【作者】 徐震霖； 何宜柱； 毛铱； 王林； 王良龙；

【Author】 XU Zhenlin;HE Yizhu;MAO Yi;WANG Lin;WANG Lianglong;School of Materials Science and Engineering,Anhui University of Technology;Key Laboratory of Green Fabrication and Surface Technology of Advanced Metal Materials,Ministry of Education;Shanghai Hanbang United 3D Tech Co.,Ltd.;Jiangsu Institute of 3D Intelligent Manufacturing Limited Company;

【机构】 安徽工业大学材料科学与工程学院； 先进金属材料绿色制备与表面技术教育部重点实验室； 上海汉邦联航激光科技有限公司； 江苏三维智能制造研究院；

【摘要】 等原子CoCrFeMnNi高熵合金具有良好的热稳定性和耐腐蚀性,而且,随着温度的降低,其抗拉强度和塑性逐渐增加。这些特性使其在航空航天、核工业和生物材料等领域都有着广阔的潜在应用前景。但是,传统的制备技术难以满足复杂构件的生产要求,激光熔覆只适用于制备高熵合金涂层,电弧熔炼高熵合金组织粗大,机械合金化制备的高熵合金存在成分偏析。增材制造技术（3D打印）的发展和应用,为高熵合金的制备提高了新思路,并得到了与传统制造方法不同的性能。激光选区熔化技术（SLM）具有制备高精度和高质量的金属复杂结构能力,并能节约生产周期和制造成本,成为广泛应用的的增材制造技术之一。为得到高相对密度的SLM成形FeCrNiCoMn高熵合金,本文采用不同的激光功率和扫描速度进行SLM成形工艺优化。然后,采用X射线衍射（XRD）、场发射扫描（FESEM）和背散射电子衍射技术（EBSD）分析了其微观组织结构。并对比研究了SLM成形高熵合金和铸造高熵合金的耐蚀性能。高熵合金粉末通过气雾法制备,主要为球形,粒径分布为20～80μm(d₅₀=43.4μm)之间。采用上海汉邦HBD-100打印设备进行激光选区熔化成形,随着激光能量密度的增加,试样相对密度先增加后减小。获得优化工艺参数:激光功率P=150 W,扫描速度V=500 mm/s,扫描间距50μm,铺粉厚度60μm。此时,试样相对密度可达99.1%。采用RIETAN-FP软件对XRD数据进行拟合,结果表明,SLM成形FeCrNiCoMn高熵合金为单相面心立方结构,每种元素均有相同的几率占据晶胞中的每个位置,晶格尺寸为3.6001（2） A。SLM成形高熵合金微观形貌为典型由熔池连接而成的层状结构,场发射高倍扫描可以观察到大量胞状晶组织。EBSD分析可知,这些胞状晶主要为的晶界角度小于5°,晶粒尺寸为1～2μm,明显区别于铸造高熵合金主要为粗大的树枝晶结构。EDS结果显示,SLM成形FeCrNiCoMn高熵合金各种元素均匀分布,没有明显的成分偏析现象。SLM成形FeCrNiCoMn高熵合金的非平衡精细组织的形成主要取决于激光成形过程中快速加热和冷却特点。而且,SLM高熵合金硬度较均匀,纳米压痕硬度为2.84±0.13 GPa。无论在NaCl溶液还是H₂S04溶液中,SLM成形的高熵合金的耐腐蚀性能优于铸造成形的高熵合金,分析认为,这是由于SLM成形高熵合金组织均匀细小,且无成分偏析。更多还原

【Abstract】 The equiatomic CoCrFeMnNi high-entropy alloy（HEA） has been extensively investigated because of its excellent properties like good thermal stability and corrosion resistance,furthermore,its strength and plasticity both increase with the decrease of experimental temperature.The promising properties contribute to its great potential in many applications,including aerospace industry,nuclear industry and biological materials.However,traditional manufacturing processes can not meet the production requirement of complex combination structure.Laser cladding only applies to surface coating.The cast HEAs have a coarse grain structure,and Cr and Mn presents obvious agglomerates in the CoCrFeMnNi HEA which was fabricated by mechanical alloying.Therefore,additive manufacturing（AM） may be considered an effective approach to improve the formability.Selective laser melting（SLM） has been extensively applied in AM,since it allows high-precision and high-performance metal parts to be fabricated without the need for part-specific instruments;it also reduces the design and production cycle and decreases the cost and time of manufacturing.The forming process was optimized using different laser power and scanning speed,to obtain high relative density alloys.Then the SLM-fabricatedCrMnFeCoNi HEA samples were investigated for microstructure characterization,by means of X-ray diffraction（XRD）,field-emission scanning electron microscopy（FESEM）and electron backscatter diffraction（EBSD）.As well as,the corrosion resistance of SLM-fabricated and cast CrMnFeCoNi HEA was studied.The spherical powder was fabricated by gas atomization with an average particle size(d₅₀) of 43.4μm.The particle size distribution was in the range of 20 ～80 μm.The sample was fabricated using a HBD-100 metal 3 D printer（Shanghai Hanbang,China）.The relative density of the SLM HEAs increased first and then deceased,with the increasing of laser energy density.The optimized process parameters were:laser power 150 W,scanning speed 500 mm/s,hatch distance 50 μm and layer thickness 60 μm.The relative density of this sample was up to 99.1%.Then,the Rietveld program RIETAN-FP was used to analyze the XRD profiles.A single family of face-centered cubic（fcc） peaks were clearly observed.Each element,has the same opportunity to occupy each site of a unit cell,and the lattice parameter was calculated as 3.6001（2） A.The SLM HEA exhibited typical layered microstructure characterized by melt pools generated by the laser beam.A large number of cellular grains were observe in highmagnification FESEM image.Besides,the grains were approximately 1～2 μm in size,with grain boundary angles lower than 5°.This was significantly different from the coarse dendrite structure of cast HE As.According to the elemental EDS maps,the constituent elements of the HE A were evenly allocated without any support of agglomerate or segregation.This was attributed to the fast solidification and large temperature gradients of the molten pool during the SLM process.Compared with cast structures,the laser additive manufactured metal parts usually possess much finer grains because of the fast heat conduction from the molten area into the nearby metal.The formation of unbalanced crystal phases resulted from these high speeds of cooling.The hardness uniformity of the SLM-fabricated CoCrFeMnNi HE A was measured,and the nanoindentation hardness was found to be 2.84±0.13 GPa.Potentiodynamic polarization tests in NaCl and H₂SO₄ solution indicated that SLM CoCrFeMnNi HE A could provide an excellent corrosion resistance than cast HE A,because of fine uniform structure without composition segregation in SLM CoCrFeMnNi HEA.更多还原