激光沉积修复DZ125合金的组织与摩擦磨损性能

在DZ125高温合金铸造基体上进行激光沉积修复实验,研究了激光沉积修复显微组织、硬度及摩擦磨损性能。结果表明:沉积区底部为宽度约8μm的平面晶、沿沉积高度方向外延生长排列紧密的柱状晶,中部为树枝晶,顶部为杂乱无章的等轴晶;沉积区层与层交界处γ'相尺寸大于层内,晶界处γ'相尺寸大于晶内;γ+γ'共晶相和MC碳化物明显沿晶界分布,沉积区中下部多为短棒状MC碳化物,沉积区顶部多现小块状以及八面体状MC碳化物。基体HV_(0.3)显微硬度为4.1～4.2 GPa,沉积区显微硬度高于基体,为4.55～4.75 GPa。沉积区磨损机理主要是轻微的磨粒磨损,耐磨性能优于基体。     

激光沉积修复单道多层DZ125双级时效热处理组织与性能

通过在DZ125铸造基体上沿纵向进行激光沉积单道多层实验,分析了DZ125沉积态与双级时效热处理试样的组织和性能。结果表明：沉积态修复区组织从底部到顶部分别为平面晶、柱状晶和等轴晶组织,修复区主要为MC碳化物,热影响区因热量的输入,MC分解为M₂₃C₆；与沉积态组织相比,双级时效热处理后,修复区组织形成了新的晶界,部分MC碳化物分解为M₆C与M₂₃C₆,γ＇相尺寸略有增大,约为600-800nm,分布均匀；热影响区碳化物尺寸略有减小,γ′相尺寸增大,呈立方体形状；双级时效热处理修复试样在1000℃下的抗拉强度为516MPa、屈服强度为386MPa,分别达到铸件的89.7％和97.7％,延伸率为13.6%,达到铸件的43.9%；热处理后修复试样的平均硬度为473HV0.3,高于沉积态试样平均硬度433HV0.3,且热处理态与沉积态试样沿修复区、热影响区到基体硬度呈降低趋势。     

激光成形修复Inconel 625合金的工艺特性和组织研究

对激光成形修复Inconel 625合金的工艺特性以及不同区域的组织进行了研究。结果表明:激光成形修复Inconed625合金的工艺范围较宽;激光功率主要影响单道修复层的宽度;扫描速度对单道修复层的尺寸影响较为显著,而送粉率的影响较小。基材的相组成包括γ(Ni-Cr)基体相、大尺寸(约10μm)块状MC型碳化物(M为Nb和Ti)、沿晶界析出的小尺寸(约0.5μm)块状MC型碳化物以及不规则形状的Laves相。修复区组织为呈外延生长的柱状枝晶,相组成为γ基体相、沿枝晶界析出的Laves相以及少量MC型碳化物。层与层界面处Laves相析出急剧增加形成层间过渡区。     

单晶合金激光增材修复接头组织和性能研究

采用激光熔化沉积技术对DD6单晶高温合金进行修复,利用光学显微镜、扫描电镜和显微硬度仪对单晶母材和增材修复接头的组织特征和力学性能进行对比研究。结果表明：激光熔化沉积修复组织为外延生长的定向凝固柱状晶组织,由γ相基体和少量晶间MC型碳化物组成;DD6单晶合金基体热影响区微观形貌和物相组成与母材相似,但其γ′相的尺寸（≤0.2μm）更小,且γ′/γ的比例明显降低。经激光熔化沉积修复后,增材修复区的显微硬度可达450～470 HV,显著高于DD6单晶基体,具有更优异的耐磨损性能。     

激光立体成形K465高温合金的组织研究

采用激光立体成形技术制备了K465镍基高温合金试样,研究了晶粒、γ′强化相及碳化物等组织的特征及演化规律。结果表明:试样中心区域内晶粒粗大,顶部边缘区域晶粒细小;试样内枝晶呈现明显的沿沉积方向外延生长特点,在接近试样底部的部分,熔覆层顶部由于重熔不完全而出现转向枝晶区;熔覆层交界处的γ′相尺寸略大于层内的γ′相,枝晶间的γ′相尺寸略大于枝晶干上的γ′相;MC碳化物呈现多种形貌,底部存在分叉发达的花瓣状MC碳化物,中部有较多短棒状MC碳化物,顶部存在棒状和八面体状的MC碳化物。     

激光成形修复K418高温合金的显微组织与开裂行为

研究了激光成形修复航空发动机涡轮叶片用K418高温合金的组织特征与开裂行为。研究发现:K418合金激光修复区组织主要由γ-FeCr0.29Ni0.16C0.06固溶体基体、方形γ′相、枝晶间杆状或骨架状初生MC碳化物和骨架状(γ+MC)共晶组成。激光成形修复所用铸件基体中MC碳化物为TiC,呈块状分布在晶内和晶界;而激光修复区中MC碳化物为(NbTi)C,呈骨架状或杆状分布于枝晶间。从基体、热影响区到修复区,γ′相形貌、尺寸和数量呈现不同特征。修复区裂纹为与液膜有关的结晶裂纹,裂纹沿枝晶晶界扩展。通过试验优化,确定了较佳的激光成形修复K418合金的工艺参数,大大降低了其开裂倾向。     

