Wetting at High Temperature - Drops and Bubbles in Contact with Solid Surfaces - page 317

Figure 14. NiB50 alloy: solid-liquid interface showing the eutectic structure and a negligible recrys-
tallization of HfB 2 at the interface.

Figure 15. Cross section SEM micrographs (BE mode) of a HfB 2 //NiB50//HfB 2 joint: T = 1300 ◦ C,
Ar/H 2 10 + 5 Pa, 10 min [157].

operating at 1300 ◦ C under the same conditions of the wetting tests using the NiB50
alloy as filler metal [139, 140, 157, 158].
Figure 15 shows the metallographic section of a HfB 2 /Ni50B/HfB 2 joint, where
a very good penetration of the filler alloy can be observed, without any voids and
any dissolution of the solid ceramic phase. Some exploratory shear tests have been
made, using a specific attachment device to an INSTRON 9501 mechanical testing
machine, to evaluate the interfacial shear strength. Very good results have been
obtained, ranging from 70 to 170 MPa [157].
For all specimens a typical brittle fracture happens in the ceramic body and not
along the joint with cracks propagating in the ceramic and sometimes across the
interfacial metallic layer.