Method for obtaining high-hardness NbTiZrx refractory intermediate entropy alloy coating on surface of zirconium alloy
Technical Field
The invention relates to the technical field of laser surface cladding treatment for processing metal materials, in particular to a method for obtaining high-hardness NbTiZr on the surface of zirconium alloyxA method for preparing a refractory entropy alloy coating.
Background
Zirconium (Zr) and its alloy have the advantages of small neutron absorption cross section, strong corrosion resistance, excellent biocompatibility and the like, and have important structural application in the fields of nuclear industry, chemical industry and biomedicine. Among them, Zr702 is a typical representative of zirconium alloys widely used in commercial applications for forming zirconium cladding for nuclear industry pressurized water reactors. After a nuclear accident of the Japanese Fudao, how to further improve the safety and the reliability of a nuclear fuel element under normal working conditions and accident conditions becomes a difficult problem which needs to be solved urgently. Research shows that the zirconium alloy surface coating can effectively improve the high-temperature resistance and oxidation resistance of the cladding. In addition, the zirconium cladding, the grid plate, cooling water and other components are easy to generate fretting friction wear, so that the mechanical properties of the material, such as strength, toughness and the like, are obviously reduced or even failed, the service life of the material in the reactor is reduced, and the normal operation and safety of the reactor are influenced. Therefore, the method for modifying the zirconium alloy surface coating is applied to improve the performance of the zirconium alloy cladding of the reactor, and is beneficial to improving the safety allowance of the nuclear reactor.
The laser surface cladding technology is a modern surface modification technology, and can obtain a coating with controllable thickness, high quality and good bonding degree with a matrix, thereby obviously changing the surface hardness, wear resistance, corrosion resistance and high-temperature performance of the material. In recent years, the laser surface cladding technology has the advantages of convenient operation, low processing cost and the like, and is also widely concerned and applied by researchers, and the laser surface cladding technology adopts a laser beam with high energy density to rapidly fuse one or more alloy elements and the surface of a base material to form a uniform and compact metallurgical bonding layer, so that the surface properties of metals and alloys are improved.
The high-entropy alloy is a new alloy different from traditional alloy, and is composed of 5 or more than 5The atomic number fraction of each element is between 5 and 35 percent. The high-entropy alloy has excellent properties such as high strength, high plasticity, high fracture toughness at low temperature and thermal stability. Researchers further develop the medium-entropy alloy containing fewer components (2-4 types) and having better comprehensive mechanical properties. Subsequently, refractory high-entropy alloys based on refractory elements have attracted considerable attention for their excellent high-temperature properties. Refractory high entropy alloys are further defined as containing 3 or more refractory elements as the main elements and the atomic number fraction of the elements can be greater than 35%, and have been developed more rapidly. Researches show that the refractory high-entropy alloy has better high-temperature mechanical property, strengthening mechanism, high-temperature oxidation resistance and wear resistance. However, at present, no research on the preparation of the refractory entropy alloy based on the laser cladding process is reported. Therefore, based on the blank of the industry, the invention prepares NbTiZr on the surface of the zirconium alloy by using a laser cladding processxAnd (3) refractory intermediate entropy alloy coating.
Disclosure of Invention
The invention aims to provide a method for obtaining high-hardness NbTiZr on the surface of zirconium alloy, which has simple operation, reliable technology, economy and practicabilityx(x is 1-1.6, wherein x is the molar fraction ratio of Zr to Nb) refractory entropy alloy coating method, and high-hardness single-layer NbTiZr is prepared on the surface of Zr702 alloy by laser surface cladding processxThe refractory entropy alloy coating has excellent performance, and the aims of improving the high-temperature oxidation resistance, the hardness and the friction and wear resistance of the zirconium alloy are fulfilled.
In order to achieve the purpose, the invention provides the following technical scheme:
obtaining high-hardness NbTiZr on surface of zirconium alloyxA method of forming a refractory entropy alloy coating comprising the steps of: (1) workpiece pretreatment: polishing a zirconium alloy workpiece to be bright, cleaning and drying; (2) coating preset treatment: mixing metal powder of Nb and Ti with the same mole fraction into paste by using an organic solvent, coating the paste on the surface of a workpiece, and then drying; (3) the laser surface cladding treatment process comprises the following steps: performing laser surface cladding treatment on the workpiece subjected to coating preset treatment; (4) Taking out the workpiece subjected to laser surface cladding treatment to obtain the workpiece with NbTiZr on the surfacexThe workpiece is coated with the refractory entropy alloy.
In a preferred embodiment of the present invention, the step (1) of pre-treating the workpiece comprises: sequentially selecting 600#, 1200#, 2000# and 3000# sandpaper to polish the sample to be bright; cleaning the sample by absolute ethyl alcohol after polishing; and then drying the surface of the workpiece.
In a preferred embodiment of the present invention, the organic solvent in step (2) is a PVA organic solvent.
