20 September 2022, Volume 46 Issue 9

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  • JIANG Bingya, CAO Tieshan, CHENG Congqian, ZHAO Jie
    Materials For Mechanical Engineering. 2022, 46(9): 1-10. https://doi.org/10.11973/jxgccl202209001
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    Heat resistant steels are a key material serving in thermal power, nuclear power and chemical industry fields under high temperature conditions. The existence of precipitates during service has an important influence on the thermal strength, toughness, microstructure stability and high temperature oxidation resistance of heat resistant steels, and the strain causes a large number of dislocations in the matrix, which promotes the nucleation of precipitates. The main alloying elements and precipitates of heat resistant steels are introduced, and the research progress on strain induced precipitation model for heat resistant steels is reviewed from three aspects: strain induced nucleation, strain induced precipitation growth and coarsening, and the engineering application of strain induced precipitation model. The future research direction of the strain induced precipitation model is prospected.
  • Testing & Research
  • LI Zhen, YANG Li, SHEN Tong, FENG Lingxiao
    Materials For Mechanical Engineering. 2022, 46(9): 11-15. https://doi.org/10.11973/jxgccl202209002
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    Two-stage vacuum nitriding process was used to modify the surface of quenched and tempered PCrNi3Mo steel. Under the condition of the same nitriding temperature and nitrogen potential, the microstructure, phase composition, hardness and wear resistance of the surface layer of the test steel were studied under the conditions of strong infiltration for 6 h and diffusion for 6 h, and compared with those by strong infiltration for 4 h and diffusion for 8 h. The results show that after nitriding, the phase of the test steel surface layer was ε-Fe2-3N phase. Under two nitriding time conditions, the thickness of nitrided layer was about 0.6, 0.7 mm, and the surface hardness was 660.3, 581.3 HV, respectively, higher than 360 HV of substrate. Under the former nitriding time condition, the compound layer in the nitriding layer had poor compactness and a great number of micropores; the hardness transition of the nitriding layer was good, and the hardness was relatively high at the distance from the surface of greater than 0.3 mm; the friction coefficient and wear amount of the nitrided layer were relatively low, and the furrow on the wear surface was shallow, indicating the wear resistance was relatively good.
  • WANG Dan, ZHONG Qingdong, YANG Jian, ZHANG Shujian
    Materials For Mechanical Engineering. 2022, 46(9): 16-23. https://doi.org/10.11973/jxgccl202209003
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    Three test steels with composition (mass fraction/%) of 0.35C,0.9Mn, 3.5Cr, 0.6Si, 0.3V, 0.05Ti (namely N1), 0.35C, 1.2Mn, 2.0Cr, 0.8Si, 0.4V, 0.11Ti (namely N2) and 0.40C,0.6Mn, 3.5Cr, 0.8Si, 0.1V, 0.23Ti (namely N3) were designed based on 40Cr steel composition, and the microstructure, electrochemical properties and corrosion resistance in 3.5wt% NaCl solution of test steels were studied. The results show that N3 test steel had the smallest grain size and the narrowest martensite lath bundle, followed by N1 test steel and N2 test steel. N1 test steel had the highest open circuit potential, the highest free-corrosion potential, the lowest free-corrosion current density, the largest absolute value of the maximum phase angle, and the largest radius of the capacitive arc. After soaking in NaCl solution for 24 h, localized pitting corrosion occurred on the surface of N1 and N3 test steel, while uniform corrosion occurred on N2 test steel. N1 test steel had high chromium content, moderate grain size, the highest surface corrosion product compactness and the best corrosion resistance.
  • MA Zhenqiang, LI Yuanyuan, CHENG Xiaomin, LIU Huachen
    Materials For Mechanical Engineering. 2022, 46(9): 24-28. https://doi.org/10.11973/jxgccl202209004
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    With nickel powder, Fe2O3, Cr2O3 and polyvinyl alcohol as raw materials, Ni/FeCr2O4 spinel structure composites with different nickel doping amounts (20%, 25%, 40%, mass fraction) were prepared by powder sintering method. The effects of nickel doping amount on the microstructure and properties of Ni/FeCr2O4 composites were studied by X-ray diffractometer, infrared spectrometer, scanning electron microscope, and mechanical tester, etc. The results show that with increasing nickel doping amount, the composite structure became denser and the volumetric shrinkage and density increased; the flexural strength was significantly improved. When the nickel doping amount was 40%, the density and flexural strength was improved by 17.3% and 22.5%, respectively, comparing with those of non-nickel doping. Nickel doping improved the emissivity of FeCr2O4 spinel around the wavelength of 1 000 nm, and slightly reduced the emissivity in the wavelength range of 250-700 nm and 1 200-1 600 nm, but the emissivity in these two bands was still higher than 0.9.
