Microstructural characterization,tribological and corrosion behavior of AA7075-TiC composites

Aluminum alloys are the potential materials in the automobile and aerospace sectors due to their lower density,easy forming and excellent corrosion resistance.The demand of high strength-to-weight ratio materials in structural applications needs the engineering industries to seek aluminum alloy with new versions of hard and brittle ceramic particles.The microstructure,hardness,wear and corrosion behaviors of AA7075 composites with 2.5wt.%and 5wt.%TiC particles were studied.Microscopic analysis is evident that the transformation of the strong dendritic morphology to non-dendritic morphology on the incorporation of TiC into AA7075.Furthermore,the precipitation of the second-phase compounds such as Al_(2)CuMg,Al_(2)Cu andFe-rich Al_6(Cu,Fe)/Al_(7)Cu_(2)Fe)is promoted by TiC particles at inter-and intra-dendritic regions.Accordingly,the hardness of composites is improved by grain boundary strengthening and particulate strengthening mechanisms.Both coefficient of friction and wear rate have an inverse relation with TiC concentration.The base alloy without TiC shows adhesive-type wear-induced deformation due to the formation of an oxide film,while composite samples exhibit a mechanically mixed layer and abrasive-type wear behavior.Composite samples shows a higher corrosion rate due to the presence of numerous precipitates which promote pitting corrosion.

Influence of bimodal grain size distribution on the corrosion behavior of friction stir processed biodegradable AZ31 magnesium alloy

In the present study,AZ31 magnesium alloy sheets were processed by friction stir processing(FSP)to investigate the effect of the grain refinement and grain size distribution on the corrosion behavior.Grain refinement from a starting size of 16.4±6.8µm to 3.2±1.2µm was attained after FSP.Remarkably,bimodal grain size distribution was observed in the nugget zone with a combination of coarse(11.62±8.4µm)and fine grains(3.2±1.2µm).Due to the grain refinement,a slight improvement in the hardness was found in the nugget zone of FSPed AZ31.The bimodal grain size distribution in the stir zone showed pronounced influence on the corrosion rate of FSPed AZ31 as observed from the immersion and electrochemical tests.From the X-ray diffraction analysis,more amount of Mg(OH)_(2) was observed on FSPed AZ31 compared with the unprocessed AZ31.Polarization measurements demonstrated the higher corrosion current density for FSPed AZ31(8.92×10^(−5)A/cm^(2))compared with the unprocessed condition(2.90×10^(−5)A/cm^(2))that can be attributed to the texture effect and large variations in the grain size which led to non-uniform galvanic intensities.

Influence of heat treatment on the machinability and corrosion behavior of AZ91 Mg alloy

In the present study,AZ91 Mg alloy was heat treated at 410℃ for 6,12 and 24 h to investigate the influence of heat treatment on machinability and corrosion behavior.The effect of soaking time on the amount and distribution of Mg 17 Al 12(β-phase)was analyzed under the optical microscope.Microhardness measurements demonstrated the increased hardness with increased heat treatment soaking time,which can be attributed to the solid solution strengthening.The influence of super saturatedα-grains on reducing the cutting force(F z)with respect to increased cutting speed was observed as prominent.The corrosion behavior of the heat treated specimens was studied by conducting electrochemical tests.Surprisingly,corrosion rate of heat treated samples was observed as increased compared with the base material.From the results,it is evident that the machinability of AZ91 Mg alloy can be improved by producing super saturatedα-grains through heat treatment but at the cost of losing corrosion resistance.

Joining of AZ91 Mg alloy and Al6063 alloy sheets by friction stir welding

In the present work,the effect of process parameters on joining of AZ91 Mg alloy and Al6063 aluminum alloy sheets during friction stir welding(FSP)was studied.A successful joint was achieved at 1100 r.p.m.tool rotational speed and 25 mm/min tool travel speed.Combination of tool rotational speed and tool travel speed has observed a profound effect on the material flow mechanisms at the nugget zone.From the microstructural studies,the joint formation was observed as mainly due to mechanical mixing of the materials.The level of metallurgical continuity at the nugget zone was observed as poor and a sharp interface at the joint was noticed.The microhardness measurements across the weld joint also revealed the lack of establishment of a perfect metallurgical bonding.X-ray diffraction analysis of weld zone showed presence of both magnesium and aluminum.Hence from the preliminary observations,it can be understood that the joining of AZ91 Mg alloy and Al6063 alloy can be achieved by FSP;however,complex issues in material mixing still need further investigations.

