Characteristics of Cr and Al Powders by High Energy Ball Milling

The variation of microstucture and phase structure of metal Cr and Al powders prepared by high energy mechanical milling was analyzed and investigated.The results show that with the continuous balling the average grain sizes of the brittle Cr powders are gradually decreased,and the diffraction peaks are widened and the peak values lower owing to the interrelation caused by both cold welding and breaking;the tough Al powders exhibit intense cold welding,and most of powders lead to adhesion to ball surface and pot wall,meanwhile,the Al powders subjected to intense deformation have led to many dislocation rings with non dislocation wind up found in the microstructure.

Micro-aluminum powder with bi-or tri-component alloy coating as a promising catalyst:Boosting pyrolysis and combustion of ammonium perchlorate

A novel design of micro-aluminum(μAl)powder coated with bi-/tri-component alloy layer,such as:Ni-P and Ni-P-Cu(namely,Al@Ni-P,Al@Ni-P-Cu,respectively),as combustion catalysts,were introduced to release its huge energy inside Al-core and promote rapid pyrolysis of ammonium perchlorate(AP)at a lower temperature in aluminized propellants.The microstructure of Al@Ni-P-Cu demonstrates that a three-layer Ni-P-Cu shell,with the thickness of~100 nm,is uniformly supported byμAl carrier(fuel unit),which has an amorphous surface with a thickness of~2.3 nm(catalytic unit).The peak temperature of AP with the addition of Al@Ni-P-Cu(3.5%)could significantly drop to 316.2℃ at high-temperature thermal decomposition,reduced by 124.3℃,in comparison to that of pure AP with 440.5℃.It illustrated that the introduction of Al@Ni-P-Cu could weaken or even eliminate the obstacle of AP pyrolysis due to its reduction of activation energy with 118.28 kJ/mol.The laser ignition results showed that the ignition delay time of Al@Ni-P-Cu/AP mixture with 78 ms in air is shorter than that of Al@Ni-P/AP(118 ms),decreased by 33.90%.Those astonishing breakthroughs were attributed to the synergistic effects of adequate active sites on amorphous surface and oxidation exothermic reactions(7597.7 J/g)of Al@Ni-P-Cu,resulting in accelerated mass and/or heat transfer rate to catalyze AP pyrolysis and combustion.Moreover,it is believed to provide an alternative Al-based combustion catalyst for propellant designer,to promote the development the propellants toward a higher energy.

EFFECT OF OXIDE LAYER THICKNESS OVER Al AND Al ALLOY POWDERS ON QUALITY OF THEIR EXPLOSIVE COMPACTS

Observations of microstructure of explosive compacts made of Al or Al-Li alloy powders by atomization with water,nitrogen or ultrasoic Ar gas were carried out under optical and scanning electron microscopes.The rsults indicate that super quality explosive compact can only be obtained by powders of which the thickness of the oxide layer is less than 30 nm.

Refinement and consolidation of pure Al particles by equal channel angular pressing and torsion

Consolidation of pure Alpowder was conducted at 200 ℃ by equal channel angular pressing and torsion （ECAPT） method. The grain refinement and consolidation behavior were deeply investigated by scan electronic microscopy （SEM） and transmission electronic microscopy （TEM）. The density, hardness and room temperature compression properties of the deformed samples were measured. The experiment results show that ECAPT is an effective method of consolidating powders at relatively low temperatures. Pure A1 particles are successfully consolidated into dense bulk material after 4 passes of ECAPT at 200 ℃. The consolidated material possesses fine grain structure and excellent mechanical properties. The refinement and consolidation mechanisms were analyzed. ECAPT is a promising method to produce the high-performance bulk materials from particles.

