Study of microstructural evolution of friction taper plug welded joints of C–Mn steels

Abstract

This paper describes the microstructural evolution of friction taper plug welded joints of C–Mn steels. Experimental and numerical analyses included calculations based on Calphad and continuous cooling transformation curves, and characterisation techniques. The studied friction taper plug welded joint contains three macroregions: plug material, thermomechanically affected zone (TMAZ) and base material. The thermomechanical conditions imposed in the studied friction taper plug welded joint precluded the formation of a heat affected zone. However, seven subregions were identified within the TMAZ region and details are discussed. The interface zone is found in the TMAZ region, where the most relevant phase transformations take place. It is suggested that the phase transformations in TMAZ region depend on local conditions, such as chemical composition, deformation rate, thermal history and the previous thermomechanical history of the parent materials.     

Preliminary studies on friction welding of sintered P/M steel preforms to wrought mild steel

Abstract

Continuous drive friction welding studies on sintered powder metallurgical (P/M) steel preforms–wrought mild steel combination are reported in the present study. The work is a preliminary study to optimise the friction welding parameters and data generated by the present work is expected to contribute to friction welding of dissimilar and similar sintered P/M preforms to wrought metals or sintered P/M preforms – a planned future research work. Sound welds were obtained with all welding parameter combinations studied. The mechanical properties of welds were comparable to those of sintered P/M steel. Sintered P/M preforms deformed to a greater extent than wrought mild steel due to their low flow stress and thermal conductivity. The sintered density and other properties of the P/M preforms were found to dictate the deformation at the interface and consequently the weld strength. The results indicate that the current approach can be extended to other combinations of sintered P/M preforms.     

Finite element analysis of steady rolling tyre with slip angle: effect of belt angle

Abstract

The purpose of the present research was to study the effect of different belt angles on the steady state rolling behaviour of a steel belted radial tyre with slip angle. To achieve this goal, a finite element model has been developed using ABAQUS computer software. The simulation started with an axisymmetric model to analyse the tyre under inflation pressure. Then a full 3D model was generated to model the tyre under static vertical load. Having obtained the tyre configuration under contact load, a steady state rolling analysis was conducted using a mixed Lagrangian/Eulerian technique. The final stage of the modelling was the inclusion of the slip angle in the model. Each set of simulations was repeated for three belt angles and the effect of the belt angle variation on the tyre structural variables, including contact pressure and area, lateral force, interlayer shear stress and total strain energy was examined. In addition, the computed value of the number of revolutions per kilometre was compared with experimentally reported data which confirms the accuracy of the present model.     

Ultrafine and nanoscaled tungsten carbide synthesis from colloidal carbon coated nano tungsten precursor

Abstract

A new process for synthesising homogeneous ultrafine and nanoscaled tungsten carbide with good stability in air from well dispersed colloidal carbon coated nano tungsten precursor with highly agglomerated nanoscaled tungsten powder as starting material in a cost effective way is introduced. It is shown that hydrogen atmosphere facilitates the carbon and tungsten reaction process. Inheritance character in grain size distribution of tungsten carbide from tungsten starting material with BET calculated grain size of 46·1 nm has been observed. When the carburisation temperature increases from 1000 to 1300°C, the Brunauer–Emmett–Teller calculated grain size of tungsten carbide powder increases from 68·6 nm to 339·4 nm and the oxygen content decreases from 0·44 to 0·10%.     

Experimental characterisation of a semi-solid A356 alloy during solidification and remelting

Abstract

Within the general framework of hot tearing research in casting processes the tensile behaviour of the semi-solid aluminium alloy A356 under remelting and solidification conditions is studied. In order to measure true-stress versus true-strain curves of the semi-solid metal, a new experimental technique has been developed to perform hot tensile tests in the mushy regime between the coherency and the solidus temperatures. The local true-strain in the semi-solid region of the tensile specimen is measured optically with a laser speckle extensometer (LSE). During the solidification tests measurement is done by using a transparent aero-gel mould. The resulting stress–strain curves and the corresponding microstructure are compared for the remelting and solidification condition.     

