Synthesis and grain growth kinetics of in-situ FeAl matrix nanocomposites （ Ⅱ ）： Structural evolution and grain growth kinetics of mechanically alloyed Fe-Al-Ti-B composite powder during heat treatment

Morphological changes, structural evolutions and grain growth kinetics of mechanically alloyed（MAed） Fe50Al50, Fe42.5Al42.5Ti5B10 and Fe35Al35Ti10B20 （mole fraction, %） powders were investigated by XRD and SEM, when being isothermally annealed at 1 073-1 373 K. The effect of different Ti and B addition on the grain growth of FeAI phase was also discussed. The results show that the nanocrystalline FeAI and in-situ TiB2/FeAl nanocomposite powders can be synthesized by subsequent heat treatment. Besides the relaxation of crystal defects and lattice stress, the transformation from Fe-based solid solution into B2-FeAl and TiB2 occurs upon heating of the MA-processed alloys. Although the grain growth takes place, the grain sizes of both FeAl and TiB2 are still in nanometer scale. The activation energies for the nanocrystalline FeAl growth in the three alloys are calculated to be 534.9, 525.6 and 1 069.6 kJ/mol respectively, according to kinetics theory of nanocrystalline growth. Alloys with different TiB2 contents exhibit unequal thermal stability. The presence of higher content TiB2 plays significant role in the impediment of grain growth.     

Microstructure evolution in nanocrystalline Cu-Nb alloy during mechanical alloying

The microstructural evolution of nanocrystalline Cu-10%Nb（mass fraction） alloy during mechanical alloying （MA） was investigated by using X-ray diffraction, optical microscopy（OM）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM） observation. Upon milling of Cu-Nb powders with coarse grains, the grain size is found to decrease gradually with lengthening milling time, and reach the minimum value （about 9 nm） after 100 h milling. The microstrain and the microhardness of the powders increase during the grain refinement. And Cu lattice parameter increases steadily over 100 h milling. The mechanisms of solid solution extension during milling were discussed. The results show that up to 10%Nb can be brought into solid solution by MA. The extension of solid solution is found to relate closely with the formation of nanocrystalline.     

Carbon solubility in Cu-based composite prepared by mechanical alloying

The powder mixture of Cu and graphite was mechanically alloyed （MA） in an oscillating type ball mill. The milling time was varied in order to investigate its influence on the microstructural evolution of mechanically alloyed powders. The phase constituent, alloying characteristics, grain size and lattice distortion of these powders were determined by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. The results show that the C is confirmed to dissolve in the Cu lattice, forming solid solution of carbon in copper the lattice parameter of copper increases with carbon concentration increasing, up to a saturation value of about 4%C（mass fraction）. Higher ball-mill energy is beneficial for twins and nanograin formation.     

Influence of Process Variables on the Structure of Mechanically Alloyed Ti_3Al-base Intermetallics

During mechanical alloying variables such as the type of mill,milling intensity,milling time,milling at-mosphere and ball-to-powder weight ratio(BPR)affect the morphology and constitution of the product.The effect of milling time,milling atmosphere and BPR on the nature of the product formed in mechanical-ly alloyed pure Ti and blended elemental binary Ti-Al,and ternary Ti-AI-Nb alloy powders was described.Mechanical alloying of pure titanium results,after long milling times,in the formation of an fcc phase.Inthe binary alloy,a solid solution of aluminum in titanium,an amorphous phase,and a fcc phase form withincreasing milling time.The fcc phase,which is probably a result of TiN formation,occurs more rapidly inair or nitrogen than in an inert atmosphere.Formation of the B2 phase in the ternary alloys depends bothon alloy composition and the milling atmosphere,with 100％ formation in all atmospheres in Ti-25Al-25Nbbut not in Ti-24Al-11Nb,and an inert atmosphere favoring formation.The times required for the formationof the different phases decrease as the BPR increases;but their sequence is unaffected.Based on this infor-mation,“milling maps”which describe phase formation as a function of the BPR and milling time are con-structed.Contamination from the milling balls increased as the BPR was increased.     

