氩弧反应熔覆TiC／Ni复合涂层的组织与性能研究

利用氩弧熔覆技术，以Ni60自熔合金粉、钛粉和石墨粉为原料，在45#钢表面原位反应合成了以TiC颗粒为增强相的Ni基复合涂层。利用金相、SEM、XRD等技术分析了涂层的显微组织，利用显微硬度仪测试了熔覆层显微硬度，用自制磨损试验机对比了熔覆层与淬火回火65Mn钢的耐磨性。结果表明，熔覆层成形良好，无裂纹、气孔等缺陷，与基体呈冶金结合；熔覆层的组织为γ—Ni奥氏体枝晶、CrB、TiB2、Cr23C6、Fe23C6及反应合成的弥散分布的球状TiC陶瓷颗粒；熔覆层显微硬度呈梯度分布，且越靠近基体表面，硬度越低；熔覆层具有优良的耐磨性能。     

原位自生TiCp／Ni60A复合涂层组织结构及长大特性

以Ni60A、钛粉和石墨粉为原料，采用高频感应熔覆技术，在16Mn钢表面原位合成了TiC颗粒增强镍基复合材料涂层。借助扫描电境、X射线衍射仪、显微硬度计对复合涂层的组织结构、TiC颗粒的生长方式和性能进行了分析。结果表明：TiC是由钛粉和石墨粉原位反应生成的，原位形成的TiC颗粒细小，分布均匀，平均尺寸为0．5～1μm。熔覆层与基体呈冶金结合，涂层无裂纹、无气孔等缺陷。熔覆层组织由TiC颗粒、γ—Ni奥氏体枝晶和枝晶间M23C6共晶组织组成。熔覆层中TiC颗粒的形状有2种，一种是规则形状的八面体，另一种是由微小的八面体TiC堆积而成的花瓣状。TiC颗粒的长大是由微小的八面体TiC颗粒堆积而成，以对角连接方式长大速度最快。涂层的维氏硬度可达9800MPa～10000MPa。     

激光熔覆原位合成TiC增强Fe基复合层组织研究

在45钢表面激光熔覆原位合成TiC颗粒增强Fe基复合涂层。利用扫描电镜、能谱仪和X射线衍射仪对TiC/Fe复合涂层的显微组织、合金成分以及物相进行分析,测试了熔覆层的显微硬度和耐磨性能。结果表明,当(Ti+C)的含量在复合粉末中的比例达到15%时,熔覆层生成了少量的TiC颗粒,其形状呈多面体和花瓣状,直径为1~5μm,长度为3~5μm,TiC增强相组织中含有Fe、Cr等元素,而不是单纯的二元碳化物。由于少量TiC颗粒的团聚现象,造成TiC激光熔覆层的显微硬度低于Fe基熔覆层,但TiC激光熔覆层磨损性能优于Fe基熔覆层。     

原位自生TiCp/Ni60A复合涂层组织结构及长大特性

以Ni60A、钛粉和石墨粉为原料,采用高频感应熔覆技术,在16Mn钢表面原位合成了TiC颗粒增强镍基复合材料涂层.借助扫描电境、X射线衍射仪、显微硬度计对复合涂层的组织结构、TiC颗粒的生长方式和性能进行了分析.结果表明:TiC是由钛粉和石墨粉原位反应生成的,原位形成的TiC颗粒细小,分布均匀,平均尺寸为0.5～1 μm.熔覆层与基体呈冶金结合,涂层无裂纹、无气孔等缺陷.熔覆层组织由TiC颗粒、γ-Ni奥氏体枝晶和枝晶间M23C6共晶组织组成.熔覆层中TiC颗粒的形状有2种,一种是规则形状的八面体,另一种是由微小的八面体TiC堆积而成的花瓣状.TiC颗粒的长大是由微小的八面体TiC颗粒堆积而成,以对角连接方式长大速度最快.涂层的维氏硬度可达9800MPa～10000 MPa.     