Structure property relations of copolymerised polypropylene /SiO2 nanocomposites prepared by solid state shear milling (S3M) method

Abstract

In the present paper, solid state shear milling (S³M) method was used to prepare the copolymerised polypropylene (Co-PP)/nano-SiO₂ composites under the conditions of solvent free and non-organic treatment. The change of phase morphology and arrangement of SiO₂ under mechanical force were firstly observed in the complex multiphase and multicomponent Co-PP/nano-SiO₂ composite. The effect of milling cycles on the phase structure and mechanical properties was studied. It was found that the S³M method was an effective way which can adjust the phase structure of composite through change of milling cycles. After 20 milling cycles, the composite can form a structure with a lot of SiO₂ particles around the ethylene–propylene copolymer phase, the Charpy notched impact strength of the composite with 4 wt-%SiO₂ particles can be largely improved from 24·2 to 38·2 kJ m^–2. While after 30 milling cycles, the composite can form a structure with SiO₂ particles dispersed more uniformly in the Co-PP matrix. However, with this structure, the prepared composite has higher stiffness but the notched impact strength could not be greatly improved. The mechanism of the toughening effect is discussed and the structure property relation established.     

Cathodic protection of UNS C71500 heat exchanger tubes in sulphide polluted Arabian Gulf sea water

Abstract

A laboratory investigation using a specially designed circulating test rig has been undertaken to study the feasibility of achieving complete cathodic protection of UNS C71500 heat exchanger tubes in sea water applications by means of sacrificial carbon steel anodes. The results have indicated that the galvanic current distribution covered the entire 6 m length of the tube. However, the presence of sulphide ions as pollutants in the sea water shifted the galvanic potentials of the tubes to less active potentials and affected the development of the protective films that normally form.     

Pilot control of an auto-balancing two-wheeled cart

The control system of an auto-balancing two-wheeled cart (ABTWC) is inherently unstable, displays a non-minimum phase and can be piloted by a joystick that has 2 d.o.f. This paper employs a state feedback technique to design the stabilizing controller for an ABTWC and develops a pilot algorithm, i.e., differential steering, which converts two joysticks' commands into two torque directives for transportation. This allows the user to operate this cart linearly for both motion and orientation control via a joystick. Control examples are given to illustrate the feasibility and the effectiveness of the proposed controller and pilot algorithm.     

Relationship between dynamic magnetoelasticity,soft magnetic properties,and amorphous structure homogeneity in new alloy Fe62.5Co6Ni7.5Zr6Cu1Nb2B15

Abstract

The magnetic, magnetoelastic, and structural properties of the Fe62.5Co6Ni7.5Zr6Cu1Nb2B15 at.- alloy, recently produced by rapid quenching from the melt, have been observed and explained with regards to the proper choice of components and their percentages. In particular, it was shown that a giant magnetoelastic wave amplitude, obtained with a very low magnetising field, is a consequence of simultaneous very high values of permeability, magnetomechanical coupling factor, and Youngs modulus. The importance of the new amorphous alloy, both for applications and basic research, is founded on its structural development by means of isothermal heat treatments. In particular, the tendency to maintain structural disorder at temperatures above where the first crystallisation occurrs is fundamental. X-ray analysis demonstrates that this property determines the presence of nanocrystalline phases after heating at a temperature well above that of the first crystallisation.     

Evolution of interface microstructure and strength properties in titanium – stainless steel diffusion bonded transition joints

Abstract

Diffusion bonding was carried out to produce transition joints between commercially pure titanium and 304 stainless steel at a temperature of 800°C for different times ranging from 30 to 180 min. in steps of 30 min under load in vacuum. The diffusion couples thus produced were studied using optical microscopy, scanning electron microscopy, and electron probe microanalysis to characterise the reaction layers formed in the diffusion zone. The chemical compositions of these layers indicate that intermetallics like σ phase, Fe₂ Ti, Cr₂ Ti, χ phase, FeTi, β-Ti, and Fe₂ Ti₄ O are formed in the reaction zone. The presence of these intermetallic compounds was also confirmed by the X-ray diffraction technique. Maximum bond strength of ~242 MPa was obtained for diffusion welded joints processed for 120 min. At this joining time, the plastic collapse of the surface asperities reaches near completion, favouring the interdiffusion of chemical species. Reduction in the bond strength of the transition joint processed for 180 min is due to the formation of a large volume fraction of voids in the reaction zone. Under tensile loading, failure takes place through α-Fe + χ phase mixture for transition joints processed in the time range of 30 – 90 min and through β titanium for joining times greater than 120 min.