Abstract
Adhesive bonding for structural applications has many advantages such as reducing the weight of vehicles and providing efficient stress transfer across joined materials. The largest asset of adhesive bonding is that they can join dissimilar materials. To achieve the highest joint strength possible when using metals, however, the metal surfaces have to be pre-treated. This can be done in a variety of ways, such as grit blasting or chemical etching. Chemically etching the surface produces the highest strength joints, but has many drawbacks. The first of which is that each metal used requires a different treatment chemistry. This reduces the materials available for selection as a result of increased pre-treatment complexity. The current work focusses on stainless steel and titanium alloy. The lap shear bond strength for both metals increased significantly after a cold atmospheric plasma (CAP) treatment and was in line with the chemical etching processes. The durability of both metals demonstrated that the plasma treatment increases the performance. For stainless steel the durability is similar to the chemical etch process. For titanium the durability performance is increased, but does not reach the level of the chemical treatment process. A combination of surface science techniques has revealed that there are three mechanisms which lead to an increased bond strength. These are: a reduction in hydrocarbon contamination, shown using X-ray photoelectron spectroscopy (XPS) and time of flight____,-____,secondary ion mass spectrometry (ToF-SIMS). The growth of the surface oxide layer, analysed using an XPS sputter depth profile, and functionalisation of the oxide layer, which has been probed using ToF-SIMS, both lead to an increase in lap shear bond strength. The feasibility of the process rests on two factors. The first is achieving equivalent mechanical properties, the second factor is the energy, resources and time required for a given treatment. The first has been satisfied in this work, the second has been investigated using a life cycle analysis approach which found that plasma treatment had a higher impact on the environment when compared to oxalic acid etching. but this assumed that the acid is 100____% efficient, which is far from the case. When simulated in a `real world' scenario, there is nearly parity between the two treatments Based on the data presented in this work, including analysis of the process life cycle, CAP has the potential as a first multi material pre-treatment for structural adhesive bonding.