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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 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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Laser quenching process optimization and microstructure and properties of H13 steel

Ma Xin, Shi Qiang, Chen Yanzhong, Li Qiang, Zhang Yueting, Zhao Long

Heat Treatment of Metals 2023, 48 (7): 266-270. doi:10.13251/j.issn.0254-6051.2023.07.044

Abstract （68）

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Surface of H13 steel was strengthened by laser quenching, and the quenching process was optimized by range analysis of orthogonal test. The microhardness and friction and wear properties of the specimen under the optimum process parameters were studied, and the phase composition and microstructure of the laser quenching surface were analyzed. The results show that the optimum laser quenching process parameters are laser power of 600 W, scanning speed of 6 mm/s and lapping rate of 20%. Under this optimum process, the average hardness of hardened layer of the H13 steel is 774 HV0.1, which is about 3 times than that of the matrix, the depth of the hardened layer is 0.87 mm, and the friction coefficient and wear amount are about 0.367 and 0.0015 g, which are 50% and 60.5% lower than those of the matrix, respectively. The hardened layer is mainly composed of lath and acicular mixed martensite, retained austenite and a small amount of cementite.

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Microstructure and wear resistance of WC particle reinforced Fe based alloy coating

Gao Wandong

Heat Treatment of Metals 2023, 48 (10): 274-278. doi:10.13251/j.issn.0254-6051.2023.10.042

Abstract （64）

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Plasma melt injection(PMI) was used to prepare WC particles reinforced metal matrix composites layer on the 45 steel. During the PMI process, different voltage parameters were applied. The clad coating were analyzed by optical microscope (OM), scanning electron microscopy (SEM),X-ray diffraction(XRD) and energy dispersive spectrometer(EDS) to study microstructure, phase composition and chemical compositions of the clad coating. And a self-made friction and wear tester was used for wear characteristics analysis. SEM analysis result reveals that the clad coating, being metallurgical bonding with base material, is crack-free, and the WC particles distribute uniformly in the clad coating. In addition, the primary phase of the clad coating contains WC, W₂C, Cr₂₃C₆, Fe₃W₃C, Cr₃C₂ and Cr₇C₃. The maximum hardness of the clad coating is about 1600 HV. The friction and wear test results show that the wear loss of the plasma clad coating with WC reduces by more than 50% compared with that of the Fe based alloy coating. The main mechanism of wear is abrasive wear, with a large number of WC particles hindering micro cutting and exhibiting high wear resistance.

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Microstructure and properties of magnetic field assisted hot dip aluminized coatings on TA15 titanium alloy surface

Li Yong, Wang Qiulin, Men Zhengxing, Zhao Yulin, Zhang Hong

Heat Treatment of Metals 2023, 48 (8): 254-259. doi:10.13251/j.issn.0254-6051.2023.08.041

Abstract （61）

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Microstructure and properties of hot dip aluminized coatings on the surface of TA15 titanium alloy under the action of alternating electromagnetic field were studied, and the thermal diffusion treatment was carried out at 800 ℃. The morphology, microstructure and element distribution of the coatings were analyzed by means of energy dispersive spectroscopy, scanning electron microscope and X-ray diffractometer. The microhardness of the coatings was tested by microhardness tester. The results show that after applying alternating electromagnetic field with current intensity of 15 A and 20 A during the process of hot dip aluminizing and thermal diffusion, the coatings bind well with the alloy substrate, no obvious crack is found, the formation of pores and cavities is significantly reduced, the dipping time is shortened, and thus the production cycle is accelerated. When the current intensity is 15 A and 20 A, the maximum hardness of the bonding zones can reach 518.7 HV0.2. When the current intensity increases to 25 A, the electromagnetic stirring effect sharply increases, and no high-quality coating can be obtained.

