微量La对6061合金显微组织及时效硬化行为的影响

采用洛氏硬度计(HRF)对稀土6061合金及其基体合金材料的时效硬化动力学曲线进行了研究.采用差示扫描量热仪(DSC)研究稀土6061合金及其基体合金材料的时效析出序列,采用金相显微镜观察了稀土6061合金及其基体合金材料的显微组织.结果表明:稀土元素La显著改变6061合金显微组织,明显加速6061铝合金的时效硬化过程,且对6061铝合金具有明显的细化及强化作用.     

合金化及热处理对汽车用6061铝合金组织与性能的影响

采用Cr和Mn微合金化的方法,考察了元素添加量对汽车用6061铝合金抗拉强度和布氏硬度的影响,并优化了合金的固溶时效热处理工艺。结果表明,6061合金的Cr和Mn的最佳添加量分别为0.15%和0.2%;添加0.15%Cr+0.2%Mn后,合金的最佳时效工艺为180℃×6 h;固溶+时效热处理后合金的抗拉强度和布氏硬度明显提高,而塑性有所降低。     

高强高弹Cu-Ti-(Cr)合金时效行为研究

以Cu-3Ti合金为研究对象,系统地研究了不同时效条件下合金组织演变及性能的差异,以此探讨了Cu-3Ti的最佳时效工艺。此外,通过添加Cr元素,探究了Cr元素对合金组织及性能的影响,并进一步研究了不同变形量下形变Cu-Ti-Cr合金的时效行为。结果表明:添加Cr元素可以减缓调幅分解进程,延迟不连续沉淀形核长大过程。虽然Cu-3Ti-0.5Cr合金在固溶状态下硬度与电导率均落后于Cu-3Ti,但在90%轧制和450℃时效12h后,硬度高于Cu-3Ti,电导率也未出现大幅下降。     

长期时效条件下Cr、Mo、W对DD98M合金铸态组织与性能的影响

基于团簇加连接原子模型和镍基高温合金理想成分式,对DD98M合金进行成分解析和再设计,降低Cr/Mo/W元素含量,得到DD98MC合金。利用真空感应熔炼制备两种合金的母合金,并进行固溶时效和1273k下的长期时效。采用X射线衍射(XRD)、扫描电镜(SEM)、电子探针(EPMA)等测试方法对两种合金时效后的铸态组织进行研究,分析高温长期时效和Cr/Mo/W对合金铸态组织和性能的影响规律。结果表明,长期时效会引起γ"相的部分分解,促进元素扩散,加剧元素偏析。随长期时效时间的延长,γ"相粗化长大乃至出现筏化,硬度降低,错配度绝对值减小,γ"相立方度降低。随Cr/Mo/W元素含量降低,错配度绝对值减小,γ"相立方度降低,硬度降低。DD98M合金长期时效出现了γ"相筏化,在晶界和晶内有粗大的γ"相形成和大量的σ相析出。 DD98MC合金长期时效只在晶界处有σ相和MC型碳化物析出。与DD98M相比DD98MC有更好的组织稳定性和机械性能。     

直流电流下时效对Cu-0.86Cr合金力学性能的影响

采用固溶+冷变形+有无直流电流下时效工艺制备了Cu-0.86Cr合金试样,研究了直流电流下时效对Cu-0.86Cr合金微观组织和力学性能的影响.结果表明,直流电流使合金时效后抗拉强度达到最大值所需的时效时间较短,并使抗拉强度极值降低,较无电流时低28MPa.同时直流电流改善了合金的塑性.组织观察表明,在时效过程中Cu-0.86Cr合金主要发生了回复.     

