锻造对热锻模具钢高温性能的影响北大核心CSCD

为了研究锻造对4Cr5W2VSi热锻模具钢高温性能的影响,采用不同工艺对4Cr5W2VSi热锻模具钢进行了锻造试验,并与未锻造试验钢进行了显微组织、高温磨损性能和高温抗氧化性能的测试与对比分析。结果表明:锻造显著细化了试验钢材的显微组织,提高了试验钢材的高温磨损性能和高温抗氧化性能。随着始锻温度从1050℃增大至1150℃,试验钢材的高温磨损体积和高温氧化速率均先减小后增大,高温磨损性能和高温抗氧化性能均先提高后下降。与未锻造试验钢相比,在始锻温度为1100℃、终锻温度为900℃、锻造比为5的工艺参数下,试验钢材高温磨损体积改善比率达46%、高温氧化速率改善比率达67%,试验钢材获得了优异的高温磨损性能和高温抗氧化性能。     

高Ni-Cr铸铁的热磨损和热疲劳性能研究

采用75SiFe孕育与REMg变质处理金属型铸造高Ni-Cr铸铁,研究了微观组织对高Ni-Cr铸铁热疲劳和热磨损性能的影响,结果表明:(1)550℃的高温磨损试验中,75SiFe孕育、REMg变质高Ni-Cr铸铁的磨损失重量随载荷的增大呈线性增长,在载荷相同的条件下,REMg变质试样的磨损失重小于75SiFe孕育试样,表现出较好的抗高温磨损性能,高Ni-Cr铸铁的高温磨损机制为氧化粘着磨损和接触疲劳磨损。(2)75SiFe孕育试样热裂纹垂直长度为15.49 mm,优于REMg变质试样热裂纹垂直长度17.69 mm,抗热裂性能较好。75SiFe孕育试样热裂纹在片状石墨尖端处基体组织内萌发,沿奥氏体和莱氏体界面扩展;REMg变质试样热裂纹在碳化物内萌生,并在碳化物内传播,造成碳化物破碎。     

下贝氏体球墨铸铁在腐蚀介质中的磨粒磨损行为

通过腐蚀磨损实验研究了下贝氏体球墨铸铁材料的腐蚀磨粒磨损行为,分析了影响腐蚀磨损失重率的主要因素.采用SEM和TEM对磨损表面特性进行了分析,根据磨损表层纵剖面的显微硬度研究了材料表层在腐蚀磨损过程中的形变硬化效应,结合下贝氏体球墨铸铁的电化学行为研究了载荷对耐腐蚀性能的影响.结果表明,下贝氏体球墨铸铁的腐蚀磨损机理为化学腐蚀失重和犁沟式磨粒磨损.载荷的提高对表面粗糙度、材料表面与磨粒之间的摩擦力以及磨粒压入材料表面的深度有显著的影响,从而导致磨粒磨损失重率显著上升.较高的载荷作用下,材料表面出现分层组织和条带状石墨,形成局部微型原电池,促使腐蚀速率提高,同时分层组织的疲劳断裂也将促使失重率进一步提升.载荷的增加使得基体中残留奥氏体内部出现大量位错的缠结,促进材料表面硬化,在一定程度上提高了材料的耐磨性能.当载荷从10 N增至200 N时,腐蚀磨损失重率从0.16 g/(cm2·h)增至0.42 g/(cm2·h).当粗糙度Ra由0.12μm增大到5.20μm时,腐蚀电流密度从0.56 m A/cm2上升至5.62 m A/cm2.下贝氏体球墨铸铁的腐蚀磨损失重曲线可分为3个阶段,分别为磨损初期的点接触加速磨损阶段、磨损中期的面接触过渡磨损阶段、磨损后期的疲劳磨损阶段.     

