搭接率与二次重熔对激光熔覆石墨/铜自润滑复合材料组织的影响

为了改善石墨/铜自润滑材料激光熔覆层的平整度,探索了激光搭接率对熔覆层平整度的影响与二次重熔处理对熔覆层表面的改善效果。结果表明,激光搭接率为75%不适合作为实际加工时的工艺参数。激光熔覆搭接率为50%或25%时,均可以获得连续致密的熔覆层,50%的搭接率适合进行单次厚度较大的熔覆,可以一次性产生一定厚度的连续致密熔覆层;25%的搭接率适合进行多次激光熔覆,产生厚度较小但相对平整性更好的连续致密熔覆层,方便黏结后续的熔覆材料,避免不同部位熔覆材料厚度的差异对熔覆层产生影响。二次重熔处理可以有效减小熔覆层表面高低落差。     

激光熔覆技术研究进展

激光熔覆技术是一种先进的材料表面改性技术,具有稀释率小、熔覆层组织致密、涂层与基体结合良好及工作环境无污染等优点。从激光熔覆喷头、激光熔覆工艺、激光熔覆材料、激光熔覆技术的工业应用这4个方面,综述了激光熔覆的研究进展。其中,在激光熔覆喷头方面,介绍了激光光斑的种类及转换原理和熔覆材料的引入方式,总结了激光束与粉束的耦合模式和熔覆喷头的种类,包括旁轴送粉熔覆喷头、光外同轴送粉喷头、光内同轴送粉喷头以及特殊工况下的熔覆喷头。在激光熔覆工艺方面,阐述了工艺参数对熔覆层宏观形貌和组织性能的影响,总结了激光熔覆复合工艺的辅助加工方法,论述了超高速激光熔覆新工艺的原理及技术优势,并介绍了激光熔覆过程控制的研究进展。在激光熔覆材料方面,阐述了熔覆材料的种类及增强相的添加方式。在激光熔覆技术的工业应用方面,介绍了激光熔覆技术在矿山机械、模具再制造以及铁路修复等领域的应用。最后对激光熔覆技术的发展趋势及应用前景做出了展望。     

送粉式激光熔覆热和熔覆材料有效利用率影响因素的研究

通过改变激光熔覆工艺参数获得相应的熔覆层并对其进行了细致的研究,对激光热有效利用率、熔覆材料有效利用率、熔覆层稀释率及有关界面问题进行了综合评述。找出了工艺参数对其影响规律,指出了送粉装置与工艺参数间的合理匹配能获得最佳的激光热有效利用率、熔覆材料有效利用率。同时,对搭接熔覆时的搭接率的确定原则进行了详细的评述。为获得良好的结合界面提供了实验证据,为制定送粉激光熔覆工艺规程提供了理论依据。     

激光熔覆工艺与粉末对覆层开裂行为的影响

在高参数阀门零件密封面上进行厚覆层激光熔覆时,发现覆层裂纹是主要的质量缺陷,讨论了熔覆工艺,覆层材料地激光熔覆层开裂行为的影响。     

双向扫描激光熔覆止裂机理及试验分析

针对激光熔覆过程中易出现的熔覆层开裂的问题,采用了单向送粉双向扫描激光熔覆工艺,较好地抑制了熔覆层的开裂.通过对激光熔覆过程温度场、应力场进行计算分析,发现采取单向送粉单向扫描工艺时,熔覆层顶部以及与基体接合处会出现明显的应力集中现象,且应力水平较大,而采取双向扫描工艺后,熔覆层内拉应力水平显著降低,且熔覆层顶部的应力...     

激光熔覆工艺参数对熔覆层质量影响研究

在42CrMo基板上激光熔覆单道钴基合金涂层,采用正交试验,探究激光功率、送粉速率、扫描速度、光斑直径等4个工艺参数对熔覆层几何形貌和稀释率的影响规律.结果表明:激光功率和扫描速度对熔覆高度和熔覆宽度影响较大,激光功率和光斑直径对稀释率影响最大.结合稀释率和熔覆高度与熔覆宽度比值综合评价,获得最优工艺参数组合为激光功率...     

工艺路径对多层多道激光熔覆残余应力的影响

采用盲孔法测量Q345钢块表面多层多道激光熔覆Co基涂层的残余应力,研究了熔覆工艺路径对激光熔覆残余应力的影响.结果表明,平行焊道方向的残余应力远大于垂直焊道方向的应力,且均为拉应力;增加激光熔覆层单层厚度,熔覆层及试板背部基材残余应力明显增大.与两层熔覆层激光焊道平行叠加的熔覆路径相比,采用两层熔覆层垂直交叉的熔覆工艺路径,降低了熔覆层的残余应力,采用分区熔覆且每个区域各熔覆层垂直交叉堆焊的熔覆工艺路径,熔覆层残余应力水平最低;熔覆前对试板进行2 mm的预弯变形对涂层残余应力影响不明显,但显著降低了试件背面的残余应力.     

模具激光表面熔覆设备和技术的进展

概述了激光表面熔覆技术近年来发展的概况;激光熔覆工艺,激光表面熔覆技术装备,以及熔覆材料概况。文中介绍了轧辊激光堆焊层厚10mm以上（单面）的新要求,以及激光熔覆层高硬度（HRC60－65）的新要求。     

氩弧熔覆Cr—Si—B系合金组织与性能

研究了氩弧熔覆层的组织与性能,通过对激光溶覆、火焰熔覆的组织化学对比分析,说明了白亮层盛开过程及产生条件。指出氩弧覆能实现熔覆层的冶金结合且具有良好的成形性,使用灵活,能得到与激光熔覆相近性能的熔覆层,可以在生产中采用氩弧熔覆工艺。     

激光熔覆涂层增韧改性方法的研究进展

激光熔覆涂层能够改善金属表面性能,实现表面强化,然而常发现由于涂层韧性降低,涂层表面出现裂纹缺陷问题。概述了激光熔覆涂层由于韧性降低造成裂纹的原因,包括温度梯度差引起的内应力、激光熔覆层中的应力集中以及熔覆层中的微小气孔等。同时归纳了影响激光熔覆层韧性的因素,包括熔覆材料的选择、激光熔覆工艺参数的设定以及熔覆材料的热处理方式等。在此基础上,重点阐述了近年来改善激光熔覆涂层裂纹缺陷问题的进展,并从中寻找增强激光熔覆涂层韧性的方法,包括在熔覆粉体中加入复合陶瓷增强相和稀土元素粉末等改变熔覆粉体组成、在基体与熔覆层之间增加过渡层、改变激光熔覆功率和扫描速率以及光斑直径等工艺参数、对熔覆前基体的预热和熔覆后涂层的热处理、外加超声振动和电磁场以及超声振动与电磁场的耦合等能场辅助等。针对各种增强激光熔覆涂层韧性方法的不足,探讨今后激光熔覆涂层增韧改性方法的研究前景。     

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.     

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。     

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.     

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.