Synthesis of Invar 36 type alloys from elemental and prealloyed powders by mechanical alloying

Invar 36 (Fe₆₄Ni₃₆) nanocrystalline powders were successfully obtained by the mechanical alloying process. The mechanically alloyed Invar 36 powders were obtained from both, Fe–Ni elemental and Fe–Ni₃Fe prealloyed powders. XRD, DSC and magnetic measurements were used to characterise the Invar 36 powders. The lattice parameter evolution versus temperature of Invar 36 powders was investigated by in-situ high-temperature X-ray diffraction (HT-XRD). For both, Invar 36 (Fe, Ni) and Invar 36 (Fe, Ni₃Fe) powders, the lattice parameter values are constant up to about 350°C. The magnetic measurement also indicated that the Invar 36-type alloys are formed after 16?h of milling.     

Studies on alloying process of a ferritic/martensitic oxide dispersion strengthened (ODS) steel prepared by mechanical alloying of elemental powders

Ferritic/martensitic oxide dispersion strengthened steel with a nominal composition of Fe–9Cr–2W–0.2Ti–0.12C–0.35Y₂O₃ was produced by mechanical alloying in a high energy horizontal Simoloyer attritor. Powder samples were collected at intervals of 0.5, 1, 2, 3, 5, 7 and 10?h and analysed by X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy and differential thermal analysis. The alloying elements (Cr and W) got dissolved in the matrix in 7?h milled powder. Crystallite size decreased rapidly with milling time up to 5?h milling and reached a stable size of ～12?nm after 7?h, whereas strain and lattice parameter were found to increase with milling time. The particle size increased up to 2?h milling and then decreased with milling time. A fine and uniform particle size of ～25?nm was obtained after 7?h milling. The alloying process and distribution of alloying elements/Y₂O₃ is studied in the present work.     

Formation of metastable and equilibrium phases during mechanical alloying of Al and Mg powders

Formation of metastable and equilibrium phases during mechanical alloying by high-energy ball milling of mixtures of Al and Mg powders was studied using X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). Different phases were formed, depending on the overall composition of the starting mixture. A powder mixture of nominal composition 40 at. pct Mg gradually becomes converted into a metastable supersaturated Al(Mg) face-centered cubic (fcc) solid solution having approximately 23 at. pct Mg in solution. Powder mixtures of nominal composition of 60 or 80 at. pct Mg gradually transform into the equilibrium γ phase during mechanical alloying, but for the composition of 80 at. pct Mg, some unalloyed Mg is left. Mechanical alloying is comparable to rapid solidification in producing metastable phases in the Al-Mg system, except that mechanical alloying is likely to leave some residual unalloyed elements. There is no indication of the formation of the other equilibrium phase, the β phase, present in the phase diagram. The reason why the β phase does not form is thought to be related to the complex structure and a very large unit cell associated with this phase. However, the β phase is obtained if the mechanical alloyed powders are heat-treated at higher temperatures.     

铌-铝化合物的机械合金化制备及机理

研究高能球磨制备Nb/Al化合物的工艺,探索在高能球磨过程中Nb、Al形成化合物的机理.结果表明,通过高能球磨可获得Al在Nb中的固溶体,固溶度与球磨转速和球磨时间成正比,并发现选用硬脂酸作为添加剂有利于Nb/Al的机械合金化.对高能球磨中机械合金化的机理进行了讨论,指出高能球磨产生的高比表面能和高密度晶体缺陷大大降低...     

Amorphization reaction of Ni-Ta powders during mechanical alloying

This study examined the amorphization behavior of Ni _x Ta_100−x alloy powders synthesized by mechanically alloying (MA) mixtures of pure crystalline Ni and Ta powders with a SPEX high energy ball mill. According to the results, after 20 hours of milling, the mechanically alloyed powders were amorphous for the composition range between Ni₁₀Ta₉₀ and Ni₈₀Ta₂₀. A supersaturated nickel solid solution formed for Ni₉₀Ta₁₀, as well. X-ray diffraction analysis reveals two different types of amorphization reactions. Through an intermediate solid solution and by direct formation of amorphous phase. The thermal stability of the amorphous powders was also investigated by differential thermal analysis. As the results demonstrated, the crystallization temperature of amorphous Ni-Ta powders increased with increasing Ta content. In addition, the activation energy of amorphous Ni-Ta powders reached a maximum near the eutectic composition.     

