Alumina Grains Research Articles

Deformation behavior of aluminum pillars produced by Xe and Ga focused ion beams: Insights from strain rate jump tests

Micro-compression testing of focused ion beam fabricated pillars is a popular technique for mechanical characterization at small scales. However, there are concerns associated with these ion-prepared samples, including irradiation damage from Ga ions and Ga segregation at grain boundaries resulting in liquid metal embrittlement. In this work, this is investigated using strain rate jump nanoindentation and micro-compression of single crystalline and ultrafine-grained aluminum with different grain boundary conditions. The extracted strain rate sensitivity and activation volume are used to study the effects of Ga and Xe ion species from fabrication and testing methods on deformation behavior of aluminum samples. Results show that the measured strain-rate sensitivity of non-equilibrium, ultrafine-grained aluminum is significantly affected by the dosage of Ga. Activation volumes suggest that the dominant deformation mechanism remains consistent despite Ga at the boundaries. Atom probe tomography reveals that Ga was observed to segregate to aluminum grain boundaries up to 2.2 at.% in the FIB prepared sample.

Microstructural Characterization and Mechanical Properties of 120-mm Ultra-thick SiCp/Al Composite Plates Joined by Double-Sided Friction Stir Welding

Applications of aluminum matrix composite (AMC) engineering components are being quickly developed and their numbers are increasing, but difficulties still exist in the direct fabrication of large AMC components. Joining thick composite plates without drawbacks has become an effective and alternative route, and friction stir welding (FSW) is the most promising and efficient technique, which should be selected first. In this work, 120-mm ultra-thick plates of 16 vol pct SiCp/2014Al composites were successfully joined by double-sided FSW. Microstructural characterization and mechanical properties of the composite joint along the transverse and thickness directions are investigated, respectively. Along the transverse direction changing from the base material (BM) to the heat-affected zone (HAZ) to the nugget zone (NZ), SiC particles are broken, blunted and uniformly distributed, and the aluminum grains are refined. The coarse precipitates are dissolved and then re-precipitated. Vickers microhardness of the composite joint gradually increases, and the peak values appear in the NZ. For the composite joint, the tensile strength is close to that of the BM showing a joint efficiency of 97 pct. Along the thickness direction varying from the top surface to middle section of the composite joint, the SiC particle size has no significant differences in the NZ, the aluminum grain size gradually decreases, and the precipitate size has some differences. Vickers microhardness of the composite joint decreases with increasing thickness in the NZ and HAZ, and no clear differences exist in the BM; tensile properties of the composite joint present few differences with varying thickness, and tensile failures usually occur in the BM. A good understanding and guide can be provided for joining ultra-thick plates of metal matrix composites by FSW in industrial applications.

The effect of annealing treatment on the evolution of the microstructure, the mechanical properties and the texture of nano SiC reinforced aluminium matrix alloys with ultrafine grained structure

In the present work, an ultrafine grained (UFG) aluminium matrix nano composite (UFANC) was prepared through a cryogenic deformation based manufacturing route. The influence of annealing on the microstructural evolution, mechanical properties and the crystallographic texture of the developed UFANC material was studied and compared with the unreinforced ultrafine grained counterpart (UFG). The presence of nano particles during deformation led to an increased generation of dislocations in the matrix. At low annealing temperatures high density dislocations provided a higher driving force for recrystallization in the UFANC. At high temperatures the grain growth in the UFANC was restricted by the pinning action of the nano reinforcement. This resulted in a higher activation energy for grain growth compared to the UFG counterpart. As a result, the UFANC retained high strength and possessed a fine microstructure even at annealing temperatures of up to 250 °C. The evolution of the texture during annealing was influenced due to the deformation at cryogenic environment. The presence of nano particles led to a more random texture in the UFANC compared to the UFG counterpart during annealing.

Microstructural deformation process of shock-compressed polycrystalline aluminum

Plastic deformation of polycrystalline materials under shock wave loading is a critical characteristic in material science and engineering. However, owing to the nanosecond time scale of the shock-induced deformation process, we currently have a poor mechanistic understanding of the structural changes from atomic scale to mesoscale. Here, we observed the dynamic grain refinement of polycrystalline aluminum foil under laser-driven shock wave loading using time-resolved X-ray diffraction. Diffraction spots on the Debye-Scherrer ring from micrometer-sized aluminum grains appeared and disappeared irregularly, and were shifted and broadened as a result of laser-induced shock wave loading. Behind the front of shock wave, large grains in aluminum foil were deformed, and subsequently exhibited grain rotation and a reduction in size. The width distribution of the diffraction spots broadened because of shock-induced grain refinement and microstrain in each grain. We performed quantitative analysis of the inhomogeneous lattice strain and grain size in the shocked polycrysalline aluminum using the Williamson-Hall method and determined the dislocation density under shock wave loading.

