Microstructural and mechanical properties of Al-Mg/Al2O3 nanocomposite prepared by mechanical alloying

The effect of milling time on the microstructure and mechanical properties of Al and Al-10 wt.% Mg matrix nanocomposites reinforced with 5 wt.% Al₂O₃ during mechanical alloying was investigated. Steady-state situation was occurred in Al-10Mg/5Al₂O₃ nanocomposite after 20 h, due to solution of Mg into Al matrix, while the situation was not observed in Al/5Al₂O₃ nanocomposite at the same time. For the binary Al-Mg matrix, after 10 h, the predominant phase was an Al-Mg solid solution with an average crystallite size 34 nm. Up to 10 h, the lattice strain increased to about 0.4 and 0.66% for Al and Al-Mg matrix, respectively. The increasing of lattice parameter due to dissolution of Mg atom into Al lattice during milling was significant. By milling for 10 h the dramatic increase in microhardness (155 HV) for Al-Mg matrix nanocomposite was caused by grain refinement and solid solution formation. From 10 to 20 h, slower rate of increasing in microhardness may be attributed to the completion of alloying process, and dynamic and static recovery of powders.     

Producing nanocrystalline bulk Mg-3Al-Zn alloy by powder metallurgy assisted hydriding-dehydriding

Nanocrystalline bulk Mg-3Al-Zn alloy with an average grain size of 48 nm has been prepared by powder metallurgy assisted hydriding-dehydriding. Evolutions of nanograined structure powders and bulk alloy have been investigated by TEM, SEM and XRD, respectively. The results showed that by milling in hydrogen for 60 h, as-hydriding powder possessed an average grain size of 5.9 nm. After a subsequent process of desorption-recombination treatment (at 350 °C) and consolidation process (extruded at 200 °C) resulted in bulk samples with an average crystallite size of 48 nm and MgH₂ was fully turned into Mg. The consolidated samples of 60 h milled powder had a final density of 1.77663 ± 0.006 g/cm³, which corresponded to 97.57 ± 0.3% of theoretical density. The highest microhardness of the nanocrystalline bulk alloy reached about 872.5 MPa, which is about three times higher than that of the coarse-grained AZ31.     

Nanophase intermetallic FeAl obtained by sintering after mechanical alloying

The preparation of bulk nanophase materials from nanocrystalline powders has been carried out by the application of sintering at high pressure. Fe–50 at.%Al system has been prepared by mechanical alloying for different milling periods from 1 to 50 h, using vials and balls of stainless steel and a ball-to-powder weight ratio (BPR) of 8:1 in a SPEX 8000 mill. Sintering of the 5 and 50 h milled powders was performed under high uniaxial pressure at 700 °C. The characterization of powders from each interval of milling was performed by X-ray diffraction, Mössbauer spectroscopy, scanning and transmission electron microscopy. After 5 h of milling formation of a nanocrystalline α-Fe(Al) solid solution that remains stable up to 50 h occurs. The grain size decreases to 7 nm after 50 h of milling. The sintering of the milled powders resulted in a nanophase-ordered FeAl alloys with a grain size of 16 nm. Grain growth during sintering was very small due to the effect of the high pressure applied.     

Bulk Mg-3Al-Zn alloy with ultrafine grain size produced by powder metallurgy

Ultrafine-grained Mg-3Al-Zn alloys with an average grain size of 180 nm have been made by powder metallurgy. First, the nanocrystalline powders with mean grain size of 45 nm were produced by ball milling under argon atmosphere, and then through vacuum hot pressing at 633 K for 40 min and warm extrusion at 373 K, bulk solid samples were compacted successfully from the mechanically milled powders, and the relative density of the samples was about 98.87% (1.8003 g/cm³). XRD, SEM and TEM analysis showed that the microstructure of the samples consists of homogeneous equiaxed grains and grain growth has taken place during the consolidation process.     

Synthesis and characterization of mechanically alloyed and shock-consolidated nanocrystalline NiAl intermetallic