Preparation and thermal stability of Zr-Ti-Al-Ni-Cu amorphous powders by mechanical alloying technique

This study examined the amorphization feasibility of Zr_70−x−y Ti _x Al _y Ni₁₀Cu₂₀ alloy powders by the mechanical alloying (MA) technique. According to the results, after 5 to 7 hours of milling, the mechanically alloyed powders were amorphous basically in the ranges of 0 to 12.5 at. pct Ti and 2.5 to 17.5 at. pct Al. These ranges are larger than those of bulk amorphous alloys prepared by a squeeze mold casting technique. Most of the amorphous mechanically alloyed powders exhibited a wide supercooled liquid region of more than 60 K before crystallization. The glass-transition and crystallization temperatures of mechanically alloyed samples were different from those prepared by squeeze casting. It is suspected that different thermal properties arise from the introduction of impurities during the MA process. The amorphization behavior of Zr₅₀Ti_7.5Al_12.5Ni₁₀Cu₂₀ was examined in detail. The X-ray diffraction and extended X-ray absorption fine structure (EXAFS) results show the fully amorphous powders formed after 5 hours of milling. A kinetically modified thermodynamic phase transformation process was observed for the glass-transition behavior in the Zr₅₀Ti_7.5Al_12.5Ni₁₀Cu₂₀ amorphous powder.     

Development of austenitic nanostructures in high-nitrogen steel powders processed by mechanical alloying

In this work, mechanical alloying was employed in producing high-nitrogen Fe18Cr11Mn stainles-steel powders. It was found that the nitrogen solubility in the powder mixtures increases exponentially with milling time at room temperature. Maximum nitrogen levels of 2.47 wt pct N were achieved after milling for 170 hours. In addition, the grain size structure continually decreased and reached a plateau at nanometric grain sizes of the order of 3 nm. In addition, measured, interplanar lattice spacing, d₍₁₁₀₎, did not follow a linear trend. Apparently, initially the nitrogen tendency was to be preferentially dissolved at dislocations and grain boundaries. However, after long milling times, the crystal lattice tended to be saturated with N. Annealing at 900 °C to 1200 °C for 2 hours led to various microstructures, where the matrix was almost always γ-iron, but Cr₂N, CrN, and α-iron were also present depending on the annealing temperatures. In particular, it was found that a fully austenitic, nanometric grain structure can be achieved by annealing at 1000 °C and 1100 °C Fe18Cr11Mn alloys with 1.02 and 0.7 wt pct N, respectively.     

Feasibility of producing intermetallic compound coatings from mechanical mixtures by flame-spraying

Conclusions The probability of intermetallic compounds being formed during the flame-spraying of composite aluminum-nickel mixtures does not exceed 20%. With the existing standard installations, it is impossible to surpass this limit merely by varying process parameters. Separate supply of the components only slightly increases the adhesional strength of coatings. The results obtained lead to the conclusion that utilization of the energy of exothermic reactions cannot be expected to increase the adhesional strength of coatings produced from mechanical composites. Use of mechanical composites may prove to be justified in the spray-deposition of P/M coatings where an increase in adhesional strength is achieved as a result of a lowering of the level of residual stresses in a soft metallic matrix.Translated from Poroshkovaya Metallurgiya, No. 8 (272), pp. 58–62, August, 1985.     