Using digital image correlation for characterizing the elastic and plastic parameters of ultrafine-grained Al 1050 strips fabricated via accumulative roll bonding process

In the present article, digital image correlation (DIC) system has been utilized to determine the elastic and plastic parameters of ultrafine grained (UFGed) Aluminum 1050 strips fabricated via accumulative roll bonding (ARB) procedure during the uniaxial tensile test. At first, elastic and plastic parameters such as elastic modulus, Poisson ratio, strength coefficient, strain hardening exponent, anisotropy coefficient and yield stress of ARBed specimens have been extracted in different ARB passes. ARB process is an exceptional process to fabricate ultrafine-grained and nanostructured sheet metals and composites. Using of UFGed materials in various industries requires accurate identification of their mechanical and physical properties. Elastic modulus and anisotropy are the most important mechanical parameter for structural design and forming process respectively. The ARB process has been done up to seven passes by the value of 50% thickness reduction during rolling in every ARB pass at the ambient temperature. Results exhibited which via rising the ARB passes, as expected the elastic parameters did not change much, but all of the plastic parameters and crystallite size changed. The values of the ultimate tensile strength (UTS) and yield stress (YS) increased sharply but strain hardening exponent and elongation at first pass decreased severely and then from third to the seventh pass increased continuously. Due to the gradient of applied shear components in the thickness direction during rolling, the anisotropy coefficient is one of the most important parameters for severe plastic deformation based on rolling. In this paper, for the first time anisotropy variations in the tensile test were continuously determined and the results of the DIC demonstrated that changing of the anisotropy in each pass were different and via raising the value of applied strained the amount of anisotropy coefficient reduced.

Properties of Alumina-Magnesia Cutting Tools

The high speed cutting tools that made from ceramic materials, alumina based, it is very important for the machining process. It has a hot hardness and abrasive resistance and chemical stability at the high temperature, but it has a brittleness and low fracture strength. In this study, synthesis samples from the α-alumina(Al 2 O 3 ) doping with magnesia (MgO) with different percentage (0.35, 0.75, 1.1 % wt.) and compare with the pure alumina properties. It is using cold uniaxial pressing (200 MPa) and sintered at (1500ᵒC) remain three hours for this samples. The purpose was to study the effect of the doping on the mechanical and physical properties and the ability to enhancing it. Numerical simulation was worked for the contact and friction between the ceramic cutting tool and the workpiece material (AISI 1006 steel). This numerical methods dependent on ABAQUS Ver.6.14 program. The results show that ability of cutting and chip formation and successfully propagation through this type of cutting tools without failure it at high speed (150-250)m/min. Also, the stress and heat generated due to ceramic cutting tool was presented The result appeared increasing in the hardness and the density value by the doping with MgO. By increase the percentage of magnesia that given enhanced the properties. The MgO as a second phase reduce alumina grain size and increase the hardness and the wear resistance to cutting tools. Small amount of magnesia enhanced the densification rate grain growth and accelerate the sintering rate. The magnesia doping enable to sinter the mixture alumina-magnesia to near theoretical density. The best result was found with 0.75% MgO at 1500 o C (HV 19GPa). Keywords: ceramic, cutting tool, Johnson cook, Abaqus ,numerical. DOI : 10.7176/IEL/9-3-05 Publication date : April 30 th 2019

Effect of SiC nanoparticles on the microstructure and texture of friction stir welded AA2024/AA6061

In the present study, the effect of SiC nanoparticles on the microstructure and texture evolution of friction stir welded AA2024/AA6061 dissimilar joint investigated. The results showed that the SiC nanoparticles homogeneously dispersed in the aluminum matrix. The Al/SiC interfaces had a good quality of bonding between particles and matrix. It was found that the new recrystallized aluminum grains tend to nucleate and grow on the 11¯1 crystal plane of SiC nanoparticle (1¯1¯1Al facet on 11¯1SiC surface). The average grain size in the stirred zone (SZ) decreased to 7.4 μm owing to the grain refinement through the occurrence of both dynamic and static recrystallization. Most grains in the center of the stirred zone grown due to the occurrence of continuous grain growth (CGG) mechanism after the stirring. Moreover, the incorporation of SiC nanoparticles led to a reduction of 26% in the mean grain size of the SZ. The average size of the precipitate particles in the stirred zone was much smaller than the thermo-mechanically affected zone (TMAZ) owing to the dissolution of precipitates during stirring and reprecipitation during cooling. In addition, the grain size of the stirred zone on the advancing side was lower than the retreating side (2.6 μm vs. 9.7 μm). The results revealed a weaker texture after FSW compared to the initial samples. The SiC nanoparticles largely suppressed the rotation of the {001}〈100〉 oriented new grains through particle pinning effect. Unlike the advancing side, there was no recrystallization texture component on the retreating side.

