Gary W. Critchlow

Review of surface pretreatments for titanium alloys

Many treatments to enhance the adhesion to titanium have been studied, especially with respect to their ability to improve the durability of bonded joints. This review examines the effectiveness of a diverse range of treatments in many durability studies and using a variety of tests. The review also identifies 23 techniques that have been used to examine the surfaces of pretreated titanium alloy. These range from complex and costly ultra-high vacuum based surface analytical techniques, such as X-ray photoelectron spectroscopy, to those which are more simple and commonly available, such as contact angles. Overall, the most effective methods are sodium hydroxide and chromic acid anodizing. The recently developed plasma spray treatment is showing much promise.

Parametric Study of Adhesively Bonded Single Lap Joints by the Taguchi Method

The single lap joint is the most studied joint in the literature in terms of both theory and practice. It is easy to manufacture and the lap shear strength is a useful parameter for strength assessment and quality control. Simple design rules exist such as the one described in ASTM 1002 standard or in a recent paper by Adams and Davies. A previous study by the present authors gave a simple predictive equation considering the type of adhesive, i.e. ductile or brittle, the adherend yield strength and the overlap length. However, other factors also affect the joint strength such as the adherend and adhesive thicknesses and the surface preparation which have not previously been addressed in the literature. In order to quantify the influence of the adhesive (toughness and thickness), the adherend (yield strength and thickness), the overlap and the surface preparation on the lap shear strength, the experimental design technique of Taguchi was used in the present study. An experimental matrix of eighteen tests was designed and each test was repeated three times. The influence of the six previously-mentioned variables could be assessed using the statistical software Statview®. In this paper a simple predictive equation is proposed for the design of single lap joints.

Influence of surface macroroughness on the durability of epoxide-aluminium joints

The influence of varying the adherend surface macroroughness on the durability of epoxide-aluminium joints has been studied. It is concluded that variations in surface macroroughness as observed by scanning electron microscopy and measured by profilometry have a small but significant effect on durability. Good durability was obtained with degreased-only aluminium despite a relatively high level of magnesium in the outermost surface.

Growth of ZnO by MOCVD using alkylzinc alkoxides as single-source precursors

Thin films of ZnO have been grown by low-pressure MOCVD using methylzinc isopropoxide, MeZn(OPri), and methylzinc tert-butoxide, MeZn(OBut), in the absence of an added oxygen source. The films were grown on to glass substrates in the temperature range 250–400 °C with growth rates of between 0.2 and 4.4 µm h–1.

Crystal Structure of Bi(OCMe2CH2OMe)3 and Its Use in the MOCVD of Bi2O3

The crystal structure of the volatile bismuth alkoxide tris(-methoxy-2-methyl-2-propanolato)bismuth(III), Bi(OCMe 2 CH 2 OMe) 3 , 1, has been determined by single crystal X-ray diffraction (XRD). The complex is mononuclear, containing a six-coordinate Bi III atom in a distorted octahedral environment. Using a solution of 1 in heptane, thin films of bismuth oxide have been deposited by liquid injection metal-organic (MO) CVD. Deposition was carried out over a wide range of substrate temperatures (250-550°C) and, using Auger electron spectroscopy (AES), films were shown to be pure bismuth oxide (Bi 2 O 3 ) with no detectable carbon.

Further studies into the effectiveness of CO2-laser treatment of metals for adhesive bonding

Abstract The effect of CO2-laser treatment on the wettability of mild steel is presented. In addition, data are presented on the initial joint strengths and durability of joints formed between a single-part epoxide and both mild steel and aluminium. A large increase in stressed durability performance was observed with the laser-treated aluminium compared with degreased-only controls. The laser treatment was shown to efficiently remove the organic contamination from the metallic substrates. Auger analysis showed that the laser interacts more with the mild steel than the aluminium adherends, to produce a relatively thick surface oxide. The changes to the mild steel surface introduced by the CO2-laser treatment facilitate an durability trials was greater with the laser-treated adherends than with degreased-only controls.

Modelling of Functionally Graded Adhesive Joints

Nowadays, there is a strong trend towards the use of functionally graded materials, with particular importance for the functionally graded joints. The main objective of this work was to study a functionally modified adhesive in order to have mechanical properties that vary gradually along the overlap of a joint, allowing a uniform stress distribution along the overlap. This allows for a stronger and more efficient adhesive joint and would permit to work with much smaller areas, reducing considerably the weight of the structure which is a key factor in the transport industry. In the proposed joint, the adhesive stiffness varies along the overlap, being maximum in the middle and minimum at the ends of the overlap. The functionally graded joint was found to have a higher joint strength compared to the cases where the adhesive has homogeneous properties along the overlap. A simple analytical model to study the performance of the functionally graded joints was developed. The differential equation of this model was solved by a power series. Numerical modelling by finite element analysis was performed to validate the analytical model developed.

Modelling cyclic moisture uptake in an epoxy adhesive

This paper presents a methodology for predicting moisture concentration in an epoxy adhesive under cyclic moisture absorption-desorption conditions. The diffusion characteristics of the adhesive were determined by gravimetric experiments under cyclic moisture conditions and the dependence of diffusion coefficient and saturated mass uptake on moisture history was determined. Non-Fickian moisture absorption was observed during absorption cycles while moisture desorption remained Fickian. The diffusion coefficient and saturated moisture content showed variation with absorption-desorption cycling. A finite element-based methodology incorporating moisture history was developed to predict the cyclic moisture concentration. A comparison is made between the new modelling methodology and a similar method that neglects the moisture history dependence. It was seen that the concentration predictions based on non-history dependent diffusion characteristics resulted in over-prediction of the moisture concentration in cyclic conditioning of adhesive joints. The proposed method serves as the first step in the formulation of a general methodology to predict the moisture dependent degradation and failure in adhesives.

Growth of aluminium films by low pressure chemical vapour deposition using tritertiarybutylaluminium

The new aluminium precursor, tritertiarybutylaluminium (TTBA), has been used successfully for the growth of high purity aluminium films by low pressure chemical vapour deposition (LPCVD). The aluminium films were grown over the temperature range 300–450°C on Si(111) substrates and had growth rates of up to 2 μm min-1. A comparison with aluminium films grown using triisobutylaluminium (TIBA) is made.

Initial investigation into the effectiveness of CO2-laser treatment of aluminium for adhesive bonding

Abstract Aluminium alloy coupons were treated by CO2-laser ablation. The degree of surface modification introduced by this treatment has been determined by a combination of Auger electron spectroscopy and scanning electron microscopy. Following laser treatment a 22% increase in initial lap shear joint strengths was observed compared with degreased-only controls.