Ni50Ti50非晶粉末在球磨时的稳定性

将Ｎｉ５０Ｔｉ５０单质混合粉末经机械合金化形成非晶态合，再进一步球磨使其产生晶化。结果表明，晶化产物为Ｎｉ３Ｔｉ金属间化合物。当Ｎｉ５０Ｔｉ５０非晶体加热时，产生的晶化产物有ＮｉＴｉ，ＮｉＴｉ２和Ｎｉ３Ｔｉ三种金属间化合物。本文通过ＤＳＣ差热分析，测定了Ｎｉ５０Ｔｉ５０非晶合金的晶化热及晶化激活能，并讨论了过度球磨时非晶晶化机制。     

机械合金化能量转换与Ni50Ti50非晶合金的形成

本文报道了球磨转速，装球量对Ｎｉ５０Ｔｉ５０单质混合粉机械合金化的影响，并建立模型用于计算工艺条件对球磨能量转换的影响，进而讨论了它与机械合金化相变反应方式的关系。粉末在每次碰撞的变形能过高时，可能形成金属间化合物，而粉末经长时间球磨获得的总能量超这一定值将引起非晶的晶化。     

机械合金化Fe－Ti合金非晶形成能力的研究

利用Ｘ光衍射和扫描电镜对机械合金化Ｆｅ－Ｔｉ非晶合金的形成过程进行了研究。试验表明，机械合金化非晶形成的过程可以分为二个阶段：粉末的破碎阶段和非晶的形成阶段。此外，对Ｆｅ－Ｔｉ合金形成非晶的成分范围进行了理论计算和试验测定。结果表明，ＦｅｘＴｉ１－ｘ可以在０．３０≤ｘ≤０．５０的范围内形成非晶，这与理论计算值基本一致。     

过共析Ti-Cr合金的机械合金化

以钛，铬元素粉为原料，在行星式球磨机上采用φ20mm的淬火钢球，以200r/min的球磨速度和15：1的球料比，研究了Ti-20%Cr(ω(B)和Ti-30%Cr(ω(B)两种合金的机械合金化（MA）规律，研究结果表明；在球磨初期的2h内钛的（011）主衍射峰强度迅速降低，（010）第二衍射峰强度提高并成为最强峰，同时铬的衍射峰强度提高；随着球磨时间的增加，钛和铬的X射线衍射峰均发生宽化，强度下降和衍射角左移并减小；当球磨时间为30-40h时，钛逐步非晶化，但在本试验条件下铬没有发生非晶化；MA的前10h是粉末晶粒细化，晶格应变和合金化进行的最迅速的时期，经该阶段球磨后铬的晶粒尺寸可以达到20nm，进一步示磨有利于获得过饱和固溶的合金粉末；两种合金在超过100h的MA过程中均未发现在固相合成Laves相TiCr2；确定30-40h为制备纳米晶或非晶过饱固溶Ti-Cr合金粉末的合理球磨时间。     

非晶化程度对不同成分Mg—Ni非晶合金电极充放电容量的影响

研究了球磨过程中的非晶化过程度对不同成分Ｍｇ－Ｎｉ非晶合金电化学吸放氢性能的影响。研究结果表明：随着合金成分的不同，非晶化程度的影响不同。当Ｎｉ含量低于５０％（原子分散）时，合金粉末中的非晶相所占比例越高，即非晶化程度越高时，合金电极的放电容量越大；而当Ｎｉ含量高于５０％（原子分数）时，非晶合金中存在少量游离态的Ｎｉ相，可提高电极的放电量。分析认为这与Ｎｉ的相的存在改善了合金的吸放氢动力学性能有关     

球磨工艺参数对MgNi非晶合金形成及性能的影响

通过机械合金化法制备了MgNi非晶合金,利用X射线衍射分析了非晶相的形成情况,并对其储氢性能和电化学性能进行了测试.对球磨工艺参数与合金微观结构及性能之间关系进行分析,结果表明,球磨机转速对MgNi非晶相的形成效率具有十分重要的影响,随着转速的增加,MgNi非晶相的形成时间大大缩短.随着球磨时间的延长,MgNi非晶相的形成趋于完全,粉末的粒径逐渐减小,粒度分布也较为均匀,但形成完全非晶后继续球磨过长时间会降低Mg-Ni合金的吸放氢性能和电化学性能.     

