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Research progress on formation and suppression of crack defects in oxide eutectic ceramics by laser additive manufacturing

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Unique strength-ductility balance of AlCoCrFeNi_(2.1)eutectic high entropy alloy with ultra-fine duplex microstructure prepared by selective laser melting

CAILIAO GONGCHENG-JOURNAL OF MATERIALS ENGINEERING 2024年第5期52卷 34-45页

作者： Yao, Jiatong su, haijun Jiang, Hao Chen, Qian Shen, Zhonglin Yu, Minghui Zhang, Zhuo Guo, Min Northwestern Polytech Univ State Key Lab Solidificat Proc Xian 710072 Peoples R China Northwestern Polytech Univ Shenzhen Res Inst Shenzhen 518057 Guangdong Peoples R China

Oxide eutectic ceramics have excellent high specific strength , high temperature resistance , corrosion resistance , oxidation and creep resistance , and so on , which are considered to be the promising materials to be used in ultra -high temperature oxidation , corrosion and other extreme environments. It shows great application prospects in the new generation of high thrust -to -weight ratio aero-engine for hightemperature hot -end structural components. Laser additive manufacturing technology has become one of the most promising cutting -edge technologies for the preparation of high-performance complex structural components in recent years. Crack defect is easy to occur in the process of laser rapid solidification of ceramics , which seriously affects the quality and performance of the oxide eutectic ceramics components. So , it has become a key factor restricting the engineering application. Two typical laser additive manufacturing technologies for ceramics including laser engineered net shaping and laser power bed fusion were briefly summarized. The crack morphology characteristics of different shaped components formed by the above two technologies were analyzed and compared. The formation mechanism of cracks in laser additive manufacturing of oxide ceramics was explored from the perspectives of microstructure characteristics ,stress state. Further ,a systematic summary was presented focusing on the improvement of microstructures and the reduction of thermal stress to inhibit crack formation through optimization of process parameters ,compositional design ,and outfield assistance. Finally ,it is pointed out that the future development trends and breakthrough directions of oxide eutectic ceramics by laser additive manufacturing in terms of and factors ,and research.

关键词： oxide eutectic ceramic laser additive manufacturing crack defect formation mechanism crack suppression DIRECTED ENERGY DEPOSITION MECHANICAL-PROPERTIES PROCESS OPTIMIZATION ALUMINA CERAMICS MICROSTRUCTURE COMPOSITE ZIRCONIA COMPONENTS STRENGTH

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Journal of Materials Science & Technology 2022年第16期111卷 298-306页

作者： Yinuo Guo haijun su Haotian Zhou Zhonglin Shen Yuan Liu Jun Zhang Lin Liu Hengzhi Fu State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Research and Development Institute of Northwestern Polytechnical University in Shenzhen Shenzhen 518057China

As a typical dual-phase eutectic high entropy alloy(EHEA),AlCoCrFeNi_(2.1)can achieve the fair matching of strength and ductility,which has attracted wide attention.However,the engineering applications of as-cast AlCoCrFeNi_(2.1)EHEAs still face challenges,such as coarse grain and low yield strength resulting from low solidification rate and temperature gradient.In this study,selective laser melting(SLM)was introduced into the preparation of AlCoCrFeNi_(2.1)EHEA to realize unique strength-ductility balance,with emphasis on investigating the effects of processing parameters on its eutectic microstructure and properties.The results show that the SLM-ed samples exhibit a completely eutectic structure consisting of ultra-fine face-centered cubic(FCC)and ordered body-centered cubic(B2)phases,and the duplex microstructure undergoes a morphological evolution from lamellar structure to cellular structure as laser energy input reducing.The SLM-ed AlCoCrFeNi_(2.1)EHEA presents an excellent match of high tensile strength(1271 MPa),yield strength(966 MPa),and good ductility(22.5%)at room temperature,which are significantly enhanced by the ultra-fine grains and heterogeneous structure due to rapid solidification rate and high temperature gradient during SLM.Especially,the yield strength increment of~50%is realized with no loss in ductility as compared with the as-cast samples with the same composition.On this basis,the precise complex component with excellent mechanical properties is well achieved.This work paves the way for the performance improvement and complex parts preparation of EHEA by microstructural design using laser additive manufacturing.

