Microstructure characteristics of Ti-43Al alloy during twin-roll strip casting and heat treatment

To shorten the fabrication process of difficult-to-form TiAl sheets, twin-roll strip casting and microstructural control were investigated in Ti-43Al alloy. A crack-free sheet with dimensions of 1000 mm × 110 mm × 2 mm was obtained. The microstructure of stip casting sheets and heat treatments was systematically studied. The macrostructure consisted of columnar crystals extending inward and centrally located equiaxed crystals with severe Al segregation were observed along the thickness direction, due to the symmetrical solidification process and decreasing cooling rates. The strip casting alloy was characterized by fine duplex microstructure with a grain spacing of 20-30 μm and a lamellar spacing of 10-20 nm. Furthermore, multiple microstructures of near gamma, nearly lamellar and fully lamellar were obtained through heat treatment process with significantly improved homogeneity of the microstructure.

Investigation of Microstructure, Microhardness and Thermal Properties of Ag-In Intermetallic Alloys Prepared by Vacuum Arc Meltings

Ag-In intermetallic alloys were produced by using vacuum arc furnace. Differential Scanning Calorimetry(DSC) and Energy Dispersive X-Ray Spectrometry(EDX) were used to determine the thermal properties and chemical composition of the phases respectively. Microhardness values of Ag-In intermetallics were calculated with Vickers hardness measurement method. According to the experimental results, Ag-34 wt%In intermetallic system generated the best results of energy saving and storage compared to other intermetallic systems. Also from the microhardness results, it was observed that intermetallic alloys were harder than pure silver and Ag-26 wt%In system had the highest microhardness value with 143.45 kg/mm^(2).

Geochemistry and Microstructure of Construction Materials from the Eastern Districts of N’Djamena Chad with a View to Their Stabilization in the Building and Pottery

The early collapse of habitats in the spontaneous neighborhoods of the South-East of N’Djamena city pushed us to carry out investigations on the soil characteristics of the Ambatta 1 (Z1), Ambatta 2 (Z2), and Siguété (Z3) neighborhoods in this city. XRF (X-Ray Fluorescence), XRD (X-Ray Diffraction), FTIR (Fourier Transform InfraRed), SEM (Scanning Electron Microscopy), and ATG/DTA (Thermogravimetry Analysis/Differential Thermal Analysis) were conducted for microstructural and thermal identification. The geochemistry of the three soils studied revealed the presence of SiO2 (49.03% - 73.80%), Al2O3 (08.35% - 17.34%), and Fe2O3 (03.79% - 10.90%) as major elements. The alkalines and alkaline earth elements include potassium K2O (02.57% - 03.07%), magnesium MgO (0.47% - 01.21%), titanium TiO2 (0.81% - 01.41%), sodium Na2O (01.01% - 01.13%) and calcium CaO (01.28% - 03.28%). The fire loss of 09.90% on average remains low. XRD revealed the presence of quartz (~64.28%), feldspar (~07.14%), which are non-clay minerals, and clay minerals like kaolinite (~14.85%), illite (~07.14%) and some traces of smectite and amphibite on all three sites. These oxides were confirmed by FTIR analysis through peaks illustrating the vibrational movements specific to these oxides. SEM shows particles in the increasingly shaped, rounded, shiny sand grains. This is the presence of quartz. These quartz micro textures of abrasive surfaces and topography with conchoidal fractures predict promising mechanical results. Smectite appears in wavy clusters, kaolinite in the form of shiny crystals, and illite materializes by the irregularity of the crystalline shape. These constituents are represented by the presence of their oxides specified by geochemistry. Thermally, the three samples overall retain more than 94% of their constituent on average for a temperature range reaching 950˚C, which predestines them for specific applications. Thus, this study aims to stabilize constructions using local materials after having mastered their constituents.

Microstructure characterization in a sensitized Al-Mg-Mn-Zn alloy

Alloying elements, present in the aluminum solid solution or the precipitates, influence the corrosion resistance of A1-Mg-Mn-Zn alloys. In this study, sensi- tizing treatment was applied to an A1-Mg-Mn-Zn alloy to modify the precipitation at the grain boundaries or in the grains. Transmission electron microscopy （TEM） and scanning electron microscope （SEM） were used to characterize various second-phase particles and determine their orientation relationship with the A1 matrix. After sensitizing treatment, z-phase （Mg32（Al, Zn）49） is observed to precipitate along the grain boundaries in a coarser size, producing a discontinuous grain boundary precipitate structure. In addition, Mn-rich particles are found to form with various shapes, such as global, plate and rhombus.

