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A detailed parametric analysis of cutting forces in diamond turning of Al6061/15SiCp composite is presented. Spectrum analysis was used to analyze the features of cutting force variation. It was found that the presence of SiC particles led to a large fluctuation in the cutting and thrust forces. The magnitude and frequency of the variation were found to be closely related to the cutting conditions. The use of higher feed rate, lower spindle speed, and smaller depth of cut significantly reduced both the magnitude and frequency of the cutting force variation. Compared with diamond turning of ductile materials, a much greater ratio of the thrust and cutting forces was obtained under various cutting conditions. Empirical cutting force equations are presented based on a nonlinear multiple regression analysis method. A good correlation between the actual and the predicted results was found. These findings can provide guidelines for the selection of optimal cutting conditions in minimizing the fluctuation of cut...

This paper describes an experimental and theoretical study of the effects of different types of waveform on the grain size and the hardness of nickel electroforms in pulse current electroforming. The highest hardness value and the finest grain size were obtained using a ramp-down waveform with relaxation time. The experimental results show that compared with the conventional rectangular waveform and with relaxation time, the hardness value can be improved by about 28% when a ramp-down waveform, also with relaxation time, is used. These results are supported by theoretical predictions and the study of the surface morphology of the electroforms by scanning electron microscopy.

A mathematical model has been established for formulating the effect of different types of waveform on surface finishing in pulse current electroforming of nickel. The model describes the change of the concentration profile of electroactive ions, micro-current distribution and the rate of protrusion growth at the cathodic surface. The theoretical predictions are compared with the experimental results: within the range of the study, a maximum discrepancy of 10% on surface roughness values between the two was found. This discrepancy could be due to the evolution of hydrogen gases at the cathodic surface during electrodeposition. The best surface finish was found by using a ramp-down waveform with relaxation time. Both theoretical predictions and experimental results show that the quality of the electroforms, in terms of surface roughness improvement, influenced by the types of waveform is of the order of ramp-down waveform>triangular waveform>ramp-up waveform>rectangular waveform, all with relaxation time. This is also supported by the study of the surface morphology of the electroforms by scanning electron microscopy.

The problem considered in this paper is the elastic/plastic bending of a sheet metal, exhibiting planar anisotropy, under conditions of plane strain. The material is assumed to be elastically isotropic, and yielding according to Hill’s quadratic yield criterion for orthotropic rolled sheets. For a given curvature of the bent sheet beyond the elastic limit, the strain distribution is obtained in closed form when the material is ideally plastic. The determination of the moment–curvature relationship in the elastic/plastic range requires numerical integration not only for a work-hardening sheet, but also for a non-hardening sheet. The numerical results are presented in a graphical form using selected values of the parameters which define the plastic properties of the material.

High-strain-rate superplasticity (HSRS) of an Al–4.4Cu–1.5Mg/21SiC W composite sheet was evaluated by tensile tests and microstructural characterization over a range of initial strain rates from 1.67×10 −3 to 1.67×10 0 s −1 and temperatures from 723 to 818 K. The strain rate sensitivity exponent of the composite was found to be approximately 0.34 at a strain rate of 10 −2 –10 0 s −1 and at temperatures between 723 and 818 K. From the experimental findings, the strain rate sensitivity exponent is almost constant during deformation. A maximum elongation of ≈446% was obtained at 3.33×10 −1 s −1 and at 793 K, which is near the partial melting temperature of the composite. The threshold stress is strongly temperature dependent. The cavitation behavior of the composite during deformation was also examined and compared with that of a typical superplastic aluminum alloy (Al7475). The experimental results revealed that the cavity growth was essentially plastic-controlled. It was suggested that the presence of liquid phase was beneficial to nucleation at the interfaces and limited the rate of cavitation growth.

In this paper, the deformation and cavitation behavior of a high-strain-rate superplastic Al2009/20SiC W composite was examined at temperatures ranging from 753 to 823 K, and at the initial strain rates from 1.67×10 −3 to 1.67×10 0 s −1 . A maximum elongation of ∼250% was obtained at an optimum initial strain rate of 3.33×10 −1 s −1 and a temperature of 808 K, which was slightly higher than the partial melting temperature of the composite. The cavitation behavior of the composite was compared with typical superplastic aluminum alloys. It was considered that the presence of the liquid phase in the composite can effectively relax the stress concentration caused by grain boundary sliding, and hence, limited the growth of cavitation.