  • SU Jun, FENG Peipei
    Materials For Mechanical Engineering. 2022, 46(9): 29-33. https://doi.org/10.11973/jxgccl202209005
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    With ZrO2, Al2O3 and aluminum powder as binders, polycrystalline cubic boron nitride (PCBN) ceramics were sintered by using a six-anvil high-pressure apparatus at a high temperature (1 300-1 600 ℃) and high pressure (5.5 GPa). The effects of sintering temperature on the phase composition, mechanical properties and cutting performance when machining centrifugal cast iron of the ceramics were studied. The results show that the main crystal phases of the PCBN ceramics sintered at different temperatures were composed of cBN, m-ZrO2, t-ZrO2, Al2O3, AlN and ZrN, and the binding phase particles uniformly dispersed in the cBN matrix. With the increase of sintering temperature, The combination of cBN and the binder phase became tighter, and the relative density, hardness, flexural strength and fracture toughness of the ceramics increased. When the sintering temperature was 1 600 ℃, the ceramics had the best comprehensive mechanical properties, with microhardness, flexural strength and fracture toughness reaching 32.87 GPa, 850.3 MPa and 5.1 MPa·m1/2, respectively. When the sintering temperature was 1 400 ℃ and 1 500 ℃, the flank wear amount of the PCBN ceramic tool was only 171, 166 μm, respectively, after cutting the centrifugal cast iron rod with a total length of 10 km, indicating that the cutting performance was relatively good.
  • Material Properties & Application
  • SHI Kunyu, ZHUANG Chenqi, WU Weijin, ZHANG Bo, YU Chuanhao
    Materials For Mechanical Engineering. 2022, 46(9): 34-39. https://doi.org/10.11973/jxgccl202209006
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    NbTiN2 coating was prepared on TC4 alloy surface by dual cathode plasma sputtering deposition. The phase composition, microstructure, hardness, adhesion to matrix and friction and wear properties of the coating were studied. The results show that the NbTiN2 coating had strong (220) preferred orientation. The coating had good surface quality, no obvious defects and a thickness of about 10 μm. The average hardness of the coating was 2 478.46 HV, about 6 times that of the matrix, and the critical load of coating in scratch test was 68.5 N, indicating that the coating was well combined with the matrix. The friction coefficient of the coating was lower than that of the matrix under the load of 2-5 N at room temperature; the wear scar was narrower than that of the matrix, and the wear rate of the coating was one order of magnitude lower than that of the matrix; the main wear mechanism of the coating was fatigue wear. At 500 ℃, the friction coefficient was higher than that at room temperature, and the wear scar of the coating was narrower and shallower; the wear rate was lower, and the wear mechanism was adhesive wear and oxidation wear, indicating the coating had better wear resistance.
  • SHAO Hui, SHAN Di, ZHANG Hui, ZHANG Saifei, SUN Feng, ZHAO Xiaohua, WANG Kaixuan, SUN Lixing, ZOU Juntao
    Materials For Mechanical Engineering. 2022, 46(9): 40-45. https://doi.org/10.11973/jxgccl202209007
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    The solid soluted Ti-55511 alloy was treated by electric heating for different holding times (10-60 s) at 905 ℃, and the evolution of black spot structure and tensile properties of the alloy were studied. The results show that the β phase of black spot structure in the alloy in solid solution state had a typical Goss and Cube texture orientation. With the electric heating time increasing from 10 s to 40 s, β grains recrystallized and the black spot structure content decreased. When electric heating for 60 s, the recrystallization grain grew to average grain size of 27.3 μm and the black spot structure area fraction decreased to 2.1%. Comparing with those of the solid soluted alloy, the tensile strength of the alloy after electric heating decreased while the elongation after fracture increased. With increasing electric heating time, the tensile strength of the electric heating reated alloy kept unchanged, and the elongation after fracture increased first and then decreased, reaching the maxium value of 20.8% when electric heating for 40 s. The fracture of the alloy after electric heating for different times showed the composite morphology of dimples and quasi-cleavage fracture.
