H13钢表面电火花沉积Nb涂层组织与性能研究

目的提高H13钢表面的力学性能和耐蚀性,延长模具的使用寿命。方法用Nb棒作为电极,氩气作为保护气体,通过电火花沉积技术在H13钢表面制备Nb沉积层。利用扫描电子显微镜分析沉积层的表面形貌、显微结构及磨痕形貌,利用X射线衍射仪分析沉积层的相组成,利用能谱仪分析沉积层的元素分布,采用显微硬度计和磨损试验机测试沉积层的显微硬度和耐磨性,采用电化学工作站对沉积层进行耐蚀性测试。结果 Nb电火花沉积层表面呈橘皮状,具有一定的粗糙度,主要由Fe_2Nb和Fe_(0.2)Nb_(0.8)等相组成。沉积层截面组织连续、致密,无明显缺陷,强化层内存在大量的微晶组织和非晶组织。Nb涂层与基体发生了元素的相互扩散和冶金结合的过程。沉积层显微硬度高达642HV,为基体的3.2倍。在同等磨损条件下,Nb沉积层磨损失重约为基体的1/3,磨痕较浅。沉积层在3.5%NaCl溶液中的电化学自腐蚀电位比基体提高了113 mV,自腐蚀电流密度显著降低。结论在H13钢表面电火花沉积Nb涂层,可有效提高其表面的显微硬度、耐磨性和耐蚀性,从而延长模具的使用寿命。     

沉积时间对AZ91D合金表面Ni-P-SiC复合镀层性能的影响

目的提高镁合金的耐蚀性和耐磨性。方法以AZ91D镁合金为基体,采用SiC颗粒质量浓度为3 g/L的Ni-P化学镀溶液,在其表面沉积不同时间,制备Ni-P-SiC复合镀层。通过扫描电子显微镜(SEM)、显微硬度测试、粗糙度仪、电化学腐蚀和磨损等试验来分析和评价Ni-P-SiC复合镀层的厚度、表面粗糙度、显微硬度、耐腐蚀性能和耐磨性能。结果 Ni-P-SiC复合镀层的厚度和表面粗糙度随沉积时间增加而增加,沉积时间为150 min时,镀层厚度可达53μm,表面粗糙度为2.5μm。沉积时间为120 min时,镀层的显微硬度最高,为641HV,此时复合镀层的耐蚀性和耐磨性最好,自腐蚀电位高达-0.73 V,腐蚀电流密度为0.78μA/cm~2,磨损体积最小,为1.04×10~(-3)mm~3。与AZ91D镁合金基体相比,沉积复合镀层后的样品更耐蚀,说明复合镀层有效改善了镁合金基体的耐蚀性。结论沉积时间对Ni-P-SiC复合镀层的性能有一定影响,在沉积时间为120 min时获得的复合镀层具有较好的耐蚀性和耐磨性。     

