Microstructures of Components Synthesized via Electron Beam Selective Melting Using Blended Pre-Alloyed Powders of Ti6Al4V and Ti45Al7Nb

摘要:

研究了电子束快速成形TI6AL4V和Ti45Al7Nb合金混合粉末的特点，得到了成分均匀的Ti22Al3.5Nb2V合金。利用光学显微镜、扫描电镜、电子探针等手段，研究了成形试样的内部组织，并测试了不同组织区域的显微硬度。结果表明：TI6AL4V和Ti45Al7Nb合金混合粉末在电子束成形后，成分均匀，组织具有沉积态特征，包括板条马氏体区和α2+β两相区，板条马氏体区位于成形零件顶部10个熔覆层厚度，在成形过程中，受再热循环的影响，已凝固形成的马氏体不断分解形成α2+β两相区，α2为短棒状，β分布于α2相之间，在成形件底部，部分α2相发生等轴化。显微硬度测试结果显示，马氏体区硬度明显高于α2+β两相区。拉伸结果显示，抗拉伸强度为1214.3 MPa，延伸率达到18%。

Abstract:

The Ti-based components were synthesized via electron beam selective melting (EBSM) using blended pre-alloyed powders of Ti6Al4V and Ti45Al7Nb with a mass ratio of about 1:1. The microstructures and the chemical compositions of EBSM component samples were investigated by optical microscopy (OM), scanning electronic microscopy (SEM), electron probe micro-analyzer (EPMA) and X-ray diffraction (XRD). The results indicate that an increase of energy density leads to a decrease of fusion defects and an increase of density of the samples. The macro-structure consists of two regions, the martensite phase region and α2+β phase region. The martensite phase is formed due to the rapid solidification, while the reheating cycles have a remarkable effect on the formation of α2+β phase. The micro-hardness of martensite region is significantly higher than that of α2+β phase region. Due to the discontinuous distribution of thick platelet α2 phase along grain boundaries and the high coordinating deformation capability of equiaxial α2 phase, the samples have a tensile strength up to 1214.3 MPa, and a large elongation of 18%.