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本文研究了激光快速动态凝固下的凝固组织特征,讨论了在激光与金属交互作用时,其熔池内的不同区域结晶组织特征和形核机理。在激光与金属的交互作用的能量密度为2.85×10~3～1.70×10~4J/cm~2,计算冷却速度达8.0×10~4℃/s 条件下,发现激光动态凝固组织主要为不规则胞状,胞状树枝状和等轴树枝状等。在此基础上,探讨了激光动态凝固组织的形核的二类机理。一类是以未完全熔化的晶粒残骸作为形核质点;另一类是以固—液界面上的微熔晶粒作为形核的基质。提出了相应的形核模型。本实验结果表明,激光动态凝固之后,在其自由表面上存在两种混晶情况,其一是尺寸相差甚大的不同尺寸晶粒的混合共存;另一是柱状晶与等轴晶的混合共存。
In this paper, the characteristics of solidification microstructure under laser rapid dynamic solidification and the crystal structure and nucleation mechanism in different regions of the molten pool during laser-metal interaction are discussed. Under the condition of energy density of 2.85 × 10 ~ 3 ~ 1.70 × 10 ~ 4 J / cm ~ 2 and the calculated cooling rate of 8.0 × 10 ~ 4 ℃ / s, it is found that the laser solidification microstructure is mainly not Regular cell, cell dendritic and equiaxial dendrites. Based on this, the second kind of mechanism of nucleation of laser solidified microstructure is discussed. One is based on incompletely melted grain wreckage as nucleation sites; the other is based on the solidification of micro-melt grains on the solid-liquid interface. Put forward the corresponding nucleation model. The experimental results show that there are two types of mixed crystals on the free surface after laser dynamic solidification. One is the coexistence of different size grains with different sizes, and the other is the coexistence of columnar grains and equiaxed grains.