An insight to wetting and joining of HfB2 and ZrB2 based ultra high temperature ceramics: A review

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2024-09, Vol.495, p.153387, Article 153387
• Main Authors: Bajpai, Shipra, Dubey, Shruti, Venkateswaran, T., Singh, Sudhanshu S., Balani, Kantesh
• Format: Article
• Language: English
• Subjects: Active metal brazing; Diffusion bonding; Joining of Hafnium diboride (HfB2) and Zirconium diboride (ZrB2); Shear strength; Wettability
• ISSN: 1385-8947
• DOI: 10.1016/j.cej.2024.153387

[Display omitted] •Progress on joining of (Hf,Zr)B2 diboride based ultra high temperature ceramics (UHTCs)•Joining of UHTCs for thermal protection, and thermal management.•Interfacial wettability and reactivity of diborides and solid-state diffusion bonding.•Role of Nickel filler on interfacial reactivity, phases, and wettability of diborides.•Molecular dynamics and density function theory to predict wettability of diborides.•Future directions of spark plasma sintering, towards joining of UHTCs. Stringent applications of HfB2 and ZrB2 based ultra-high temperature ceramics (UHTCs) for hypersonic and re-entry space vehicles necessitate their joining with ceramics or metallic structural alloys. Brazing is the most used joining method for diborides requiring good wettability; consequently, this article critically reviews the high temperature interfacial wettability of diborides in contact with different metals like Ag, Au, Ni, Cu, etc. Contact angle data of various metals in contact with diboride is summarized in this paper along with the assessment of the underlying wetting mechanisms. Surface oxides, testing atmosphere, and other aspects affecting the wettability are evaluated along with the approaches to improve it. High melting point (∼1450 °C) and lower contact angle (∼20°) of Nickel on diborides makes it a good choice as filler material; thus, a detailed case study considering its wettability, phase diagram etc. is reviewed to elicit interfacial reactivity with HfB2 and ZrB2. Molecular dynamic simulation and density function theory predicting the wettability and adhesion of various metals on the surface of diborides are also discussed, which exemplify visualization of the experimentally observed values. Microstructural evolution during different joining methods; i.e. active metal brazing, diffusion bonding, welding etc.; are described in detail providing an insight into the final properties of the joint in terms of interfacial strength (shear and bending strength) and thermal stability (oxidation resistance, plasma exposure etc.). The impact of thermal expansion mismatch, residual stresses, and chemical reactions induced during joining are also highlighted to assist in parameter selection. This article concludes with the summary on the current state of the art in the joining diborides followed by scope for future research directions.