PREPARATION OF Ti-Al BASED NANOPHASE COMPOSITE POWDER BY MECHANICAL ALLOYING

ＰＲＥＰＡＲＡＴＩＯＮＯＦＴｉＡｌＢＡＳＥＤＮＡＮＯＰＨＡＳＥＣＯＭＰＯＳＩＴＥＰＯＷＤＥＲＢＹＭＥＣＨＡＮＩＣＡＬＡＬＬＯＹＩＮＧ①ＷｕＮｉａｎｑｉａｎｇ，ＷｕＪｉｎｍｉｎｇ，ＬｉＷｕ，ＷａｎｇＧｕａｎｇｘｉｎ，ＬｉＺｈｉｚｈａｎｇＤｅｐａｒｔｍ...     

Mechanical alloying of dispersion-hardened Ni3Al-B from elemental powder mixtures

Mechanical alloying and hot extrusion were studied as a means to dispersion harden an intermetallic compound based on Ni ₃ Al- B from elemental powder mixture. The oxide used for the dispersoids was partially stabilized zirconia. During mechanical alloying the microstructure evolved according to the characteristic stages found in other mechanical alloying systems. Completion of the alloying reaction required 16 h, beyond which loss of the crystalline property set in. Experimental observation of the grain refinement during mechanical alloying agreed with a prediction based on an existing model. Compared to V- cone mixing, the mechanical alloying produced a homogeneous distribution of fine dispersoids. The refined grain structure and dispersoids resulted in a high tensile yield strength over a wide range of temperatures.     

机械合金化制备Ti(Al,C)复合粉末组织结构研究

目的通过原位合成技术获得Ti(Al,C)复合粉末。方法在不同球磨时间条件下,采用机械合金化方法制备Ti(Al,C)复合粉末,其中Ti粉和Al粉的摩尔比为1:1。采用扫描电子显微镜(SEM)以及X-射线衍射仪(XRD)分析球磨后粉末的显微组织结构及物相,研究不同球磨时间对制备Ti(Al,C)复合粉末物相演变、组织结构及粒子间界面结合状态的影响。结果在球磨过程中,球磨时间越长,粉体的粒径越小,当球磨时间增长到一定程度时,延展性好的Al粉颗粒发生扁平化且其表面积不断增大,使得碎化后的Ti粉颗粒不断嵌入至Al粉颗粒中,最终形成Ti(Al)固溶体。同时根据XRD分析发现,随着球磨时间的延长,Ti(Al,C)复合粉末中的Al峰逐渐减小,说明Al不断固溶到Ti中,形成了一定量的Ti(Al)固溶体。结论通过机械球磨技术在球磨一定时间后可原位合成Ti(Al)固溶体,这说明随着Ti与Al之间的相互扩散,有利于形成Ti(Al)固溶体。     

Al57.1C42.9混合粉在机械合金化过程中的固态反应与相变

利用Ｘ射线，透射电镜和红外光谱研究了Ａｌ５７．１Ｃ４２．９混合粉在高能球磨中的结构变化，Ａｌ和石墨反应形成了Ａｌ４Ｃ３，Ａｌ４Ｃ３的合成是一个受扩散控制的逐渐生成过程，它是在较低温度下进行的纳米尺度界面反应，继续球磨，Ａｌ４Ｃ３的晶粒不断细化，长程有序结构逐渐破坏，致使自由能升高，超过了非晶态的自由能，导致了Ａｌ４Ｃ３失稳转变成均匀的单相晶态。     

球磨工艺对机械合金化合成Ti3SiC2的影响

以3Ti/Si/2C/0.2Al单质混合粉体为原料,采用机械合金化法制备Ti3SiC2材料.研究球磨工艺(球磨时间、球料比和球径大小、过程控制剂)对机械合金化合成Ti3SiC2影响.结果表明,机械合金化(球料比10:1,球径10 mm)单质混合粉体7 h后,原料粉体发生化学反应,生成了TiC和Ti3SiC2粉体和块体产物.球料比和球径大小对反应合成Ti3SiC2影响并不显著,但明显影响反应的孕育期.适当增大球径和球料比可明显缩短反应的孕育期,采用较大的磨球或过高的球料比会降低球磨效率,延长孕育期;添加过程控制剂(乙醇),不但会延长反应的孕育期,而且抑制反应合成Ti3SiC2.     