等离子熔覆原位合成TiC陶瓷颗粒增强复合涂层的组织与性能

利用等离子熔覆技术,在廉价的碳钢表面原位合成了TiC/Ni基复合材料涂层.借助金相显微镜、扫描电镜、X射线衍射仪、显微硬度计对复合涂层的组织、结构、性能进行了测试.结果表明:当Ti C含量为10%～20%时,熔覆层成形良好,与基体呈冶金结合,无裂纹、气孔等缺陷;熔覆层的组织为γ-Ni枝晶、M23C6、CrB及原位合成的TiC陶瓷颗粒,TiC大部分呈球状,少量呈方块状,尺寸为1～2 μm,靠近熔覆层底部的TiC颗粒比近表层的为小,均弥散分布于熔覆层中;熔覆层显微硬度达HV0.1 1000,是碳钢基体的4倍.     

激光熔覆原位自生TiC颗粒增强Ni基复合涂层的组织与性能

采用激光熔覆技术在H13钢表面制备出原位自生TiC颗粒增强Ni基复合涂层,利用扫描电镜、能谱仪和X射线衍射仪对熔覆层组织、成分和物相进行了分析,并测试了熔覆层显微硬度和耐磨性能.结果表明,激光熔覆层与基体呈良好的冶金结合,涂层中无裂纹、气孔等缺陷.涂层组织由γ-Ni、Cr7C3和TiC等相组成,原位自生TiC颗粒多呈菱形,尺寸在1～3μm之间,涂层显微硬度(800～1000 HV0.2)明显高于基体的显微硬度(300 HV0.2).激光熔覆层中存在颗粒强化和细晶强化等多种强化作用,显著提高了H13钢的耐磨性能.     

氩弧反应熔覆TiC/Ni复合涂层的组织与性能研究

利用氩弧熔覆技术,以Ni60自熔合金粉、钛粉和石墨粉为原料,在45增强相的Ni基复合涂层.利用金相、SEM、XRD等技术分析了涂层的显微组织,利用显微硬度仪测试了熔覆层显微硬度,用自制磨损试验机对比了熔覆层与淬火回火65Mn钢的耐磨性.结果表明,熔覆层成形良好,无裂纹、气孔等缺陷,与基体呈冶金结合;熔覆层的组织为γ-Ni奥氏体枝晶、CrB、TiB2、Cr23C6、Fe23C6及反应合成的弥散分布的球状TiC陶瓷颗粒;熔覆层显微硬度呈梯度分布,且越靠近基体表面,硬度越低;熔覆层具有优良的耐磨性能.     

Q235钢表面氩弧熔覆TiC复合涂层的组织与性能

以Ti粉、C粉、Fe粉为原料,利用氩弧熔覆技术在Q235钢表面原位合成了TiC增强Fe基复合涂层,分析了涂层的显微组织和物相,测定了涂层的硬度。结果表明:复合涂层与基体界面无气孔、裂纹,呈冶金结合;熔覆层组织由树枝晶、等轴晶组成,TiC主要分布于晶粒内和晶界处;涂层显微硬度随TiC含量的增加而增大。     

Ni对钛合金表面稀土激光熔覆层中TiC生长的影响

利用同步送粉激光熔覆技术,在Ti811钛合金表面激光熔覆原位合成了TiC和TiB_2颗粒增强镍基复合涂层。利用X射线衍射仪(XRD)、扫描电镜(SEM)、能谱分析仪(EDS)分析了熔覆层的显微组织和物相组成,利用显微硬度计测试了熔覆层的显微硬度。试验结果表明,激光熔覆涂层与基体呈冶金结合,涂层的物相主要由α-Ti、TiC、Ti_2Ni和TiB_2组成,其中TiC呈树枝晶状和花瓣状,TiB_2呈长条状。平衡状态下TiC以正八面体晶体结构存在,但熔体中存在的Ni元素会影响TiC平衡状态,使其最终呈现六边形形貌。稀土氧化物Y_2O_3的加入有利于促进晶粒细化,提高熔覆层组织均匀性及表面硬度。熔覆层的显微硬度显著提高,最高硬度为900HV0.5左右,约为基底硬度的2.25倍。     

氩弧熔覆Fe基复合涂层的组织与性能

利用氩弧熔覆技术,以Ti粉、C粉、Fe粉为原料在Q235钢基体表面上原位合成高硬度复合涂层.采用金相显微镜观察分析涂层显微组织,利用洛氏硬度仪测试熔覆层的硬度.结果表明:熔覆层组织由树枝晶、等轴晶组成,TiC主要分布于晶粒内和晶界处,涂层显微硬度随TiC含量的增加而增大.     

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).     

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.     

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.     

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.