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Effect of laser quenching process parameters on microstructure and properties of Cr12MoV steel

Feng Aixin, Zhao Jian, Lin Jinhao

Heat Treatment of Metals 2023, 48 (10): 255-259. doi:10.13251/j.issn.0254-6051.2023.10.039

Abstract （61）

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Effect of laser quenching on microstructure and properties of Cr12MoV steel was studied, and the effects of different laser power (1050, 1200, 1350 W) and scanning speeds (3, 4, 5 mm/s) on microstructure, hardness and residual stresses of the laser quenching surface were analyzed. The results shows that after laser quenching, the surface hardness of the Cr12MoV steel increases obviously, and the surface residual stress changes from tensile stress to compressive stress. When the laser power is 1200 W and the scanning speed is 4 mm/s, the surface macromorphology is flat, the microstructure is refined, the surface microhardness reaches the maximum value of 653.68 HV, and the residual compressive stress reaches -259.29 MPa.

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Effect of CoNiCrAl coating and stress on creep microstructure and elemental diffusion of directionally solidified nickel-based superalloy

Liu Qian, Cao Tieshan, Wang Wei, Chi Qingxin, Cheng Congqian, Zhao Jie

Heat Treatment of Metals 2024, 49 (3): 262-268. doi:10.13251/j.issn.0254-6051.2024.03.043

Abstract （59）

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By designing the specimens with/without CoNiCrAl coatings as stepped ones to exclude other environmental factors, the effect of stress on the creep microstructure and elemental diffusion of DZ411 superalloy at 950 ℃ was studied, and the protective effect of the coating on the specimen was analyzed. The results show that the coating can significantly increase the creep life of the specimen. It is find that the greater the stress in the specimen, the higher the degree of degradation of the γ' phase and the higher the degree of compactness, especially the γ' phase in the high-stress zone is completely rafted, and that in the rest zones shows different degrees of spheroidization. The coating of the coated specimen in the high-stress zone is seriously damaged, while the coating in the low-stress and the non-stress zones only undergo slight oxidation. The degree of oxidation on the surface of the uncoated specimen increases with the increase of stress, though that in the high stress zone is more serious and with defects such as cracks and looseness, while the surface of the low stress position is still kept more complete. In addition, the element diffusion also changes with the stress, and different oxides are formed on the surface of the specimens, among which the Ti element content of the coated specimen gradually decreases from the matrix to the oxide layer surface, and decreases with the decrease of stress, while the Cr element content continues to increase from the surface to the inside and then decreases.

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Effect of ultrasonic surface rolling process on corrosion resistance of 304 stainless steel

Chen Xinjian, Sui Rongjuan, Wang Yanfei, Cheng Yanhai, Gao Linhao

Heat Treatment of Metals 2024, 49 (9): 268-274. doi:10.13251/j.issn.0254-6051.2024.09.045

Abstract （58）

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Effect of ultrasonic surface rolling process (USRP) on the corrosion resistance of 304 stainless steel surface was investigated. The surface morphology, microstructure, residual stress and surface roughness were analyzed by means of scanning electron microscopy, X-ray diffraction analysis, and metal surface roughness meter, respectively. The corrosion resistance and integrity of the oxide film was assessed using electrochemical tests and o-phenanthroline color development experiments. The results indicate that the value of R_a for the 304 stainless steel is reduced from 0.60 μm to 0.28 μm after USRP treatment. The surface grain size is reduced from 23.13 μm to 20.80 nm, and the surface residual stress is changed from 20 MPa to -329 MPa. Compared with the untreated specimen, the minimum corrosion current density I_corr of the USRP treated specimen is 0.94×10^-5 A/cm², which is reduced by 71%. The oxide film resistance R_p is 2.59×10⁶ Ω·cm², increased by 2 times. The range of color rendering value of phenanthroline is narrowed and the color rendering area is decreased, indicating that the surface defects are reduced and the quality of the surface oxide film is improved. For the 304 stainless steel, USRP treatment promotes the grain refinement near the surface layer, produces residual compressive stress, reduces surface defects, denseres oxide film, and then blocks the electrochemical reaction process, and improves the corrosion resistance.

