Current and future structural applications for composite laminates frequently involve design solutions combining composite laminates and metal; the materials must be joined. Two conventional means of joining are available: mechanical joining and adhesive bonding. Both methods have critical disadvantages. A novel surface treatment for metals developed at TWI, Surfi-Sculpt™ leads to the formation of surface protrusions on metal surfaces. These protrusions are typically 1.0 mm high and 0.6 mm diameter. The surface modified metal can be bonded with composite laminates to form a Comeld™ joint. These joints can be described as a combination of mechanical fastening and adhesive bonding. There are many possible variables which could be applied to the metal surface. The variables include the shape, height, orientation and distribution (distribution pattern and density) of the protrusions. The aim of this work was to optimise the protrusions with respect to their geometry and distribution using the finite element modelling method for the Comeld™ joint under tensile loading with titanium alloy and cross-ply carbon prepreg composites. The simulations require multi-scale modelling techniques to transfer results between the global model, which is the reflection of the whole joint, and the unit cell models containing a protrusion. The two-dimensional simulations focused on the protrusion geometric parameters whereas the three-dimensional simulations focused on the protrusion spatial arrangement including the distribution pattern and density. Modelling of the entire joint geometry with two and three-dimensional global models was carried out using smeared properties for the adhesive layer which includes the protrusions. These models yield results for both quasi-static properties and stress distributions for these joints. Results from the simulations show critical effects on stress distributions arising from changing protrusion geometry. These joints show significant advantages over conventional joining technologies and their application would allow improved performance for combinations of metal and composite laminates.

Kissing bonds (KBs) refer to the situation where two surfaces are only partially bonded or are debonded but touching or in very close proximity. This may be the consequence of poor adhesion, environmental degradation or impact damage. This defect is not visible macroscopically and because of their intimate contact which makes it more difficult to detect using a non destructive technique (NDT) than conventional defects such as voids or cracks etc. The success of NDT evaluation and widespread use of adhesive bonding rely greatly upon comprehensive knowledge of morphology, surface chemistry and mechanics associated with KBs. Two approaches were successfully taken to produce reliable and repeatable KBs: by surface contamination using a mould release agent (Frekote®700-NC); and by weakening the electrically-debonding adhesive, ElectRelease™, with a low voltage. Significant changes in morphology and elemental distribution of the contaminant at/near the Frekote contaminated interfaces were found. Some morphological and chemical changes at/near the anodic metal/ElectRelease™ interface were also evident. Additional information about chemical interactions at/or near the contaminated interface due to the presence of Frekote and the application of the electric field confirmed the changes in morphology and elemental distribution. Double-lap joints with KBs were tested in tension with local strains captured by strain gauges and extensometer. Significant reduction in failure strength was apparent when using Frekote and ElectRelease™ subjected to the electric field. The tests were simulated using finite element analysis. Cohesive elements were introduced along the predicted failure interfaces taking into account the adhesion loss associated with KBs. The experimental failure load and local strain results were in good agreement with the finite element predictions. The ways that KBs were produced and the understandings in morphology, surface chemistry and their failure mechanisms contributed to the modified criteria of KBs and the development of the non-linear ultrasonic technique investigated by the NDT group at the University of Bristol. The morphology, surface chemistry and failure mechanisms of KBs in adhesive joint are now better understood.

Aluminium Lost Foam castings were made using gravity and counter-gravity filling techniques. Tensile strength was found to be most uniform in those castings which had been filled slowly from the bottom and where the metal front had remained stable throughout filling sequence. Pores containing carbon deposits were found on the fracture surfaces of all the castings made and this suggested that the defect was caused by polymer entrapment. A Saffman-Taylor instability was observed at the interface between Hg and a viscous glucose syrup which were contained in an analogue, that was used simulate the casting of Lost Foam moulds at room temperature. The liquid degradation products of the polystyrene patterns were also found to be viscous, although this was reduced by treatment with Br. Under the same conditions of temperature and velocity, the interface observed during the filling of a Br-treated pattern was planar whereas that of an untreated pattern was unstable. This demonstrated not only that the interfacial instability entrapped polymer degradation products, which adversely affected casting quality, but was probably of the Saffman-Taylor type.