Laser forming is regarded as a process without rivals in the forming of hard and brittle materials. In this paper, the deformation behaviour of Al6013/SiC p aluminium matrix composite sheets in laser bending is investigated for the first time. Aluminium alloys being highly reflective to lasers, the operating range for the sheet is quite narrow, beyond which the sheet will either be melted or be unable to deform. The experimental results show that the final bending angle is related strongly to the laser power, the processing velocity, the number of irradiations, and the sheet geometry. It is interesting to note that smaller bending angles are obtained when the laser-scanning direction is parallel to the rolling direction of the sheet. A linear relationship between bending angle and line energy is also obtained when the line energy ranges from 2.5 to 5.5 J/mm for a 0.32 mm thick sheet. It is considered that the process should be operated in this range in order to have better control of the bending angle.

It is well known that crystal rotation which occurs in deformation processes may affect the mechanical and plastic properties of textured materials. In the present paper, the effect of crystal rotation on springback of a textured copper strip is examined. A model proposed previously by the authors for the prediction of springback of narrow and thin strips has been further extended to take crystal rotation into consideration. Based on the measured orientation distribution function of the strip, it is found that the influence of crystal rotation on the deformation behavior of the strip is significant. A reduction in elastic modulus, and circumferential and radial stresses are obtained. An improvement in the predicted springback angle is observed when crystal rotation is taken into consideration, though more research efforts still require to further enhance the accuracy of the model.

It is well known that the mechanical and deformation properties of metal matrix composites (MMCs) are related to their microstructures. However, less work has been carried out in laser bending to examine the dependency of microstructures of MMCs on deformation behaviour. In this paper, two aluminium-based metal matrix composites, Al2009/20 vol% SiCw and Al2009/20 vol% SiCp were investigated. A YAG laser was used to scan the composites both parallel and perpendicular to their rolling directions. It was reported that under the same processing conditions, a larger bending angle was obtained for the Al2009/SiCp composite. No significant change in microstructures was observed for both composites after bending. Experimental findings also revealed that for the particulate reinforced composite, a larger laser bending angle was obtained when the laser scanning direction was perpendicular to the rolling direction, whereas no significant difference was observed for the Al2009/SiCw composite. These phenomena were shown to relate to the shape and distribution of reinforcements.

Anisotropy is known to be an important factor in affecting springback and deformation behaviour of cold rolled integrated circuit (IC) leadframes. Less work has been carried out to study the effect of grain shape on springback of IC leadframes, though it is considered to be a source of plastic anisotropy. In this paper, a plane stress model based on the concept of relaxed constraints has been developed to investigate the effect of grain shape on springback of a cold rolled copper alloy. Comparisons between the predictions by the relaxed constraint model and the conventional full constraints model and the experimental results have been made. It is found that significant improvement has been obtained by using the new model.

This paper studies experimentally and theoretically the effect of different types of shaped waveform on the surface finish of nickel electroforms in pulse current electroforming. Experimental results show that the quality of the electroforms, in terms of surface roughness improvement, influenced by the types of waveform is of the order of ramp and triangular both with relaxation time>rectangular>ramp and triangular sawtooth. The results show that at the same cathodic peak current density, pulse period, and a fixed electrodeposition time or electrodeposition thickness, the surface roughness can be reduced by as much as two to three times when a relaxation time was used in the cases of ramp and triangular waveforms. These results are supported by the theoretical predictions and the study of the surface morphology of the electroforms by scanning electron microscopy.

Excimer laser surface treatment was utilized to improve the corrosion resistance of an Al-2009/SiC w composite. After laser treatment, the corrosion potential of the composite was increased to a more noble level, and the corrosion current was greatly decreased. This is considered to be due to the reduction of SiC whiskers and Cu-bearing compounds in the laser-modified layer. Moreover, the N 2 -treated specimen exhibited a much greater resistance to corrosion than the air-treated specimen. This was attributed to the formation of the AlN phase in the laser-modified layer.