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Electrochemical corrosion behavior of FeCoCrNiMoBSi high-entropy alloy coating prepared by laser cladding

Du Xinyu, Zhai Changsheng, Rong Haisong, Xie Fang, Zheng Hongxing, Zhang Xi, Zhang Xin, Liu Gang

Heat Treatment of Metals 2024, 49 (8): 261-267. doi:10.13251/j.issn.0254-6051.2024.08.044

Abstract （55）

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FeCoCrNiMoBSi high-entropy alloy (HEA) coating was fabricated on the 316L stainless steel substrate via laser cladding. The microstructure, electrochemical corrosion and immersion corrosion properties of the HEA coating in H₂SO₄ solution were investigated. The results show that the laser clad HEA coating exhibits a bilayer structure, consisting of a columnar crystal at the bottom and an equiaxed crystal at the top. In the 0.3 mol/L H₂SO₄ solution, the self-corrosion potential, self-corrosion current density and polarization resistance of the HEA coating are 0.091 V, 11.499 μA/cm² and 9839.90 Ω, which are 2.12 times, 6.17% and 12.2 times, respectively, of the 316L stainless steel substrate. The HEA coating exhibits larger capacitance arc radius and impedance modulus value. Additionally, in the 50% H₂SO₄ solution, the corrosion rate of the HEA coating is lower, approximately 0.098 mg/(dm²·d), 316L stainless steel substrate shows conspicuous heterogeneous corrosion, whereas the corrosion surface of the HEA coating remains uniformly flat, showing homogeneous corrosion rate. The comprehensive results show that the corrosion resistance of the FeCoCrNiMoBSi high-entropy alloy coating on the 316L stainless steel substrate is significantly better than that of the substrate itself.

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Effect of laser shock peening on microstructure and fatigue property of TA15 titanium alloy with double holes

Han Peipei, Zang Xu, Dong Zhi, Li Shijian, Jiao Qingyang, Deng Xiguang

Heat Treatment of Metals 2023, 48 (7): 254-258. doi:10.13251/j.issn.0254-6051.2023.07.042

Abstract （54）

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TA15 titanium alloy were treated by laser shock peening (LSP) to study the effect of LSP on microstructure and fatigue property of the titanium alloy specimens with double holes. The results show that when the specimens are treated by LSP with laser energy of 25 J, circular spot diameter of ?4 mm and shock times of 2, a large number of high-density dislocations and dislocation walls are formed in the TA15 titanium alloy crystal, and introducing residual compressive stress of up to -500 MPa simultaneously on the material surface which can balance the tensile stress generated under fatigue load, effectively suppress fatigue crack initiation and slow down crack propagation rate. The LSP can obviously improve the fatigue life of the titanium alloy specimens with double holes, which is increased by 60%-89% compared to that of the untreated specimen. This is because the large residual compressive stress introduced by LSP greatly reduces the effective stress intensity factor at the crack tip. When the effective force intensity factor is less than the fracture toughness of the material, the fatigue crack growth will be suppressed or stopped, thus improving the fatigue life.

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Effect of austenitizing process on structure and cracks of galvanized layer on 22MnB5 hot stamped steel

Zhao Jingxuan, Liang Jian, Zhang Lingling, Dong Yikang, Wang Lihui, Miao Bin, Shen Chunguang, Zheng Shijian

Heat Treatment of Metals 2024, 49 (11): 296-301. doi:10.13251/j.issn.0254-6051.2024.11.046

Abstract （52）

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22MnB5 hot-dip galvanized hot stamped steel was heated to different austenitizing temperatures for different time for hot stamping. The effect of austenitizing process for hot stamping on the microstructure and cracks of the galvanized layer on hot stamped steel was investigated through characterization of the microstructure, surface oxides and cracking of the galvanized layer by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) analysis. The results indicate that the galvanized layer is primarily composed of α-Fe (Zn) and a small amount of brittle Fe₃Zn₁₀ after austenitizing. With an increase in heating temperature from 870 ℃ to 890 ℃, the galvanized layer thickness reaches the maximum, and there is a noticeable decrease in the presence of Fe₃Zn₁₀, leading to a reduction of cracks after hot stamping. However, the galvanized layer thickness slightly decreases at 910 ℃ due to Zn volatilization, resulting in the formation of a large amount of Mn, Zn and other elemental oxides on the surface, and the content of Fe₃Zn₁₀ in the galvanized layer significantly increases, leading to a large number of cracks after hot stamping. When the holding time at 890 ℃ is extended from 370 s to 400 s, the Fe-Zn reaction is promoted, more α-Fe(Zn) phases are formed, resulting in an increase of the galvanized layer thickness, but with no significant change of the surface oxidation degree.

