高频感应钎焊金刚石界面特征

讨论了在相同高频感应钎焊工艺条件下用两种不同成分的NiCr钎料钎焊镀Ti金刚石和无镀层金刚石的界面特征。利用扫描电镜、能谱仪和X射线衍射研究了深腐蚀处理后的钎焊金刚石颗粒。结果表明,钎料成分不同、金刚石镀Ti与否,金刚石表面生成的碳化物成分和形态各异。钎焊镀Ti金刚石表面的碳化物致密且呈法向生长,而钎焊无镀层金刚石表面的碳化物疏松且切向生长。钎焊金刚石颗粒的研磨试验证实,界面碳化物成分和形态的不同决定了它们同金刚石结合强度的高低。     

局部感应钎焊金刚石锯片的研究

在适当工艺条件下,通过高频感应钉焊方法,以Ni-Cr合金作为钉料,在钢基体上钎焊镀钛金刚石与无镀层金刚石。微观分析发现,在钎焊镀钛金刚石表面生成规则致密的Cr-C化合物,而钎焊无镀层金刚石表面只生成少量疏松无序的Cr-C化合物。通过进一步设计试验表明,这足因为Ti改变了钎焊后金刚石表面碳化物形成机制。钎焊金刚石的表面形念影响钎焊后金刚石一钎料界面微观结构,使金刚石磨粒损耗形式大为不同,进而影响被加工材料表面质量。AZ63镁合金被切割30 m后截面形貌可显示,用钎焊镀钛金刚石锯片切割后的表面比钎焊无镀层金刚石锯片更光滑。     

钎焊镀钛金刚石钻头的研制及其钻进性能分析

分别使用Ni-Cr和Cu-Sn-Ti等2种合金钎料真空钎焊制作镀钛和无镀层金刚石钻头,通过钻进玻化砖试验,研究了4类钻头的钻进性能。试验结果表明:Ni-Cr钎料钎焊制作的镀钛金刚石钻头与无镀层金刚石钻头比较,钻头平均寿命下降了41.7%;Cu-Sn-Ti钎料钎焊制作的镀钛与无镀层金刚石钻头比较,钻头平均寿命相当,但镀钛金刚石钻头的钻孔效率更高,并对其机理进行了分析。      

微粉金刚石表面镀钛对钎焊磨具性能的影响

在微粉金刚石磨具的制备过程中,金刚石热损伤和磨粒与结合剂间界面特性是影响磨具性能的主要因素。利用电铸与钎焊相结合的工艺把表面镀钛和未镀钛两种微粉金刚石磨料制备成磨具,并将其用于氧化铝陶瓷的磨削试验。通过对钎焊后金刚石磨粒与钎料的界面分析,磨削力、磨粒脱落率以及工件表面粗糙度的比较,探讨磨粒表面镀钛对钎焊微粉金刚石磨具性能的影响。结果表明,镀钛微粉金刚石表面镀层在钎焊过程中对微粉金刚石起到包裹隔离的作用,可以降低微粉金刚石的热损伤和石墨化;在利用两种钎焊微粉金刚石磨具磨削氧化铝陶瓷时,镀钛微粉金刚石磨具的磨削力较小,磨料的脱落率也较少,且工件表面粗糙度值更低。综合比较,磨粒表面镀钛后,可以减弱微粉金刚石的热损伤,提高磨具的磨削性能。     

镍基钎料真空钎焊镀钨金刚石的研究

为减轻镍基钎料真空钎焊金刚石接头的热损伤与残余应力，采用镀钨金刚石磨粒代替常规金刚石磨粒并将其钎焊到1045钢基体上，对钎焊镀钨金刚石接头的连接性能、热损伤程度及残余应力进行深入研究与分析。结果表明：镍基钎料对镀钨金刚石磨粒展现出良好的润湿性，与钎焊常规金刚石接头相比，钎焊镀钨金刚石接头在结合界面处的裂纹数量及尺寸明显减小。常规金刚石表面生成了致密有序的板条状Cr₃C₂层，而镀钨金刚石表面则形成了向钎料中生长的无序粒状Cr₃C₂层。在镀层的隔离保护作用下，钎焊后的镀钨金刚石磨粒表面的石墨化程度更低，力学性能更优异。同时，镀钨金刚石表面更薄、形貌更合理的Cr₃C₂层有效地缓解了镀钨金刚石接头内部的残余应力，其最大残余压应力相较于常规金刚石的降低9.43%。     