The combined influence of Mg and Ca on microstructural evolution of alumina

AbstractThe solubility limits of Ca and Mg co‐doped in alumina at 1600°C were determined by equilibrating alumina saturated with Ca and Mg. This resulted in the formation of MgAl2O4 (Mg spinel), CaO·6Al2O3 (CA6), Ca2Mg2Al28O46 (CAM‐II), and alumina grains saturated with Mg and Ca. Under these conditions, the amount of Ca and Mg in the alumina grains represents the solubility limits. The solubility limits were measured using a fully standardized wavelength dispersive spectrometer mounted on a scanning electron microscope. In the co‐doped state, the solubility limit of Ca in alumina was 32 ± 13 ppm, and the solubility limit of Mg in alumina was 210 ± 43 ppm. The presence of Ca results in an increase of the solubility limit of Mg in alumina from 132 to 210 ppm, suggesting that the increased Mg in solution results in more Mg excess at the alumina grain boundaries, thus contributing to a decreased grain‐boundary mobility by solute‐drag.

The effect of microstructure evolution on mechanical properties in novel alumina-montmorillonite composites

Fabrication of alumina matrix composites reinforced with montmorillonite (MMT) is introduced in this work. Specimens were prepared with the use of powder metallurgy and consolidated using the Spark Plasma Sintering (SPS) method. Investigations were then carried out on the influence of MMT addition on microstructure, mechanical properties and tribological performance of the alumina matrix composites. Scanning Electron Microscopy (SEM) revealed significant changes in microstructure where elongated, abnormally overgrown grains of alumina can be observed in areas contacted with montmorillonite. This unusual bimodal microstructure greatly influenced the measured mechanical properties and friction study. Tribological examinations exhibited outstanding results, where samples with montmorillonite addition demonstrate significant improvement in the wear in comparison to pure unmodified alumina sinters.

Achieving strength-ductility synergy in cold spray additively manufactured Al/B4C composites through a hybrid post-deposition treatment

Cold spray additive manufacturing (CSAM) provides a potential solid state manufacturing route to fabricate variety of aluminum matrix composites (AMCs) with reduced possibility of undesired chemical reactions and residual thermal stresses. This study presents a hybrid (i.e. hot compression + hot rolling) post-deposition treatment to reinvigorate the mechanical properties of cold spray additively manufactured Al/B4C composites. The as-deposited samples were initially subjected to 30% thickness reduction via hot compression treatment at ∼500 °C followed by a hot rolling treatment with 40% thickness reduction in 2 passes. Electron backscatter diffraction (EBSD) and high resolution transmission electron microscopy (HRTEM) results revealed that after hybrid post-deposition treatment (involving 70% accumulative thickness reduction), the aluminum grains in the matrix were extensively refined due to simultaneous operation of continuous dynamic recrystallization (CDRX) and geometric dynamic recrystallization (GDRX). Furthermore, interfacial defects were remarkably reduced while the nature of Al/Al and Al/B4C interfacial bonding was changed from sheer mechanical interlocking to metallurgical bonding which facilitated efficient transference of applied load to uniformly dispersed bimodal B4C particles. As a result, ultimate tensile strength (UTS) and elongation (EL) of the as-deposited sample were simultaneously improved from ∼37 to 185 MPa and ∼0.3% to 6.2%, respectively.

Effect Of Cold Rolling On The Porosity ,Hardness Properties Of The Spray Deposited Al-18%Pb And Al-22%Pb Alloys

Abstract Al-18%Pb and Al-22%Pb alloys processed through the spray deposition technique to obtain the homogeneous distribution of the Pb paricles into the aluminum grains, where as in case of conventional methods Pb paricles not distributed homogeneously . Optimum uniformity obtained at the pressure 10bar , spray deposition distance about 430mm and rotor inclination angle about 00. The spray deposits cold rolled for various percentage thickness reductions , porosity , hardness and wear properties were studied . the porosity of the sprayed deposits lower than the conventional one in comparison . the mechanical properties of the spray deposited alloys shows increment than the cast alloys . the wear resistance of spray deposited Al-18%Pb is showed better than the Al-22%Pb alloy.

