Evolution mechanism of the interfacial reaction layers in the joints of diffusion bonded Mo and Al foils

Mo foil （10 -20 μm in thickness） and Al foil （20 -60 μLm in thickness） were vacuum diffusion bonded at 600 - 640 ~C under 20 MPa for 54 min - 6 h. The joints were examined by scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS） to study the evolution mechanism of the reaction layers. The results show that Al atoms diffuse into Mo grain boundaries and form reaction products as Mo3Al8, MoAl4 , MoAl5 and MoAl12. The surface oxide film is eroded by the growths of the reaction products that plow into the lamellar texture of Mo grain boundaries. Mo3Al8 layer grows by ＂taking root＂ downwards and transforms into MoAl4 and MoAl5 phases upwards by absorbing Al atoms. MoAl12 layer grows up from MoAl5 layer in the same way. When the supplement of Al atoms ceases, MoAl12 transforms reversely into MoAl5 and MoAl5 into MoAl4 via the loss of Al atoms. However, MoAl4 continues to precipitate from Mo3Als layer. At last, there are MoAl4 and Mo3Al8 remained on the joint interface.

Effect of Reaction Layers on the Residual Stress of the Brazed TiC Cermets/Steel Joints

For the first time, considering the effect of reaction layers, numerical simulation calculation of residual stress on brazed TiC cermets/steel joint was studied by finite element method （FEIVl）. The calculation results show that, when the joint is brazed at 1123 K for 300 s （low brazing parameters）, the maximum shear stress value occurs on （Cu, Ni） layer near TiC cermets, which is 92.16 MPa as the temperature is 300 K. When the joint is brazed at 1273 K for g00 s （high brazing parameters）, the maximum shear stress value occurs on （Cu, Ni）＋（Fe, Ni） layer, which is 39.18 MPa as the temperature is 300 K. The fracture sites of the joints obtained from numerical simulation calculation accord with experimental results.

Interfacial reaction between zirconium alloy and graphite mold/yttrium oxide ceramic mold

Zirconium alloys are active in the molten state and tend to react with the mold during casting. The casting technology of zirconium is not yet well established; especially in selecting the mold materials, which are difficult to determine. In the present work, the interfacial reactions between zirconium casting and casting mold were studied. The zirconium alloy was melted in a vacuum arc skull furnace and then cast into the graphite mold and ceramic mold, respectively. The zirconium casting samples were characterized using SEM, EDS and XRD with an emphasis on the chemical diffusion of elements. A reaction layer was observed at the casting surface. Chemical analysis shows that chemical elements C, O and Y from the mold are diffused into the molten zirconium, and new phases, such as ZrC, Zr30, YO1.335 and Y6ZrO11, are formed at the surface. In addition, an end product of zirconium valve cast in a yttria mold has a compact structure and good surface quality.

Brazing of Ti_2 AlNb Based Alloy with Amorphous Ti-Cu-Zr-Ni Filler

Amorphous Ti-Cu-Zr-Ni filler foils with low melting point of 1 133 K were synthesized using a melt-spinning method in argon atmosphere. A Ti2A1Nb based alloy was brazed at 1 153-1 223 K for 600-3 000 s. The effects of brazing temperature （Tb） and time （tb） on the shear strength of the joints were investigated. The results showed that the joint strength was significantly affected by the reaction layer thickness. The optimum brazing parameters can be determined as follows： Tb=l 173 K, and tb=600 s. The maximum tensile strength of the joint obtained can reach 260 MPa. Furthermore, the activation energy Q and the growth velocity A0 of the reaction layer in the brazed joints were calculated to be 161.742 kJ/mol and 0.213 m2/s, respectively. The growth of the reaction layer （y） could be expressed by the expression： ya =0.213exp（-19 454/Tb）tb.