The synthesis, microstructural characterization and microhardness of nanocrystalline B2-phase NiAl intermetallic are discussed in this paper. Nanophase NiAl powders were prepared by mechanical alloying of elemental Ni and Al powders under an argon atmosphere for different times (0–48 h). The alloyed nanocrystalline powders were then consolidated by shock compaction at a peak pressure of 4–6 GPa, to 83% dense compacts. Characterization by transmission electron microscopy (TEM) revealed that the microstructure of the shock-consolidated sample was retained at the nanoscale. The average crystallite size measurements revealed that mechanically alloyed NiAl grain size decreased from 48±27 to 9±3 nm with increasing mechanical alloying time from 8 to 48 h. The long-range-order parameters of powders mechanically alloyed for different times were determined, and were observed to vary between 0.82 for 5 h and 0.63 for 48 h of milling time. Following shock compaction, the long-range-order parameter was determined to be 0.76, 0.69 and 0.66, respectively, for the 16, 24 and 48 h alloyed specimens. Both the mechanically alloyed nanocrystalline NiAl powder and the shock-consolidated bulk specimen showed evidence of grain boundary dislocations, subgrains, and distorted regions. A large number of grain boundaries and defects were observed via high resolution TEM (HRTEM). Shear bands were also observed in the mechanically alloyed NiAl intermetallic powders and in the shock-consolidated compacts. Microhardness measurements of shock-consolidated material showed increasing microhardness with increasing crystallite size refinement, following Hall–Petch behavior.     

Microstructure evolution and mechanical properties of nanocrystalline FeAl obtained by mechanical alloying and cold consolidation

In the present study high energy mechanical milling followed by cold temperature pressing consolidation has been used to obtain bulk nanocrystalline FeAl alloy. Fully dense disks with homogenous microstructure were obtained and bulk material show grain size of 40 nm. Thermal stability of the bulk material is studied by XRD and DSC techniques. Subsequent annealing at a temperature up to 480 °C for 2 h of the consolidated samples enabled supersaturated Fe(Al) solid solution to precipitate out fine metastable Al₅Fe₂, Al₁₃Fe₄ and Fe₃Al intermetallic phases. Low temperature annealing is responsible for the relaxation of the disordered structure by removing defects initially introduced by severe plastic deformation. Microhardness shows an increase with grain size reduction, as expected from Hall-Petch relationship at least down to a grain size of 74 nm, then a decrease at smallest grain sizes. This could be an indication of some softening for finest nanocrystallites. The peak hardening for the bulk nanocrystalline FeAl is detected after isochronal ageing at 480 °C.     

Structural and magnetic properties of nanocrystalline NiFeCuMo powders produced by wet mechanical alloying

The NiFeCuMo nanocrystalline soft magnetic powders were successfully obtained by wet mechanical alloying route in a planetary ball mill using benzene (C₆H₆) as process control agent (PCA). The milling time used was ranging from 2 up to 20 h. The synthesis conditions and alloy formation have been investigated by X-ray and neutron diffraction as well as their influence on the intrinsic physical properties. Nanometer scale (≈10 nm) crystallites were obtained. A decrease of the samples magnetization has been observed and attributed to the stresses induced during the milling and to the benzene adsorbed on the powders surface. Differential scanning calorimetry investigation shows the presence of an exothermic peak related to the presence of benzene. The adsorbed benzene, internal stresses and crystalline defects removal took place during the heat treatment at 350 °C for 4 h, leading to an improvement of the powders magnetization.     

Spark plasma sintering of (Ti0.9W0.1) C powders prepared by mechanical alloying

Nanocrystalline (Ti_0.9W_0.1)C powder with a diffraction crystallite size of about 10 nm was synthesized by mechanical alloying. The formation of (Ti_0.9W_0.1)C carbide was detected by XRD measurements and microscopic observation. The sintering of these powders by a spark plasma sintering (SPS) at different temperatures were also studied. The results show that the maximum hardness was obtained for more relative density materials, meanwhile, the grain size is large. The micro-hardness and the relative density of the powder milled for 10 h and sintered at 1200 °C for 5 min under 100 MPa reach, respectively, 2978 HV and 98.35%.     

机械合金化对Cr-W粉末及烧结材料组织的影响

通过机械球磨法制备原子比为4:1的Cr-W预合金粉末,对球磨后的Cr-W粉末进行XRD、SEM、TEM分析,探讨球磨时间对Cr-W粉末形貌、晶粒大小、组织结构及烧结Cr-W合金固溶度的影响。结果表明：采用机械合金化法,可以制备纳米级的Cr-W预合金粉末;球磨初期,晶粒尺寸、微应变变化较大,48 h后趋于稳定获得小于30 nm的纳米晶粉末;经72 h球磨后,粉末中有固溶体形成;球磨过程伴随着晶格常数的变化;球磨时间越长的粉末,烧结后各相分布越均匀,固溶程度越高     

Fabrication of W-20wt.%Ti alloy by pressureless sintering at low temperature

A powder metallurgical technology of low temperature and pressureless is used to fabricate a W-20wt.%Ti alloy using milled TiH₂ powders and micro-sized W powders. The microstructure of the milled TiH₂ powders and the bulk W–Ti alloy were studied. It is indicated that TiH₂ nanoparticles with the size of 8 to 15 nm were obtained after milling for 48 h and the decomposition temperature decreased from 520.2 °C to 395.5 °C. The W-20wt.%Ti alloy prepared at 1200 °C for 80 min had a relative density of 97.8% which was composed of α-Ti, W and β(W/Ti) solid solution. A preparation mechanism of the W–Ti alloy is also proposed based on the experimental results.     