Microstructure Characterization and Fracture Toughness of Laves Phase-Based Cr–Nb–Ti Alloys

Three Laves phase-based alloys with nominal compositions of Cr2Nb-xTi （x = 20, 30, 40, in at%） have been prepared through vacuum non-consumable arc melting. The results show that the microstructures of Cr2Nb-（20, 30） Ti alloys are composed of the primary Laves phase C15-Cr2（Nb,Ti） and bcc solid solution phase, while the microstructure of Cr2Nb-40Ti alloy is developed with the eutectic phases C15-Cr2（Nb,Ti）/bcc solid solution. The measured fracture toughness of ternary Laves phase C15-Cr2（Nb,Ti） is about 3.0 MPa m1/2, much larger than 1.4 MPa m1/2 for binary Laves phase Cr2Nb. Meanwhile, the fracture toughness of Cr2Nb-xTi （x = 20, 30, 40） alloys increases with increasing Ti content and reaches 10.6 MPa m1/2 in Cr2Nb-40Ti alloy. The eutectic microstructure and addition of Ti in Cr2Nb are found to be effective in toughening Laves phase-based alloys.

Characterization of Microstructure and Stability of Precipitation in SIMP Steel Irradiated with Energetic Fe Ions

A type of home-made reduced activation martensitic steel, high silicon （SIMP） steel, is homogeneously irradiated with energetic Fe ions to the doses of 0.1, 0.25 and 1 displacement per atom （dpa）, respectively, at 300℃ and i dpa, at 400℃. MicrostructurM changes are investigated in detail by transmission electron microscopy with cross-section technique. Interstitial defects and defect dusters induced by Fe-ion irradiation are observed in ali the specimens under different conditions. It is found that with increasing irradiation temperature, size of defect clusters increases while the density drops quickly. The results of element chemical mapping from the STEM images indicate that the Si element enrichment and Ta element depletion occur inside the precipitates in the matrix of SIMP steel irradiated to a dose of 1 dpa at 300℃. Correlations between the microstructure and irradiation conditions are briefly discussed.

Effect of Cu on microstructure,mechanical properties,and texture evolution of ZK60 alloy fabricated by hot extrusion−shearing process

As-cast Mg-6Zn-xCu-0.6Zr(x=0,0.5,1.0,wt.%)alloys were fabricated by permanent mold casting;then,the alloys were subjected to homogenization heat treatment and extrusion-shearing(ES)process.The microstructure and mechanical properties of the alloys were evaluated by OM,SEM/EDS,XRD,TEM,EBSD and tensile tests.The results show that the hard MgZnCu phase in Cu-added alloy can strengthen particle-stimulated nucleation(PSN)effect and hinder the migration of dynamic recrystallization(DRX)grain boundary at an elevated temperature during ES.The ZK60+0.5Cu alloy shows an optimal tensile strength–ductility combination(UTS of 396 MPa,YS of 313 MPa,andδ=20.3%)owing to strong grain boundary strengthening and improvement of Schmid factor for{0001}■basal slip.The aggregation of microvoids around the MgZnCu phase mainly accounts for the lower tensile elongation of ZK60+1.0Cu alloy compared with ZK60 alloy.

Formation,characteristics and control of sludge in Al-containing magnesium alloys:An overview

Sludge consisting of heavy element phases and oxides is often generated during the casting operation of aluminum(Al)and magnesium(Mg)alloys.With the help of the well-established Sludge Factor(SF)formula,it is relatively easy to control the sludge generation in aluminum alloys.But formation mechanisms and characteristics of sludge in die casting magnesium alloys are still unclear.To ensure the production of high quality die cast components at a low cost,a full understanding of sludge in die casting Mg alloys and its proper control measures need to be developed,since excessive sludge formation affects deleteriously material and operation cost,and casting performance.In the present report,the formation,characteristics and control of Mg die-casting sludge,based on the established knowledge of sludge formation and sludge factor in Al die casting alloys,are reviewed.Previous work on characterization and assessment of sludge in die cast Mg alloys are reviewed.Metallurgical principles for control of sludge in ingot production in association with die casting of Mg alloys are discussed.Rapid assessment of Mg oxide and intermetallics relevant to sludge formation in Mg alloys are highlighted.

