Cr/C比对中铬铸铁复合抗磨辊圈组织和耐磨性的影响

中铬铸铁复合抗磨辊圈服役过程中,外层中铬铸铁层起主要的抗磨和粉碎物料的作用。本文主要研究了Cr/C比对中铬铸铁组织、力学性能和耐磨性的影响。研究结果表明,Cr/C比的不同会影响碳化物的形态和数量,Cr/C比(3.17)较高时,碳化物主要为菊花状和弥散分布的块状的(Cr, Fe)_7C_3,碳化物面积占比为8.90%,冲击韧度为8.6 J,硬度为52 HRC;Cr/C比(2.66)较低时,碳化物主要为网状的(Fe, Cr)_3C和板条状的(Cr, Fe)_7C_3,碳化物面积占比为13.31%,冲击韧度为5.3 J,硬度为56 HRC。且Cr/C比高时,由于具有较高的韧性,可以缓解磨损过程中应力集中,延迟磨屑的剥落,具有更高的耐磨性。     

钒对过共晶Fe-Cr-Ni-C耐磨涂层的影响

采用反应等离子熔覆工艺制备过共晶Fe-Cr-Ni-C耐磨涂层,涂层组织主要由奥氏体和(Cr,Fe)_7C_3型碳化物以及少量的马氏体组织组成。大量硬度较高的(Cr,Fe)_7C_3型碳化物均匀分布在以奥氏体为主的基体中,使涂层兼具较高的耐低应力磨料磨损能力以及良好的抗氧化性和耐蚀性等优异的综合性能,得到广泛应用。但粗大的脆性初生(Cr,Fe)_7C_3型碳化物在磨损过程中容易发生破碎而剥落。为了提高Fe-Cr-Ni-C涂层的耐磨性,本文研究了不同钒含量对涂层组织和性能的影响。采用粉末等离子熔覆工艺,在Fe-Cr-Ni-C自熔性合金粉末的基础上分别加入2%、4%、6%、8%的钒,制备出不同钒含量的过共晶Fe-Cr-Ni-C涂层。利用光学显微镜、扫描电子显微镜、X射线衍射仪、显微硬度计、磨料磨损试验等手段,对涂层的组织和性能进行分析。试验结果表明,钒主要分布在(Cr,Fe)_7C_3型碳化物中,形成强度更高的(Cr,Fe,V)_7C_3型碳化物。涂层的硬度和耐磨性随着钒含量的增加逐渐提高;当钒含量为6%时,涂层成形良好,涂层中没有发现裂纹,相对于不加钒的Fe-Cr-Ni-C涂层,耐磨性提高了1.65倍。所以在Fe-Cr-Ni-C耐磨涂层中加入适量的钒,可以增加(Cr,Fe)_7C_3型碳化物的强度,有效提高涂层的耐磨性。     

Fe/C配比对等离子堆焊Fe-Cr-C合金组织及性能的影响

研制了一种Fe-Cr-C合金粉块,粉块化学成分中w(Cr)/w(C)为5∶1,仅改变Fe/C配比,并采用等离子焊机在Q235钢板表面进行铺粉堆焊试验。采用金相显微镜、光谱仪(OES)、磨损实验和硬度检测等方法,研究Fe/C配比对Fe-Cr-C堆焊合金组织及性能的影响。结果表明:Fe元素在熔敷过程中起到助熔作用,当不添加Fe粉时,焊道无法成形;当Fe/C配比为4∶1时,焊道成形最好,堆焊合金中析出的M_(7)C_(3)型碳化物晶粒尺寸细小,弥散分布在马氏体基体表面;随着Fe/C配比的提高,Fe的助熔作用会减少堆焊合金烧损,但是C含量的降低导致显微组织中硬质相尺寸增大。当Fe/C配比为10∶1时,由于硬质相缺碳严重,形成M_(23)C_(6)型碳化物,耐磨粒磨损性能变差。     

激光熔覆原位合成(Ti,Nb)C强化Ni45涂层的微观组织与耐磨性研究

通过激光熔覆技术在Cr12MoV模具钢上原位制备了(Ti,Nb)C增强Ni45复合涂层,研究了(Ti,Nb)C对涂层组织和性能的影响。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、电子背散射衍射(EBSD)和透射电子显微镜(TEM)等分析了(Ti,Nb)C/Ni45涂层的组织和相组成。利用磨损实验机对涂层耐磨性进行了测试。结果表明:(Ti,Nb)C/Ni45涂层的相组成包括γ-Ni基体、正交晶系Ni_3B、正交晶系CrB、正交晶系(Cr,Fe)_7(C,B)_3、立方晶系Cr_(23)C_6和立方晶系(Ti,Nb)C颗粒;Cr_(23)C_6主要分布在(Ti,Nb)C和γ-Ni基体之间的相界面附近。(Ti,Nb)C增强相颗粒的出现和碳化物相((Cr,Fe)_7(C,B)_3和Cr_(23)C_6)的增加使(Ti,Nb)C/Ni45涂层的耐磨性提高了约3.6倍。     

Nb-Ni-Ti-B强化药芯焊丝堆焊金属组织结构及耐磨性分析

针对Nb-Ni-Ti-B强化药芯焊丝堆焊金属进行研究,采用XRD和SEM分析了样品的相结构和显微结构;研究发现焊丝熔敷金属中的Fe2B能使熔敷金属堆焊层更加稳固,具有良好的抗剥离性能,Fe2B的硬度高、耐磨性好、分布均匀,镶嵌在熔敷金属的基体中有着骨架的作用,使该合金具有了良好的耐磨性;堆焊金属中的TiC为NbC提供了凝结核,形成NbC+TiC复合相,在提高耐磨性的同时有利于促进NbC弥散分布。NbC+TiC复合相弥散分布在熔敷金属中,部分NbC+TiC复合相嵌于Fe2B组织中有利于固化Fe2B组织。通过Nb-Ni-Ti-B强化药芯焊丝堆焊金属与5C-27Cr型高碳高铬合金焊丝熔敷金属磨损试验比较,Nb-Ni-Ti-B强化堆焊金属相对5C-27Cr型高碳高铬合金的耐磨性为2.08。     