  • ZOU Chunlei, YU Hang, REN Huiyuan, GU Jinbo, ZHOU Jian, CHI Hongxiao
    Materials For Mechanical Engineering. 2022, 46(9): 46-51. https://doi.org/10.11973/jxgccl202209008
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    Annealed Cr12Mo1V1 die steel was treated by single quenching+tempering, double-quenching+tempering, single quenching+cryogenic treatment+tempering and double-quenching+cryogenic treatment+tempering processes, respectively. The single quenching process was 1 030 ℃×0.5 h oil quenching. The double-quenching process was 1 050 ℃×0.5 h oil quenching+1 030 ℃×0.5 h oil quenching. The cryogenic treatment was -60 ℃×1 h+-120 ℃×1 h. The effects of double-quenching+cryogenic treatment on the microstructure and mechanical properties of the test steel were studied contrastively. The results show that comparing with the single quenching+tempering process, the double-quenching+tempering process could improve the distribution uniformity of eutectic carbides, and make the carbides be spherical. The addition of cryogenic treatment had little effect on the improvement of the morphology and uniformity of eutectic carbides, but reduced the residual austenite content. The hardness of the test steel after the double-quenching+tempering treatment was similar to that after the single quenching+tempering treatment, while the impact absorption energy and bending strength increased by 22% and 12%, respectively. The addition of cryogenic treatment had little effect on the hardness, impact toughness and flexural strength of the test steel.
  • WU Fan, WANG Bingxu, HU Ming, YANG Jinlin, HU Zirui, CUI Weiwei, ZHANG Yu
    Materials For Mechanical Engineering. 2022, 46(9): 52-56. https://doi.org/10.11973/jxgccl202209009
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    Nano-lubricating oils were prepared by adding equal mass fraction (1%, 2%, 3%) of SnO2 nanoparticles and oleic acid into poly-α-olefin (PAO6) base oil. The tribological performance of the nano-lubricating oil in steel ball-brass block tribo-pairs was studied by reciprocating sliding friction-wear tests and compared with that of non-nano-lubricating oils, and the frictional reduction and anti-wear mechanism was also discussed. The results show that when lubricating in the nano-lubricating oil with no less than 2mass% SnO2 nanoparticles, the average friction coefficient of the tribo-pair and the width and depth of the wear scar on the brass surface were all lower than those with the corresponding lubricating oil without SnO2 nanoparticles. When the mass fraction of SnO2 nanoparticles was 2%, the nano-lubricating oil had the best frictional reduction and anti-wear performance; comparing with those lubricated in PAO6 base oil, the average friction coefficient and the width and depth of wear scars were reduced by 31%, 42%, 50%, respectively. The excellent frictional reduction and anti-wear properties of the nano-lubricating oil were attributed to the lubricating film formed by oleic acid and the protective layer formed by SnO2 nanoparticles.
  • CHEN Yanfei, ZHU Zhengqiang, YANG Qunyi
    Materials For Mechanical Engineering. 2022, 46(9): 57-63. https://doi.org/10.11973/jxgccl202209010
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    Torsional deformation at 720 ℃ and 500 ℃×60 min annealing treatment were carried out on the 8 mm diameter recycled copper rods prepared by fire refined high conductivity (FRHC) waste copper refining process and continuous casting and rolling process. The effects of torsional deformation and annealing treatment on the microstructure, mechanical properties and electrical conductivity of the copper rod were studied. The results show that twins were generated in the recycled copper rod structure during continuous casting and rolling process, and the twin crossover and the interaction between twins and dislocations caused by torsional deformation made the grains refined. The tensile strength of the recycled copper rod after torsional deformation increased from 215 MPa without torsional deformation to 273 MPa, but the elongation after fracture decreased from 40% to 21%;the hardness increased and the electrical conductivity decreased from 99.37%IACS to 86.78%IACS. After annealing treatment, the recycled copper rod had a structure with equiaxed crystals with more uniform size. The tensile strength was reduced to 208 MPa, while the elongation after fracture increased to 55%; the hardness decreased and the electrical conductivity increased to 98.21% IACS.
