Cyclic oxidation behavior of b-NiAlDy alloys containing varying aluminum content at 1200 1C

b-NiAlDy cast alloys containing varying aluminum content were prepared by arcmelting. The microstructures and cyclic oxidation behavior of the alloys at 1200 1C were investigated. Grain refinement was achieved by increasing aluminum content in the alloy, which is beneficial to selective oxidation. The Ni–55Al–0.1Dy alloy showed excellent cyclic oxidation resistance due to the formation of a continuous, dense and slow-growing oxide scale. In contrast to this, severe internal oxidation as well as large void formation at the scale/alloy interface occurred in the Ni–45Al–0.1Dy alloy. The aluminum content dependence of the reactive element effects in b- NiAlDy was established that Dy doping strengthened the scale/alloy interface by pegging mechanism in high-aluminum alloys but accelerated internal oxidation in low-aluminum alloys during high-temperature exposure.     

Effect of niobium alloying level on the oxidation behavior of titanium aluminides at 850°C

This work addresses the alloying of titanium aluminides used in aircraft engine applications and automobiles. The oxidation resistance behavior of two titanium aluminides of α₂ + γ(Ti₃Al + TiAl) and orthorhombic Ti₂NbAl, recognized as candidates for high-temperature applications, was investigated by exposure of the alloys for 100 h in air. Thus, oxidation resistance was expressed as the mass gain rate, whereas surface aspects were analyzed using scanning electron microscopy in conjunction with energy-dispersive X-ray spectroscopy, and the type of oxidation products was analyzed by X-ray diffraction and Raman spectroscopy. The orthorhombic Ti₂NbAl alloy was embrittled, and pores and microcracks were formed as a result of oxygen diffusion through the external oxide layer formed during thermal oxidation for 100 h.     

High-temperature oxidation behaviour of novel Co-Al-W-Ta-B-(Mo,Hf,Nb) alloys with a coherent γ/γ'–dominant microstructure

In this work,2at% Mo,2at% Nb and 2at% Hf were substituted for the same amount of W into a Co-9Al-9W-2Ta-0.02 B alloy(hereafter referred as to 2Mo, 2Nb and 2Hf alloys, respectively, while the original alloy is denoted as 0Me alloy). The effect of the Mo, Hf and Nb additions on the isothermal oxidation resistance, oxide scale evolution and failure mechanism, of the Co-9Al-9W-2Ta-0.02 B alloy when exposed at 800 °C and 900 °C for 100 h was investigated. It was found the Mo, Hf and Nb additions degraded the oxidation resistance of the Co-9Al-9W-2Ta-0.02 B alloy, while the 2Mo alloy always displayed the poorest oxidation resistance, resulted from heavy spallation of the oxide scale. An oxide scale composed of an outer Co_3O_(4+)CoO layer, a middle complex oxide layer enriched with Al, W and Ta, and a γ/needle-like Co_3W zone adhering to the γ/γ' substrate was gradually formed; moreover, a continuous or discontinuous Al_2O_3 layer and dispersive Al_2O_3 dots or slices were observed within the γ/needle-like Co_3W zone, depending on the oxidation temperature and added elements(Mo, Hf and Nb). The formation of volatile MoO_3 in the oxide scale of the 2Mo alloy enhance the exfoliation of the oxide products, resulting in severe spallation and poor oxidation resistance.     

Oxidation behavior of high-strength FeCrAl alloys in a high-temperature supercritical carbon dioxide environment

The oxidation behavior of three high-strength FeCrAl alloys was investigated in supercritical carbon dioxide environment at 650 ℃. After exposure for 500 h, the weight gains of the FeCrAl alloys gradually decreased with increasing Al content. The oxide scales are primarily composed of α-Al_2O_3 and spinel oxides. With increasing Al content, the amount of α-Al_2O_3 increases and the C content decreased in the oxide scale and sub-scale matrix.Moreover, larger(Nb,Mo)C carbides formed in the sub-scale matrix and their number decreased with the increase of Al content.     

