钛合金TIG焊接头晶粒尺寸非线性梯度特征

以显微组织与晶粒尺寸统计分析为基础,研究了TC4钛合金不同TIG焊工艺的焊接接头显微组织及其晶粒尺寸变化,引入了晶粒梯度特征值概念,以表征钛合金焊接接头显微组织的非均匀性.结果表明,TC4钛合金TIG焊接头显微组织的晶粒尺寸从焊缝中心经热影响区至母材呈现非线性变化,晶粒尺寸变化率(晶粒梯度)在柱状晶区(CZ)和粗晶区(CGZ)交界处出现最大值,称之为晶粒梯度特征值;随着TIG焊热输入增大,晶粒梯度特征值逐渐减小,但相对位置不发生改变.晶粒尺寸梯度特征值能够反映钛合金焊接接头组织的不均匀性,这对于探索钛合金焊接接头的服役性能具有重要的意义.

Nonlinear gradient features of grain size in TIG welded joint for titanium alloy

In the paper, based on the grain size observation and statistics analysis on TIG welded joints of TC4 titanium alloy, the gradient features of the gain sizes in welded joints with different heat input are studied experimentally for characterizing the microstructure heterogeneity by introducing a conception of grain gradient eigenvalue.The results show that the grain size in the TIG welded joint nonlinearly changes from the center of weld metal after the heat affected zone to the base metal, and the size changing rate(grain gradient) has a maximum value in the boundary between the columnar zone(CZ) and coarse grain zone(CGZ).The grain size gradient maximum value proposed as the grain gradient eigenvalue is inversely proportional to heat input in TIG welding and its position is independent with the heat input.The concept of the gain gradient eigenvalue can represent the microstructure heterogeneity in the welded zone and heat affected zone, and is significantly important for evaluating the service properties of titanium alloy welded joint.