Examination of the distribution of the tensile deformation systems in tension and tension-creep of Ti-6Al-4V (wt.%) at 296 K and 728 K

The deformation behaviour of an α + β Ti–6Al–4V (wt.%) alloy was investigated during in situ deformation inside a scanning electron microscopy (SEM). Tensile experiments were performed at 296 and 728 K (~0.4Tm), while a tensile-creep experiment was performed at 728 K and 310 MPa (σ/σ_ys = 0.74). The active deformation systems were identified using electron backscattered diffraction-based slip-trace analysis and SEM images of the specimen surface. The distribution of the active deformation systems varied as a function of temperature. Basal slip deformation played a major role in the tensile deformation behaviour, and the relative activity of basal slip increased with increasing temperature. For the 296 K tension deformation, basal slip was less active than prismatic slip, whereas this was reversed at 728 K. Twinning was observed in both the 296 and 728 K tension experiments; however, no more than 4% of the total deformation systems observed was twins. The tension-creep experiment revealed no slip traces, however grain boundary ledge formation was observed, suggesting that grain boundary sliding was an active deformation mechanism. The results of this work were compared with those from previous studies on commercially pure Ti, Ti–5Al–2.5Sn (wt.%) and Ti–8Al–1Mo–1V (wt.%), and the effects of alloying on the deformation behaviour are discussed. The relative amount of basal slip activity increased with increasing Al content.     

SEM and TEM analysis of composite of ZrO2-Ti system

3Y-ZrO₂-Ti composites obtained by slip casting method were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, the Vickers hardness was measured. The experiments show the complex microstructure of composites. The tetragonal zirconium dioxide (t-ZrO₂) and monoclinic zirconium dioxide (m-ZrO₂) as a composite matrix were detected at XRD analysis. SEM observations revealed that Ti -rich phase are uniform distributed in composites. Moreover, the large and very fine precipitations were found. The very fine Ti rich precipitations were located at ZrO₂ grain boundaries as well as in the triple-points. TEM experiments confirmed that in the sintered composites 3Y-ZrO₂ – 10%Ti the uniaxial ZrO₂ grains (100–600 nm), fine monoclinic martensitic plates and fine round monoclinic particles (20–40 nm) of ZrTiO₂ phase were exist. The complex microstructures of 3Y-ZrO₂-Ti composites have a high hardness as a result of existing fine ZrTiO₂ and other Ti oxides precipitations.     

Enhanced interface interaction between modified carbon nanotubes and magnesium matrix

Carbon nanotube (CNT)/metal interface interaction is critical to the mechanical properties of CNT-reinforced metal matrix composites (MMCs). In this paper, in order to realize the chemical modification of the interface interaction between CNTs and Mg matrix, different types of defects (monovacancy, carbon and oxygen adatoms, as well as p-type boron and n-type nitrogen substitution) are introduced in CNTs to investigate the effect of the defects on the interface interaction (E_ib) between CNT and Mg (0 0 0 1) surface. Moreover, two models (adsorption model and interface model) are compared and validated to investigate the interface interaction. It is revealed that the CNT with the carbon adatom has the highest E_ib with the Mg (0 0 0 1), and the effect of boron doping on E_ib is superior to the intermediate oxygen which has already been proved experimentally in the enhancement of the interface interaction in MMCs. In terms of the electronic structure analysis, we reveal the micro-mechanism of the increase of E_ib under the action of different types of defects, and propose that the presence of holes (boron dopant) and the unsaturated electrons in CNTs can generate the chemical interaction between CNT and Mg matrix effectively. Our results are of great scientific importance to the realization of robust interfacial bonding between CNTs and Mg matrix via the reinforcement modification, so as to enhance the mechanical properties of CNTs reinforced Mg matrix composites.     

Effect of heat treatment on the mechanical and microstructural characterization of Mg-AZ91E/TiC composites

Mg-AZ91E/TiC_p composite was fabricated using a spontaneous infiltration technique at 950 °C under an argon atmosphere. The composites produced have 37 vol.% of metal matrix and 63 vol.% of TiC-like reinforcement. The obtained composites were subsequently solution heat-treated at 413 °C during 24 h, cold water quenched, and subsequently artificially aged at 168 and 216 °C during 16 h in an argon atmosphere. Effect of heat treatment on the microstructure and mechanical properties was evaluated. Microstructural characterization was analyzed using different techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM). Interface between matrix and reinforcement was examined using transmission electron microscopy (TEM), and mechanical properties were evaluated by measuring the elastic modulus and hardness. Mg, TiC, Al, and Mg₁₇Al₁₂ phases through XRD were detected. Meanwhile, using TEM analysis in heat-treated composites MgAl₂O₄, MgO, and Al₂O₃ were identified. The as-fabricated composite have elastic modulus and hardness of 162 GPa and 316 Hv, respectively. After solution heat treatment and aging at 168 °C during 12 h, the composites reaches values of 178 GPa and 362 Hv for the elastic modulus and hardness, respectively. Time of aging was correlated with measures of elastic modulus and hardness.     

