Mechanical alloying and microstructure of a Nb–20% V–15% Al alloy

A niobium-based alloy with 20% V–15% Al (at.%) was synthesized by mechanical alloying of elemental powders. During milling, the splitting of Nb X-ray peaks into two components was observed. Each component was found to correspond to a niobium solid solution (Nb_I and Nb_II) with a different lattice parameter. The intensities of Nb_I peaks on X-ray diffraction patterns decreased with the milling time and disappeared completely after 180 h of milling while the intensities of Nb_II peaks gradually increased. The powders were hot pressed and microstructural and phase analyses of the consolidated material were carried out. The microstructure consisted of Nb solid solution, Nb₃Al-base intermetallic with the A15 crystal structure and dispersoid Al₂O₃. Also an unexpected, detrimental, Nb₂Al-base σ phase was found. The volume fraction of the σ phase depended on the temperature of consolidation.     

Formation of intermetallic compounds in the Cr–Al–Si ternary system

The microstructure and composition of binary and ternary intermetallics have been studied in ternary diffusion couples of Cr and an Al–Si eutectic alloy. The ternary intermetallic always formed in the liquid part of the diffusion couple as a dendritic structure. Two intermetallics compounds, CrSi₂ and Cr₅Si₃, of the Cr–Si binary system have been observed. The CrSi₂ intermetallic has a high solubility of up to 20 at.% Al and forms as faceted plates. A number of intermetallics, namely, CrAl₇, Cr₂Al₁₁, CrAl₄, Cr₄Al₉, Cr₅Al₈ and Cr₂Al, of the Cr–Al system have been observed. The solubility of Si varies from as low as 0.8 at.% in Cr₂Al to as high as 9 at.% in Cr₄Al₉. A schematic of the reaction scheme of the Cr–Al–Si system is presented. This has been based on the observed microstructure and composition of phases.     

Production and Characterization of (Al, Fe)-C (Graphite or Fullerene) Composites Prepared by Mechanical Alloying

(Al, Fe)-C_graphite and (Al, Fe)-C_fullerene composites have been prepared by mechanical alloying using ball milling of powders. Consolidation has been achieved by a spark plasma sintering technique (SPS). Results of XRD and TEM indicate that pure fullerene withstands milling. SEM results show homogeneous powders after milling but with different morphologies depending on the specific system. Milling produces a fine mixture of Al or Fe and graphite or fullerene. SPS produces a dense material with a nanocrystalline structure. The sintered samples have a metallic matrix (Al or Fe) with a fine dispersion of AI₄C₃ in the case of Al-C_{( graphiteorfullerene)}, Fe₃,C in the case of Fe-C_(graphite), and fullerene in the case of Fe-C _(fullerene), Hardness measurements show that higher values are obtained in the Al-C_(fullerene), and Fe-C_{(graphite )} specimens.     

粉末冶金(FeNiMnAl_(x))_(50)Cu_(50)中熵合金的微观组织与力学性能EI北大核心CSCD

对物理法制备的再生铜合金粉末进一步合金化,通过机械合金化(MA)结合放电等离子烧结(SPS)的方法制备了(Fe_(40)Ni_(40)Mn_(20))_(50)Cu_(50),(Fe_(38)Ni_(38)Ni_(38)Mn_(19)Al_(5))_(50)Cu_(50),(Fe_(36)Ni_(36)Mn_(18)Al_(10))50 Cu_(50)和(Fe_(32)Ni_(32)Mn_(16)Al_(20))_(50)Cu_(50)四种中熵合金块体,并研究了Al元素的含量对中熵合金微观组织与力学性能的影响。结果表明:在高能球磨60 h之后合金粉末完成合金化,四种中熵合金粉末均形成单一FCC相的过饱和固溶体且有微量WC杂质。经SPS烧结后,(Fe_(40)Ni_(40)Mn_(20))_(50)Cu_(50),(Fe_(38)Ni_(38)Mn_(19)Al_(5))_(50)Cu_(50)和(Fe_(36)Ni_(36)Mn_(18)Al_(10))50 Cu_(50)形成了由富Cu的FCC1相和富Fe-Ni的FCC2相组成的双相FCC结构,并具有超细晶+微米晶的多尺度结构;而(Fe_(32)Ni_(32)Mn_(16)Al_(20))_(50)Cu_(50)由富Cu的FCC主相和少量富Fe-Mn的FCC2相及富Ni-Al的BCC相(B2)组成。随着Al含量的提高,四种中熵合金的塑性逐渐降低,而强度和硬度逐渐提高。(Fe_(40)Ni_(40)Mn_(20))_(50)Cu_(50)合金的压缩屈服强度、抗压强度和维氏硬度分别为878 MPa,1257 MPa和248.5HV。与(Fe_(40)Ni_(40)Mn_(20))_(50)Cu_(50)相比,(Fe_(32)Ni_(32)Mn_(16)Al_(20))_(50)Cu_(50)的压缩屈服强度和硬度分别提高了50.1%和50.4%,断裂应变由19.55%下降至8.31%。     