Mechanical Properties and Wear Behavior of Aluminum Grain Refined by Ti and Ti+B

Grain refinement, by adding master alloys, is an important industrial process for aluminum casting operations. In this work, microstructure, microhardness, tensile properties, surface roughness and wear behavior of Al and both Al-0.15Ti and Al-0.05Ti-0.01B microalloys were investigated. The addition of Ti and B to pure Al reduced the grain size by 83%. The grain refinement effect was due to the presence of Al3Ti and TiB2 particles, which activated the columnar-to-equiaxed transition and improved both microhardness and tensile properties. The presence of both Al3Ti and TiB2 particles was confirmed using thermodynamic calculations. Average microhardness values increased form 39 HV for pure Al to 95 and 76 HV for Al-Ti and Al-Ti-B microalloys, respectively, by solid solution hardening. The enhanced wear behaviour of Al was due to the coarse-grained structure where the plastic deformation mechanism took place. Whereas, grain pull-out dominated the wear behavior of fine-grained specimens. It was concluded that the material with a smooth surface has high friction coefficient and low wear rate.

Aluminium grain refinement by Ti(C, N) nanoparticles additions: principles, advantages and drawbacks

Ti(C, N) is a ceramic particle with high melting point, high hardness, high thermal and chemical stability. And incorporated Ti(C, N) particles is demonstrated to refine the grain and improve the mechanical properties of aluminium and its alloys. In this article, effects of the addition amount of Ti(C, N) particles on grain refinement and mechanical properties of aluminium alloy are reviewed, and the mechanisms of aluminium alloy refined by Ti(C, N) are described. In addition, due to the poor wettability of Ti(C, N) nanoparticles with aluminium alloy melt and the large specific surface area of Ti(C, N) nanoparticles, the Ti(C, N) nanoparticles are prone to aggregate in molten aluminium, which severely limits the application of Ti(C, N) in aluminium alloy. And effective approaches to improving the wettability of Ti(C, N) nanoparticles refine aluminium alloys are provided.

Influence of dry micro abrasive blasting on the physical and mechanical characteristics of hybrid PVD-AlTiN coated tools

The current study investigates the effect of the micro abrasive blasting (MAB) on the physical and mechanical characteristics of the cutting tools before and after coating deposition. Cutting tools were subjected to micro blasting by alumina (Al2O3) grains at varying pressure so as to improve the efficacy of the coating process. AlTiN coating of thickness 1.45 μm was deposited onto the tool surface by arc enhanced high power impulse magnetron sputtering (HiPIMS) hybrid deposition technique. The coatings were characterized using nano indentation, atomic force microscopy and micro scratch test. The results of nano indentations on the coated surface revealed the influence of the micro abrasive blasting technique and pressure on the superficial hardness. Surface morphology results showed better-adhered surface in case of cutting tools subjected to micro abrasive blasting before the deposition due to an increase in density of the nucleation sites for growth of aluminum which can be judged with the help of higher aluminum content in the energy dispersive x-ray analysis. The film adhesion of the coating onto the tool substrate is observed to be improved significantly with an increase in blasting pressure in the case of the samples subjected to micro abrasive blasting before coating. Additionally, X-ray diffraction analysis was performed to investigate crystallographic phases. The attained results provide insight concerning the optimum selection of micro abrasive blasting technique along with the pressure, for enhancing the cutting performance of coated tools during the machining of nickel-based superalloy Nimonic C 263.

Low-Temperature High-Frequency Induction Brazing of 5052 Aluminum Alloy to Stainless Steel with Sn-Zn Solder

Low-temperature high-frequency induction brazing of 5052 aluminum alloy to stainless steel was carried out using Sn-30Zn with reactive-flux 88ZnCl2-10NH4Cl-2NaF wt.%. The influence of processing parameters on microstructures, mechanical property and fracture behavior was investigated. Intermetallic compounds were not observed at the interface of the steel. The brazing seam consisted of Sn-Zn eutectic structures, Zn-rich solid solution and oxide inclusion. The diffusion of Sn and Zn into the aluminum grain boundary led to an intergranular penetration layer. When brazing at 370°C for 30 s, the joint fractured in the brazing seam and the shear strength reached the highest at 87 MPa. The fracture surface of the joint presented ductile characteristics. The diffusion of F− in the flux made the oxide film expand and crack. Zn2+ permeated through the crack of the film and then reacted with Al, which removed the film from aluminum substrate.

