Structural Studies of Dispersoids in Fe–15 wt% Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–5 wt% Ti Model ODS Alloys During Milling and Subsequent Annealing

Oxide dispersion strengthened (ODS) steels have very high thermal stability and creep resistance due to reinforcement of hard and stable nano-sized ceramic dispersoids in metallic matrix which act as barriers to dislocation motion. This study established the role of Ti in the structural evolution of yttria during mechanical milling and subsequent annealing in a Fe–15 wt% Y₂O₃–5 wt% Ti model ODS alloy, using electron microscopy and XRD techniques. The alloy was synthesized in a high energy planetary ball mill in Ar atmosphere by varying the milling durations in the range of 0 (un-milled) to 60 h. The XRD result revealed amorphisation of Y₂O₃/Ti during milling and evolution of YTiO₃ complex oxide upon annealing at 1273 K for 1 h. The electron microscopy studies revealed the refinement of alloy powders from ~50  μm to few nanometers during milling. Electron diffraction analysis and high resolution transmission electron microscopy of 60 h milled as well as and annealed powder showed formation of different types of Y–Ti–O complex oxides such as Y₂Ti₂O₇, Y₂TiO₅ and YTiO₃.     

Wetting of molten cerium on typical carbon materials(graphite,CVD-diamond and NWCNT) and molten Cu-Ce alloys on graphite at 950℃

A series of experiments were conducted to investigate the wettability of graphite plate,graphite paper,NWCNTs Buckypaper,CVD-diamond by molten Ce and graphite plate by Cu-Ce binary alloy using a modified sessile drop method at 950℃.The remarkable apparent equilibrium contact angles(graphite plate(0°)相似文献   

Mechanical and Thermal Properties of Pulsed Electric Current Sintered (PECS) Cu-Diamond Compacts

In this work, dispersion strengthening of copper by diamonds is explored. In particular, the influence of 50- and 250-nm diamonds at contents of 3 and 6 vol. pct on the mechanical and thermal properties of pulsed electric current sintered (PECS) Cu composites is studied. The composite powders were prepared by mechanical alloying in argon atmosphere using a high-energy vibratory ball mill. The PECS compacts prepared had high density (>97 pct of T.D.) with quite evenly distributed diamonds. The effectiveness of dispersoids in increasing the microhardness was more pronounced at a smaller particle size and larger volume fraction, explained by Hall–Petch and Orowan strengthening models. The microhardness of Cu with 6 and 3 vol. pct nanodiamonds and pure sm-Cu (submicron-sized Cu) was 1.77, 1.46, and 1.02 GPa, respectively. In annealing experiments at 623 K to 873 K (350 °C to 600 °C), the composites with 6 vol. pct dispersoids retained their hardness better than those with less dispersoids or sm-Cu. The coefficient of thermal expansion was lowered when diamonds were added, being the lowest at about 14 × 10^?6 K^?1 between 473 K and 573 K (200 °C and 300 °C). Good bonding between the copper and diamond was qualitatively demonstrated by nanoindentation. In conclusion, high-quality Cu-diamond composites can be produced by PECS with improved strength and better thermal stability than for sm-Cu.     

Phase Evolution and Mechanical Properties of Nano-TiO2 Dispersed Zr-Based Alloys by Mechanical Alloying and Conventional Sintering

The present study deals with the synthesis of 1.0 to 2.0 wt pct nano-TiO₂ dispersed Zr-based alloy with nominal compositions 45.0Zr-30.0Fe-20.0Ni-5.0Mo (alloy A), 44.0Zr-30.0 Fe-20.0Ni-5.0Mo-1.0TiO₂ (alloy B), 44.0Zr-30.0Fe-20.0Ni-4.5Mo-1.5TiO₂ (alloy C), and 44.0Zr-30.0Fe-20.0Ni-4.0Mo-2.0TiO₂ (alloy D) by mechanical alloying and consolidation of the milled powders using 1 GPa uniaxial pressure for 5 minutes and conventional sintering at 1673 K (1400 °C). The microstructural and phase evolution during each stage of milling and the consolidated products were studied by X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy (TEM), and energy-dispersive spectroscopy. The particle size of the milled powder was also analyzed at systemic intervals during milling, and it showed a rapid decrease in particle size in the initial hours of milling. XRD analysis showed a fine crystallite size of 10 to 20 nm after 20 hours of milling and was confirmed by TEM. The recrystallization behavior of the milled powder was studied by differential scanning calorimetry. The hardness of the sintered Zr-based alloys was recorded in the range of 5.1 to 7.0 GPa, which is much higher than that of similar alloys, developed via the melting casting route.     