碳钢坩埚表面渗铝复合涂层

以碳钢板为基板材料, 通过表面渗铝和高温化学反应在其表面形成复合保护涂层。研究了反应层厚度与反应温度、时间之间的关系, 并用光学显微镜、XRD对涂层形貌、相组成进行了表征。实验结果表明: 反应产物层厚度随反应温度、时间的增加而增加; 复合涂层由过渡层和反应产物层组成, 过渡层组成为Fe₃Al及少量Fe₂Al₅、Fe₁₄Al₈₆、Al₂O₃, 反应产物层组成为TiB₂、MgO和少量的Mg₂TiO₄、Mg₂B₂O₅、Fe₃Al、FeAl、Ti₂B₅。      

PROCESSING AND ALLOYING OF MODIFIED IRON ALUMINIDES

Alloying additions of Ti and Mo have been shown earlier to enhance the high temperature strength of Fe₃Al by stabilizing the DO₃ ordered structure to higher temperatures. However, these more complex alloys are quite brittle in the as-cast state at room temperature. The current work has explored several methods of improving the room temperature ductility including thermal-mechanical processing, consolidation of rapidly solidified powders, and further alloying. Of the various approaches, alloying appears to offer the most promise. Ductility achieved through powder processing may require additional efforts to preserve the high temperature strength.     

Analysis of the microstructure of Cr–Ni surface layers deposited on Fe3Al by TIG

A series of Cr–Ni alloys were overlaid on a Fe₃Al surface by tungsten inert gas arc welding (TIG) technology. The microstructure of the Cr–Ni surface layers were analysed by means of optical metallography, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicated that when the appropriate TIG parameters were used and Cr25–Ni13 and Cr25–Ni20 alloys were used for the overlaid materials, the Cr–Ni surface layers were crack-free. The matrix of the surface layer was austenite (A), pro-eutectoid ferrite (PF), acicular ferrite (AF), carbide-free bainite (CFB) and lath martensite (LM), distributed on the austenitic grain boundaries as well as inside the grains. The phase constituents of the Cr25–Ni13 surface layer were γ-Fe, Fe₃Al, FeAl, NiAl, an Fe–C compound and an Fe–C–Cr compound. The microhardness of the fusion zone was lower than that of the Fe₃Al base metal and Cr25–Ni13 surface layer.     

Synthesis, phase transformation and dielectric properties of sol–gel derived Bi2Ti2O7 ceramics

Sol–gel derived Bi₂Ti₂O₇ ceramic powders have been prepared from methoxyethoxides of bismuth and titanium (molar ratio of Ti/Bi = 1.23 and water/alkoxides = 1.31). The Bi₂Ti₂O₇ phase was stable at a low temperature (700 °C), but it then transformed into mixed phases of Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁ at 850–1150 °C. The single phase of Bi₂Ti₂O₇ reoccurred at 1200 °C. Dielectric properties and ferroelectric behavior of samples sintered at 1150 and 1200 °C were examined. Under frequency of 1 MHz, samples sintered at 1150 and 1200 °C had a dielectric constant of 101.3 and 104.2, and a loss tangent of 0.0193 and 0.0145, respectively. Only the sample sintered at 1150 °C showed ferroelectric behavior, where remanent polarization is 3.77 μC cm⁻² and coercive field is 24 kV cm⁻¹. Thus, the Bi₂Ti₂O₇ did not exhibit ferroelectricity, but the mixed phase of Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁ did.     