The development of high lead-count integrated circuit (IC) packages imposes more stringent demands on the forming quality of IC leadframes. A thorough study on the springback of narrow strips becomes highly essential. However, most of the published works on the springback problem still only consider wide strips and are based on the plane-strain assumption, which are inappropriate for leadframe geometry. In this paper, a strain-hardening plane-stress bending model has been proposed to predict the deformation behavior and springback of narrow strips. Springback prediction for a typical leadframe material has been illustrated. Comparisons between the theoretical predictions and the experimental results and those obtained by two theoretical models reported in the literature have been made. Much improvement has been observed in using the present model. The results of the analysis are of high significance and can provide useful guidelines for tool-designers.

An initial non-uniformity in thickness of a sheet metal, which is commonly assumed as a basis for the theoretical prediction of limit strains in the biaxial stretching process, is considered here as a feature of the mathematical idealization of a complex process, rather than as a material imperfection existing in a real sheet metal. The present concept permits the degree of initial inhomogeneity to vary with the stress ratio, as well as with the mechanical properties of the material. When such a variation is allowed for in a suitable manner, the predicted forming limit curves exhibit a relatively small dependence on the degree of normal anisotropy of the sheet metal, and follow a trend that is in agreement with what is observed experimentally. The results demonstrate the importance of the non-quadratic yield function when dealing with sheet metals with a range of R-values of less than unity.

In order to meet the stringent requirements for high lead count packages, a thorough understanding of springback behavior becomes essential in the forming of integrated circuit leadframes. Plastic anisotropy of leadframe materials is known to be one of the key factors affecting springback. However, insufficient theoretical work has been done in the past to study the effect of plastic anisotropy on springback in integrated circuit leadframe forming. In this paper, a new plane stress bending model, taking account of plastic anisotropy, has been proposed to predict the deformation behavior and springback of narrow strips. Comparisons between theoretical predictions and experimental results have been made. It is shown that the results predicted by the anisotropic model are in better agreement with the experimental observations than those given by the isotropic plane stress model. These findings are significant because they provide useful guidelines for tool designers.

This paper investigates the design requirements for physical function on developing child patients’ garment. The requirements of style design for physical functions were collected from two questionnaire surveys through personal interviews with child patients and medical staff in the Queen Mary Hospital, the teaching hospital of the University of Hong Kong. Chisquare tests were adopted to test for associations between the responses and a range of variables. The style specifications include styles design for different age groups, sexes, medical needs, design details for top and bottom garment, selection of fasteners and accessories. The results generated ideas for the design of child patients' garment based on their physical needs during hospitalization.

In recent years, much attention has been paid to electroforming as a high-tech manufacturing technique for many micro-devices such as optical readout disk moulds and micro-transducers. However, most of the present research works are focused on using square-wave pulse current to enhance surface finishing and deposit quality, little research result having been reported on the use of other waveforms. In this paper, triangular-, sine- and square-wave pulse currents are used in the investigations. It is shown that a better surface finishing and a smaller grain size can be obtained by using a triangular wave. Different orientation densities of [1 0 0] fiber texture are observed for different waveforms, which are considered to be related to the change of the amount of inhibiting chemical species during the electrodeposition process.

The elevated temperature deformation behavior of an Al6013/15SiC P composite sheet was investigated by uniaxial tensile tests at temperatures ranging from 723 to 853 K and at initial strain rates between 1.67×10 −3 and 1.67×100 s −1 . The strain rate sensitivity exponent was found to be approximately 0.17 which was apparently below that of a superplastic material. A maximum elongation of ∼177% was obtained at an initial strain rate of 6.67×10 −1 s −1 and at a temperature of 773 K. The apparent activation energy was calculated to be approximately 370 kJ/mole which is much higher than that of its unreinforced counterpart. The fracture surface morphology showed a large amount of localized plastic deformation in the aluminum matrix and numerous large cavities. The experimental results were compared with that of a high-strain-rate superplastic Al6061/20SiC W . It was considered that premature failure at the reinforcement/matrix interfaces was the main reason for the Al6013 composite not showing superplastic properties.

This paper presents the displacement analysis of the three variants of a spatial kinematic loop containing 3R and 1CP joints using vector algebraic method. The closed-form input-output displacement equations of this mechanism are derived as forth-order polynomials. Analytical steps and expressions are laid out uniformly and simply.