Performance of MWCNT-Reinforced SAC0307/Cu Solder Joint Under Multiple Reflow Cycles

The evolution of interfacial microstructure and its effect on shear strength under multiple reflow cycles for multi-walled carbon nanotubes (MWCNT)-reinforced Sn0.3Ag0.7Cu solder/copper joint was investigated. The melting characteristics, wettability and mechanical properties of the solder alloy were assessed. The addition of MWCNT in the range of 0.01–0.05 wt% improved the wettability, melting behaviour and mechanical strength of the SAC0307 solder alloy. The nanoparticles in small weight fraction (0.01–0.05 wt%) addition were more effective in retarding intermetallic compounds growth at the interface. Amongst all compositions studied, the SAC0307–0.05MWCNT nanocomposite showed significant improvement in the performance of SAC0307/Cu solder joint under multiple reflow condition. The nanoparticles’ reinforcement above 0.1 wt% of the solder alloy was ineffective in improving the solder performance due to increased clustering in the matrix.     

The microstructure and magnetization reversal behavior of melt-spun (Nd1−xCex)-Fe-B ribbons

In this study,the alloy ingots with nominal compositions of(Nd_(1-x)Ce_x)_(31)Fe_(bal)Co_(0.2)Ga_(0.1)B(x=0, 0.1 wt%,0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%) were prepared and then melt-spun to form nanocrystalline ribbons at the wheel speed of 20 m/s. XRD results show that all melt-spun ribbons exhibit the tetragonal structure(Nd,Ce)_2 Fe_(14)B phase with the space group P42/mmm. The Curie temperature and lattice constant decrease with the increase of Ce content. The Curie temperature decreases gradually from 306 to 247 ℃with the increase of Ce content. Those results indicate that Ce element has been incorporated into Nd_2 Fe_(14)B main crystalline phase and formed(Ce,Nd)-Fe-B hard magnetic phase. It is also found that the remanence ratio(M_r/M_s) decreases from 0.693 to 0.663 and the coercivity(H_c) decreases from 18.7 to14.2 kOe with the increase of Ce content. However, a relatively high coercivity of 18.3 kOe for(Nd_(1-x)Ce_x)_(31)Fe_(bal)Co_(0.2)Ga_(0.1)B(x = 0.2) melt-spun ribbon is achieved. The coercivity is sensitive to microstructure. The AFM patterns show the sample(x = 0.2) has the most uniform and finest microstructure. The magnetization reversal behavior(δM plots) is discussed in detail. The positive δM value is observed in every sample, which confirms the existence of exchange coupling interaction. Evidently, theδM maximum value reaches 0.9 in the sample(x = 0.2). It is indicated that the intergranular exchange coupling effect is the strongest, which is consistent with coercivity enhancing.     

The influence of milling parameters on the characteristics of milled and spray-dried NiCoCrAlY–Al2O3 composite powders

Spray-drying process was selected to agglomerate ball milled NiCoCrAlY–Al₂O₃ composite powders. The effect of the starting alloy powder size on the morphology of composite powder was studied. The parameters of milling were optimised by orthogonal experiment to improve the powder’s flowability and apparent density. Then the optimised powder was sprayed by air plasma spray to prepare NiCoCrAlY–Al₂O₃ composite coating. The results showed that the size distribution of starting particles decided the deformation of alloy particles and the characteristics of agglomerated powders eventually. With the decreasing size range of the starting alloy particles, the sphericity of agglomerated powders increased. The optimised milling parameters were as follows: solid content, 60?wt-%; BPR, 4:1; the rotating speed, 350?rev?min^?1; and milling time, 5?h. And the contribution of solid content was the largest. The Al₂O₃ splats showed good adhesion with alloy matrix when the composite powder melted in good condition.     

Characteristics on microstructure and mechanical performances of 6111Al influenced by Ce-containing precipitates

In this work,the effects of Ce addition(0,0.1 wt%,0.3 wt%,0.5 wt%and 0.7 wt%)on the evolution of microstructure and mechanical properties of 6111 Al alloy and strengthening mechanism of 6111 Al-Ce alloy were systematically investigated by a polarizing microscope,a scanning electronic microscope,an energy dispersive spectroscope and a high-resolution transmission electron microscope.The results indicate that with 0.3 wt%Ce addition,theα-Al grains show the equiaxed crystal morphology with the average size decreasing from 137 to 57μm and numerous small AlCeSi phases with lump-like or platelike morphology are distributed closely along the grain boundary.The peak yield strength,ultimate tensile strength and elongation of 6111 Al-Ce alloy reach to 279 MPa,316 MPa and 12.1%,respectively,which is attributed to the grain refinement strengthening and the formation of nanosized Al11Ce3 precipitates.Eventually,this investigation gives us instructive suggestion to prepare the new kind of aluminum alloy with high strength and high ductility.     

