Mo_(0.2)FeCoCrNi高熵合金定向凝固枝晶分裂与取向偏转
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摘要
为了研究Mo_(0.2)FeCoCrNi高熵合金定向凝固组织的形成规律,文中通过对比分析试样上端最终过渡区与稳态生长区成分分布,准确界定Mo_(0.2)FeCoCrNi高熵合金中的溶质与溶剂,并计算出平衡溶质分配系数与偏析度,采用液相淬火方法分析不同抽拉速度下Mo_(0.2)FeCoCrNi高熵合金固液界面形貌。对比分析铸态组织与不同抽拉速度高熵合金定向凝固组织,研究树枝晶尖端分裂与晶体生长的取向关系。研究结果表明:在2～200μm·s~(-1)的抽拉速度范围内均存在树枝晶尖端分裂情况,随着抽拉速度的增大枝晶主干变短,枝晶分枝变长,枝晶两分枝的夹角变大。树枝晶尖端两分枝的竞争生长,导致枝晶主干发生偏转,逐渐与热流方向平行。
The paper studies the formation rule of directional solidification microstructure of Mo_(0.2) FeCoCrNi high entropy alloy.The distribution of solute and solvent in Mo_(0.2) FeCoCrNi high entropy alloy was accurately defined by comparing and analyzing the composition distribution of the final transition zone and the steady growth zone at the upper end of the sample.The equilibrium solute partition coefficient and segregation degree were calculated.The interface morphology of Mo_(0.2) FeCoCrNi high entropy alloy at different pull-out speeds was analyzed by liquid phase quenching.The as-cast microstructure and directionally solidified microstructure of high entropy alloy with different pull-out speeds were analyzed.The relationship between the dendritic tip splitting and the crystal growth was studied.The results show that the dendrite tip splitting exists in the range of 2～200μm·s~(-1) pull-out velocity.With the increase of the pull-speed,the dendritic stem becomes shorter,the dendritic branch becomes longer,and the angle between the two branches of the dendrite becomes larger.The dendritic trunk deflects become gradually parallel to the heat flow direction because of the competitive growth of the two branches at the tip of the dendrite.
The paper studies the formation rule of directional solidification microstructure of Mo_(0.2) FeCoCrNi high entropy alloy.The distribution of solute and solvent in Mo_(0.2) FeCoCrNi high entropy alloy was accurately defined by comparing and analyzing the composition distribution of the final transition zone and the steady growth zone at the upper end of the sample.The equilibrium solute partition coefficient and segregation degree were calculated.The interface morphology of Mo_(0.2) FeCoCrNi high entropy alloy at different pull-out speeds was analyzed by liquid phase quenching.The as-cast microstructure and directionally solidified microstructure of high entropy alloy with different pull-out speeds were analyzed.The relationship between the dendritic tip splitting and the crystal growth was studied.The results show that the dendrite tip splitting exists in the range of 2～200μm·s~(-1) pull-out velocity.With the increase of the pull-speed,the dendritic stem becomes shorter,the dendritic branch becomes longer,and the angle between the two branches of the dendrite becomes larger.The dendritic trunk deflects become gradually parallel to the heat flow direction because of the competitive growth of the two branches at the tip of the dendrite.
引文
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[2]BEN-JACOB E,GARIK P.The Formation of Patterns in Non-equilibrium Growth[J].Nature,1990,343(6258):523.
[3]BRENER E,MULLER-KRUMBHAAR H,TEMKIND.Kinetic Phase Diagram and Scaling Relations for Stationary Diffusional Growth[J].Europhysics Letters,2007,17(6):535.
[4]SINGER H M,SINGER-LOGINOVA I,BILGRAM JH,et al.Morphology Diagram of Thermal Dendritic Solidification by Means of Phase-field Models in Two and Three Dimensions[J].Journal of Crystal Growth,2006,296(1):58.
[5]XING H,DONG X L,WU H J,et al.Degenerate Seaweed to Tilted Dendrite Transition and Their Growth Dynamics in Directional Solidification of Non-axially O-riented Crystals:A Phase-field Study[J].Scientific Reports,2016,6:26625.
[6]CHEN Y,BILLIA B,LI D Z,et al.Tip-splitting Instability and Transition to Seaweed Growth During Alloy Solidification in Anisotropically Preferred Growth Direction[J].Acta Materialia,2014,66:219.
[7]宇红雷.定向凝固晶粒竞争生长行为研究[D].西安:西北工业大学,2015.YU Honglei.Research on Competitive Grain Growth During Directional Solidification[D].Xi’an:Northwest Polytechnic University,2015.(in Chinese)
[8]AKAMATSU S,FAIVRE G,IHLE T.Symmetrybroken Double Fingers and Seaweed Patterns in Thinfilm Directional Solidification of a Nonfaceted Cubic Crystal[J].Physical Review E,1995,51(5):4751.
[9]PROVATAS N,WANG Q Y,HAATAJA M,et al.Seaweed to Dendrite Transition in Directional Solidification[J].Physical Review Letters,2003,91(15):155502.
[10]AMOOREZAEI M,GUREVICH S,PROVATASN.Orientation Selection in Solidification Patterning[J].Acta Materialia,2012,60(2):657.
[11]WANG Z J,WANG J C,YANG G C.Phase Field Investigation on Cellular Tip Splitting During Directional Solidification[J].Scripta Materialia,2009,61(9):915.
[12]LIU G,LIU L,LIU X,et al.Microstructure and Mechanical Properties of Al0.7CoCrFeNi High-entropy-alloy Prepared by Directional Solidification[J].Intermetallics,2018,93:93.
[13]REN M X,LI B S,FU H Z.Formation Condition of Solid Solution Type High-entropy Alloy[J].Transaction of Nonferrous Metals Society of China,2013,23(4):991.
[14]LIU W H,LU Z P,HE J Y,et al.Ductile CoCrFeNiMox High Entropy Alloys Strengthened by Hard Intermetallic Phases[J].Acta Materialia,2016,116:332.