激光沉积修复GH738合金时效热处理组织及性能研究

研究了双极时效热处理对激光沉积修复GH738合金显微组织及力学性能的影响。结果显示：沉积态显微组织为典型的外延柱状枝晶,枝晶间距为约10 μm。经过时效处理后,修复区组织开始长大、合并。沉积态未发现γ＇相,枝晶间存在立方状的MC型碳化物,枝晶干存在颗粒状M23C6型碳化物。经双级时效处理后,修复区析出γ＇相：稳定化温度为820℃时,γ＇相平均尺寸约为37nm,碳化物在晶界处呈断续状析出。随着稳定化温度升高,γ＇相及碳化物尺寸均有所增大,其中稳定化温度为840 ℃时,γ＇相平均尺寸约为76 nm,碳化物呈项链状析出;稳定化温度为860℃时,γ＇相平均尺寸无明显增大,部分γ＇相发生明显粗化,尺寸达到150 nm,晶界处碳化物开始呈包膜状析出。力学性能测试结果显示：时效处理后试样抗拉强度明显提高,随着稳定化温度升高,抗拉强度先升高后降低,断后伸长率不断降低。     

热处理对激光沉积DZ125合金组织与摩擦磨损性能的影响

研究了不同热处理制度对激光沉积DZ125高温合金显微组织、硬度及摩擦磨损性能的影响规律。结果表明：沉积区枝晶形貌为外沿生长的柱状枝晶，平均一次枝晶间距约为10.8μm，经单级时效（870 ℃/20h，AC）和双级时效（1100 ℃/4h，AC to 870 ℃/20h，AC）热处理后，试样的枝晶形貌与沉积态差别不大，γ"相均发生粗化现象，且双级时效热处理后的γ"相粗化程度更高、尺寸分布更为均匀；双级时效热处理制度下，不同低温时效温度γ"相的平均尺寸和含量不同，其中 1100 ℃/4h，AC to 870 ℃/20h，AC制度下，γ"相的平均尺寸和含量最大；经单级时效和双级时效热处理后，碳化物中Ti元素含量均呈下降趋势；双级时效热处理后，析出两种形貌不规则的MC碳化物，分别为富含Cr、Co元素的M23C6型碳化物和富含W、Mo元素的M6C型碳化物；单级时效和双级时效热处理试样的磨损机理均为磨粒磨损，双级时效热处理试样的显微硬度及耐磨性能均优于单级时效。     

激光沉积修复GH738合金时效热处理组织及性能

研究了双极时效热处理对激光沉积修复GH738合金显微组织及力学性能的影响。结果显示:沉积态显微组织为典型的外延柱状枝晶,枝晶间距约为10μm。经过时效处理后,修复区组织开始长大、合并。沉积态未发现γ′相,枝晶间存在立方状的MC型碳化物,枝晶干存在颗粒状M_23C_6型碳化物。经双级时效处理后,修复区析出γ′相:稳定化温度为820℃时,γ′相平均尺寸约为37 nm,碳化物在晶界处呈断续状析出。随着稳定化温度升高,γ′相及碳化物尺寸均有所增大,其中稳定化温度为840℃时,γ′相平均尺寸约为76 nm,碳化物呈项链状析出;稳定化温度为860℃时,γ′相平均尺寸无明显增大,部分γ′相发生明显粗化,尺寸达到150 nm,晶界处碳化物开始呈包膜状析出。力学性能测试结果显示:时效处理后试样抗拉强度明显提高,随着稳定化温度升高,抗拉强度先升高后降低,断后伸长率不断降低。     

激光沉积修复GH536/GH738合金的组织及力学性能

采用GH536合金粉末对GH738合金损伤试样进行激光沉积修复试验研究,通过正交试验法优化工艺参数,得到较小熔深、无缺陷的修复试样;测试分析了修复试样的显微组织、室温拉伸性能及显微硬度。结果表明:合金修复区为外延生长的柱状晶组织,修复区边缘柱状晶取向较一致,修复区中心柱状晶出现一定角度转向;合金修复区枝晶干上主要为富含Mo、Cr的M6C碳化物,晶界处出现少量细小的M23C6碳化物。相比于基体,合金热影响区中γ′相数量减少并呈粗化趋势,MC碳化物发生分解。激光沉积修复试样室温抗拉强度为GH738锻件的66.5%,高于GH536锻件强度;断后伸长率分别低于GH738锻件及GH536锻件的;修复区域的显微硬度分别低于GH738基体的显微硬度,高于GH536锻件的显微硬度。     

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.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。