不同固溶处理对Cu-Cr系合金组织和性能的影响

热处理工艺调控是提升Cu-Cr系合金性能的有效方法。Cu-Cr系合金的固溶工艺大多选择温度较低的Cu-Cr两相区进行,导致Cr相固溶程度不完全,抑制后续析出强化效果。本研究提出采用高温单相区固溶工艺改善析出强化效果,主要研究不同固溶工艺(Cu-Cr两相区(950℃,4 h)和Cu单相区(1050℃,6h))对Cu-Cr系合金组织和性能的影响。采用电子探针(EPMA)对两种固溶工艺后的元素分布进行表征,并对峰值时效态合金的微观结构采用XRD和TEM进行表征分析。结果表明：与两相区固溶相比,单相区固溶后铸态Cr相充分固溶,时效过程中更多纳米Cr相弥散析出;合金力学性能相比两相区固溶后峰值时效态有较大提升,其中屈服强度提升29.3%,抗拉强度提升25.6%,而导电率并未明显下降。强度理论计算结果表明,析出强化所贡献的屈服强度增量为323.4 MPa,贡献56.9%,析出强化是本研究中最主要的强化机制。     

高密度钨合金的研究现状与发展趋势

从合金材质与添加元素、粉末制备与改性、合金烧结及烧结后处理,大变形强化处理等方面论述了高密度钨合金的研究现状和发展趋势。高密度钨合金中添加合金元素(如Co、Mn、Cr、Ta、La、Ce、Y)用以强化合金;采用新型烧结技术(如微波烧结、放电等离子烧结)以实现低温快速烧结;采用冷等静压、热压、热等静压等工艺方法以制备大尺寸的复杂零部件;采用喷射沉积,CVD涂层、电镀等方法来制取耐磨、耐腐蚀钨合金材料,是目前制备高密度钨合金的研究方向。     

Cu-Cr-Fe合金的时效析出行为

采用真空熔炼方法制备了Cu-0.32Cr-1.82Fe、Cu-0.33Cr和Cu-1.87Fe合金,随后分别进行了固溶-时效和固溶-冷变形-时效处理.采用XRD物相分析、点阵参数测量、硬度和电导率测试等手段,研究了合金在不同热处理状态下的时效行为.结果表明,同时添加Cr、Fe元素能够显著提高合金硬度,但对导电性能影响不大.Cu-0.32Cr-1.82Fe合金经1 000℃×2 h固溶处理、80%变形,在480℃时效60 min后其硬度(HV)和电导率分别可达215和31.9 MS/m.     

Cr对标准阴极铜组织与力学性能的影响

在大气环境下采用普通中频感应电炉熔炼制备了Cu-Cr合金,研究了铬对标准阴极铜组.织与力学性能的影响,Cr的加入量分别为0.30%、0.5 3%、0.76%和0.99%.结果表明,在本实验条件下,Cr可以有效地加入到Cu液中.铸态及固溶时效Cu-Cr合金中只存在α-Cu相与Cr相.铸态时部分Cr溶于基体中,部分Cr以第二相形式存在;固溶时效后基体中可分解析出更多弥散分布的Cr相.Cr元素对纯铜有强化作用,合金的铸态和热处理态试样的拉伸强度及硬度均随Cr元素加入量的增大而增加.固溶时效热处理能有效提高铸态Cu-Cr合金的力学性能.     

直流电流下Cu-0.33Cr-0.06Zr合金的时效动力学

采用固溶+冷变形+不同直流电流密度下的时效工艺制备了Cu-0.33Cr-0.06Zr(质量分数,下同)合金试样。进行了450℃下不同时效时间及不同电流密度的时效试验,研究了时效电流和时间对Cu-0.33Cr-0.06Zr合金导电性能的影响。采用透射电镜观察时效合金组织,探讨了不同电流密度下该合金的时效析出动力学。结果表明,合金在电流密度为100A/cm2的直流电流下时效,电导率低于无电流时效的;而在电流密度为400 A/cm2下时效2h后,电导率达到49.5MS/m,接近峰值,高于无电流时效的。时效后合金析出Cr相和CuZr3相,通过对电导率与析出相体积分数关系的分析,确定了合金在不同温度下时效的相变动力学Avrami经验方程和电导率方程。     

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.