Showing papers in "Materials Science and Engineering A-structural Materials Properties Microstructure and Processing in 2007"

Twinning and the ductility of magnesium alloys Part I: “Tension” twins

Abstract: Magnesium and its alloys do not in general undergo the same extended range of plasticity as their competitor structural metals. The present work is part I of a study that examines some of the roles deformation twinning might play in the phenomenon. A series of tensile test results are reported for the common wrought alloy AZ31. These data are employed in conjunction with a simple constitutive model to argue that View the MathML source twinning (which gives extension along the c-axis) can increase the uniform elongation in tensile tests. This effect appears to be similar to that seen in Ti, Zr and Cu–Si and in the so called TWIP phenomenon in steel.

Twinning and the ductility of magnesium alloys: Part II. “Contraction” twins

Abstract: Magnesium and its alloys do not in general undergo the same extended range of plasticity as their competitor structural metals. The present work presents part II of a study that examines some of the roles deformation twinning might play in the phenomenon. A series of tensile and compression tests results are reported for common wrought alloys: AZ31, ZK60 and ZM20. These data are combined with EBSD analysis and simple flow stress models to argue the following: (i) that “contraction” double twinning (which enables contraction along the c axis) can decrease the uniform elongation, and (ii) that compression double twinning can also account for shear failure at low strains. The last of these is described as a combined consequence of strain softening of the continuum and the local generation of twin sized voids.

Modeling the temperature dependent effect of twinning on the behavior of magnesium alloy AZ31B sheet

Abstract: Uniaxial compression test data were obtained from magnesium alloy AZ31B sheet material tested along three sample directions (rolling, transverse and normal direction) over the temperature range T = 22–250 ◦ C. The yield point during in-plane compression is insensitive to temperature, up to 200 ◦ C, suggesting that athermal mechanisms are responsible for yielding. The in-plane compression samples exhibit very low r-values, which provides another signature of significant twinning activity in magnesium sheet, in addition to the characteristic sigmoidal strain hardening curve. By varying the critical resolved shear strengths (CRSS) and hardening behaviors of the deformation mechanisms, it is possible to model the changes in the flow stress profile, the strain anisotropy, and texture evolution using a viscoplastic self-consistent polycrystal model. Notably, the CRSS values for basal slip were observed to be constant, while that of twinning increased slightly, and the CRSS values of thermally activated slip

FIB damage of Cu and possible consequences for miniaturized mechanical tests

Abstract: Cu specimens were exposed to Ga + ion bombardment for varying conditions of ion energy, ion dose, and incident angle in a focussed ion beam workstation Conventional transmission electron microscopy investigations were employed to analyze the Ga + ion induced damage The extent of visible damage was minimized by reducing the ion energy and furthermore by using grazing incident ions Concentration depth profiles of the implanted Ga were measured by Auger electron spectroscopy Concentrations of up to 20 at% Ga were found several nanometers below the surface Ga contents of more than 2 at% were detected within a depth of up to ∼50 nm Mechanical consequences in terms of possible hardening mechanisms are discussed, taking into account the experimental findings along with Monte Carlo simulations A non-negligible influence of the ion damage is predicted for submicron-sized samples

Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy

Abstract: AA2219 aluminium alloy has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to-weight ratio. Compared to the many fusion welding processes that are routinely used for joining structural aluminium alloys, friction stir welding (FSW) process is an emerging solid state joining process in which the material that is being welded does not melt and recast. The welding parameters and tool pin profile play a major role in deciding the weld quality. In this investigation an attempt has been made to understand the influences of rotational speed and pin profile of the tool on friction stir processed (FSP) zone formation in AA2219 aluminium alloy. Five different tool pin profiles (straight cylindrical, tapered cylindrical, threaded cylindrical, triangular and square) have been used to fabricate the joints at three different tool rotational speeds. The formation of FSP zone has been analysed macroscopically. Tensile properties of the joints have been evaluated and correlated with the FSP zone formation. From this investigation it is found that the square tool pin profile produces mechanically sound and metallurgically defect free welds compared to other tool pin profiles.