Microstructure evolution and its effect on flow stress of TC17 alloy during deformation in α+β two-phase region

The microstructure evolution and its effect on flow stress of TC17 alloy during deformation in the α+β two-phase region were investigated via microstructure characterization and isothermal compression tests. Results showed that the spheroidized rate of α phase at 820 and 850℃ slightly increased with increasing strain. With increasing deformation temperature, the spheroidized rate of α phase showed a slight increasing trend, but the volume fraction of α phase significantly decreased. The flow stress at 780 ℃ and 1 s^-1 decreased continuously and steady state condition was not achieved up to strain of 1.2 due to dislocation annihilation and α lamellae rotation. Under this condition, the dynamic spheroidization was retarded. At the deformation temperatures of 820 and 850℃, and a strain rate of 1 s^-1, a steady state flow stress was observed at strains above 0.8 due to the balance between work hardening and dynamic softening. The dynamic softening was attributed to the α lamellae rotation, dynamic recovery and a little spheroidization.

Microstructures and mechanical properties of as-cast Mg-Sm-Zn-Zr alloys with varying Gd contents

The effect of Gd content on the microstructure and tensile properties of as-cast Mg-Sm-Zn-Zr alloy has been systematically investigated.In the Mg-3Sm-0.5Zn-0.5Zr alloy, the intermetallic compounds with multiple morphologies are identified as Mg_(3)Sm phase. In addition to Mg_(3)RE phase, Mg_(5)RE phase originated from Gd addition is observed in Gd-modified alloys. It should be noted that the lattice parameters of all the observed intermetallic compounds are significantly reduced by Zn segregation. The segregation behavior of Zn in Mg_(3)Sm phase is inhibited to some extent by Gd addition due to the electronegativity difference between Sm/Gd and Zn elements. In addition, the increased Gd content effectively leads to much more accumulation of solute atoms in front of the liquid-solid interface during solidification, which can prominently promote nucleation in liquid region and then refine grains. The tensile yield stress of the present alloys is thus improved with increasing Gd addition. Finally, Gd-modified alloys exhibit significantly age-hardening effect, which can be mainly attributed to the high-volume fraction and high density nano-scale precipitates.

Study on crystallization and microstructure of Li_2O-Al_2O_3-SiO_2 glass ceramics

Lithium aluminosilicate （LAS） glasses are generally difficult to prepare because of their high melting temperature. In this study, the preparation of LAS glasses was achieved at a relatively low melting temperature. The batch containing MgO-ZnO-LiEO- Al2O3-SiO2 was melted in a platinum crucible at 1550℃ for 2 h and was then followed by two- or three-step heat treatment processes for nucleation and crystal growth. The characterizations were carried out by differential thermal analysis, X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and UV-Vis-NIR scanning spectrophotometry. The hexagonal stuffed β-eucryptite solid solution crystallized at 840-960℃. Most of the hexagonal β-eucryptite solid solution transformed into the tetragonal β-spodumene solid solution at 1100℃. Almost all the aluminum atoms entered into the tetrahedral sites in the aluminosilicate network of the 6- eucryptite/β-quartz solid solution. All of the Al atoms did not belong to the aluminosilicate network of the β-spodumene solid solution. The glass ceramic with a mean grain size of 10-20 nm is transparent, the transmittance reaches -85% in the visible light wavelength.

Effect of extrusion ratios on hardness,microstructure,and crystal texture anisotropy in pure niobium tubes subjected to hydrostatic extrusion

Nb tubes were fabricated through hydrostatic extrusion at extrusion ratios of 3.1 and 6.1 at ambient temperature,and then their microstructure,texture,and Vickers hardness were investigated based on electron back-scattered diffraction(EBSD)data.The fraction of low-angle boundaries(LABs)largely decreased with a sharp decrease in mean grain sizes after hydrostatic extrusion and was not proportional to extrusion ratios,assuming that mixed-asymmetrical junctions forming LABs dissociate at high extrusion ratios from the external stress(>981 MPa)with thermal activation by the generated heat.The correlation between grain size and Vickers hardness followed the Hall−Petch relationship despite the texture gradient of theá111ñcyclic fiber textural microstructure at low extrusion ratios and theá100ñtrue fiber textural microstructure at high extrusion ratios.The increase in hydrostatic pressure on the Nb tubes contributed to texture evolution in terms of extrusion ratios due to the difference between{110}<111>and{112}<111>components based on EBSD data.