Low frequency damping behavior associated with sintering process in Al powder compact

The internal friction behavior of Al green power compact duxing the sintering process was studied as a function of temperature. The internal friction measurements were performed from room temperature to 600 °C. Two typical internal friction peaks were detected corresponding to heating and cooling processes, respectively. The heating peak corresponds to a recrystallization process of deformed Al particles, which is influenced by many extrinsic parameters, such as measuring frequency, strain amplitude, heating rate, power particle size and compacting pressure. However, the intrinsic nature of the peak is originated from the micro-sliding of the weak-bonding interfaces between Al particles and increased dislocation density induced in compressing. The cooling peak with the activation energy of (1.64±0.06) eV is associated with the grain boundary relaxation, which can be interpreted as the viscous sliding of grain boundaries. The similar phenomena are also found in the Mg green powder compact.

Effect of mechanical activation on TiC synthesis reaction in Al-Ti-C powder mixture

After milling in a high energy ball miller for various times, the synthesis reaction process of the Al Ti C powder mixture were investigated by difference thermal analysis (DTA) and X ray diffractometry (XRD). According to the patterns of reaction peaks on the DTA curves, the activation energy of each reaction was calculated. The experimental results of DTA show that the synthesis reaction of Al Ti C powder mixture can be enhanced after high energy milling. The longer the milling time, the lower the reaction temperature. The synthesis reaction of TiC is transformed from Ti+C→TiC to Al 3Ti+C→TiC+3Al with long period milling. Meanwhile, the activation energy of the reaction reduces with increasing milling time. The effect of milling time on reduced activation energy for low temperature region is more significant than that for high temperature region.

Effects of selective laser melting process parameters on powder formability of Ti6Al4V

Taking Ti6Al4V titanium alloy powder as the research object,on the basis of single layer scanning and single channel scanning experiment,this paper studies the influence of selective laser melting(SLM)process parameters on Ti6Al4V alloy material formability,and block forming experiment is carried out.Through the design of orthogonal experiment,morphology observation of sample and density analysis,results show that the best block molding parameters of SLM technology in Ti6Al4V alloy powder are laser power of 400 W,lap rate of 1 and the scanning speed of 750 mm/min,density can up to 96.17%.

Mechanical and ballistic properties of powder metal 7039 aluminium alloy joined by friction stir welding

7039 Al alloy plates which were used as armor materials were produced by powder metallurgy method. The prepared mixed powders were pressed and plated by extrusion process. These plates, after being subjected to T6 heat treatment, were joined double-sided by friction stir welding method. Microstructure and microhardness of the welded plate were investigated. It was determined that the finest grain structure and the lowest hardness value occurred in the stir zone as 2-6 mm and HV 80.9, respectively. In order to determine the ballistic properties of welded plates, 7.62 mm armor piercing projectiles were shot to the base metal（BM）, heat affected zone（HAZ）, and thermomechanically affected zone＋stir zone（TMAZ＋SZ）. Ballistic limits（v_（50）） of these zones were determined. The ballistic limits of the BM, TMAZ＋SZ, and HAZ of the plate were approximately 14.7%, 15.3%, and 17.9% lower than that of the standard plate at the same thickness, respectively. It was determined that the armor piercing projectiles created petaling and ductile hole enlargement failure types at the armor plate. Ballistic and mechanical results can be enhanced by hot-cold rolling mills after extrusion and particle reinforcement.

Structure of the Intermetallic Compound Ni_3Al Synthesized under Compression of the Powder Mixture of Pure Elements Part Ⅰ: Phase Composition and Microstructure of Main Phase

It was shown by TEM and X-ray analysis that there are four types of grains of the main Ni3Al phase in the structure of the intermetallic obtained by the self-propagation high temperature method (SHS). Every type of grains has its own domain and dislocation structure. There are mono- and polydomains with and without dislocations. The grains of the main phase of monoand polydomains without dislocations and polydomains with dislocations were formed by diffusion in the solid phase. In these conditions NiAl3 phase is located on the grain boundary of the main phase. The Ni2Al3 phase is located at the triple joints of the main phase.