Processing and properties of carbon nanotubes reinforced aluminum composites

Abstract: Carbon nanotubes reinforced aluminum matrix composites were fabricated by isostatic pressing followed hot extrusion techniques. Differential scanning calorimetric, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy has been carried out to examine the reaction condition of nanotubes and aluminum, and to analyze the composites structure. The effects of nanotubes content on mechanical properties of composites were investigated. Experimental results showed that nanotubes are homogeneously distributed in the composites. Some nanotubes act as bridges across cracks, others are pulled-out on fracture surfaces of composites. However, nanotubes react with aluminum and form Al4C3 phases when the temperature is above 656.3 °C. The nanotubes content affects significantly mechanical properties of composites. Meanwhile, the 1.0 wt.% nanotube/2024Al composite is found to exhibit the highest tensile strength and Young's modulus. The maximal increments of tensile strength and Young's modulus of the composite, compared with the 2024Al matrix, are 35.7% and 41.3%, respectively.

The principles of grain refinement in equal-channel angular pressing

Abstract: Equal-channel angular pressing (ECAP) is a convenient processing tool for introducing very significant grain refinement, typically to the submicrometer level, in a wide range of metals. It is shown by experiment that processing by ECAP produces very similar microstructures in single crystals and in polycrystalline materials. Thus, after a single ECAP pass, aluminum single crystals and polycrystalline high-purity aluminum both exhibit microstructures consisting of bands of elongated subgrains and the experiments on single crystals have established unambiguously that these bands lie with their longer axes oriented parallel to the primary slip system. A model for grain refinement is developed incorporating the major experimental observations. Calculations of the shearing patterns for different processing routes lead to the conclusion that an equiaxed microstructure is achieved most rapidly in ECAP when slip occurs on three orthogonal planes over a wide range of angles: an example is route BC where the sample is rotated by 90° in the same sense about the longitudinal axis after every pass through the ECAP die.

Dynamic recrystallization in AZ31 magnesium alloy

Abstract: The effects of temperature and strain rate, as the most important thermomechanical processing (TMP) parameters, on the microstructural evolution of AZ31 magnesium alloy were studied. This was performed applying hot compression tests at a temperature range of 250–450 °C with various strain rates. The results indicated that the amount and the size of dynamically recrystallized grains are increased as Zener–Hollomon parameter decreased. In addition, the evolution of dynamically recrystallized grains was examined with increasing strain. In general, the amount of dynamically recrystallized grain is observed to increase with strain in a sigmoidal form. However, the related grain size was remained constant as strain increased.

Densification mechanisms in spark plasma sintering of nanocrystalline ceramics

Abstract: Effect of the particle size on the possible electric discharge during the SPS was examined. Nanoparticle compacts enable accumulation of high electric charge, and discharge under conventional voltages used for the SPS. The critical particle size for the electric discharge is both morphological and material dependent. The early stages of densification of the nanocrystalline powder compact proceed either by the plastic deformation or grain-rotation coalescence and sliding, aided by softening of the particle surfaces. The active densification mechanism depends on the changes both in the mechanical and electrical properties with temperature. Densification of 11 nm nc-MgO particles with low yield stress proceeds by plastic deformation already at 700 °C. However, densification of 34 nm nc-YAG particles with high yield stress proceeds by nano-grain rotation aided by particle surface softening. Densification at the final stages of SPS is associated with diffusional processes, where curvature driven grain growth predominates.

Influence of {10-12} extension twinning on the flow behavior of AZ31 Mg alloy

Abstract: Uniaxial compression tests were performed on samples cut along the extrusion direction from AZ31 Mg alloy tubes. A stage of increasing work hardening rate was observed on representative true sigma-epsilon curves. Specimens compressed to various strain levels were examined by optical microscopy and electron backscattered diffraction (EBSD) techniques. The results indicate that the widespread formation of intersecting {10-12} extension twins is responsible for the increased strain hardening rate. (c) 2006 Elsevier B.V. All rights reserved.