Development of nano-structure Cu-Zr alloys by the mechanical alloying process

Cu-Zr alloys have many applications in electrical and welding industries for their high strength and high electrical and thermal conductivities. These alloys are among age-hardenable alloys with capability of having nano-structure with high solute contents obtainable by the mechanical alloying process. In the present work, Cu-Zr alloys have been developed by the mechanical alloying process. Pure copper powders with different amounts of 1, 3 and 6 wt% of commercial pure zirconium powders were mixed. The powder mixtures were milled in a planetary ball mill for different milling times of 4, 12, 48 and 96 h. Ball mill velocity was 250 rpm and ball to powder weight ratio was 10:1. Ethanol was used as process control agent (PCA). The milling atmosphere was protected by argon gas to prevent the oxidation of powders. The milled powders were analysed by XRD technique and were also investigated by SEM observations. Lattice parameters, crystal sizes and internal strains were calculated using XRD data and Williamson-Hall equation. Results showed that the lattice parameter of copper increased with increasing milling time. The microstructure of milled powder particles became finer at longer milling time towards nano-scale structure. SEM observations showed that powder particles took plate-like shapes. Their average size increased initially and reached a maximum value then it decreased at longer milling times. Different zirconium contents had interesting effects on the behavior of powder mixtures during milling.     

Interdiffusion in <Emphasis Type="Italic">L</Emphasis>1<Subscript>2</Subscript>-Ni<Subscript>3</Subscript>Al Alloyed with Re

Ternary interdiffusion in L1₂-Ni₃Al with ternary alloying addition of Re was investigated at 1473 K using solid-to-solid diffusion couples. Interdiffusion flux of Ni, Al, and Re were directly calculated from experimental concentration profiles and integrated for the determination of average ternary interdiffusion coefficients. The magnitude of main interdiffusion coefficients and was determined to be much larger than that of the main interdiffusion coefficient A moderate tendency for Re to substitute for Al sites was reflected by its influence on interdiffusion of Al, quantified by large and positive coefficients. Similar trends were observed from ternary interdiffusion coefficients determined by Boltzmann-Matano analysis. Profiles of concentrations and interdiffusion fluxes were also examined to estimate binary interdiffusion coefficients in Ni₃Al, and tracer diffusion coefficients of Re (5.4 × 10⁻¹⁶ ± 2.3 × 10⁻¹⁶ m²/s) in Ni₃Al.     

The effects of process control agents on mechanical alloying mechanisms in the Ti---Al system

During the mechanical alloying (MA) of ductile materials, it is often found that welding becomes so dominant that a very fine layered structure or homogeneously alloyed powders cannot be obtained. It is often desired to add an appropriate amount of process control agent (PCA) to powders in order to retain the equilibrium state between welding and fracturing processes. The present work investigated the effects of PCAs on MA mechanisms in the Ti---Al system. It was found that the amount of PCA and the energy transfer from ball to powder during MA influenced the mechanism of MA. As the amount of PCA and/or energy transferred from ball to powder increased, the mechanism of MA changed from a substitutional diffusion to a penetration of metallic atoms into interstitial sites. The penetration of metallic atoms seems to play an important role in the formation of the metastable f.c.c. phase, for which the lattice parameter is about 4.2 Å in the Ti---Al system.     

Influence of Mg particle size on the reactivity and superconducting properties of in situ MgB2

The effects of starting Mg particle size on the reactivity of Mg with B, and on remnant Mg in in situ MgB₂, and their influence on the superconducting system are studied. Samples were prepared by a powder-in-sealed tube (PIST) method, heat treated at 850 °C for 2 h in air and were characterized using XRD, SEM and magnetization measurements. As the particle size of Mg powder increases, residual Mg increases significantly. The MgB₂ prepared using smaller sized Mg powder does not have any residual Mg and show the best infield critical current density (J_C (H)).     

