Z.Y. Wu R.K. Shiue C.S. Chang
材料科学技术（英）
The transmission electron microscopy was employed to investigate the microstructure of infrared brazed high-strength Ti alloy using the Ti-15Cu-15Ni filler metal. Coarse primary Ti2Ni and transformed β-Ti are observed in the 300 s brazed specimen. Blocky Ti2Ni and eutectoid Ti2Cu intermetallics are disappeared from the joint with increasing the brazing time to 1800 s. Both acicular α-Ti and retained β-Ti dominate the entire brazed joint.
关键词:
Infrared Brazing
,
Ti
,
Ti-Cu-Ni filler
,
Microstructure
Jian Zhang Jinguo Li Tao Jin Xiaofeng Sun Zhuangqi Hu
材料科学技术（英）
A single crystal Ni-base superalloy was processed with withdrawal rates between 2 and 7 mm/min. The as-cast microstructures, heat treatment response and creep property have been characterized as a function of the withdrawal rate. As expected, the primary and secondary dendrite arm spacing decreased with increasing withdrawal rate; microsegregation degree and porosity distribution were also varied with different withdrawalrates. The withdrawal rate of 2 mm/min resulted in a noticeable residual microsegregation even after full heat treatment. The samples solidified at 7 mm/min exhibited a high density of cast porosities, and this led to a dramatical decline of the creep strain. 4 or 6 mm/min appeared to be the optimum withdrawal rate in the present study, which resulted in a uniform microstructure and an optimum density of cast porosity.
关键词:
Single crystal superalloy
,
Withdrawal rate
,
Microstructure
,
Creep
Waled Elthalabawy Tahir Khan
材料科学技术（英）
The excellent corrosion resistance, formability and strength make stainless steels versatile for diverse applications. However, its high specific strength and good crashworthiness make it suitable for transportation and aerospace industry. On the other hand, the need to reduce the weight of vehicle and aerospace components has created renewed interest in the use of magnesium alloys. Due to their differences in physical and metallurgical
properties, bonding of the 316L steel and AZ31 magnesium alloy using conventional fusion welding methods encountered many limitations. Therefore, the use of liquid phase forming interlayers is required to overcome the differences in their properties, eliminates the need for a high bonding pressure to achieve intimate contact between the bonded surfaces. Both Cu and Ni interlayers successively formed a eutectic phase with magnesium. The formation of intermetallics and Mg diffusion caused the eutectic phase to isothermally solidify with increasing bonding time. The formation of ternary intermetallic phases (λ1 and B2) impaired the bond shear strength particularly at the end of the isothermal solidification stage where no eutectic phase was observed.
However, the joints showed a higher shear strength value of 57 MPa when bonding with Cu interlayer at 530°C for 30 min compared to 32 MPa when Ni interlayer was used at 510°C for 20 min.
关键词:
Magnesium alloy
,
Stainless steel
,
Eutectic Bonding
,
Microstructure
,
Shear strength
W.D. Wang
材料科学技术（英）
Solid state phase transformation characteristics of the body centred β(Ti) into the hexagonal closed packed α(Ti) in Ti45Al8Nb-(0, 0.3, 0.5 and 0.8 at. pct) B alloys were investigated by heat treatment to clarify γ/α2 lamellar microstructure refinement induced by B addition. Experimental results confirmed two kinds of boron-reduced grain refinement mechanisms through refining either β phase thenα phase (β-refinement) or α phase directly (α-refinement) to refine lamellar microstructure at room temperature; however, the role of α-refinement dominated the as-cast lamellar microstructure refinement over β-refinement in Ti45Al8NbxB alloy. It was also found that during the α-refinement the convoluted flake- and plate-like borides along β grain boundaries assisted nucleation of α phase, and the particle-like borides near β grain boundaries impeded α phase growth.
