Synthesis and some properties of Ti3SiC2 by hot pressing of Ti,Si and C powders Part 2 – Mechanical and other properties of Ti3SiC2

Abstract

Some properties of the remarkable Ti₃SiC₂ based ceramic synthesised by hot pressing of elemental Ti, Si, and C powders have been investigated. Its flexural strength by using three point bending tests and fracture toughness by using single edge notched beam tests were measured at room temperature to be in the range 310–427 MPa and about 7·MPa m^1/2, respectively. This material is a relative 'soft' ceramic with a low hardness of 4 GPa. Ti₃SiC₂ is similar to the soft metals and is a damage tolerant material that is able to contain the extent of microdamage. An oxidation test has been performed in the temperature range 1000–1400°C in air for 20 h. The oxidation resistance below 1100°C was good. Two oxidized layers were formed, the outer layer consisting of pure rutile-type TiO₂, and the inner layer a mixture of SiO₂ and TiO₂. The average coefficient of thermal expansion (CTE) of Ti₃SiC₂ was measured to be 9·29 × 10^?6 K^?1 in the temperature range 25–1400°C. The thermal shock resistance of Ti₃SiC₂ was evaluated by quenching the samples from 800°C, 1200°C, and 1400°C, respectively. The retained flexural strength drops dramatically at quenching temperature, but shows a slight increase after quenching from 1400°C compared with quenching from 800°C and 1200°C.     

Evaluation of hot strip mill backup roll cladding

Abstract

A new cladding material based on the Fe–Cr–Mo–V–C alloy system, suitable for submerged arc welding, has been designed for the refurbishment of forged and cast backup rolls used in the finishing stands of hot strip rolling mills. The work undertaken includes mechanical analysis, mechanical testing, and microstructural characterisation. The mechanical analysis indicated the nature and level of stresses operating near the surface of rolls; mechanical testing allowed material performance to be anticipated. An optimal post-weld heat treatment procedure, which maximises strength while minimising material strain hardening, was subsequently chosen. The microstructure of the candidate cladding material is a mixture of lower bainite and martensite, containing a very fine distribution of molybdenum carbides. In situresults have shown that welded rolls outperform traditional rolls, as the amount of steel rolled per millimetre of cladding material is 40% higher than with forged rolls and double that obtained with cast rolls.     

Development of high performance Mg–Al2O3 composites containing Al2O3 in submicron length scale using microwave assisted rapid sintering

Abstract

In the present study, magnesium composites reinforced with different volume fraction of submicron size Al₂O₃ particulates were synthesised using powder metallurgy technique incorporating an innovative microwave assisted rapid sintering technique. The sintered materials were subsequently hot extruded for characterisation in terms of microstructural, physical and mechanical properties. Microstructural characterisation results revealed a reasonably uniform distribution of Al₂O₃ particulates, minimal porosity and good matrix reinforcement interfacial integrity. The average coefficient of thermal expansion (CTE) value for Mg–Al₂O₃ composites was found to decrease with increasing amount of submicron Al₂O₃ particulates. Mechanical characterisation of the composites revealed an increase in hardness, elastic modulus, 0·2% YS and ultimate tensile strength (UTS) with the increase in amount of alumina particulates. Ductility exhibited the reverse trend. An attempt is made in the present study to correlate the effect of the presence of submicron alumina and its increasing amount with the microstructural, physical and mechanical properties of magnesium.     

Compressive behaviour of open cell Al–Al2O3 composite foams fabricated by sintering and dissolution process

Abstract

The sintering and dissolution process (SDP) was used to produce the fine open cell Al–Al₂O₃ composite and pure Al foams with the relative density of 0·25–0·40 and the pore size of 112–400 μm. The composite foam exhibited much higher yield strength and Young's modulus than the pure Al foam, and thus had an elevated plateau stress. Moreover, the composite foam showed a unique dependence of the compression stress on the pore size, i.e. it increased with increasing pore size, which was quite different from that for the common metal foams.     

Investigation of radiation damage to microcapsules in environmental SEM

Abstract

The radiation damage to a specimen in the chamber of electron microscopes has been studied extensively in the past few years. However, for the specific case of specimens with a core/shell structure, such as microcapsules and biological cells, there has been little experimentation devoted to understanding how the radiation may affect their mechanical properties. In the present work, single melamine formaldehyde (MF) microcapsules were imaged using an environmental electron microscope (ESEM) under both dry and wet modes under conditions of different accelerating voltages. The changes in the morphology (shape) were monitored as a function of radiation time. In addition, a newly developed ESEM based nanomanipulation technique was used to measure how the force imposed on single MF microcapsules for a given deformation changed with radiation time, in order to identify a time window within which the radiation damage to the microcapsules may be negligible in order to be able to study the mechanical properties of the particles. Based on the findings, the nanomanipulation technique was applied to measure the force versus displacement for compressing single microcapsules to rupture, including determination of their rupture mode.     

