Boundary trend of α1/(α1 +α2) phase region at lower Cu side in Al-Zn-Cu system

The range of miscibility gap above 300 ℃ at low Cu side in Al-Cu-Zn ternary system was obtained by EPMA of the designed alloys and diffusion-couples treated for equilibrium. The results about the boundary trend of the α1 / (α1 α2 ) phase region was obtained. The α1 / (α1 α2 ) boundary moves towards the lower Zn side with the increase of Cu content. The results are opposite to traditional phase diagrams obtained by experiments, but consistent with recent thermodynamic calculations.     

PHASE BOUNDARY OF α_2 PRECIPITATION IN Ti-Al-La TERNARY SYSTEM

The phase boundary,of α_2 precipitation at 600℃ in Ti-AI-La ternary system has been de-termined by TEM examination,which shows three kinds of phase regions,namely thesingle α phase region,the transitional phase region where there is superlattice reflection butno α_2 precipitation,and the α+α_2 region.A point of maximum aluminium content was foundto exist on the α/(α+α_2)boundary and the track of the boundary was explained in terms ofthe internal oxidation of lanthanum and the electron concentration rule for α_2 formation.     

Investigation on process and microstructure of Ti/Ni/Cu joints by electron beam welding

In this article, the electron beam welding of the Cu alloy （ QCrO. 8） with Ti alloy （TC4） sheet was processed and the joint microstructure as well as the welding process were studied. The results show that brittle reaction layer which was mainly composed of TiCu, Ti2Cu, Ti2Cu3 and TiCu2formed at the weld fusion line, regardless of welding on the middle or on the Cu side. The mechanical properties of the joint were severely deteriorated by the layer that tensile strength was only 89. 4 MPa for welding on the Cu side. The microstructure of the joint was improved with pure nickel as filler metal for the electron beam welding. The weld was mainly composed of solid solution. Intermetallic compound phase decreased signifwantly in fusion line compared with the joint without filler metal. The mechanical properties of the joint were obviously improved that the average tensile strength was 205.2 MPa and the bending strength was 413.3 MPa with O. 5 mm offset of electron beam on the Cu side.     

Improvement in the Oxidation Resistance of Tungsten by Sol-Gel Derived Al2O3 Coating

An Al2O3 coating was prepared from aluminum isopropoxide as precursor on tungsten substrate.The dependences of crystalline and phase in Al2O3 coating on temperature were studied.The results show the coatings being compact,uniform and crack-free can be obtained by suitable experiment.The main phase of coating is α-Al2O3.Compared to the uncoated specimens,the ones with coatings synthesized by sol-gel process provide excellent oxidation resistance at high temperature.     

Thermodynamic analysis of β → α(α_2) phase transformation temperature in a Ti-Al-H alloy system

The T0 face equation of a Ti-Al-H alloy system was set up by the regular solution model,and the relationship between the β phase stabilizing parameter of hydrogen and the equilibrium phase compositions was attained.According to the T0 face equation and the thermodynamic parameters from literature,the effect of hydrogen on the β→α(α2) transformation temperature was evaluated.The calculated results were in a better consistence with the measured ones.     

Influence of aging modes on microstructure and mechanical properties of AZ80 magnesium alloy

The microstructure and mechanical properties of AZ80 magnesium alloy after solid solution and aging treatments were studied by using optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy(SEM) as well as tensile testing. The results indicated that β-Mg17Al12 phase was getting to distribute discontinuously along the grain boundary after treated at 395℃ ageing for 12 h followed by water-cooling, but it did not dissolve into α-Mg completely. The residual β-Mg17Al12 phase distributed along the grain boundary and had block-like or island shapes. The size of α-Mg was getting to be coarsening but not significantly. The β-Mg17Al12 precipitates appeared in discontinuous and continuous patterns from supersaturated α-Mg solid solution after aged at 200℃. The precipitation patterns were associated with the aging time essentially. The tensile strength and elongation of the alloy increased significantly but the hardness and yield strength decreased after solid solution treatment. However, with the prolonging of aging time, the hardness and strength of alloy increased while the ductility decreased.     

