Understanding process-induced microstructures in RBa2Cu3O7

During the processing of rare earth (R)-barium-copper-oxygen superconductors, a variety of microstructures can be induced. Many processes are designed to avoid forming some structures, but these same processes can result in other structures which degrade the superconducting properties. Because liquid phases can be detrimental, for example, low-temperature calcination is often employed. But the CO₂ gas evolved during calcination leads to the formation of a nanoc-rystalline microstructure which may affect superconducting properties. Textures and defects can be induced by high-temperature and high-pressure deformation. For commercial dreams to become reality, these processing-induced microstructures, and their effects on properties, will have to be understood and controlled.     

A new approach for the synthesis of polyaniline microstructures with a unique tetragonal star-like morphology

Shape-controllable polyaniline (PANI) microstructures with a unique tetragonal star-like morphology were synthesized by a rapid initiated strategy with glycine (Gly) as dopant. The results demonstrate that the morphology of PANI microstructures is significantly influenced by the molar ratio of aniline to glycine. The PANI prepared in this study exhibits nanofiber-like morphology with exceptionally high crystallinity. These nanofibers can self-assemble into tetragonal star-like microstructures with a unique alignment. The chemistry, morphology, and crystal structure of glycine doped star-like microstructures were studied using SEM, UV–vis, FT-IR, XRD and cyclic voltammetry (CV).     

Aging properties and microstructures of Ti-B20 titanium alloy

A new metastable beta titanium alloy of Ti-Al-Mo-V-Cr-Fe-Zr-Sn system was designed and named Ti-B20. In order to investigate the aging properties and microstructures of the new alloy .subjected to different solution treatments, the tensile and Vickers hardness tests were carried out and the optical microscope and scanning electron microscope analysis were performed. The results show that the new alloy displays rapid aging response, high age strengthening effect and fine deposition. In addition, beta solution results in ultra high age hardening effect with low tensile ductility, whereas excellent combination of aging strength and ductility can be obtained after solution treated below beta transus temperature.     

不同结构纳米晶镍钴合金的力学性能

采用直流电沉积方法制备晶粒尺寸为15 nm的Ni-49.2%Co(质量分数)和16 nm的Ni-66.7%Co(质量分数)合金。采用XRD、TEM和MTS?810万能材料试验机对其微观结构和力学性能进行分析。结果表明：两种合金分别是单相FCC结构和FCC与HCP共存的双相结构。固溶强化和晶粒细化的作用使两种Ni-Co合金都具有很高的抗拉强度;且Co元素的引入降低材料的层错能,提高其应变硬化能力,使Ni-Co合金的塑性也明显提高;Ni-49.2%Co合金的抗拉强度(σb )和断裂伸长率(δ)分别为1650 MPa和9%,Ni-66.7%Co合金的σb和δ分别为2200 MPa和12%。Ni-66.7%Co合金中FCC和HCP结构相互协调,在变形过程中释放内应力,使材料应变硬化能力得以保持,所以获得更高的强度和塑性。     

Magnetic properties and microstructures of SnO2 doped Mn-Zn ferrites

The effects of additive SnO2 (0.4wt.%), with and without SiO2 (0.02wt.%) and/or CaO(0.04wt.%), on the microstructure and magnetic properties of Mn-Zn ferrites were reported. The results reveal that SnO2 on its own increases the initial permeability ( μi) slightly, but SnO2 with SiO2 and/or CaO decreases the values of μi. However, ferrites with SnO2 additions have reduced power losses. The separate contributions of hysteresis loss and eddy current loss to the total power loss show that SnO2 (with or without SiO2 and/or CaO) doping increases the hysteresis loss slightly, but SnO2 doping alone reduces the eddy current loss significantly (～14%). The additions of SiO2 or CaO further decrease the eddy current loss, and by interaction of SnO2-CaO-SiO2, the eddy current loss is reduced by more thaN20%. These magnetic and microstructural effects were discussed in terms of the additive-impurity interaction, the existence of grain boundary phases, and the effective bulk and grain boundary resistivities of the ferrites.     

Mechanical properties and microstructures of a wrought AZ91 alloy

Effects of hot plastic deformation on microstructures and tensile properties of AZ91 alloy were investigated. Compared with as-T4 microstructures, the as-extruded samples of AZ91 alloy with fine grains exhibit better strength and ductility due to dynamic recrystallization. The succeeded rotation forging also provides freer grains while the strength increases, but the elongation decreases. Simultaneously, wrought AZ91 alloy shows more balance properties than as-T4 condition ones. An interesting elongation of 228.5% is attained in the as-extruded AZ91 alloy in spite of the coarse grains with the size of 85 μm. The two-step method enhances the superplastic property of AZ91 alloy. The microstructure is still keeping the same scale of grains after superplastic testing.     