Ablation behaviors of ultra-high temperature ceramic composites

Abstract: In order to improve the oxidation resistance of carbon fibers reinforced carbon matrix composites (C/C and the thermal shock resistance of ultra-high temperature ceramics (UHTCs), large numbers of ZrB, based particles were introduced into CIC composites to fabricate the C/CC UHTC composites by powder infiltration (PI) and isothermal chemical vapor infiltration (ICV1). The effects of UHTC additive, heat flux and ablation time on the ablation behaviors of the C/C-UHTC composites were investigated through exposure to an oxyacetylene torch flame with ultra-high temperature. The ZrB, addition to the C/C pronouncedly improved the ablation resistance of the material under a 3920 kWm(2) heat flux and the C/C-ZrB2 showed a better ablation-resistive property compared to the C/C-4ZrB(2)-ISiC, C/C-2ZrB(2)-ISiC, C/C-2ZrB-ISiC-1HfC and C/C-2ZrB(2)-ISiC-ITaC. With decrease of the heat flux from 3200 to 2380 kW/m(2), the presence of a small amount of SiC in the C/C-ZrB, was found to have a positive role of improving the ablation resistance; the C/C-4ZrB(2)-ISiC exhibited a good ablation-resistive endurance under 2380 kW/m(2). The HfC addition was proved to effectively enhance the ablation property of the C/C-lZrB2-2SiC while the TaC addition severely deteriorated the property. (C) 2007 Elsevier B.V. All rights reserved.

Molecular dynamics study of the stress–strain behavior of carbon-nanotube reinforced Epon 862 composites

Abstract: Single-walled carbon nanotubes (CNTs) are used to reinforce epoxy Epon 862 matrix. Three periodic systems – a long CNT-reinforced Epon 862 composite, a short CNT-reinforced Epon 862 composite, and the Epon 862 matrix itself – are studied using the molecular dynamics. The stress–strain relations and the elastic Young's moduli along the longitudinal direction (parallel to CNT) are simulated with the results being also compared to those from the rule - of - mixture . Our results show that, with increasing strain in the longitudinal direction, the Young's modulus of CNT increases whilst that of the Epon 862 composite or matrix decreases. Furthermore, a long CNT can greatly improve the Young's modulus of the Epon 862 composite (about 10 times stiffer), which is also consistent with the prediction based on the rule - of - mixture at low strain level. Even a short CNT can also enhance the Young's modulus of the Epon 862 composite, with an increment of 20% being observed as compared to that of the Epon 862 matrix.

Sigma phase precipitation in duplex stainless steel 2205

Abstract: Sigma phase precipitation is known to embrittle duplex stainless steel. Accordingly, heat treatment and welding must be performed carefully. Nucleation and diffusional growth of sigma phase in th ...

Experimental study on the thermal and mechanical properties of multi-walled carbon nanotube-reinforced epoxy

Abstract: In this study, multi-walled carbon nanotubes (CNTs) were infused into Epon 862 epoxy through a high intensity ultrasonic liquid processor and then mixed with EpiCure curing agent W using a high-speed mechanical agitator. The trapped air and reaction volatiles were removed from the mixture using a high vacuum. Dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and flexural tests were performed on unfilled, 0.1, 0.2, 0.3, and 0.4 wt% CNT-filled epoxy to identify the loading effect on the thermal and mechanical properties of composites. DMA studies revealed that filling the carbon nanotube into epoxy can produce a 90% enhancement in storage modulus and a 22 °C increase in Tg. However, due to the lower crosslink density of the nanophased systems, a 6 °C decrease in decomposition temperature was observed in the 0.4 wt% CNT/epoxy in the TGA test. The flexural results showed that modulus increased with higher CNT loading percentages and the 0.3 wt% CNT-infusion system showed the maximum strength enhancement. Based on the experiment's results, a nonlinear constitutive equation was established for neat and nanophased epoxy.

