Temperature-gradient induced microstructure evolution in heat-affected zone of electron beam welded Ti-6Al-4V titanium alloy

• 来源期刊: 材料科学技术（英文版）
• 年，卷（期）: 2019,（8）
• 页码范围: 1681-1690
• 页数: 10页
• 语种: 英文

摘要

The heat-affected zone (HAZ) of electron beam welded (EBW) joint normally undergoes a unique heat-treating process consisting of rapid temperature rising and dropping stages,resulting in temperature-gradient in HAZ as a function of the distance to fusion zone (FZ).In the current work,microstructure,elements distribution and crystallographic orientation of three parts (near base material (BM) zone,mid-HAZ and near-FZ) in the HAZ of Ti-6Al-4V alloy were systematically investigated.The microstructure observation revealed that the microstructural variation from near-BM to near-FZ included the reduction of primary α (αp) grains,the increase of transformed β structure (βt) and the formation of various α structures.The rim-α,dendritic α and abnormal secondary α (αs) colonies formed in the mid-HAZ,while the "ghost" structures grew in the near-FZ respectively.The electron probe microanalyzer (EPMA) and electron back-scattered diffraction (EBSD) technologies were employed to evaluate the elements diffusion and texture evolution during the unique thermal process of welding.The formation of the various α structures in the HAZ were discussed based on the EPMA and EBSD results.Finally,the nanoindentation hardness of"ghost" structures was presented and compared with nearby βt regions.