TA15钛合金激光表面重熔快速凝固晶粒异常粗化

研究了热轧退火近aTA15钛合金激光表面重熔快速凝固组织及激光扫描速度对快速凝固组织的影响.结果发现:无论激光扫描速度如何加快,采用激光表面重熔快速凝固技术都不能细化TA15钛合金重熔区晶粒组织,TA15钛合金激光表面重熔区快速凝固β晶粒组织"异常"粗化,重熔区中β晶粒尺度分别是原始基材中a晶粒的10～20倍和β晶粒的32～62倍.分析表明,TA15钛合金激光表面重熔熔池的快速凝固是一个以熔池底部热影响区项部与熔体接触的未熔母材β晶粒为衬底的直接外延生长(无形核)过程,因此热影响区顶部与熔体接触的未熔母材β晶粒大小决定了重熔区快速凝固β晶粒的大小.激光加热表面重熔熔池形成过程中,熔池底部与熔体接触的未熔母材β晶粒在短时超高温作用下发生了严重长大,是导致钛合金激光表面重熔区β晶粒组织"异常"粗化的直接原因.     

钛合金表面激光重熔微弧氧化层的组织结构及摩擦磨损性能

为改善TC21钛合金表面微弧氧化(micro arc oxidation,MAO)涂层的微观结构致密性和耐磨性能，对MAO涂层进行了激光重熔改性，并对重熔后涂层的微观结构、成分、相组成以及硬度、摩擦磨损性能等进行了表征测试。结果显示，重熔MAO涂层由重熔外层、重熔内层和热影响层3层结构组成，其中外层和内层主要由Al₂TiO₅、rutile-TiO₂和α-Al₂O₃组成，热影响层由α-Ti和β-Ti转变组织组成，重熔MAO涂层的硬度显著增大。在摩擦磨损实验中，重熔MAO涂层摩擦系数低于MAO涂层和TC21钛合金基体，其磨损机制以粘着磨损为主，并伴有轻微的磨粒磨损。激光重熔MAO涂层显著提高了TC21钛合金摩擦磨损性能。     

奥氏体不透钢堆焊层激光表面重熔组织及耐腐蚀性能

激光重熔表面热处理技术可提高零件表面获得高的硬度、耐磨性及耐蚀性等,在化工和核电等行业有较好的应用前景,但国内对不锈钢堆焊层焊后表面热处理的研究较少.针对这一现状,对奥氏体不锈钢堆焊层表面进行激光重熔处理,观察其显微组织,并检测重熔表面显微硬度及耐腐蚀性.结果表明,激光重熔后表面显微组织呈细小的树枝-胞状晶奥氏体;激光重熔试样显微硬度大幅提高,较焊态试样提高87.6％;在9.8％的H2SO4溶液中,激光重熔表面处理后的堆焊层金属较易形成钝化膜,耐腐蚀性较好;10％草酸溶液电解试验中,焊态堆焊层金属晶间腐蚀敏感性较高,激光重熔区域为细小的奥氏体晶粒,不易形成连续的“贫铬区”,激光重熔堆焊层金属的晶间腐蚀敏感性较小.     

奥氏体不锈钢堆焊层激光表面重熔组织及耐腐蚀性能

激光重熔表面热处理技术可提高零件表面获得高的硬度、耐磨性及耐蚀性等,在化工和核电等行业有较好的应用前景,但国内对不锈钢堆焊层焊后表面热处理的研究较少。针对这一现状,对奥氏体不锈钢堆焊层表面进行激光重熔处理,观察其显微组织,并检测重熔表面显微硬度及耐腐蚀性。结果表明,激光重熔后表面显微组织呈细小的树枝-胞状晶奥氏体;激光重熔试样显微硬度大幅提高,较焊态试样提高87.6%;在9.8%的H2SO4溶液中,激光重熔表面处理后的堆焊层金属较易形成钝化膜,耐腐蚀性较好;10%草酸溶液电解试验中,焊态堆焊层金属晶间腐蚀敏感性较高,激光重熔区域为细小的奥氏体晶粒,不易形成连续的"贫铬区",激光重熔堆焊层金属的晶间腐蚀敏感性较小。     

激光重熔调控合金组织和性能研究进展

激光重熔是一种以高能量激光束在合金表面连续扫描,从而使合金表层快速熔化、冷却的表面改性技术,它通过细化组织、减少偏析、形成过饱和固溶体等方式来提高材料表面耐磨性、抗腐蚀性能等。讨论了温度场对熔池形态演化的影响以及重熔层的微观组织凝固机理;叙述了激光重熔表面强化技术在改善合金耐磨性和耐腐蚀性方面的研究进展。最后对激光重熔表面改性技术的实际应用进行了展望。     