An analytical model has been developed to predict the ablation rate of fiber reinforced polymers as a function of the fiber volume fraction and the excimer laser incident fluence. An ablation experiment was carried out to determine the effective laser absorption coefficient and the threshold fluence of ablation for a liquid crystal polymer (LCP) and the reinforcement phase, i.e., glass fiber. Employing these results in the model, the ablation rate of the LCP composite for different incident fluences was obtained. The theoretical predictions on ablation rate compare extremely well with the experimental results. In addition, the experimental results show that accumulation of gases, debris fragments, etc. in front of the sample can significantly affect the ablation rate of the composite material, especially at high pulse frequencies (>40 pulses/s).

Wool fibre treated by low-temperature plasma (LTP) using different non-polymerising gases was dyed with chrome dye. The rate of dyeing, the time of half-dyeing (t1/2), the final dyebath exhaustion, the chromium exhaustion and the chromium fixation were studied. The results showed that LTP treatments can alter the dyeing properties to various degrees. The nature of the LTP gases plays an important role in affecting the behaviour of chrome dyeing.

Over the last decade, there have been numerous research works conducted on laser bending. However, less research effort has been spent on investigating the laser bending of thin sheets using a low power laser. In the present study, a low power Nd:YAG laser is used to experimentally examine the bending behaviour of a thin steel alloy strip which is now being used for integrated circuit leadframes. In the experiments, a machine vision system has been used to measure bending angles in a more accurate and efficient way. The experimental results show that the final bending angle in a multiple-irradiation laser bending process is related strongly to the laser power, the processing velocity, the number of irradiations and the holding time between each laser irradiation. A threshold line energy of about 0.14 J mm −1 is observed, and a linear relationship between the bending angle and the line energy is found when the latter is below 1 J mm −1 .

It is well established that most superplastic materials cavitate during deformation, and that the presence of cavitation may lead either to premature failure or to degradation of the mechanical properties of post-formed components. However, research works on the cavitation behavior of high-strain-rate superplastic MMCs are at present limited to PM64/SiC{sub P}, Al6061/20Si{sub 3}N{sub 4P(W)}, IN9021/15SiC{sub P} and Al2124/20Si{sub 3}N{sub 4W}. Furthermore, the cavitation behavior of MMCs deformed under complex stress states which are commonly applied in industrial processes has less been investigated. The purpose of this paper is hence to provide a first description of the cavitation behavior of a high-strain-rate superplastic aluminum matrix composite (Al6061/20SiC{sub w}) under uniaxial and equibiaxial tension, and the findings will be compared with that of a typical superplastic alloy (Al7475).

This investigation studies the laser machining behavior of a glass fiber reinforced liquid crystalline polymer (LCP) composite by using two different types of lasers, namely; pulsed Nd:YAG and excimer. A theoretical model is established to predict the maximum depth-of-drill of the YAG laser machined holes. Moreover, the effects of the YAG laser output parameters on the geometry and the quality of the machined surface of the hole are discussed. The laser machining characteristics of the composite are compared for the two different types of lasers in terms of laser absorptivity. The results show that the glass fiber reinforced LCP has a higher absorption towards UV radiation than infrared light. Scanning electron microscopy examinations were also conducted to assess the surface quality of the machined holes. In YAG laser drilling, a high pulse energy or excessive pulses caused severe carbonization of the surface, and many cracks formed. On the other hand, excimer laser did not cause any significant carbonization of the surface; however, a large number of voids were found in the process affected zone.

In recent years, there have been a lot of research efforts in studying high-strain-rate superplasticity of aluminum matrix composites. However, the superplastic deformation behavior of the composites has not been fully understood. Superplastic deformation mechanism in aluminum matrix composites was considered to be grain boundary sliding and interfacial sliding. In this paper, the model proposed recently by the authors to explain the superplastic deformation of a particulate reinforced aluminium matrix composite at temperatures above and below its solidus temperatures is further developed. The theoretical predictions are in agreement with the published experimental findings.

Although high-strain-rate superplasticity of metal-matrix composites (MMCs) has attracted much research attention in the last decade, most researchers still use uni-axial tensile tests to investigate the formability of MMCs. In this paper, a new fully-computer-controlled superplastic bulge tester has been developed to study the hot formability of an aluminum-matrix composite sheet under complex stress states. Thin 20 vol.% SiC whisker-reinforced 2009 aluminum sheets (2009Al/20SiC W ) with thicknesses of 2.0 and 2.3 mm were bulged at a constant polar strain-rate of 2.0×10 −1 s −1 and at a optimum temperature of 808 K in elliptical dies with aspect ratios of 1:1, 4:3, 2:1, 8:3 and 4:1. The forming-limit diagram of the MMC was determined for the first time. It was shown that the forming limits increases with increasing sheet thickness, and that the general shape of the curve is different from that of conventional forming-limit curves.

