纳米复合Al-Ni-Y系铝合金的制备技术

部分晶化非晶铝合金因其优异力学性能备受关注,对块体非晶铝合金制备技术的研究意义重大.本工作通过紧耦合惰性气体雾化技术制备了Al82Ni10Y8非晶及纳米晶粉末,随后利用超高压固结成形技术对雾化粉末进行致密化.制备所得的块体材料获得了非晶及纳米晶的复合结构.利用差示扫描量热分析,X射线衍射,扫描电镜和透射电镜等测试手段对合金的热稳定性,物相组成,微观组织和形貌进行了分析,并探讨了合金的可能致密化机理.     

电弧堆焊铁基非晶/纳米晶复合涂层的组织及性能研究

以铁基非晶合金Fe41Co7Cr15Mo14C15B6Y2作为焊芯制备低氢型非晶堆焊焊条,利用手工电弧堆焊,调控堆焊工艺参数,在Q235钢上制备两种不同非晶/纳米晶组分的复合堆焊层。利用XRD/SEM/TEM探索不同堆焊工艺下的结构组织演变及非晶/纳米晶的组成比例变化,研究了不同比例非晶/纳米晶复合堆焊层的晶化特征、硬度和耐磨性变化。实验结果表明,堆焊层为铁基非晶/纳米晶复合涂层,与基体达到了良好的冶金结合;涂层中非晶相含量最高可达47.44%,纳米晶粒尺寸为10~48 nm,堆焊层的最高硬度达1 226HV1,其耐磨性可达Q235钢的8倍;两组堆焊层的晶化激活能分别为Ex(150 A)=107.476 kJ/mol,Ex(160A)=58.104 kJ/mol;随着堆焊热输入的增加,堆焊层中非晶相的含量降低,纳米晶粒尺寸增大,堆焊层的晶化温度、热稳定性、硬度和耐磨性有所降低。     

球磨法制备Mg基非晶合金及其热稳定性

采用机械合金化法制备了Mg65Cu25Gd10非晶粉末,并研究了球磨的转速、球料比和球磨时间等工艺参数对非晶形成的影响.研究表明当球料比为20∶1,转速为200r/min时较为合适,形成非晶所需的最短时间为40h.采用差示扫描量热仪(DSC)研究了球磨得到的非晶粉末的热稳定性,得到了热力学参数玻璃转化温度Tg、开始晶化温度Tx,过冷液相区宽度ΔTx和晶化焓ΔH等,并将其与熔炼法获得的样品进行对比,发现其热力学参数不受工艺过程的影响,仍然具有很好的热稳定性.同时,用Kissinger方程式对非晶粉末的晶化动力学进行了计算,得到了Tg和Tx的表观激活能.     

Mssbauer在测定Al—V—Fe纳米晶合金中相组成的应用

采用机械合金方法制备Al—V—Fe纳米晶合金粉末,合金粉末由纳米尺度的铝晶粒加非晶颗粒组成。利用Mossbauer测定表明合金由单铁组态、双铁组态固溶体以及非晶相组成,三者的含量分别为22.644%,16.746%,60.610%。     

块体非晶合金Gd_（36）La_（20）Al_（24）Co_（20）晶化行为的研究

为深入理解非晶合金的晶化行为,有效控制合金的微观结构和性能,本文利用铜模铸造法制备了Gd36La20Al24Co20块体非晶合金,通过X射线衍射和差示扫描量热法对该非晶合金的热稳定性和晶化行为进行了研究.结果表明：Gd36La20Al24Co20块体非晶合金的晶化激活能为282.5 kJ/mol;与轻稀土基非晶合金相比...     