In a preferred embodiment of the present invention, the process parameters of the coating pre-treatment in step (2) are as follows: the concentration of the PVA organic solvent is 8-12 wt.%, the preset thickness of the coating is 300-.
In a preferred embodiment of the present invention, in the laser surface cladding treatment in step (3), inert gas is used as shielding gas, and the process parameters of the laser surface cladding treatment are as follows: the laser power is 54-108W, the laser peak value is 1-3KW, the pulse width is 3-6ms, the defocusing amount is 0-4mm, and the scanning speed is 5-10 mm/s.
In a preferred embodiment of the present invention, the inert gas is argon having a purity of 99.9%.
In a preferred scheme of the invention, the technological parameters of laser surface cladding treatment are as follows: the laser power is 72W, the laser peak value is 2KW, the pulse width is 6ms, the defocusing amount is 0mm, and the scanning speed is 6 mm/s.
In a preferred embodiment of the present invention, after the workpiece is taken out in the step (4), the workpiece is provided with NbTiZrxAnd (3) polishing the surface of the workpiece with the refractory intermediate entropy alloy coating to be smooth.
In a preferable scheme of the invention, x is 1-1.6, wherein x is the molar fraction ratio of Zr to Nb, and the surface of the workpiece is NbTiZrxThe thickness of the entropy alloy coating in the refractory is 240-310 mu m.
In a preferred embodiment of the present invention, the zirconium alloy workpiece is Zr 702.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention adjusts the combination of Nb and Ti by selecting proper metals of Nb and TiThe single-layer NbTiZr is successfully obtained on the surface of the Zr702 alloy by adopting the pulse laser surface cladding technology and adjusting the laser cladding proper parameters in proper proportionxAnd (3) refractory intermediate entropy alloy coating. Single-layer NbTiZr with certain thickness prepared on Zr702 alloy surfacexThe refractory intermediate entropy alloy coating is better in metallurgical bonding with a matrix, and NbTiZrxThe refractory mid-entropy alloy coating has a single Body Centered Cubic (BCC) phase and has high hardness. The invention obtains NbTiZr on the surface of the zirconium alloyxThe thickness of the entropy alloy coating in the refractory is about 240-310 mu m, the coating hardness is greatly improved compared with that of the Zr702 alloy, the coating hardness is about 500HV and is about 2.5 times of that of the Zr702 alloy substrate, which shows that the single-layer NbTiZrxThe refractory entropy alloy coating has better friction and wear resistance. The result shows that a single-layer NbTiZr with a certain thickness is prepared on the surface of the Zr702 alloy by the pulse laser surface cladding technologyxThe entropy alloy coating in the refractory can effectively improve the hardness of the surface of the Zr702 alloy.
2. The invention provides a single-layer NbTiZrxThe preparation process of the refractory intermediate entropy alloy coating is convenient to operate, simple in equipment, economical, practical, reliable in technology and stable in quality, and plays a very good role in improving the service performance of the zirconium alloy material.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
FIG. 1 shows the XRD test results of the surface coating and the surface of the zirconium alloy substrate obtained by the present invention.
FIG. 2 shows the results of comparing the surface hardness tests of the zirconium alloy surface coating obtained by the present invention with those of the zirconium alloy substrate.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to be limiting. The operations referred to in the following examples are conventional ones unless otherwise specified.
Example 1
Selecting a prepared 18X 12X 2mm Zr702 plate, and firstly sequentially selecting 600#, 1200#, 2000# and 3000# sandpaper to polish the sample to be bright. And cleaning the sample by using absolute ethyl alcohol after polishing, and finally drying the surface of the sample. Placing a sample with a clean surface on a special carrier, mixing metal powder with NbTi (Nb and Ti have the same mole fraction) into paste by using a PVA organic solvent, coating the paste on the surface of a workpiece, and then placing the workpiece in a drying box for drying, wherein the process parameters of the preset treatment of the coating are as follows: 10 wt% of PVA organic solvent, 500-600 μm of preset coating thickness, 80 ℃ of drying temperature and 8h of drying time.
And clamping the dried sample on a special clamp, putting the special clamp on a working station of a working chamber of pulse laser equipment, and adopting argon with the purity of 99.9 percent as protective gas. And starting pulse laser equipment, loading voltage and carrying out pulse laser surface cladding treatment on the surface of the workpiece. The main parameter ranges of the pulse laser surface cladding treatment are as follows: 54W of laser power, 1.5KW of laser peak value, 6ms of pulse width, 0mm of defocusing amount and 6mm/s of scanning speed.
The XRD test results of the coating after laser treatment are shown in FIG. 1; this example shows NbTiZr prepared at a laser power of 54Wx(x ═ 1) the refractory mid-entropy alloy coating has a single Body Centered Cubic (BCC) phase. In this example, a single layer of NbTiZr obtained on the surface of the zirconium alloyxThe thickness of the entropy alloy coating in the refractory is about 240 mu m.
