Tensile behaviour and ductility of 10 vol.-% Saffil short fibre reinforced aluminium

Abstract

The tensile behaviour of Saffil short fibre reinforced aluminium composites has been investigated in terms of Young's modulus, yield strength, ultimate tensile strength, and strain to failure. A rationale is given for the unusually high strain to failure found in this material by applying a failure criterion based on damage accumulation, recently developed for particulate reinforced MMCs.     

Effect of nickel on microstructure and mechanical properties of heat affected zone of low carbon steel

Abstract

In the present study, the effect of nickel along with varying heat input on the microstructure and mechanical properties of the heat affected zone (HAZ) of a low carbon steel was investigated. Experiments were carried out in which low carbon steel specimens with five different nickel contents, 1, 2, 2.9, 4.1, and 5.2 wt-%, were welded using a submerged arc welding machine with heat inputs of 0.5, 1, and 2 kJ mm^-1. Following welding, the microstructure, hardness, and toughness of the HAZs were determined. From the results, attempts were made to establish a relationship between heat input, nickel content, microstructure, hardness, and toughness. Charpy impact testing and microstructural observation showed that, for a heat input of 0.5 kJ mm^-1, nickel contents between 2.9 and 5.2 wt-% were effective in forming lower transformation products, such as martensite, thereby producing lower toughness values. It was subsequently found that, taking into consideration the microstructure, hardness, and toughness of the HAZ, a lower heat input for a nickel content of 1 wt-% and a medium heat input for nickel contents between 2 and 5.2 wt-% gave good results.     

Influence of solder thickness on interfacial structures and fatigue properties of Cu/Sn/Cu joints

Abstract

Copper plates were soldered with tin foil of different thicknesses to examine the influence of the solder thickness on formation of secondary phases at the interface and fatigue properties. In the case of an initial solder thickness of 60 μm, the thickness of the η (Cu₆ Sn₅) phase and the ? (Cu₃ Sn) phase linearly increased with the square root of the bonding time. The fatigue strength was 3 MPa and the fatigue life decreased with increasing stress amplitude and had a low scatter. In the fatigue process, fine cracks appeared in the η phase and propagated in the solder layer. This process was different from the case of static shear fracture. In the case of a 5 μm solder thickness, the solder was replaced by secondary phases in a short time, and only the ? phase remained at the interface after a bonding time of more than 300 min. The fatigue strength was 13 MPa and was independent of the interfacial structure, but the fatigue life showed a large scatter. In the fatigue test, unstable fracture occurred along the interfaces, similar to that observed in static shear fracture. From these results, it was concluded that solder joints become brittle with decreasing solder thickness.     

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.     

Effects of particle size on deformation behaviour of metal matrix composites

Abstract

By incorporating the dislocation strengthening effect into the Mori–Tanaka method, a new hybrid approach is developed in the present paper for calculating the deformation response of SiCp/Al composites. The diameters of the particles are 1, 5, 20 and 56 μm. Both numerical and experimental results indicate a close relationship between the particle size and the deformation behaviour of the composites at a constant particle volume fraction. The yield strength and plastic work hardening rate of the composites increase with decreasing particle size. The predicted stress–strain behaviour of the composites is in qualitative agreement with the experimental results. By incorporating Weibull statistics for particle fracture, the results simulated are agreed well with the experimental results for particle size >5 μm.     

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.     

Validation of ion level analysis as method to assess in vitro total hip replacement wear

Abstract

Currently in vitro hip simulator wear of metal on metal hip replacements is carried out by gravimetric means. However, this is time consuming and cannot be used to assess wear between measurement intervals. Measuring ion levels (Co and Cr) by inductively coupled plasma mass spectroscopy has been proposed as an alternative method. A standard hip simulator test was conducted using clinically available parts and wear assessed by gravimetric means; additionally, the serum lubricant was assessed for Co and Cr ion levels. A strong correlation in the ion levels and gravimetric was observed, indicating that this method would provide an appropriate alternative wear measurement technique in hip simulator testing.     

Laser welding with activating flux

Abstract

The effect on laser welding of activating flux, originally developed to improve penetration depth for tungsten inert gas welding, was investigated. Both mild and stainless steels were tested. Results show that weld penetration capability relates closely to the laser power level and welding speed of the process. Significant improvement in penetration was only observed when laser welding was performed in the conduction mode (i.e. weld aspect ratio <1). For the range of parameters studied, the best penetration capability improvements achievable for mild steel, type 304 stainless steel, and duplex stainless steel were found to be 41, 53, and 63% respectively. These data are of use in the selection of parameters for laser welding with activating flux.     

Changes in toughness at low oxygen concentrations in steel weld metals

Abstract

Oxides in steel weld metals can initiate fracture or can improve toughness by influencing the development of beneficial microstructures. In this work, the authors conducted experiments in which the oxygen concentration was varied from 20 to 560 ppmw (parts per million by weight) in weld metals with tensile strength in the range 580–780 MPa. It is demonstrated that low and medium strength weld metals benefit from oxides up to a concentration of ～200 ppmw as consistent with previous research, because acicular ferrite is stimulated in the microstructure. By contrast, oxides are detrimental to the toughness of high strength weld deposits at low oxygen concentrations under 140 ppmw, because the microstructure remains a predominantly martensite and the oxides simply serve to nucleate fracture. In high strength weld metal, therefore, good toughness is achieved even at low oxygen concentration of 20 ppmw O.