Relation between oxidation microstructure and the maximum energy product loss of a Sm_2Co_(17) magnet oxidized at 500℃

The oxidation microstructure and maximum energy product （BH）max loss of a 8m（Co0.76, Fe0.1, Cu0.1, Zr0.04）7 magnet oxidized at 500 ℃ were systematically investigated. Three different oxidation regions were formed in the oxidized magnet： a continuous externM oxide scale, an internal reaction layer, and a diffusion zone. Both room-temperature and high-temperature （BH）max losses exhibited the same parabolic increase with oxidation time. An oxygen diffusion model was proposed to simulate the dependence of （BH）max loss on oxidation time. It is found that the external oxide scale has little effect on the （BH）max loss, and both the internal reaction layer and diffusion zone result in the （BH）max loss. Moreover, the diffusion zone leads to more （BH）max loss than the internal reaction layer. The values of the oxidation rate constant k for internal reaction layer and oxygen diffusion coefficient D for diffusion zone were obtained, which are about 1.91×10^-10 cm^2/s and 6.54×10^-11 cm^2/s, respectively.

CdS Quantum Dots-sensitized TiO_2 Nanotube Arrays for Solar Cells

CdS quantum dots（QDs） sensitized TiO2 nanotube arrays photoelectrodes were investigated for their photovoltaic performance of quantum dots-sensitized solar cells. The highly ordered TiO2 nanotube arrays（TNAs） were synthesized on Ti foils by anodic oxidation method. Then CdS quantum dots were deposited onto the TiO2 nanotube arrays by successive ionic layer absorption and reaction（SILAR） method to serve as the sensitizers. Cd（NO3）2 and Na2S were used as the precursor materials of Cd＋ and S2- ions, respectively. It is found that the CdS QDs sensitizer may significantly increase the light response of TiO2 nanotube arrays. With increasing CdS QDs deposition cycles, the visible light response increases. Maximum photocurrent was obtained for the QDs that have an absorption peak at about 500 nm. Under AM 1.5 G illuminations（100 mW cm^-2）, a 4.85 mA/cm^2 short circuit current density was achieved, and the maximium energy conversion efficiency of the asprepared CdS QDs-sensitized TNAs solar cells was obtained as high as 0.81% at five SILAR cycles.

Modeling development on the meso-scale reacting transport phenomena in proton exchange membrane fuel cells

The catalyst layer （CL） of proton exchange mem-brane fuel cell （PEMFC） involves various particles and pores in meso-scale, which has an important effect on the mass, charge （proton and electron） and heat transport coupled with the electrochemical reactions. The coarse-grained molecular dynamics （CG-MD） method is employed as a meso-scale structure reconstruction technique to mimic the self-organization phenomena in the fabrication steps of a CL. The meso-scale structure obtained at the equilibrium state is further analyzed by molecular dynamic （MD） software to provide the necessary microscopic parameters for understanding of multi-scale and-physics processes in CLs. The primary pore size distribution （PSD） and active platinum （Pt） surface areas are also calculated and then compared with the experiments. In addition, we also highlight the implementation method to combine microscopic elementary kinetic reaction schemes with the CG-MD approaches to provide insight into the reactions in CLs. The concepts from CG modeling with particle hydrodynamics （SPH） and the problems on coupling of SPH with finite element modeling （FEM） methods are further outlined and discussed to understand the effects of the meso-scale transport phenomena in fuel cells.

Formation mechanism of interface reaction layer between microporous magnesia refractories and molten steel and its effect on steel cleanliness

The ceramic filter in continuous casting tundish can effectively improve the cleanliness of high-performance steel by regulating tundish flow field to promote the removal of inclusions and adsorbing or blocking fine inclusions in the molten steel into the mold.The interaction between microporous magnesia refractories used as tundish filter and molten interstitial-free(IF)steel at 1873 K was investigated to reveal the formation mechanism of their interface layer and its effect on steel cleanliness by laboratory research and thermodynamic calculations.The results show that the magnesium–aluminum spinel layer at the interface between the molten IF steel and the microporous magnesia refractories is formed mainly by the reaction of MgO in the refractory with the[Al]and[O]in the molten steel,significantly reducing the total O content,the size and amount of inclusions of the molten steel.In addition,the interparticle phases of microporous magnesia refractories at high temperature can adsorb Al_(2)O_(3) and TiO_(2) inclusions in the molten steel into interparticle channels of the refractories to form high melting point spinel,impeding the further penetration of the molten steel.As a result,the consecutive interface layer of high melting point spinel between microporous magnesia refractories and molten steel can improve the cleanliness of the molten steel by adsorbing inclusions in the molten steel and avoid the direct dissolution of refractories of the tundish ceramic filter immersed in the molten steel,increasing their service life.