Effect of Bi modification treatment on microstructure,tensile properties,and fracture behavior of cast Al-Mg_2Si metal matrix composite

Bi has a good modification effect on the hypoeutectic Al-Si alloy, and the morphology of eutectic Si changes from coarse acicular to fine fibrous. Based on the similarity between Mg2Si and Si phases in crystalline structure and crystallization process, the present study investigated the effects of different concentrations of Bi on the microstructure, tensile properties, and fracture behavior of cast Al-15wt.%Mg2Si in-situ metal matrix composite. The results show that the addition of the proper amount of Bi has a significant modification effect on both primary and eutectic Mg2Si in the Al-15wt.%Mg2Si composite. With an increase in Bi content from 0 to lwt.%, the morphology of the primary Mg2Si is changed from irregular or dendritic to polyhedral shape; and its average particle size is significantly decreased from 70 to 6 μm. Moreover, the morphology of the eutectic Mg2Si phase is altered from flake-like to very short fibrous or dot-like. When the Bi addition exceeds 4.0wt.%, the primary Mg2Si becomes coarse again. However, the eutectic Mg2Si still exhibits the modified morphology. Tensile tests reveal that the Bi addition can improve the tensile strength and ductility of the material. Compared with those of the unmodified composite, the ultimate tensile strength and percentage elongation after fracture with 1.0wt.% Bi increase 51.2% and 100%, respectively. At the same time, the Bi addition changes the fracture behavior from brittle to ductile.

Effect of electromagnetic interaction on microstructure and corrosion resistance of 7075 aluminium alloy during modified indirect electric arc welding process

The effects of applying an electromagnetic interaction of low intensity (EMILI) on the microstructure and corrosion resistance of 7075-T651 Al alloy plates (13 mm in thickness) during modified indirect electric arc (MIEA) welding were investigated. The welding process was conducted in a single pass with a heat input of ~1.5 kJ/mm. The microstructural observations of the welds were correlated with the effect of EMILI on the local mechanical properties and the corrosion resistance in natural seawater by means of microhardness measurements and electrochemical impedance spectroscopy, respectively. Microstructural characterization of the welds revealed a grain refinement in the weld metal due to the electromagnetic stirring induced by EMILI of 3 mT during welding. In addition, observations in the scanning electron microscope showed that the precipitation of Cu-rich phases and segregation of eutectics were reduced in the heat affected zone (HAZ) also as an effect of EMILI. The high corrosion dissolution of the 7075-T651 welds in natural seawater and the extent of overaging in the HAZ were reduced when welding with EMILI of 3 mT. Thus, EMILI along with the MIEA technique may lead to welded joints with better microstructural characteristics, improved mechanical properties in the HAZ and reduced electrochemical activity.

Material microstructures analyzed by using gray level Co-occurrence matrices

The mechanical properties of materials greatly depend on the microstructure morphology. The quantitative characterization of material microstructures is essential for the performance prediction and hence the material design. At present,the quantitative characterization methods mainly rely on the microstructure characterization of shape, size, distribution,and volume fraction, which related to the mechanical properties. These traditional methods have been applied for several decades and the subjectivity of human factors induces unavoidable errors. In this paper, we try to bypass the traditional operations and identify the relationship between the microstructures and the material properties by the texture of image itself directly. The statistical approach is based on gray level Co-occurrence matrix（GLCM）, allowing an objective and repeatable study on material microstructures. We first present how to identify GLCM with the optimal parameters, and then apply the method on three systems with different microstructures. The results show that GLCM can reveal the interface information and microstructures complexity with less human impact. Naturally, there is a good correlation between GLCM and the mechanical properties.

Microstructures and mechanical properties of nanocrystalline NiTi intermetallics formed by mechanosynthesis

The formulation of nanocrystallinc NiTi shape memory alloys has potential effects in mechanical stimulation and medical im- plantology. The present work elucidates the effect of milling time on the product＇s structural characteristics, chemical composition, and mi- crohardness for NiTi synthesized by mechanical alloying for different milling durations. Increasing the milling duration led to the formation of a nanocrystalline NiTi intermetallic at a higher level. The formation of nanocrystalline materials was directed through cold fusion, fractur- ing, and the development of a steady state, which were influenced by the accumulation of strain energy. In the morphological study, uninter- rupted cold diffusion and fracturing were visualized using transmission electron microscopy. Particle size analysis revealed that the mean particle size was reduced to -93 μm after 20 h of milling. The mechanical strength was enhanced by the formation of a nanocrystalline in- termetallic phase at longer milling time, which was confirmed by the results of Vickers hardness analyses.

