Study on Design Techniques of a Long Life Hot Forging Die with Multi-Materials

A new design technique for the long life hot forging die has been proposed. By finite element analysis, the reason for the failure of hot forging die was analyzed and it was concluded that thermal stress is the main reason for the failure of hot forging die. Based on this conclusion, the whole hot forging die was divided into the substrate part and the heat-resistant part according to the thermal stress distribution. Moreover, the heat-resistant part was further subdivided into more zones and the material of each zone was reasonably selected to ensure that the hot forging die can work in an elastic state. When compared with the existing techniques, this design can greatly increase the service life because the use of multi-materials can alleviate the thermal stress in hot forging die.     

Fragmentation in an Al–7 wt-%Si alloy studied in real time by X-ray synchrotron techniques

Abstract

One mechanism for the formation of equiaxed grains is the detachment of dendrite fragments which is believed to be at the origin of the central equiaxed core region in casting processes. Unfortunately, the dynamics of the fragmentation phenomena cannot be revealed by classical methods. Investigation of a unrefined Al–7 wt-%Si alloy using in situ and real time synchrotron X-radiography and X-ray topography at the European Synchrotron Radiation Facility, has allowed verification of the existence of dendrite fragmentation and of cascade fragmentation during directional solidification, and to study the evolution of the growth and sedimentation of the equiaxed grains formed from these fragments. An examination of the crystallographic misorientation of dendrites as fragmentation is ongoing. These results contribute to the understanding of the characteristics of the columnar to equiaxed transition and to knowledge of the origin of new equiaxed grains in unrefined alloys.     

Dynamic materials modelling concepts applied to analysis of hot rolling of commercial aluminium alloys

Abstract

A typical industrial hot rolling operation applied to a commercial Al–1%Mg alloy has been analysed in terms of some concepts from dynamic materials modelling (DMM), particularly the so called dissipator co-content J and the efficiency of power dissipation through microstructural changes η. The calculation of the parameter η for every deformation condition of the hot rolling schedule has been conducted assuming that this variable depends not only on the mean deformation temperature and strain rate but also on the strain applied to the material. All the analysis has been conducted on the basis of a constitutive equation previously determined for this material on a rational basis, which is capable of describing the strain, strain rate, and temperature dependence of the flow stress. It has been determined that, for this material, η can be significantly dependent on strain under certain deformation conditions, particularly low deformation temperatures and relatively high strain rates. It has also been shown that for the materials analysed, η is much more dependent on deformation temperature than on strain rate. A comparative analysis carried out with aluminium of various purities indicates that η is much lower for the alloy when it is deformed under similar conditions. In this sense, it has been suggested that such results could be interpreted in terms of the impurity content of the material and the interaction of the alloying atoms with the dislocation structure developed during high temperature deformation. However, this is only possible if the hypothesis advanced by Prasad and co-workers, that the power dissipation efficiency is associated with the dynamic microstructural processes that occur during deformation, is considered valid. The present results indicate that, contrary to previous findings, in terms of DMM concepts there are no specific conditions of temperature and strain rate for the optimum processing of the materials investigated.     

The Use of Electrochemical Scanning Tunneling Microscopy to Study the Initial Stages of Electrodeposition in situ; Overpotential Deposition of Pb and Pt on HOPG

The advent of the Electrochemical Scanning Tunneling Microscope has opened up the possibility of studying the structural development of electrodeposits in situ on a near atomic scale. The principles of Scanning Tunneling Microscopy, the incorporation of electrochemical cells and the application of such instruments to electrocrystallization studies are reviewed briefly. The overpotential depositions of Pb and Pt on graphite are used as examples to illustrate the wealth of information which can be extracted. The Pb exhibits a deposit topology consistent with conventional diffusion controlled mechanisms whilst Pt shows much more complex behaviour. The potential and limitations of the instrument are discussed.     

Evaluation of internal and subsurface quality of continuously cast billets and slabs by ultrasonic techniques

Abstract

The paper highlights the developments made in ultrasonic techniques at R&D and SS Division of Tata Steel Ltd in detecting, measuring and analysing the continuously cast billets/slabs with respect to its internal as well as subsurface quality. Different continuously cast billets and slabs could be ranked according to their cleanliness levels even with the conventional ultrasonic flaw detector. The effectiveness of ladle furnace treatment and vacuum degassing (RH degassing) in improving cleanliness level in slabs of extra deep drawing grade and that of electromagnetic stirring in low and high carbon billets, could be successfully assessed using these techniques. In order to convert the down graded first and last slabs of a sequence of auto grade interstial free into the prime grade slabs, the scarfing depth and cutting length were optimised based on the ultrasonic results. Some results using a computer controlled ultrasonic multiscan imaging system, on continuously cast steel billets, have also been presented.     

Effect of interpersonal relationships upon verbal conditioning.

"Two conditioning experiments were conducted in which E used 'mmm-hmm' to reinforce sentences which S began with pronouns 'I' or 'We.' Experiment I relied upon instructions to create a condition of either High- or Low-Attraction between S and E. Experiment II utilized… [a] scale to establish Compatible and Incompatible groups in terms of interpersonal needs… . Ss who were incompatible, or not attracted to E, suppressed the effects of reinforcement until removed from E's presence. The implications of these findings for generalizing from verbal conditioning situations to the patient-therapist relationship in clinical settings was discussed." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanical properties of metal injection moulded 316L stainless steel using both prealloy and master alloy techniques

Abstract

Stainless steel 316L MIM components can be made from either prealloyed powders or from master alloys blended with carbonyl iron powder. In this study these two techniques were compared using prealloyed and master alloyed gas atomised powders of ? 16 μm and ? 22 μm sizes. Four different compounds were prepared, characterised and injection moulded into tensile bars. The bars were compared for green strength, green defects, sintered strength and microstructure. The green components are stronger when carbonyl iron powder is used with the gas atomised master alloy. This material also seems to be less susceptible to moulding defects. The sintering strength of the material produced using the pre-alloyed powder was higher than the master alloyed prepared material. Little difference in mechanical properties existed between the materials fabricated from gas atomised prealloyed ? 16 μm and the ? 22 μm powders. Also, the viscosity of the mixtures was higher for the ? 16 μm material and the master alloy mixtures than for the –22 μm gas atomised prealloyed powders.     

Damage to gold surfaces induced by cathodic polarisation

Abstract

Prolonged cathodic polarisation of gold and gold alloy electrodes in the hydrogen evolution potential range is a typical operating condition in electroplating applications. Electrodic hydrogen evolution gives rise to superficial failures such as blistering and cracking. These types of damage can eventually cause electroformed objects to fail by macroscopic cracking. The development of these defects is connected with the evolution of the morphology and of the crystallographic and electronic properties of the electrode. In particular, progressive roughening can be detected, giving rise to unexpected and irreproducible behaviour of cathodic systems based on gold and its alloys. In this paper the time dependent behaviour of cathode modification brought about by hydrogen evolution, giving rise to morphological and related electrocatalytic effects, is investigated. The study is based on in situ and ex situ optical microscopy and electrochemical measurements (cyclic voltammetry and impedance spectroscopy) carried out in neutral aqueous solutions containing chloride.