Mg17 Al12、Al2Ca、Al2Nd、Al2Er金属间化合物稳定性与电子结构的第一性原理研究

采用基于密度泛函理论的Castep程序软件包,优化了Mg17Al12、Al2Nd、Al2Er及Al2Ca相晶胞结构,计算了化合物的形成热、结合能和态密度等,分析了化合物结构稳定性与其电子结构的内在联系。结果表明:四种化合物的形成热和结合能均为负值,且化合物的合金化能力和结构稳定性强弱顺序依次为Al2Er、Al2Nd、Al2Ca、Mg17Al12。态密度结果表明: Al2Er和Al2Nd具有较强结构稳定性的主要原因是（1）在费米面低能级区Al(3p)轨道分别与Nd(4f)、(5d)和 Er(4f)、(5d)轨道价电子发生强烈杂化作用;（2）Al2Nd和Al2Er成键电子数较多;（3）这两种化合物的电子参与成键能力较大。电荷密度结果表明：Mg17Al12、Al2Ca、Al2Nd、Al2Er中均存在金属键、离子键、共价键,四种化合物中Al2Er、Al2Nd共价键较强,Al2Ca离子键最强,Mg17Al12中以较强的金属键为主。     

Mg17Al12、Al2Y及Al2Ca相稳定性与弹性性能第一原理研究

采用基于密度泛函理论的Castep和Dmol程序软件包,计算了Mg17Al12、Al2Y及Al2Ca相的结构稳定性、弹性性能与电子结构。形成热和结合能计算结果表明:Al2Y具有最强的合金化形成能力和结构稳定性;热力学性质计算结果表明:在298~573 K温度范围内,Al2Y的Gibbs自由能始终最小,其结构热稳定性最好,Al2Ca次之,Mg17Al12最差,Y和Ca合金化Mg-Al系合金形成Al2Y及Al2Ca利于提高镁合金的高温抗蠕变性能;弹性常数的计算结果表明:3种金属间化合物均为脆性相,Mg17Al12的塑性最好;采用弹性常数计算结果预测的Al2Y熔点最高,其结构热稳定性最好。态密度和Mulliken电子占据数的计算结果表明:Al2Y结构最稳定的原因,主要源于体系在Fermi能级以下区域成键电子存在强烈的共价键作用。     

Ca、Sr和Ba掺杂Mg_2Si弹性性能和电子结构的第一性原理研究

采用第一性原理平面波赝势方法研究了合金元素X(X=Ca、Sr、Ba)掺杂Mg2Si的占位情况:(1)取代Mg原子位置;(2)取代Si原子位置;(3)间隙固溶到Mg2Si晶胞中。分析合金系Mg7Si4X,Mg8Si3X,Mg8Si4X的形成热和结合能可知,Mg7Si4X的形成热和结合能均为负值,且最小。表明Mg7Si4X更容易形成稳定化合物,具有较强的合金化能力,且Ca,Sr,Ba掺杂Mg2Si时有优先占据Mg原子的倾向。研究Mg7Si4X的弹性模量和电子结构发现:Mg7Si4Ca、Mg7Si4Sr为脆性相;Mg7Si4Ba为延性相,塑性最好;掺杂Ca,Sr,Ba使Mg2Si逐渐由脆性向韧性转变。Ca,Sr,Ba的掺入均使Mg2Si的电子态密度发生偏移,费米能级处的电荷密度增加,导电性增强,共价键作用减弱,合金系结构稳定性减弱。     

Mg_(17)Al_(12)、Al_2Ca、Al_2Nd、Al_2Er金属间化合物稳定性与电子结构关系的第一性原理研究

采用基于密度泛函理论的Castep程序软件包,优化了Mg_(17)Al_(12)、Al_2Nd、Al_2Er及Al_2Ca等相的晶胞结构,计算了化合物的形成热、结合能和态密度等,分析了化合物结构稳定性与其电子结构的内在联系。结果表明:4种化合物的形成热和结合能均为负值,且化合物的合金化能力和结构稳定性强弱顺序依次为Al_2Er、Al_2Nd、Al_2Ca、Mg_(17)Al_(12)。态密度结果表明,Al_2Er和Al_2Nd具有较强结构稳定性的主要原因是:(1)在费米面低能级区,Al 3p轨道分别与Nd 4f、5d和Er 4f、5d轨道价电子发生强烈杂化作用;(2)Al_2Nd和Al_2Er成键电子数较多;(3)这_2种化合物的电子参与成键能力较大。电荷密度结果表明:Mg_(17)Al_(12)、Al_2Ca、Al_2Nd和Al_2Er中均存在金属键、离子键、共价键,4种化合物中Al_2Er、Al_2Nd共价键较强,Al_2Ca离子键最强,Mg_(17)Al_(12)中以较强的金属键为主。     

Mg17Al12相Ca合金化结构稳定性的第一原理研究

采用第一原理赝势平面波方法,计算了Mg17Al12相Ca合金化前后的能态与电子结构.计算结果显示:当Ca分别置换Mg17Al12相中Mg(Ⅰ)、Mg(Ⅱ)和Mg(Ⅲ)原子时,(Mg17-xCax)Al12相(x=0,1,4,12)的负生成热逐渐升高、结合能逐渐增大,表明Ca置换Mg17Al12相中Mg(Ⅲ)原子时其Ca合金化能力最强,合金化后形成的(Mg5Ca12)Al12相结构稳定性最高.电子态密度(DOS)分析结果表明:Ca合金化后Mg17Al12相结构稳定性升高的主要原因是由于合金化后来自Al(p)和Ca(s)的价电子使其在低能区的成键电子数增多.     