Dynamic study in partial transient liquid phase bonding of Si_3N_4

Dynamics in partial transient liquid phase bonding (PTLP bonding) of Si_3N_4 ceramic with Ti/Cu/Ti multi-interlayer was systematically studied through micro-analysis of joint interfaces. The results show that growth of reaction layer and isothermal solidification procession do at the same time. Growth of reaction layer and moving of isothermal solidification interface obey the parabolic law governed by the diffusion of participating elements during the PTLP bonding. Coordination of the above two dynamics process is done through time and temperature. When reaction layer thickness is suitable and isothermal solidification process is finished, the high bonding strength at room temperature and high temperature are obtained.

Effects of rare earth metal addition on microstructure of hot-dip 55%Al-Zn-Si coatings

Optical microscope(OM),scanning electron microscope(SEM),energy dispersive spectrometer (EDS) and X-ray Diffraction(XRD) were used to study the effects of rare earth on the microstructural characteristics of 55%Al-Zn-1.6%Si hot -dip coatings on steel.The results of OM,SEM and EDS showed that by adding RE into the 55%Al-Zn-1.6%Si bath,the saw-toothed shape of intermetallic reaction layer of coating became smooth,and the thickness of the overlay and intermetallic reaction layer decreased.The XRD results revealed that the intermetallic reaction layer was comprised of two different regions,a bright phase closest to the steel substrate with phases of Fe_2Al_3 and a dark phase closest to the metallic coating with phases of FeAl_3/α-Fe-Al-Si.

Investigation on Cracking in Surfacing Layer of Ni_3Al Base Alloy

Investigation has been made on the causes of hot cracking in the surfacing layer of Ni_3Al basealloy by analysing the solidification process of fusion pool and the distribution of thermal stresses. The re-sults show that the cracking is directly related to both the occurrence of eutectic phase β' (NiAI) within theinterdendritic region and high thernial stresses in the surfacing layer ,and which are caused by selecting highwelding rate. When the process of electric arc weld is changed from straight line rnovement to that along’Z’pattern,the cracking in the surfacing layer of Ni_3Al base alloy is prevented owing to being reduced of boththe cooling rate of liquid in the fusion liool and the speed of the moving heat source. Lowering the outputpower of the electric arc welding could lead to the reducing of rnelting volume of the base material ,and lowerthe arnount of iron atoms dissolving in the fusion pool ,so that the trend of the eutectic reaction within the in-terdendritic region is reduced,and which is helpful to suppress the cracking in the surfacing layer of Ni_3Albase alloy.

Corrosion behavior of Gd_(2)Zr_(2)O_(7)thermal barrier coatings under Fe-containing environmental sediment attack