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Effect of B₄C addition on morphology and properties of Stellite6+B₄C laser clad layers on 42CrMo steel surface

Zhang Zejiang, Li Xinmei, Zhu Chunjin, Li Hang, Yang Dingli

Heat Treatment of Metals 2024, 49 (7): 200-207. doi:10.13251/j.issn.0254-6051.2024.07.031

Abstract （49）

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In view of the surface modification of shearer picks, effect of B₄C addition (3%, 5% and 7%) on the cross-section morphology, microhardness, wear resistance and corrosion resistance of the Stellite6+B₄C laser clad layers on 42CrMo steel was studied by means of X-ray diffractometer, scanning electron microscope, Vickers microhardness tester, multifunctional friction and wear testing machine and electrochemical workstation. The results show that the cross-section morphology of the clad layer is good when the B₄C addition is 3% and 5%, however, when the B₄C addition is 7%, there are many defects on the surface of the clad layer. With the increase of B₄C addition, the microhardness of the clad layer increases from 781.04 HV to 1044.72 HV, the average friction coefficient decreases and the wear loss decreases first and then increases. When the B₄C addition is 7%, the average friction coefficient of the clad layer is 0.42, but due to the poor forming quality, the wear loss is the highest as 1.9 mg. When the B₄C addition is 5%, the wear loss is the least as 0.6 mg. The corrosion resistance of the clad layer first increases and then decreases with the increase of B₄C addition. When the B₄C addition is 5%, the self-corrosion potential of the clad layer is the highest, the self-corrosion current density is the smallest, and the charge transfer resistance R_ct is the largest, the best corrosion resistance of the clad layer is obtained.

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Fatigue crack propagation properties of industrial pure iron intensified by high energy shot peening

Liu Rongwei, Huang Zhiguo, Liu Xiangyu, Sun Yangfeng, Wei Yandong, Cui Xihe, Hou Helong, Xu Lindong

Heat Treatment of Metals 2024, 49 (4): 257-263. doi:10.13251/j.issn.0254-6051.2024.04.041

Abstract （48）

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High-energy shot peening was adopted to form self-nanocrystallization layer on the surface of industrial pure iron, and its effects on fatigue crack propagation rate, microstructure, microhardness and fatigue fracture morphology of the base metal were comparatively analyzed by fatigue crack propagation test. The results show that high-energy shot peening has a significant inhibitory effect on initiation and propagation of the fatigue crack when the stress intensity factor is lower than 50 MPa·m^1/2, but it is not obvious for that higher than 50 MPa·m^1/2. After high-energy shot peening, the grains on surface structure of the specimen are seriously extruded and fragmented, and the surface hardness is about 40% higher than that of the base metal, while the hardness decreases rapidly with the increase of the depth from surface. The maximum effect depth of high-energy shot peening reaches 3.88×10^-4mm. From the surface to the inside of the shot peening specimen, it can be divided into surface damage zone, nano layer, severe grain deformation zone, grain deformation zone and unaffected zone, and there is no obvious boundary between different zones.

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Effect of TiC content on microstructure and wear resistance of AlCoCrFeNi high-entropy alloy clad layer

Zhang Hongliang, Wang Mingxin, Zhang Jingbing, Li Yutao, Jin Tounan

Heat Treatment of Metals 2024, 49 (9): 275-279. doi:10.13251/j.issn.0254-6051.2024.09.046