金刚石表面镀钛及其在胎体中结合状态的研究

采用真空蒸发-扩散镀的方法在金刚石表面镀钛,研究了镀覆温度和保温时间对金刚石表面形貌、镀层厚度、镀层物相的影响规律,分析了镀钛金刚石的抗氧化性能,研究了镀钛金刚石及其在铁基胎体中的结合状态。结果表明:在低温下（680℃）镀覆时,金刚石表面开始出现TiC;随镀覆温度升高或保温时间延长,镀层逐渐致密并增厚,在720℃镀覆时出现Ti沉积,在820℃镀覆时由于应力原因产生裂纹并导致镀层的破坏;镀层可隔绝金刚石与氧的直接接触,大幅度延缓氧对金刚石的侵蚀作用;镀钛后金刚石在胎体中可实现牢固的冶金键合。      

Ni-Cr合金钎焊镀钛金刚石的研究

本文利用真空炉中钎焊的方法,采用Ni-Cr合金钎料,适当控制钎焊温度,保温时间和冷却速度,实现了镀钛金刚石与钢基体的高强度连接.并用深腐蚀处理钎焊后的试样,使金刚石脱离基体,用扫描电镜,X-射线能谱,对金刚石表面的碳化物进行了分析,剖析了Ni-Cr合金与镀钛金刚石的接口微区结构.结果表明:在钎焊过程中,钎料在金刚石表面形成富铬层并与金刚石表面的C元素反应生成Cr7C,和Cr3C2,其中Cr7C3呈笋状生长,Cr3C2呈片状生长,而Ti却并没有在表面形成碳化物.这主要是因为Ti元素与Ni的结合力大于Ti与C的结合力,因此,实现Ni-Cr合金与镀钛金刚石高强度冶金结合的,是活性钎料中的Cr元素.     

真空微蒸发镀钛对金刚石晶体形貌及性能的影响

采用真空微蒸发镀覆技术对由铁基触媒高温高压合成的金刚石单晶进行了镀钛处理.以相同粒度和型号的普通金刚石为对比样品,讨论了镀钛处理对金刚石晶体形貌及性能的影响.结果表明,金刚石表面形成致密、连续的金属镀层使其纯净度和透光性下降;界面反应的发生和碳化物过渡层的生成,增加了晶体的表面粗糙度,晶体结晶形态发生微变.金刚石会因镀层对表面缺陷的弥合和与晶体的冶金结合而得到强化.在镀层的保护下,金刚石可免受热损伤,热稳定性得到提升.     

钛镀层对金刚石/铝导热复合材料的显微组织与热学性能的影响

采用高温盐浴法对金刚石表面进行镀钛处理来改善金刚石和铝基之间的界面结合,镀钛后的金刚石颗粒表面略显粗糙,表面的镀层均匀;采用真空热压烧结法制备高导热金刚石/铝复合材料,研究了金刚石表面镀钛对复合材料显微组织、热膨胀系数和热导率的影响。结果表明:金刚石表面的钛镀层改善了金刚石各晶面与铝基体的结合状态,增加了金刚石和铝之间的界面结合强度;当铝基体在镀钛金刚石颗粒形成的骨架结构中膨胀时,可以被骨架很好的约束,从而降低了复合材料的热膨胀系数;金刚石表面钛镀层减少了复合材料的孔洞,增加了致密度,从而提高了复合材料的热导率。     

金刚石表面盐浴镀Ti层研究

研究了盐浴镀钛处理的工艺参数,确定了其合理配方.采用SEM、XRD等检测方法对盐浴镀及相关处理后金刚石表面镀覆层进行了成分、显微组织、相结构和性能分析.结果表明,经盐浴镀后金刚石表面能形成较致密的镀覆层,抗压强度提高,比未镀覆层平均提高了2.7倍.经过相应的盐浴镀覆处理后,金刚石表面与镀层之间形成了碳化物(TIC).盐浴镀所形成的镀层对金刚石表面有保护作用,使金刚石的耐热蚀性增强.     

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.     

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。