Microstructure and hardness of Mg-based composites reinforced with Mg<Subscript>2</Subscript>Si particles

Magnesium powders were mechanically alloyed with SiO₂ powder particles having different particle sizes using high-energy ball milling techniques under Ar atmosphere for 1 h. The powders were consolidated with cold pressing under 560 MPa. They were then sintered at 550°C for 45 min under Ar atmosphere. The composites obtained on the Mg-SiO₂ system were investigated using the Archimedes principle, a differential scanning calorimeter, X-ray diffraction, optic microscopy, and scanning electron microscopy. For the mechanically alloyed powders, the solid-state reaction of the synthesis of Mg₂Si and MgO progressed further during sintering of the materials. The results showed that the strengthening mechanisms were dependent on dispersion hardening of fine Mg₂Si and MgO particulates dispersed homogeneously in the matrix.     

Structural evolution of mechanically alloyed Al-12Si/TiB2/h-BN composite powder coating by atmospheric plasma spraying

In the present study, mechanically alloyed Al-12Si/TiB₂/h-BN composite powder was deposited onto an aluminum substrate by atmospheric plasma spraying. The effect of mechanical alloying (MA) and plasma spray parameters on composite powder and coating structure were investigated. It has been observed that the MA process has a significant effect on the composite powder morphology and reactivity between the selective powders. Results also demonstrate that, at relatively high milling time h-BN decomposes into B and N and forms a solid solution. Also, it has been found that, the relative amount of the in-situ formed AlN through the reaction between h-BN and Al and/or the decomposition of Al-B-N solid solution is independent from the plasma parameters (arc current and secondary gas flow rate). However, spray parameters remarkably affects the coating hardness due to coarsening of Si during the solidification of the coating.     

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.     

机械合金化对Mg_2Ni相形成的影响

用两步法 (即由机械合金化和压制烧结两个步骤组成 )制备了Mg2 Ni合金。实验证明 :混合粉经机械合金化后 ,晶粒细化 ,增加了固态扩散的能力 ,有利于固相反应进行 ,使Mg2 Ni产率明显提高。不同温度烧结处理的结果表明 :烧结温度是影响Mg2 Ni相形成的重要因素 ,烧结温度达到 843K ,Mg Ni粉基本能完全转变为Mg2 Ni相。     

Pressure-composition-isotherm behavior of nano-/amorphous Mg<Subscript>2</Subscript>NiH<Subscript>x</Subscript>

It has recently been shown that the hydriding properties of the nanocrystalline metal hydrides are far superior to those of the polycrystalline ones. Especially in the case of the Mg-based hydrogen storage alloys, nanostructural modifications have been studied for the purpose of improving their hydrogenation kinetics. In previous studies, I reported on the successful fabrication of Mg₂NiH_x from Mg and Ni chips with hydrogen induced mechanical alloying (HIMA). Observation of the microstructure showed that the synthesized particles (processed with a 66:1 ball to chips mass ratio and 96 hr HIMA) are composed of amorphous and nanocrystalline composite phases with a grain size of less than 10 nm. The aim of the present work was to examine the hydriding/dehydriding behavior of nanocrystalline metal hydrides using a Sieverts type automatic pressure-composition-isotherm (PCI) apparatus at 393, 423, 453, 483, 513 and 543 K. The specimen was characterized by X-ray diffraction after PCI measurement. The influence of hydrogenation behavior on the phase transition of nano-/amorphous Mg₂Ni is a key factor in commercial application. The particles synthesized at 66:1 BCR and 96 hr HIMA revealed a good hydrogen capacity of 2.25 mass% at 483 K.     

机械合金化对Mg2Ni相形成的影响

用两步法（即由机械合金化和压制烧结两个步骤组成）制备了Mg2Ni合金,实验证明：混合粉经机械台金化后,晶粒细化,增加了固态扩散的能力,有利于固相反应进行,使Mg2Ni产率明显提高,不同温度烧结处理的结果表明：烧结温度是影响Mg2Ni相形成的重要因素,烧结温度达到843K,Mg-Ni粉基本能完全转变为Mg2Ni相。     