Abstract （48）

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AlCoCrFeNi-2xMo-xTiC (x=0, 0.1, 0.25, 0.4) high entropy alloy clad layer was prepared on 40CrNiMo steel surface by laser cladding method. The effect of TiC and Mo content on the microstructure and wear resistance of the AlCoCrFeNi-2xMo-xTiC alloy clad layer was studied through XRD, SEM, EBSD, TEM, and wear resistance tests. The results show that after in-situ formation of TiC, the microstructure of the clad layer consists of BCC and TiC phases. As the atom fraction of TiC increases, the size of carbide precipitates gradually increases, and the grain size of the clad layer is significantly refined, decreasing from 109 μm to 15 μm. The AlCoCrFeNi-0.8Mo-0.4TiC clad layer has the highest hardness of 750 HV0.3, which is 300 HV0.3 higher than the AlCoCrFeNi alloy clad layer. The hardness and wear resistance of the clad layer increase with the increase of atom fraction of TiC. The wear surface of the AlCoCrFeNi alloy clad layer has more debris, and the wear mechanism is adhesive wear. The wear mechanism of the AlCoCrFeNi-0.2Mo-0.1TiC, AlCoCrFeNi-0.5Mo-0.25TiC, and AlCoCrFeNi-0.8Mo-0.4TiC alloy clad layers are abrasive wear.

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Preparation and properties of TiC coating on 45 steel by laser cladding

Liu Zhiling, Chang Mingfeng, Han Guisheng, Dai Jiaoyan, Xu Jinfu

Heat Treatment of Metals 2024, 49 (3): 269-274. doi:10.13251/j.issn.0254-6051.2024.03.044

Abstract （47）

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TiC coatings were cladded on the surface of 45 steel by a CO₂ constant current laser using Ni60+TiC gradient layer structure. The effect of process parameters(laser power, scanning rate and overlap rate) on the microstructure and properties of TiC coatings was investigated. The results show that the surface cracks of the coating decrease and then increase with the increase of laser power and scanning rate. The surface cracks disappear when the laser power is 4.0 kW and the scanning rate is 400 mm/min. With the increase of the overlap rate, the surface cracks of the coating increase and then decrease, and the surface cracks of the coating disappear when the overlap rate is 50%. The optimal process parameters are laser power 4.0 kW, scanning rate 400 mm/min, and overlap rate 50%. The thickness of TiC gradient coating is about 1.2 mm after the best process, and it is metallurgically bonded with the base layer. The microstructure of the most superficial layer is dendritic TiC and a small amount of Ni-based solid solution, the microstructure of the gradient layer is TiC+Ni-based solid solution, TiC content from the surface to the inside is in a gradient decrease, Ni-based solid solution content from the surface to the inside is in a gradient increase. The hardness of TiC coating decreases from 1968 HV0.2 to 240 HV0.2. In addition, the wear rate of the TiC coating is 1.757×10^-15m³/(N·m).

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Friction and wear performance of sulfurized layer on gray cast iron

Li Yelin, Jia Bo, Shi Zhengliang, Hu Wenxiang, Guan Yunqi, Zheng Huiyun

Heat Treatment of Metals 2023, 48 (10): 266-273. doi:10.13251/j.issn.0254-6051.2023.10.041

Abstract （47）

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Solid lubricating layers of sulfurized layer and phosphate layer were prepared on the surface of gray cast iron by low temperature ion sulfurization technology and chemical conversion technology, respectively. SEM-EDS, XRD, nano-indentation apparatus and X-ray stress analyzer were used to analyze the component elements, microstructure, thickness, hardness, residual stress and wear scar morphologies of the solid lubricating layers. The anti-friction and wear properties of the gray cast iron substrate and surface solid lubrication layer were studied by friction and wear test. The wear volume after friction and wear test was analyzed by using three-dimensional white light interferometer. The results show that both the phosphate layer and the porous structure of the sulfurized layer on the surface of gray cast iron have the characteristics of oil storage lubrication, while the surface hardness and residual stress of the sulfurized layer are higher than that of the phosphate layer. The sulfurized layer is detected to be a covalent bond compound FeS with antifriction and lubrication effect, which is formed when the active sulfur atoms infiltrate into the matrix, there is also a dynamic equilibrium process of active sulfur atoms transfer and recombination during the grinding process of gray cast iron substrate and sulfurized layer. Therefore, compared with the phosphate layer under the same friction conditions, the friction coefficient of the sulfurized layer is reduced by 23.5% and the wear rate is decreased by 31.6%, i.e., the anti-friction, wear-resisting and wear-resisting properties of sulfurized layer is better than that of phosphate layer, the COP of compressor parts after sulfurizing treatment is significantly improved.