Relationship between microstructure and tensile properties on a near-β titanium alloy after multidirectional forging and heat treatment

In this study, a new near-beta titanium alloy, Ti-4Al-1Sn-2Zr-5Mo-8V-2.5Cr, was prepared by induction skull melting(ISM) and multidirectional forging. The effect of aging heat treatment on microstructure and tensile properties of the alloy after solution treatment in the twophase(α + β) region was investigated. The micros tructure results show that the globular primary α phase(α_p) and the needle-like secondary α phase(α_s) are precipitated in the β matrix. The size of α_s increases with the increase in aging temperature,while the content of α_s goes up to a peak value and then decreases. The tensile testing results show that the strength increases first and then decreases with the increase in temperature. The variation of ductility presents the opposite way compared with the trend of strength level.When aged at 500 ℃, the alloy exhibits an excellent balance of tensile strength(1529 MPa) and elongation(9.22%). And the relative mechanism of strengthening and toughening was analyzed and discussed.     

Phase diagrams of Li2MoO4-Na2MoO4 and Na2MoO4-K2MoO4 systems

The phase diagrams of the Li2MoO4-Na2MoO4 and Na2MoO4-K2MoO4 systems have been reassessed using differential thermal analysis together with high-temperature and room-temperature X-ray diffraction analysis. The results showed that the compound Li2MoO4.6Na2MoO4 did not exist; however, it confirmed the existence of the compound Li2MoO4.3Na2MoO4 in the Li2MoO4-Na2MoO4 systen＇ls. With regard to the system of Na2MoO4-K2MoO4, we could not confirm the results reported by Bukhanova who claimed that the system was eutectic type with 1：1 and 1：2 intermediate compounds, refuting the statement of Amadori who thought there was an apparent phase boundary at high temperature in α-solid solution region of the Na2MoO4-K2MoO4 binary system. The revised phase diagrams of these systems are illustrated in this article. These experimental results are in agreement with the computerized prediction using the support vector machine-atomic parameter method for the assessment of phase diagrams.     

Microstructure of Sm2Co17 magnets and its influence on coercivity

Sm(CobklFe0.197Cu0.049Zr0.026)7.5 magnet with Hci of 2105 kA/m and β18-200℃ of - 0.17 % /℃ was made by sintering processing. The magnet has uniform celluler structure. The cell interior is a rhombohedarl 2 : 17 phase,and the boundary is a hexagonal 1 : 5 phase. The average cell size is 93 nm and the cell boundary thickness is 20 nm.The cells are enriched in Fe, and the cell boundaries are enriched in Cu. More Cu-riched 1 : 5 cell boundary phase would be helpful to obtain a higher coercivity and lower temperature coefficient. White secondary phase mainly consisting of Sm can decrease the coercivity of the magnets, but the closely paralleled grooves can increase coercivity.     

Effects of nugget alloying on microstructures and properties of resistance spot welded joints of aluminum and steel

The resistance spot welding of 6063-716 aluminum alloy and l6 Mn steel was studied by nugget alloying.The results indicated that the Al-steel joint had characteristics of welding-brazing.The nugget zone consisted mainly of α-Al solid solution with dislocations and fine Mg_2Si particles.The interface zone had a double-layer structure:Fe_2Al_5 layer at steel side and Fe_4Al_(13) layer at Al nugget side.The nugget alloying has a significant effect on the joint properties by changing phase composition and refinement of grains.When alloy elements Cu,Zn,Ti and Ni were added,the tensile shear load of Al-steel joints reached 2 780 N,2 910 N,2 915 N and 2 929 N respectively,which increased by 24.1%,29.9%,30.1%and30.7%respectively compared with that(2 241 N) of joint without nugget alloying.Therefore,it is an effective way for improving mechanical properties of resistance spot welded Al-steel joints.     

Dependence of phase selection on cooling rates in as-cast A1-Si-Mg alloys

The effect of cooling rate on the solidification process of Al-2.06%Si-1.58%Mg was numerically and experimentally investigated. The solidification paths and the phase precipitation sequence were predicted based on the solute transportation analysis in the solidification process by coupling the thermodynamic calculation. Due to the different solute diffusion speeds, the solidification paths can be largely influenced by the cooling rates. Different phase precipitation sequences can be obtained through calculation under different cooling rates. And the later experiments have also proved this phenomenon. In the researched Al-2.06%Si-1.58%Mg alloy, the solidification sequences are α（Al）-α（Al）＋Si-α（Al）＋Mg2Si＋Si under low cooling rate and α（Al）- α（Al）＋Mg2Si-α（Al）＋Mg2Si＋Si under high cooling rate, respectively. The experimental results confirm the calculation predications.     