Synthesis of (Bi0.5Na0.5)TiO3 (BNT) and Pr doped BNT using the soft combustion technique and its properties

In this work, bismuth sodium titanate (Bi_0.5Na_0.5)TiO₃ (BNT) and praseodymium (Pr)-doped BNT were successfully produced using the soft combustion technique. The effects of Pr doping on stoichiometry, microstructure, density and dielectric properties were studied. Pure Pr-doped BNT was obtained in all samples containing 5, 10 and 20 mol% Pr after calcination at 800 °C for 3 h. The produced powders were then pressed into pellets and sintered at 1100 °C for 3 h. The very similar ionic radii of Pr³⁺ with Bi³⁺ and Na⁺ made it possible to substitute both Bi and Na. The crystallite size and grain size decreased with increasing Pr amount because Pr acted as grain growth inhibitor, both for calcined powders and for sintered pellets. Maximum density was obtained in 5 mol% Pr-doped BNT, beyond which density decreased. The maximum dielectric constant of 756 was obtained in 5 mol% Pr-doped BNT and decreased at higher levels of Pr doping. Pr doped into BNT also caused a decrease in dielectric loss.     

机械合金化Al—Mg—Si—Cu元素粉末的特性

Al,Mg,Si和Cu元素粉末按6061铝合金成分配比进行了机械合金化（MA）,对其物相、合金化特性、晶格常数、晶粒尺寸及点阵应变作了测定和分析讨论。MA初期晶粒尺寸可以达到纳米级,最小晶粒尺寸20nm;粉末点阵应变最终达0．2％;Al晶格常数变化的总趋势是不断减小;塑性较好的元素粉末可在“面上”作短程扩散,合金化易于进行,可实现完全合金化;硬度较高的脆性元素粉末可在“面上”作短程扩散,合金化易于进行,可实现完全合金化;硬度较高的脆性元素粉末只在“点上”作短程扩散,合金化不易进行,难以实现完全合金化。     

Synthesis of nanocrystalline NiAl by mechanical alloying

The nanocrystalline NiAl intermetallic compound was synthesized by mechanical alloying of the elemental powders. The structural changes of powder particles during mechanical alloying were studied by X-ray diffractometery, scanning electron microscopy and microhardness measurements. The mechanical alloying resulted in the gradual formation of nanocrystalline NiAl with a grain size of 20 nm. It was found that NiAl phase develops by continuous diffusive reaction at Ni/Al layers interfaces. The NiAl compound exhibited high microhardness value of about 1035 Hv.     

机械合金化W-Ni-Fe纳米复合粉的制备及结构研究

W,Ni,Fe粉末按照91.16W6．56Ni2.26Fe和95W5Ni的成分配比进行了机械合金化(MA)．通过调整球磨转速、球磨时间等工艺参数研究了其对粉末结构的影响,并对机械合金化粉末的物相、合金化特性、晶粒尺寸、点阵畸变及粉末形貌和颗粒度作了测定和分析讨论.机械合金化使晶粒细化并产生孪晶和位错．有利于原子扩散形成过饱和固溶体和非晶；高的球磨能有利于形成非晶相、晶粒细化和点阵畸变，350r／min球磨20h后晶粒尺寸可达25nm；输入的球磨能不同．粉末粒度的变化路径不同，但都会经历长大，变小和稳定三个不同阶段.     

Synthesis of nano-RuAl by mechanical alloying

Single phase RuAl has been synthesised directly by an abrupt reaction during mechanical alloying (MA). The structural evolution during MA and subsequent thermal stability of as- milled powders have been analysed by thermal analysis (DSC) and isothermal annealing. The results indicate that there are two stages of alloying and reaction between Ru and Al in MA before single phase RuAl is obtained under the present milling conditions, and that the as-milled single phase RuAl undergoes reordering, strain relaxation and grain growth at high temperatures. The grain size of 20–40 nm after annealing at 1073 K for 0.5 h shows a strong stability of the nano-grained RuAl.     