Hot-press sintering of MA Fe-based nanocrystalline／amorphous soft magnetic powder

Microstructures and magnetic properties of Fe84 Nb7 B9, Fe80 Ti8 B12 and Fe32 Ni36 (Nb/Ⅴ) 7 Si8 B17 powders and their bulk alloys prepared by mechanical alloying(MA) method and hot-press sintering were studied. The results show that: 1) After MA for 20 h, nanocrystalline bcc single phase supersaturated solid solution forms in Fe84-Nb7 B9 and Fe8o Ti8 B12 alloys, amorphous structure forms in Fe32 Ni36 Nb7 Si8 B17 alloy, duplex microstructure composed of nanocrystalline γ-(FeNi) supersaturated solid solution and trace content of Fe2B phase forms in Fe32 Ni36-V7 Si8 B17 alloy. 2) The decomposition process of supersaturated solid solution phases in Fe84 Nb7 B9 and Fe80 Ti8 B12alloys happens at 710 -780 ℃, crystallization reaction in Fe32 Ni36 Nb7 Si8 B17 alloy happens at 530 ℃ (the temperature of peak value) and residual amorphous crystallized further happens at 760 ℃ (the temperature of peak value), phase decomposition process of supersaturated solid solution at 780 ℃ (the temperature of peak value) and crystallization reaction at 431 ℃ (the temperature of peak value) happens in Fe32 Ni36 V7Si8B17 alloy. 3) under 900 ℃, 30 MPa,0.5 h hot-press sintering conditions, bulk alloys with high relative density(94.7%- 95.8%) can be obtained. Except that the grain size of Fe84 Nb7B9 bulk alloy is large, superfine grains (grain size 50 - 200 nm) are obtained in other alloys. Except that single phase microstructure is obtained in Fe80 Ti8B12 bulk alloy, multi-phase microstructures are obtained in other alloys. 4) The magnetic properties of Fe80 Ti8 B12 bulk alloy(Bs = 1.74 T, Hc = 4.35 kA/m) are significantly superior to those of other bulk alloys, which is related to the different phases of nanocrystalline or amorphous powder formed during hot-press sintering process and grain size.     

Synthesis of TiAl-Al2O3 composites by high energy milling and hot-press sintering

A sub-microstructure titanium aluminide alloy/Al2O3 （3A） composite was obtained by crystallization of the amorphous powders, which were prepared by mechanical alloying （MA） in a planetary ball milling system using Ti-AI-TiO2 as raw materials. The experimental results show that, when the milling time increases up to 30 h, the hep Ti（Al） supersaturated solid solution disappears, only amorphous phase is left. The compact samples were synthesized by hot-press to 1 200 ℃ with the amorphous as a precursor; the final phases of the matrix and strengthened phase are y-TiAl and Al2O3. The phases come from in situ crystallization and transformation. The samples, fabricated from the amorphous phase by hot press sintering, have high bending strength and fracture toughness.     

Synthesis of TiAl-Ti2AlN composites by in-situ crystallization

The amorphization process during mechanical alloying （MA） was investigated for the Ti-50%/Al （mole fraction） powder mixtures with no special protection conditions. During the milling process, with the milling time prolonging, the metallic powder Ti and Al were finely mixed, gradually, aluminum completely dissolved into titanium to form an Ti（Al） hcp supersaturated solid solution, and finally, transformed to the amorphous phase after milled for about 39 h. As a result of heat treatment in hot press sintering processing for the mechanically alloyed amorphous powders in vacuum, a submicrostructure intermetallics of TiAl/TizAIN composite can be produced by in-situ crystallization. Furthermore, the structure evolution, phase formation and transformation during the heat treatment were also investigated by X-ray diffractometry and differential thermal analysis. The results show that the reaction involves many transitional stages, including formation of TiAl3 and transformation into TiAl and Ti3Al. The examination show that the composite materials fabricated by this in-situ crystallization from amorphization have good mechanical properties due to fine grain size and uniform microstructure.     

Influence of Ce on microstructure and mechanical properties of LA141 alloys

LA141-（0-1.2）Ce alloys were prepared with vacuum induction melting method. The effects of Ce addition on the microstructure and mechanical properties of LA 141 alloys were studied. The microstructure and phases composition of these alloys were analyzed by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffractometry. The mechanical properties of these alloys were measured with tensile tester. The results show that Ce has refining effect on the alloys. In the alloys, some Al2Ce compounds exist, which make the A1 content dissolved in a and β phases decrease and the hard brittle Mg17Al12 phase refined. The refining effect improves the mechanical properties of alloys. When Ce content is 0.9%（mass fraction）, the tensile strength reaches 206.8 MPa and the elongation is two times as high as that of LAl41 alloy. Due to the generation of Al2Ce, the content of Al solid soluted in β phase decreases resulting in the decrease of alloy hardness with the addition of Ce.     