多弧离子镀Ti/TiN膜的耐磨耐蚀性研究

本文介绍了AZ31镁合金镀Ti/TiN双层膜工艺,分析了膜层形貌,并对AZ31与镀膜样品进行了摩擦磨损和腐蚀试验。结果表明:在摩擦磨损试验中,AZ31的平均摩擦系数是0.3066,磨损失重率为0.25‰;而镀Ti/TiN膜的AZ31的平均摩擦系数仅为0.1849,磨损失重率仅为0.08‰,说明镀Ti/TiN膜的AZ31获得优良的耐磨性能。在动力学扫描极化试验中,镀Ti/TiN膜的AZ31的腐蚀电位是-20 mV,腐蚀电流是4.26×10-6mA/cm2,腐蚀速率是1.97×10-2mm/a;而AZ31的腐蚀电位是-250 mV,腐蚀电流是10.8257 mA/cm2,腐蚀速率是499.4435 mm/a,腐蚀电位向正方向转移230 mV,腐蚀电流、腐蚀速率极大减少。AZ31镁合金镀Ti/TiN膜极大地提高了镁合金的耐腐蚀性能。     

磁控溅射镀钛提高 AZ31 镁合金耐磨耐蚀性能的研究

目的提高AZ31镁合金的耐磨及耐腐蚀性能。方法采用磁控溅射技术对镁合金进行表面镀钛处理,用扫描电镜研究膜基界面形貌及界面成分,分析结合性能。通过摩擦磨损试验,对比分析镁合金基体和镀Ti膜样品的耐磨性能;通过Tafel极化曲线,对比分析镁合金基体和镀Ti膜样品的耐蚀性能。结果 Ti膜均匀致密,与镁合金基体结合良好。镁合金镀Ti膜后,摩擦系数和磨损失重率下降,腐蚀电位向正方向移动了430 m V,腐蚀电流密度从10.83 m A/cm2下降到2.62×10-7m A/cm2。结论磁控溅射镀Ti膜提高了AZ31镁合金的耐磨和耐蚀性能。     

激光熔覆NiCr/Cr3C2-Ag-BaF2/CaF2金属基高温自润滑耐磨覆层的组织结构及摩擦学性能

利用激光熔覆技术在不锈钢表面制备了NiCr/Cr3C2-Ag-BaF2/CaF2金属基高温自润滑耐磨覆层,用X射线衍射仪分析了复合粉末及其激光熔覆耐磨覆层的物相组成,用扫描电子显微镜分析了耐磨覆层横截面的显微组织结构特征.在干滑动磨损试验条件下测试了覆层的耐磨性能,并用扫描电子显微镜观察和分析了覆层的摩擦磨损机理.试验结果表明,激光熔覆NiCr/Cr3C2-Ag-BaF2/CaF2金属基高温自润滑耐磨覆层,从室温到500 ℃试验温度范围内表现出了良好的减摩抗磨效果,并且随着温度的升高覆层材料表现出了不同的摩擦磨损机理,从室温到200 ℃温度范围主要表现为粘着磨损和磨粒磨损共同作用,温度超过200 ℃后主要表现为塑性变形和轻微的粘着磨损.     

