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Preparation and thermal stability of VNbMoTaWCo-nitride diffusion barrier layer

Li Rongbin, Zhang Xia, Jiang Chunxia

Heat Treatment of Metals 2022, 47 (6): 196-201. doi:10.13251/j.issn.0254-6051.2022.06.037

Abstract （105）

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VNbMoTaWCoN_x films (x=N₂ flow rate) were prepared by DC magnetron sputtering in different N₂ flow parameter. At N₂ flow ratio of 20%, a Cu/VNbMoTaWCoN₂₀/Si triple-layer stack structure was prepared by depositing a 15 nm thick VNbMoTaWCoN₂₀ film on the cleaned silicon substrate and depositing a 50 nm thick Cu film on the top. The sheet resistance, phase structure, roughness and surface morphology of the Cu/VNbMoTaWCoN₂₀/Si structure samples before and after annealing at 500 ℃ were analyzed and characterized by four probe resistance tester (FPP), X-ray diffractometer (XRD), atomic force microscope (AFM), field emission scanning electron microscope (SEM), and then the thermal stability and diffusion barrier properties of the VNbMoTaWCoN₂₀ film were studied. The results indicate that when the N₂ flow ratio is 20%, the VNbMoTaWCoN₂₀ film before annealing is amorphous with some locally dispersed nanocrystals, and with flat and smooth film surface, with the best density and the smallest roughness. After the Cu/VNbMoTaWCoN₂₀/Si triple-layer stack structure is annealed at 500 ℃ for 8 h, though agglomeration occurs on the surface of the Cu film, but no Cu-Si compound is found, and the sheet resistance of the film is still maintained at a low value 0.065 Ω/sq. The amorphous structured VNbMoTaWCoN₂₀ film as diffusion barrier layer annealed at 500 ℃ for 8 h showes excellent thermal stability and diffusion barrier properties.

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Development of QPQ technology in China

Luo Defu

Heat Treatment of Metals 2022, 47 (7): 227-233. doi:10.13251/j.issn.0254-6051.2022.07.039

Abstract （103）

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In response to the call of the country to improve the green low-carbon circular development economic system, the development of QPQ technology in China was reviewed, and the current situation of China's QPQ technology in the direction of green and low-carbon was introduced. Futhermore, the development direction of green QPQ technology is prospected and some suggestions are put forward.

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Effect of zinc coating weight on its growth law

Ma Shalong, Ding Wenhong, Fang Yu, Lu Xiaoxuan, Hu Ying

Heat Treatment of Metals 2022, 47 (10): 246-250. doi:10.13251/j.issn.0254-6051.2022.10.042

Abstract （99）

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Microstructure and phase distribution of the galvanized layer under different zinc coating weight were analyzed by means of scanning electron microscopy (SEM) and energy spectrum analyzer (EDS). The results show that when the zinc coating weight is 80 and 120 g/m², the δ phase is fence-like, and the ζ phase changes from loose to dense, when the zinc coating weight is 275 g/m², the δ phase is dense and the ζ phase is loose. Among the three types of zinc coating weight, the thickness of the δ phase accounts for the least proportion of the total thickness, and the thickness of each phase is proportional to the zinc coating weight. When the zinc coating weight is less, the surface of galvanized layer is loose and porous, with grooves similar to grain boundaries. With the increase of the zinc coating weight, the surface of galvanized layer becomes dense and flat, and the depth of the grooves becomes significantly shallower and less. Therefore, the zinc coating weight affects its microstructure, which in turn affects the zinc-iron alloy phase structure.

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Research of impact of shot peening on stainless steel surface

Zhang Junshuang, Liu Fengling, Tang Tao, Chen Long, Lan Wei

Heat Treatment of Metals 2022, 47 (6): 232-239. doi:10.13251/j.issn.0254-6051.2022.06.042

Abstract （93）

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Surface hardness, magnetic properties and residual stress of stainless steel were analyzed from the shot peening strengthening method, and the influence of shot peening parameters on stainless steel materials was reviewed, the mechanism of shot peening is revealed, and the effect of shot peening on the residual stress in stainless steel was analyzed. The relationships between material properties and hardness, and the effects of shot peening time and shot size on the surface properties of stainless steel are introduced in detail, and the development direction of shot peening on stainless steel surfaces treatment is prospected.

