Joining of Engineering Ceramics to Metals

Abstract

In this research, successful joining of Al₂O₃ to Al₂O₃ was achieved through novel brazing methods involving the Ti-Al, Ti-Al-Ni, and Ti-Al-Fe systems. Subsequently, the Ti-Al-Ni-based braze was employed to join Al₂O₃ and Ti6Al4V alloy. Additionally, the study demonstrated the feasibility of using a commercially available Pd-40wt%Ni braze and a novel Ni-14wt%Zr braze for effectively joining Al₂O₃ to Ti6Al4V alloy. Furthermore, successful bonding of small components of Al₂O₃ and Ti6Al4V alloy was achieved using a commercial Ti-15wt%Ni-15wt%Cu braze. However, this method faced challenges when applied to larger samples with dimensions of 25 mm x 25 mm and a thickness of 4 mm. The project investigates brazing as method of joining, using a braze that can withstand high temperature application as well as, accommodate the difference in coefficient of thermal expansion (CTE) between the braze and the ceramic-metal. Aluminium Oxide (Al₂O₃) were used to bond with both Titanium (Ti) and Ti6Al4V alloy. Thus, it allows the understanding of both reactive and non-reactive systems of bonding. Moreover, a titanium aluminide (TiAl) braze was used in the latter case. TiAl braze seems to be amongst the best options with regards to high temperature restriction. The braze seems to have poor ductility at room temperature which means that it can have poor resistance to force and stress. Further investigations such as SEM and EDAX were used to identify the reactions. When nickel was used as a braze, LM, a strong bond was developed, leading to investigating Ni element further. Wettability results show that enough addition of Ni or Fe to TiAl braze can enhance the joint. SEM results shows that nickel dissolves into the substrate with no interfacial compounds noticed. This dissolution is causing damage to the interface of the ceramic. Fe shows identical results to Ni. Four braze systems were used to bond metal to ceramic (Al₂O3 / Ti6Al4V), two of which are commercial – Pd-Ni (PALNI) and Ti-Cu-Ni (TICUNI) – whilst the other two were novel and developed by this project – Ti-Al28%-Ni3.6% and Ni-Zr14% (weight-percentage). Analysis from SEM and EDAX showed that Palni and NiZr were most efficient in terms of wetting, flowability, and strength. Three braze systems: Ti-Al28%-Ni3.6%, Pd-Ni40%, and Ni-Zr134% were heat-treated at 450°C for 500hrs post-brazing. While other braze systems had either formed brittle phases or broken at handling, Pd-40Ni and Ni-14Zr braze systems showed good bonding results. Metal-to-ceramic brazed with Palni or Ni-14Zr were tested for single lap shear test. Furthermore, initial brazing hardness was then compared to heat-treated hardness using nano-indentation. In addition to hardness, results for toughness and young’s modulus were obtained. The comparison of before and after heat treatment, has showed that no further chemical reaction took place, suggesting a reliable joint for industrial use.