Mo(Si,Al)2粉末材料的机械合金化合成

通过机械合金化由MoSi2,Mo和Al粉末合成了Mo(Si1-x,Alx)2粉末材料,用X射线衍射分析了相的变化和粉末的晶粒度,用扫描电镜观察球磨后的粉末形貌与粒度,并根据Burgio模式估算了生成Mo(Si,Al)2相的球磨能.结果表明MoSi2,Mo和Al混合粉经高能球磨5 h后生成了MoSi2和Mo(Si,Al)2,没有单质粉末剩余,也无Al-Mo中间相产生;球磨40 h后的粉末粒度为亚微米级,晶粒度在21 nm～40 nm之间,Mo(Si,Al)2相的机械合金化合成机理为类自蔓延反应,其生成所需的球磨能量约为15.4 kJ/g.     

Mechanical alloying and field assisted hot pressing of nanocrystalline B2-NiAl intermetallic compound

Abstract

Ordered B2-NiAl intermetallic compound powder was successfully synthesised by mechanical alloying after 20 h in an attritor mill, starting from elemental Ni and Al powders and without subsequent heat treatment. NiAl powder obtained was homogenous and had a nanocrystalline microstructure. It was consolidated by field assisted hot pressing (FAHP), in a novel configuration with a Gleeble 3800 thermomechanical simulator. The powder was also processed by hot isostatic pressing (HIP) in order to compare both methods. The consolidation was successful by both methods obtaining above 98% of NiAl theoretical density (5·86 g cm^?3). The results showed that the consolidation process by FAHP technique is effective and uniform throughout the sample as indicated by homogenous hardness values, obtaining microstructure and properties similar to those obtained with HIP technique, with certain advantages over it. The achieved room temperature yield strength of 850 MPa and fracture strain 26–28% corresponds to the bulk values of NiAl intermetallic.     

机械合金化制备Al-10Pb纳米相复合结构的热稳定性

利用X射线衍射仪、扫描电镜和透射电镜,研究机械合金化制备的Al-10%Pb(质量分数)纳米相复合结构的热稳定性。结果表明Al-10%Pb纳米相复合结构中Pb相的长大可以用LSW理论描述。但是Pb相的长大激活能显著低于常规多晶材料中溶质原子(Pb)在溶剂基体(Al)晶格中扩散的激活能,而接近于溶剂基体(Al)的晶界自扩散激活能。这主要是由于纳米相复合结构中Pb相的长大机制与常规两相合金不同所致。在纳米相复合结构中,溶质原子的迁移以沿溶剂基体的晶界扩散为主,纳米相基体高的晶界分数可促进扩散的进行。     

机械合金化制备近球形无镍高氮奥氏体不锈钢粉末的研究

在流动氮气氛下,采用机械合金化技术制备出了无镍高氮奥氏体不锈钢粉末.结果表明:在转速为400r/min和球料比为10∶1的球磨条件下,混合粉末氮含量随球磨时间的延长呈线性增长的关系,其一元线性回归方程为WN=0.19357 0.01887t;随球磨时间的延长,粉末体内逐渐发生α相向γ相的转变,球磨超过96h后粉末体全部是由γ奥氏体单相组成;原始混合粉末颗粒随球磨时间的延长由不规则形状逐渐向近球形趋近,这种近球形粉末一般具有良好的流动性和较高的摇实密度,对后续注射成形等工艺十分有利.     

Preparation of TiAl15Si15 intermetallic alloy by mechanical alloying and the spark plasma sintering method

This work is devoted to the preparation of alloys based on intermetallic compounds in the Ti–Al–Si system by powder metallurgy using mechanical alloying and the spark plasma sintering (SPS) method. The aim was to describe the formation of intermetallic phases during mechanical alloying of TiAl15Si15 (wt-%) alloy and to consolidate the powder prepared by optimised conditions. Phase composition, microstructure and hardness of compacted alloy were determined. Four hours of mechanical alloying is sufficient time for preparation of pure elements free material composed only of intermetallic phases. After consolidation, the TiAl15Si15 alloy has a homogeneous structure composed of silicide (Ti₅Si₃) in aluminide (TiAl) matrix. The hardness of the material reaches 865?±?42 HV 5.