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Microstructure and properties of CrAlSiN coating deposited on TC4 titanium alloy

Wu Yiruo, Xie Feng, Zhang Yuexia, Zhang Yujun, Liu Manhong, Hu Hanjie, Chen Quanlong, Zhou Zhiming

Heat Treatment of Metals 2022, 47 (6): 202-207. doi:10.13251/j.issn.0254-6051.2022.06.038

Abstract （87）

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In order to improve surface hardness and wear resistance of TC4 titanium alloy, the surface modification on the alloy was carried out by a combination of plasma nitriding and multi-arc ion plating technology. Microstructure, hardness, wear resistance and corrosion resistance of the TC4 titanium alloy, nitrided layer and CrAlSiN coating were studied by means of scanning electron microscopy, Vickers microhardness tester, three-position profiler, high-speed reciprocating friction and wear tester and electrochemical workstation. The results show that after nitriding treatment, surface hardness of the TC4 alloy is increased by about 2 times. The average hardness of the CrAlSiN coating prepared on this basis is as high as 3222 HV0.025, and there are a few large particles and pits on the coating surface. The average friction coefficient of the CrAlSiN coating is 0.22, and the wear mechanism is mainly adhesive wear. The material of the grinding pair adheres to the surface of the coating, and the coating is almost wear-free, and the wear resistance is significantly improved. The self-corrosion potential of the CrAlSiN coating is -0.542 V, which is 0.205 V higher than that of the TC4 titanium alloy substrate (-0.747 V), indicating that the electrochemical corrosion resistance of the CrAlSiN coating deposited on the basis of nitrided layer is significantly improved.

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Microstructure evolution after carburizing and quenching of 16MnCr5 steel high power diesel engine camshaft

Fang Guoliang, Wang Maolin

Heat Treatment of Metals 2022, 47 (7): 269-271. doi:10.13251/j.issn.0254-6051.2022.07.046

Abstract （87）

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Microstructure and hardness along the radial direction of the 16MnCr5 low carbon alloy steel camshaft after carburizing and quenching and low temperature tempering process were studied by means of OM, SEM, XRD and hardness test. The results show that the 940 ℃ carburazing period is suitable for 16MnCr5 steel. Microstructure of the camshaft changes significantly along the radial direction, as the surface structure is high-carbon acicular martensite and 10% retained austenite with hardness reaching 750 HV and effective hardened layer depth of above 1.5 mm, and the matrix structure is a mixed structure of bainite and low carbon martensite.

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Progress in laser cladding of cobalt-based alloys and prospects for their application in nuclear field

Ren Weize, Duan Xuxing, Pei Zeyu, Chen Qing, Zhao Zirui

Heat Treatment of Metals 2024, 49 (4): 264-273. doi:10.13251/j.issn.0254-6051.2024.04.042

Abstract （87）

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Laser cladding is an advanced surface modification technology with the advantages of small deformation, low dilution rate and high bonding strength between cladding layer and base material. Cobalt-based alloys have excellent wear resistance, corrosion resistance, high temperature resistance and other characteristics. Cobalt-based alloy cladding prepared by laser cladding technology can improve the working performance and service life of parts in special service environments (high temperature, high pressure, strong radiation). In addition, the laser cladding cobalt-based alloy technology has been highly concerned by experts and scholars at home and abroad, and widely used in nuclear industry, rail transportation, hydropower and other fields. The present paper analyzes the current research status of the laser cladding cobalt-based alloy technology at home and abroad, and summarizes the research results on the cobalt-based alloy material system, process parameters, performance research and industrial applications. Finally, an outlook for the application of laser cladding cobalt-based alloy technology in the nuclear field is given.

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Effect of thermal spraying process on properties of NiCrFeAl/hBN composite coating

Zhou Zimin, Xiong Shengjian, Chen Haohui, Li Zhang, Wang Changliang, Guo Mengqiu, Cui Xiufang, Jin Guo

Heat Treatment of Metals 2022, 47 (6): 208-215. doi:10.13251/j.issn.0254-6051.2022.06.039

Abstract （85）

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In order to improve the mechanical properties of oxyacetylene flame sprayed NiCrFeAl/hBN composite coating, L₉(3⁴) orthogonal test method was used and taking the surface Rockwell hardness and bonding strength as the main judgment indexes, the influence order of the three main parameters (oxygen-fuel ratio, spraying speed, spraying spacing) of oxyacetylene flame spraying were analyzed, and the performance of the coating prepared by the optimal process was verified. The results show that the spraying spacing is the main factor affecting the performance of the coating, and the optimal process parameters are O₂/C₂H₂ of 26/20, spraying speed of 600 mm/s, spraying spacing of 12 mm, which lead to more uniform internal structure of the coating, better melting bonding, smooth surface, less unmelted particles, and the average bonding strength of the coating is up to 10.3 MPa, the average surface Rockwell hardness is 54.9 HR15Y.