Green synthesis of ceria powders with special physical properties by carbon dioxide carbonization

In order to improve the application values of Ce element, in this paper, rare earth chloride solution was used as raw material, the pH value was controlled by inorganic alkali, the ceria powders with special physical properties were prepared by carbon dioxide carbonization method. According to characterization of SEM, XRD, and TG-DSC, Ce(OH)3 prepared at pH = 7.5 exhibits smaller particle size than that prepared at other conditions. CeO_2 precursor obtained by direct carbonization of Ce(OH)3 shows smaller particle size and narrow size distribution, CeO_2 precursor forms at first by carbonization of Ce(OH)3 with the continuous addition of CO2 gas,and the chemical component is indicated to be Ce_2 O(CO_3)_2·6 H_2 O.Cubic phase CeO_2 powders are obtained by calcined at 750 ℃ for 4 h. The mean particle size D_(50) is0.941 μm, and particle size distribution is smaller than 1. The microscopic appearance is homogeneous,with a spherical-like shape and a grain size of 200-500 nm. The light quality characteristics of sedimentation volume and accumulation density are obviously better than those of carbonate precipitation products. The carbonization method can be used not only to obtain ultra-fine rare earth oxides with fine particle size, narrow distribution and high dispersion properties, but also to achieve the reuse of carbon dioxide greenhouse gas.     

Microstructure and Mechanical Behavior of Powder Metallurgy Mg98.5Gd1Zn0.5 Alloy

The Mg_98.5Gd₁Zn_0.5 alloy produced by a powder metallurgy route was studied and compared with the same alloy produced by extrusion of ingots. Atomized powders were cold compacted and extruded at 623 K and 673 K (350 °C and 400 °C). The microstructure of extruded materials was characterized by α-Mg grains, and Mg₃Gd and 14H-LPSO particles located at grain boundaries. Grain size decreased from 6.8 μm in the extruded ingot, down to 1.6 μm for powders extruded at 623 K (350 °C). Grain refinement resulted in an increase in mechanical properties at room and high temperatures. Moreover, at high temperatures the PM alloy showed superplasticity at high strain rates, with elongations to failure up to 700 pct.     

铜基预合金粉末制备金刚石锯片的性能研究

采用共沉淀法制备了不同铜铁配比（质量比:45:35、50:30、55:25）的铜基预合金粉末,利用真空热压法烧结得到含金刚石的铜基结合剂刀头,通过激光焊接的方法制备出铜基结合剂金刚石锯片,研究了铜基预合金粉末中铜铁含量（质量分数）对金刚石锯片性能的影响。利用扫描电子显微镜观察锯片断面的显微组织形貌,并测量不同铜铁含量锯片的硬度和磨损量。结果表明:在三种配比中,当铜和铁质量比为50:30时,铜基结合剂与金刚石间的结合最佳,锯片性能最好,硬度最高（HRB 118）,锯片的磨损量最少（1.16 g）。     

Interfacial segregation of Ti in the brazing of diamond grits onto a steel substrate using a Cu-Sn-Ti brazing alloy

Diamond grits were brazed onto a steel substrate using a prealloyed Cu-10Sn-15Ti (wt pct) brazing alloy at 925 °C and 1050 °C. Due to the relatively high concentration of Ti in the brazing alloy, the braze matrix exhibited a composite structure, composed of β-(Cu,Sn), a Cu-based solid solution, and various intermetallic compounds with different morphologies. The reaction of Ti with diamond yielded a continuous TiC layer on the surfaces of the diamond grits. On top of the TiC growth front, an intermetallic compound, composed of Sn and Ti, nucleated and grew into a randomly interwoven fine lacey structure. An interfacial structure developed as the interwoven fine lacey phase was semicoherently bonded to the TiC layer, with the Cu-based braze matrix filling its interstices. The thickness of such a composite layer was increased linearly with the square root of isothermal holding time at 925 °C, complying with the law of a diffusion-controlled process. However, at 1050 °C, the segregation behavior of Ti and Sn to the interfaces between the TiC layer and the braze matrix diminished, due to the increased solubility of Ti in the Cu-based liquid phase. The enhanced dissolution of Ti in the Cu-based liquid phase at 1050 °C also caused the precipitation of rod-like CuTi with an average diameter of about 0.2 μm during cooling. SnTi₃ was the predominant intermetallic compound and existed in three different forms in the braze matrix. It existed as interconnected grains of large size which either floated to the surface of the braze matrix or grew into faceted grains. It also exhibited a nail-like structure with a mean diameter of about 1 μm for the rod section and a lamellar structure arising from a eutectic reaction during cooling.     

