Wettability and transient liquid phase bonding of hafnium diboride composite with Ni–Nb alloys

An effective joining strategy suitable for ultra-high temperature ceramics will have to be developed for their wider application. In the present study, the wetting behavior of molten Ni–Nb alloys that will form during the transient liquid phase (TLP) bonding when a Ni/Nb/Ni interlayer is used to bond a HfB2 composite processed with MoSi2 addition was systematically investigated. In addition, a trial TLP bond of HfB2 composite with a Ni/Nb/Ni interlayer was also performed at 1,500 °C. Pure Ni was found to melt at a temperature well below its normal melting point during the heating period, which is mainly attributed to the interfacial reaction between HfB2, MoSi2, and the droplet. The contact angles of all Ni–Nb alloys rapidly decreased with time and showed good wetting against HfB2 composite. Among them, the pure Ni droplet totally disappeared around 1,400 °C during heating. SEM–WDS microstructural analysis on the cross section of the wetting sample revealed that the reaction layer contained multiple intermetallic compounds involving Si, suggesting the reaction with the sintering aid MoSi2. With the 40 at.% Nb addition, less interfacial reaction at the Ni–Nb alloy/HfB2 composite interface was observed. Consequently, it was revealed that a well-bonded interface was achieved when HfB2 composite was bonded using the Ni/Nb/Ni interlayer.