in 3.5% NaCl solution is 70 μA/cm2, which is more than one order of magnitude larger than that of the embodiment 1.

Comparative Embodiment 2

[0018] The difference from the embodiment 1 is that copper (Cu) content is increased and the components of the magnet, in terms of atomic percent, are (Pr.sub.0.2Nd.sub.0.8).sub.14Fe.sub.77.95(Cu.sub.1.5Al.sub.0.2Ga.sub.0.2Zr.sub.0.1).sub.1B.sub.6.05, and the magnet is not treated with low-temperature oxidation. Test results of AMT-4 permanent magnet characteristic measuring instrument show that the remanence of the magnet is 13.6 kG and the coercivity is 11.7 kOe, which are significantly decreased compared to the embodiment 1. Test results of AMETEK electrochemical workstation show that the corrosion current of the magnet in 3.5% NaCl solution is 52 μA/cm.sup.2, which is more than one order of magnitude larger than that of the embodiment 1.

Comparative Embodiment 3

[0019] The difference with the embodiment 1 is that the magnet is not treated with low-temperature oxidation and is performed surface coating treatment with a bright silver-copper-nickel coating with thickness of 10 Test results of AMT-4 permanent magnet characteristic measuring instrument show that the remanence of the magnet is 13.7 kG and the coercivity is 14.2 kOe, which are decreased compared to the embodiment 1. Test results of AMETEK electrochemical workstation show that the corrosion current of the magnet in 3.5% NaCl solution is 10 μA/cm.sup.2, which is larger than that of the embodiment 1.

Embodiment 2

[0020] Components of NdFeB magnet, in terms of atomic percent, are [Nd.sub.0.65(La.sub.0.35Ce.sub.0.65).sub.0.35].sub.16(Fe.sub.0.97Co.sub.0.03).sub.76.15(Ga.sub.0.35Cu.sub.0.2Al.sub.0.2Nb.sub.0.1Zr.sub.0.05).sub.2B.sub.5.85. After vacuumizing to 3×10.sup.−3 Pa in a tube furnace, O.sub.2 is introduced with a flow rate of 200 mL/min, a temperature of low-temperature oxidation is controlled at 300° C., and a reaction time is controlled at 0.5 hours. A thickness of an oxide thin layer in-situ grown on the magnet surface is 200 nanometers (nm). Test results of AMT-4 permanent magnet property measuring instrument show that the remanence of the magnet after surface oxidation treatment is 12.4 kG and the coercivity is 11.1 kOe. Test results of AMETEK electrochemical workstation show that corrosion voltage of the magnet in 3.5% NaCl solution after surface oxidation treatment is −430 millivoltages (mV).

Comparative Embodiment 4

[0021] The difference with the embodiment 2 is that the magnet is not treated with low-temperature oxidation. Test results of AMT-4 permanent magnet characteristic measuring instrument show that the remanence of the magnet is 12.4 kG and the coercivity is 11.2 kOe, which are similar to the embodiment 2. Test results of AMETEK electrochemical workstation show that the corrosion potential of the magnet in 3.5% NaCl solution is −870 mV, which is significantly lower than that of the embodiment 2.

Embodiment 3

[0022] Components of NdFeB magnet, in terms of atomic percent, are (Pr.sub.0.2Nd.sub.0.8).sub.18Fe.sub.75.55(Ga.sub.0.7Al.sub.0.15Zr.sub.0.15).sub.0.55B.sub.5.9. After vacuumizing to 2×10.sup.−4 Pa in an atmosphere furnace, ammonia gas (NH.sub.3) is introduced with a flow rate of 80 mL/min, a temperature of low-temperature nitridation is controlled at 400° C. and a reaction time is controlled at 1 hour. A thickness of a nitride layer in-situ grown on the magnet surface is 300 nm. Test results of AMT-4 permanent magnet characteristic measuring instrument show that the remanence of the magnet after surface nitridation treatment is 13.6 kG and the coercivity is 17.5 kOe. Test results of AMETEK electrochemical workstation show that the corrosion current of the magnet in 3.5% NaCl solution after surface nitridation treatment is 11 μA/cm.sup.2.

Comparative Embodiment 5

[0023] The difference with the embodiment 3 is that the magnet is not treated with low-temperature nitridation. Test results of AMT-4 permanent magnet characteristic measuring instrument show that the remanence of the magnet is 13.5 kG and the coercivity is 17.4 kOe, which are similar to the embodiment 3. Test results of AMETEK electrochemical workstation show that the corrosion current of the magnet in 3.5% NaCl solution is 317 μA/cm.sup.2, which is more than one order of magnitude larger than that of the embodiment 3.

Embodiment 4

[0024] Components of NdFeB magnet, in terms of atomic percent, are [(Pr.sub.0.1Nd.sub.0.9).sub.0.75(Y.sub.0.15Ce.sub.0.85).sub.0.25].sub.15(Fe.sub.0.9Co.sub.0.1).sub.77.4(Cu.sub.0.3Ga.sub.0.15Al.sub.0.25Si.sub.0.2Nb.sub.0.1).sub.1.5B.sub.6.1. After vacuumizing to 1×10.sup.−3 Pa in a tube furnace, a mixture of O.sub.2 and nitrogen (N.sub.2) is introduced with a ratio of 7:3 and a flow rate of 500 mL/min, a temperature of low-temperature oxidation and nitridation is controlled at 350° C. and a reaction time is controlled at 12 hour. A thickness of an oxynitride layer thin layer in-situ grown on the magnet surface is 5 μm. Test results of AMT-4 permanent magnet characteristic measuring instrument show that the remanence of the magnet after surface oxidation and nitridation treatment is 12.6 kG and the coercivity is 13.0 kOe. Test results of AMETEK electrochemical workstation show that corrosion potential of the magnet in 3.5% NaCl solution after surface oxidation and nitridation treatment is −240 mV.

Comparative Embodiment 6

[0025] The difference with the embodiment 4 is that the magnet is not treated with low-temperature oxidation and nitridation treatment. Test results of AMT-4 permanent magnet characteristic measuring instrument show that the remanence of the magnet is 12.6 kG and the coercivity is 13.3 kOe, which are similar to the embodiment 4. Test results of AMETEK electrochemical workstation show that the corrosion voltage of the magnet in 3.5% NaCl solution is −730 mV, which is significantly lower than that of the embodiment 4.