Fe3Al基摩擦材料的烧结致密化过程研究

利用热压烧结方法制备了以Fe3Al金属间化合物为基体，以Cu、石墨、MoS2、Al2O3为添加剂的一种复合摩擦材料，并对其烧结致密化过程以及影响因素进行了试验研究。结果表明，材料的致密化过程受到原始粉料组成、粒度以及烧结工艺参数（如烧结温度、压力、保温时间）等多种因素的共同影响，其中Cu的液相烧结在材料致密化过程中起到重要作用。最佳工艺参数为：烧结温度1050～1100℃，压力10～12MPa，保压20～30min，保温45-60min，此时致密度为90％-95％。烧结过程中未发现晶粒异常长大，经1050℃烧结1h的摩擦材料中Fe3Al的晶粒尺寸为400～600nm。     

机械合金化和添加微量Y2O3对制备细晶钨合金

采用机械合金化、添加微量Y2O3和冷等静压、液相烧结工艺制备Ф25mm的晶粒度为3～4μm的细晶93W-4.9Ni-2.1Fe(质量分数%,下同)合金棒材,研究粉末机械合金化、添加微量Y2O3、烧结温度和保温时间对合金棒材烧结致密化和显微组织的影响。结果表明:在1480℃液相烧结时钨晶粒发生明显球化,在此温度下降低保温时间对控制钨晶粒长大有较大影响,保温时间为30min时,钨晶粒尺寸为5～8μm;保温时间为60min时,钨晶粒为8～10μm。添加微量稀土氧化物Y2O3可以进一步有效地抑制晶粒的长大,降低合金的钨晶粒尺寸和提高组织均匀性,在1480℃烧结60min时,钨晶粒为3～4μm,而且晶粒尺寸分布更均匀。     

超细/纳米W-20Cu复合粉末的液相烧结机制

采用溶胶-喷雾干燥及氢还原工艺制备超细/纳米W-20 Cu复合粉末:将粉末压制成形,在1 340～1 420℃烧结5～180 min,并研究其致密化行为及晶粒长大机制.结果表明:烧结温度对液相烧结致密化起主要作用,W-20Cu复合粉末在液相烧结早期发生了显著的致密化,在1 420℃烧结5 min时,致密度可达到89％以上;随烧结时间的延长,致密度增加,在1 420℃烧结90 min时,相对密度最高,达到99.1％.液相烧结时,W晶粒不断长大并逐渐球化,且其晶粒大小G与时间烧结t符合G3＝G30+kt关系,服从溶解-析出机制.烧结温度对W晶粒长大影响显著,当温度从1 340℃上升到1 420℃时,其晶粒长大动力学系数从1.59×10-2 μm3/min增大到2.47×10-2 μm3/min,这说明液相的形成、颗粒重排、溶解-析出及W晶粒长大使得细晶W-Cu坯体获得近全致密.     

Fe3Al基复合材料的制备及其摩擦磨损行为

用球磨机械合金化工艺制备Fe3Al粉末，采用粉末冶金工艺，选择不同的烧结温度和烧结压力，获得了Fe3Al基复合材料。对材料的物理力学性能、摩擦磨损性能和微观结构进行分析测试，借助磨损表面扫描图像，分析了该材料的磨损形式，探讨了其磨损机理。结果表明：在烧结温度为1050℃，烧结压力为10～15MPa的工艺条件下制得的Fe3Al基复合材料有较好的摩擦磨损性能。其摩擦机理为：疲劳磨损和磨粒磨损为主，兼有磨粒和粘着磨损混合形式。     

微波烧结WC-Co硬质合金致密化与晶粒生长

分别采用微波烧结和常规烧结制备WC-8Co硬质合金,通过1 000~1 400℃温度范围烧结以及1 400℃保温0~240 min的微波和常规烧结实验,测量各样品的收缩率、密度和晶粒尺寸,分析其致密化行为和晶粒生长,研究烧结温度和保温时间对合金致密化和晶粒生长的影响。结果表明,与常规烧结比较,微波烧结促进YG8硬质合金的致密化,且获得的合金组织均匀,晶粒细小。另外,保温时间对微波烧结YG8硬质合金的晶粒生长几乎没有影响。     