Microstructure and compressive properties of multicomponent Alx(TiVCrMnFeCoNiCu)100−x high-entropy alloys

Abstract: The microstructure and compressive properties of Al x (TiVCrMnFeCoNiCu) 100− x ( x = 0, 11.1, 20 and 40 at.%) high-entropy alloys were studied. With the increase of Al content, the number of phases in the alloys gradually decreases. When Al content is 20 at.%, only bcc solid-solution structure is found in the alloy. The effect of high mixing entropy does facilitate the formation of simple solid solutions, making the total number of phases well below the maximum equilibrium number allowed by the Gibbs phase rule. The solid-solution strengthening mechanism and the structure transformation from fcc to bcc make the alloys have fairly high compressive strength; among them the compressive strength of Al 11.1 (TiVCrMnFeCoNiCu) 88.9 alloy reaches 2.431 GPa.

Processing and mechanical properties of SiC reinforced cast magnesium matrix composites by stir casting process

Abstract: Elemental Mg and Mg-alloy (AZ91D) based composites reinforced with 15 vol.% silicon carbide (SiC) particulates (average particle size 15 μm and 150 μm) were synthesised by stir casting technique. Particle distribution, particle–matrix interfacial reaction, hardness and mechanical properties in the as cast as well as T4 heat-treated conditions were investigated. The composite materials show uniform distribution of SiC particulates. The average grain size decreases with the presence of SiC particulates and the grain size further decreases as the particle size decreases. The AZ91D alloy composite shows an increase in hardness and elastic modulus compared to monolithic alloys. The improvement in elastic modulus of composite containing 15 μm size SiC particles is significantly higher than the composite with 150 μm size particles. The ultimate tensile strength and ductility of composite materials were reduced compared to unreinforced alloy.

The influence of aluminum on hot deformation behavior and tensile properties of high-Mn TWIP steels

Abstract: The influence of aluminum (0–3 wt.%) on the high-temperature flow stress and recrystallization kinetics of two austenitic 25 wt.% Mn-bearing TWIP steels were investigated and compared with the behavior of a low-carbon steel. In addition, tensile properties were determined over the temperature range from −80 to 200 °C. It was observed that the hot deformation resistance is slightly higher for the 25Mn3Al than for the 25Mn steel, but in both steels significantly higher than for the low-carbon steel. The static recrystallization kinetics is significantly retarded in both steels compared to the rate in the low-carbon steel. The activation energies of hot deformation and static recrystallization are higher than those for the low-carbon steel. In contrast to the high temperature behavior, below RT, the 25Mn steel possessed a higher tensile strength and a higher work hardening rate than the 25Mn3Al steel due to strain-induced martensite formation. With increasing temperature up to 200 °C, the deformation mode changed gradually to mechanical twinning. In the 25Mn3Al steel, the elongation increased with decreasing temperature as a result of enhanced mechanical twinning.

Enhanced mechanical behavior of a nanocrystallised stainless steel and its thermal stability

Abstract: This paper discusses the mechanical properties of a nanocrystallised stainless steel obtained using surface mechanical attrition treatment (SMAT) and the underlying grain refinement mechanism using transmission electron microscopy (TEM). It was shown that grain refinement down to the nanometer range has the potential to significantly improve the mechanical properties of a 316L stainless steel which becomes comparable in strength to titanium alloys. Hence, promising structural applications could be considered for such a material. At the same time, the thermal stability of this nanocrystallised material was studied in the temperature range from 100 to 800 °C. The results show that the nanometer scaled microstructure is retained up to 600 °C and that a controlled annealing treatment could even lead to enhancement of both strength and ductility of this material. All these results are explained in terms of microstructural investigations, X-ray diffraction measurements, tensile and bending tests as well as microhardness measurements.

Influence of friction stir welding parameters on grain size and formability in 5083 aluminum alloy

Abstract: Friction stir welding (FSW) has received a great deal of attention as a new solid-state welding technique. In the present study, the relationship between the microstructure of stir zone and the mechanical property of FS-welded 5083 aluminum alloy was investigated. The microstructures of the stir zones consisted of fine equiaxed grains at various FSW conditions in FS-welded 5083 Al alloy. However, the grain size of the stir zone decreased with the decrease in friction heat flow during FSW. The ductility in FS-welded 5083 Al alloy increased with the decrease in friction heat flow. It was indicated that the formability in FS-welded 5083 Al alloy was improved by the refinement of grain size of the stir zone.