Formation of ■ phase in Cu-Ge peritectic alloys

Rapid growth behavior of ■ phase has been investigated in the undercooling experiments of Cu-14%Ge, Cu-15%Ge, Cu-18.5%Ge and Cu-22%Ge alloys. Alloys of the four compositions obtain the maximum undercoolings of 202 K(0.17TL), 245 K(0.20TL), 223 K(0.20TL) and 176 K(0.17TL), respectively. As the content of Ge increases, the microstructural transition of "α (Cu) dendrite ■ peritectic phase →■ peritectic phase →■ dendrite (ε ■ ) eutectic" takes place in the alloy at small undercooling, while the microstructural transition of "fragmented α (Cu) dendrite ■ peritectic phase →■peritectic phase →■ dendrite ε phase" happens in the alloy at large undercooling. EDS analysis of the Ge content in ■ peritectic phase indicates that undercooling enlarges the solid solubility of α dendrite, which leads to a decrease in the Ge content in ■ phase as undercooling increases. In the Cu-18.5%Ge alloy composed of ■ peritectic phase, the Ge content in ■ phase increases when undercooling increases, which is due to the restraint of the Ge enrichment on the grain boundaries by high undercooling effect.     

Effects of phosphorus addition on the properties of Sn-9Zn lead-free solder alloy

This article explores the effects of phosphorus addition on the wettability between Sn-9Zn solder alloy and Cu substrates, the oxidation behavior and the corrosion behavior of Sn-9Zn solder alloy. Spreading test was used to characterize the wettability of Sn-9Zn-xP solder alloys to Cu substrates. The oxidation and corrosion behaviors of Sn-9Zn-xP solder alloys were determined by means of weight gaining, and secondary ion mass spectrometry was used to analyze the oxygen content. The role and mechanism of P in the solder alloys were also discussed. It is found that the addition of P can significantly improve the wettability of the solder alloys. Incorporating P into Sn-9Zn solder alloy obviously decreases the oxygen content and enhances the oxidation and corrosion resistance. Microstructure observations show that an appropriate amount of P can greatly refine coarse rod-like Zn-rich phases in Sn-9Zn solder alloy.     

Influence of an emulsifier on the pressure desensitization of emulsion explosives

The desensitization degree of emulsion explosives (EE) was calculated with the peak pressure of explosion shock waves tested in water. To an explosive, the less the desensitization degree, the better the compression resistance, so the compression resistance of an explosive can be compared and analyzed quantificationally with the desensitization degree. The influence of an emulsifier on the pressure desensitization of EE was studied, including the content and category of emulsifiers. Three kinds of emulsifiers (Span-80, compound emulsifier, and T-152) were used in the tests. The experimental results show that both the content and category of emulsifiers make a great effect on the pressure desensitization of EE. The desensitization degree of EE reduces with the emulsifier content being increased, but there is an optimal content of an emulsifier for the compression resistance of EE. While the content of Span-80 reaches 4wt%, the desensitization degree of EE becomes a minimal value, and augments somewhat if the emulsifier content is increased more. That is to say, the compression resistance of EE becomes the highest while the content of Span-80 is 4wt%, and the compression resistance will decline if the content of Span-80 is increased more. The compression resistance of the explosive emulsified by compound emulsifier is the highest among all the explosives, when the content of the whole components and manufacturing engineering are kept invariable.     

Review： Perspectives on the metallic interconnects for solid oxide fuel cells

The various stages and progress in the development of interconnect materials for solid oxide fuel cells (SOFCs )over the last two decades are reviewed. The criteria for the application of materials as interconnects are highlighted. Interconnects based on lanthanum chromite ceramics demonstrate many inherent drawbacks and therefore are only useful for SOFCs operating around 1000℃. The advance in the research of anode-supported flat SOFCs facilitates the replacement of ceramic interconnects with metallic ones due to their significantly lowered working temperature. Besides, interconnects made of metals or alloys offer many advantages as compared to their ceramic counterpart. The oxidation response and thermal expansion behaviors of various prospective metallic interconnects are examined and evaluated. The minimization of contact resistance to achieve desired and reliable stack performance during their projected lifetime still remains a highly challenging issue with metallic interconnects. Inexpensive coating materials and techniques may play a key role in promoting the commercialization of SOFC stack whose interconnects are constructed of some current commercially available alloys. Alternatively, development of new metallic materials that are capable of forming stable oxide scales with sluggish growth rate and sufficient electrical conductivity is called for.     