Influence of heat treatment on microstructure and mechanical properties of the interface in an EN AW-6082/1.4310 composite extrusion

The presented paper deals with a unidirectional steel wire reinforced aluminum matrix composite manufactured by composite extrusion. The main objective of this work was to determine the effect of heat treatment, and the influence of long solution annealing times on the composites interface regarding microstructural changes and the resulting interface strength. For evaluation of the microstructure high resolution transmission electron microscope (TEM) investigations accompanied with electron dispersive X-ray spectroscopy (EDX) were performed. It could be shown that diffusion from the steel wire into the aluminum matrix occurs and that the diffusion paths as well as particle formation is influenced by the preceded heat treatment. Diffusion paths in the range of 40–150 nm could be observed for Al, Fe, Cr and Ni. After annealing times over 5 h an extensive growth of an intermetallic reaction layer was found. The mechanical properties of the interface were determined by push-out-tests and tensile tests radial to the interface, which provided the debonding shear strength σ_deb and for the latter experiment the interfacial radial strength σ_IR. It has become apparent that debonding shear strength is highly influenced by matrix properties. In radial tensile tests the failure is predominantly controlled by the chemical bond of the interface. It was shown that interface strength of specimen with small reaction zones of about 3 μm were beneficial for the mechanical behavior in both loading conditions. Longer annealing times showed a drastic decrease of interface shear strength. It was concluded from EDX measurements and in comparison with literature that the reaction zone is dominated by the growth of Al₅Fe₂ (η-phase).     

Effect of variable particle size reinforcement on mechanical and wear properties of 6061Al–SiCp composite

Abstract

The influence of reinforcement particle size variation plays a major role on the properties of Al–SiC_p composite. Therefore, this study aim to investigate the mechanical and wear performance of single particle size (SPS) and multiple particle size (MPS) Al–SiC_p composite prepared by stir casting process. The SPS comprises three categories; fine (15 μm), intermediate (40 μm) and coarse (80 μm) particle sizes and combination of the three sizes accounts for the MPS in the ratio 1:1:2, respectively. Oxidation of the SiC_p and addition of 1 wt% Mg during composite processing resulted to interface reaction products such as MgO (magnesium oxide) and MgAl₂O₄ (magnesium aluminate) which suppresses the potential formation of undesired Al₃C₄ (aluminium carbide). The study reveals that MPS composite improved the hardness and impact properties with enhanced wear performance compared to SPS composite. Characterization of the composite morphology and phases was performed using scanning electron microscope and X-ray diffraction analysis. This study provides an effective method of optimizing the properties of Al–SiC_p composite by integrating MPS with low volume fraction of reinforcement phase.     

Validation of the rotational vector Preisach model with measurements and simulations of vectorial minor loops

Carbon nanotube reinforced Cu–Ti alloy (CNT/Cu–Ti) composites are fabricated by a powder metallurgical method. The interfacial bonding of CNT/Cu–Ti composites is evidently improved, which is attributed to the formation of a thin layer of TiC at the interface. The thermal conductivity of the composites increases by 7.5 % and 15.1 % compared to that of Cu–Ti matrix at CNT loadings of 5 vol.% and 10 vol.%, respectively. The matrix-alloying is therefore an effective way to enhance the thermal conductivity of CNT/Cu composites.     

Thermal and structural characterization of Cu–Al–Mn–X (Ti,Ni) shape memory alloys

In this study, the Cu–Al–Mn–X (X = Ni, Ti) shape memory alloys at the range of 10–12 at.% of aluminum and 4–5 at.% manganese were produced by arc melting. We have investigated the effects of the alloying elements on the transformation temperatures, and the structural and the magnetic properties of the quaternary Cu–Al–Mn–X (X = Ni, Ti) shape memory alloys. The evolution of the transformation temperatures was studied by differential scanning calorimetry with different heating and cooling rates. The characteristic transformation temperatures and the thermodynamic parameters were highly sensitive to variations in the aluminum and manganese content, and it was observed that the nickel addition into the Cu–Al–Mn system decreased the transformation temperature although Ti addition caused an increase in the transformation temperatures. The effect of the nickel and the titanium on the thermodynamic parameters such as enthalpy and entropy values was investigated. The structural changes of the samples were studied by X-ray diffraction measurements and by optical microscope observations at room temperature. It is evaluated that the element Ni has been completely soluble in the matrix, and the main phase of the Cu–Al–Mn–Ni sample is martensite, and due to the low solubility of the Ti, the Cu–Al–Mn–Ti sample has precipitates, and a martensite phase at room temperature. The magnetic properties of the Cu–Al–Mn, Cu–Al–Mn–Ni and Cu–Al–Mn–Ti samples were investigated, and the effect of the nickel and the titanium on the magnetic properties was studied.     