Study on amino-functionalized multiwalled carbon nanotubes

Abstract: Functionalization with amine groups of MWNTs was achieved after such steps as carboxylation, acylation and amidation. XRD, Raman, FTIR, XPS, scanning electron microscopy (SEM) were used to investigate and determine the chemical structure and texture of the amino-functionalized MWNTs. By comparing with each other, it was found that the amino-functionalized MWNTs can improve their dispersion in H2O. However, concerning the results of XPS, SEM and dispersity analyses, other reactions may also have occurred, which influenced their dispersity in organic solvents.

Preparation and properties of montmorillonite modified asphalts

Abstract: Modified asphalts were prepared by melt blending with different contents of montmorillonite (MMT) and organomodified montmorillonite (OMMT). The X-ray diffraction (XRD) results show that the MMT modified asphalt may form an intercalated structure, whereas the OMMT modified asphalt may form an exfoliated structure. The addition of MMT and OMMT to asphalt increases both the softening point and viscosity of the modified asphalts at high temperatures. Furthermore, the modified asphalts exhibited higher complex modulus, lower phase angle. As a consequence, the MMT and OMMT modified asphalts displays enhanced viscoelastic properties, which improve its resistance to rutting at high temperatures. Compared with MMT, OMMT showed better effect in improving softening point and rutting resistance of asphalt, which contributes to the formation of exfoliated structure in OMMT modified asphalt. Storage stability tests disclose that the asphalts modified with MMT or OMMT are very stable when montmorillonite content is less than 3 wt%.

Thermal, electrical and magnetic studies of magnetite filled polyurethane shape memory polymers

Abstract: Thermal, electrical and magnetic properties of polyurethane shape memory polymer (SMP) samples filled with 0–40 vol% magnetite particles prepared by mixing and injection molding were investigated. Shape recovery in the shape memory polymer was initiated by a magnetizing field of H = 4.4 kA/m at a frequency f = 50 Hz. Electric resistivity was decreased by magnetite particles from ρ el ≈ 10 10 Ω m to ρ el ≈ 10 6 Ω m. The percolation threshold is achieved at a magnetite concentration of approximately 30 vol%. Thermal conductivity increases from 0.19 W/m K to 0.60 W/m K with magnetite fraction in the polymer. Thermal conductivity values are compared with several theoretical and semi empirical models. The Agari–Uno model shows a very good correlation to measured values. Changes in specific heat capacity with temperature were also measured and could be correlated with the morphology of the polymer. With a hysteresis recorder the power losses in magnetization reversal of the filled SMP were estimated. Using measured specific heat capacity and power losses the time for an increase of sample temperature from room temperature up to shape recovery temperature was calculated to be t ≈ 4 min. Time dependent photographic pictures of the shape recovery process showed a good accordance between the calculated and observed time for the shape recovery.

Improved processing and oxidation-resistance of ZrB2 ultra-high temperature ceramics containing SiC nanodispersoids

Abstract: We have studied the hot-pressing behavior of ZrB 2 /SiC ultra-high temperature ceramics (UHTCs) as a function of: (i) SiC starting-powder size, (ii) SiC vol%, (iii) ZrO 2 doping, and (iv) colloidal dispersion of ZrB 2 /SiC powder mixtures. It has been found that the addition of SiC promotes densification of ZrB 2 at a moderate hot-pressing temperature of 1650 °C. It has also been found that ball-milling of the ZrB 2 /SiC starting-powder mixtures using ZrO 2 balls media results in the doping of the powder mixture with ZrO 2 , which promotes hot-pressing densification. Reduction in the SiC starting-powder size, and colloidal dispersion of the powders, both have been found to promote hot-pressing densification of ZrB 2 /SiC materials; the highest density achieved in such ZrB 2 /SiC ceramics is 99.9%. Detailed microstructural characterization of the ZrB 2 /SiC ceramics using electron microscopy shows that some of these materials contain a Zr(O,B) 2 phase, and amorphous films at interphase interfaces. Oxidation studies reveal that SiC grain-size reduction results in improved oxidation-resistance in ZrB 2 /SiC materials. The ZrB 2 /SiC ceramics produced here possess modest hardness and toughness properties. The results presented here point to a new strategy for improving processing and oxidation-resistance of ZrB 2 /SiC materials: dispersion and reduction of SiC grains.