  • Physical Simulation & Numerical Simulation
  • TAN Qingbiao, WANG Bo, DONG Hongzhi, WANG Donghong, ZHU Guoliang
    Materials For Mechanical Engineering. 2022, 46(9): 64-69. https://doi.org/10.11973/jxgccl202209011
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    ProCAST finite element analysis software was used to numerically simulate the filling and solidification process of K417 nickel-based superalloy ingot with large height-diameter ratio. The location, quantity and cause of the formation of secondary shrinkage defects in the solidification process of the alloy ingot, and the influence of pouring temperature and pouring speed on secondary shrinkage defects was simulated and studied, and were verified by experiments. The results show that the shrinkage defect distribution of alloy ingot obtained by numerical simulation was consistent with that of onsite casting ingot, indicating the accuracy of numerical simulation. The secondary shrinkage defects could be mitigated by increasing the pouring temperature and decreasing the pouring speed to some extent. However, the defects could not be completely eliminated. Under the condition of 1 530 ℃ and 1.40 kg·s-1 pouring speed, the alloy ingots had the fewest shrinkage defects.
  • ZHANG Yuntao, DENG Xiaowei, WU Yiwen, YU Hongjie, YU Zhengyue
    Materials For Mechanical Engineering. 2022, 46(9): 70-75. https://doi.org/10.11973/jxgccl202209012
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    Indentation load-depth curves of metallic materials were obtained by continuous spherical indentation tests. The curves were transformed into the representative stress-strain data by calculation, and then the data was fitted to obtain the strain hardening exponent n. The detecting method for n values by continuous spherical indentation tests was corrected by using the material plastic expansion index to determine the complete plastic deformation interval of the material, using the iterative algorithm to correct the plastic constraint factor, and considering the indentation accumulation effect to obtain the true contact depth. The correction method was used to calculate n values of eight materials including 6061 aluminum alloy, 6063 aluminum alloy, 45 steel, ST steel, AIF1 alloy, X52 steel, X60 steel and SK3 steel, and the obtained n values were compared with those by uniaxial tensile tests. The results show that the relative errors between the n values obtained by the uncorrected method and the tensile tests were more than 10%. After correction by the three methods, the relative errors were reduced; all were reduced to less than 5% except the relative error of X60 steel, that was 8.6%.
  • HUANG Feihong, WANG Gangming, XU Yiwei, HUANG Haibo, LI Chao, PEI Jiaqing
    Materials For Mechanical Engineering. 2022, 46(9): 76-81. https://doi.org/10.11973/jxgccl202209013
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    Molecular dynamic tribological models for vulcanized nitrile rubber with different crosslinking densities (0.4, 0.8, 1.2, 1.6)-iron substrate were established, and then the effect of the crosslinking density on the friction coefficient, relative atomic concentration, friction interface temperature and mean square displacement of rubber molecular in shear friction were analyzed. The accuracy of the model was experimentally verified. The results show that with the increase of crosslinking density, the friction coefficient of the friction pair of vulcanized nitrile rubber-iron substrate increased; the change trend was consistent with the test results. Vulcanization cross-linking could effectively improve the stiffness between rubber molecules, and restrict the movement of molecular chains, resulting in a decrease in the relative atomic concentration at the friction interface and the mean square displacement of rubber molecules. The increase in the stiffness of the rubber molecular improved the relative displacement between the rubber matrix and the iron substrate, and the moving of iron substrate needed to overcome more atomic bonding; so the adhesion friction force increased, resulting in an increase in the friction coefficient of the friction interface. The increase in the relative displacement also led to more energy loss, making the friction interface generate more heat; so the temperature of the friction interface rose.
  • WU Yiming, WANG Yan, ZHANG Minghe, FENG Yunli
    Materials For Mechanical Engineering. 2022, 46(9): 82-88. https://doi.org/10.11973/jxgccl202209014
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    Hot compression tests at deformation temperatures of 900-1 100 ℃ and strain rates of 0.01-10 s-1 were conducted on Fe-10Mn-2Al-0.1C (mass fraction/%) medium Mn steel by using a Gleeble-1500 thermo-mechanical simulator. The Zener-Hollomon constitutive model of the test steel was established by a strain compensation method with the test data, and verified by the tests. The hot processing maps of the test steel at true strains of 0.2, 0.4, 0.6, 0.8 were established on the basis of the dynamic material model (DMM). The results show that the correlation coefficient between the flow stresses predicted by the established constitutive model and the measured stresses was 0.987, indicating that the model can be used to describe the thermal deformation behavior of the test steel. According to the calculation by the constitutive model, when the true strain increased from 0.1 to 0.8, the hot deformation activation energy of the test steel was reduced from 476 kJ·mol-1 to 342 kJ·mol-1. According to the hot processing maps, the optimal hot working conditions of the test steel were determined as deformation temperatures of 900-940 ℃ and strain rates of 0.01-0.03 s-1, and deformation temperatures of 1 070-1 100 ℃ and strain rates of 0.1-0.56 s-1; the power dissipation efficiency under these conditions was 32%-38%.