Structural characteristics and magnetic properties of bulk nanocrystalline Fe_(84)Zr_2Nb_4B_(10) alloy prepared by mechanical alloying and spark plasma sintering consolidation

Magnetic properties of Fe84Zr2Nb4B10 sample were investigated. The sample was produced from nanocrystalline powders made by the mechanical alloying (MA) and consolidation using the spark plasma sintering (SPS) technique. Effects of milling time on phase transformation, structural characteristics, and magnetic properties of powders were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and physical property measure system (PPMS), respectively. Results show that nanostructured α-Fe supersaturated solid solution is obtained in the final MAed products. The saturation magnetization (Ms) increased with increasing milling time and became constant at 130 h, but the coercivity (Hc) increased firstly and then decreased. The consolidated bulk sample exhibited a high density of 6.893 g·cm-3, there was no phase change during SPS process, and the saturation magnetization and susceptibility of the SPSed bulk sample improved in comparison with the milled powders. The variation of magnetic parameters can be explained by nano-scale effect and Herzer model.     

Surface hardening of titanium alloys by oxygen-diffusion-permeation

The surface oxygen-diffusion-permeation behaviors of T based alloys were investigated.MEF4A optical microscopy and HMV-2000 micro-hardness tester were employed to characterize the microstructure and micro-hardness of the oxygen-permeated alloys.The results show that the micro-hardness of Ti based alloys are sharply enhanced by the permeation of oxygen.The microstructure and micro-hardness of oxygen-permeated layer are strongly related to the oxygen-diffusion-permeation techniques.The solid solution of oxygen in α phase can improve the transformation temperature from αphase to βphase and enlarge the region of α phase so as to improve the microhardness of surface layer.Therefore,surface oxygen-diffusion-permeation would be a feasile method to reinforce Ti based alloys based on the solid solution of oxygen in α-Ti.At last,a diffusion-solution model was put forward.     

Synthesis and grain growth kinetics of in-situ FeAl matrix nanocomposites (Ⅱ): Structural evolution and grain growth kinetics of mechanically alloyed Fe-Al-Ti-B composite powder during heat treatment

Morphological changes, structural evolutions and grain growth kinetics of mechanically alloyed(MAed) Fe50Al50, Fe42.5Al42.5Ti5B10 and Fe35Al35Ti10B20 (mole fraction, %) powders were investigated by XRD and SEM, when being isothermally annealed at 1 073-1 373 K. The effect of different Ti and B addition on the grain growth of FeAl phase was also discussed. The results show that the nanocrystalline FeAl and in-situ TiB2/FeAl nanocomposite powders can be synthesized by subsequent heat treatment. Besides the relaxation of crystal defects and lattice stress, the transformation from Fe-based solid solution into B2-FeAl and TiB2 occurs upon heating of the MA-processed alloys. Although the grain growth takes place, the grain sizes of both FeAl and TiB2 are still in nanometer scale. The activation energies for the nanocrystalline FeAl growth in the three alloys are calculated to be 534.9, 525.6 and 1 069.6 kJ/mol respectively, according to kinetics theory of nanocrystalline growth. Alloys with different TiB2 contents exhibit unequal thermal stability. The presence of higher content TiB2 plays significant role in the impediment of grain growth.     

Synthesis of amorphous Ti—Al alloys by mechanical alloying of elemental powders

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合金化元素对纳米晶铝合金热稳定性的影响

为研究加入Fe和Ti扩散系数有限的元素对纳米晶铝合金热稳定性的影响,制备Al?10％Fe(质量分数)和Al?10％Fe?5％Ti(质量分数)合金.将初始混合粉末在真空下球磨100 h,用高频感应加热烧结系统将球磨后的粉末制备成块体样品.采用X射线衍射仪、维氏显微硬度仪、场发射扫描电子显微镜和透射电子显微镜对球磨后的粉末...     

机械合金化过程中Fe50Als50二元系的结构演变

利用高能球磨和后续热处理技术制备纳米晶Fe5A150（摩尔分数，％）合金粉体。采用X射线衍射、透射电镜和扫描电镜对元素混合粉在机械合金化过程中的结构演变及热处理对合金化粉体结构的影响等进行分析，讨论其机械合金化合成机制。结果表明：球磨过程中Al向Fe中扩散，形成Fe（A1）固溶体。机械合金化合成Fe（Al）遵循连续扩散混合机制；球磨30h后，粉体主要由纳米晶Fe（A1）构成，晶粒尺寸5．65nm；热处理导致Fe（A1）纳米晶粉体有序度提高，转变为有序的B2型FeAl金属间化合物，粉体的晶粒尺寸增大，但仍在纳米尺度范围。     