关键词： Selective laser melting High-entropy alloy Eutectic structure Rapid solidification Tensile properties

Cracking behavior of newly-developed high strength eutectic high entropy alloy matrix composites manufactured by laser powder bed fusion

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Journal of Materials Science & Technology 2023年第32期163卷 81-91页

作者： Yinuo Guo haijun su Hongliang Gao Zhonglin Shen Yuan Liu Di Zhao Peixin Yang Quandong Hu Zhuo Zhang Research&Development Institute of Northwestern Polytechnical University in Shenzhen Shenzhen 518057China State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China

A novel AlCoCrFeNi2.1 eutectic high entropy alloy(EHEA)composite doped with SiC particles was designed and fabricated by laser powder bed fusion(LPBF).Its microstructure characteristic,tensile properties,and metallurgical defects,with an emphasis on cracking behavior,have been investigated.The results showed that the addition of SiC particles into the AlCoCrFeNi_(2.1)matrix enabled the development of a{100}texture and highly elongated columnar grains,which were the main contributors to mechanical behavior anisotropy.The ultimate tensile strength of 1466±26 MPa and elongation of 9%±3%achieved in the as-deposited EHEA composite surpassed those of advanced metal alloys subjected to additive manufacturing processes.Unfortunately,severe horizontal and longitudinal cracks,as well as a few micro-cracks were observed in the as-deposited bulk samples.Micro-cracks were verified to be associated with the aggregation of carbon and oxide particles.They formed in the final stage of solidification owing to insufficient liquid feeding ability and solidification contraction.The formation of macroscopic cracking was induced by the tensile stress accumulations at sample edges,and the stress concentration areas where microcracks and pores were located were the predominant propagation location.This work provides guidelines for defect control in SiC-reinforced EHEA,assisting in the high-performance design and integrated manufacturing of EHEA composite components.

关键词： Laser powder bed fusion Eutectic high entropy alloy Composites Defects

Tailoring Microstructure and Microsegregation in a Directionally Solidified Ni-Based SX superalloy by a Weak Transverse Static Magnetic Field

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Acta Metallurgica Sinica(English Letters) 2022年第7期35卷 1164-1174页

作者： Yong Zhao haijun su Guangrao Fan Chenglin Liu Taiwen Huang Wenchao Yang Jun Zhang Lin Liu Hengzhi Fu State Key Laboratory of Solidifi cation Processing Northwestern Polytechnical UniversityXi’an 710072China

A weak transverse static magnetic field(WTSMF,0–0.5 T)is applied to the directional solidification process of a DD3 Ni-based SX superalloy,aiming to tailor the microstructure and microsegregation of alloys.The mechanisms of microstructural refinement and microsegregation distribution caused by a WTSMF during directional solidification are discussed.It is shown that the primary dendrite arm spacing is rapidly reduced from 181 to 143μm,and the average size ofγ′phase is significantly refined from 0.85 to 0.25μm as the magnetic field increases from 0 to 0.5 T.At the same time,the volumefractions ofγ/γ′eutectic and the segregation coefficient are also gradually decreased.The 3D numerical simulations of the multiscale convection in liquid phase show that the modifications of the microstructure and microsegregation in DD3 are mainly attributed to the enhanced liquid flow caused by thermoelectric magnetic convection(TEMC)at dendrite/sample scale under the WTSMF.The maximum of the TEMC increases with increasing the magnetic field intensity.This work paves a simple way to optimize the microstructure and microsegregation in directionally solidified Ni-based SX superalloys without changing the processing parameters and composition.

