Search

The article presents a list of papers related to materials science published in volumes 39, 40 and 41 of the periodical. The articles include "Adhesively-Bonded Joints and Repairs in Metallic Alloys, Polymers and Composite Materials," by A. Baldan, "Thermo-Mechanical Fatigue of Shape Memory Alloys," by E. Hornbogen and "Models in Thermoluminescence," by C. Furetta and G. Kitis.

The article presents a list of articles related to materials science published in volumes 39, 40, and 41. The articles include "Adhesively-bonded joints and repairs in metallic alloys, polymers and composite materials," "Observations of common microstructural issues associated with dynamic deformation phenomena: Twins, microbands, grain size effects, shear bands, and dynamic recrystal," and "Role of entropy of fusion in phase transformation and selfdiffusion."

The article presents a list of articles published in the "Journal of Materials Science," including "Adhesively-Bonded Joints and Repairs in Metallic Alloys, Polymers and Composite Materials," "Thermo-Mechanical Fatigue of Shape Memory Alloys," "Role of Entropy of Fusion in Phase Transformation and Self-Diffusion," "Synthetic Routes, Properties and Future Applications of Polymer-Layered Silicate Nanocomposites," and "Models in Thermoluminescence."

The article presents several review papers published in the Volumes 39 and 40 of the "Journal of Materials Science" including "Adhesively-Bonded Joints and Repairs in Metallic Alloys, Polymers and Composite Materials," by A. Baldan, "Thermo-Mechanical Fatigue of Shape Memory Alloys," by E. Hornbogen, "Recent Developments in Polyurethane-based Conducting Composites," by J. Njuguna and K. Pielichowski, "A Review of Anode Materials Development in Solid Oxide Fuel Cells," by San Ping Jiang, Siew Hwa Chan, and "Advances in the Study on Wear of Metals by Polymers," by Si-Wei Zhang and Ren-Yang He.

Lists research papers in the volumes 39 and 40 of the "Journal of Materials Science". "Adhesively-bonded joints and repairs in metallic alloys, polymers and composite materials," by A. Baldan; "Thermo-mechanical fatigue of shape memory alloys," by E. Hornbogen; "Role of entropy of fusion in phase transformation and self-diffusion," by G.P. Tiwari, J.M. Juneja and Y. Illjima.

Presents review papers in the volumes 39 and 40 of the February 15, 2005 issue of the "Journal of Materials Science". Adhesively-bonded joints and repairs in metallic alloys, polymers and composite materials; Thermo-mechanical fatigue of shape memory alloys; Electrical applications of carbon materials,

Lists review papers published in vols. 39 and 40 of the "Journals of Materials Science" publication. "Adhesively-bonded joints and repairs in metallic alloys, polymers and composite materials," by A. Baldan; "Thermo-mechanical fatigue of shape memory alloys," by E. Hornbogen; "Models in thermoluminescence," by C. Furette and G. Kitis; "Electrical applications of carbon materials," by D.D.L. Chung.