  • BAI Shaoyun, Lü Yanming, ZHAO Peng, PAN Yu, LIU Haocheng, HUANG Qiang
    Materials For Mechanical Engineering. 2022, 46(9): 89-95. https://doi.org/10.11973/jxgccl202209015
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    The finite element model of arc additive manufactured GH4169 nickel-based superalloy was established by Simufact Welding software, and the model was verified by tests. The thermodynamic field and deformation during multilayer single-pass forming under different deposition paths (unidirectional deposition, reciprocating deposition) and different interlayer cooling times (0, 60, 120 s) were analyzed. The results show that the simulated thermal cycle curve and residual stress during arc additive manufacturing agreed with the test results, and the relative errors were less than 9% and 3%, respectively, verifying the accuracy of the model. Compared with unidirectional deposition path, the reciprocating deposition path could improve the homogeneity of heat distribution and stress field distribution of the formed parts; the influence area of stress field and heat accumulation was relatively small, the temperature and residual stress were relatively low, and the deformation symmetry was relatively good. With increasing interlayer cooling time, the heat accumulation, residual stress and deformation decreased, but the decrease amplitude was reduced gradually. The forming quality of arc additive manufactured GH4169 nickel-base superalloy was good by applying the reciprocating deposition path and interlayer cooling for 60 s.
  • LI Cong, DING Zhili, CHEN Jian, ZHOU Xing
    Materials For Mechanical Engineering. 2022, 46(9): 96-105. https://doi.org/10.11973/jxgccl202209016
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    Hot compression tests were carried out on Ti-10V-2Cr-3Al titanium alloy at the strain rate of 0.1-0.001 s-1 and deformation temperature of 730-880 ℃, and the hot deformation behavior and microstructure of the alloy were studied. The exponential equation and hyperbolic sine equation in the phenomenological Arrhenius equation were used to describe the relationship between flow stresses and deformation temperatures and strain rates. The constitutive equation corrected by strain compensation was established and verified. The results show that the true stress of the alloy increased with increasing strain rate or decreasing deformation temperature under test conditions. At the strain rate of 0.01 s-1, spherical and short rod-like α phases appeared in the test alloy after compression in the α+β phase region (730, 790 ℃), and the softening mechanism was dynamic spheroidization and dynamic recrystallization; recrystallized β grains appeared after compression in the β phase region (820, 880 ℃), and the softening mechanism was dynamic recrystallization. When the strain rate was in the range of 0.1-0.05 s-1 and 0.01-0.001 s-1, the flow behavior of the test alloy could be described by the corrected exponential equation and the corrected hyperbolic sine equation, respectively. The average relative error between the predicted flow stresses and the experimental flow stresses was 5.36%, indicating that the corrected equations had good predictive ability.
  • Failure Analysis
  • ZHU Haibao, CHEN Zhuoting, BAI Jia, GUO Yanjun, LIU Ming, TIAN Linan, QIAO Lijie
    Materials For Mechanical Engineering. 2022, 46(9): 106-109. https://doi.org/10.11973/jxgccl202209017
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    During the maintenance period, the crack defect was detected during the magnetic particle inspection of the welded joint of the outlet header of a high temperature superheater in a power plant. The failure analysis of the pipe socket welded joint was carried out by stress distribution simulation, microstructure observation and hardness test. The results show that during the long-term high-temperature service, the coarse-grained area of the heat affected zone of the welded joint of the high temperature superheater outlet header was seriously aging, and the aging grade reached level of 4.5; the high-temperature mechanical properties significantly decreased. At the same time, the improper on-site installation of strong counterpart caused the additional secondary stress concentration of the tube panel. Under the additional secondary stress, the cracks initiated at the coarse-grained area of the heat affected zone on the upper half circle of the welded joint of the pipe socket. With the extension of service time, the substrate structure in the crack was decarbonized, and high temperature creep cracking occurred in the welded joint.