Tribological behavior of Al-based self-lubricating composites

Abstract

Aluminum-based composites containing either SiC (Al10%SiC) as the hard phase or a combination of SiC and MoS₂ (Al10%SiC4%MoS₂) have been synthesized following stir casting route. To overcome the poor wetting characteristics, magnesium was added in one of the composites (Al10%SiC4%MoS₂4%Mg) to improve the bonding between matrix and second phase. The results suggested an enhancement in hardness and strength of the composite containing SiC–MoS₂ and Mg, thus indicating the effectiveness of Mg addition in improving the interfacial bonding strength. Tribological performance of the composites has been examined by carrying out pin-on-disk wear tests under dry sliding conditions at different normal loads of 9.8, 14.7, 19.6, and 24.5 N and at a constant sliding speed of 1 m/s. Both the friction coefficient and the wear rate have been found to reduce with addition of MoS₂; however, bonding between the matrix and reinforcements was not good. Al10%SiC4%MoS₂4%Mg has shown the best tribological performance at all the loads in terms of the lowest friction coefficient and the lowest wear rate. The wear mechanism has been found to be a combination of adhesion and abrasion as indicated by the presence of some abrasive grooves and delaminated flakes at the worn surface and the X-ray examination of wear debris for all the materials used in the present investigation.     

Semiconducting SnO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> (S-T) composites for detection of SO<Subscript>2</Subscript> gas

SnO₂-TiO₂ (S-T) composites with different molar ratios were prepared by mechanical mixing followed by sintering at 700 °C for 4 h in air. The structural and microstructural properties of the composites were investigated using powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). S-T composites were investigated by introducing SO₂ to test their chemical stability using PXRD and SEM coupled with energy dispersive X-ray (EDX) analysis. The sensing performance was measured at different temperatures using various SO₂ concentrations (10–100 ppm). A composite comprising 25 mol% of SnO₂ and 75 mol% TiO₂ (S25-T75) exhibited the highest sensitivity comparing to other S-T composites studied under the presently investigated conditions. t ₉₀ (90 % of response time) was found to be ～5 min for thick pellet (~2 mm in thickness). SO₂ sensing mechanism has been explained through the band structure model.     

Deformation-induced dissolution of the intermetallics Ni3Ti and Ni3Al in austenitic steels at cryogenic temperatures

An anomalous deformation-induced dissolution of the intermetallics Ni₃Al and Ni₃Ti in the matrix of austenitic Fe–Ni–Al(Ti) alloys has been revealed in experiment at cryogenic temperatures (down to 77 K) under rolling and high pressure torsion. The observed phenomenon is explained as the result of migration of deformation-stipulated interstitial atoms from a particle into the matrix in the stress field of moving dislocations. With increasing the temperature of deformation, the dissolution is replaced by the deformation-induced precipitation of the intermetallics, which is accelerated due to a sufficient amount of point defects in the matrix, gained as well in the course of deformation at lower temperatures.     

Dry sliding wear characteristics of in situ synthesized Al-TiC composites

Abstract

Aluminum-based composites containing 0.06, 0.09, 0.12 fractions of in situ-synthesized TiC (Titanium carbide) particles have been prepared through in-melt reaction from Ai–SiC–Ti system following a simple and cost-effective stir-casting route. The TiC forms by the reaction of Ti with carbon which is released by SiC at temperatures greater than 1073 K. However, some amount of titanium aluminide (Al₃Ti) is also formed. The formation of TiC has been confirmed through X-ray diffraction studies of the composite. The hardness and tensile strength have been found to increase with increasing amount of TiC. The friction and wear characteristics of the composites have been determined by carrying out dry sliding tests on pin-on-disc machine at different loads of 9.8 N, 19.6 N, 29.4 N, 39.2 N at a constant sliding speed of the 1 m/s speed. The wear rate i.e. volume loss per unit sliding distance has been found to increase linearly with increasing load following Archard’s law. However, both the wear rate and friction coefficient have been observed to decrease with increasing amount of TiC in the composite. This has been attributed to (i) a relatively higher hardness of composites containing relatively higher amount of TiC resulting in a relatively lower real area of contact and (ii) the formation of a well-compacted mechanically mixed layer of compacted wear debris on the worn surface which might have inhibited metal–metal contact and resulted in a lower wear rate as well as friction coefficient.     