高能球磨制备Al-Pb-Si-Sn-Cu纳米晶粉末的特性

通过机械合金化制备了Al-15％Pb-4％Si-1％Sn-1．5％Cu(质量分数)纳米晶粉末。采用X射线衍射(XRD)，扫描电镜(SEM)和透射电镜(TEM)对不同球磨时间的混合粉末的组织结构、晶粒大小、微观形貌以及颗粒中化学成分分布情况进行了研究。结果表明混合粉末经过球磨后形成了纳米晶，其组织非常均匀。球磨对Pb的作用效果明显大于对Al的作用效果，经过40h球磨后Pb粒子达到40nm，而Al在球磨60h后晶粒为65nm；经球磨后，Cu和Si固溶于Al的晶格中，而Sn则固溶于Pb晶格中，并且Al和Pb发生了互溶，形成了Pb(Al）超饱和固溶体；在球磨过程中硬度高的脆性粒子Si难于完全实现合金化。     

Microstructural, optical and quantum confinement effect study of mechanically synthesized ZnTe quantum dots

ZnTe quantum dots (QD) have been synthesized in a quick single-step process by mechanically alloying a stoichiometric mixture of elemental Zn and Te powders at room temperature under Ar with 1 h of milling. The detailed microstructure of these powdered QD has been characterized by both Rietveld analysis of X-ray powder diffraction data and high resolution transmission electron microscopy. The results reveal that almost monodispersed spherical QD of ∼5 nm size were synthesized after 15 h of milling. These QD all belong to the cubic (Zn blende) phase and contain different kinds of stacking faults but with low lattice strain. The UV-vis absorbance spectra of ZnTe QD depict a significant blue shift with decreasing size of QD and the band gap estimated taken from the sharp absorbance peak position is greater than that of the bulk counterpart. The band gap increases with increasing milling time up to 15 h with a continuous decrease in the size of these QD and, therefore, their optical properties can be fine tuned by varying the milling time.     

Fabrication of in-situ Ti-Si-C fine grained composite by the self propagating high temperature synthesis (SHS) process

An attempt has been made to synthesise a Ti-Si-C composite with fine TiC and Ti-Si phase dispersed composite, using titanium, silicon and carbon powders using SHS dynamic compaction. The Ti-Si-C bulk composite with a high hardness (22.50 GPa), with a homogeneous distribution of a softer Ti-Si phase having more than 99% density of theoretical value has been successfully synthesised by the SHS dynamic process. The composite was found to be consisting of titanium carbide and titanium silicide. SEM and EDX analysis showed uniform distribution of phases and an average grain size varying around 1-2 μm. Nanoindentation studies revealed modulus of composite about 400 GPa with an elastic recovery of 30%.     

工艺参数对Nd:YAG烧结致密化的影响

以高纯Y_2O_3、Al_2O_3和Nd_2O_3粉体为原料,少量纳米SiO_2为烧结助剂,采用真空烧结方法制备致密的Nd:Y_2Al_5O_(12)(Nd:YAG)陶瓷,并研究球磨处理原料粉体、Y_2O_3原料颗粒度和烧结气氛对Nd:YAG烧结致密化的影响.结果表明,机械合金化氧化物混合粉体,可明显细化氧化物颗粒,促进Nd:YAG的烧结.在1600℃保温8h,对球磨20h的粉体压坯真空烧结得到的Nd:YAG块体相对密度达99%,晶粒大小约为10μm;采用纳米Y_2O_3,粉体作真空烧结原料,可提高烧结活性,获得细晶和高致密度的Nd:YAG陶瓷,对混合粉体球磨20h压坯烧结可得到晶粒大小为2μm、相对密度为98.5%的Nd:YAG块体;在氩气保护下常压烧结,得到的Nd:YAG块体组织难以辨认,而且残留许多孔隙.     

Effects of milling and subsequent consolidation treatment on the microstructural properties and hardness of the nanocrystalline chromium carbide powders

The influence of milling and subsequent consolidation treatments on the microstructural properties and hardness of the fabricated Cr₃C₂, Cr₇C₃ and Cr₂₃C₆ ceramic powders are investigated. For this reason, the elemental powders of Cr and C were mixed with proper ratio and then milled to the nanometer crystallite sizes (between 6 and 20 nm) and then were consolidated by using uniaxial cold press and subsequent heat treatment (at 1100 °C for 1 h) in Argon atmosphere. Microstructures of consolidated samples were characterized using X-ray diffraction (XRD) and microhardness measurements. A drastic increase in crystallite size of the samples was observed due to the effect of heat treatment. However, the as-consolidated samples still maintained their nanocrystalline characteristic with an average grain size of less than 100 nm. Besides, a very high hardness of 25 GPa was achieved for the Cr₃C₂ composition. This high hardness is attributed to the formation of carbide phases in the consolidated samples.