The effect of severe plastic deformation on precipitation in supersaturated Al-Zn-Mg alloys

Abstract: Experiments were conducted to examine the influence of equal-channel angular pressing (ECAP) on the development of precipitation microstructures in two supersaturated Al–Zn–Mg alloys. The results show that ECAP leads to an ultrafine grain size with finely dispersed η precipitates. It is concluded that processing by ECAP promotes the precipitation processes because dislocations act as nucleation sites for precipitates. Spherical precipitates were observed in the alloys processed by ECAP whereas long rod-like precipitates were also observed after ageing without ECAP. Calculations show the yield strengths estimated from the characteristic parameters of the precipitation microstructure are in good agreement with the values determined by mechanical testing.

Effect of structure evolution induced by ultrasonic peening on the corrosion behavior of AISI-321 stainless steel

Abstract: A nanocrystalline surface layer was produced on an AISI-321 stainless steel by severe plastic deformation via ultrasonic peening (UP). The microstructural evolution of the surface layer was characterized by means of X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). The volume fraction of strain-induced α-martensite as a function of the effective strain ( e ¯ ) was evaluated quantitatively using XRD and magnetic measurements. Considering the e ¯ magnitudes and the TEM data obtained, it is concluded that a grain refinement of austenitic structure passes ahead of the α-martensite formation, particularly in the top surface layer. The nanocrystalline austenitic grain structure (mean grain size ∼ 15 nm) was observed at e ¯ = 0.45 , while the startup of the strain-induced martensitic transformation was revealed at the strain extent of 0.62. The nanostructured surface layer formed after straining to e ¯ = 0.8 already contains mainly the martensite nanograins characterized by an average size of about 10 nm. Grain size increased gradually up to 60 nm within the layer containing both austenite and martensite phases at a depth of about 30 μm from the treated surface. Both the microhardness behavior of the stainless steel surface and its corrosion performance in 3.5% NaCl solution can be enhanced by the UP. They are shown to be in correlation with: (i) the grain refinement process and (ii) the increase in the volume fraction of strain-induced α-martensite.

Oxidation of AISI 304 and AISI 439 stainless steels

Abstract: The oxidation behaviour of AISI 304 and AISI 439 stainless steels was studied at high temperatures, under various oxygen pressures and in the presence or not of water vapour. Thermogravimetric analyses were conducted in isothermal conditions from 850 to 950 °C for 50 h and microstructural and chemical analyses of the oxide films grown by oxidation were performed by SEM and EDX. The oxide films were also analysed by grazing X-ray diffraction and by X photoelectron spectroscopy (XPS). The AISI 439 steel has higher oxidation resistance than AISI 304, above 850 °C, under high oxygen pressures. On the other hand, the AISI 304 steel has higher oxidation resistance under low oxygen pressures in the whole temperature range. In order to check whether the growth kinetics of Cr 2 O 3 formed by the oxidation of stainless steels was controlled by oxygen or/and chromium diffusion through the oxide film, the oxidation constants were theoretically calculated on the basis of diffusion data using Wagner's Theory. The calculated values of the oxidation constants agree reasonably well with experimental values, therefore confirming the role of diffusion processes on the growth of chromia on stainless steels.