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Microstructure and high temperature oxidation resistance of Cr-coated Zr-4 alloy prepared by magnetron sputtering and multi-arc ion plating

Zou Yang, Liu Shihong

Heat Treatment of Metals 2022, 47 (7): 245-252. doi:10.13251/j.issn.0254-6051.2022.07.042

Abstract （84）

PDF （640KB）（38）

In order to compare the microstructure and high temperature oxidation resistance of Cr-coated Zr-4 alloy prepared by magnetron sputtering and multi-arc ion plating, Cr-coated Zr-4 alloy were prepared by DC magnetron sputtering and multi-arc ion plating, respectively. And the high temperature oxidation resistance was studied in air atmosphere. The results show that the Cr-coated Zr-4 alloy specimen prepared by magnetron sputtering has smooth surface, and the Cr coating grows preferentially along the (211) crystal plane, while there are a lot of droplets on the surface of the Cr-coated Zr-4 alloy specimen prepared by multi-arc ion plating, and the Cr coating grows preferentially along the (110) crystal plane. The results of high-temperature oxidation experiments show that the oxidation mass gain of the Cr-coated Zr-4 alloy specimen prepared by magnetron sputtering is about half of that of the multi-arc ion plating. The oxidized microstructure shows that the specimen prepared by magnetron sputtering still has a residual Cr coating with a thickness of about 4 μm, and the O atoms only diffuse to a distance of about 8 μm from the surface, while the Cr coating of the specimen prepared by multi-arc ion plating was completely oxidized, and a large number of O atoms diffused into the Zr-4 alloy matrix at a depth of about 1 mm from the surface of the specimen. Therefore, the Cr-coated Zr-4 alloy prepared by magnetron sputtering has better high temperature oxidation resistance.

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Effect of heat treatment on microstructure and properties of coatings on GCr15 bearing steel prepared by flame spraying+induction remelting technology

Zhang Xi, Zhang Haoran, Xie Fang, Yan Jisen, Wu Bingbing, Kong Fanxiao

Heat Treatment of Metals 2023, 48 (8): 242-247. doi:10.13251/j.issn.0254-6051.2023.08.039

Abstract （81）

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Using Ni-Cr borosilicon powder (HG-201) as coating material, coatings on surface of GCr15 bearing steel were prepared by flame spraying+induction remelting composite melt coating technology, and then heat treated by different processes. Effects of different heat treatments on the microstructure, interface morphology, microhardness, impact property and impact fracture morphology of the coatings were studied by means of SEM, OM, microhardness test and impact test. The results show that the composite melt coating can refine the grain and improve the microhardness and impact property of GCr15 steel. The average impact absorbed energy of composite melt coated GCr15 steel is improved by 335.85% compared with that of conventional quenched GCr15 steel. After austempering or austempering+tempering treatment, the retained austenite and internal stress in the composite melt coated GCr15 steel are further eliminated, but the microhardness and impact property are slightly decreased, and the impact fracture of coatings shows the fracture mode of facet quasi-cleavage.

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Effect of scanning speed on microstructure and properties of 316L stainless steel coatings by high-speed laser cladding

He Wei, Wang Yanyan, Shu Linsen

Heat Treatment of Metals 2023, 48 (8): 248-253. doi:10.13251/j.issn.0254-6051.2023.08.040

Abstract （81）

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316L stainless steel coating was prepared on 27SiMn steel substrate by high-speed laser cladding technology, the surface morphology, microstructure, microhardness and friction and wear properties of the clad coating were tested and analyzed. The effect of scanning speed on microstructure and properties of high-speed laser clad coating was studied. The results show that, when the scanning speed is 75 mm/s, the coating quality and metallurgical combination effect is the best. The coating microstructure is uniform, the joint is dominated by cellular crystals, and the middle and upper part is dominated by columnar crystals and equiaxed dendrites without secondary crystal arms, with the increase of scanning speed, the grain is obviously refined. When the scanning speed is 105 mm/s, compared with the coating at scanning speed of 45 mm/s, the microhardness increases from 210.4 HV0.5 to 391.5 HV0.5, which increases by 1.87 times. The friction coefficient of the coating is 0.521, and the wear loss is 2 mg. Therefore, the macroscopic properties of the coating can be significantly improved with the increase of scanning speed, and the microhardness and wear resistance of the coating can be improved by the fine grain strengthening at high scanning speed.