In the present paper, the following topics are reviewed in detail: (a) the available adhesives, as well as their recent advances, (b) thermodynamic factors affecting the surface pretreatments including adhesion theories, wettability, surface energy, (c) bonding mechanisms in the adhesive joints, (d) surface pretreatment methods for the adhesively bonded joints, and as well as their recent advances, and (e) combined effects of surface pretreatments and environmental conditions on the joint durability and performance. Surface pretreatment is, perhaps, the most important process step governing the quality of an adhesively bonded joint. An adhesive is defined as a polymeric substance with viscoelastic behavior, capable of holding adherends together by surface attachment to produce a joint with a high shear strength. Adhesive bonding is the most suitable method of joining both for metallic and non-metallic structures where strength, stiffness and fatigue life must be maximized at a minimum weight. Polymeric adhesives may be used to join a large variety of materials combinations including metal-metal, metal-plastic, metal-composite, composite-composite, plastic-plastic, metal-ceramic systems. Wetting and adhesion are also studied in some detail in the present paper since the successful surface pretreatments of the adherends for the short- and long-term durability and performance of the adhesive joints mostly depend on these factors. Wetting of the adherends by the adhesive is critical to the formation of secondary bonds in the adsorption theory. It has been theoretically verified that for complete wetting (i.e., for a contact angle θ equal to zero), the surface energy of the adhesive must be lower than the surface energy of the adherend. Therefore, the primary objective of a surface pretreatment is to increase the surface energy of the adherend as much as possible. The influence of surface pretreatment and aging conditions on the short- and long-term strength of adhesive bonds should be taken into account for durability design. Some form of substrate pretreatment is always necessary to achieve a satisfactory level of long-term bond strength. In order to improve the performance of adhesive bonds, the adherends surfaces (i.e., metallic or non-metallic) are generally pretretead using the (a) physical, (b) mechanical, (c) chemical, (d) photochemical, (e) thermal, or (e) plasma method. Almost all pretreatment methods do bring some degree of change in surface roughness but mechanical surface pretreatment such as grit-blasting is usually considered as one of the most effective methods to control the desired level of surface roughness and joint strength. Moreover, the overall effect of mechanical surface treatment is not limited to the removal of contamination or to an increase in surface area. This also relates to changes in the surface chemistry of adherends and to inherent drawbacks of surface roughness, such as void formations and reduced wetting. Suitable surface pretreatment increases the bond strength by altering the substrate surface in a number of ways including (a) increasing surface tension by producing a surface free from contaminants (i.e., surface contamination may cause insufficient wetting by the adhesive in the liquid state for the creating of a durable bond) or removal of the weak cohesion layer or of the pollution present at the surface, (b) increasing surface roughness on changing surface chemistry and producing of a macro/microscopically rough surface, (c) production of a fresh stable oxide layer, and (d) introducing suitable chemical composition of the oxide, and (e) introduction of new or an increased number of chemical functions. All these parameters can contribute to an improvement of the wettability and/or of the adhesive properties of the surface. [ABSTRACT FROM AUTHOR]

The factors affecting the mechanical and environmental durability (or stability), and performance of the adhesively bonded joints in various adherends including metallic alloys, polymers and composite materials are studied in detail. The primary function of a joint is to transfer load from one structural member to another. In most bonded joints the load transfer takes place through interfacial shear. At present the use of adhesive bonded joints are largely applied to secondary non-critical structures. Whereas the use of adhesive bonding in primary structural applications has been somewhat limited because of the difficulty in defining and predicting joint strength, and designing the joint geometry to optimize strength and reliability. The determination of adhesive joint strength is complicated primarily by the nature of the polymeric material itself. Since these problems are mainly mechanical in nature, stress analysis is required to understand how the force loads are distributed along the adherends and adhesive layer. Most structural engineers consider the durability or stability of a joint to be fatigue related. This is only partly true for adhesive bonds as most durability issues are driven by environmental resistance rather than fatigue loads. The environmental resistance of an adhesive bond is determined by the chemical bonds formed during cure of the adhesive and the resistance of the chemical bonds to environmental degradation. Environmental resistance is fundamental to the durability of a bonded joint or repair. Most in-service failures are caused by environmental degradation of the interface between the bonding surface and the adhesive. Although the use of adhesive bonding is increasing rapidly, there are still important issues which need to be addressed in joint analysis, design, durability, and performance considerations. Therefore, the study of joints usually involves consideration of (a) joint geometries, (b) materials (i.e., adhesives and adherends), (c) loading conditions (i.e., static and dynamic loadings), (d) failure modes (i.e., cohesive, adhesive or mixed failure modes), and (e) temperature and moisture or environmental effects (humidity, solvents, corrosion, temperature extremes, thermal cyling etc.). Therefore, in the present paper the adhesive joints are critically assessed in terms of these factors which affect the durability and performance of them. There are two basic mathematical approaches for the analysis of adhesively bonded joints: (a) closed-form or analytical model and (b) numerical solutions (i.e., finite element analysis, FEA). In the closed-form approach, a set of differential equations and boundary conditions is formulated. The solutions of these equations are analytical expressions which give values of stresses at any point of joint. The analytical approach for the solution of complex stress distributions in the joints has been progressively refined until recent times. In the second approach, solutions of differential equations are obtained by numerical methods or the continuum is represented by a discrete model at the outset. The solution of these equations gives displacements at the determined points from which strains and stresses can be obtained for any point within the model. Among the numerical methods, finite element analysis (FEA) has been extensively used with success. The two- and three-dimensional finite element analyses approaches have been extensively applied by many workers to analyse the adhesive joints considering the linear and geometric nonlinearities. [ABSTRACT FROM AUTHOR]

Alloys based on intermetallics have been considered for high temperature structural applications. However, many of these alloys suffer from intrinsic brittleness and low fracture toughness at ambient temperature. Therefore, ductile-phase-toughened intermetallic composites are being investigated as a means to improve the fracture toughness. A subset of this class of materials is in-situ composites produced by directional solidification of intermetallic eutectics. In this paper, we review recent developments related to the processing and properties of these composites. [ABSTRACT FROM AUTHOR]