Roles of titanium-rich precipitates as inoculants during solidification in low carbon steel

The effect of titanium on the as-cast structure and the growth form of titanium precipitates, and the effect of cooling rate on the size and distribution of titanium precipitates were studied. It is shown that Ti-rich precipitates acting as heterogeneous nucleation sites play an important role in refining the grain size and increasing the equiaxed grain ratio. Cooling rate has a great effect on the size and distribution of precipitates. The number of precipitates increases and the size decreases with the increase of cooling rate. Ti-rich particles acting as heterogeneous nucleation sites at the onset of solidification are observed in the experiment. This result suggests that TiN nucleated on Ti₂O₃ is an effective inoculant for δ-ferrite during solidification in low carbon steel.     

STUDY ON VISCOELASTIC BEHAVIOR OF PAPER COATING

INTRODUCTIONPaper coating is a mixed system composed of various minerals and polymers with different structures. The properties of paper coating are important factors affecting quality of coating paper and coating process. For a long time, the performances of paper coating are confined to its macroscopic properties, such as solid content, viscosity, pH value, etc. These parameters are easy to measure and convenient for transverse comparison among coatings with different formula. But for …     

Creep behavior and effect factors of a TiAl–Nb alloy at high temperature

The effect of solution treatment on the microstructure and creep properties of forged TiAl–Nb alloys was investigated. The results showed that the microstructure of forged alloy mainly consisted of γ/α₂ lamellar colonies and fine equiaxed recrystallized γ/α₂ grains. During the solution treatment the microstructure of the alloy transformed into a fully lamellar structure due to the lamellar colonies growth by consuming equiaxed grains. Compared with the forged alloy the creep life of the solution treated alloy at 800 ?°C/220 ?MPa increased from 116 ?h to 339 ?h. The better creep resistance may be attributed to the transform of fine equiaxed γ/α₂ grain to the lamellar colonies with serrated grain boundaries due to the solution treatment. The deformation mechanism of the solution treated alloy during creep is considered to be dislocation slipping within the lamellar γ/α₂ phases, and the dislocation movement may be hindered by the γ/α₂ interface and the formation of dislocation tangles. The interaction of the dislocations with the tangles may increase the resistance of the dislocation motion and hence improve the creep resistance of the alloy. It was found that during the creep of the forged alloys the cracks mainly initiated at the equiaxed grain, and in the solution treated alloy the cracks initiated at the grain boundaries. As creep continued the cracks propagated and connected to each other, leading to the damage and rupture of the forged and solution treated alloys.     

机械搅拌对ZA27合金组织的影响

研究了机械搅拌对ＺＡ２７合金组织的影响，同时给出了温度与固相率的对应值．结果表明，在机械搅拌下，ＺＡ２７合金的凝固组织为等轴晶或玫瑰状聚集体，由枝晶残体和棒状与球状粒子组成，且随着温度的降低，初生相逐渐球状化和分散化；初生晶非树状化是由于枝晶臂颈缩折断，合并生长所致；机械搅拌加剧了晶臂颈缩，促进了颈缩折断；固相间存在着合并生长     

Ti3SiC2代替石墨金属基自润滑材料研究进展

Ti₃SiC₂是一种新型的金属陶瓷材料,该材料兼具金属与陶瓷材料的双重性能,具有良好的导电性、导热性、加工性、耐腐蚀性与高温抗氧化性,同时该材料还具有超低的摩擦因数.基于其独特性能,大量科研工作开始投入到使用Ti₃SiC₂代替石墨制备金属基自润滑复合材料中.介绍了近年来石墨及以Ti₃SiC₂作为固体润滑颗粒制备的金属基自润滑复合材料的研究现状及进展.探讨了石墨和Ti₃SiC₂与金属界面结合问题,并对比两种复合材料的力学性能和摩擦学性能.最后指出以Ti₃SiC₂代替石墨制备金属基自润滑材料的可行性以及未来的发展方向.     