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Effect of surface quenching process on hardened layer of 42CrMo steel for large bearing ring

Wei Shitong, Wu Changjiang, Zheng Leigang, Hu Xiaoqiang, Lu Shanping

Heat Treatment of Metals 2022, 47 (10): 218-223. doi:10.13251/j.issn.0254-6051.2022.10.037

Abstract （80）

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42CrMo medium carbon bearing steel was surface quenched with different temperatures and quenching mediums. Then the microstructure and hardness of different regions of the quenched specimens were tested and analyzed by means of Rockwell hardness tester, metallographic microscope, scanning electron microscope and transmission electron microscope. The results show that after surface quenching treatment, according to the hardness from large to small, the specimen can be divided into three different regions: hardened zone, transition zone and base material. The depth of surface hardened layer increases with the increase of surface quenching heating temperature, and that of oil quenching is significantly reduced compared with that of water quenching. Microstructure analysis shows that the microstructure in the water quenching hardened zones are all martensite, while the oil quenching has a slow cooling rate, which causes that the hardened zone is martensitic+ferrite. The transition zones under different surface quenching conditions are all martensite+tempering sorbite. Furthermore, the base material is the tempered sorbite in the original quenched and tempered state. Differences in the microstructure of hardened zone, transition zone and base material leads to differences in hardness in different regions. In practical applications, appropriate heating temperature for water quenching should be selected according to the required depth of the hardened layer.

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Properties of rare earth modified Fe-based composite coating on Cr12MoV steel surface by laser cladding

Dong Xiaochuan, Pan Gaofeng, Li Yang, Wu Runmou, Zhou Zheng, Zhang Xiaoyan

Heat Treatment of Metals 2022, 47 (7): 234-240. doi:10.13251/j.issn.0254-6051.2022.07.040

Abstract （78）

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CMC PMagic2L coating was prepared on the Cr12MoV steel surface by laser cladding technology, and the modified Fe-base composite coating was formed by adding rare earth oxide CeO₂. The effect of adding rare earth oxide CeO₂ on microstructure and properties of the coating was studied by means of optical microscope, scanning electron microscope, microhardness tester and friction and wear testing machine. The results show that CeO₂ can improve the grain refinement of clad layer and enlarge the width of heat affected zone. The hardness of clad layer increases with the increase of CeO₂ content. Compared with the coating without CeO₂, although the thickness of the heat affected zone increases, but the average hardness of the clad layer in modified Fe-based composite coating with 1%CeO₂ increases by 22.1%, the wear resistance is also significantly improved, and the wear volume is reduced by 43.66%. The clad layer has compact structure, which can effectively achieve the purpose of surface strengthening of the die.

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Tribological properties of plasma-sprayed boron nitride nanoplatelet reinforced Ni₃Al composite coating

Lou Xuyao, Zhou Bo, Song Ying, Lu Xiaolong

Heat Treatment of Metals 2022, 47 (8): 266-270. doi:10.13251/j.issn.0254-6051.2022.08.044

Abstract （76）

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Boron nitride nanoplatelet (BNNP) reinforced Ni₃Al composite coatings were fabricated by using plasma spray. The results show that the main phases of the coating contain in-situ synthesized Ni₃Al and trace amounts of Al₂O₃. Compared with monolithic Ni₃Al coating, the BNNP/Ni₃Al composite coating displays a good combination of improved wear resistance and relatively low coefficient of friction, especially the wear resistance of the composite is increased up to 1.5 times. The addition of BNNPs induces a change of the dominant wear mechanisms from brittle fracture and three-body abrasive wear associated with the monolithic Ni₃Al coating to mild abrasive wear along with the BNNP/Ni₃Al composite coating. Furthermore, the formation of BNNP tribolayer on the worn surface of the composite coating not only contributes to the self-lubrication function but also significantly suppresses contact damage of both the composite coating and its counterpart.