一氧化钛基金属陶瓷粘结相的研究

本文对铜基与铁铬基两个系列的合金用作一氧化钛（TiO）基金属陶瓷仿金材料的粘结相进行了研究。结果表明：纯Cu及Fe－Cr合金在TiO上的润湿性较差，不宜作TiO的粘接相，Cu中加入少量Mo，C，可明显改善其润湿性，Cu－Mo-C中加入适量的Al、Ni、Si，可使合金的颜色接近黄金且有较好的耐蚀性，并能与TiO保持很高的界面结合强度，适用于TiO陶瓷的粘结相，Fe－Cr合金中加入表达活性物质A中显著改善在TiO上的润湿性，抑制Fe与TiO间的界面反应，与TiO间形成很高的界面强度，可用做TiO陶瓷的粘结相。     

Amorphous Phase Formation Analysis of Rapidly Solidified CoCr Droplets

This paper investigates amorphous phase formation and rapid solidification characteristics of a CoCr alloy. High cooling rate and high undercooling-induced rapid solidification of the alloy was achieved by impulse atomization in helium atmosphere. Two atomization experiments were carried out to generate powders of a wide size range from liquid CoCr at two different temperatures. Amorphous fraction and kinetic crystallization properties of impulse atomized powders were systematically quantified by means of differential scanning calorimetry. In addition, different but complementary characterization tools were used to analyze the powders microstructures. The fraction of amorphous phase within the investigated powders is found to be promoted by high cooling rate or smaller powder size. The critical cooling rate for amorphous phase formation, which is influenced by the oxygen content in the melt, is found to be ~3 × 10⁴ K s^?1 and corresponds to a 160-µm-diameter powder atomized in helium. Hardness of the powders is found to follow a trend that is described by the Hall–Petch relation when a relatively high fraction of crystalline structures is present and decreases with the fraction of amorphous phase.     

A comparison study of hydrogen storage performances of SmMg11Ni alloys prepared by melt spinning and ball milling

The melt spinning(MS) and ball milling(BM) technologies are thought to be efficient to prepare nanostructured Mg and Mg-based alloys for improving their hydrogen storage performances. In this paper, two technologies, viz. melt spinning and ball milling, were employed to fabricate the SmMg_(11)Ni alloy. The structure and hydrogen storage performance of these two kinds of alloys were researched in detail. The results reveal that the as-spun and milled alloys both contain nanocrystalline and amorphous structures. By means of the measurement of PCT curves, the thermodynamic parameters of the alloys prepared by MS and BM are ΔN_(Ms)(des) = 82.51 kJ/mol and ΔH_(BM)(des) = 81.68 kJ/mol, respectively, viz.ΔH_(MS)(des) ΔH_(BM)(des). The as-milled alloy shows a larger hydrogen absorption capacity as compared with the as-spun one. The as-milled alloy exhibits lower onset hydrogen desorption temperature than the as-spun one. As to the as-milled and spun alloys, the onset hydrogen desorption temperatures are557.6 and 565.3 K, respectively. Additionally, the as-milled alloy shows a superior hydrogen desorption property than the as-spun one. On the basis of time that required by desorbing hydrogen of 3 wt% H_2, the as-milled alloy needs 1488.574,390 and 192 s corresponding to hydrogen desorption temperatures 593,613,633 and 653 K, while the as-spun alloy needs 3600,1020,778 and 306 s corresponding to the same temperatures. The dehydrogenation activation energies of the as-milled and spun alloys are 100.31 and105.56 kJ/mol, respectively, the difference of which is responsible for the much faster dehydriding rate of the as-milled alloy.     