Example 2
Selecting a prepared 18X 12X 2mm Zr702 plate, and firstly sequentially selecting 600#, 1200#, 2000# and 3000# sandpaper to polish the sample to be bright. And cleaning the sample by using absolute ethyl alcohol after polishing, and finally drying the surface of the sample. Placing a sample with a clean surface on a special carrier, mixing metal powder with NbTi (Nb and Ti have the same mole fraction) into paste by using a PVA organic solvent, coating the paste on the surface of a workpiece, and then placing the workpiece in a drying box for drying, wherein the process parameters of the preset treatment of the coating are as follows: 10 wt% of PVA organic solvent, 500-600 μm of preset coating thickness, 80 ℃ of drying temperature and 8h of drying time.
And clamping the dried sample on a special clamp, putting the special clamp on a working station of a working chamber of pulse laser equipment, and adopting argon with the purity of 99.9 percent as protective gas. And starting pulse laser equipment, loading voltage and carrying out pulse laser surface cladding treatment on the surface of the workpiece. The main parameter ranges of the pulse laser surface cladding treatment are as follows: the laser power is 72W, the laser peak value is 2KW, the pulse width is 6ms, the defocusing amount is 0mm, and the scanning speed is 6 mm/s.
The XRD test results of the coating after laser treatment are shown in FIG. 1; this example shows NbTiZr prepared at a laser power of 72Wx(x ═ 1.1) the refractory mid-entropy alloy coating had a single body-centered cubic (BCC) phase. In this example, a single layer of NbTiZr obtained on the surface of the zirconium alloyxThe thickness of the entropy alloy coating in the refractory is about 260 mu m.
Example 3
Selecting a prepared 18X 12X 2mm Zr702 plate, and firstly sequentially selecting 600#, 1200#, 2000# and 3000# sandpaper to polish the sample to be bright. And cleaning the sample by using absolute ethyl alcohol after polishing, and finally drying the surface of the sample. Placing a sample with a clean surface on a special carrier, mixing metal powder with NbTi (Nb and Ti have the same mole fraction) into paste by using a PVA organic solvent, coating the paste on the surface of a workpiece, and then placing the workpiece in a drying box for drying, wherein the process parameters of the preset treatment of the coating are as follows: 10 wt% of PVA organic solvent, 500-600 μm of preset coating thickness, 80 ℃ of drying temperature and 8h of drying time.
And clamping the dried sample on a special clamp, putting the special clamp on a working station of a working chamber of pulse laser equipment, and adopting argon with the purity of 99.9 percent as protective gas. And starting pulse laser equipment, loading voltage and carrying out pulse laser surface cladding treatment on the surface of the workpiece. The main parameter ranges of the pulse laser surface cladding treatment are as follows: the laser power is 108W, the laser peak value is 3KW, the pulse width is 6ms, the defocusing amount is 0mm, and the scanning speed is 6 mm/s.
The XRD test results of the coating after laser treatment are shown in FIG. 1; this example shows NbTiZr prepared at a laser power of 108Wx(x ═ 1.6) the refractory mid-entropy alloy coating had a single body-centered cubic (BCC) phase. In this example, a single layer of NbTiZr obtained on the surface of the zirconium alloyxOf refractory intermediate entropy alloy coatingsThe thickness is about 310 μm.
Example 4
NbTiZr coated samples prepared in examples 1-3xThe hardness of the coated zirconium alloy workpiece was compared to the uncoated zirconium alloy substrate workpiece.
Measuring microhardness by using a Buehler-Omnimet Vickers hardness tester, wherein the parameters of the Vickers hardness tester are as follows: load 100N, hold load 10 s. Each sample was tested at 12-15 points and averaged.
Tests show that the pulse laser surface cladding of the invention is utilized to prepare single-layer NbTiZr with certain thickness on the surface of the zirconium alloy Zr702xThe entropy alloy coating in the refractory enables the surface of the zirconium alloy Zr702 to have more excellent hardness performance. FIG. 2 is a comparison of hardness tests of Zr702 workpieces with composite coatings prepared in examples 1-3 with uncoated Zr702 base workpieces. As shown in FIG. 2, the surface hardness of the Zr702 workpiece prepared in the example 1 under the laser power of 54W is as high as about 511HV, which is improved by about 2.6 times compared with the hardness (about 198 HV) of the Zr702 substrate; in the embodiment 2, the surface hardness of the Zr702 workpiece prepared under the laser power of 72W is as high as about 540HV, and is improved by about 2.7 times compared with the hardness of a Zr702 substrate; in example 3, the surface hardness of the Zr702 workpiece prepared under the laser power of 108W is as high as about 361HV, and is improved by about 1.8 times compared with the hardness of a Zr702 substrate.
While embodiments of the invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.