Besides altering the kinetics of precipitation, the reinforcements with alumina particles appear to alter the relative proportions of the various phases formed in the matrix alloy during ageing. Alumina also seems to reduce the volume fractions of hardening phase in these materials, especially at higher contents. One reason for this effect could be the dislocation relief of the matrix strain associated with the early precipitates. Additionally, the diffusion of Mg and its subsequent incorporation into the reinforcement at the Al2O3/Al interface could also result in Mg depletion from the matrix, accounting for the reduction of the β (Mg2Si) particle sizes. Magnesium incorporation into interfacial alumina to form MgAl2O4 has been observed in these materials. This paper shows that the nature and morphology of the second phases depend the heat treatment conditions on. [ABSTRACT FROM AUTHOR]

The formation of a Ni3Al(γ′)+Ni7Hf2 unidirectionally solidified lamellar eutectic composite has been investigated in this paper. The results show that Ni-5.8Al-32Hf alloy, which has the Ni3Al+Ni7Hf2 eutectic structure, is a suitable composition of D.S eutectic material. The melting range of this composition is 41 °C as determined by DTA. The critical ratio of G/R for Ni3Al+Ni7Hf2 eutectic is found to be 5× 105 °C · s · cm−2, and the lamellar Ni3Al+Ni7Hf2 eutectic aligned parallel to the direction of solidification was made with R = 5 μm/s and G = 250 °C/cm. The investigation shows that the lamellar eutectic has a preferred crystallographic orientation between the Ni3 Al and Ni7Hf2 lamellae, i.e., (111)NiAl//(100)NiHf and [110]NiAl//[010]NiHf. The lamellar Ni7Hf2 did not degrade or coarsen obviously, and no harmful phase formed in the interface of Ni3Al/Ni7Hf2 after long time soaking of 1100 °C/110 h. This demonstrates that the Ni3Al+Ni7Hf2 lamellar eutectic has high interface thermal stability. [ABSTRACT FROM AUTHOR]

In the present study, amorphous Ni60Nb20Zr20 and Ti50Cu28Ni15Sn7 alloy powders were synthesized separately using a mechanical alloying (MA) technique. The dual-amorphous-phased (Ti50Cu28Ni15Sn7)100− x (Ni60Nb20Zr20) x ( x = 0, 10, 20, and 30 vol%) powders were prepared by mixing the corresponding amorphous powders. The dual-amorphous-phased powders were then consolidated into bulk amorphous/amorphous composite (BA/AC) alloy discs. The amorphization status of as-prepared powders and bulk BA/AC composite discs was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The microstructure of the BA/AC discs showed that the Ni60Nb20Zr20 phase is distributed homogeneously within the Ti50Cu28Ni15Sn7 matrix. The (Ti50Cu28Ni15Sn7)70(Ni60Nb20Zr20)30 BA/AC disc exhibited a relative density of 96.6% and its Vickers microhardness was 726 kg/mm2. [ABSTRACT FROM AUTHOR]

Ceramic particle reinforced aluminum metal matrix composites (MMCs) have resulted in potential use in aerospace and automobile industries. The composites have been processed by mechanical milling followed by traditional powder metallurgy route. The Al crystallite size is reduced to 27 nm after 60 h of milling. Results of the corrosion tests, evaluated using the potentiodynamic method in the NaCl solution, indicate that corrosion of the investigated composite materials depends on the weight fraction of the reinforcing particles. It has been found out, based on the determined anode polarization curves, that the investigated materials are susceptible to pitting corrosion. Moreover, experimental results suggest that the milled composite material Al–Zn/Al2O3p has higher corrosion resistance in the selected environment compared to unmilled composite Al–Zn/Al2O3p. Polarization curves show that the milling procedure improves the composite corrosion resistance in passive conditions. This is illustrated by the corrosion potential, which becomes nobler with milling. [ABSTRACT FROM AUTHOR]

