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Microstructure and mechanical properties of laser melting deposited Ti_2Ni_3Si/NiTi Laves alloys

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中国有色金属学会会刊：英文版 2007年第6期17卷 1230-1235页

作者：董李欣王华明 Laboratory of laser Materials processing and Manufacturing School of Materials Science and EngineeringBeihang University

Two Ti2Ni3Si/NiTi Laves phase alloys with chemical compositions of Ni-39Ti-11Si and Ni-42Ti-8Si (%, mole fraction, the same below), respectively, were fabricated by the laser melting deposition manufacturing process, aiming at studying the effect of Ti, Si contents on microstructure and mechanical properties of the alloys. The Ni-39Ti-11Si alloy consisting of Ti2Ni3Si primary dendrites and Ti2Ni3Si/NiTi eutectic matrix is a conventional hypereutectic Laves phase alloy while the Ni-42Ti-8Si alloy being made up of NiTi primary dendrites uniformly distributed in Ti2Ni3Si/NiTi eutectic is a new hypoeutectic alloy. Mechanical properties of the alloys were investigated by nano-indentation test. The results show that the decrease of Si and the increase of Ti contents change the microstructures of the alloys from hypereutectic to hypoeutectic, which influences the mechanical properties of the alloys remarkably. Corrosion behaviors of the alloys were also evaluated by potentiodynamic anodic polarization curves.

关键词： Ti2Ni3Si NiTi 合金激光熔化沉积微观结构机械性质

High-cycle fatigue crack initiation and propagation in laser melting deposited TC18 titanium alloy

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International Journal of Minerals,Metallurgy and Materials 2013年第7期20卷 665-670页

作者： Yang Wang Shu-quan Zhang Xiang-jun Tian Hua-ming Wang Laboratory of laser Materials processing and Manufacturing School of Materials Science and Engineering Beihang University

This article examines fatigue crack nucleation and propagation in laser deposited TC18 titanium alloy. The Widmanstatten structure was obtained by double-annealing treatment,. High-cycle fatigue （HCF） tests were conducted at room temperature with the stress ratio of 0.1 and the notch concentration factor Kt = 1. Fatigue cracks initiated preferentially at micropores, which had great effect on the HCF properties. The effect decreased with the decrease of pore size and the increase of distance from the pore location to the specimen surface. The crack initiation region was characterized by the cleavage facets of a lamella and the tearing of β matrix. The soft a precipitated-free zone formed along grain boundaries accelerated the crack propagation. Subsurface observation indicated that the crack preferred to propagate along the grain boundary α or border of a lamella or vertical to a lamella.

关键词： titanium alloys fatigue crack initiation crack propagation laser melting deposition

Microstructure of Nano-Y_2O_3/Cobalt Based Alloy Composite Coating by laser Cladding

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Journal of Rare Earths 2004年第5期22卷 683-686页

作者：何宜柱李明喜袁晓敏斯松华 Research Center for laser processing Anhui University of Technology Ma'anshan 243002 China

Composite coatings made of nano-Y_2O_3/cobalt-based alloy and produced by crosscurrent CO_2 laser on Ni-based superalloy are introduced. Cross-section or surface of the coatings was examined to reveal their microstructure using optical microscope, SEM, including EDS microanalysis, TEM and XRD. The results show that some equilibrium or non-equilibrium phases, such as γ-Co, Cr_(23)C_6, Y_2O_3 and ε-Co exist in the coatings. Fine and short dendritic microstructure and columnar to equiaxed transition (CET) occurred by adding nano-Y_2O_3 particles. With the increasing amount of nano-Y_2O_3 (1%, mass fraction), fully equiaxed crystallization appeared. These are caused by nano-Y_2O_3 particles acting as new nucleation site and rapid solidification of the melt. The results also show that inhomogeneous dispersion of nano-Y_2O_3 results in the formation of ε-Co phase in the coatings. The sub-microstructure of the clad is stacking fault. The mechanism of the formation of equiaxed grains is also analyzed.