Effects of Treatment Temperature on the Microstructure and Magnetic Properties of Fe-N Thin Films

Fe-N thin films were fabricated on both 100Si and NaCl substrates by RF magnetron sputtering under low nitrogen partial pressure. The microstructure and magnetic properties of Fe-N thin films were investigated with the increase of the substrate temperature (Ts) and the annealing temperature (Ta). It is more difficult for nitrogen atoms to enter the Fe lattice under higher Ts above 150℃. The phase evolution is visible at higher Tα above 200℃. The phase transformation of α"-Fe16N2 occurred at 400℃. The change of crystal size with Ta was clearly visible from bright and dark field images.The clear high-resolution electron microscope (HREM) images of 110α, 111γ, 112α, and 200α,phases were observed. The interplanar distances from TEM (transmission electron microscope) and HREM match the calculated values very well. From the results of the vibrating sample magnetometer(VSM), the good magnetic properties of Fe-N films were obtained at 150℃ of Ts and 200℃ of Tα,respectively.     

SOLUBILITIES OF Ce,Nd AND Y IN α-Fe

The solubilities of Ce,Nd and Y in α-Fe at 873 to 1153 K have been deter mined by meansof electron microprobe quantitative analyses.The temperature dependences of the solubilitieswere obtained from the experimental data.The results have been compared with those deter-mined by three other technigues,very good agreement was obtained between the results of allthese techniques.     

Inelastic constitutive equation of plasma-sprayed ceramic thermal barrier coatings

Ceramic thermal barrier coatings (TBCs) are a very important technology for protecting the hot parts of gas turbines (GTs) from a high-temperature environment. The coating stress generated in the operation of GTs brings cracking and peeling damage to the TBCs. Thus, it is necessary to evaluate precisely such coating stress in a TBC system. We have obtained a stress-strain curve for a freestanding ceramic coat specimen peeled from a TBC coated substrate by conducting the bending test. The test results have revealed that the ceramic coating deforms nonlinearly with the applied loading. In this study, an inelastic constitutive equation for the ceramic thermal barrier coatings deposited by APS is developed. The obtained results are as follows: (1) the micromechanics-based constitutive equation was formulated with micro crack density formed at splat boundary, and (2) it was shown that the numerical results for a nonlinearly deformed beam simulated by the developed constitutive equation agreed with the experimental results obtained by cantilever bending tests.     

Effect of sigma phase precipitation on microstructure and properties of cast ZG0Cr26Ni5Mo3Cu3 duplex stainless steel under different heat treatments

ZG0Cr26Ni5Mo3Cu3 Duplex Stainless Steel(DSS) was solution treated at 1,060 ℃ for 3 h, followed by water cooling. Tempering treatments were conducted at 720, 750 and 780 ℃, respectively, for 16 h, followed by air cooling. The microstructures of ZG0Cr26Ni5Mo3Cu3 duplex stainless steel samples treated at different tempering temperatures were observed by scanning electron microscope(SEM) and energy dispersal spectroscopy(EDS), and the phase consitutions were analyzed using X-ray diffraction(XRD). The effects of the precipitation of sigma(σ) phase on the duplex phase percentage, hardness, impact toughness and corrosion resistance of the DSS were studied. Results showed that microstructures of ZG0Cr26Ni5Mo3Cu3 after solution treatment consists of ferrite(α) phase and austenite(γ) phase; after being tempered at different temperatures, σ phase appeared due to a eutectoid-type reaction of α→σ+γ2 during tempering treatment. It was observed that σ phase distributed along the grain boundary. The volume fraction of σ and γ phases increased with increasing tempering temperature in the range of 720 to 780 ℃, whereas the volume fraction of α phase showed the opposite trend. When the percentage of σ phase increased, the hardness of steel also increased. In the solution treated steel, hardness was measured to be only 244.0 HB, because σ phase did not appear. However, it increased to 391.8 HB when the DSS was tempered at 780℃because a great of deal of σ phase appeared. The impact toughness and corrosion resistance of DSS decreased when the percentage of σ phase increased.     