To avoid the problems associated with specifying the exact nature of the heat input from welding arcs, an analogue model is proposed which simulates the quasi-static thermal field produced around the isothermal contour of the molten weld pool boundary during the welding of thin plate. The design of an electrical analogue based directly on Rosenthal's equation (1) governing the quasistatic heat flow about a moving source is shown to be impractical although this approach identifies the physical significance of the two parameter ratios. To overcome the difficulties associated with the direct analogue, a simple transformation of Rosenthal's equation is employed and the design of an indirect or 0 field analogue of this transformed equation is developed. The details of the construction and commissioning of such an analogue are reported. The application of this analogue to studying the quasi-static thermal field is tested by comparing analogue predicted and experimentally measured temperature histories of points in the HAZ for a range of autogenous TIG melt runs on thin mild steel plate. The experimental results are obtained from a purpose built automatic welding rig which incorporates a facility for determining the shape of the molten weld pool during welding. The results from these comparative tests show a good agreement between predicted and measured temperature histories and the application of the 0 field analogue to studying the thermal field during welding is discussed.

Physical vapour deposition technologies have been on the fast track of development for the last two decades due to their ability to meet demands for special materials and performance tools. The ever increasing complexity of the required coating microstructure and chemical composition can be achieved only by the development of PVD technology and in particular plasma sources for vapour generation that can provide the necessary tools. This thesis describes plasma diagnostic studies of plasma discharges, developments of plasma sources and deposition of CrN coatings. Initially the project investigated vacuum arc plasma discharges used in the Hauzer HTC1000/ABS industrially sized coater. The attention was concentrated to the plasma pretreatment by low energy (1200 - 3600 eV) Cr ion implantation into substrates, which contributed to an enhanced adhesion of subsequently deposited TiAIN coatings. Optical emission spectroscopy (OES), electrostatic probes, and time-of-flight (TOF) spectroscopy were used to study the interactions of the arc plasma with the gas atmosphere in the chamber. It was shown that increasing the pressure of Ar gas had a strong effect on the composition of the generated metal ion flux as the density of highly charged metal species reduced significantly to the benefit of gas ionisation. The mechanisms behind these observations are discussed and supported by further experiments. Based on the plasma diagnostic results, a novel two-stage pretreatment method was developed which allowed an enhanced adhesion due to faster sputter cleaning of the substrate surface and more efficient metal ion incorporation in the substrate material. In the final stages of the project a novel high power pulsed magnetron sputtering (HIPIMS) process utilising peak power densities of 3000 Wcm[-2] was investigated. OES studies showed the first evidence of doubly charged Cr and Ti ions generated by the HIPIMS discharge. Peak plasma densities of 10[13] cm[-3] were measured and, in the case of Cr, metal ions were found to constitute 30% of the total deposition flux to substrates. The influence of power on the plasma density, plasma composition and time evolution of the plasma was studied in detail using OES and electrostatic probes. The conditions for glow-to-arc transition were investigated. CrN coatings (thickness 2 mum) were deposited for the first time using HIPIMS of Cr in a nitrogen atmosphere. The microstructure observed in transmission electron microscopy cross sections was highly dense and droplet free and contributed to an excellent corrosion and wear resistance superior to 20 mum thick electroplated hard Cr, and CrN coatings deposited by arc and unbalanced magnetron sputtering. The HIPIMS discharge was used also for pretreatment of substrates with metal ions analogous to the one performed previously with arc discharge. High adhesion was achieved as indicated by the scratch test critical load value Lc = 85 N.Finally, at an intermediate stage of the PhD project, an alternative source providing metal ionisation was studied. It was based on a radio frequency (RF) powered coil that was inductively coupled to a magnetron sputtering discharge. Energy resolved mass spectroscopy and OES in a laboratory-sized version of the plasma source revealed elevated metal ion densities and high ion energies of the order of 60 eV. This source was upscaled, installed, and tested successfully in the industrially sized Hauzer coater. The ion-to-neutral ratio at the substrate position could be increased 5-fold for a similar increase in RF power.

The most widely used surface treatment to protect engineering components is the deposition of hard chromium by electroplating. The coatings are known to be quite thick (up to 20 mum), reasonably hard (-HV1000), but contain micro-cracks. This wet deposition process is well understood, but it has technical limitations and is under high political pressure because of the environmental pollution by hexavalent chromium. The physical vapour deposition (PVD) technique is an alternative method to produce high quality coatings. PVD is an almost pollution free technique, because the process occurs under vacuum. CrN by PVD is one of the most promising PVD coatings as a candidate to replace eventually electroplated hard chromium. The growth characteristics of CrN coatings are less understood than those of TiN, the well-known PVD coating material. This thesis anticipates to fill this technological gap. Along a wide range of experiments based on the deposition of CrN[x] coatings, XRD, SEM, SNMS and tribological analysis have been used to complete a thorough understanding of CrN[x] growth. The experiments show that there exist several different phases within the Cr-N system: bcc-Cr, hcp-Cr[2]N, fcc-CrN, and mixed phases. This is not fundamentally new, but the work has resulted in two new modifications, which are highly interesting candidates for the industry, including electroplating replacements, namely high nitrogen containing metallic bcc-Cr (solid solution with up to 18 at.% nitrogen) in the hardness range up to HV1800 and a very hard fcc-CrN phase with hardness values between HV1500 and HV3000, similar to TiN.The solid solution bcc-Cr-N is very dense fine-grained, reasonably hard (almost twice as hard as electroplated hard chromium), very smooth, and with a Young's modulus very similar to that of (hardened) steel. The hard fcc-CrN phase (approximately three times harder than electroplated hard chromium) could only be obtained by the current experiments in a rather non-conventional magnetron sputtering parameter window: a combination of a high substrate bias voltage (> -200 V) and a high partial pressure of nitrogen (a multitude of the argon partial pressure). This phase shows a strong {100} preferred crystallographic orientation and shows an excellent behaviour against corrosion and wear.