The magnetic properties of nickel deposits are known to be related to their crystallographic textures. Although there has been significant work investigating the relationship between crystallographic textures and magnetic properties of sputtered ferro-magnetic films, relatively less effort has been spent on studying electroformed nickels. Orientation distribution functions and coercivity of the nickel deposits, electroformed by using a nickel sulphamate bath and pulse-reverse currents, have been determined and their relationship examined. It was found that the [100] fibre texture with different orientation densities was formed at different on-times and off-times, and that at the same deposition thickness the coercivity increased with increase in the orientation density of the [100] fibre texture. This findings are of high significance as they can serve as guidelines for the production of nickel deposits with defined magnetic properties through the control of crystallographic te xture by varying the pulse parameters in pulse-reverse current electroforming.

Recently, some published experimental results have revealed that springback of some common types of integrated circuit (IC) leadframes in roller forming is highly related to their anisotropic properties. In this paper, a new plane stress bending model based on the approach of Crystallographic Mechanics of Textured Polycrystals (CMTP) has been developed to predict the deformation behaviour and springback of a copper alloy. Based on the texture data obtained from the measured orientation distribution function, springback of the copper alloy in the rolling direction was determined to be greater than that perpendicular to the rolling direction. It was also found that the springback increased with increasing die radius. The predictions were compared to the experimental findings, and the trends of them were in reasonable agreement.

There has been much research on the tube inversion process. However, the effect of anisotropy on the process is less reported. In this paper, a numerical method based on the Hill's plastic anisotropic theory and the membrane theory of shells has been proposed to analyse the tube inversion process with consideration of anisotropy. In the present method, a system of first-order ordinary differential equations have been developed. By solving these equations, the deformation behaviour of the tube and the effect of the anisotropy on the process can be obtained. The predicted loads were found to be in good agreement with experimental results and the plastic anisotropy of the sheet has been shown to have a significant effect on the process. This simple numerical method is demonstrated to be practical, accurate and appropriate for the analysis of other axisymmetric tube-forming process.

In 1984, a 20 vol.% SiC-whisker-reinforced 2124 aluminum composite was first reported by Nieh and Wadsworth to behave superplastically. In order to understand the superplastic deformation mechanism, a lot of attempts have been made. However, up to present, the superplastic deformation mechanisms for aluminum composites have not yet been fully understood. In the present study, the superplastic behavior of a SiC whisker reinforced 6061 aluminum matrix composite has been investigated and its superplastic deformation characteristics discussed.

Previous studies showed that the feltability and wettability of wool fabrics were improved after the application of plasma treatment. In the present paper, further study on the plasma treatment was carried out to investigate its effect on other fabric properties including (i) performance properties (tearing strength, tensile strength and elongation), (ii) aesthetic properties (pilling resistance and crease recovery) and (iii) comfort properties (air permeability, wettability and antistatic). Pure wool 2/1 twill fabrics were treated by plasma using three non-polymerising gases namely oxygen, nitrogen and 25% hydrogen / 75% nitrogen gas mixture. The operation conditions, i.e. power, pressure and treatment duration, were the same for all plasma treatments. Different tests were conducted to investigate the effect of plasma treatment on the properties of treated fabrics. The results of experiments showed that plasma treatment did give different degrees of influence on the properties of wool fabric. In addition, the effectiveness of different gases plasma treatment was compared of which the gas mixture plasma gave the best modification effect.

The effect of low temperature plasma (LTP) on polyester (PET) is investigated by examining the changes in the dyeing properties of treated PET fabrics. An optimum condition for LTP treatment is determined by orthogonal analysis and this treatment condition was used through out the study. After LTP treatment, the PET fabric samples exhibit better hydrophilicity and the dyeability of the fabric is increased and such improvement is more pronounced in the case of high energy disperse dyes. Scanning electron microscope (SEM) observation also reveals that the surface of the treated PET fibre becomes rough with the formation of microtroughs.