Effect of aluminum content on machining characteristics of AZ31 and AZ91 magnesium alloys during drilling

Magnesium(Mg)and its alloys are now becoming the promising choice for various structural applications due to their low density and high specific strength compared with other light metals such as aluminum and its alloys.Among all Mg alloys,AZ(aluminum and zinc)series is the most widely used alloy system for various structural applications.But,machining of magnesium and its alloys involves certain issues due to their brittle nature and risk of inflammability unlike other nonferrous metals.Particularly,alloys with considerable amount of secondary phase may exhibit different machining characteristics during metal cutting operations.In the present study,two AZ series alloys AZ31 and AZ91 were selected and drilling operation was performed to assess the effect of the secondary phase amount and distribution on machining characteristics.Drilling operation was carried out at different sets of process parameters and cutting forces were obtained and the chips which have been produced during drilling were analyzed.From the results,it can be clearly understood that the presence of secondary phase(Mg_(17)Al_(12))has a significant influence on cutting forces.Increase in cutting speed has reduced the required cutting force and load fluctuations in all the cases.

Joining of AZ31 and AZ91 Mg alloys by friction stir welding

Two dissimilar magnesium(Mg)alloy sheets,one with low aluminium(AZ31)and another with high aluminium(AZ91)content,were successfully joined by friction stir welding(FSW).The effect of process parameters on the formation of hot cracks was investigated.A sound metallurgical joint was obtained at optimized process parameters(1400 rpm with 25 mm/min feed)which contained fine grains and distributed β(Mg_(17)Al_(12))phase within the nugget zone.An increasing trend in the hardness measurements has also confirmed more amount of dissolution of aluminium within the nugget zone.A sharp interface between nugget zone and thermo mechanical affected zone(TMAZ)was clearly noticed at the AZ31 Mg alloy side(advancing)but not on the AZ91 Mg alloy side(retreating).From the results it can be concluded that FSW can be effectively used to join dissimilar metals,particularly difficult to process metals such as Mg alloys,and hot cracking can be completely eliminated by choosing appropriate process parameters to achieve sound joint.

An investigation on the hardness and corrosion behavior of MWCNT/Mg composites and grain refined Mg

In the present work,multi walled carbon nanotubes(MWCNT)reinforced magnesium(Mg)matrix composite was fabricated by friction stir processing(FSP)with an aim to explore its mechanical and electrochemical behavior.Microstructural observations showed that the thickness of the produced composite layer was in the range of 2500μm.FSP resulted uniform distribution of CNT near the surface while agglomerated layers in the subsurface.Grain refinement of Mg achieved by FSP improved the hardness but significant enhancement in the hardness value was observed for FSPed MWCNT/Mg composites.Potentiodynamic polarization studies revealed that the increase in corrosion current density was observed for MWCNT/Mg composite compared with grain refined Mg and pure Mg,implying the significance of secondary phase(MWCNT)in decreasing the corrosion resistance of the composite.

Machining characteristics of fine grained AZ91 Mg alloy processed by friction stir processing

AZ91Mg alloy was considered and friction stir processing(FSP)was adopted to achieve grain refinement to investigatethe effect of grain size and secondary phase on machining characteristics during drilling at various speeds and feeds.Super saturatedAZ91Mg alloy was obtained after FSP and the grain refinement was achieved from(166.5±8.7)μm to(21.7±13.5)μm.Surprisingly,hardness reduced for FSP AZ91Mg alloy(88.95±6.1)compared with AZ91alloy(108.2±15.6),which was attributed to the reducedsecondary phase.However,the mean cutting force for FSP-treated(FSPed)AZ91Mg alloy was marginally increased.The edgedamage of the drilled holes was lower for FSPed AZ91Mg alloy compared with unprocessed AZ91Mg alloy.Hence,it can beunderstood that the grain refinement may slightly increase the cutting forces during drilling but better edge finishing can be achievedin machining of AZ91Mg alloy.

SO₄^2-/SnO₂-Catalyzed C3-alkylation of 4-hydroxycoumarin with secondary benzyl alcohols and <i>O</i>-alkylation with <i>O</i>-acetyl compounds

Sulfated tin oxide (STO) has been found to be an efficient reusable solid superacid catalyst for C3-alkylation and O-alkylation of 4-hydroxycoumarins with benzylic, allylic alcohols/and corresponding acetates respectively, in acetic acid under reflux conditions with good yield of products.