纳米晶合金粉芯的超重力渗流制备及磁性能

为了探索粉芯的新制备工艺,以Fe73.5Cu₁Nb₃Si13.5B₉纳米晶合金铁芯为原料,使用机械破碎法制粉,并采用超重力渗流工艺制备了7种不同粒度配比的纳米晶合金粉芯,借助SEM、XRD、VSM分别对纳米晶粉末的形貌、结构和磁性能进行了表征,研究了粉末粒度配比对纳米晶合金粉芯的形貌、密度、有效磁导率、损耗及品质因数的影响。结果表明,机械破碎法制得的粉末虽带尖角,但矫顽力低,利用超重力渗流工艺制备的粉芯其粉末表面基本被树脂完全包覆。同时,通过适当的粉末粒度匹配,发现性能最佳粉芯的粉末粒度配比为:100~200目占60%,200~400目占20%,400~1 000目占20%。该种粉芯的密度为4.46 gcm³,在100~3 000 kHz频率范围内有效磁导率比较稳定,且在3 000 kHz时为28.2。当设定磁感应强度为20 mT,频率为500 kHz时,其损耗为99.1 W/kg。另外,根据实验结果可知,该工艺能够制备出频率在MHz以上具有较低损耗的粉芯。     

超声电沉积制备纳米铜粉末的机理研究

利用超声电沉积法制备金属纳米铜粉,平均粒径30nm,分散性较好;利用XRD、TEM等进行了成分、粒度、形貌及结构分析,对影响纳米粉末制备的主要工艺因素进行分析和优化。试验表明,电流密度对纳米粉末形成起控制作用,表面活性剂和超声场对粉末分散更为重要。     

铁基非晶纳米晶涂层组织及磨损性能研究

利用高速电弧喷涂技术在45钢基体上制备了FeCrBSiMnNbY系非晶纳米晶涂层.采用扫描电镜、能谱分析仪、透射电镜和X射线衍射仪等设备对涂层的组织结构进行了表征,着重分析了非晶纳米晶的形成机制,并利用湿砂橡胶轮式磨损试验机对涂层的磨损性能进行了研究.结果表明:涂层的组织主要由非晶相和α(Fe,Cr)相纳米晶组成;α(Fe,Cr)相纳米晶均匀分布于非晶基体内.涂层的组织均匀,结构致密,平均孔隙率为1.7%;非晶纳米晶涂层具有较高的硬度和良好的耐磨性,其失效机制主要为脆性断裂机制.     

球磨CeMg12+100%Ni合金热力学及电化学贮氢性能

用球磨工艺制备CeMg12+100%Ni电极合金,研究了球磨工艺对合金结构及电化学性能的影响。结果表明球磨CeMg12+100%Ni合金具有非晶纳米晶结构,由Mg2Ni相以及Ni相组成,其含量随球磨时间的延长而增加,这在一定程度上改善了合金的电化学放电性能。球磨非晶纳米晶具有较好的结构稳定性,在吸氢后形成的氢化物相仍保持非晶纳米晶尺度,这有利于降低氢化物的热稳定性,改善电化学放电性能。     

凝固条件对非晶合金的微观结构和性能的影响

采用不同凝固控制的方法,研究了凝固条件对非晶合金的微观结构、热稳定性以及力学性能的影响。研究表明,高温下铜模喷铸样品为完全非晶结构,而低温喷铸和电弧原位吸铸所制备的样品中存在着一些纳米量级的析出相。高温喷铸样品表现出非晶合金典型的脆断行为,但低温喷铸和原位电弧吸铸样品则表现出较高的强度和良好的塑性变形能力。高温甩带样品初始晶化温度高于相应的低温甩带样品,其长期热稳定性优于低温甩带样品,表明浇铸温度的升高增强了非晶合金的热稳定性。     

超高分子量聚乙烯/金属复合材料的摩擦磨损性能

用MM-200型摩擦磨损试验机研究了Ag、Cu、Co、Cr、Fe、Mo、W、Ni、Zn、Pb、Sn、Al等金属粉末填充超高分子量聚乙烯(UHMWPE)复合材料的摩擦磨损性能,利用扫描电子显微镜观察了复合材料磨损表面形貌.结果表明:在低速条件下,金属填料可降低UHMWPE复合材料的摩擦系数;在高速条件下,金属填料对UHMWPE复合材料的摩擦系数影响不尽相同.Ag、Cu、Co、Cr、Fe、Mo、W、Ni、Zn、Pb等金属填料可使UHMWPE的耐磨性显著提高, 而Sn、Al导致UHMWPE的磨损率增大;Ag的减摩抗磨效果最佳.     