The work in this thesis has developed theoretical models to predict the microstructural behaviour of weld materials. Three different types of boiler shell weld materials from nuclear power plants have been investigated. The materials considered differ mainly in the manganese concentration and their microstructure after different temperature exposures during industrial use. Element segregation can be predicted according to the typical reactor conditions and therefore the influence of longer life times can be evaluated. Sufficient experimental data have been taken by application of advanced transmission electron microscopes which offer images of high quality. The application of a thermodynamic software package MTDATA to predict the free concentration of each element for model prediction has been. Phosphorus, of great interest because it causes embrittlement, is enhanced at the grain boundary and increases with operating temperature and life time. Its interaction with carbon and manganese is of interest. Site-competition between carbon, phosphorus and manganese has to be applied. These site competition model prediction results fit best to the experimental data.

This study was carried out in order to investigate the effect of cutting parameters on the conventional hobbing process in which the response is analysed and practically tested. The investigation is n six sections: (i) Assessment of cutting torques and power consumed during hobbing. (ii) The study of the variation of gear teeth surface roughness (iii) Investigation of generated vibrations during hobbing (iv) Analysis of the mechanics of uncut-chip (v) The study of tool wear and tool life (vi) A general viewpoint of the economic problem in hobbing. In section (i) tests were conducted in order to assess readily a method of determining cutting torque encountered by hob shaft. Power consumed during hobbing was also measured by changing various cutting parameters. Observations were taken when hobbing spur and helical gears. Unlike others, the effect of cutting speed was shown to have a significant effect both upon cutting torques and power consumed. In section (ii) the nature of gear teeth surface was discussed. Axial feed, hob speed and hob D.P. were seen to have a highly significant influence on surface roughness. In section (iii) investigation was carried out into the effect of cutting parameters upon the machine tool vibration. Stability was shown to depend strongly upon speed, feed and hob D.P. In section (iv) a practical method to calculate volume of metal removed during hobbing is presented and a theoretical analysis of uncut-chip thickness and width is attempted. In section (v) the wear mechanism in hobbing is discussed, "rake face" wear proved to oe a suitable tool-life criterion when cutting materials less than (20 HB) under normal cutting consitions. Cutting speed was seen to have the highest significant influence on tool life, while axial feed was not significant. Section (vi) combines all the previous effects of cutting parameters to give a general viewpoint of the economic problem in hobbing, where power, surface roughness and tangential cutting force were the only constraints restricting the operability region for the given machining conditions.

No description available.

To improve the efficiency of turbine aero engines, higher operating temperatures and weight savings are being investigated. Alloys such as RR1000 are being trialled as they perform better at higher temperatures than current nickel-based superalloys. To achieve weight savings, inertia welding is being trialled for turbine discs but current post weld heat treatments reduce fatigue life. In this investigation, a number of novel post weld heat treatments were trialled aimed at improving post weld microstructure and fatigue properties. Extensive microstructural characterisation and mechanical testing were used to assess the effect of these treatments on both parent and weld materials. Post weld heat treatment (PWHT) was found to have a great effect on the size and distribution of γ' and carbides, particularly when a PWHT temperature of 980ºC or above was used. The effect of this microstructural change on the hardness of the weld and parent material has also been characterised. Extensive total life fatigue testing was carried out at 650ºC. It was found that failure can occur in both the parent and weld material, although it is deduced that the yield stress of the weld needs to be surpassed to see weld failure (plasticity in the weld). Increasing dwell time at peak load reduced the life of these components. Two mechanisms for crack growth were observed with initiation either at the surface or at a large Hf rich particle subsurface. Oxidation was found to have a large effect on both initiation and growth of fatigue cracks. By introducing a sharp pre-fatigue crack into samples, static load testing was used to determine a threshold value of K (stress intensity factor) for growth and growth rates were plotted at different K values. It was seen in these tests that PWHT had a large effect on growth rates and threshold values of K.