Effects of minor B additions on tensile strength,fracture toughness and oxidation resistance of Nb–Si based alloys

The effects of minor additions of B on microstructure, ambient tensile strength, fracture toughness and high-temperature oxidation resistance of Nb–Si based alloys were investigated. The added contents were designed as 0.05, 0.10 and 0.20 ?at.%. The results show constituent phases in 0.05B and 0.20B alloys were Nbss, α-Nb₅Si₃; while only 0.10B alloy consisted of γ-Nb₅Si₃. Minor B was prioritized into Nbss and redundant one dissolved into silicide enhanced volume fraction of the silicide. With increasing concentrations of boron, the microstructure was refined at first and then coarsened, while the tensile strength was enhanced remarkably. Compared with other two alloys, the 0.10B alloy containing γ-Nb₅Si₃ shows both the best fracture toughness and oxidation resistance. The important roles of γ-Nb₅Si₃ in balancing overall properties are emphasized.     

Cu-Ni-Al系合金铸态组织研究

对Cu-Ni-Al系合金的铸态组织进行研究,使企业更好地认识和了解Cu-Ni-Al系列合金,进而更好地开发利用该合金.采用金相显微镜、扫描电子显微镜和能谱仪,对Cu-Ni-Al和Cu-Ni-Al-Ti合金进行观察和分析.结果表明：Cu-9.0Ni-1.4Al合金铸态组织中枝晶组织与偏析区（Ni₃Al）界限十分明显,且枝晶组织比较粗大.而Ti的加入促使Ni和Cu的分布变得均匀,并且Ti的加入使合金中有魏氏体产生,致使合金的力学性能降低,减小了合金的变形能力,导致Cu-9.0Ni-1.4Al-0.5Ti合金在热轧时有开裂的现象发生.并且能谱分析显示Ni₃Al存在于枝晶中和枝晶间,说明Ni₃Ti的稳定性较好,在高温时就有Al₃Ti形成,在固溶扩散过程中,Ni₃Ti被排挤到枝晶之间,形成第二相.     

Microstructure evolution of Ti–6Al–4V under cold rolling + low temperature nitriding process

A new nitriding process modifying both the surface and the matrix is proposed to improve the poor wear resistance and low hardness of the titanium alloy surface. The treatment of solid solution treatment, cold rolling and low temperature nitriding was used for surface modification. The results showed that the microstructure of the Ti–6Al–4V(TC4) titanium alloy sample changed from the original α+β phase to the residual α phase, metastable β phase and martensite α′ phase after solution treatment. The results of cold rolling experiments indicated that with the increase of rolling amount, many defects generated, and the grains were first elongated and then partially broken. During the process of low-temperature nitriding the recrystallization occurred, which effectively avoided the problem of coarse matrix structure. It has been found that after low-temperature nitriding, thin strip-like α-phase with dispersed distribution, which is a typical aging structure, formed. The XRD test results indicate that steady state nitrides Ti₂N formed on the surface of the sample, but the content of Ti₂N was relatively low. Based on the morphology of content of the surface and cross-section it is believed that a special type of nitriding layerformed after low-temperature nitriding. The mechanical performance test results indicate that the wear resistance and hardness of the alloy increased significantly.     

A Ti–Zr–Cu–Ni–Co–Fe–Al–Sn amorphous filler metal for improving the strength of Ti–6Al–4V alloy brazing joint

Ti_(50)Zr_(27)Cu_8Ni_4Co_3Fe_2Al_3Sn_3(at%) amorphous filler metal with low Cu and Ni contents in a melt-spun ribbon form was developed for improving mechanical properties of Ti–6Al–4V alloy brazing joint through decreasing brittle intermetallics in the braze zone. Investigation on the crystallization behavior of the multicomponent Ti–Zr–Cu–Ni–Co–Fe–Al–Sn amorphous alloy indicates the high stability of the supercooled liquid against crystallization that favors the formation of amorphous structure. The Ti–6Al–4V joint brazed with this Ti-based amorphous filler metal with low total content of Cu and Ni at 1203K for 900s mainly consists of α-Ti, β-Ti,minor Ti–Zr-rich phase and only a small amount of Ti_3Cu intermetallics, leading to the high shear strength of the joint of about 460 MPa. Multicomponent composition design of amorphous alloys is an effective way of tailoring filler metals for improving the joint strength.     