W-30Cu纳米复合粉末液相烧结致密化与晶粒长大机制

采用喷雾干燥-煅烧、还原工艺制备超细W-30Cu复合粉末,将粉末模压成形,在1340～1420℃液相烧结15～120min,研究其致密化行为及晶粒长大机制。结果表明:W-30Cu复合粉末在液相烧结早期发生了显著的致密化,1340℃烧结15 min致密度可达到90%以上;随烧结时间的延长致密度增加,1380℃烧结90 min相对密度达到99.1%。液相烧结过程中,W晶粒不断长大并逐渐球化,且其晶粒大小G与烧结时间t符合G3∝kt关系,服从液相烧结溶解-析出机制。烧结温度对W晶粒长大影响显著,当温度从1340℃上升到1420℃时,其晶粒长大动力学系数从1.61×10-2μm3/min增大到4.65×10-2μm3/min,液相的形成、颗粒重排、溶解-析出及W晶粒长大使细晶W-Cu获得近全致密。     

WC-7Co硬质合金放电等离子烧结工艺

采用放电等离子烧结(spark plasma sintering,SPS)技术制取WC-7Co硬质合金。研究了烧结温度、烧结压力对烧结WC-7Co硬质合金力学性能的影响,探讨了最佳烧结热压比,分析了粉末烧结致密化过程和晶粒长大机制。结果表明,WC-7Co硬质合金在1150℃烧结时,随着压力的增加,烧结致密性呈现先增加后降低的变化趋势,在30 MPa时可获得最佳烧结致密性。在升温速率为100℃/min,保温时间为5 min,烧结温度为1150℃,热压比为38℃/MPa的工艺条件下,利用SPS技术可制备组织致密、综合力学性能良好的WC-7Co硬质合金。     

Mo_2FeB_2基金属陶瓷烧结过程中显微组织和力学性能的变化

采用真空烧结法制备了Mo2FeB2基金属陶瓷。运用XRD、SEM、EDS研究了Mo2FeB2基金属陶瓷的烧结过程中显微组织的变化并测试了不同烧结温度下所得金属陶瓷材料的力学性能。实验结果表明:进入L1液相(奥氏体+Fe2B)烧结阶段后,金属陶瓷由于颗粒重排致密度大幅度提高,但溶解-析出过程进行得较缓慢,晶粒基本没有长大。提高烧结温度至L2液相(奥氏体+L1+Mo2FeB2)生成后,由于溶解-析出过程明显加剧,晶粒长大趋势明显,但致密化程度进一步提高。当烧结温度达到1280℃,保温时间为40min时,烧结体接近完全致密,所得材料组织均匀具有较佳力学性能。     

溶胶-喷雾干燥超细/纳米晶W-20Cu复合粉末的烧结行为

采用喷雾干燥-氢气还原法制备超细/纳米晶W-20Cu(质量分数,%)复合粉末,粉末压坯直接从室温推入高温区烧结不同时间后直接取出水淬,研究其烧结致密化和显微组织的变化。结果表明,超细/纳米晶W-20Cu粉末在1000～1200℃烧结时发生迅速致密化。粉末压坯在1200℃烧结60min,其材料致密度已达到96.4%。1420℃烧结90min时致密度达到99%以上。1100～1420℃烧结时其烧结致密化活化能不断减小,从1100℃时的276.3kJ/mol减小到1420℃时的29.1kJ/mol。当温度低于1200℃时,W晶粒长大不明显,当温度超过1300℃时,W晶粒开始有明显长大。随温度的升高W晶粒发生显著球形化,1420℃烧结时发现其晶粒长大符合G3=kt的Ostwald机制,此时晶粒长大动力学系数K仅为0.024μm3/min。     