Synthesis and characterization of in situ nanocrystalline intermetallic phase reinforced AlTiSi amorphous matrix composite

Composites with partially amorphous matrix were synthesized by mechanical alloying of an Al₅₀Ti₄₀Si₁₀ elemental powder blend in a high energy planetary ball-mill, followed by high pressure (8 GPa) low temperature (350–450°C) sintering. Microstructural studies and compositional micro-analysis were carried out using scanning and transmission electron microscopy, and energy dispersive spectroscopy, respectively. Phase evolution as a function of milling time and isothermal temperature and their thermal stability was determined by X-ray diffraction at room or elevated temperature and differential scanning calorimetry, respectively. The microstructure of composites sintered between room temperature and 450°C showed nano-size (≈50 nm) crystalline precipitates of Al₃Ti dispersed in an amorphous matrix. The composites sintered at 400°C with 8 GPa pressure exhibited the highest density (3.58 Mg/m³), nanoindentation hardness (8.8 GPa), Young's modulus (158 GPa) and compressive strength (1940 MPa). A lower hardness and modulus on sintering at 450°C is attributed to additional amorphous to nanocrystalline phase transformation and partial coarsening of Al₃Ti.     

Microstructure and mechanical properties of nano-Y2O3 dispersed ferritic steel synthesized by mechanical alloying and consolidated by pulse plasma sintering

Ferritic steel with compositions 83.0Fe–13.5Cr–2.0Al–0.5Ti (alloy A), 79.0Fe–17.5Cr–2.0Al–0.5Ti (alloy B), 75.0Fe–21.5Cr–2.0Al–0.5Ti (alloy C) and 71.0Fe–25.5Cr–2.0Al–0.5Ti (alloy D) (all in wt%) each with a 1.0?wt% nano-Y₂O₃ dispersion were synthesized by mechanical alloying and consolidated by pulse plasma sintering at 600, 800 and 1000°C using a 75-MPa uniaxial pressure applied for 5?min and a 70-kA pulse current at 3?Hz pulse frequency. X-ray diffraction, scanning and transmission electron microscopy and energy disperse spectroscopy techniques have been used to characterize the microstructural and phase evolution of all the alloys at different stages of mechano-chemical synthesis and consolidation. Mechanical properties in terms of hardness, compressive strength, yield strength and Young's modulus were determined using a micro/nano-indenter and universal testing machine. All ferritic alloys recorded very high levels of compressive strength (850–2850?MPa), yield strength (500–1556?MPa), Young's modulus (175–250?GPa) and nanoindentation hardness (9.5–15.5?GPa), with up to 1–1.5 times greater strength than other oxide dispersion-strengthened ferritic steels (<1200?MPa). These extraordinary levels of mechanical properties can be attributed to the typical microstructure of uniform dispersion of 10–20-nm Y₂Ti₂O₇ or Y₂O₃ particles in a high-alloy ferritic matrix.     

Novel Cu–Cr alloy matrix CNT composites with enhanced thermal conductivity

Carbon nanotubes (CNTs) are incorporated into the Cu–Cr matrix to fabricate bulk CNT/Cu–Cr composites by means of a powder metallurgy method, and their thermal conductivity behavior is investigated. It is found that the formation of Cr₃C₂ interfacial layer improves the interfacial bonding between CNTs and Cu–Cr matrix, producing a reduction of interfacial thermal resistance, and subsequently enhancing the thermal conductivity of the composites. The thermal conductivity of the composites increases by 12 % and 17 % with addition of 5 vol.% and 10 vol.% CNTs, respectively. The experimental results are also theoretically analyzed using an effective medium approximation (EMA) model, and it is found that the EMA model combined with a Debye model can provide a satisfactory agreement to the experimental data.     