机械合金化纳米晶合金Ni50Bi50的结构和磁性

研究了Ｎｉ５０Ｂｉ５混合粉末在机械合金化过程中结构和磁性的变化。Ｘ射线衍射、差示扫描量热分析和比饱和磁化强度的测量结果表明：混合粉末的晶粒尺寸随球磨时间的增加而减小。球磨２００ｈ时，样品的晶粒尺寸为１５ｎｍ。机械合金化可以提高Ｂｉ在Ｎｉ中的固溶渡。     

机械合金化法制备W—Cu合金的研究

采用高能球磨的机械合金化法制备W—Cu合金,对其在实验过程中的工艺条件进行了研究。结果表明：随着球磨时间的延长,粉末的粒度逐渐细化,比表面积逐渐增大。球磨过程分为三个阶段。最佳工艺条件是：当球料比为5：1,W：Cu为8：2,球磨时间达到30h时,铜粉和钨粉基本形成固溶体。球磨过程加入少量的无水乙醇,防止在球磨过程中粉末被氧化。     

机械合金化Fe—Ti合金非晶形成能力的研究

利用Ｘ光衍射和扫描电镜对机械合金化Ｆｅ－Ｔｉ非晶合金的形成过程进行了研究。试验表明，机械合金化非晶形成的过程可以分为二个阶段；粉末的破碎阶段和非晶的形成阶段。此外，对Ｆｅ－Ｔｉ合金形成非晶的成分范围进行了理论计算和试验测定。     

机械合金化合成Fe-Ni-C系非晶态合金

用机械合金化方法合成了Fe—Ni—C系非晶态合金,用X射线衍射仪对球磨不同时间的Fe—Ni—C系混合粉末进行了分析．结果表明：在Fe—Ni合金中加入C可促使其形成非晶;原子分数分别为Fe40Ni40C20、Fe60Ni20C20的混合粉末在一定的机械合金化条件下可获得非晶．     

机械合金化能量转换与Ni_(50)Ti_(50)非晶合金的形成

本文报道了球磨转速,装球量对 Ni_(50)Ti_(50)单质混合粉机械合金化的影响,并建立模型用于计算工艺条件对球磨能量转换的影响,进而讨论了它与机械合金化相变反应方式的关系。粉末在每次碰撞的变形能过高时,可能形成金属间化合物,而粉末经长时间球磨获得的总能量超过一定值将引起非晶的晶化。     

Formation of a FCC Al_(54)Ti_(23)C_(23) Metastable Phase by Ball Milling

The powder mixture of Al, Ti and graphite has been mechanically alloyed in a planetary ball mill.The structural evolution of as-milled powder sample has been characterized by XRD, DTA. The results show that the amorphous phase is formed first at an early milling stage, then crystallization occurs during further milling, leading to formation of a nanocrystalline fcc metastable phase. In contrast, during annealing the amorphous phase is crystallized to the equilibrium phase instead of the fcc phase. This indicates that crystallization during ball milling is different from that induced by annealing     

Phase Development and Crystallization Kinetics of NiTi Prepared by Mechanical Alloying

NiTi alloy is produced by mechanical alloying(MA). It becomes amorphous after milling for enough time, such as 100 h in this paper. DSC measurement shows that the crystallization temperature is 676 K for the amorphous powder. Activation energy of crystallization is 199.98kJ/mol for MA powder, which is lower than that of amorphous prepared by magnetron sputtering.Avrami parameter of crystallization is 1.07.     

高能球磨时间和退火温度对制备TiNi合金粉的影响

为获得高能球磨时间和退火温度对TiNi机械合金粉特性的影响机制,采用X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线能谱仪(EDS)、差示扫描量热法(DSC)等分析方法对TiNi合金粉进行了研究。结果表明,机械合金的相成分随着在氩气保护气氛中的球磨时间和退火温度的不同而发生变化。球磨22h的产物是非晶态TiNi合金、Ti的固溶体、Ni的固溶体,球磨27h的产物是非晶态TiNi合金粉和Ni固溶体相,球磨30h发生了明显的固相反应,生成了TiNi、Ni3Ti、Ti3Ni4等物相;在650℃/5h和1000℃/5h下的退火产物都是Ni3Ti、Ti2Ni、TiNi2、TiNi和TiC,但在上述2个退火温度下TiNi并不是主要物相,其中在650℃退火时TiNi的含量明显更低。     

机械合金化Co-Zr非晶软磁合金粉末的形成及热稳定性分析

研究了Co-Zr二元相图上4个共晶点成分配方Co90Zr10、Co53Zr47、Co35Zr65和Co21Zr79在球磨条件下的非晶态合金形成能力。采用X射线衍射和差热分析(DTA)对粉末的结构及热稳定性进行了分析。XRD分析结果表明,4种配方在一定的球磨时间内都能形成非晶态合金,其中非晶形成能力最强的为Co35Zr65。DTA分析结果表明,该合金系具有较高的热稳定性,并具有较高的非晶形成能力。球磨时间对非晶的形成有重要影响,球磨时间过长,使形成的非晶态合金粉体反而向晶体转化。     

Structural Modification of Al_(6)5Cu_(16.5)Ti_(18.5) Amorphous Powder through Annealing and Post Milling:Improving Thermal Stability

To improve thermal stability of the Al65Cu16.5Ti18.5 amorphous powder,structural modification of the amorphous powder was performed through annealing and post milling.Annealing above the crystallization temperature(Tx) not only induced nanoscale intermetallics to precipitate in the amorphous powder,but also increased Cu atomic percentage within the residual amorphous phase.Post milling induced the amorphization of the nanocrystal intermetallics and the formation of Cu9Al4 from the residual amorphous phase.Thus,a mixed structure consisting of amorphous phase and Cu9Al4 was obtained in the powder after annealing and post milling(the APMed powder).The phase constituent in the APMed powder did not change during the post annealing,which exhibited significantly improved thermal stability in comparison with the as-milled amorphous powder.     