Environmental sediments mainly consisting of CaO–MgO–Al_(2)O_(3)–SiO_(2)(CMAS)corrosion are a serious threat to thermal barrier coatings(TBCs),in which Fe element is usually ignored.Gd_(2)Zr_(2)O_(7)TBCs are famous for their excellent CMAS resistance.In this study,the characteristics of Fe-containing environmental sediments(CMAS-Fe)and their corrosiveness to Gd_(2)Zr_(2)O_(7)coatings were investigated.Four types of CMAS-Fe glass with different Fe contents were fabricated.Their melting points were measured to be 1322–1344℃,and the high-temperature viscosity showed a decreasing trend with increasing Fe contents.The corrosion behavior of four types of CMAS-Fe to Gd_(2)Zr_(2)O_(7)coatings at 1350℃was investigated.At the initial corrosion stage(0.1 h),anorthite was precipitated in CMAS-Fe with a high Ca:Si ratio,while Fe-garnet was formed in the melt with the highest Fe content.Prolonging the corrosion time resulted in the formation of a reaction layer,which exhibited an interpenetrating network composed of Gd-oxyapatite,ZrO_(2),and residual CMAS-Fe.Some spinel was precipitated within the reaction layer.After 1 h or even longer time,the reaction layers tended to be stable and compact,which had comparable hardness and fracture toughness to those of Gd_(2)Zr_(2)O_(7)coatings.Under the cyclic CMAS-Fe attack,the residual CMAS-Fe in the interpenetrating network provided a pathway for the redeposited CMAS-Fe infiltration,resulting in the continuous growth of the reaction layer.As a result,the Gd_(2)Zr_(2)O_(7)coatings had a large consumption in the thickness,degrading the coating performance.Therefore,the Gd_(2)Zr_(2)O_(7)coatings exhibit unsatisfactory corrosion resistance to CMAS-Fe attack.

CMAS-phobic and infiltration-inhibiting protective layer material for thermal barrier coatings

Calcium-magnesium-alumina-silicate(CMAS)corrosion has attracted special attention in the thermal barrier coating(TBC)field.At high temperatures,when CMAS melts,it adheres to the coating surface and penetrates the interior,severely destroying the TBC.In this study,a promising CMAS-phobic and infiltration-inhibiting material,GdPO4,on which molten CMAs is difficult to wet and penetrate,was proposed.These desirable attributes are explained by analyzing the material characteristics of GdPO_(4) and its interfacial reaction with CMAS.GdPO4 is demonstrated to have low surface energy,making it difficult for molten CMAS to wet and adhere to the surface.When in contact with molten CMAS,a double-layer structured reaction layer consisting of an acicular upper sublayer and a compact lower sublayer is formed on the GdPO4 surface,which can effectively impede molten CMAS spreading and penetration.First-principles calculation results revealed that the reaction layer has low surface energy and low adhesion to CMAS,which are favorable for molten CMAS phobicity.Additionally,the formation of the reaction layer increases the viscosity of the molten CMAS,which can increase melt wetting and penetration.Hence,GdPO4,which exhibits excellent CMAS-phobicity and infiltration-inhibiting ability,is a promising protective layer material for TBCs against CMAS adhesion and attack.

Microstructure of reaction layer and its effect on the joining strength of SiC/SiC joints brazed using Ag-Cu-In-Ti alloy

The SiC/SiC joints were vacuum brazed at 700℃,740℃,780℃and 800℃for 10 min respectively,using Ag-Cu-In-Ti active filler alloy.The microstructure and joining strength of the joints were characterized by electron probe X-ray microanalyser(EPMA),energy dispersive spectroscopy(EDS),transmission electron microscopy(TEM)and four-point bending strength test.The interface of the joints was composed of three parts:SiC substrate,reaction layer and filler alloy.A representative microstructure of the reaction layer:In-containing layer/TiC layer/Ti5Si3 layer was found from the TEM image.The forming of the In-containing layer could be attributed to the crack or delamination of SiC/TiC interface.The In-containing layer intensified the coefficient of thermal expansion(CTE)mismatch of SiC and the reaction layer,and affected the joining strength.With the increase of the reaction layer’s thickness,the joining strength firstly increased,then declined,and the maximum four-point bending strength reached 234 MPa.

Effects of cold metal transfer mode on the reaction layer of wire and arc additive-manufactured Ti-6Al-4V/Al-6.25Cu dissimilar alloys

Components of Ti and Al dissimilar alloys were obtained by wire and arc additive manufacturing using two cold metal transfer(CMT)modes.Direct current CMT(DC-CMT)mode was used for Ti alloy deposition,and DC-CMT or CMT plus pulse(CMT+P)mode was used for the Al alloy deposition.During deposition of the first Al alloy layer,little and a significant amount of Ti alloy were melted using DC-CMT and CMT+P mode,respectively.TiAl_(3)formed in the reaction layer when DC-CMT mode was used,while TiAl_(3),TiAl,and Ti3Al formed in the reaction layer when CMT+P mode was used.Compared to using DC-CMT mode,more cracks occurred when using CMT+P.The nanohardness of the reaction layer was between that of the Al and Ti alloys,irrespective of the CMT modes.The average tensile strengths of the samples using DC-CMT and CMT+P mode were 108 MPa and 24 MPa,respectively.DC-CMT mode was more suitable for the wire and arc additive manufacturing of Ti/Al dissimilar alloys.