Synthesis of Aluminium-Cementite Metal Matrix Composite by Mechanical Alloying

Cementite powder was prepared from elemental iron and graphite powder by mechanical alloying (MA) in a specially built dual-drive planetary mill. The phase evolution, particle-size distribution, and morphology of particles were studied during 40 hours grinding period. X-ray diffraction (XRD) shows formation of cementite and other iron carbides along with elemental iron after milling, whereas after annealing only cementite is present. Initially particle size increases with milling due to ductility of iron powder and then reduces with further milling.

Al-cementite composite was synthesized by mixing cementite with Al powders, and then by hot pressing or cold compaction and sintering. XRD analysis of Al-Fe₃C composite shows Fe₃C, FeAl, Al, and other iron carbides along with Al₄C₃ after sintering. Scanning electron microscope (SEM) micrograph of hot-pressed samples shows excellent compatibilility between Al matrix and cementite particles.     

球磨参数对ODS奥氏体不锈钢机械合金化效果的影响

为了研究球磨参数对ODS奥氏体不锈钢机械合金化效果的影响,以Fe、Cr、Ni、W、Ti纯金属元素粉末和纳米Y2O3为原料进行混合(配比为Fe-18Cr-8Ni-2W-1Ti-0.35Y2O3,质量分数),通过高能球磨的方式实现混合粉末的机械合金化.研究球磨时间、转速的变化对粉末粒度、成分均匀度和固溶程度的影响.结果表明,在真空环境下,球料比为10∶1、转速为380r/min、球磨时间60h时,粉末达到了很好的机械合金化效果,成分分布均匀;当球磨时间延长到100h时,粉末颗粒达到最细,继续球磨,粉末将出现明显的团聚.对最优机械合金化工艺参数获得的粉末进行热压致密化研究表明,随着温度的升高,试样的密度随之升高,维氏硬度随之降低.     

Thermal stability and elevated temperature mechanical properties of electroslag remelted Fe-16wt.%Al-(0.14–0.5)wt.%C intermetallic alloys

Addition of carbon in the range of 0,14–0.5 wt.% to the Fe₃Al-based intermetallic Fe-16wt.%Al (Fe-28at.%Al) alloy results in the formation of a thermally stable dispersion of Fe,AIC carbide phase. The volume fraction of these precipitates increases with increase in carbon content. Processing of these alloys through a combination of air induction melting and electroslag remelting leads to enhanced elevated temperature mechanical properties compared to those reported for the low (< 0.01 wt.%) carbon alloys with similar Al contents. Enhancement of up to 30% in elevated temperature yield strength was observed at the test temperatures (600, 700 and 800°C) used. The improvement in mechanical properties may be attributed to the presence of strengthening Fe₃AlC phase as well as the interstitial carbon present in the alloy matrix. The addition of carbon also leads to improved room temperature mechanical properties in contrast with other alloying additions (such as Mo, Ti and Si) used for enhancing elevated temperature properties of Fe₃Al-based intermetallic alloys. It is suggested that carbon may be an important alloying addition to these alloys.     

Synthesis of MoSi2–Al2O3 nanocomposite by mechanical alloying

MoSi₂–Al₂O₃ nanocomposite was synthesized by mechanical alloying (MA) of MoO₃, SiO₂ and Al powder mixture. The structural evolution of the powders was studied by X-ray diffraction (XRD). Both β-MoSi₂ and -MoSi₂ were obtained after 3 h of milling. The spontaneous formation of β-MoSi₂ during milling proceeded by a mechanically induced self propagating reaction (MSR), analogous to that of the self propagating high temperature synthesis (SHS). After 70 h of milling the β-phase transformed to -phase. The crystallite size of -MoSi₂ and Al₂O₃ after milling for 100 h was 12 and 17 nm, respectively. Residual Mo and Si in the 3 and 70 h milled samples formed β-MoSi₂ and Mo₅Si₃ during heating at 1000 °C, respectively.     