Thermal behaviours of mechanically alloyed Ti50Al50 in a nitrogen atmosphere

Thermal behaviours of mechanical alloyed Ti₅₀Al₅₀ powders in a nitrogen atmosphere are investigated in this paper. X-ray diffraction and differential thermal analysis were used to determine their characteristics. At the initial milling stage, large amounts of defects were introduced and the grain sizes were gradually refined. The enthalpy changes of formation of -TiAl and ₂-Ti₃Al were decreased with increasing milling times. No obvious dissolution of nitrogen into the powder particles occurred at this stage. With increasing milling time, an amorphous phase containing nitrogen gradually occurred. The amorphous phase and small amounts of Ti solid solution were obtained after milling for 30 h in a N₂ atmosphere. The thermal process included two stages. Firstly, the amorphous phase crystallized at low temperature and resulted in the formation of a nanophase; secondly, the grain growth of this nanocrystalline phase occurred at high temperature. The annealing products are different for the milling products obtained at the initial stage (-TiAl + ₂-Ti₃Al) and final stage (-TiAl + Ti₂AlN), which is attributed to the different nitrogen contents in the milled products. The activation energies for the crystallization and grain growth are 251.9 and 296.9 kJ mol^–1, respectively.     

Microstructural phase evaluation of high-nitrogen Fe–Cr–Mn alloy powders synthesized by the mechanical alloying process

In this study, the formation of Fe18Cr8MnxN alloys by mechanical alloying (MA) of the elemental powder mixtures was investigated by running the milling process under nitrogen and argon gas atmospheres. The effect of the milling atmosphere on the microstructure and phase contents of the as-milled powders was evaluated by X-ray diffraction and transmission electron microscopy. The thermal behavior of the alloyed powders was also studied by differential scanning calorimetry. The results revealed that in the samples milled under nitrogen, three different phases, namely ferrite (α), austenite (γ), and a considerable amount of amorphous phase are present in the microstructure. In contrast, in the samples milled under argon, the structure contains the dominant crystalline ferrite phase. By progression of MA under the nitrogen atmosphere, the ferrite-to-austenite phase transformation occurs; meanwhile, the quantity and stability of the amorphous phase increase, becoming the dominant phase after 72 h and approaching 83.7 wt% within 144 h. The quantitative results also showed that by increasing the milling time, grain refinement occurs more significantly under the nitrogen atmosphere. It was realized that the infused nitrogen atoms enhance the grain refinement phenomenon and act as the main cause of the amorphization and α-to-γ phase transformation during MA. It was also found out that the dissolved nitrogen atoms suppress the crystallization of the amorphous phase during the heating cycle, thereby improving the thermal stability of the amorphous phase.     

Influence of mechanical alloying on structural,thermal, and magnetic properties of Fe50Ni10Co10Ti10B20 high entropy soft magnetic alloy

A multicomponent with functional Fe₅₀Ni₁₀Co₁₀Ti₁₀B₂₀ (at.%) high entropy soft magnetic alloy powders were produced from the elemental powders by mechanical alloying (MA). The MA processes were carried out under argon gas atmosphere at a speed of 250 rpm, carrying milling and rest in every 20-min period to prevent the mixture from overheating. Scanning electron microscopy and energy-dispersive X-ray spectroscopy, X-ray diffraction, differential thermal analysis, and vibrating sample magnetometer analysis were utilized to characterize various powdered samples with respect to MA time (0–50 h). The results show that in the first 2.5 h of MA, the mixture of crystalline phases transformed into a nanocrystalline supersaturated α-Fe solid solution phase. With prolonging milling time, the amorphous phase appeared after 20 h of MA. In the final stage of MA (50 h), the saturation magnetization (Ms) and the coercivity (Hc) were 89.7 emu/g and 32.5 Oe, respectively, proposing the alloy as a very good high entropy soft magnet in nature.

     

Thermodynamic Aspects of Nanostructured CoAl Intermetallic Compound during Mechanical Alloying

The nanostructured CoAl intermetallic compound was produced by mechanical alloying (MA) of the Co50Al50 elemental powder mixture in a planetary high energy ball mill. The ordered B2-CoAl structure with the grain size of about 6 nm was formed via a gradual reaction after 10 h of MA. A thermodynamic analysis of the process was also done. The results showed that the intermetallic compound of CoAl had the minimum Gibbs free energy compared to solid solution and amorphous states indicating the initial MA product was the most stable phase in the Co-Al system which was changed to a partially disordered structure with a steady long-range order of 0.82 at further milling. This amount of disordering caused the enthalpy of final product to show an increase of about 5.1 kJ·mol-1. Calculation of enthalpy related to the triple defect formation revealed that the enthalpy required for Al anti-sites formation was about 3 times greater than that for Co anti-sites formation.