Growth of isothermally-solidified titanium joints using a multi-component Zr–Ti–Cu–Ni–Be amorphous alloy as a brazing filler

The growth and microstructure properties of Ti (grade 2) joints brazed by a Zr41.2Ti13.8Ni10.0Cu12.5Be22.5 bulk metallic glass alloy filler have been investigated with regard to the control through isothermal solidification. Two characteristic joints were prepared at different isothermal brazing conditions: an acicular growth structure including a continuous segregation in the central area (at 830 °C for 300 s), and a structure with coarse acicular grains throughout the joint (at 830 °C for 1800 s). The primary phase solidified isothermally was hexagonal α-Ti, and upon subsequent cooling, the secondary α- and γ-phases formed at the intercellular regions through a eutectoid decomposition of β-Ti. The γ-phase was identified as having a phase formula of [Ti,(Zr)]2(Cu,Ni) with a tetragonal Ti2Cu structure (a = 2.955 Å, c = 10.827 Å, space group = I4/mmm). This phase was grown on primary α-Ti grains with an orientation relationship of 10 1 ¯ 0 α ∥ (200)γ and 1 2 ¯ 1 3 ¯ α ∥ [031]γ. The isothermally-solidified, primary α-Ti grains dominating the entire joint were epitaxially grown, depending on the orientation of the randomly oriented Ti parent grains.