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Effect of laser scanning rate on microstructure and wear resistance of NiCr/Cr₃C₂ coating

Dong Hui, Gan Shaoming, Du Yongqi, Bai Jiaxin, Cheng Yuchen, Li Ming, Zhu Chaoxuan

Heat Treatment of Metals 2023, 48 (11): 282-287. doi:10.13251/j.issn.0254-6051.2023.11.046

Abstract （46）

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NiCr/Cr₃C₂ composite coating was prepared by laser cladding at three laser scanning rates. The microstructure, hardness and friction and wear properties of the coatings were characterized using scanning electron microscope (SEM), X-ray diffractometer (XRD), micro-hardness tester and friction and wear testing machine. The results show that the structure in clad layer transfer from dendrite to equiaxed as the laser scanning rate increases from 2 mm/s to 4 mm/s, and the defects transfer from pores to large gaps and microcracks. When the scanning rate is below 3 mm/s, the melting and decomposition of Cr₃C₂ results in the clad layer mainly containing Cr₇C₃. As the laser scanning rate increases, the melting degree of Cr₃C₂ decreases, and the clad layer is mainly composed of Cr₇C₃ and Cr₃C₂. Therefore, the hardness of the clad layer increases from 400 HV0.3 to 780 HV0.3 when the laser scanning rate rises from 2 mm/s to 4 mm/s. The wear mechanism of the clad layer at different laser scanning rates is mainly abrasive wear, but due to its dense structure and higher hardness, the wear loss of the clad layer at scanning rate of 3 mm/s is the smallest and the wear resistance is the best.

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Effect of heat treatment on hardness and wear resistance of laser clad Co-based alloy coating

Yang Dongjie, Bai Qiaofeng, Ouyang Changyao, Wang Rui, Wei Runze

Heat Treatment of Metals 2023, 48 (7): 271-276. doi:10.13251/j.issn.0254-6051.2023.07.045

Abstract （45）

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Co-based alloy coating was prepared on the surface of ductile iron by laser cladding technology. Microstructure of the specimens under different heat treatment processes was analyzed and the effects of different processes on the hardness and wear resistance of the cobalt-based alloy coating were discussed. Compared with untreated specimens, the hardness of heat-treated specimens is improved. The hardness changes of the specimens treated at 950 ℃ for 1 h and 2 h, respectively, are similar, which are 51.35 HRC and 51.15 HRC, and that subsequent aged at 825 ℃ are 52.50 HRC and 52.08 HRC. The wear amount of the untreated specimen is the highest and the wear resistance is the worst. The wear loss of the specimen treated by 950 ℃×1 h + 825 ℃×24 h reduces by 5.3%, and that of the treated by 950 ℃×3 h+825 ℃×24 h reduces by 12.8%, which shows better wear resistance.

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Effect of boronizing temperature on properties of boronized layer on 45 steel

Wang Lan, Xie Yuanna, Weng Chenhao, Song Jianfeng

Heat Treatment of Metals 2024, 49 (10): 258-263. doi:10.13251/j.issn.0254-6051.2024.10.042

Abstract （45）

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Effect of different boronizing temperatures (800, 850, 900 ℃) on thickness, hardness, fracture toughness, brittleness and corrosion resistance of boronized layer on 45 steel was studied. The hardness, crack morphology of indentation and elastic modulus of boronized layer were tested by Vickers hardness tester. The elastic modulus of boronized layer was measured by nanohardness tester, and the fracture toughness and brittleness of boronized layer were characterized quantitatively. The corrosion resistance of boronized layer was characterized by electrochemical workstation. The results show that after boriding at different temperatures, as the boronizing temperature increases, the thickness and hardness of the boronized layer increase, the fracture toughness decreases and the brittleness increases. After boronizing at 800 ℃, the self-corrosion potential of the boronized layer is the highest, the self-corrosion current density is the lowest and the corrosion resistance is the best. Comprehensively, the optimal boronizing process for 45 steel is boronizing at 800 ℃ for 4 h.

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