Magnesium based surface metal matrix composites by friction stir processing

Surface metal matrix composites(MMCs)are a group of modern engineered materials where the surface of the material is modified by dispersing secondary phase in the form of particles or fibers and the core of the material experience no change in chemical composition and structure.The potential applications of the surface MMCs can be found in automotive,aerospace,biomedical and power industries.Recently,friction stir processing(FSP)technique has been gaining wide popularity in producing surface composites in solid state itself.Magnesium and its alloys being difficult to process metals also have been successfully processed by FSP to fabricate surface MMCs.The aim of the present paper is to provide a comprehensive summary of state-of-the-art in fabricating magnesium based composites by FSP.Influence of the secondary phase particles and grain refinement resulted from FSP on the properties of these composites is also discussed.

Non-spherical aluminum nanoparticles fabricated using picosecond laser ablation

We report the picosecond laser ablation of aluminum targets immersed in a polar organic liquid(chloroform,CHCl3)with^2 ps laser pulses at an input energy of^350μJ.The synthesized aluminum nanoparticles exhibited a surface plasmon resonance peak at^340 nm.Scanning electron microscopy images of Al nanoparticles demonstrated the spherical morphology with an average size of(27±3.6)nm.The formation of smaller spherical Al nanoparticles and the diminished growth could be from the formation of electric double layers on the Al nanoparticles.In addition to spherical aluminum nanoparticles,triangular/pentagonal/hexagonal nanoparticles were also observed in the colloidal solution.Field emission scanning electron microscopy images of ablated Al targets demonstrated laser induced periodic surface structures(LIPSSs),which were the high spatial frequency LIPSSs(HSF-LIPSSs)since their grating period was^280 nm.Additionally,coarse structures with a period of^700 nm were observed.

Developing Mg–Zn surface alloy by friction surface allosying: In vitro degradation studies in simulated body fluids

A new variant of friction-assisted process named friction surface alloying(FSA)for developing surface alloys was demonstrated in the present work.In FSA,the dispersed phase is melted and allowed to react with the matrix material to form an alloy at the surface of a metallic substrate.In the present work,magnesium(Mg)sheets and zinc(Zn)powder were selected,and fine grained(~3.5μm)Mg–Zn surface alloy with improved hardness was produced by FSA.X-ray diffraction studies confirmed the formation of intermetallic phases of Mg and Zn at the surface.From the in vitro degradation studies carried out by immersing in simulated body fluids,a lower corrosion rate was observed for the Mg–Zn surface alloy compared with pure Mg.The surface morphologies after immersion studies indicated large degraded areas on the base Mg compared with Mg–Zn.The results demonstrate the potential of FSA in developing Mg-based surface alloys without melting the substrate to impart better surface properties.

Cerebral dopamine neurotrophic factor transfection in dopamine neurons using neurotensin-polyplex nanoparticles reverses 6-hydroxydopamine-induced nigrostriatal neurodegeneration

Overexpression of neurotrophic factors in nigral dopamine neurons is a promising approach to reverse neurodegeneration of the nigrostriatal dopamine system,a hallmark in Parkinson's disease.The human cerebral dopamine neurotrophic factor(h CDNF)has recently emerged as a strong candidate for Parkinson's disease therapy.This study shows that h CDNF expression in dopamine neurons using the neurotensinpolyplex nanoparticle system reverses 6-hydroxydopamine-induced morphological,biochemical,and behavioral alterations.Three independent electron microscopy techniques showed that the neurotensin-polyplex nanoparticles containing the h CDNF gene,ranging in size from 20 to 150 nm,enabled the expression of a secretable h CDNF in vitro.Their injection in the substantia nigra compacta on day 21 after the 6-hydroxydopamine lesion resulted in detectable h CDNF in dopamine neurons,whose levels remained constant throughout the study in the substantia nigra compacta and striatum.Compared with the lesioned group,tyrosine hydroxylase-positive(TH^(+))nigral cell population and TH+fiber density rose in the substantia nigra compacta and striatum after h CDNF transfection.An increase inβIII-tubulin and growth-associated protein 43 phospho-S41(GAP43 p)followed TH^(+)cell recovery,as well as dopamine and its catabolite levels.Partial reversal(80%)of drugactivated circling behavior and full recovery of spontaneous motor and non-motor behavior were achieved.Brain-derived neurotrophic factor recovery in dopamine neurons that also occurred suggests its participation in the neurotrophic effects.These findings support the potential of nanoparticle-mediated h CDNF gene delivery to develop a disease-modifying treatment against Parkinson's disease.The Institutional Animal Care and Use Committee of Centro de Investigación y de Estudios Avanzados approved our experimental procedures for animal use(authorization No.162-15)on June 9,2019.