Influence of thermal exposure on the microstructures and mechanical properties of a superalloy

The effects of long-term aging on microstructures and their influence on tensile and stress-rupture behavior of a corrosion resistant nickel-base superalloy are investigated. Samples are aged isothermally at 1073, 1123, or 1173 K for different times of up to 10,000 h and mechanical tests are performed on samples in both standard heat treatment (SHT) and aged conditions. Scanning electron microscopy (SEM) studies reveal that the coarsening kinetics of γ′ follows a linear law at different temperatures with the calculated activation energy, i.e., 255 kJ/mol, for γ′ growth according to Lifshitz-Slyozof-Wagner (LSW) theory. After long-term aging for more than 1 khours, σ phase appears in the alloy. The kinetics of σ formation can be described by the Johnson-Avrime-Mehl equation. Tensile experiments at room temperature and 1173 K and endurance experiments at 1173 K/274 MPa are performed to test the effect of σ phases on these properties and no remarkable harmful effect is found. γ′ coarsening can be used to explain the reduction of yield stress, which is tested by the Labusch-Schwarz hardening theory. Although the presence of the σ phase clearly does affect the fracture process, the σ phase does not embrittle the alloy.     

镀锌管螺纹加工方式对管牙显微组织和性能的影响

对采用滚压和切削两种成形方式加工的镀锌管螺纹管牙的显微组织、力学性能和极化曲线进行了对比研究。结果表明:滚压加工成形方式明显改善了管牙的表面质量,管牙表层和浅表层的显微组织因强烈塑性形变而明显细化且呈细长纤维状;严重的加工硬化使显微硬度显著升高,最高可达约240 HV;单管牙扣的最大抗拉力约为29.88 k N;此外,滚压加工方式使管牙表面镀锌层得以部分保留,从而提高了螺纹的耐蚀性。相比之下切削加工成形方式所加工的管牙表面粗糙,内部显微组织仍为等轴晶,表层和次表层显微硬度一般在184~194 HV之间,力学性能相对较差,单管牙扣的最大抗拉力为21.56 k N,仅为滚压成形的72.2%;管牙表面镀锌层被切除,螺纹耐蚀性显著下降。     

Al-Ti-C-Sr对A356合金组织和性能的影响

在A356熔体中分别加入自制的Al-5Ti-0.25C-2Sr和Al-5Ti-0.25C-8Sr中间合金,研究了这两种中间合金对A356合金显微组织和力学性能的影响.结果表明,向A356中分别添加质量分数0.5%的Al-5Ti-0.25C-2Sr和Al-5Ti-0.25C-8Sr后,A356合金晶粒尺寸由42.5 μm分别减小至33.2 μm和30.6 μm,共晶硅从粗大的针片状转变为细小的短杆状或点状;T5处理后,添加Al-5Ti-0.25C-8Sr的A356合金的共晶硅粒状化效果较未添加Al-Ti-C-Sr的和添加Al-5Ti-0.25C-2Sr的好一些,其共晶硅颗粒均匀细小,圆整度高;加入质量分数0.5%的Al-5Ti-0.25C-2Sr或Al-5Ti-0.25C-8Sr后,T5态A356合金的抗拉强度由217.6 N/mm2分别提高到235.8 N/mm2和248.2 N/mm2,伸长率由10.1%分别提高到11.2%和11.8%.     

6061铝合金焊接接头的组织与性能分析

通过金相技术、力学性能试验和SEM技术研究了6061-T6铝合金真空电子束焊接接头的金相组织、力学性能和断口形貌特征.结果表明:焊接接头的拉伸强度低于母材.预热和重熔可以同时降低电子束焊接接头的强度和塑性,尤其对接头的塑性影响更大.焊缝区和热影响区的硬度均低于母材,预热和重熔可以降低焊接接头的硬度.焊缝区组织主要为等轴晶和树枝柱状晶,熔合区组织主要为柱状晶.预热和重熔使得焊缝区的晶粒组织变得粗大,焊接接头的拉伸断口断面上分布的韧窝尺寸较小,且韧窝的大小接近,未发生明显的塑性流动,呈现出铸态断口特征.     