Improvement of oxidation resistance of Nb–Ti–Si based alloys with additions of Al,Cr and B at different temperatures

The effects of Cr, Al and B addition on the microstructure and high-temperature oxidation behaviors (at 1200, 1250 and 1300 ?°C) of Nb–Ti–Si based alloys were investigated. The results showed that the addition of Cr stabilized α-Nb₅Si₃, while Al promoted the formation of β-Nb₅Si₃ and adding B promoted the formation of γ-Nb₅Si₃. Among the three elements, Al and Cr were beneficial to oxidation resistance at 1200 ?°C, and B was favorable to the oxidation resistance at 1300 ?°C. At 1250 ?°C, Al and B had the same effects on the improvement of oxidation resistance. The ratio of these alloying elements might play an important role in enhancing oxidation resistance. The oxidation resistance of the three kinds of silicides was compared, and the sequence was: γ-Nb₅Si₃> β-Nb₅Si₃> α-Nb₅Si₃. To predict the effects of the investigated alloying elements on the oxidation resistance of Nb–Ti–Si based alloys in a wider range of concentration, an artificial neural network (ANN) model was established, showing excellent accuracy and generalization ability. With the instructions of the ANN model, the oxidation resistance can be optimized with less additions of alloying elements.     

Microstructure and heat treatment for Ni3Al-based single crystal alloy with different crystal orientations

Ni₃Al-based single crystal alloy IC6SX with different crystal orientations were prepared by seed crystal method. The microstructure and heat treatment of the alloy were investigated. The results showed that the microstructure of the alloy was in dendrite structure, and the crystal orientation had significant effect on the dendrite morphology of this alloy. The precipitated phases of (MoNi)₆C and NiMo appeared in the microstructure of the three alloys with different crystal orientations during solidification process. Compared with other two alloys, the volume fractions of precipitated phases of both (MoNi)₆C and NiMo was the most in the alloy with [111] orientation and the least in the alloy with [001] orientation. The solidus and liquidus temperatures of the alloy IC6SX tested by differential scanning calorimetry (DSC) were 1356 °C and 1387 °C, respectively. Meanwhile, the effect of different solution temperatures on the microstructure of the alloy with different orientations was studied. The results showed that the precipitated phases of (MoNi)₆C and NiMo were eliminated with the solid solution treatment under the condition of 1300 °C/10 h. However, the incipient melting of the alloys occurred due to the dissolution of low melting point phases. As the temperature dropped to 1280 °C, the area of incipient melting in the alloy with different orientations decreased gradually. However, there was no incipient melting appearing in the three alloys with different orientations when the solution treatment temperature dropped to 1260 °C.     

Optimization of mechanical properties of Sn-3.8Ag-0.7Cu alloys by the additions of Bi,In and Ti

Bi, In and Ti were added to Sn-3.8Ag-0.7Cu (SAC387) solder alloy to optimize the mechanical performance. The alloying effects of Bi, In and Ti on the microstructure, thermal and mechanical properties of SAC387 based solder alloys were investigated. The results demonstrate that adding 3.5 ?wt % of Bi could refine the microstructure, optimize the thermal properties, and improve the tensile strength. Meanwhile, the ductility of the solder alloys reduced evidently. Adding 2.8 ?wt % of In into SAC387–3.5 ?wt %Bi alloy could increase both the strength and ductility, which is attributed to the beneficial effect of In addition, as adding In could improve the solubility of Bi in the β-Sn matrix. Meanwhile, the melting point was reduced, and the wettability improved with the addition of In. Introducing amounts of Ti into SAC387–3.5 ?wt % Bi-2.8 ?wt % In alloy could further increase the strength. However, the ductility was significantly reduced when 0.8 ?wt % of Ti was added due to the formation of the coarse Ti₂Sn₃ phase. The undercooling was remarkably reduced with the addition of Ti. The nanoindentation tests demonstrate that the hardness increased mainly due to the hardening effect of the Bi addition. Among all the samples prepared, alloy SAC387–3.5 ?wt % Bi exhibited the highest creep resistance at the ambient temperature. Further adding In and Ti into SAC387–3.5 ?wt % Bi alloys reduced the creep resistance of the solder alloys. The mechanism associated with the different mechanical responses is also discussed in this study.