激光熔化沉积制备TiB+TiC/Ti6Al4V复合材料微观组织研究

Microstructure of TiB+TiC/Ti6Al4V composite prepared by laser melting deposition

激光熔化沉积制备的钛合金微观组织中常出现异常粗大的柱状晶粒,限制了其在复杂承力结构件方面的应用。为降低原始晶粒的尺寸,提高合金强度,本文基于原位自生反应原理,在Ti6Al4V粉末中添加少量的颗粒增强体B_(4)C得到混合粉末,并通过激光熔化沉积工艺制备出熔覆层以及多层钛基复合材料(TMC)。利用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)和显微硬度仪等测试手段研究了B_(4)C的添加对Ti6Al4V合金微观组织的影响规律,并对其作用机制进行了分析。研究表明:B_(4)C的添加降低了原始β晶粒的尺寸,并强化了合金基体。当添加1wt.%B_(4)C颗粒时,晶粒的外延生长得到有效抑制,原始β晶粒开始出现柱状晶向等轴晶转变(CET)的趋势,柱状晶粒尺寸由原始的平均600μm减小到50μm。同时,B_(4)C与钛基体发生原位反应形成的混杂增强相TiB和TiC富集在晶界,构成三维网状结构,不仅限制了晶内α相的生长,同时也起到了第二相强化的作用,使基体的硬度较基材提高了15%以上。

In the microstructure of titanium alloys prepared by laser melting deposition(LMD),the columnar grains are often very large,which restricts its application in complex load-bearing structures.In order to reduce the size of the original grains and increase the strength of the alloys,based on the principle of in-situ autogenous reaction,a small amount of particle reinforcement B_(4)C was added to Ti6Al4V powder to obtain a mixed powder,and a cladding layer and a multi-layer titanium matrix composite(TMC)were prepared by an LMD process.Using optical microscope(OM),scanning electron microscope(SEM),transmission electron microscope(TEM),and microhardness tester,the influence of B_(4)C addition on the microstructure of Ti6Al4V alloy was studied and its mechanism was analyzed.Results show that B_(4)C addition not only refined the originalβgrains,but also strengthened the alloy matrix.When B_(4)C addition was 1wt.%,the epitaxial growth of the grains was effectively restrained,the originalβgrains experienced a trend of columnar grains to equiaxed grains transformation(CET),and the average diameter of the columnar grains reduced from 600μm to 50μm.At the same time,the hybrid reinforced phases TiB and TiC formed by the in-situ reaction between B_(4)C and titanium matrix enriched in the grain boundaries and formed a three-dimensional network structure,which not only restricted the growth of intracrystallineαphase,but also realized a second phase strengthening,leading to the increase in the hardness of the matrix by more than 15%compared with the base material.