双相不锈钢00Cr25Ni7Mo4N敏化过程中的脆化机理研究

研究了双相不锈钢00Cr25Ni7Mo4N在晶间腐蚀试验中发生的脆断现象,采用金相法、扫描电镜和透射电镜对材料的脆断机理进行了分析。研究发现双相不锈钢00Cr25Ni7Mo4N在敏化时有R相、Fe3Cr3Mo2Si2相等脆性相析出,导致材料脆化,冲击韧性下降。最后,给出了双相不锈钢00Cr25Ni7Mo4N热加工后的使用要求。     

机械合金化制备FeSiAl合金粉末的研究

采用机械合金化的方法制备了FeSiAl合金粉末样品。以硅钢粉和铝粉为原料,按摩尔分数Fe3Si0.4Al0.6配比,研究其机械合金化过程,并对机械合金化的机制进行探讨。用激光粒度仪、X射线衍射(XRD)和扫描电子显微镜分析材料的粒度、形貌和结构。研究表明,Fe3Si0.4Al0.6混合粉末球磨30h后,粉末粒径可达18μm;Fe3Si0.4Al0.6混合粉末经高能球磨20h后,形成具有bcc结构的α固溶体;球磨继续进行,合金化的粉末和晶粒不断细化。     

铝合金表面激光熔敷铜基复合材料涂层的工艺和组织

在ＺＬ１０４铝合金表面激光熔敷铜基混合粉末（ｗ（Ｂ）／％：２０Ｎｉ,８．０Ｃｏ５．０Ｆｅ,６．８Ｍｏ,１．５Ｃｒ,３．５Ｓｉ,０．２ＲＥ,其余为Ｃｕ）,制备了高硬度铜基复合材料涂层。研究发现,熔敷层稀释率随光宽度和扫描速度增大而减小,随激光束产大而显著增大;     

Site Occupancy of Alloying Elements and Their Effects on the D03 Phase Stability in Fe3Al

The effects of ternary solutes Ti, Co, V, Cr, Ta, W and Mo on the D03 phase stability of Fe3Al intermetallics are investigated by tight-binding linear Muffin-tin orbital method. The predicted site preferences of these elements in Fe3Al are in agreement with the experimental observations. The calculated local magnetic moment of Fe3Al is identical to the experimental. In addition, it is found that the D03 phase stability of Fe3Al doped with Ti, V, Co and Cr depends on ‘energy gap’ of energy band near Fermi level, while the D03 phase stability of Fe3Al doped with Ta, W and Mo may be affected by Madelung energy.     

Synthesis of austenitic stainless steel powder alloys by mechanical alloying

Fe–18Cr–xNi (x = 8, 12, 13, 15, and 20 wt%) blended elemental powders were subjected to mechanical alloying in a high-energy SPEX shaker mill. The milled powders were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy and transmission electron microscopy techniques. It was shown that the sequence of phase formation in the Fe–18Cr–8Ni, Fe–18Cr–12Ni and Fe–18Cr–13Ni compositions was ferrite in the early stages of milling and then formation of austenite, which eventually transformed to stress-induced martensite on continued milling. The time for the formation of the austenite phase was shorter for the 12Ni and 13Ni powder blends than for the 8Ni powder. However, in the Fe–18Cr–15Ni and Fe–18Cr–20Ni compositions, the initial phase to form was ferrite and then a fully austenitic structure had formed on milling the powder for 10 h. No martensitic transformation occurred in this case on continued milling. The phase formation and microstructural features were confirmed by X-ray diffraction and transmission electron microscopy and diffraction techniques. A new metastable phase diagram was proposed outlining the stability of the austenite phase in ternary Fe–Cr–Ni alloys.     