关键词： Transverse static magnetic field Microstructure Segregation coefficient Ni-based single-crystal superalloy Thermoelectric magnetic convection

Effect of seed orientations on crystallographic texture control in faceted Al2O3/YAG eutectic ceramic during directional solidification

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Journal of Materials Science & Technology 2023年第15期146卷 86-101页

作者： Yuan Liu haijun su Zhonglin Shen Di Zhao Yinuo Guo Shanding Li Min Guo Lin Liu Hengzhi Fu State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Research&Development Institute of Northwestern Polytechnical University in Shenzhen Shenzhen 518057China

Crystallographic texture control is a major challenge in directionally solidified multiphase eutectic ceramics with complex faceted growth characteristics.In this study,the Czochralski(CZ)technique is proposed to prepare eutectic single crystal ceramic with large size(30 mm×125 mm).A highly oriented and unique texture of Al_(2)O_(3)/Y_(3)Al_(5)O_(12)(YAG)eutectic ceramic is formed via the 112¯0Al_(2)O_(3) single crystal seed induction based on crystallographic orientation tailoring.The orientations of Al_(2)O_(3)/YAG eutectic are more strictly constrained by single crystal seed induction on the basis of the minimum interface energy principle,resulting in a defined single orientation relationship along the solidification direction.In particular,the single crystallographic orientation can be obtained in a short competitive solidification distance under the influence of epitaxial solidification from single crystal seed.Therefore,it has been confirmed that the orientations of 112¯0Al_(2)O_(3) and 111YAG are preferentially stabilized with the minimum under-cooling during directional solidification.Crystallographic orientation disturbances and instabilities due to polycrystalline crystal seed are avoided.Finally,the successful texture control inducted by 112¯0Al_(2)O_(3) single crystal seed can provide a promising orientation design pathway for faced oxide eutectic solidification.

关键词： Seeding method Directional solidification Al_(2)O_(3)/YAG eutectic single crystal ceramic Crystallographic orientation

Formation and Evolution of surface Morphology in Overhang Structure of IN718 superalloy Fabricated by Laser Powder Bed Fusion

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金属学报:英文版 2023年第9期36卷 1433-1453页

作者： Haotian Zhou haijun su Yinuo Guo Yuan Liu Di Zhao Peixin Yang Zhonglin Shen Le Xia Min Guo State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an710072China Research&Development Institute of Northwestern Polytechnical University in Shenzhen Shenzhen518057China

Controlling the overhang surface quality is still a formidable challenge in manufacturing the components with complex structures during laser powder bed fusion(LPBF).This study systematically uncovers the effects of the volume energy density(VED)and overhang angle on the evolution of surface morphology and corresponding surface roughness(Ra)of top and down-skin surfaces of IN718 superalloy samples.The results show that balling,Plateau-Rayleigh instability,open pore and humping caused by the material stacking are the main factors contributing to the apparent deterioration of top surface quality.When the VED is 80–100 J/mm^(3),the high down-skin surface roughness is attributed to the serious dross caused by recoil pressure and sinking of the melt pool.Using insufficient VED(15–50 J/mm^(3))can easily lead to poor metallurgical bonding and material spalling on the down-skin surface.In addition,overhang angle also significantly affects down-skin surface roughness due to the stair effect and the adhered unmelted powders.An improvement in the surface quality of down-skin surface is observed when the overhang angle increases.Based on the finding of this investigation,an optical VED(59.5 J/mm^(3))significantly improves the top and down-skin surface quality and porosity of overhang samples.This study provides an insight into synergy ascension of the top and down-skin surface quality in the overhang structure.

关键词： Laser powder bed fusion IN718 superalloy surface roughness Overhang structure

Unveiling the dynamic instability mechanism of microstructure transformation in faceted oxide eutectic composite ceramics

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Journal of Materials Science & Technology 2023年第13期144卷 224-234页

作者： haijun su Yuan Liu Qun Ren Zhonglin Shen Min Guo Xi Li Jun Zhang Lin Liu Hengzhi Fu State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Research&Development Institute of Northwestern Polytechnical University in Shenzhen Shenzhen 518057China Department of Material Science and Engineering Shanghai UniversityShanghai 200072China

