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Kong D.-J.,Changzhou University | Kong D.-J.,Jiangsu Province Engineering Technology Research Center for Large Heavy Gear Transmission | Zhang L.,Changzhou University | Fu G.-Z.,Changzhou University
Binggong Xuebao/Acta Armamentarii | Year: 2014

The surface of 40CrNiMo high strength steel is treated with CO2 laser, the effect of laser quenching on tensile property of the sample is investigated through the tensile comparative test, and the fracture morphologies of 40CrNiMo before and after surface laser quenching are analyzed by scanning electron microscope and energy dispersive spectrometer, respectively. The results show that the yield strength, tensile strength and elongation of 40CrNiMo steel after laser quenching are increased by 25.3%, 24.4% and 7.1%, respectively, while the section shrinkage is decreased by 7.6%. 40CrNiMo steel has obvious yield stage after laser quenching, showing a continuous yield feature.compared with the primitive sample, the yield strength and tensile strength of 40CrNiMo steel after laser quenching increase, but there are no obvious improvements in the tensile failure mode and the delamination, and the quasi cleavage morphology and low porosity appear at the fracture near the surface of the sample after laser quenching. Source


Kong D.,Changzhou University | Kong D.,Jiangsu Province Engineering Technology Research Center for Large Heavy Gear Transmission | Fu G.,Changzhou University | Wang W.,Changzhou University | And 2 more authors.
Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology) | Year: 2014

The surface of 40CrNiMo high tension steel for super-large gear ring was quenched with CO2 laser, and the structure change was observed using metallographic microscope. The section morphology was analyzed using SEM, the surface roughness before and after laser quenching was measured using profile meter, and the friction and wear test was processed. The friction coefficient and wear property before and after laser quenching were investigated, and the effect of laser quenching on the mechanism of friction and wear was discussed. The results show that the phase transformation hardened layer is formed by laser quenching, composing of the fine acicular martensite, and micro-hardness HV is 480-500. The surface roughness of the sample by quenching and tempering treatment is 35.1 nm, while that by laser quenching is 36.1 nm, as a result, laser quenching basically has no effect on its accuracy and deformation. The effect of reducing friction by laser quenching is obvious, under the loads of 6, 8 and 10 N, the average value of friction coefficient by laser quenching decreases by 6.7%, 9.1% and 22.2% than that by tempering sample, respectively. The wear failure form is improved by laser quenching, under the loads 6, 8 and 10 N, the wear mass loss ratio of the sample by laser quenching decreases by 88.73%, 91.42% and 87.45% than that of the quenched and tempered sample, respectively, and high hardness of martensite is its main mechanism of improving wear properties. Source


Fu G.,Changzhou University | Fu G.,Graduates Research Station of Jiangsu Province | Kong D.,Changzhou University | Kong D.,Jiangsu Province Engineering Technology Research Center for Large Heavy Gear Transmission | And 4 more authors.
Zhenkong Kexue yu Jishu Xuebao/Journal of Vacuum Science and Technology | Year: 2014

The AlCrN coatings were synthesized by cathodic arc ion plating on substrate of Ti-based cermet. The impacts of the deposition conditions, such as the pressure, nitrogen flow rate, deposition rate, and substrate temperature, on the microstructures and mechanical properties of the AlCrN coating were evaluated. The AlCrN coatings were characterized with scanning electron microscope, and atomic force microscope. The results show that the compact AlCrN coatings have a major impact on enhancement of micro-hardness and wear-resistance of the Ti-based cermet substrate, but weakly affect its surface roughness. The average grain sizes of the substrate and AlCrN coatings were 1460 and 1432 nm, respectively. In addition, the spectral power distribution of the anisotropic AlCrN coatingswas found to be irregular. Source


Kong D.,Changzhou University | Kong D.,Jiangsu Province Engineering Technology Research Center for Large Heavy Gear Transmission | Fu G.,Changzhou University | Wang W.,Changzhou University | Zhang L.,Changzhou University
Zhenkong Kexue yu Jishu Xuebao/Journal of Vacuum Science and Technology | Year: 2014

The AlCrN coating was deposited by cathodic arc ion plating on substrate of TiC. The surfaces of the AlCrN coating and its interface were characterized with scanning electron microscope, energy dispersive spectrometer and X-ray diffraction and the Mechanism of interfacical diffusion combination was discussed. The results show that thefairly uniform, compact AlCrN coatings significantly improve the wear-resistance and oxidation-resistance of the substrate. The AlN and CrN phases were found to coexist in the AlCrN coatings with Al-rich surfaces. The formation of a functional hardness gradientpossibly accounted for an enhancement of the wear-resistance and oxidation-resistance. The interfacial diffusion of Ti, C, N, and Al resulted in metallurgical bonding and a strong interfacial adhesion. Source


Kong D.,Changzhou University | Kong D.,Jiangsu Province Engineering Technology Research Center for Large Heavy Gear Transmission | Zhang L.,Changzhou University | Song R.,Changzhou University | And 2 more authors.
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2013

The surface of 40CrNiMo high strength steel is quenched with CO2 laser, and the fatigue limits of 40CrNiMo before and after laser quenching are obtained through the tension-tension fatigue experiments based on Locati theory. The fracture morphologies of 40CrNiMo before and after laser quenching are investigated by scanning electron microscope. The mechanism of laser quenching on 40CrNiMo's fatigue strength is analyzed. The results show that a layer of hardened zone, martensite and compressive residual stress after laser quenching is formed on the sample surface, and the fatigue strength of 40CrNiMo is increased significantly from 626 MPa to 715 MPa, increasing by 14.2%. The fatigue crack sources of the sample in quenching and tempering state are produced in the surface, while that are transferred to the subsurface after laser quenching. The fatigue crack sources expand slowly to be fracture. Grain refinement and compressive residual stress by laser quenching are the main mechanism. Source

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