放电等离子烧结制备Ti-22Al-25Nb合金及致密化机理

以Ti-22Al-25Nb(摩尔分数,%)预合金粉末为实验初始原料,采用放电等离子烧结工艺(SPS)方法,在温度为950～1200℃,保温时间为10～20min,压力为35～80MPa的条件下制备晶粒小、组织致密的粉末冶金Ti-22Al-25Nb合金。研究烧结温度、烧结压力和保温时间对预合金粉末致密化过程的影响,分析粉末的烧结致密化机理,揭示烧结温度、烧结压力和保温时间对Ti-22Al-25Nb烧结合金的相对密度、相组成、显微组织以及力学性能的影响规律,明确烧结合金的室温断裂机制。结果表明:经950℃、80MPa、10min烧结的Ti-22Al-25Nb合金相对密度达到99.43%,具有更优异的综合力学性能,其室温伸长率、屈服强度和抗拉强度分别达到9.38%、933.57 MPa和990.01 MPa。     

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.     

新型的治疗阿尔茨海默氏症药物(1-二甲基磷酰基-2,2,2-三氯)-乙基-1-醇烟酸醋对体外神经细胞的作用

目的: 观察本实验室合成的一种治疗阿尔茨海默氏症(AD)的药物(1-二甲基磷酰基-2, 2, 2 -三氯)-乙基^-1-醇烟酸醋(NMF),对体外培养的皮层神经细胞活性的影响以及对海人藻酸(KA)所致的神经损伤的保护作用。方法: 采用体外培养皮层神经元的方法,解剖分离 15 d胚胎小鼠皮层神经细胞, 接种于 96孔板,48 h 后加药并培养 72 h,以 MIT 法 观察 NMF 对小鼠皮层神经细胞活性的影响;同时将接种于 24 孔板的细胞预先给予 NMF,d 3 时加或不加KA处理后,以台盼蓝染色鉴别并计数死、活细胞,可得出细胞的存活率。结果: NMF 明显促进胎鼠皮层神经元活性,其中 NMF1、0. 1、10nmol·L^-1促进神经元活性增殖率分别高达 34.7%、37.4%、36. 7%, NMF 明显促进正常胎鼠皮层神经元存活卒,与对照组比较,10nmol·L^-1 NMF 对皮层神经元的存活率分别提高 39.3%、73.5%。 NMF能显著 对抗 KA 所致的神经元损伤,与 KA 损伤组相比, NMF0.1、10、10nmol·L^-1对损伤皮层神经元的保护率分别为 77.30%、80.10%、84.15%。结论: NMF 明 显促进胎鼠皮层神经元的洁性、提高正常皮层神经元,的存活卒,并能有效地保护KA所致的神经元损伤,提示 NMF 是一种很有潜力的治疗 AD 的药物。     

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.     

Three-Dimensional Growth of Coherent Ferrite in Austenite: A Molecular Dynamics Study

Coherent second phase often exhibits anisotropic morphology with specifi c orientations with respect to both the second and the matrix phases. As a key feature of microstructure, the morphology of the coherent particles is essential for understanding the second-phase strengthening eff ect in various industrial alloys. This letter reports anisotropic growth of coherent ferrite from austenite matrix in pure iron based on molecular dynamics simulation. We found that the ferrite grain tends to grow into an elongated plate-like shape, independent of its initial confi guration. The fi nal shape of the ferrite is closely related to the misfi t between the two phases, with the longest direction and the broad facet of the plate being, respectively, consistent with the best matching direction and the best matching plane calculated via the Burgers vector content(BVC) method. The strain energy calculation in the framework of Eshelby's inclusion theory verifi es that the simulated orientation of the coherent ferrite is energetically favorable. It is anticipated that the BVC method will be applicable in analysis of anisotropic growth and morphology of coherent second phase in other phase transformation systems.     

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.