Deformation analysis of a friction stir-welded thin sheet aluminum alloy joint

The deformation characteristics of a friction stir welded thin sheet aluminum alloy joint were analyzed via numerical simulations.The simulated results were compared with the experimental results obtained for the deformation of actual welded joints.The results revealed that the deformation of the joint was described by an asymmetric distribution with a large deformation region occurring mainly in the advancing side.This asymmetric deformation was mainly caused by the direct mechanical force applied by the welding tool to the workpiece.Furthermore,the deformation characteristics of the fixed points on both sides of the weld revealed that the deformation of the retreating side fluctuated significantly during the welding process.That is,the retreating side exhibited less welding stability than the advancing side.The stress distribution of the welded joint showed that a high stress region was formed at the end of the weld.In addition,the final stress distribution of the welded joint resulted mainly from the shear stress in the x-y direction.     

Microstructures and hardness of Ti-6Al-4V alloy staging castings under centrifugal field

By means of induction melting technology, Ti-6A1-4V alloy staging casting was made with the same rotation velocity and centrifugal radius. The effects of casting modulus on the grain size, the thickness of lamellar α＋β phase, and the Vickers hardness, as well as the relationships between Vickers hardness, grain size and thickness of lamellar α＋β phase were investigated. The results show that the greater the modulus, the larger the grain size and the thickness of lamellar α＋β phase, and the less the Vickers hardness. The relationship between Vickers hardness and grain size meets the Hall-Petch equation： Hv=353.45＋74.17dG^-1/2. The relationship between the Vickers hardness and the thickness of lamellar α＋β phase is expressed as Hv=2.45d^2α＋β-35.96dα＋β ＋ 476.84.     

Phase fraction evolution in hot working of a two-phase titanium alloy: experiment and modeling

In the present work, the coupled effects of initial structure and processing parameters on microstructure of a two-phase titanium alloy were investigated to predict the microstructural evolution in multiple hot working. It is found that microstructure with different constituent phases can be obtained by regulating the initial structure and hot working conditions. The variation of deformation degree and cooling rate can change the morphology of the constituent phases, but do not alter the phase fraction. The phase transformation during heating and holding determines the phase fraction for a certain initial structure. β-α-βtransformation occurs during heating and holding.β to αtransformation leads to a significant increase in content and size of lamellar α. The α to β transformation occurs simultaneously in equiaxed α and lamellar α. The thickness of lamellar a increases with temperature, which is caused by the vanishing of fine α lamellae due to phase transformation and coarsening by termination migration. By assuming a quasi-equilibrium phase transformation in heating and holding,a modeling approach is proposed for predicting microstructural evolution. The three stages of phase transformation are modeled separately and combined to predict the variation of phase fraction with temperature.Model predictions agree well with the experimental results.     

Deformation mechanism at impact test of Al-11% Si alloy processed by equal-channel angular pressing with rotary die

Al-11%Si(mass fraction)alloy was transformed into a ductile material by equal-channel angular pressing(ECAP)with a rotary die.Two mechanisms at impact test,slip deformation by dislocation motion and grain boundary sliding,were discussed.The ultrafine grains with modified grain boundaries and the high content of fine particles(<1μm)were necessary for attaining high absorbed energy.The results contradict the condition of slip deformation by dislocation motion and coincide with that of grain boundary sliding.Many fine zigzag lines like a mosaic were observed on the side surface of the tested specimens.These observed lines may show grain boundaries appeared by the sliding of grains.     

Microstructure and interface fracture of LPPS Ni／Fe and Cu／Ni sprayed materials

The interfaces of two materials, Ni/Fe and Cu/Ni, deposited by low pressure plasma spraying method,were studied by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDS). The adhesion between coatings and substrates was measured with the aid of Knoop interfacial indentation testing method. The results show that the interfacial micrcstructures have strong influence on the mechanical properties. Cu/Ni interface is weak link with NiO amorphousphase. Ni/Fehave strong in-interracial layer consists primarily of Fe and Ni oxide crystalline phases, containing dispersive (Fe, Ni) spotlike intermetaUic compound phase in nanometer dimension, and the interracial interdiffusion was detected. The micro-mechanism of interracial fracture was discussed.