关键词： metal materials Y_2O_3 nanocrystalline laser cladding Co-based alloy equiaxed grain rare earths

Abrasive wear property of laser melting/deposited Ti_2Ni/TiNi intermetallic alloy

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中国有色金属学会会刊：英文版 2007年第6期17卷 1358-1362页

作者：高飞王华明 Laboratory of laser Materials processing and Manufacturing School of Materials Science and EngineeringBeihang University

A wear resistant intermetallic alloy consisting of TiNi primary dendrites and Ti2Ni matrix was fabricated by the laser melting deposition manufacturing process. Wear resistance of Ti2Ni/TiNi alloy was evaluated on an abrasive wear tester at room temperature under the different loads. The results show that the intermetallic alloy suffers more abrasive wear attack under low wear test load of 7, 13 and 25 N than high-chromium cast-iron. However, the intermetallic alloy exhibits better wear resistance under wear test load of 49 N. Abrasive wear of the laser melting deposition Ti2Ni/TiNi alloy is governed by micro-cutting and plowing. Pseudoelasticity of TiNi plays an active role in contributing to abrasive wear resistance.

关键词： TiNi Ti2Ni 磨损金属合金

Effects of Cover Sheets on the Nugget Growth and Fracture Behavior of Resistance Spot Welded Q&P980 Steel Joints

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Chinese Journal of Mechanical Engineering 2022年第4期35卷 360-373页

作者： Zhanxiang Ling Ting Chen Liang Kong Min Wang Shanghai Key Laboratory of Materials laser processing and Modifcation Shanghai Jiao Tong UniversityShanghai 200240China

The resistance spot weldability of galvanized ultra-high-strength steels is not satisfed,the joints are prone to interfacial fracture and the weldable current range is *** solve the problems,a novel method called resistance spot welding with double-sided cover sheets was introduced to weld a galvanized Q&P980 steel with the thickness of 1.2 *** thin SPCC mild steel sheets were chosen as cover sheets and were placed symmetrically at both sides between the Q&P980 steels and the electrodes,then the RSW process was carried *** with the traditional RSW method,the joints obtained by using the novel method achieved larger tensile shear strength and energy absorption,which increased by 26.9%and 52.6%,*** increasing the welding current,the failure mode transferred from interfacial fracture to nugget pull-out fracture or base metal tearing *** contrast,the joints always showed interfacial fracture without cover *** improvement of the joint performance was mainly attributed to the enlargement of the *** the help of fnite element simulation,it was found that the cover sheets helped increase the contact area and reduced the current density during welding,which postponed the expulsion,and a larger area could be evenly *** application of the novel method can be easily extended to the resistance spot welding of other ultra-high-strength steels with various thicknesses.

关键词： Resistance spot welding Q&P980 steel Cover sheet Mechanical property

Two-photon absorption and stimulated emission in poly-crystalline Zinc Selenide with femtosecond laser excitation

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Opto-Electronic Advances 2022年第1期5卷 1-12页

作者： Qianliang Li Walter Perrie Zhaoqing Li Stuart P Edwardson Geoff Dearden laser Engineering group School of EngineeringUniversity of LiverpoolLiverpoolL693GQUnited Kingdom laser processing Research Centre School of MechanicalAerospace and Civil EngineeringUniversity of ManchesterManchester M139PLUnited Kingdom

The optical nonlinearity in polycrystalline zinc selenide(ZnSe),excited with 775 nm,1 kHz femtosecond laser pulses was investigated via the nonlinear transmission with material thickness and the Z scan *** measured two photon absorption coefficientβwas intensity dependent,inferring that reverse saturated absorption(RSA)is also relevant dur-ing high intensity excitation in *** low peak intensity I<5 GW cm^(-2),we findβ=3.5 cm GW^(-1) at 775 *** spec-tral properties of the broad blueish two-photon induced fluorescence(460 nm-500 nm)was studied,displaying self-ab-sorption near the band edge while the upper state lifetime was measured to be τ_(e)~3.3 *** emission was ob-served when pumping a 0.5 mm thick polycrystalline ZnSe sample within an optical cavity,confirmed by significant line narrowing fromΔλ=11 nm(cavity blocked)toΔλ=2.8 nm at peak wavelength λ_(p)=475 nm while the upper state life-time also *** results suggest that with more optimum pumping conditions and crystal cooling,polycrystal-line ZnSe might reach lasing threshold via two-photon pumping atλ=775 nm.