The hydrogen sorption properties of the nanocomposite 85 wt.% Mg–15 wt.% Mg2Ni0.8Co0.2 obtained by mechanical alloying in inert atmosphere were investigated. Absorption measurements were performed under a hydrogen pressure P = 1 MPa at temperartures ranging from 373 to 573 K, while desorption studies proceeded at P = 0.15 MPa and temperatures of 573 and 553 K. The addition of the intermetallic compound Mg2Ni0.8Co00.2 was shown to improve the hydriding kinetics of magnesium. The composite exhibited a high hydrogen capacity which did not decrease even after a large number of absorption–desorption cycles. Comparison of the hydriding kinetics of the intermetallic compounds Mg2Ni and Mg2Ni0.8Co0.2 indicated facilitation of the process by the presence of cobalt in the alloy. Magnetic measurement data on Mg2Ni0.8Co0.2 showed formation of superparamagnetic precipitations of nickel and cobalt playing the role of active centres for dissociative chemisorption of hydrogen. The behaviour of the composite was explained by the catalytic effect of the intermetallic Mg2Ni0.8Co00.2, the existence of Ni and Co clusters on the surface and the process of mechanical alloying. [ABSTRACT FROM AUTHOR]

Magnesium MMCs reinforced with TiB2−TiC particulates were fabricated successfully via a master alloy route using a low cost Al-Ti-B4C system as starting material system. Microstructural characterization of the (TiB2−TiC)/AZ91 composite shows relatively uniform distribution of TiB2 and TiC particulates in the matrix material. Moreover, the results show that the hardness and wear resistance of the composites are higher than those of the unreinforced AZ91 alloy. [ABSTRACT FROM AUTHOR]

Investigates the effect of porosity on the electrical conductivity of the metal matrix composite. Application of composites in the electronic and electrical industries; Difference between the thermal expansion coefficients of the reinforcement and the matrix alloy; Details on the nominal composition of the alloy.

Investigates the effect of compact density on the fabrication of in situ Mg–TiC composites. Importance of metal matrix composite (MMC) technology in the improvement of the wear resistance, elastic modulus, and tensile strength of unreinforced metals and alloys; Offer of better matrix materials for the development of lightweight MMCs by magnesium; Attractive advantages of self-propagation high-temperature synthesis for synthesis of refractory materials.

Plane-wave shock deformation has been shown to produce deformation twins or twin-faults in essentially all metal and alloys. In FCC metals and alloys twinning depends upon stacking-fault free energy (SFE) and a critical twinning pressure; which increases with increasing SFE. For impact cratering where the shock wave is spherical and a prominent deviatoric (shear) stress is involved, metals and alloys with high SFE form microbands coincident with {111} plane traces while low SFE metals and alloys either form mixtures of twins and microbands or microtwins. Oblique shock loading of copper also produces mixtures of twins and microbands. Both microtwins and microbands increase in volume fraction with increasing grain size. BCC iron is observed to twin in both shock loading and as a result of impact cratering. Impact craters, shaped charges, and other examples of extreme deformation and flow at high strain rates exhibit various regimes of shear bands and dynamic recrystallization as a mechanism for solid-state flow. Deformation twins and microbands are also often precursors to this process as well. Examples of these phenomena in FCC materials such as Al, Ni, Cu, stainless steel and brass, and BCC materials such as Fe, W, Mo, W-Ta, and Ta are presented; with emphasis on optical metallography and transmission electron microscopy. [ABSTRACT FROM AUTHOR]

The study on the structure stability of AA3003 alloy produced by an intense plastic straining process named accumulative roll bonding (ARB) has been conducted. The results show that continuous recrystallization took place in the ARBed 3003 alloy with increasing the annealing time at 250°C and increasing the annealing temperature to 275°C. While, discontinuous recrystallization began in some regions after 300°C annealing, and nearly finished after 400°C annealing. Furthermore, an unusual tensile behavior was observed in this alloy after annealing at 250–275°C. The Hall-Petch dependence was observed in the plot of microhardness versus d-1/2 of the ARBed 3003 alloy, but its dependence slope was changed. The ultra-fine grains (<1 μm) formed in the ARBed 3003 alloy can be stable until annealing at 250°C for 1 h, and the fine grains (<2 μm) can be stable until annealing at 275°C for 1 h. Therefore, grain structure formed in the ARBed 3003 alloys after intense plastic strain is reasonably stable. In addition, the mechanism of structure stability and mechanical behavior were also discussed. [ABSTRACT FROM AUTHOR]