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Effect of pulsed bias duty ratio on structure and properties of TiSiN film

Wei Yongqiang, Gu Yanyang, Zhao Zhongqing, Jiang Zhiqiang

Heat Treatment of Metals 2022, 47 (8): 279-286. doi:10.13251/j.issn.0254-6051.2022.08.046

Abstract （75）

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Arc ion plating method was used to deposit TiSiN films on M2 high-speed steel(M2 HSS) and Si wafer substrates by changing the pulsed bias duty ratio. Effect of pulsed bias duty ratio on morphology, element composition, phase structure, nano-hardness and corrosion resistance of the TiSiN films was studied. The results show that when the pulsed bias duty ratio is 30%, the number of macroparticles on the surface of the TiSiN film reaches a maximum of 832, and when the duty ratio is 60%, the number of macroparticles decreases to 451. With the increases of pulsed bias duty ratio from 20% to 50%, the film thickness on the surface of the Si specimen increases from 390.8 nm to 2.339 μm. When the duty ratio is 30%, the content of Si element in the film is up to 13.88at%, the (220) crystal plane is the preferred orientation, the grain size reaches the minimum value of 5.05 nm, the hardness reaches 28.34 GPa, and the self-corrosion current density reaches the minimum value of 0.5306 μA/cm². When the duty ratio is 40%, the (111) crystal plane is the preferred orientation, the content of Si element is reduced to the minimum value of 0.46at%. When the duty ratio is 50%, the grain size of the (111) crystal plane reaches 13.22 nm, the hardness reaches the maximum value of 42.08 GPa, and the self-corrosion potential reaches the maximum value of -0.324 V (vs SCE). When the duty ratio is more than 40%, the number of macroparticle defects and the Si content in the TiSiN film are reduced. Meanwhile the preferred orientation of grain growth of the TiSiN film changes from (220) to (111), and the hardness and corrosion resistance of the TiSiN films are improved.

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Analysis of cracks in laser clad Fe-based amorphous alloy coating

Ouyang Changyao, Bai Qiaofeng, Han Binhui, Yan Xianguo

Heat Treatment of Metals 2022, 47 (5): 252-256. doi:10.13251/j.issn.0254-6051.2022.05.044

Abstract （75）

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Cracks occurred when Fe-based amorphous alloy coating was cladding on the surface of 304 stainless steel substrate by using laser cladding technology. The crack forming mechanism was studied by means of qualitative analysis of the elements, hardness and precipitates around the cracks. The results show that the coating mainly contains α-Fe, α-Cr, carbides (M₇C₃, M₅C₂), silicides (CrSi₂, FeSi) and other phases. The cracks are mainly caused by the large thermal stress in the heat-affected zone and the high melting point and high hardness carbon silicide formed by the segregation of C and Si elements. The structure near the crack zone is relatively loose and there are more gaps and pores. At the same time, the combination of the hard phase is not strong, so that the hardness near the crack zone is lower than that of other defect-free areas at the same level.

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Microstructure and properties of electro-spark deposited Invar/amorphous composite coatings

He Yanling, Wang Yanfang, Si Jiajia, Shi Zhiqiang

Heat Treatment of Metals 2022, 47 (11): 238-244. doi:10.13251/j.issn.0254-6051.2022.11.041

Abstract （74）

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Invar, Invar/amorphous and Invar/amorphous/Invar coatings were deposited on the 45Mn2 steel surface by electro-spark deposition technique using invar alloy electrode and pre-put Fe-based amorphous powders. The phase composition, microstructure, tribology behavior and electrochemical corrosion behavior in 3.5%NaCl solution of the deposited coatings were analyzed. The results show that the prepared coatings are continuous and uniform with a metallurgical bonding to the substrate. A 60 μm crack-free Invar/amorphous/Invar coating is obtained by an Invar bond layer produced on the substrate firstly. The Invar deposited coating is mainly consisted of FCC Fe-Ni solid solution, the Invar/amorphous and Invar/amorphous/Invar coatings are amorphous/solid composite structure. The average microhardness and friction coefficient of the Invar, Invar/amorphous and Invar/amorphous/Invar coatings are 176.6, 757.7, 772.8 HV0.1 and 0.44, 0.21, 0.19, respectively. Increasing the amorphous content of the deposited coating can improve the hardness, reduce the friction coefficient and improve the wear resistance. No obvious passivation phenomenon of the deposition coatings in 3.5% NaCl solution can be observed. The self-corrosion potential, self-corrosion current density of the substrate, Invar, Invar/amorphous and Invar/amorphous/Invar coatings are -0.74, -0.54, -0.34, -0.31 V and 7.08, 5.15, 3.78, 3.11 μA·cm^-2, respectively. The Invar/amorphous/Invar coating prepared by electro-spark deposition technology can effectively improve the wear resistance and corrosion resistance of the 45Mn2 steel substrate.