机械合金化结合热压烧结制备(TiC+TiB2)/Cu复合材料

通过对体系进行机械合金化,随后将其与Cu粉进行混合和热压烧结制备了(TiC+TiB_2)/Cu复合材料。研究表明,机械合金化促使B_4C粉末分解并向Ti粉末中的固溶形成Ti-C-B的三元混合体系,有效降低了体系的反应温度,并在随后的热压烧结中生成(TiC+TiB_2),其原因是在Ti-C-B体系中生成TiB_2相比TiB具有更低的吉布斯自由能变。当增强相含量较低时,强化相颗粒细小弥散地分布在铜基体中,且与基体界面结合良好,可显著提高复合材料的硬度;但随着含量的增加,强化相的团聚现象加剧,与基体的界面结合方式也转变为简单的机械包裹,其强化效应并不能得以体现。此外,由于机械合金化提高了体系反应的活性,有效地避免了Ti向铜基体中的固溶,当增强相的设计含量为15vol%时所制备的(TiC+TiB_2)/Cu复合材料与直接混合Cu-Ti-B_4C粉末制备的复合材料相比导电率大幅提升。     

The evaluation of W/ZrC composite fabricated through reaction sintering of two precursors: Conventional ZrO2/WC and novel ZrSiO4/WC

In this study the W-ZrC composites fabricated by in situ reaction sintering of two precursors were compared, 1-The conventional WC and ZrO₂ which are ball milled with established molar ratio of 3–1 for 12 hours, gelcasted to form a green body and then undergo a pressure less sintering cycle, 2-A new and innovative way in which for the first time ZrSiO₄ was used instead of ZrO₂, and by testing different molar ratio between WC and ZrSiO₄ it was understood that the optimum ratio is 3–1 once again. Furthermore the starting ZrO₂ and ZrSiO₄ powder were selected in nano size and it was understood that by using nano powders the amount of unreacted and unwanted phase reduce, the reaction progress and the mechanical proprieties improve. Although the reaction sintered WC/ZrO₂ possess better properties, regarding the cost considerations, reaction sintering of WC/ZrSiO₄ is a much cheaper process.     

机械合金化Fe-40Al合金粉末工艺研究

以Fe粉、Al粉末为对象,采用机械合金化制备Fe-40Al合金复合粉末,研究球磨工艺参数对Fe-40Al合金粉末形貌及组织结构的影响规律,为机械合金化制备适合冷喷涂用Fe-40Al合金粉末提供最佳的工艺参数。研究结果表明,球磨后的Fe-40Al合金粉末具有独特的层状组织结构,随着球磨时间的延长,Fe-40Al合金粉末的平均粒径不断减小,由于Fe、Al相互扩散作用加强,粉末内部的层状结构不断细化而消失;随着球料比增加,机械合金化效率显著提高,相同球磨时间内Fe-40Al合金粉末粒径减小的幅度显著增大,同时粉末内部合金化过程加剧,导致层状结构快速消失。     

Thixoforming of AA 2017 aluminum alloy composites

A comparative evaluation has been carried out on the microstructure of aluminum based SiC and Al₂O₃ particle reinforced composites produced by semi-solid direct squeeze forming of composite powder at temperatures of 635-645 °C. The study is focused on the distribution of the reinforcement and the intermetallic phases, the porosity content, the microstructure of the matrix phase, the interfacial state and mechanical properties. The particle size of the reinforcements, the time of the high-energy ball milling procedure for the fabrication of composite powder and the semi-solid forming temperature had a strong influence on the quality of sample in terms of distribution of reinforcement and interfacial interaction. Ball milling improves the interface formation between reinforcement and matrix and influences the remelting behaviour. Increasing ball milling time and decreasing semi-solid forming temperature with isothermal holding time resulted in relatively homogenous microstructures and in a reduced amount of interaction between SiC and metal matrix. Best results were obtained for 5 vol.% SiC_p composites after 3 h ball milling, semi-solid formed at 635 °C and held for 10 min.     

Application of statistical methodology for the evaluation of mechanically activated phase transformation in nanocrystalline TiO2

Response surface methodology was employed to study the effect of three factors, namely as milling time, milling speed and ball to powder weight ratio, on the mechanical activation of polymorphic phase transformation in nanocrystalline TiO₂ powder and identify the probable interactions between these factors. The response was the rutile percentage after annealing the samples. Based on the statistical analysis, ball to powder weight ratio was found as the most effective factor and just one statistically significant interaction was found between milling speed and ball to powder ratio. It was also shown that increasing the milling time has no significant effect on the phase transformation since the required activation energy for the phase transformation is unattainable under these conditions. The rutile percentage was calculated from X-ray diffraction patterns of the samples via Rietveld refinement method. Raman spectroscopy was employed to verify the phase composition analysis based on X-ray diffraction results.