Structure of the Intermetallic Compound Ni_3Al Synthesized under Compression of the Powder Mixture of Pure Elements Part Ⅱ: Influence of Alloying by Boron on the Phase Composition and the Microstructure of Grains of the Main Phase

The Ni_3B phase was formed when boron (0.5 at. pct B) was added to the intermetallic of sto- ichiometric and off-stoichiometric (Ni-24 at. pct Al) compounds. In the alloy of stoichiometric composition the particles of Ni_3B phase has the size around 0.1μm and is located on the grain boundary of the main phase. The decreasing of concentrations of Al in the ofF-stoichiometric alloy leads to increase in the degree of the long-range order parameter, increasing the concen- trations of boron in the solid solution and decreasing its localization on the grain boundary. Microalloying of boron leads to increasing in the fraction of grain monodomains with disloca- tions up to 0.7 in the alloy of the off-stoichiometric composition and up to 1 in the alloy of the stoichiometric composition. It was established the correlation between the degree of the concentration inhomogeneity, average density of the dislocations and the average long range-order parameter.

A quasi-isentropic model of a cylinder driven by aluminized explosives based on characteristic line analysis

A quasi-isentropic study on the process of driving a cylinder with aluminized explosives was carried out to examine the influence of the aluminum(Al) reaction rate on cylinder expansion and the physical parameters of the detonation products. Based on the proposed quasi-isentropic hypothesis and relevant isentropic theories, the characteristic lines of aluminized explosives driving a cylinder were analyzed,and a quasi-isentropic model was established. This model includes the variation of the cylinder wall velocity and the physical parameters of the detonation products with the Al reaction degree. Using previously reported experimental results, the quasi-isentropic model was verified to be applicative and accurate. This model was used to calculate the physical parameters for cylinder experiments with aluminized cyclotrimethylenetrinitramine explosives with 15.0 % and 30.0 % Al content. The results show that this quasi-isentropic model can be used not only to calculate the cylinder expansion rule or Al reaction degree, but also to calculate the physical parameters of the detonation products in the process of cylinder expansion. For explosives with 15.0 % and 30.0 % Al, 24.3 % and 18.5 % of the Al was found to have reacted at 33.9 μs and 34.0 μs, respectively. The difference in Al content results in different reaction intensity, occurrence time, and duration of two forms of reaction(diffusion and kinetic) between the Al powder and the detonation products;the post-detonation burning reaction between the Al powder and the detonation products prolongs the positive pressure action time, resulting in a continuous rise in temperature after detonation.

Effect of Spark Plasma Sintering on Microstructures and Properties of Al-Fe Alloy

2024 Aluminum alloy powder( 60wt%) and Fe-based amorphous powder( 40 wt%) were adopted. They were mechanical machined for 48hours after being mixed. Bulk material was gained after Spark Plasma Sintering. The sintering parameters included sintering temperature,heating or cooling rates,pressure and holding time. 300 ℃- 800 ℃ were adopted while the heating or cooling rate was 100 ℃ / min and with the pressure of 50 MPa in the experiments. The holding time was 10 min or 20 min at different temperatures, respectively. Bulk materials after sintering were examined by Scanning Electron Microscopy and X-Ray Diffraction. The micro-hardness and relative density also were tested. The sintering temperature had the most significant influence on the microstructure and property of the bulk material. The influence of holding time came second while the heating or cooling rates and pressure were fixed. The density became larger with the increase of the temperature. The compactness was best at 500℃. The pressure and generation of high-temperature phases were the factors which affected the density and the compactness.

Surface Modification and Suspension Stability of Ultrafine Al(OH)_3 Particles

The influence of single and compound dispersant on the sedimentation performance of modifiedultrafine Al(OH)3powder aqueous suspension was studied by the determination of the settlement rate and the Zeta potential.The results showed that the type and dosage of the dispersant have remarkable impacts on the dispersion stability.Using the mixture of DP-270and Sodium C16alkylbenzenesulfonate(mass ratio=1∶1)in the Al(OH)3aqueous suspension,the dispersion stability was improved effectively.As for spherical partic...

