用脉冲激光熔覆方法在TC6钛合金表面制备具有柱状组织特征的钛合金涂层,研究了涂层的组织特征和液--固前沿热力学参数的变化及其对柱状组织的影响.结果表明, 该涂层的组织形态具有典型的柱状特征, 涂层仍由α’马氏体构成,但是其尺寸更加细小, 柱状组织中主要合金元素分布的均匀性显著提高.柱状组织是在“液相→β相”转变过程中由$G/R$比值所决定的原始柱状β相结构在室温下的残留. 在凝固过程中,固液界面处$G/R$值的变化决定了所获得的柱状β相形态的变化,并最终导致柱状组织向非柱状组织转变.
A TC6 titanium alloy coating with columnar microstructure was prepared on the substrate of TC6 titanium alloy by pulse laser cladding successfully and studied by SEM, XRD and EPMA. The results showed that, the microstructure of the coating showed a typical columnar characteristic. The coating was still composed of α′ martensite which was finer than that of conventional heat treatment or welding. The distributions of main alloying elements were more homogeneous in columnar structure than in substrate. With the solidification theory and calculated results of temperature gradient (G) and solidification velocity (R) at the solidification interface, the formation of columnar structure was studied. The columnar structure was formed in the transition of “liquid phase→ β phase” and determined by G/R ratio at the solidification interface. In cooling process, the morphology of columnar β-phase was retained. With the variety of G/R ratio at the solidification interface, the morphology of the columnar structure varied and finally transformed to other structures.
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