关键词:
Titanium aluminides
,
Phase transformation
,
Microstructure
Zhengrong PAN
金属学报(英文版)
The effects of 0.5 wt pct In on Al-3.3Cu-0.8Li alloy were studied. Instead of T1 (Al2CuLi) phase, there was an unknown cubic phase acting as the dominant precipitates in the In-added alloy in T6 temper, which disappeared in T8 temper. The orientation relationship between this phase and matrix was given by SAEDs: (001)p//(001)α, [010]p//[010]α. Both measuring directly from HREM images or calculating from it's FFTs gave an close lattice parameter about 0.83~nm. 3DAP composition analysis revealed the presence of Al, Cu and Li in the atomic percentages: 60%Al, 30%Cu and 10%Li. Thus, this cubic phase is considered to be Li-rich γ1 (Al4Cu9) phase or a new phase designated as χ (Al5Cu6Li2). Different from the traditional report providing heterogeneous nucleation sites for the precipitates, In was detected neither around nor in the cubic phase by EDX and 3DAP.
关键词:
Indium
,
Precipitation
,
Microstructure
,
HRTEM
,
3DAP
石盼盼
,
孙爱民
,
马书懿
,
王丹
,
张明发
低温物理学报
采用固相反应法制作了在不同烧结温度对Sn掺杂下的YBCO一系列样品.本文采用了X-射线衍射仪,电阻测量和SEM对样品物相形成,微观结构,晶格常数以及超导转变温度进行表征,测量结果表明:不同的烧结温度会影响Sn离子的形式,随着温度的升高,Y-123峰明显减弱,杂峰相增多.本文分析了晶格常数与超导性存在必然联系,SEM结果表明第二相粒子的形成以及表面形貌都与温度有关.
关键词:
YBCO超导
,
Sn掺杂
,
微观结构
,
烧结温度(℃)
Guofeng Wang Kaifeng Zhang
材料科学技术（英）
Ni-Mn nanocomposite reinforced by Al2O3 particles was fabricated by pulse electrodeposition. The average grain size is 60 nm and the content of Mn and Al2O3 particles is 0.3 and 0.6 wt pct, respectively. The superplastic deformation behavior was further studied at the temperatures ranging from 673 to 873 K. A maximum elongation of 530% is obtained in the tension test at a temperature of 773 K and at a strain rate of 1.67×10-3 s-1. The curves of the flow stress vs strain rate have features similar to the trend of conventional superplastic materials. The test temperature (773 K) equals to 0.35Tm, which means the material obtains low temperature superplasticity. The microstructures of the composite were examined and grain growth was observed during deformation.
关键词:
Electrodeposition
,
纳米复合材料
,
低温超塑性
,
显微组织
Mingguang Wang
材料科学技术（英）
Transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) have been used to study the microstructural properties of La0.7Ca0.3MnO3 films on (001) LaAlO3 substrates prepared by direct current magnetron sputtering technique. The as-grown thin films with different thickness are perfectly coherent with the substrates. The film suffers a tetragonal deformation in the area near the interface between the film and the substrate. With increasing thickness, the film is partially relaxed. It was found that La0.7Ca0.3MnO3 films consist of two types of oriented domains described as: (1) (110)f [001]f||(001)s[100]s and (1¹10)f [001]f||(001)s[100]s and (2) (110)f [001]f||(001)s[010]s and (1¹10)f [001]f//(001)s[010]s. Upon annealing, the film is relaxed by the formation of mis¯t dislocations. Other than mis¯t dislocations, two types of threading dislocations with Burgers vector of <100> and <110> were also identified.
关键词:
Colossal magnetoresistance
,
null
,
null
,
null
Gaohui Wu
,
Meihui Song
,
Ziyang Xiu
,
Ning Wang
,
Wenshu Yang
材料科学技术（英）
M40 carbon fibre reinforced rare earth magnesium alloy ZM6 composites with fibre volume fraction about 60% were fabricated by pressure infiltration method. The microstructure, interfacial morphology, and precipitation were studied by scanning electron microscopy, transmission electron microscopy, and energy dispersive X-
ray spectrometer. It was shown that the interfaces between Mg alloy and fibres were well bonded and free from cracks. The Mg12Nd phase was preferentially precipitated at the fibre/matrix interfaces, leading to the segregation of Nd at the interfaces and the dramatic decrease of Mg12Nd precipitation in the matrix far from interfaces. Crystal defects such as high-density dislocations and twins were observed in the matrix near the fibre/matrix interface. A high bending strength (1393 MPa) and elastic modulus (190 GPa) were achieved in M40/ZM6 composite.
关键词:
Magnesium matrix composites
,
null
,
null
,
null