The deformation and fracture behavior of as-solutionized SiCw/AZ91 magnesium matrix composite was observed during the in-situ tensile straining in a transmission electron microscope. The results indicated that the dislocation slip was impeded by the SiC whiskers, a large number of dislocation pile-ups occurred around the whiskers. Microcracks nucleated predominately at the SiC whisker rich regions and the matrix near SiCw-AZ91 interfaces. The SiC whiskers and twins prohibited the crack propagation. The microcracks linked with each other and connected with the main crack, leading to the catastrophic failure of the composite. The fracture processes of the composite were found to be matrix-controlled. The poor ductility of the composite was attributed to the low inherent ductility of the magnesium alloy matrix and the local stress concentration because of the addition of the SiC whiskers. [ABSTRACT FROM AUTHOR]

XDTM technique has been successfully used to prepare TiB short fibre reinforced Ti-6Al matrix composites. Macrostructure and microstructure have been observed by optical microscopy and SEM in order to study the influence of cooling rate on the morphology, size and distribution of TiB. Due to the cooling rate, there exist three kinds of macrostructure: fine grain zone, columnar grain zone and coarse equiaxed grain zone, corresponding to the cooling rate of 100–500 K/s, 20–50 K/s and less than 10 K/s respectively. In the fine grain zone, TiB distributes randomly in matrix with main rod morphology with ∼3 μm in width and ∼50 μm in length. In the columnar and coarse grain zone, a colony structure was observed in which TiB distributes with a special orientation direction with matrix. A lamellar TiB with up to 50 μm width and 200 μm length was also formed. It was indicated that the decreasing of the cooling rate changes the morphology of TiB from rod to lamellar shape, and markedly increase the length and aspect ration of TiB, from ∼50 μm to ∼200 μm and from about ∼15 to ∼200, respectively. TEM results show that the rod TiB has a hexagonal cross section. Vickers hardness testing shows a little reinforcement geometry dependence, but the average hardness of 484 MPa is much higher than that of unreinforced matrix alloy. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry (DSC) was used to study the kinetics of S′ and θ′ precipitation in AA2618 and its composite containing 15 vol % Al2O3 particles . The unreinforced alloy and the composite were fabricated by a proprietary casting method, followed by extrusion. The DSC studies were carried out on as-quenched samples of the test materials. The precipitation of the S′ and θ′ phases in both materials was found to be kinetically controlled and obey the modified Avrami-Johnson-Mehl equation. The growth mechanisms for S′ and θ′ formation in AA2618 seemed unaffected by the addition of Al2O3 particles. The growth parameters obtained for the precipitation of these phases in the matrix alloy and the composite were not significantly different. [ABSTRACT FROM AUTHOR]

An investigation of microstructural development in three arc-cast Ni–Al–Cr–Ti multiphase alloys derived from the B2 type β-NiAl phase is presented. Detailed microstructural characterization of Ni–25 at % Al–20 at % Cr–15 at % Ti, Ni–26 at % Al–21 at % Cr–11 at % Ti and Ni–25 at % Al–24 at % Cr–15 at % Ti materials by transmission electron microscopy (TEM), is described. Microstructural development is examined in both the as-cast condition and after 140 h homogenization treatments at both 850 and 1100 °C. The formation of a eutectic between an L21-type β′ phase (Heusler phase, with a nominal composition of Ni2AlTi) and elemental α-Cr is examined. The precipitation of α within β(′) and vice versa, in both the inter- and intradendritic regions, is considered. The formation of L12-type γ′ (nominally Ni3Al) precipitates within the β and β′-phases is discussed, as is the transformation of β to two-phase β/β′ during ageing. © 1998 Chapman & Hall [ABSTRACT FROM AUTHOR]

Vickers microhardness has been measured at room temperature on a numerous compounds and alloys containing Ce (4f) and/or U (5f) metals (all together on 43 samples with different compositions represented by the parameter x) belonging to the following series of systems: Y1 - xUxRu2Si2, Ce1 - xYxRu2Si2, Ce1 - xYxCu2.05Si2, Ce1 - xLaxCu2.05Si2, Ce1 - xUxAl2, Ce1 - xUxNiSn. The significant changes were observed for all examined series of the systems with the discernible maximum or minimum in the recorded hardness curves. Whereas the maximum could be easily explained by the available theories, explanation of the minimum needs additional studies. [ABSTRACT FROM AUTHOR]

Reports on the characteristic fatigue-creep life map of a ferrous-nickel-chromium alloy melted in vacuum and in air at high temperature. Variation of both the fatigue stress and creep stress with the change of the minimum stresses; Examination of the time-dependent strain-stress curves based on deformation and fracture mechanisms; Provision of fracture characteristics for tested casting alloy melted in vacuum.