Synthesis, characterization and annealing of mechanically alloyed nanostructured FeAl powder

Elemental powders of Fe and Al were mechanically alloyed using a high energy rate ball mill. A nanostructure disordered Fe(Al) solid solution was formed at an early stage. After 28 h of milling, it was found that the Fe(Al) solid solution was transformed into an ordered FeAl phase. During the entire ball milling process, the elemental phase co-existed with the alloyed phase. Ball milling was performed under toluene to minimise atmospheric contamination. Ball milled powders were subsequently annealed to induce more ordering. Phase transformation and structural changes during mechanical alloying (MEA) and subsequent annealing were investigated by X-ray diffraction (XRD). Scanning electron microscope (SEM) was employed to examine the morphology of the powders and to measure the powder particle size. Energy dispersive spectroscopy (EDS) was utilised to examine the composition of mechanically alloyed powder particles. XRD and EDS were also employed to examine the atmospheric and milling media contamination. Phase transformation at elevated temperatures was examined by differential scanning calorimeter (DSC). The crystallite size obtained after 28 h of milling time was around 18 nm. Ordering was characterised by small reduction in crystallite size while large reduction was observed during disordering. Micro hardness was influenced by Crystallite size and structural transformation.     

Nanocrystalline Al/Al12(Fe,V)3Si alloy prepared by mechanical alloying: Synthesis and thermodynamic analysis

Al–Al₁₂(Fe,V)₃Si nanocrystalline alloy was fabricated by mechanical alloying (MA) of Al–11.6Fe–1.3V–2.3Si (wt.%) powder mixture followed by a suitable subsequent annealing process. Structural changes of powder particles during the MA were investigated by X-ray diffraction (XRD). Microstructure of powder particles were characterized using scanning electron microscopy (SEM). Differential scanning calorimeter (DSC) was used to study thermal behavior of the as-milled product. A thermodynamic analysis of the process was performed using the extended Miedema model. This analysis showed that in the Al–11.6Fe–1.3V–2.3Si powder mixture, the thermodynamic driving force for solid solution formation is greater than that for amorphous phase formation. XRD results showed that no intermetallic phase is formed by MA alone. Microstructure of the powder after 60 h of MA consisted of a nanostructured Al-based solid solution, with a crystallite size of 19 nm. After annealing of the as-milled powder at 550 °C for 30 min, the Al₁₂(Fe,V)₃Si intermetallic phase precipitated in the Al matrix. The final alloy obtained by MA and subsequent annealing had a crystallite size of 49 nm and showed a high microhardness value of 249 HV which is higher than that reported for similar alloy obtained by melt spinning and subsequent milling.     

Aging behaviour of cobalt free chromium containing maraging steels

Abstract

This paper reports an investigation of the aging behaviour of two Co free Cr containing maraging steels (Fe–1·0Si–11·2Cr–1·3Mo–9·1Ni–1·2Al–1·0Ti and Fe–0·8Si–17·2Cr–6·1Ni–0·4Al–0·9Ti, all at.-%), using hardness measurements, electron microscopy of replicas and thin foils, atom probe field ion microscopy (APFIM), and thermochemical calculations. Two different families of intermetallic phases (Ti₆Si₇Ni₁₆G phase and η Ni₃Ti) have been found to contribute to age hardening. The composition and morphology of these precipitates were studied in deformed and undeformed alloys after aging at 420–570°C for various times. In addition, reverted austenite has been found in the aged structure. Results obtained using APFIM are compared with equilibrium thermodynamic calculations and previous APFIM studies of conventional Cr free low Al and Si maraging steels having higher Mo contents.

MST/1558     

Effects of sintering aids on the densification of Mo–Si–B alloys

The effects of seven sintering aids (0.5?at.% Ni, Co, Fe, Cr, Zr, Nb, and Pd) on the densification of Mo–Si–B alloys of six different compositions (Mo, Mo–0.2Si, Mo–0.2Si–0.02B, Mo–2.5Si–2.5B, Mo–7Si–5B, and Mo–8.9Si–7.7B?at.%) are systematically investigated. It was found that Ni, Co, and Fe are effective in enhancing densification of Mo–Si–B alloys, and Ni is the most effective sintering aid. This study supports a previously proposed hypothesis that activated sintering results from enhanced mass transport in the sintering-aid-induced quasi-liquid intergranular films (a type of grain boundary complexion). The relative effectiveness of these sintering aids can be rationalized by analyzing several key thermodynamic parameters that control the stability of premelting-like grain boundary complexions. Future studies are needed to develop interfacial thermodynamic models and methods for computing “grain boundary complexion (phase) diagrams” for multicomponent systems, which can be a useful component for the “Materials Genome” project that will enable better predictions of the activated sintering and other materials phenomena.