Microstructure of multilayer interface in an Al matrix composite reinforced by TiNi fiber

A multilayer interface was formed in the Al matrix composite which was reinforced by 30% volume fraction of TiNi fiber. The composite was fabricated by pressure infiltration process and the interface between the TiNi fiber and Al matrix was investigated by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). When the TiNi fiber was pre-oxidized in the air at 773 K for 1 h, three layers have been found and characterized in the interface: TiNi–B₂ layer near the TiNi fiber, Ti–Al compound layer with Ti and granular TiO₂ near the Al matrix, and Ti–Ni compound layer between TiNi–B₂ and Ti–Al compound layers. The effect of the multilayer interface on the mechanical properties of the composite was also discussed. The result showed that the uniaxial tensile strength of the composite at room temperature was 318 MPa, which was very close to the theoretical calculation value of 326 MPa. Moreover, the composite with good ductility exhibited a typical ductile-fracture pattern.     

Effect of irradiation and pre-ageing temperature on the mechanical properties of Al–Si alloy

Al–1wt.%Si alloy samples in the solid solution state were irradiated with doses of gamma rays up to 1.75 MGy for 2 h in the temperature range from 423 to 553 K. Induced variations in structure, mechanical and electrical properties were traced by suitable techniques. Observed changes in the measured parameters, internal friction Q ^?1, thermal diffusivity D _th, dynamic elastic modulus Y and resistivity, ρ, were explained in terms of the role and mode of interaction of lattice defects in irradiated and thermally treated samples. Composition inhomogeneity and variations in mass distribution in the matrix were also considered. The structure identification of the samples was carried out by using conventional X-ray diffraction techniques and transmission electron microscopy micrographs.     

Microstructure evolution and properties of Al/Al–Mg–Si alloy clad wire during heat treatment

In this paper, heat treatment was carried out on Al/Al–Mg–Si alloy clad wire, and microstructure evolution and properties of Al/Al–Mg–Si alloy clad wire during heat treatment were investigated. During solution, contents of Mg and Si in inner matrix increased due to dissolution of primary Mg₂Si, and they also increased in outer matrix because Mg and Si diffused across the interface. Tensile strength of the clad wire increased firstly and then decreased, and elongation continuously increased, while conductivity continuously decreased with the increase in solution time. In aging process, Mg₂Si precipitated in both inner core and outer layer, and the content and average diameter of the precipitate increased with the increase in aging time. The content of precipitate was higher, and the average diameter was bigger in inner core. Tensile strength of the clad wire increased firstly and then decreased with the increase in aging time, and the elongation continuously decreased, while the conductivity continuously increased. The peak tensile strength of 202 MPa occurred at 8 h, when the corresponding elongation was 20 % and the conductivity reached 56.07 %IACS. Even tensile strength of the prepared clad wire approximately equaled to that of Al–0.5Mg–0.35Si alloy 203 MPa, the conductivity was obviously improved from 54.2 to 56.07 %IACS.     

Design of Some Oxide/Metal Composite Supports and Catalysts

Textural, mechanical and catalytic properties of porous composite materials Al₂O₃/Al, MeO _x (Me)/Al₂O₃/Al with metal particles homogeneously distributed in the alumina matrix were studied. These materials were prepared by mixing the powdered components with aluminum followed by hydrothermal treatment and calcination. The macroporous structure was shown to be controlled by the size of large (>microns) particles in starting blends. The mesoporous structure is primarily determined by the properties of alumina formed by dehydration of hydroxide produced in turn via aluminum oxidation by water. The mechanical strength of porous cermets is determined by the number and properties of contacts between micron-size components of composites. Improved catalytic performance of composites is ensured by the developed macroporous structure providing enhanced mass transfer inside the cermet granules.     

Effect of interfacial debonding and matrix cracking on mechanical properties of multidirectional composites

In composites, debonding at the fiber–matrix interface and matrix cracking due to loading or residual stresses can effect the mechanical properties. Here three different architectures — 3-directional orthogonal, 3-directional 8-harness satin weave and 4-directional in-plane multidirectional composites — are investigated and their effective properties are determined for different volume fractions using unit cell modeling with appropriate periodic boundary conditions. A cohesive zone model (CZM) has been used to simulate the interfacial debonding, and an octahedral shear stress failure criterion is used for the matrix cracking. The debonding and matrix cracking have significant effect on the mechanical properties of the composite. As strain increases, debonding increases, which produces a significant reduction in all the moduli of the composite. In the presence of residual stresses, debonding and resulting deterioration in properties occurs at much lower strains. Debonding accompanied with matrix cracking leads to further deterioration in the properties. The interfacial strength has a significant effect on debonding initiation and mechanical properties in the absence of residual stresses, whereas, in the presence of residual stresses, there is no effect on mechanical properties. A comparison of predicted results with experimental results shows that, while the tensile moduli E ₁₁, E ₃₃and shear modulus G ₁₂ match well, the predicted shear modulus G ₁₃ is much lower.