Influence of graphite and copper in mechanical properties of aluminum silicon alloy

The present work deals with the mechanical behaviour of the Al-Si-Cu/graphite composite at different strain rates. Stir casting technique was used to fabricate the Al-Si alloy and composite. In order to improve the wettability of graphite with the alloy, graphite particulates were ball milled with Copper and preheated to 400°C. The uniaxial tensile tests were conducted at various strain rates in the range of 10^?4s^?1 to 10^?2s^?1. The ultimate tensile strength of the composite was higher than that of the alloy for all strain rates. The hardness of the composite was also better than that of alloy. The elongation of the alloy was more than that of composite for all strain rates. The uniform distribution of graphite and silicon particles were observed from the microstructure. The fracture mode of alloy and composite were analyzed.     

Corrosion behavior of Ce-doped Ni-10Cu-11Fe-6Al (wt%) inert anode in molten CaCl2 salt

In this research the effect of cerium dopingon corrosion behavior of Ni-10 Cu-11 Fe-6 Al(wt%) alloy as a novel inert anode in titanium electrolytic production was investigated. The samples, including un-doped and Ce-doped nickel-based alloys, were prepared using vacuum induction melting(VIM) process and then exposed to the electrolysis in molten calcium chloride at 900C at à1.6 V versus graphite reference electrode for different immersion time. The surface and cross-section of the samples were characterized using scanning electron microscopy(SEM), and their electrochemical behavior was investigated by electrochemical impedance spectroscopy(EIS). The results show that the un-doped samples have greater number of voids and porosities as compared to that of the 0.0064 wt% Ce-doped samples(as the optimum content of cerium in the alloy). Thus, the nickel-based alloy becomes less sensitive to the pitting by addition of cerium. The corrosion penetration depth reaches about 244 mm after 16 h of electrolysis in the un-doped sample, while was approximately 103 mm for the 0.0064 wt% Ce-doped sample, which is an indication that the corrosion penetration depth decreases by adding small amounts of Ce.     

Submicron LaB6 powders with high purity prepared in large scale by salt-assisted combustion synthesis

LaB₆ powders were synthesized in large scale by salt-assisted combustion synthesis (CS) with different NaCl diluent contents. The variety of phases, particle size and purity of the powders were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and transmission electron microscope (TEM). With increase of NaCl content, the adiabatic combustion temperature of the reaction system linearly declines, the average particle size of leached products decreases, the impurity phases are easier to remove, and the products purity enhances obviously. When NaCl content is 40 wt%, the purity of the superfine powders of LaB₆ is more than 98 wt%, and the average particle size is 380 nm.     

The effect of Mn on the structural and magnetic behaviour of Fe–6Si–8B alloy produced by high energy ball Milling

The alloys of Fe–6Si–8B and Fe–6Si–8B–1Mn were prepared using high energy planetary ball mill. X-ray diffraction patterns of the milled samples confirmed the formation of the alloys by dissolution of Si in Fe after 30 and 24 h of milling for the Fe–6Si–8B and Fe–6Si–8B–1Mn samples respectively. The lattice parameter was found to increase continuously with milling time and the rise was steeper for the quaternary alloy. After 36 h of milling, the crystallite size for the two samples were reduced to 98 and 86 nm respectively. Mössbauer spectra suggested the formation of minor amount of α-Fe₂O₃. The value of saturation magnetization was 162 Am²/kg for Fe–6Si–8B alloy obtained after 18 h of milling. However, the value decreased with increased milling time as well as with Mn-addition. The remanance value showed similar tendency as that for saturation magnetization. In contrast, the coercivity value was found to be increasing with milling time and with Mn-addition.     

Fabrication of Ni-Ti Alloy by Self-Propagating High-Temperature Synthesis and Spark Plasma Sintering Technique

This work is focused on the possibilities of preparing Ni-Ti46 wt pct alloy by powder metallurgy methods. The self-propagating high-temperature synthesis (SHS) and combination of SHS reaction, milling, and spark plasma sintering consolidation (SPS) are explored. The aim of this work is the development of preparation method with the lowest amount of undesirable phases (mainly Ti₂Ni phase). The SHS with high heating rate (approx. 200 and 300 K min^?1) was applied. Because the SHS product is very porous, it was milled in vibratory disk milling and consolidated by SPS technique at temperatures of 1173 K, 1273 K, and 1373 K (900 °C, 1000 °C, and 1100 °C). The microstructures of samples prepared by SHS reaction and combination of SHS reaction, milling, and SPS consolidation are compared. The changes in microstructure with increasing temperature of SPS consolidation are observed. Mechanical properties are tested by hardness measurement. The way to reduce the amount of Ti₂Ni phase in structure is leaching of powder in 35 pct hydrochloric acid before SPS consolidation.