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Single-track forming control method for in-situ synthesis of WC by laser cladding

Xiao Shihong, Lian Guofu, Huang Xu, Feng Meiyan

Heat Treatment of Metals 2022, 47 (6): 222-231. doi:10.13251/j.issn.0254-6051.2022.06.041

Abstract （73）

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Central composite design of response surface method was adopted to establish a mathematical model between the laser power, scanning speed, gas flow rate, WC powder ratio and the width, height, and cross-sectional area of the clad layer. The validity of the mathematical model was established by the analysis of variance and model verification. The clad width is proportional to the laser power, but inversely proportional to the scanning speed, gas flow rate and powder ratio. The clad height and cross-sectional area is proportinal to the laser power, but inversely proportional to the rising of scanning speed and powder ratio. Finally, the process parameters were optimized with the target of maximizing the clad width and cross-sectional area and minimizing the height. An experimental validation indicates that the error rates between the predicted and actual values for the clad width, height and cross-sectional area are 9.439%, 5.153% and 4.835%, respectively. The average error rate is less than 6.5%, further verifying the accuracy of the established model. The research results provide a theoretical reference for the prediction, control and optimization of process parameters of the forming quality of in-situ synthesis WC by laser cladding.

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Influence of thermal barrier coatings on multiaxial thermo-mechanical fatigue properties of single crystal superalloy

Gao Dong, Qian Lingyi, Guo Yunshan, Huang Aihua

Heat Treatment of Metals 2022, 47 (6): 216-221. doi:10.13251/j.issn.0254-6051.2022.06.040

Abstract （72）

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Y₂O₃(7%-8%, mass fraction)-ZrO₂ thermal barrier coatings were deposited on the surface of CMSX-4 single crystal alloy hollow test tube by electron beam physical vapor deposition process, then thermo-mechanical fatigue (TMF) and thermal gradient mechanical fatigue (TGMF) tests of the tube with/without coatings were investigated at 500-1000 ℃ under mechanical strain control. The results indicate that the thermal barrier coatings can improve the fatigue life of the single crystal alloy to a certain extent, and the fatigue life of the in-plane (IP) coated specimens is slightly higher than that of the out-plane (OP) coated specimens at the same strain amplitude. Furthermore, the fracture analysis results indicate that there is significant difference in the fatigue fracture between the IP-TMF coated specimens and the OP-TMF coated specimens. Obvious fatigue striation can be observed on the fracture surface of the OP-TMF coated specimens, and creep and oxidation have little effect on the fracture, while the fracture of the IP-TMF coated specimens is obviously related to the creep and oxidation of the material.

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Effect of gas nitriding on oxidation behavior of F92 steel in air at 700 ℃

Wang Bo, Huang Yijun, Xiong Dingbiao, Zhao Weiwei, Lou Yumin, Zhao Ningning

Heat Treatment of Metals 2022, 47 (6): 240-248. doi:10.13251/j.issn.0254-6051.2022.06.043

Abstract （70）

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High temperature oxidation behavior of as-delivered and nitrited F92 steel was studied in static air at 700 ℃ by using scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and the influence of gas nitriding on oxidation behavior of the F92 steel was elucidated. The results show that an expanded ferrite phase supersaturated with nitrogen and CrN phase are formed on the surface of the nitrided specimen. Thin and dense (Cr, Fe, Mn)₂O₃ and MnCr₂O₄ oxide layers are formed on the surface of the as-delivered F92 steel with good protection. In addition, there are two kinds of nodular oxides on the surface of as-received F92 steel, one is composed of continuous Fe₂O₃, and the other is independent composed of outer Fe₂O₃ and inner Cr-rich (Cr, Fe, Mn)₃O₄. Nitriding aggravates the oxidation of F92 steel, and an internal oxidation zone is observed inside the matrix. The oxide film on the surface of the nitrided specimen has a double-layer structure, in which the outer layer is Fe₂O₃ and the inner layer is Cr-rich Fe-Cr oxide. The expanded nitrogen supersaturated ferrite phase and CrN phase formed during the nitriding process of F92 steel and the CrN precipitation phase precipitated during the oxidation process reduce the activity of chromium and hinder the formation of protective chromium-rich oxides, resulting in a decrease of antioxidant property.

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