Synthesis of nanocrystallite by mechanical alloying and in situ observation of their combustion phase transformation in Al3Ti

Elemental powders of stoichiometric Al₃Ti were mechanically alloyed (MA) in order to investigate the phase formation during the milling process. Furthermore the stability of MA powders were studied under transmission electron microscopy (TEM). The results indicate that a supersaturated Al(Ti) solid solution with nanocrystalline size has been formed after mechanical alloying for 360 ks in consuming the elemental powders of Al and Ti and no further phase transformation can be detected upon longer milling. The MA powders are unstable being irradiated by electron beams under the TEM observation, exothermically forming various intermetallic compounds. The combustion phase transformation processes and products are depending on the time of mechanical alloying. The structural changes and phase transformations during both mechanical alloying process and annealing process were also characterized by using X-ray diffraction measuring.     

Structural evolution during mechanical milling and subsequent annealing of Cu–Ni–Al–Co–Cr–Fe–Ti alloys

This study reports the structural evolution of high-entropy alloys from elemental materials to amorphous phases during mechanical alloying, and further, to equilibrium phases during subsequent thermal annealing. Four alloys from quaternary Cu_0.5NiAlCo to septenary Cu_0.5NiAlCoCrFeTi were analyzed. Microstructure examinations reveal that during mechanical alloying, Cu and Ni first formed a solid solution, and then other elements gradually dissolved into the solid solution which was finally transformed into amorphous structures after prolonged milling. During thermal annealing, recovery of the amorphous powders begins at 100 °C, crystallization occurs at 250–280 °C, and precipitation and grain growth of equilibrium phases occur at higher temperatures. The glass transition temperature usually observed in bulk amorphous alloys was not observed in the present amorphous phases. These structural evolution reveal three physical significances for high-entropy alloys: (1) the annealed state of amorphous powders produces simple equilibrium solid solution phases instead of complex phases, confirming the high-entropy effect; (2) amorphization caused by mechanical milling still meets the minimum criterion for amorphization based on topological instability proposed by Egami; and (3) the nonexistence of a glass transition temperature suggests that Inoue's rules for bulk amorphous alloys are still crucial for the existence of glass transition for a high-entropy amorphous alloy.     

Formation mechanism of Fe<Superscript>3</Superscript>Al and FeAl intermetallic compounds during mechanical alloying

Fe and Al elemental powder mixtures with composition Fe⁷⁵Al²⁵ and Fe⁵⁰Al⁵⁰ were mechanically alloyed in a planetary ball mill under different conditions. The structural changes of powder particles were studied by x-ray diffractometery and scanning electron microscopy. Mechanical alloying of Fe⁷⁵Al²⁵ and Fe⁵⁰Al⁵⁰ first produced a fine Fe/Al layered microstructure which transformed directly to the corresponding intermetallic compounds, Fe³Al and FeAl, with nanocrystalline structure at longer milling time. No intermediate phase, i.e. solid solution, was formed during mechanical alloying as a precursor to the intermetallic phase. The rate of mechanical alloying process was found to be dependent on milling variables such as rotation speed of mill, ball-to-powder weight ratio and number of milling balls.     

Nickel Enriched Diffusion Layers on a NiAl Alloy

The intermetallic phase NiAl is a perspective material for high-temperature and shape memory effect applications. Formation of Ni₅Al₃, Ni₂Al, Ni₃Al phases which influence the extent of martensitic transformation in NiAl have been studied up to now with controversial results. We have investigated (using SEM and local elemental analyses) the microstructure of nickel enriched surface layers on a Al-79 wt.% Ni alloy. The layers were prepared by diffusion annealing and subsequently given two different heat treatments: at 930°C outside the Ni₅Al₃ region and at 500°C within the Ni₅Al₃ region of the phase diagram. In the specimen which was only diffusion annealed separate islands of Ni₅Al₃ phase elongated in the direction of the concentration gradient could be recognized within the nickel enriched surface layer. In the samples additionally annealed at 500°C, a well defined continuous layer of the Ni₅Al₃ phase situated 0.4 mm below the specimen surface was found. In the samples annealed at 930°C, isolated Ni₃Al precipitates were observed. Their number and size gradually increased with increasing nickel content.     

