激光熔覆原位合成强化相的结晶过程

Crystallization of in-situ synthesized reinforced phase by laser cladding

在Ti-3Al-2V表面激光熔覆原位合成TiB/TiN复合强化钛基复合涂层。采用XRD、SEM、EPMA和TEM等方法分析原位合成强化颗粒的显微形貌和生长方式。结果表明:熔覆层中存在两种原位合成强化相TiB和TiN;面心立方结构的TiN具有较高的各向同性,在快速凝固条件下呈现树枝晶和等轴晶形貌;TiB具有两种形态,初生TiB具有空心结构针棒状TiB,空心结构内部孔洞不规则,各处壁厚不均匀;共晶的TiB呈现细小、实心的针棒状组织形貌。TiB为B27结构,点阵常数为α=0.628 nm,b=0.312 nm和c=0.461 nm;TiB沿[0 1 0]方向的生长速度最快,堆垛层错的方向平行于(1 0 0)面,并且伴随位错的产生。

In-situ synthesized TiN and TiB reinforced titanium matrix composites were fabricated on surface of Ti-3Al-2V alloy by laser cladding. The coating were evaluated and characterized by X-ray diffractometry（XRD）, scanning electron microscopy（SEM）, electron probe microanalyzer（EPMA） and transmission electron microscopy（TEM）. The results show that there are two in-situ synthesized reinforced phases in the coating TiN and TiB. The high isotropic structure and high cooling speed of laser cladding lead to TiN with dendrite/equiaxed grains. TiB shows two different shapes, little primary TiB shows coarse needle platelet with hollow shape, the hollow structure is not regular and the wall thickness is different. The eutectic TiB shows fine solid needle platelet. TiB is B27 structure with lattice constants a=0.628 nm, b=0.312 nm and c=0.461 nm. TiB grows fast in the direction of [0 1 0]. The stacking fault is parallel to（100） and it is accompany with the generation of dislocation.