45钢表面激光重熔温度场数值模拟

根据传热学理论和数值模拟方法研究温度场的分布规律,在考虑了热物性参数、换热系数、相变潜热随温度变化的因素,应用ANSYS有限元软件的参数化设计语言建立了45钢表面激光重熔连续移动三维瞬态温度场有限元模型。结果表明:提高激光功率对增大相变硬化区效果不大,反而形成较大的熔池而使重熔表面粗糙。与激光功率相比,激光扫描速度对试样温度场的影响较小。经过激光重熔后,形成重熔区、相变硬化区和基体三个区域。实验结果较好地验证了模拟结果,表明所建立的温度场计算模型是正确和可靠的。通过该计算模型,可以掌握金属表面激光重熔过程加热和冷却规律,为制备高性能表面改性层选择合适的工艺参数提供依据。     

激光重熔轨迹对Fe基Ni/WC喷涂层摩擦学性能的影响

为探究激光重熔轨迹对喷涂Fe基Ni/WC金属陶瓷涂层摩擦学性能的影响,利用火焰喷涂设备在45钢基体表面制备Fe基Ni/WC金属陶瓷涂层,分别采用矩形、平行、圆形3种扫描轨迹对涂层表面进行激光重熔。利用SEM、EDS、XRD等分别测定涂层显微组织、微区组织成分、物相结构和残余应力。利用MMG-10型摩擦磨损试验机进行常温干摩擦磨损实验。结果表明:圆形扫描轨迹下的重熔层组织结构为晶粒更为细小的等轴晶,增大了裂纹源形成和扩展的阻力。重熔层主要为α(Fe,Ni)、M_(23)C_6和WC、W2C等硬质相颗粒,起到弥散强化和固溶强化的作用,进而提高重熔层硬度。圆形轨迹重熔层较其他两种轨迹表现出更好的摩擦性能,硬质相颗粒镶嵌在软质基体中,起到强韧结合的作用。圆形轨迹下的磨损量较矩形轨迹降低了58.3%,残余应力降低了14.5%;硬质相和氧化膜的协同作用使得重熔表面变得光滑,从而降低摩擦因数。     

激光功率对DH36船用钢力学性能及强化机制的影响

目的 提高DH36船用钢表面力学性能及研究其强化机制。方法 采用不同激光功率对DH36船用钢表面进行激光重熔。随后使用OM、SEM、TEM、万能力学试验机和维氏硬度计研究了激光功率对DH36船用钢组织转变、析出相和力学性能的影响。利用Rosenthal模型计算出了熔池内的温度梯度、冷却速率和凝固速度。分析讨论了不同激光功率下重熔层内显微组织的转变过程。比较了不同激光功率作用后DH36船用钢的拉伸性能和显微硬度。结果 激光功率为1 500 W时,最大的屈服强度和抗拉强度分别为495.7 MPa和615.5MPa。重熔层内显微硬度沿z方向呈逐渐下降趋势,激光功率为1 000 W时,具有最大的硬度值448HV。随着激光重熔功率(P)的增加,熔池内的温度梯度的最大值(G_max)单调增加,而凝固速度的最大值(R_max)则与P无关。当v=10 mm/s时,激光重熔DH36钢的熔池内有R_max=0.098 3 m/s。在P=2 500 W时,熔池内有G_max=107 700 K/m。功率为1 000 W时,晶粒内...     

激光重熔对金属陶瓷Mo-ZrO_2组织和耐蚀性能的影响

针对金属陶瓷Mo-ZrO2抗液态铁腐蚀问题,采用CO2激光器对金属陶瓷Mo-ZrO2进行表面重熔。采用X射线衍射仪和扫描电子显微镜分析重熔后金属陶瓷表面的相组成和形貌,用光学显微镜和SEM分析测试了重熔层厚度和孔隙率。结果表明:在激光快速加热和冷却作用下,Mo-ZrO2表面大部分金属钼以MoO3的形式挥发,氧化锆经熔化、凝固,在表面形成以柱状晶为主的氧化锆重熔层;重熔层的厚度随着激光能量密度增大而增大,最大可达430.2μm;随着激光能量密度增加,重熔层孔隙率出现先增加后降低的变化,最低达到4.29%;重熔层与基体的结合强度,随着激光能量密度的增加而递减;当激光能量密度为4J/mm2,最大结合强度为17.33 MPa。在1 650℃高温条件下,进行6h熔融金属腐蚀试验,激光重熔使金属陶瓷降低了Mo和Zr元素向熔池扩散速率,显著提高金属陶瓷Mo-ZrO2抗液态铁腐蚀性能。     

20#钢激光熔覆-重熔Ni基涂层及其高温磨损行为

应用激光熔覆法,采用镍基NiCrSiB粉末,在20#钢表面制备了熔覆涂层,并用激光重熔涂层。观察了熔覆-重熔层的形貌,检测了其相组成和高温耐磨性能,结果表明:所制得熔覆-重熔层组织均一、致密,与基体形成了良好的冶金结合;经重熔处理后,熔覆层表面的裂纹显著减少;熔覆-重熔层的硬度提高到基体的5倍,高温磨损率约为基体的1/3。熔覆-重熔层耐磨能力的增强除因其与基体形成了良好的冶金结合和硼化物、硼碳化物等析出相的强化作用外,也是重熔减少微裂纹的结果。     

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.