Microstructure and tribological properties of in situ synthesized TiN/Ti3Al intermetallic matrix composite coatings on titanium by laser cladding and laser nitriding

TiN reinforced Ti₃Al intermetallic matrix composite (TiN/Ti₃Al IMC) coatings were in situ synthesized on a pure Ti substrate with Ti + Al mixed powders in nitrogen atmosphere by laser cladding and laser nitriding. It was found that the growth morphologies of the TiN reinforced phase in the TiN/Ti₃Al IMC coatings were granular-like, flake-like, and undeveloped dendrites at lower N₂ flow rate; and granular-like, undeveloped and developed dendrites at higher N₂ flow rate. In addition, the volume fraction of the TiN phase increased with increasing nitrogen flow rate. The hardness of the TiN/Ti₃Al IMC coatings was higher than that of the Ti₃Al coating, which increased with increasing volume fraction of the TiN phase. Friction and wear tests revealed that the wear resistance of TiN/Ti₃Al IMC coatings was superior to those of pure Ti and Ti₃Al coating. It is well worth noting that the TiN/Ti₃Al IMC coatings showed excellent wear resistance under lower normal loads.     

Fe/Al异质金属接头界面组织演变、生长动力学及力学性能

采用真空扩散连接方法研究Fe/Al异质金属接头界面组织演变规律、金属间化合物(intermetallic compound,IMC)生长动力学及力学性能。结果表明：焊接温度为550 ℃时,接头界面无IMC生成,当焊接温度超过575 ℃时,界面由Fe₂Al₅及少量FeAl₃ IMC构成,且随焊接温度升高IMC层迅速长大。在120 min保温时间条件下,接头剪切强度随焊接温度的升高先增加后降低,当焊接温度为575 ℃时,接头剪切强度达到最大值37 MPa。在550~625 ℃范围内,基于热力学分析得出Fe₂Al₅的吉布斯自由能ΔG_Fe-Al最低,而FeAl₃的ΔG_Fe-Al次之,在接头界面处IMC生成顺序为Fe₂Al₅→FeAl₃。Fe/Al接头界面IMC的生长随焊接温度呈抛物线规律,其生长激活能为282.6 kJ·mol^-1。在575,600,625 ℃条件下,界面IMC的生长速率分别为1.13×10^-14,3.59×10^-14,1.21×10^-13 m²·s^-1。     

氢燃料电池用镁-钛基合金储氢性能研究

采用高能振动球磨法,制备了Mg₃₅Ti₆₅合金,并添加(10%La_0.4Ce_0.1Pr_0.3Nd_0.2Ni_4Co_0.5Mn_0.3Al_0.2)作为改性剂,制备了储氢合金Mg₃₅Ti₆₅/(10%La_0.4Ce_0.1Pr_0.3Nd_0.2Ni_4Co_0.5Mn_0.3Al_0.2),研究了改性剂的添加及球磨时间对合金显微组织、吸放氢性能的影响规律。结果表明:球磨Mg₃₅Ti₆₅时间为20h时,能获得单一的BCC固溶体相,加入质量分数为10%的改性剂球磨0.5h时能明显地改善其储氢性能,8MPa,573K下100s内吸氢质量能达到3%,随着球磨时间的增加,其相结构发生改变,吸氢量及动力学性能逐渐变差。     

Mechanical Alloying of β‐Type Ti–Nb for Biomedical Applications

β‐Type Ti–Nb powders which are needed as precursors for porous implant materials were produced by mechanical alloying of elemental powders. The effect of different fractions of the inorganic milling agent NaCl on the phase reactions during the milling process was investigated by means of X‐ray diffraction and scanning and transmission electron microscopy. It was demonstrated, that addition of ≥2 wt% NaCl during continuous ball milling is efficient for establishing a nanostructured β‐phase alloy and for the achievement of high powder yield.