Microstructure and mechanical properties of reaction-bonded B_(4)C–SiC composites

Reaction-bonded B_(4)C–SiC composites are highly promising materials for numerous advanced technological applications.However,their microstructure evolution mechanism remains unclear.Herein,B_(4)C–SiC composites were fabricated through the Si-melt infiltration process.The influences of the sintering time and the B_(4)C content on the mechanical properties,microstructure,and phase evolution were investigated.X-ray diffraction results showed the presence of SiC,boron silicon,boron silicon carbide,and boron carbide.Scanning electron microscopy results showed that with the increase in the boron carbide content,the Si content decreased and the unreacted B_(4)C amount increased when the sintering temperature reached 1650°C and the sintering time reached 1 h.The unreacted B_(4)C diminished with increasing sintering time and temperature when B_(4)C content was lower than 35wt%.Further microstructure analysis showed a transition area between B_(4)C and Si,with the C content marginally higher than in the Si area.This indicates that after the silicon infiltration,the diffusion mechanism was the primary sintering mechanism of the composites.As the diffusion process progressed,the hardness increased.The maximum values of the Vickers hardness,flexural strength,and fracture toughness of the reaction-bonded B_(4)C–SiC ceramic composite with 12wt%B_(4)C content sintered at 1600°C for 0.5 h were about HV 2400,330 MPa,and 5.2 MPa·m^(0.5),respectively.

Hardening effect and precipitation evolution of an isothermal aged Mg-Sm based alloy

The age-hardening behavior and precipitation evolution of an isothermal aged Mg-5Sm-0.6Zn-0.5Zr(wt.%) alloy have been systematically investigated by means of transmission electron microscopy(TEM) and atomic-resolution high-angle annular dark field scanning transmission electron microscopy(HAADF-STEM). The Vickers hardness of the present alloy increases first and then decreases with ageing time. The sample aged at 200 ℃ for 10 h exhibits a peak-hardness of 90.5 HV. In addition to the dominant β_(0)’ precipitate(orthorhombic,a = 0.642 nm, b = 3.336 nm and c = 0.521 nm) formed on {11-20}α planes, a certain number of γ’’ precipitate(hexagonal, a = 0.556 nm and c = 0.431 nm) formed on basal planes are also observed in the peak-aged alloy. Significantly, the basal γ’’ precipitate is more thermostable than prismatic β_(0)’ precipitate in the present alloy. β_(0)’ precipitates gradually coarsened and were even likely to transform into β_(1) phase(face centered cubic, a = 0.73 nm) with the increase of ageing time, which accordingly led to a gradual decrease in number density of precipitates and finally resulted in the decreased hardness and mechanical property in the over-aged alloys.

Microstructure Evolution of a Nickel-Base Alloy Resistant to High Temperature during Aging

In the present study, the microstructural evolution during aging at 1023, 1073, 1123 and 1173 K of a 35Cr-45Ni heat resistant alloy, produced in the form of centrifugally cast tubes, was characterized by means of light optical microscopy, scanning electron microscopy (SEM) with secondary and backscattered electron imaging, energy-dispersive X-ray spectroscopy (EDS) and Vickers hardness tests. The evolution of the Vickers hardness at 1023 K for aged samples shows that the microstructure is stable during the analyzed aging period. At 1073 K, the rate of increase in hardness is lower than 1023 K and this behavior would be associated with morphological changes observed in primary interdendritic carbides and secondary carbides in the matrix. At 1123 K and 1173 K, an atypical behavior in Vickers hardness curve is presented;where it can be seen that at certain aging times, the hardness decreases significantly. A microstructural analysis of these samples indicates that they have a region free of precipitates (near interdendritic edges) where the hardness is lower. Probably, these regions are areas poor in chromium.

In-situ SEM characterization of fracture mechanism of TiB/Ti-2Al-6Sn titanium matrix composites after electroshocking treatment

In this article,in-situ scanning electron microscope characterization of the tensile properties of TiB/Ti-2Al-6Sn titanium matrix composite(TMC)was conducted before and after electroshocking treatment(EST).After EST,the tensile strength increased by 113.2 MPa.The effect of EST on the tensile strength and fracture behavior of TiB was investigated using in-situ characterization of the fracture morphology and crack propagation path of the matrix and TiB.Before EST,TiB fracture introduced cracks that extended into the matrix,resulting in material failure.After EST,the refined TiB improved the bearing capacity of the matrix,thereby improving TMC strength.Moreover,after EST,the cracks were introduced into the matrix,and resulting the fracture of matrix first.With an increase in the external load,cracks in the matrix were observed to propagate to TiB,and the refined TiB was fractured,detached,and pulled out,resulting in the formation of pores.Analyzing the propagation path of the main crack after EST showed that the deflection angle of the main crack increased.The micro structure of the fracture surface indicated that the fracture of the matrix was plastic,whereas that of TiB was brittle.After EST,the size and area of the dimples increased,confirming the increase in plasticity.The results revealed that the comprehensive mechanical properties of TiB/Ti-2Al-6Sn improved after EST.Hence,EST is an efficient method for tailoring the micro structures and mechanical properties of TMCs.