Wear behaviour of Fe/M7C3 metal matrix composites with various microstructures during dry sliding

Abstract

The wear mechanisms of iron based metal matrix composites and the wear behaviours of various microstructures were systematically studied by dry sliding wear testing and SEM examination. The experimental results show that three dominant wear mechanisms appeared in succession with increasing normal load during dry sliding. The transition of the wear mechanisms depended mainly upon the conditions of testing, and additionally it was seen that changes in microstructure of the steel had no marked effect on the transition. In the case of mild wear, no obvious differences in wear volume were found for the various microstructures. However, considerable differences in the wear volumes were observed under conditions of severe wear characterised by adhesion and delamination. The experimental results also indicate that the differences in wear resistance of the various microstructures were caused by differences in microstructural thermal stability, resistance to plastic deformation, resistance to nucleation and propagation of microcracks and especially by differences in energy consumption in these layers during wear.     

Evolution of textures in hot rolled Nb - Ti and V - Nb microalloyed steels

Abstract

A considerable texture gradient in the through thickness direction was observed during hot rolling of Nb - Ti and V - Nb microalloyed steels. The most intense deformation texture for Nb- Ti steels was {113}〈110〉 at all depths, whereas for V - Nb steels the plane was shifted to {115}〈110〉 ; the angular difference between {113} and {115} is about a degree. The recrystallisation texture of austenite, {100}〈001〉 , transformed into {100} 〈011〉 component in the ferrite and indicated an increase in the intensity with increase in depth for both Nb - Ti and V - Nb steels. However, the intensity of this {100}〈011〉 texture was less for Nb - Ti steels compared to V - Nb steels at all depths. The reduced intensity of {100}〈011〉 texture in Nb -Ti steels is likely to be the reason for the superior formability and improved toughness of Nb - Ti steels as compared with V - Nb steels. The {100}〈011〉 type of texture has an undesirable effect on the edge formability of steels.     

Stress-free temperature in a mixed-adhesive joint

Adhesive joints used in supersonic aircraft fuselage need to withstand low (?55°C), as well as high (200°C) temperatures. However, there are no adhesives suitable for the whole temperature range. A solution would be a joint with a combination of a low-temperature adhesive and a high-temperature adhesive, called a mixed-adhesive joint. In a bonded joint, the thermal stresses are generated essentially by the different thermal expansion properties of the adhesive and the adherends and, to a lesser extent, by the shrinkage of the adhesive produced by curing. The case of a mixed-adhesive joint is more complicated because there are two adhesives with different glass transition temperatures (T _g). To determine the stress-free temperature in a mixed adhesive joint, sandwich specimens of aluminium–adhesive–CFRP (carbon-fibre-reinforced plastic) were fabricated and the thermal strains were measured with strain gauges. In a mixed adhesive joint, two stress-free temperatures were found: the stress-free temperature of the high temperature adhesive, which is its cure temperature, and the stress-free temperature of the low temperature adhesive, which is its T _g.     

Optimum design of co-cured steel–composite tubular single lap joints under axial load

In this paper, an optimum design method for co-cured steel-composite tubular single lap joints under axial load is proposed based on a failure model which incorporates the nonlinear mechanical behavior of the steel adherend and the failure mode of joints such as composite adherend failure and steel adherend failure. The design parameters considered were the test temperature, the stacking sequence of the composite adherends, the thickness ratio of the steel adherend to the composite adherend, and the existence of scarf in the steel adherend. Stress analysis of the cocured steel-composite tubular single lap joints was performed considering the nonlinear mechanical behavior of the steel adherend, and the fabrication residual thermal stress and thermal degradation of the composite adherend. The method developed may be employed in the joining of hybrid composite structures such as golf clubs and automotive composite propeller shafts in which a carbon/epoxy shaft has normally been bonded to a metal shaft with epoxy adhesives.     

Plasma surface modification of carbon fibers: a review

The properties of the fiber/matrix interface in carbon fiber-reinforced composites play a dominant role in governing the overall performance of the composite materials. Understanding the surface characteristics of carbon fibers is a requirement for optimizing the fiber-matrix interfacial bond and for modifying fiber surfaces properly. Therefore, a variety of techniques for the surface treatment of carbon fibers have been developed to improve fiber-matrix adhesion as well as to enhance the processability and handling of these fibers. Many research groups have studied the effects of plasma treatments, correlating changes in surface chemistry with the interfacial shear strength. This article reviews the recent developments relative to the plasma surface modification of carbon fibers.