关键词： ZnSe femtosecond laser nonlinear absorption stimulated emission fluorescence

Modified Gray Level Difference-Based Thresholding Segmentation and its Application in X-Ray Welding Image

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Journal of Shanghai Jiaotong university(Science) 2013年第4期18卷 448-453页

作者：佟彤蔡艳孙大为吴毅雄 Shanghai Key Laboratory of Materials laser processing and Modification Shanghai Jiaotong University

Thresholding is a popular image segmentation method that often requires as a preliminary and indis- pensable stage in the computer aided image process, particularly in the analysis of X-ray welding images. In this paper, a modified gray level difference-based transition region extraction and thresholding algorithm is presented for segmentation of the images that have been corrupted by intensity inhomogeneities or noise. Classical gray level difference algorithm is improved by selective output of the result of the maximum or the minimum of the gray level with the pixels in the surrounding, and multi-structuring of neighborhood window is used to represent the essence of transition region. The proposed algorithm could robustly measure the gray level changes, and accurately extract transition region of an image. Comparisons with other approaches demonstrate the superior performance of the proposed algorithm. K

关键词： image segmentation transition region gray level difference welding image

Investigation on LCF Behavior of Welded Joint at Di erent Temperatures for Bainite Steel

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Chinese Journal of Mechanical Engineering 2019年第2期32卷 73-80页

作者： Ke Xu Xiongfei Wang Haichao Cui Fenggui Lu Shanghai Key Laboratory of Materials laser processing and Modifcation School of Materials Science and Engineering Shanghai Jiao Tong University

The current research of low cycle fatigue(LCF) is mainly focused on the components with uniform *** with these typical components, LCF behavior of welded components are more complex due to their great gradient microstructure, especially for di erent temperature. In this paper, LCF properties were conducted on the welded joint at di erent temperatures for bainite steel, and the failure mechanism was systematically *** parameters derived from fitting curves indicated that welded joint had worse plastic deformation resistance and experienced more significantly strain hardening e ect at 300 °C. The joint failed in the weld metal at room temperature, which attributed to the softening in weld metal combined with cyclic strain hardening e ect in heata ected zone, which meant the joint was more sensitive with the hardness at this condition. When it came to 300 °C,more cracks appeared near to HAZ and the heterogeneous distributed surface inclusion was responsible for the fracture transition to HAZ adjacent to bainite steel rather than the softest zone in HAZ, reflecting the joint was more sensitive with the surface inclusion at 300 °C. This research could support the design on loading of welded component at di erent temperature, and further ensure the safe operation.

关键词： Low cycle fatigue Welded joint Di erent temperatures Failure mechanism

Research on Electron Beam Welding of in situ TiB_(2p)/ZL101 Composite

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Journal of Shanghai Jiaotong university(Science) 2010年第4期15卷 479-483页

作者：崔海超芦风桂彭坤唐新华姚舜 Shanghai Key Laboratory of Materials laser processing and Modification Shanghai Jiaotong University

Electron beam welding of in situ TiB2p reinforced aluminum composites was studied. The results show that no obvious pores or cracks is presented in the weld seam. The grains in the weld seam are remarkably refined and TiB2 particles distribute much more homogeneously than that in base metal. The hardness values of fusion zone and heat affected zone （HAZ） are both increased in comparison with that of base metal. There are no interface reactions between TiB2 particle and A1 matrix. This results supply the evidence that the novel TiB2p reinforced aluminum composites can be well joined with the electron beam welding.

关键词： electron beam welding(EBW) composites particle distribution hardness