Cr含量对白口铸铁碳化物类型转变机理的影响

从碳化物形核和碳化物长大两方面研究Cr含量对白口铸铁碳化物类型及析出机理的影响。研究表明:Cr的加入使白口铸铁中的碳化物类型发生如下转变:Fe_3C→(Fe,Cr)_3C→(Fe,Cr)_3C+(Fe,Cr)_7C_3→(Fe,Cr)_7C_3。Cr改变了铁液中碳化物形核的热力学条件,Cr原子可置换铁液中的Fe原子形成(Fe,Cr)_3C碳化物,从而导致碳化物晶体结构发生畸变。Cr含量越高,畸变程度越严重,碳化物晶体结构由M_3C转变为M_7C_3型碳化物的临界含Cr量为10%。随Cr量的增加,评价固液微观结构的Jackson因子增加,碳化物生长速度变慢,因此,碳化物断网趋向增加,碳化物形貌从连接成网络的蜂窝状变为杆状。     

原位合成(Ti,V)C增强铁基耐磨复合材料的研制

采用激光熔覆技术，通过调节钒含量制备多组Fe-Ti-V-C合金系统. 借助金相、SEM和XRD等分析手段对熔覆层组织和碳化物形貌进行分析. 结果表明，熔覆层中随着钒含量的提高，基体组织由F向F+M转变；颗粒状复合碳化物(Ti,V)C的数量逐渐增多，当加入钒含量超过13.3%时，初生(Ti,V)C形态由颗粒状转变为花瓣状. 此外湿砂磨粒磨损试验表明,适量钒显著改善了熔覆层的耐磨性，当钒含量为13.3%时，大量颗粒状复合碳化物(Ti,V)C均匀弥散分布在铁素体及针状马氏体基体上，使得熔覆层具有最佳的耐磨性.     

元素V对奥氏体焊缝金属晶间腐蚀敏感性的影响

采用透射电镜(TEM)分析技术研究了1Cr19Ni23N焊条熔敷金属中钒含量对组织及对熔敷金属抗晶间腐蚀性能的影响.结果表明,低钒含量焊条熔敷金属组织中沿奥氏体晶界析出M23C6型富铬碳化物,在晶界附近形成贫铬层,导致晶间腐蚀的发生;高钒含量焊条熔敷金属组织中,V优先于Cr与C形成细小弥散的碳化钒分布在晶粒内部,使得该焊条在保持原较高碳含量的基础上,通过改变碳化物形态和分布达到了保持高强度和改善晶间腐蚀敏感性的目的.     

低合金钢表面Fe基B4C耐磨涂层组织与性能

目的在低合金结构钢表面制备一层高硬度、高耐磨的铁基陶瓷颗粒增强层,并研究熔覆层的微观结构及性能。方法利用等离子熔敷技术,在16Mn钢基体上熔敷Fe58合金粉与B_4C陶瓷粉的混合粉末。结果在16Mn钢表面成功制备了高硬度、高耐磨的铁基陶瓷颗粒增强层,陶瓷颗粒增强层致密、均匀、无气孔、无裂纹,且与基体结合良好。XRD及SEM结果表明,熔覆层生成了细小、均匀的碳、硼化物增强相,熔覆层与基体的相容性好,界面呈冶金结合,熔覆层的增强相主要有Fe2B、FeB、Cr7BC4、Cr7C3及B_4C相,Fe与B的化合物Fe2B、FeB呈链状沿晶界分布在(Fe,Ni)固溶体上,并与(Fe,Ni)固溶体在晶界形成网状结构。铬的碳、硼化物Cr7BC4和Cr7C3及未完全反应的B_4C陶瓷相,则呈不规则块状和点状在晶内弥散分布。熔覆层断面的显微硬度及表面磨粒磨损测试结果表明,熔覆层断面的显微硬度分布均匀,平均硬度可达11.9GPa,是16Mn钢基体的7.95倍,耐磨粒磨损性能是基体的7倍以上。结论晶内弥散分布的B_4C、Cr7BC4和Cr7C3硬质相与晶界成链状分布的Fe2B、FeB共同作用,使熔覆层的硬度、耐磨性明显提高。     

激光与电子束熔覆(Cr,Fe)7C3复合层组织及耐磨性对比

以Fe/Cr/C粉末为添加粉末,采用CO2激光扫描和电子束扫描在903钢表面原位合成(Cr,Fe)7C3表面复合层。对两种熔覆层进行金相分析、扫描电镜(SEM)和X射线衍射(XRD)分析对比。结果表明： 电子束熔覆层的组织均匀性较好,表层有大量(Cr,Fe)7C3初生碳化物,底部则为初生奥氏体枝状晶和(Cr,Fe)7C3/γFe共晶组织。基于电子束扫描时束流可变的工艺特点,实际应用时容易制备可控组织梯度的熔覆层。激光熔覆层也具有一定的组织梯度,但其组织均匀性较差,表层主要有γFe枝状晶和(Cr,Fe)7C3/γFe共晶组织及马氏体组织,底部则主要为马氏体组织。两种熔覆层的显微硬度体现了其中碳化物的数量及分布,电子束熔覆层碳化物含量较高,其显微硬度也较大。低应力磨损状态下,电子束熔覆层和激光熔覆层的相对耐磨性分别是基材的10.5倍和4.3倍。     

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.