Induced properties of polyester fabric due to irradiation of excimer laser, including surface luster, wettability, dyeability and stability of the resulting micro-structures in the fibre surface are investigated. After excimer laser treatment, the irradiated polyester fabric samples exhibit better hydrophobicity at room temperature and the dyeability of the fabric is improved. The study on surface reflectance shows that excimer laser treatment results in a reduction and a more uniform distribution of fabric glossiness: the treated polyester fabric samples have a silk-like appearance. Scanning electron microscope (SEM) observation reveals that the resulting structures on the fibre surface is virtually unaffected by hot air and hot water and is chemically as stable as its untreated counterpart.

Nickel deposits are rather seldom randomly oriented; they usually exhibit a column-like orientation with a definite [hkl] axis along the electric field direction in the electroforming process. However, up to present, most of the studies in electroforming nickels are still using a nickel sulfate bath which is now not commonly used in precise-electroforming or micro-electroforming. In this paper, an experimental investigation on the effect of pulse current on texture in micro-electroforming nickel has been carried out using a nickel sulphamate bath. It was reported that strong and weak [100] texture were formed at different pulse current conditions. These phenomena were considered to be related to the change of the amount of inhibiting chemical species at different conditions.

Superplastic tensile tests of a SiC p reinforced 8090 aluminum alloy composite were carried out at strain rates ranging from 7.25 × 10 −4 to 3.46 × 10 −1 s −1 and at temperatures from 773 to 873 K. A maximum elongation of 300% was obtained at a strain rate of 1.83 × 10 −1 s −1 when tested at a temperature of 848 K which was slightly above the solidus temperature of the composite. Several important superplastic factors such as strain rate sensitivity, threshold stress and activation energy were calculated. The superplastic behavior of some particulate reinforced aluminum alloy based composites and several aluminum alloys was compared in view of the strain rate, the optimum testing temperature and the relationship between the flow stress and the strain rate. Considering the accommodation process for dislocation movements, the constitutive equations for superplastic deformation at temperatures above and below the solidus temperature of the composite were developed. Experimental results of the stress-strain relationship obtained at temperatures near to the solidus temperature of the composite compare well with the theoretical constitutive predictions.

Superplastic deformation mechanism in particulate reinforced aluminum alloy matrix composites was analyzed under the light of dislocation movements. The superplastic behavior of some particulate reinforced aluminum alloy based composites and the corresponding monolithic aluminum alloys was compared in view of strain rate, optimum testing temperature and the relationship between flow stress and strain rate. Under the consideration of the accommodation process for dislocation movements, the constitutive equations for superplastic deformation at temperatures below and above the solidus temperature of the composite were developed. To verify the theoretical predictions, superplastic tensile tests were conducted on the SiCp reinforced 8090 aluminum alloy composite. Experimental results of the stress-strain relationship obtained at temperatures near to the solidus temperature of the composite compare well with the theoretical constitutive predictions.

Since the introduction of the concept of the forming-limit diagram to represent acceptable limit strains during sheet metal forming by Keeler and Backofen in 1963, it has become a major research topic and a considerable number of experimental and theoretical studies have been carried out. In most of the theoretical models, a type of defect is introduced and accommodated into the theoretical formulation. However, these models have met with only partial success. Moreover, in real materials, there do exist various types of defects, and their effects on limit strains may be overlapping and interacting. A single theoretical model that can fully explain or predict the formation of localised necking in a wide range of materials seems unrealistic. In this paper, a model based on the upper-bound theorem has been proposed to assess the susceptibility to localized necking of defect-free sheets under biaxial stretching. Without assuming a defect, the effects of the work hardening, anisotropy and geometry of a sheet on the limit strains have been analyzed. The significance of the findings is discussed.

Superplastic tensile tests of a 17 vol.% SiCp/8090 Al-Li composite were carried out at strain rates ranging from 7.25 × 10-4 s-1 to 3.46 × 10-1 s-1 and at temperatures from 773 K to 873 K. A maximum elongation of 300% was obtained at a strain rate of 1.83 × 10-1 s-1 when tested at a temperature of 848 K which was slightly above the solidus temperature of the composite. The effect of a small fraction of liquid phase on high-strain-rate superplasticity was discussed. Finally, the activation energy of high-strain-rate superplastic deformation was calculated and high-strain-rate superplastic mechanism was discussed.

