Interaction of HfB2 with Nickel and Ni–20% Cr Alloy (Nichrome)

Wettability and interfacial phenomena in the liquid‐phase bonding of refractory diboride ceramics: Recent developments

“…The process used to produce transition metal borides may also affect their wetting properties and even melting behavior of metals (Section 2) because of possible introduction of impurities into ceramics during their production. For example, as remarked in Section 2.1, 3−4 wt% (WC+Co) milling impurities in HfB 2 ceramic resulted in a smaller contact angle of pure Ni (θ = 3 • −5 • ) 18 than that reported by Passerone et al 21 for HfB 2 containing HfSi 2 or B 4 C as sintering aids.…”

“…The solid-state interaction between Me-X alloys containing a sufficient amount of a reactive additive X for MB 2 can form a continuous interfacial reaction product, XB x (Figure 2B, Stage 2). Examples have been reported by Grigoriev et al 18 for Ni-Cr/HfB 2 couple heated to a temperature below the melting point of the Ni-Cr alloy (20 wt% Cr), where a continuous Cr 2 B interfacial layer was reactively formed. On the contrary, pure Ni does not form any reaction product by the solid-state interaction with the same substrate.…”

“…The formation of a liquid layer between a boride and a metal helps to establish true contact in the couple of dissimilar materials and facilitates the mass transfer through the interface since the diffusion rate in a liquid is a few orders of magnitude higher than that in a solid. In the sessile-drop wettability tests, contact melting has been experimentally observed during contact heating of solid Ni (T m Me = 1723 K) with MB 2 substrates because Ni started to melt at a much lower temperature, for example, in Ni/ZrB 2 couple, melting started at 1423 K (complete melting at 1523 K) 15 , in Ni/HfB 2 , at 1573 K (HfB 2 free of sintering aids) 16 , 1433 K (HfB 2 +MoSi 2 ) 17 and 1573 K (HfB 2 with 3−4 wt% (WC+Co) milling impurities) 18 . In the case of pure Cr (T m Me = 2173 K), contact melting starts at 1873 K, 1923 K, and 2073 K on TiB 2 , W 2 B 5 , and ZrB 2 substrates, respectively 19 .…”

“…A similar behavior was reported by Passerone et al 20,21 , who experimentally proved the formation of Ni 21 B 6 Hf 2 phase due to the liquid-state interaction in the Ni-17B/HfB 2 couple and confirmed it also by thermodynamic calculations and analysis of phase equilibria in the Ni-Hf-B system. For the liquid-state interaction, Grigoriev et al 18 observed the formation of Ni 20 B 2 Hf 6 phase in the Ni/HfB 2 couple and in the Ni-Cr/HfB 2 couple with hypoeutectic Ni-Cr alloys, while Ni 3 B 6 Cr 2 phase was noted in the Ni-Cr/HfB 2 couple with hypereutectic Ni-20Cr alloy (contrary to the observation of Cr 2 B phase formation in case of the solid-state interaction in the same system).…”

“…Additionally, the formation of interfacial reaction product by the solid-state interaction makes the contact melting of the Ni-Cr alloy more complicated because first, the liquid phase is formed between the alloy sample and reactively formed the Cr 2 B layer and next, the F I G U R E 3 Schematic illustration of phenomena taking place during liquid-phase interaction (A) complemented with substrate dissolution, wetting, and liquid metal penetration inside the substrate along grain boundaries and release of non-metallic inclusions from the substrate, and subsequent solidification of Me/MB 2 couples (B) complemented with re-crystallization of the MB 2 phase through the liquid phase by the dissolution-precipitation mechanism due to heterogenous nucleation and growth of secondary MB 2 precipitates at the surface of MB 2 substrate and non-metallic inclusions liquid phase reacts with HfB 2 to form a multicomponent eutectic. 18…”