B2型金属间化合物深过冷组织演化规律和高塑性机理

Structure defects, trace elements, constitution and quantity of secondary phases have significant effets on the ducility and plasticity of intermetallics with B2 structures (hereafter B2). All those microstructures mentioned above have more or less relationship to their solidificaiton histories. Therefore,preparation of sigle phase B2 is the key for this research.Undercooling technique is the most reasonable and effective method to synthesize sigle phase alloy with composition uniformity. Moreover, using this technique can not only prepare sigle phase alloy, but also can study microstructural evolution, dendritical growth model and intrinsical plasticity and ductility. Therefore, in this study we will prepare single phase NiSc and CoSc B2 intermetallics with composition uniformity by using a combinational processes of glass fluxing and cyclical-superheating undercooling technology. Firstly, we will follow strictly stoichiometric composition for the undercooling test, and also select nonstoichiometric compositions to prepare B2 in order to find out the compositional region in which single phase B2 can be prepared. Secondly,our research efforts will contribute to the study of nucleation, growth model and microstructure evolution using varaity of microstructure observation means and dendritic growth model. Thirdly,we will also contribute our efforts to investigate the compositional region in which single phase B2 can be obtained with nonstoichiometric compositions. The defect types of the single phase B2 prepared with nonstoichiometric compositions will be investigated using such as TEM and electron probe microanalysis (EPMA) equipments. Finally, based on the microstructual and defect type analyzing results, we will focus on the intrinsic plasticity research on the B2 with deforming test at different deformation rate and temperature. After these research, our objective is to reveal the relationship among the nonequilibrium microstructure,growth model,defect type and intrinsic plasticity.

B2型金属间化合物（简称B2化合物）凝固组织结构缺陷类型（空位或反位原子）、微量元素偏析规律、第二相及分布对其韧塑性具有重要影响。考虑到组织与凝固历史相关，本研究用熔融玻璃净化结合循环过热深过冷快速凝固技术，研究深过冷态B2化合物组织演化规律、金属凝固生长模式；研究B2化合物不同过冷组织塑性特性，揭示其本征塑性。用深过冷技术研究严格（或偏离）化学计量成分的NiSc和CoSc两种均质单相B2化合物的制备机理。用组织观察和枝晶生长模型研究非平衡凝固下B2化合物的形核、枝晶生长和组织演化规律，丰富B2金属间化合物非平衡凝固理论。用电镜等分析手段研究非平衡态获得均质单相B2化合物的成分范围和化合物结构缺陷类型。用变形和变型激活能理论研究B2化合物非平衡组织本征塑性及不同应变速率下B2化合物变形机理。最终明晰B2化合物非平衡组织演化、生长模式、结构缺陷类型和本征塑性的关系。

采用深过冷、水冷铜模吸铸和离心铸造快速凝固及第一性原理研究了B2-MSc(M为Ni或Co)金属间化合物的组织演化、缺陷和塑性。使M-50%Sc获得了170K和124K的深过冷，凝固形核点在净化剂-试样-石英坩埚的结合处。过冷M-50%Sc熔体凝固以枝晶生长，过冷Ni-50%Sc熔体快速定向凝固临界过冷度DT1*=37.2K，DT=37.2K～170K范围内枝晶尖端半径基本不变。没有一次粒化，二次粒化临界过冷度DT2*=170K。因Sc活泼，没有获得单相B2-MSc。170K范围内，因Sc的氧化和单或双反位NiSc，Ni-50%Sc凝固组织为B2-NiSc+(Ni2Sc+NiSc)共晶。.B2-MSc生长的动力学过冷，即原子进入和堆积到确定晶面形成有序排列是晶体生长首要控制因素，溶质扩散是第二因素。.因脆性Ni2Sc相，快速凝固态Ni-50%Sc强度低（86MPa），塑性差。经均匀化热处理后，强度为130MPa，延伸率为0.65%，硬度为HRC63。过冷Ni-50%Sc合金经51.5%轧制变形，纵截面组织为纤维状B2-NiSc和纤维之间不大于1微米的断续Ni2Sc颗粒。沿轧制方向Ni2Sc颗粒为“连续”流线分布，垂直于轧制方向Ni2Sc颗粒为“断续”流线分布。沿轧制方向的压缩强度282.7MPa，延伸率8.1%；垂直于轧制方向压缩强度334.9MPa，延伸率11.5%。沿着轧制方向的屈服强度、强度和塑性均约为垂直于轧制方向的～70%。因此，脆性Ni2Sc是影响B2-MSc性能的关键。.G/BNiSc=0.43，G/BNi2Sc=0.78，泊松比NiSc=0.31，泊松比Ni2Sc=0.19。所以，NiSc本征塑性，而Ni2Sc本征脆性。当过冷度DT大于63K，会形成VNi、VSc空位和Ni单或双反位NiSc。G/B缺陷NiSc值为0.47，缺陷对泊松比和Cauchy压力值影响很小，因此，缺陷型B2-NiSc缺陷金属间化合物塑性会得到提高。.B2-NiSc和Ni2Sc两相变形过程中无法协同一致，裂纹首先在B2-NiSc/Ni2Sc晶界萌生，经Ni2Sc折断并诱发B2-NiSc快速滑移至破坏。破坏的控制环节是晶界。