The influence of CaO on alumina grain boundary mobility

The influence of CaO on the evolving microstructure of alumina has been studied in a range of concentrations below the solubility limit. The amount of Ca in the alumina was determined by conducting fully standardized wavelength dispersive spectroscopy, and the change in grain boundary mobility as a function of the amount of dopant was characterized using scanning electron microscopy. Unlike segregating dopants which reduce grain boundary mobility by solute-drag, CaO increases the rate of grain growth, and a trend of increased mobility with increasing dopant level was shown. The increased mobility with Ca segregation is believed to be due to an increase in vacancy concentration in the vicinity of the grain boundaries, thus facilitating faster grain boundary motion.

First-principles calculation of multiple hydrogen segregation along aluminum grain boundaries

The segregation of multiple hydrogen atoms along aluminum (Al) grain boundaries (GBs) and fracture surfaces (FSs) was investigated through first-principles calculations considering the characteristics of GBs. The results indicate that hydrogen segregation is difficult along low-energy GBs. The segregation energy of multiple hydrogen atoms along GBs and FSs and the cohesive energy was obtained for three types of high-energy Al GBs. With increasing hydrogen segregation along the GBs, the cohesive energy of the GB decreases and approaches zero with no decrease in GB segregation energy. The GB cohesive energy decreases in parallel with the volume expansion of the region of low electron density along the GB.

Enhancement of microstructure and mechanical properties of hypereutectic Al\u201316%Si alloy by ZnO nanocrystallites

This study was carried out to examine the mechanical properties of hypereutectic Al–16% Si alloy with the introduction of zinc oxide (ZnO) nanoparticles (NPs) synthesized by simple sol–gel method. The microstructure of the synthesized ZnO NPs was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The microstructure of the synthesized ZnO NPs reflects the formation of the wurtzite-type ZnO and the average crystallite sizes around 35 nm. Hypereutectic Al–16% Si with varies concentration of ZnO NPs (0.5, 1, 1.5 and 3%) was synthesized utilizing permanent mold casting technique. Energy-dispersive spectrometer (EDS) and scanning electron microscopy (SEM) of hypereutectic Al–16 wt% Si alloys after the dispersion of these nanoparticles were analyzed. The results revealed that an addition of ZnO nanoparticle to hypereutectic Al–16wt % Si alloy enhanced the tensile strength, impact energy and the hardness. The maximum tensile strength, impact energy and hardness of this alloy was 200 MPa, 5.38 J, 60 BHN, respectively, which occurred at 3 wt% of ZnO NPs. This enhancement in mechanical properties can attributed to the decomposition and dissolution of the nano-oxide particles in aluminum alloy melt and grain growth restriction.

High-temperature mechanical properties of AlSi10Mg specimens fabricated by additive manufacturing using selective laser melting technologies (AM-SLM)

Mechanical properties (tensile strength and creep) of AlSi10Mg specimens fabricated by selective laser melting (SLM) in the Z-direction were investigated in the 25–400 °C temperature range. Specimens were tested after stress relief treatment. The results revealed that yield stress (YS) significantly decreases and the elongation increases at temperatures higher than 200 °C. The ultimate tensile stress (UTS) continuously decreases with temperature. The creep parameters, namely stress exponent n and apparent activation energy Q, were found to be 25 ± 2 and 146 ± 20 kJ/mole, respectively. It was shown that plastic deformation during creep is governed by dislocation movements in primary aluminum grains. The tested material is actually an aluminum composite reinforced by sub-micron Si particles. The creep resistance of AlSi10Mg alloy fabricated by selective laser melting is close to that for aluminum matrix particles reinforced composites.

Processing of Ultralight Porous Al2O3-Ceramics by Biotemplating of Bamboo

Biomorphic alumina ceramic with a long, large and oriented growth of alpha alumina grains suitable for the devices such as prosthetic implants, dental implant and control drug release etc. Ultralight porous alumina was synthesized from a carbonaceous preform derived from bamboo using biotemplating technique. Carbonaceous preform (C-preform) of bamboo precursor was prepared by controlled thermal processing in a muffle furnace for pore formation. Al2O3 was inserted into C-preforms by sol-gel method applying repeated infiltration of low viscous Al2O3-sol and then dried and sintered at 1500°C in air atmosphere resulting of an ultra-light monophasic Al2O3 ceramics with replication of the pore structure of the bamboo C-preforms. The microstructure of porous Al2O3 was characterized by scanning electron microscopy (SEM). Open hierarchical porous structures surrounded by alumina struts web with nominal porosity of 80% inside the biomaterial are visualized which lacking of interconnectivity and low strength.