Microstructure control is a great challenge in the high-temperature gradient directional solidification of eutectic composite ceramics due to the complex solidification behavior.Herein,the microstructure trans-formation of faceted Al_(2)O_(3)/Er_(3)Al_(5)O_(12) thermal emission eutectic composite ceramics is explored over wide ranges of compositions(13.5 mol%-22.5 mol%Er_(2)O_(3))and solidification rates(2-200μm/s).Entirely cou-pled eutectics with primary phases suppressed are fabricated and the coupled zone is broadened in a wide range of 15.5 mol%-22.5 mol%Er_(2)O_(3) at low solidification rates.The competitive growth between eutectic and dendrite is evaluated on the basis of the maximum interface temperature criterion.In ad-dition,the mechanisms of irregular eutectic spacing selection and adjustment under different solidifi-cation rates are revealed based on Magnin-Kurz model.A successful prediction of lamellar to rod-like eutectics is achieved associated with the dynamic instability of lamellar eutectic and the corresponding enlarged coexistence region is mapped based on the interface undercooling.According to the well mi-crostructure tailoring,the flexural strength of Al_(2)O_(3)/Er_(3)Al_(5)O_(12) eutectic composite ceramics has improved from 508 MPa up to 1800 MPa due to the refined eutectic spacing with low fluctuation.The eutectic composite ceramics show strong selective optical absorption and the intensity increases with the refin-ing microstructure.The as-designed Al_(2)O_(3)/Er_(3)Al_(5)O_(12) composites with microstructural tailoring have great potential as integrations of structural and functional materials.

关键词： Directional solidification Laser floating zone melting Al_(2)O_(3)/Er_(3)Al_(5)O_(12)eutectic composite ceramics Eutectic growth mechanism Microstructure transformation

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基于时空图注意力网络的服务机器人动态避障

计算机工程 2024年第2期50卷 105-112页

作者：杜海军余粟上海工程技术大学电子电气工程学院上海201620

为了解决服务机器人在具有自主决策能力的密集人群中容易发生碰撞、假死和路径不自然等问题,在深度强化学习的框架下提出基于时空图注意力网络的服务机器人动态避障算法。时空图注意力网络作为邻近策略优化(PPO)算法的决策函数,首先采... 详细信息

为了解决服务机器人在具有自主决策能力的密集人群中容易发生碰撞、假死和路径不自然等问题,在深度强化学习的框架下提出基于时空图注意力网络的服务机器人动态避障算法。时空图注意力网络作为邻近策略优化(PPO)算法的决策函数,首先采用门控循环单元控制机器人对环境的记忆和遗忘程度,提取环境的时间特征,使其对行人运动趋势有一定的预测作用;然后采用图注意力网络获取机器人和行人在空间上的隐式交互特征,使机器人能寻找无碰撞路径;最后在PPO算法中对时空图注意力网络进行训练,使得机器人在人群中完成无碰撞导航任务。在人均2.5 m^(2)的动态封闭环境中对算法进行实验验证,结果表明,与非学习型的动态窗口算法相比,该算法导航成功率提高71个百分点,与基于学习型的DSRNN-RL算法相比,该算法导航成功率提高3个百分点同时导航路径更短。Gazebo环境下的实时导航测试结果表明,所提算法的平均推理时间为21.90 ms,可以满足实时导航的要求。

关键词：服务机器人动态避障深度强化学习时空图注意力网络实时导航

High temperature calcium-magnesium-alumina-silicate(CMAS)corrosion behavior of directionally solidified Al_(2)O_(3)/YAG eutectic ceramic

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Journal of Materials Science & Technology 2023年第34期165卷 66-74页

作者： Yuan Liu haijun su Zhonglin Shen Di Zhao Yinuo Guo Xiang Li Hao Jiang Dong Dong Chubin Yang State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Research&Development Institute of Northwestern Polytechnical University in Shenzhen Shenzhen 518057China Jiangxi Provincial Engineering Research Center for Magnesium Alloy Gannan Normal UniversityGanzhou 341000China

1.Introduction Modern turbine engines can be substantially damaged when the airborne silicate-based particles(fly ash,desert sand,volcanic ash,runway debris,etc.)are ingested into jet engines at high temperatures(1150−1250℃)[1-4],leading to severe CaO-MgO-Al_(2)O_(3)-SiO_(2)(CMAS)corrosion during their service life.In order to extend the engine life,many efforts have been devoted to thermal barrier coatings(TBCs)and environmental barrier coatings(EBCs)to protect the substrate from corrosion by molten CMAS[5-7].To be specific,thermochemical and thermomechanical corrosion are the two main mechanisms of CMAS corrosion[8].The structure and composition of the coatings were changed due to the chemical reaction between the molten CMAS and coating,the detrimental phases were then precipitated[9,10].

关键词： corrosion eutectic coating