Characterization and formation mechanism of nanocrystalline (Fe,Ti)3Al intermetallic compound prepared by mechanical alloying

The nanocrystalline (Fe,Ti)₃Al intermetallic compound was synthesized by mechanical alloying (MA) of elemental powder with composition Fe₅₀Al₂₅Ti₂₅. The structural changes of powder particles during mechanical alloying were studied by X-ray diffractometry and microhardness measurements. Morphology and cross-sectional microstructure of powder particles were characterized by scanning electron microscopy. It was found that a Fe/Al/Ti layered structure was formed at the early stages of milling followed by the formation of Fe(Ti,Al) solid solution. This structure transformed to (Fe,Ti)₃Al intermetallic compound at longer milling times. Upon heat treatment of (Fe,Ti)₃Al phase the degree of DO₃ ordering was increased. The (Fe,Ti)₃Al compound exhibited high microhardness value of about 1050 Hv.     

原位颗粒增强Fe3Al基纳米复合材料的显微结构与力学性能

采用机械合金化及真空热压烧结制备硼化物颗粒原位增强Fe。Al基纳米复合材料块体。对球磨粉体及热压块体的相组成、烧结块体的微观结构、断口形貌及力学性能进行了测试分析。结果表明,Fe-A1-Ti-B混合粉在球磨过程中,Al、Ti、B逐渐溶人Fe中,形成纳米晶Fe（A1,Ti,B）过饱和固溶体,结构趋于非晶态。经1200℃保温1h后热压烧结的块体由Fe。A1及原位形成的TiB2及FezB等构成,其晶粒尺寸分别约为17nm,22nm和11nm。含5at％（Ti37B67）的Fe3Al基纳米复合材料块体的致密度大于95％,抗弯强度和硬度分别为1440MPa和461．3HV10,弯曲断口为主体脆性断裂,同时呈现出一定韧性特征。     

The FeAl–30%TiC nanocomposite produced by mechanical alloying and hot-pressing consolidation

Intermetallic matrix composites reinforced with particles such as TiC have attracted a great deal of attention over the past few years. In the present study, the mechanical alloying process followed by hot-pressing consolidation was used to produce FeAl–30%TiC nanocomposite. Since the reduction of grain size to the nanometer scale improves mechanical properties of materials, this composite may be attractive for structural applications. An elemental powder mixture of Al35Fe35Ti15C15 (in at.%) was milled in a high-energy ball mill. The phase transformations in the powder during milling were studied with the use of X-ray diffraction (XRD). Transmission electron microscopy and differential scanning calorimetry were used for examining the microstructure and the thermal stability of the milling product. The results obtained show that high-energy ball milling as performed in this work leads to the formation of a bcc phase identified as the Fe(Al) solid solution and a fcc phase identified as TiC, and that both phases are nanocrystalline. Subsequently, the milled powder was sintered at 750 °C under pressure of 4 GPa. The XRD investigations of the consolidated pellet revealed that after sintering, the material remained nanocrystalline and that there were no phase changes, except for the ordering of Fe(Al), i.e. formation of FeAl intermetallic compound, during the sintering process. The average hardness of the obtained nanocomposite is 1287 HV_0.2 (12.6 GPa) and its density is 98% of the theoretical value.     

Synthesis of TiB2 nanocrystalline powder by mechanical alloying

1 Introduction TiB2 has been widely used in some industrial fields owing to its high melting temperature, hardness, elastic modulus, electro-conductibility and thermal diffusivity, and excellent refractory properties and chemical inertness. Usually, TiB2…     

Fe73.5Cu1Nb3-xTixSi13.5B9 (x=0, 1, 2, 3)合金粉的结构与磁性

将Fe73.5Cu1Nb3-xTixSi13.5B9(x=0,1,2,3)合金快淬带进行高能球磨制成粉末样品,在550℃真空退火1h,研究了磁粉的相结构及磁性。结果表明,随球磨时间延长,不添加Ti的Fe73.5Cu1Nb3Si13.5B9合金中析出晶化相的晶格常数增大。添加Ti的Fe73.5Cu1Nb3-xTixSi13.5B9(x=0,1,2,3)合金在球磨60h后再退火,可以得到单一α-Fe(Si)软磁相,且随Ti含量增大,析出晶化相的晶格常数减小,饱和磁化强度增大、矫顽力降低。