The microprocesses of the amorphous-to-quasicrystalline transformation in Zr65Ni10Cu7.5Al7.5Ag10 bulk metallic glass were studied in detail by transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). It was found that the amorphous-to-quasicrystalline transformation in the present system undergoes a series of interprocesses and follows the sequence of the phase transformation of amorphous →FCCZr2Ni→Tetragonal Zr2Ni→Tetragonal Zr2Ni with a domain structure →Quasicrystals. HRTEM indicated that a domain structure with a high density of stacking faults was formed in the sample at the stage just prior to the formation of quasicrystals. This special structure seems to possess the structural symmetries similar to those of icosahedral quasicrystals. Nanobeam energy dispersive x-ray spectrum revealed that atomic diffusion was involved in all interprocesses of the phase transformations. This suggests that the amorphous-to-quasicrystalline transformation in the present bulk metallic glass is a nonpoly...

Recently, certain discontinuously reinforced aluminum based metal matrix composites (MMCs) have demonstrated high-strain-rate superplasticity. These findings are significant since one of the major shortcomings of conventional superplastic forming process is that the forming rate is too low. Models based on rheology seem to be unable to explain fully the high-strain-rate superplastic behavior of MMCs, particularly if the test temperature is near to the solidus temperature of the material. In view of this, this paper presents a model based on grain boundary sliding and interfacial sliding to explain high-strain-rate superplasticity of MMCs under the condition that a partially continuous film is present at grain boundaries. The theoretical model was verified by experimental findings of a 17 vol.% SiC{sub p}/8090 aluminum-lithium based composite of which the average particle size of the reinforcement phase was 3 {micro}m.

The effect of grain size and strain on the flow stress of polycrystals has long been studied. However, the effect especially for polycrystalline iron, still cannot be fully explained by most of the models. In this paper, a unified equation based on a one-parameter approach has been proposed to predict the relation between flow stress and grain size at various strains. The predictions are found to be consistent with the published experimental data.

Tailorable magnetic properties and magneto-caloric effect were achieved in the Gd-Co binary amorphous alloys. It was found that the Curie temperature (Tc) of the GdxCo100-x (x=50, 53, 56, 58, 60) metallic glasses can be tuned by changing the concentration of Gd as Tc =708.8-8.83x, and the mechanism involved was investigated. On the other hand, a linear correlation between the peak value of magnetic entropy change (-Δ Smpeak) and Tc-2/3 is found in the amorphous alloys with a linear correlation coefficients of above 0.992. Therefore, the -ΔSmpeak of the Gd-Co binary amorphous alloys under different magnetic fields can be easily tailored by adjusting the composition of the alloy.

In this paper, a numerical procedure has been proposed to predict limit strains of textured sheets under equi-biaxial tension by means of the MK model and taking into account of crystal rotation. Limit strains have been predicted for three common crystallographic orientations and an annealed aluminium sheet. The effect of crystal rotation on limit strains was shown to be significant. However, no general trend of the effect has been observed. It is argued that the effect is quite complicated and dependent on various factors such as the initial orientation or texture, groove orientation and the initial inhomogeneous factor. The incorporation of texture change in the analysis of sheet metal forming was found essential.

It has been demonstrated that the deposit quality of nickel electroforms can be enhanced by using a magnetic field. Less research work has been carried out to examine the effect of magnetic fields on the surface finish of nickel electroforms using a nickel sulphamate bath and low magnetic flux densities. In this paper it has been found that the surface finish of nickel electroforms can be improved by applying a magnetic field. The best surface finish is obtained at a magnetic field of 5 mT and at a current density of 8 A dm -2 . A change in the intensity of the (200) peak is observed in the nickel electroforms under different magnetic flux densities. In this paper the effect of a magnetic field on surface finish has been examined theoretically. it is believed that the presence of a magnetic field may increase the diffusion layer thickness and hence improve the surface finish.

Many studies show correlation between the experimental stress-strain curves of sheet metals as determined from different deformation modes, such as plane strain tension and balanced biaxial tension, predicted from a uniaxial tensile test by the equivalent concept, through different anisotropic yield criteria. In this paper, an attempt is made to predict the balanced biaxial stress-strain curves of aluminium and copper sheets from their uniaxial tension data, without using the concept of equivalent stress or strain. The model takes into account a sheet's initial preferred orientations, external imposed constraints, and crystal rotations along the strain path that the sheet metal will follow.