缓蚀剂在PVC热稳定剂生产废水作为冷却水用过程中的应用研究

目的通过在生产废水中加入缓蚀剂,减少废水中氯离子的腐蚀性能,使其成为生产中的冷却水,实现节能环保。方法采用失重法,研究废水温度对Q235钢腐蚀速率的影响,确定废水的腐蚀温度。研究L-抗坏血酸和L-半胱氨酸在废水中的最佳用量,制备成复配缓蚀剂,研究复配缓蚀剂膜形成的最佳时间。用塔菲尔曲线、阳极极化曲线及交流阻抗法,研究存在与不存在复配缓蚀剂膜的Q235钢的自腐蚀电流密度、极化腐蚀电流密度和极化阻抗。用SEM研究复配缓蚀剂膜腐蚀前后的形貌变化。结果在60℃的生产废水中,L-抗坏血酸的最佳用量为165 mg/L,L-半胱氨酸的最佳用量为18 mg/L,复配缓蚀剂膜的形成时间为24h。无缓蚀剂膜时,Q235钢的自腐蚀电流密度为4.918×10-5 A/cm~2;在500 m V过电位下,极化腐蚀电流密度为1.667×10-2 A/cm~2,极化阻抗为529?×cm~2。形成复配缓蚀剂膜的Q235钢片的自腐蚀电流密度为3.433×10-7 A/cm~2,极化腐蚀电流密度为4.132×10-6 A/cm~2,极化阻抗很大。复配缓蚀剂的缓蚀率为80.15%,明显高于单一缓蚀剂。SEM测试表明,在过电位为500 m V时,无缓蚀剂膜的Q235钢腐蚀十分严重,有复配缓蚀剂膜的Q235钢几乎不腐蚀。结论在PVC热稳定剂生产废水中加入适量的缓蚀剂,具有较好的缓蚀性能,基本满足作为冷却水的要求。     

基于响应面法优化激光选区熔化成型CoCrMo合金工艺及其电化学行为

为了快速直接制造结构复杂、性能优异的个性化医用金属植入体,保证成型件具有良好的组织结构和生物特性,通过激光选区熔化技术对满足ASTMF75要求的CoCrMo合金进行增材制造。通过正交试验和响应曲面设计方法优化致密度工艺参数,观察成型件的微观组织,分析试样在模拟人体体液环境中的耐腐蚀性,并探究热处理工艺对其耐腐蚀性的影响。结果表明:在激光功率168 W、扫描间距0.06 mm、扫描速度550 mm/s时,成型零件的致密度可以达到98.58%,且微观组织均匀。电化学实验结果显示试样的腐蚀电流密度值约为40μA/cm2,经过退火热处理后,腐蚀电流密度仅为20.86μA/cm2,其耐腐蚀性能优于铸造CoCrMo合金的,这为选区激光熔化成型CoCrMo合金在医学植入体方面的应用提供了依据。     

等离子喷涂制备NiCoCrAlY/BaF2/CaF2/C/Y自润滑涂层及其高温摩擦性能

通过等离子喷涂技术制备润滑相BaF2∶CaF2∶C比分别为3.1∶1.9∶7和15.5∶9.5∶4.9的两种NiCoCrAlY/BaF2/CaF2/C/Y复合涂层,研究了所选固体润滑剂在高温摩擦中对涂层润滑性能和机械性能的影响,分析BaF2/CaF2/C的综合作用,在500℃和800℃时分别对涂层进行高温摩擦试验。结果表明:500℃时,摩擦面比较粗糙,涂层的摩擦因数较高,磨损较为严重,表现出明显的剥落现象;800℃时,涂层表面没有BaF2/CaF2/C等润滑相的存在,发生了摩擦化学反应,摩擦表面生成了一层光滑致密的氧化膜,并存在一定程度的材料转移现象。经过X射线衍射(XRD)分析表明,在高温和摩擦的共同作用下,涂层表面有BaCrO4生成,摩擦因数最低可达0.268,对应的磨损量为0.351 6mm3,有效降低了涂层的摩擦和磨损。在涂层的性能测试中,各润滑相之间的协同作用较好。     

钽离子注入对GZ51K镁合金力学性能及耐蚀性能的影响

研究了钽(Ta)离子注入对GZ51K生物镁合金力学性能和耐蚀性的影响,通过扫描电镜、纳米压痕、摩擦磨损试验和电化学试验对镁合金形貌及性能进行了分析。结果表明:适当剂量的Ta离子注入能有效改善GZ51K镁合金表面的力学性能和耐蚀性能。随注入剂量的增加,其硬度不断升高,而摩擦系数和腐蚀电流密度先下降后上升。当注入剂量为2×1016ions/cm2时,其摩擦系数与腐蚀电流密度降到最低,与基体相比,分别下降了约60%与90%。     

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.     

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.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

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.