Effect of Mn on microstructures and mechanical properties of Al-Mg-SiCu-Cr-V alloy

In order to improve the performances of the Al-Mg-Si-Cu-Cr-V alloy,various amounts of Mn(0-0.9wt.%) were added.The effect of this Mn on the microstructures and mechanical properties of Al-Mg-Si-Cu-Cr-V alloys in different states,especially after hot extrution and solid solution treatment,was systematically studied using scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and mechanical tests at room temperature.The results show that 0.2wt.% Mn can both refine the as-cast microstructure of the alloy and strengthen the extrusion+T6 state alloy without damaging the plasticity badly due to the formation of Al 15(FeMn) 3 Si 2 and Al 15 Mn 3 Si 2 dispersoids.Compared with the extrusion+T6 state alloy without Mn addition,the ultimate tensile strength and yield strength of the alloy with 0.2wt.% Mn addition are increased from 416.9 MPa to 431.4 MPa,360.8 MPa to 372 MPa,respectively.The elongation of the extrusion+T6 state alloy does not show obvious change when the Mn addition is less than 0.5wt.%,and for the alloy with 0.2wt.% Mn addition its elongation is still as high as 15.6%.However,when over 0.7wt.% Mn is added to the alloy,some coarse,stable and refractory AlVMn and Al(VMn)Si phases form.These coarse phases can reduce the effect of Mn on the inhibition of re-crystallization;and they retain the angular morphology permanently after the subsequent deformation process and heat treatment.This damages the mechanical properties of the alloy.     

时效对超高强含Sc铝合金组织和性能的影响

采用维氏硬度测量、室温拉伸性能测试和显微组织结构分析,研究了不同时效制度下Al-Zn-Cu-Mg-Sc-Zr合金的力学性能、腐蚀性能和显微组织.结果表明,该合金具有显著的时效硬化效应,随时效温度的升高,合金达到时效硬度峰值的时间缩短.合金适宜的时效制度为120℃24h.此时,合金的抗拉强度、屈服强度、伸长率和维氏硬度分别为696N/mm2、654N/mm2、11.1％和211.2HV.合金中主要强化相为GP区和η'相,主要强化作用为沉淀强化及弥散强化.时效过程中Al3Sc和Al3(Sc,Zr)质点表现出较强的热稳定性;合金抗晶间腐蚀能力随时效时间的延长而增强.     

Effects of microstructures on mechanical properties of Ti-63 titanium alloy

The microstructure and mechanical properties of Ti-63 pancakes were investigated under different heat-treatment modes. Pancake No. 1, with an as-forged bimodal structure, was β annealed at 930°C for 1 h. Its structure was changed to a Widmanstatten structure with continuous grain boundary α phase and long lamellar α phase. The pancake showed a good combination of strength, ductility and fracture toughness. Pancake No. 2, with an as-forged bimodal structure, was aged at 540°C for 8 h after annealing at 930°C for 1 h. Other than the fine secondary α precipitates, it showed a similar microstructure to that of pancake No. 1. The fine precipitates can enhance the pancake’s strength while reducing the ductility and fracture toughness. Pancake No. 3, with an as-forged basket-weave structure, was annealed at 750°C for 1 h. Its structure was nearly unchanged and it achieved a better ductility but a slightly lower fracture toughness than pancake No. 1.     

Fabrication,microstructures and High-Strain-Rate properties of TiC-reinforced titanium matrix composites

TiC ceramic particulate-reinforced titanium matrix composites were fabricated and the resultant densification, microstructure, and static and dynamic mechanical properties were studied. Comparing Ti with TiH₂ powders as host materials for TiC ceramic reinforcement by pressureless vacuum sintering, TiH₂-started composites showed better sinterability and resistance to both elastic and plastic deformation than Ti-started ones. When TiH₂ and TiH₂-45 vol.% TiC samples were hot pressed, TiH₂ matrices transformed to alpha prime Ti and alpha Ti phase, respectively. It is interpreted that the diffusion of an alpha stabilizer carbon from TiC into the matrix is one of the plausible reasons for such a microstructural difference. The 0.2% offset yield strengths of the hot pressed TiH₂ and TiH₂-45 vol.% TiC samples were 1008 and 1446 MPa, respectively, in a static compressive mode (strain rate of 1×10⁻³/s). Dynamic compressive strengths of the samples were 1600 and 2060 MPa, respectively, at a strain rate of 4×10³/s.