Effects of trace Nb addition on microstructure and properties of Ti–6Al–4V thin-wall structure prepared via cold metal transfer additive manufacturing

Publication date: Available online 24 February 2020Source: Journal of Alloys and CompoundsAuthor(s): Jian Gou, Zhijiang Wang, Shengsun Hu, Junqi Shen, Yinbao Tian, Guancheng Zhao, Youquan ChenAbstractTo refine the coarse columnar prior-β grains across the layers in the cold metal transfer additive manufacturing (CMTAM) of a Ti–6Al–4V thin-wall structure, the addition of trace Nb, which functioned as heterogeneous nuclei, is proposed. After the addition of trace Nb powder, intra-layer bands were obtained in each layer of the Ti–6Al–4V wall, which divided each layer into two parts according to the existing forms of Nb, including a rich unmelted-Nb-powder zone and a (β-Ti, Nb)-phase-rich zone. The unmelted Nb powder with an average diameter of 170 nm—which acted as heterogeneous nuclei, promoting the columnar-to-equiaxed transition of prior-β grains—mainly existed in the lower zones of the layers. A random distribution of (β-Ti, Nb) phases was observed in the upper zones of the layers, which experienced the highest loads (398.8 mN) with indentation displacement of 2000 nm in nanoindentation tests. The trace Nb addition affected the interplanar distances of (β-Ti, Nb) phases and changed the solidification mode from planar to cellular. Tensile tests revealed that the average ultimate tensile strength increased from 990 to 1149 MPa, as the solution strengthening of the (β-Ti, Nb) phases played the dominant role in strengthening, while the average strain de...
Source: Journal of Alloys and Compounds - Category: Chemistry Source Type: research