Study of effect of aging on martensitic transformation and tribological properties of TiNi alloy using DSC,neutron diffraction,and micromechanical probing techniques

Abstract

Recent studies have demonstrated that TiNi shape memory alloy exhibits excellent wear resistance, benefiting from their pseudoelasticity (PE) due to a thermoelastic martensitic transformation. The maximum wear resistance of the alloys corresponds to an optimum balance between the PE and hardness, which is strongly influenced by heat treatment. In this work, the effect of aging treatment on martenstic transformation behaviour, mechanical properties, including the pseudoelasticity and hardness, and wear behaviour of a Ti–51 at.-%Ni alloy was investigated using differential scanning calorimetry, neutron diffraction, and micromechanical probing techniques. The main objective of the study was to understand the aging effect on wear behaviour of the TiNi alloy and explore the mechanisms involved for further improvement of this novel tribo-alloy.     

Effect of ZnO coating of whiskers on thermal expansion properties of aluminium borate whisker reinforced aluminium composites

Abstract

The pure aluminium composites reinforced by ZnO coated aluminium borate whiskers were fabricated by squeeze casting. The microstructure of the composite was observed using an optical microscope and the thermal expansion behaviours of the composites were investigated in the range from 50 to 400°C. In addition, the effects of heat treatment and thermal cycling on the thermal expansion behaviours of the composite were also investigated. The results show that the coefficient of thermal expansion of as cast composites decreases with the ZnO coating content increasing. However, heat treatment time and thermal cycling lead to an increase in the CTE of the composite.     

Multipass rolling of aluminium alloys: finite element simulations and microstructural evolution

Abstract

Use of numerical predictive methods such as finite element analysis is becoming progressively more common for modelling industrial hot metal working and forming processes. These tools are used not only to predict the thermomechanical behaviour of metals but increasingly to predict microstructural changes by linking them to physical models of recrystallisation and textural evolution. This paper describes the development and application of a fully integrated model for the prediction of thermomechanical and microstructural behaviour during multipass hot rolling of aluminium alloy AA 3104. Finite element code ABAQUS/standard has been used in the work and the process is modelled assuming plane strain conditions. It is shown that for this alloy the static recrystallisation which occurs during interpass cooling does not significantly influence the thermomechanical response during subsequent rolling passes.     

Macrostructural changes of polymer replicated open cell cordierite based foams upon sintering

Abstract

The goal of this work was to clarify the macrostructural changes that take place upon sintering of open cell cordierite based foams. A methodology, based on optical image analysis, was developed to assess the structure of open-cell foams, which allowed evaluating the macrostructure of both cordierite based foams obtained by the replication process and their polymeric templates. The parameters used to describe the structures were the size of the cell and the window, the window shape factor, the strut thickness and the volume fraction of the material. The experimental evidence gathered opened the way to understand the physical/chemical transformations involved in the polymer burnout and the ceramic sintering processes, as well as their influence on the ceramic final structure. The observed trends provide guidance for tailoring 'replicated' cordierite based foams, in view of the required application.     

CMC material for train brake systems

Abstract

A continuous carbon fibre/silicon nitride matrix composite material has been produced by an inexpensive method. According to this method, the space between 2D carbon fibre preforms is filled with a S₃ N₄ powder by a pressure infiltration method. High particle packing densities are achieved within the fibre preforms in this way. The compact body is heat treated to form a porous framework without shrinkage, and is then strengthened with an inorganic matrix synthesised from a liquid pre-ceramic polymer. The densification degree, microstructure, and thermal and mechanical properties of the composite material are characterised. The C/Si₃ N₄ composite material pyrolysed at 1300°C is considered to be a very promising material for low temperature applications such as brake discs for rapid train systems.     

Effect of modified AA4043 filler on partially melted zone cracking of Al-alloy gas tungsten arc welds

Abstract

The effect of grain refiners (zirconium, Tibor and scandium) added to the fusion zone through AA4043 filler on the partially melted zone (PMZ) cracking in gas tungsten arc (GTA) welded AA6061 alloy was investigated. Welds of AA6061 in thermal tempers of artificially aged condition (T6) were made with continuous current and pulsed current techniques. Varestraint testing was carried out to study PMZ cracking in welds, and optical SEM examination performed to evaluate it. Addition of grain refiners to the fusion zone improved the PMZ cracking resistance very significantly. Pulsed current technique was also found to improve the resistance to PMZ cracking, as a result of the possible reduction in the strain in the PMZ owing to the ductile fine grained fusion zone. Severe PMZ cracking in the welds of AA4043 filler without grain refiners was attributed to a greater amount of silicon rich eutectic at the grain boundaries of the PMZ.     

Early accident simulating testing of radioactive material packages in road vehicles

Abstract

Beginning as early as the 1960s, concerns were voiced as to the adequacy of the package test standards imposed by the transport regulations promulgated by the International Atomic Energy Agency. One concern that was frequently raised and has continued to the present time is that the test standards do not necessarily simulate real accidents. The purpose of the crash tests described here that were done with typical packages carried in full scale vehicles was to assess the IAEA standards, their adequacy and to suggest changes to them that might be needed. It was also hoped that the tests, which were performed in the USA and in the UK, would show to regulators, to users of the regulations and to the public that current regulations already provide a very high level of safety for real world accidents. With time, much of the original information regarding these tests and their results has been lost. The few documents that remain have been surveyed and this paper presents summaries from this survey of the tests and their results.     

Measurement of autoclave thermal profiles during high pressure steam de-waxing of investment shells Part 1 - Vessel profiles

Abstract

Investment casting research is being carried out by the University of Birmingham, sponsored by EPSRC and a consortium of industrial companies. The programme is aimed at developing a fundamental understanding of the process, with a view to routinely producing sound, net shape castings. A key stage within the investment process is that involving the removal of wax from the unfired ceramic shell. This important process is carried out within the confines of a sealed pressure vessel, more commonly referred to as a Boilerclave*, with external pressure gauges as the only indication of what is actually happening inside the cavity. To metaphorically 'see' inside the vessel would allow the factors controlling de-wax to be characterised and controlled. This paper contains results obtained at The University of Birmingham using a specially instrumented steam autoclave that allows visual data capture, thermal and steam pressure profiles within the chamber, and thermal instrumentation of waxes and shells to be obtained. Results of thermal and pressure profiles inside the vessel body are presented and implications of these results upon the mechanism of wax removal and the effect upon ceramic shells are discussed.     

Thermal characteristics of tubular single lap adhesive joints under axial loads

When an adhesive joint is exposed to high environmental temperature, the tensile load capability of the adhesive joint decreases because both the elastic modulus and failure strength of the adhesive decrease. The thermo-mechanical properties of a structural adhesive can be improved by addition of fillers to the adhesive. In this paper, the elastic modulus and failure strength of adhesives as well as the tensile load capability of tubular single lap adhesive joints were experimentally and theoretically investigated with respect to the volume fraction of filler (alumina) and the environmental temperature. Also the tensile modulus of the filler containing epoxy adhesive was predicted using a new equation which considers filler shape, filler content, and environmental temperature. The tensile load capability of the adhesive joint was predicted by using the effective strain obtained from the finite element analysis and a new failure model, from which the relation between the bond length and the crack length was developed with respect to the volume fraction of filler.