Cr颗粒对Ni-Graphene复合沉积层组织结构及性能的优化

目的电沉积技术制备Ni-Cr-Graphene复合沉积层,调查不同Cr颗粒浓度对复合沉积层组织结构及性能的优化影响。方法利用电沉积技术在镍铝青铜(NAB)表面制备出Ni-Cr-Graphene复合沉积层。采用X射线衍射仪(XRD)、扫描电镜(SEM)、能谱仪(EDS)与拉曼光谱仪(Raman),对复合沉积层的形貌、成分与组织结构(晶粒大小、结晶形状及结晶织构)进行表征,并采用显微硬度计与电化学工作站分别对沉积层的硬度及耐腐蚀性能进行调查。结果Graphene颗粒使得纯Ni沉积层中的Ni晶粒尺寸由175.3 nm减小到Ni-0Cr-4Graphene沉积层中的Ni晶粒尺寸60.5nm。随着Cr颗粒质量浓度进一步从0g/L增加到100 g/L,Ni-Cr-Graphene复合沉积层中的Cr质量分数从0%增加到23.8%,且Ni晶粒尺寸进一步减小到Ni-100Cr-4Graphene沉积层的29.1nm,Ni[200]结晶织构被消除。Graphene与Cr颗粒显著提高了Ni-CrGraphene复合沉积层的表面硬度,所有复合沉积层的显微硬度均高于纯Ni沉积层(260.1HV0.2),且在100 g/L Cr颗粒浓度下,沉积层平均显微硬度为489.8HV0.2。同时Graphene与Cr颗粒改善了Ni-Cr-Graphene复合沉积层在3.5%NaCl溶液中的耐腐蚀性能,在100 g/L Cr颗粒浓度下,复合沉积层的自腐蚀电位(Ecorr)为-0.21 V,自腐蚀电流密度(Jcorr)为0.25μA/cm^2,其相对纯Ni沉积层Jcorr(7.01μA/cm^2)降低了1个数量级。结论溶液中Cr颗粒浓度的增加引起了Ni-Cr-Graphene复合沉积层中Cr含量的增加,使得更多Cr颗粒与Graphene颗粒共同作为Ni金属结晶形核点,促进了Ni的晶粒细化与织构转变,最终提高了复合沉积层的硬度与耐腐蚀性能。     

电沉积Ni/WC-Co纳米复合镀层制备及腐蚀性能研究

利用直流电沉积方法将WC-Co双纳米颗粒和Ni复合镀于黄铜基体,采用XRD和SEM表征复合镀层相组成和表面形貌,用显微硬度计测定其硬度并用电化学方法评估镀层的耐蚀性.结果表明,与纯Ni镀层相比,纳米复合镀层中Ni平均晶粒尺寸略有降低,约为18 nm;显微硬度提高58%,约为HV 500.在3.5%NaCl溶液中纯Ni镀层自腐蚀电流密度和自腐蚀电位分别为1.467μA/cm2和-0.179 V,纳米复合镀层则分别为8.369μA/cm2和-0.265 V.Ni/WC-Co纳米复合镀层的硬度显著提高,但其耐蚀性降低.     

石墨烯粒径对Ni-Co-石墨烯复合镀层性能的影响

为了得到性能优异的复合镀层,在镀液中添加不同粒径的石墨烯,采用复合电沉积技术,制备了Ni-Co-石墨烯复合镀层。表征了镀层的表面形貌、相结构、显微硬度、耐磨性和耐蚀性能,并同Ni-Co合金对比。结果显示,石墨烯很好地嵌入到了镀层中,而且石墨烯的存在并没有改变镀层基质的晶体结构;添加石墨烯提高了复合镀层的显微硬度(HV),最高可达8050 MPa;降低了复合镀层的摩擦系数,在一定程度上减少了粘着磨损的面积;复合镀层的自腐蚀电流密度为1.0905×10~(-5 )A/cm~2,低于Ni-Co合金镀层的自腐蚀电流密度1.8298×10~(-5 )A/cm~2。石墨烯的添加提高了复合镀层的硬度,耐磨性和耐蚀性。     

灭茬刀具刃口表面制备Ni-Co-TiN复合镀层的组织与性能

为了提升灭茬刀具的表面硬度及耐腐蚀性能,进而延长其使用寿命,文中采用超声辅助喷射电沉积法在灭茬刀具常用45钢表面制得Ni-Co-TiN复合镀层。通过正交试验方法,确定镀层制备的最优工艺参数。利用透射电镜(TEM)、扫描电镜(SEM)、X射线衍射仪(XRD)和能谱仪(EDS)测试镀层的微观结构、表面形貌、相结构及元素组成,并采用显微硬度计和电化学工作站对镀层显微硬度和耐腐性能进行测试。正交试验结果表明,Ni-Co-TiN复合镀层制备的最优工艺参数为：镀液喷射速度4 m/s,超声波功率120 W,TiN纳米粒子含量10 g/L,极间距8 mm。采用最优工艺参数制备的Ni-Co-TiN复合镀层,其镍晶粒尺寸得到明显细化,TiN粒子弥散分布于镀层中。该镀层的显微硬度高达489.82 HV,其自腐蚀电位为-0.342 V和自腐蚀电流密度为2.15×10-6 A/cm2。     