Concentration effect of the near-infrared quantum cutting of 1788-nm luminescence of Tm^(3+) ion in(Y_(1-x)Tm_x)_3Al_5O_(12) powder phosphor

In the present paper, the concentration effect of near-infrared quantum cutting of Tm3＋ ion in （Y1-xTmx）3Al5Ol2 powder phosphor is studied by means of experiments and calculations. In addition, the absorption spectra, visible-to-near- infrared excitation and emission spectra, and fluorescence lifetimes are measured. It is found that （Y1-xTmx）3Al5O12 powder phosphor has a strong four-photon near-infrared quantum cutting luminescence of 1788.0-nm 3F4 →3H6 fluores- cence of Tm3＋ ion, when excited by 357.0-nm light. It is also found that the up-limit of the four-photon near-infrared quantum cutting luminescence efficiency of （Yo.700Tmo.300）3Al5 O12 powder phosphor is approximately 302.19%. To the knowledge of the authors, this is the first time that a near-infrared quantum cutting efficiency up-limit exceeding 300% has been reported. The results of this manuscript are valuable in aiding the probing of the new generation Ge solar cell.

In-situ Preparation of Al/TiAl_3(P) Composite by Direct Reaction between Molten Al and TiO_2 Powder

TiAl3 particle reinforced pure Al composite has been made by direct reaction among molten Al, TiO2 and a flux. The composite exhibits high Synthetically properties. The strength and hardness are higher than those of pure Al matrix by 71.5% and 134% respectively However, the elongation is 20.36%, slightly lower than that of the Al matrix.

An approach to prepare uniform graphene oxide/aluminum composite powders by simple electrostatic interaction in water/alcohol solution

The homogenous dispersion of graphene in Al powders is a key challenge that limits the development of graphene-reinforced metal matrix composites with high performance.Here,uniform distribution of graphene oxide(GO)coated on flake Al powders were obtained by a simply stirring and ultrasonic treatment in the water/alcohol solution.The effect of water volume content on the formation of GO/Al composite powders was investigated.The results showed that GO adsorbed with synchronous reduction on the surface of Al powders,but when the water content was higher than 80%in the solution,Al powders were totally changed into Al(OH)3.With optimizing the water content of 60%in the solution,reduced GO was homogenously coated onto the surface of flake Al powders.The formation mechanism can be ascribed to the balance control between the liquid/solid interaction and the hydrolysis reaction.

Alkali-activation reactivity of chemosynthetic Al_2O_3-2SiO_2 powders and their ^(27)Al and ^(29)Si magic-angle spinning nuclear magnetic resonance spectra

Pure Al2O3-2SiO2 powders were prepared by sol-gel and coprecipitation methods, and their alkaliactivation reactivities were compared. The alkali-activation reactivity of the powder prepared by the so]-gel method was higher than that of the powder prepared by the coprecipitation method. The powders were investigated by 27Al and 29Si magic-angle spinning nuclear magnetic resonance spectroscopy （MAS NMR） to understand the relationship between their structure and alkali-activation reactivity. The 27Al MAS NMR data showed that the five-coordinate AI content of the powder prepared by the sol-gel method was higher than that of the powder prepared by coprecipitation. The higher content of five-coordinate Al corresponded to higher alkali-activation reactivity. The 29Si MAS NMR data showed that for the powder prepared by the sol-gel method, silicon was replaced by aluminum at secondary coordination sites of the central Si atoms during calcination. However, for the powder prepared by single-batch coprecipitation, the main change was from a low degree of polycondensation to a high degree of polycondensation.

In Situ Aluminum Alloy Coating on Magnesium by Hot Pressing

In the present study, pure magnesium was in situ coated with pre-alloyed Al–Cu–Mg alloy through hot pressing. The produced samples were characterized by means of hardness, wear properties and microstructure characterization. A ball-on-disk test was used to determine the dry sliding wear characteristics of the compacts. The results showed that the hot pressing technique has been successfully applied for producing magnesium parts with compatible wear resistance and hardness to aluminum. The in situ coating of Al on Mg by hot pressing resulted in an increase in hardness of about 30% compared with the pure Mg substrate. The wear rate and friction coefficient of the samples decreased with Al coating and increased with an increase in the applied load during the wear tests, compared with the uncoated material.