Metallurgical microstructure control in metal-silicon reactions

A comprehensive review on interfacial reactions to form silicides between metal and Si nanowire or wafer is given.Formation of silicide contacts on Si wafers or Si nanowires is a building block needed in making current-based Si devices.Thus,the microstructure control of silicide formation on the basis of kinetics of nucleation and growth has relevant applications in microelectronic technology.Repeating events of homogeneous nucleation of epitaxial silicides of Ni and Co on Si in atomic layer reaction is presented.The chemical effort on intrinsic diffusivities in diffusion-controlled layer-typed intermetallic compound growth of Ni2Si is analyzed.

Growth kinetics of interfacial reaction layer products between cubic boron nitride and Cu-Sn-Ti active filler metal

In the present investigation,the growth kinetics of interfacial reaction layer products between cubic boron nitride(CBN) and Cu-Sn-Ti filler metal has been thoroughly investigated.Detailed morphological and compositional features of respective compounds have been demonstrated for a wide brazing temperature ranging from 1153 K to 1223 K.It is found that within 30 minutes brazing holding time,the reaction layer growth is largely determined by the population of Ti N via effective Ti diffusion with an activation energy of 223.51 k J/mol,leading to parabolic growth patterns.It is further revealed that TiN grows both in axial and length dimensions,which eventually extends to the forefront and covers the reaction layer.

Effect of a chemical reaction on magnetohydrodynamic boundary layer flow of a Maxwell fluid over a stretching sheet with nanoparticles

The influences of the convective boundary condition and heat generation/absorption on magnetohydro- dynamic boundary layer flow of a Maxwell fluid over a stretching surface in the presence of nanoparticles have been numerically investigated. In the model, the physical mechanisms responsible for Brownian motion and thermophoresis with a chemical reaction are considered. Similarity equations are derived and then solved using the shooting method with the fourth-order Runge-Kutta integration scheme, The rates of heat and mass transfer are enhanced with a destructive chemical reaction and Blot number. The opposite influence is found with a generative chemical reaction in the presence of Brownian motion and the thermophoretic property.

Synthesis of Mg-Al-carbonate layered double hydroxide by an atom-economic reaction

A clean method for preparing layered double hydroxides （LDHs） has been developed, featured by using the hydroxides of two different metals as starting materials by atom-economic reactions. The reactions were carried out under hydrothermal conditions in either a high pressure autoclave or a microwave digester. The compositions, structural parameters and thermal behavior of the resulting LDHs are very similar to those of materials produced by using the separate nucleation and aging steps （SNAS） method. The major advantage of the new method is that no by-product is produced, so that filtration and washing processes are unnecessary. The consequent reduction in water consumption is beneficial to the environment.

BiVO_4 semiconductor sensitized solar cells

Semiconductor sensitized solar cells(SSSCs) are promising candidates for the third generation of cost-effective photovoltaic solar cells and it is important to develop a group of robust, environment-friendly and visible-light-responsive semiconductor sensitizers. In this paper, we first synthesized bismuth vanadate(Bi VO4) quantum dots by employing facile successive ionic layer adsorption and reaction(SILAR) deposition technique, which we then used as a sensitizer for solar energy conversion. The preliminary optimised oxide SSSC showed an efficiency of 0.36%, nearly 2 orders of magnitude enhancement compared with bare Ti O2, due to the narrow bandgap absorption of Bi VO4 quantum dots and intimate contact with the oxide substrate. This result not only demonstrates a simple method to prepare Bi VO4 quantum dots based solar cells, but also provides important insights into the low bandgap oxide SSSCs.