石墨烯颗粒对Ni-Co-石墨烯复合镀层的表面性能影响

为了得到性能更加优异全面的复合镀层,使用复合电沉积技术制备不同石墨烯颗粒大小的Ni-Co-石墨烯复合镀层,并制备了Ni-Co合金镀层。测试镀层的表面形貌,相结构,显微硬度,耐磨性和耐蚀性能。结果显示,石墨烯在电沉积中很好的嵌入到了镀层基质中,而且石墨烯的存在并没有改变镀层基质的晶体结构;石墨烯的填加增加了复合镀层的显微硬度,最高可达805HV;降低了复合镀层的摩擦系数,在一定程度上减少了粘着磨损的面积;复合镀层的自腐蚀电流密度可以降低到1.0905×10-5A/cm2,低于Ni-Co合金镀层的自腐蚀电流密度。说明了石墨烯的添加增强了复合镀层的硬度,耐磨性和耐蚀性。     

直流与脉冲电沉积Ni-Cr合金镀层的结构及耐蚀性

用直流电沉积(DC)、脉冲电沉积(PC)技术在低碳钢表面制备Ni-Cr合金镀层,采用X射线衍射(XRD)、扫描电镜(SEM)、原子力显微镜(AFM)等方法,研究了电沉积方式对合金镀层晶粒结构和表面形貌的影响;用浸泡法和电化学极化法测试了合金镀层在3.5%(质量分数)Na Cl溶液中的耐蚀性。结果表明,电沉积方式对镀层结构和性能有较大影响:PC方式得到的合金镀层,其纳米晶尺寸更小(由45 nm减小为26 nm),镀层表面致密性更高;表现在性能上,与DC相比,PC合金镀层的显微硬度更大(由7000 MPa增加到8250 MPa),耐蚀性更好(自腐蚀电位由–0.624V正移到–0.477 V,腐蚀电流密度由1.911×10~(-4)A/cm~2减小到2.587×10~(-5) A/cm~2)。     

酸性环境中pH对低碳钢表面Ni-Mn合金沉积层的影响

研究了酸性沉积液中pH对Ni-Mn合金沉积层的影响,采用电化学阻抗谱和动电位极化曲线研究了制得的Ni-Mn沉积层的耐蚀性,测试了沉积层的微观硬度.结果表明,随着沉积液中pH的升高,Ni-Mn合金沉积层中的锰含量不断增大,硬度也不断增大,而腐蚀电流密度先降低后略有升高.在pH为5.0时,Ni-Mn沉积层腐蚀电流密度最低,其对应的腐蚀电位也较正,表现出了较好的耐蚀性,此条件下制得的合金层中锰的质量分数为0.84％.对合金层的SEM和XRD分析表明,合金层呈圆胞状颗粒沉积,较为平整致密,且形成了NiMn合金相.     

CeO2改性对感应熔覆自润滑复合涂层性能的影响

利用高频感应熔覆技术在35CrMo钢表面制备CeO2改性镍基自润滑复合涂层.借助光学显微镜(OM)、X射线衍射仪(XRD)、硬度计、摩擦磨损试验机、电化学工作站等研究了不同CeO2含量对涂层微观组织、硬度、耐磨性和耐蚀性的影响,并分析了磨损机制.结果 表明:适量CeO2可改善复合涂层的组织、细化晶粒、减少缺陷.复合涂层主要物相为γ-Ni、Cr23C6、TiB2和h-BN等.随着CeO2含量增加,复合涂层的硬度、耐磨性和耐蚀性均先增加后降低.添加2 mass％CeO2后,复合涂层的硬度最大,为711.1 HV0.2,摩擦系数和磨损量均最小,分别为0.39和43.2 mg,其磨损机制为粘着磨损和轻微的磨粒磨损.当CeO2含量为1 mass％时,复合涂层的自腐蚀电位为-0.34187 V,自腐蚀电流密度为5.4 μA/cm2,耐蚀性最佳.     

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.