3103铝基PS版析出相的第一性原理研究

采用基于密度函数理论(DFT)的全势线性缀加平面波(FPLAPW)的方法,结合JMat Pro软件,研究了3103铝合金PS版凝固过程中的析出相与基体间费米能级差异及其弹性性质等。结果表明:在3103铝基PS版中除α-Al之外,存在的析出相主要有α-Al(Fe,Si)、Al_6Mn、Al_(18)Cr_2Mg_3、Mg_2Si、Al_3Ti,Al_3Zr、Al_2Cu以及Mg Zn_2相;其中Mg_2Si电极电位与Al基体相差最大,最易与基体形成微腐蚀电池,使PS版的耐腐蚀性下降。通过计算各个相的形成热及结合能,表明除α-Al(Fe,Si)相之外,各个相的形成均为放热过程且Al_3Ti、Al_3Zr相结合能最大,结构最稳定。     

Sn合金化MgZn_2相及Mg_2Sn相结构稳定性的第一原理研究

采用基于密度泛函理论CASTEP和DMol程序软件包,从合金形成热、结合能、热力学性能和电子结构等方面,研究Sn合金化MgZn2相及Mg2Sn相的结构稳定性,探讨Sn合金化改善ZA62镁合金抗蠕变性能的机理。结果表明:当Sn和Al分别置换ZA62镁合金中MgZn2相的Zn(Ⅰ)和Zn(II)原子时,仅Sn与Al置换的MgZn2相中Zn(Ⅰ)原子能形成稳定的MgZn2固溶体结构,而Sn在MgZn2相中的固溶量有限;与合金化形成的固溶体结构相比,其稳定性比未合金化时的弱,而析出的第二相金属间化合物Mg2Sn的结构比MgZn2的更稳定。而不同温度下热力学性能的计算结果表明:合金体系中形成了结构稳定性强的Mg2Sn,其结构稳定性在温度373～473K的范围内并不因温度的升高而消失,仍比MgZn2的高;由于ZA62镁合金体系中形成了高热稳定性的Mg2Sn相,Sn合金化有利于ZA62镁合金抗蠕变性能的提高。电子态密度和Mulliken电子占据数的分析结果表明:与MgZn2、Mg2AlZn3及Mg2SnZn3固溶体相比,热稳定性强的Mg2Sn相形成的主要原因在于Mg2Sn体系中存在强烈的离子键与共价键的共同作用。     

Al_2Sr和Mg2sr相结构稳定性与弹性性能的第一原理计算

采用基于密度泛函理论的CASTEP和DMOL程序软件包,计算了Mg_(17)Al_(12),Al_2Sr和Mg_2Sr柏的结构稳定性、弹性性能和电子结构.合金形成热和结合能的计算结果显示,Al_2Sr具有最强的合金化形成能力和结构稳定性.Gibbs自由能的计算结果表明,随着温度的升高,Mg_(17)Al_(12),Al_2Sr和Mg_2Sr的结构稳定性发生了变化,在实际工作温度高于423 K以上时,Al_2Sr的结构稳定性最好,Sr合金化Mg-Al基合金形成Al_2Sr有利于提高镁合金的高温抗蠕变性能.体模量(B)、弹性各向异性系数(A)、Young's模量(E)、剪切模量(G)和Poisson比(v)的计算结果表明,Mg2Sr为延性相,而Mg_(17)Al_(12)和Al_2Sr为脆性相,Mg_2Sr的塑性最好.态密度和Mulliken电子占据数的计算结果表明,Al_2Sr结构最稳定的原因主要源于体系存在强烈的共价键作用,而Mg_(17)Al_(12)结构隐定性优于Mg_2Sr是体系中离子键与共价键共同作用的结果.     

Ta合金化对γ′-Ni3Al相弹性性质与电子结构的影响

基于密度泛函理论,采用第一性原理赝势平面波方法计算了合金元素Ta掺杂对y’-Ni3Al相弹性常数与电子结构的影响.计算结果表明:Ta的加入能有效提高Ni3Al相的弹性性质,使其弹性模量提高12.86％,形成的Ni3(Al,Ta)金属间化合物是一种塑性相,但其本征脆性要比Ni3Al大;使用总化学键的重叠布居,定量地计算了金属间化合物的共价键性能,结果显示Ta的添加能增加Ni3Al相共价键的强度;价电荷密度及态密度的进一步分析指出:Ni3(Al,Ta)相中化学键有方向共价键和金属键共存的特征.     

MgCu2,Mg2Ca和MgZn2 Laves相力学性质和电子结构的第一性原理计算

通过基于密度泛函理论的第一性原理计算方法,对MgCu2,Mg2Ca和MgZn2的力学性能和电子结构进行计算,计算所得晶格参数与实验值和文献值相吻合。合金形成热和结合能的计算结果表明,MgCu2具有最强的合金形成能力和结构稳定性。计算了MgCu2,Mg2Ca和MgZn2的弹性常数,推导了体模量、剪切模量、弹性模量和泊松比。结果表明,MgCu2、Mg2Ca和MgZn2均为延性相,MgCu2的刚度最大,MgZn2的塑性最好。通过对结合能和弹性常数的计算,预测了MgCu2、Mg2Ca和MgZn2的熔点。通过对态密度（DOS）、Mulliken布居数、电子占据数和差分电荷密度的计算,分析了MgCu2、Mg2Ca和MgZn2的结构稳定性和力学性能机制。最后,计算和讨论了3种金属间化合物的Debye温度。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.