Experimental study on performance of passive and active solar stills in Indian coastal climatic condition

This present work is aimed to examine the effect of mass flow rate on distillate output and performance of a solar still in active mode.Outdoor experiments were conducted at the coastal town,Kakinada(16°93′N/83°33′E),Andhra Pradesh,India.A solar still with a 30°of fixed cover inclination,1 m2 of effective basin area,and a flat-plate collector(FPC)with an effective area of 2 m2 were used.An attempt was also made earlier in passive mode to optimize the water depth for the same solar still for maximum yield and distillation efficiency.For the passive still,it is observed that the capacity of heat storage and heat drop are significant parameters that affect the still performance.For the selected still design,the study reveals that 0.04 m water depth is the optimum value for specific climatic conditions.In the active solar still,with the optimum water depth,different flow rates of 0.5,1 and 1.5 L/min are considered through FPC.It is observed that both the mass flow rate and the variation of internal heat transfer coefficients with the mass flow rate have a significant effect on the yield and performance of the still.The experimental results show that the combination of 1.5 L/min mass flow rate and an optimum water depth of 0.04 m leads to a maximum yield for the active solar still.The enhanced yield of the active solar still is 57.55%,compared with that of the passive solar still,due to increase in area of radiation collection and more heat absorption rate.

Intense violet-blue emission and paramagnetism of nanocrystalline Gd^(3+) doped ZnO ceramics

Nanocrystalline Zn1-xGdxO(x=0,0.02,0.04,0.06,and 0.08)ceramics were synthesized by ball milling and subsequent solid-state reaction.The transmission electron microscopy(TEM)micrograph of as synthesized samples revealed the formation of crystallites with an average diameter of 60 nm,and the selected area electron diffraction(SAED)pattern confirmed the formation of wurtzite structure.A red shift in the band gap was observed with increasing Gd^(3+)concentration.The photoluminescence of nanocrystalline Gd^(3+)doped ZnO exhibited a strong violet-blue emission.Concentration dependence of the emission intensity of Gd^(3+)in ZnO was studied,and the critical concentration was found to be 4 mol%of Gd^(3+).The Gd^(3+)doped ZnO exhibited paramagnetic behavior at room temperature,and the magnetic moment increased with Gd^(3+)concentration.

Origin of giant dielectric permittivity and weak ferromagnetic behavior in(1−x)LaFeO_(3−x)BaTiO_(3)(0.0≤x≤0.25)solid solutions

The solid solutions of(1-x)LaFeO_(3–x)BaTiO_(3)(0.0≤x≤0.25)have been synthesized successfully by the conventional solid-state reaction method.Room temperature(RT)X-ray diffraction studies reveal the stabilization of orthorhombic phase with Pbnm space group.Complete solubility in the perovskite series was demonstrated up to x=0.25.The dielectric permittivity shows colossal dielectric constant(CDC)at RT.The doping of BaTiO_(3)in LaFeO_(3)exhibit pronounced CDC up to a composition x=0.15,further it starts to decrease.The frequency-dependent dielectric loss exhibits polaronic conduction,which can attribute to presence of multiple valence of iron.The relaxation frequency and polaronic conduction mechanism was shifted towards RT as function of x.Moreover,large magnetic moment with weak ferromagnetic behavior is observed in doped LaFeO_(3) solid solution,which might be the destruction of spin cycloid structure due to insertion of Ti in Fe–O–Fe network of LaFeO_(3).

Modeling of aggregation kernels for fluidized beds using discrete particle model simulations

Aggregation is one of the many important processes in chemical and process engineering. Several researchers have attempted to understand this complex process in fluidized beds using the macro-model of population balance equations （PBEs）. The aggregation kernel is an effective parameter in PBEs, and is defined as the product of the aggregation efficiency and collision frequency functions. Attempts to derive this kernel have taken different approaches, including theoretical, experimental, and empirical techniques. The present paper calculates the aggregation kernel using micro-model computer simulations, i.e., a discrete particle model. We simulate the micro-model without aggregation for various initial conditions, and observe that the collision frequency function is in good agreement with the shear kernel. We then simulate the micro-model with aggregation and calculate the aggregation efficiency rate.