Controlled release of ketoprofen from electrospun poly(vinyl alcohol) nanofibers

Abstract: Poly(vinyl alcohol) (PVA) as a biodegradable hydrophilic polymer has unique properties. It absorbs water and swells easily, but the swelling is inhibited by salts. Its physico-chemical properties depend on the degree of hydrolysis. The solubility of PVA in water increases greatly as its degree of hydrolysis increases. In the current work, new systems for the delivery of ketoprofen as non-steroidal anti-inflammatory drug (NSAID) were developed. New electrospun fibers containing ketoprofen and made from partially and fully hydrolyzed poly(vinyl alcohol) (PVA) were developed as drug delivery system. Moreover, electrospun PVA fibers were stabilized against disintegration in water by treatment with alcohol such as methanol. The release of ketoprofen from the electrospun fibers was determined by UV spectrophotometer at the body temperature (37 °C) and at the room temperature (20 °C). The results showed that upon the treatment of electrospun PVA with alcohol, the burst release was eliminated.

Effect of carboxyl-terminated poly(butadiene-co-acrylonitrile) (CTBN) concentration on thermal and mechanical properties of binary blends of diglycidyl ether of bisphenol-A (DGEBA) epoxy resin

Abstract: Six blend samples were prepared by physical mixing of epoxy resin with varying concentrations of liquid carboxyl-terminated butadiene acrylonitrile (CTBN) copolymer having 27% acrylonitrile content. The blend samples were cured with aromatic amine. A comparative study of Fourier-transform infrared (FTIR) spectra showed the modification as a result of chemical reactions between epoxide group, curing agent and CTBN. The tensile strength of cured blend samples decreased slightly from 11 to 46% where as the elongation-at-break showed an increasing trend with increasing rubber content, i.e., up to 25 phr, in the blend samples. Appreciable improvements in impact strength were also observed in the prepared blend systems. The glass transition temperature ( T g ) of the epoxy resin matrix was slightly reduced on the addition of CTBN. The cured resin showed a two-phase morphology where the spherical rubber domains were dispersed in the epoxy matrix.

Effect of Y for enhanced age hardening response and mechanical properties of Mg–Gd–Y–Zr alloys

Abstract: In this study, compositional dependence of age hardening response and tensile properties were investigated for Mg–10Gd–xY–0.4Zr (x = 1, 3, 5 wt.%) alloys. With increasing Y content, the age hardening response of the alloys enhanced and tensile properties increased. The Mg–10Gd–5Y–0.4Zr alloy exhibited maximum tensile strength and yield strength at aged-peak hardness, and the values were 302 MPa and 289 MPa at room temperature, and 340 MPa and 267 MPa at 250 °C, respectively. The strong peak age hardening was attributed to the precipitation of prismatic β′ plates in a triangular arrangement. The cubic shaped β phase was also observed at grain boundaries. The remarkable improvement in strength is associated with a uniform and high dense distribution of β′ and cubic shaped β precipitate phases in Mg matrix. Elongation of Mg–10Gd–0.4Zr alloys decreased with increasing Y content, and the elongation of Mg–10Gd–5Y–0.4Zr alloy was less than 3% below 250 °C, whereas the alloys containing 1 wt.% and 3 wt.% Y exhibited higher elongation than 5% at room temperature.

Microstructure and texture of a lightly deformed TRIP-assisted steel characterized by means of the EBSD technique

Abstract: The microstructural and textural changes after a tensile strain of 10% were observed by orientation contrast measurements in a TRIP-assisted steel. On the undeformed samples it was shown that the electron back scatter diffraction (EBSD) technique could be used successfully for determining the volume fraction of the microstructural constituents bainite, ferrite and austenite, whereas after deformation only the BCC and FCC phases could be separated. The results show that the tensile strain of 10% gave rise to a drop in residual austenite content from 10 to 4%, which was also confirmed by magnetic measurements. The texture data showed only minor orientation rotations after 10% tensile strain for the BCC ferrite and bainite grains, whereas the residual austenite did show a significant texture change. By meticulously monitoring the local intra-granular misorientations it was concluded that the BCC phases (ferrite and bainite) took up the larger part of the nominal strain whereas the residual austenite primarily responded to the mechanical load by a partial (stress-induced) martensite transformation. Hence, the texture change observed in the residual austenite could be attributed to the orientation selective character of the phase transformation.