Evidence of multimicrometric coherent γ′ precipitates in a hot‐forged γ–γ′ nickel‐based superalloy

This paper demonstrates the existence of large γ’ precipitates (several micrometres in diameter) that are coherent with their surrounding matrix grain in a commercial γ–γ’ nickel‐based superalloy. The use of combined energy dispersive X‐ray spectrometry and electron backscattered diffraction (EBSD) analyses allowed for revealing that surprising feature, which was then confirmed by transmission electron microscopy (TEM). Coherency for such large second‐phase particles is supported by a very low crystal lattice misfit between the two phases, which was confirmed thanks to X‐ray diffractograms and TEM selected area electron diffraction patterns. Dynamic recrystallization of polycrystalline γ–γ’ nickel‐based superalloys has been extensively studied in terms of mechanisms and kinetics. As in many materials with low stacking fault energy, under forging conditions, the main softening mechanism is discontinuous dynamic recrystallization. This mechanism occurs with preferential nucleation on the grain boundaries of the deformed matrix. The latter is then being consumed by the growth of the newly formed grains of low energy and by nucleation that keeps generating new grains. In the case of sub‐solvus forging, large γ’ particles usually pin the migrating boundaries and thus limit grain growth to a size which is determined by the distribution of second‐phase particles, in good agreement with the Smith–Zener model. Under particular circumstances, the driving force associated with the difference in stored energy between the growing grains and the matrix can be large enough that the pinning forces can be overcome, and some grains can then reach much larger grain sizes. In the latter exceptional case, some intragranular primary γ’ particles can be observed, although they are almost exclusively located on grain boundaries and triple junctions otherwise. In both cases, primary precipitates have no special orientation relationship with the surrounding matrix grain(s). This paper demonstrates the existence of high fractions of large γ’ precipitate (several micrometres in diameter) that are coherent with their surrounding matrix grain, in a commercial γ–γ’ nickel‐based superalloy. Such a configuration is very surprising, because there is apparently no reason for the coherency of such particles.     

Microstructures of Rene 142 nickel-based superalloy fabricated by electron beam melting

Rene 142, a commercial, columnar grained, gas turbine airfoil Ni-based superalloy, has been fabricated from a pre-alloyed, atomized powder by additive manufacturing using electron beam melting. Monolithic components having [0 0 1] oriented, columnar grain structures exhibited a creep-optimized 59% volume fraction of cuboidal, coherent, γ′-phase precipitates averaging 275 nm on the side, and with γ/γ′ channel widths ranging from 25 to 75 nm. Transmission electron microscopy, utilizing bright and dark field imaging of optimally oriented γ/γ′ interfaces showed prominent misfit coherency strains as δ-fringe patterns. Corresponding hardness measurements also indicated the possibility of creep strength comparable with the commercial alloy. The notable feature of this study was the monolithic development of desirable superalloy properties without conventional, multi-step heat treatments.     

Ti-Nb复合微合金化高强度钢强化机理研究

以国内某钢厂的热轧高强度钢为研究对象,进行拉伸试验,利用OM和TEM分析了钢显微组织、第二相析出粒子形貌和尺寸等.结果表明,实验钢的屈服强度657 MPa、抗拉强度744 MPa、伸长率18.7％.微合金元素的加入使钢材晶粒明显细化,屈服强度的细晶强化增量为321.5 MPa,为提高材料强度的主要强化机制;研究析出的第二相粒子可知,基体中纳米级析出的(Nb,Ti)(C,N)粒子阻碍位错运动,是提高材料强度的主要机制之一,起到析出强化作用,屈服强度的析出强化量为78.58 MPa.     

2099铝锂合金均匀化退火的微观组织及Al3Zr析出分析

研究2099铝锂合金铸态及均匀化处理后的微观组织和成分分布以及该合金最佳均匀化处理状态时Al3Zr的析出情况。结果表明:2099铝锂合金铸态的微观组织存在严重的枝晶偏析,很多低熔点共晶相分布在晶界,合金中Cu和Mg元素在晶界分布不均匀;经过一系列不同温度和时间的均匀化处理后,2099铝锂合金铸态微观组织中的非平衡相逐渐溶解,各元素分布趋于均匀;2099铝锂合金的过烧温度为515℃,最佳的均匀化制度为505℃/24 h;经该制度均匀化处理后,Al2CuMg、Al2CuLi和AlLi相大部分回溶进α(Al)基体中,通过透射电镜可观察到Al3Zr析出相以及α(Al)基体的超点阵结构;并且该均匀化制度与均匀化动力学方程得到的结论基本一致。     

Strengthening contribution of precipitates and anisotropy of yield strength in Al-Li alloys 2090 and 2090 Ce

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高性能铜合金QBD-6

采用电磁搅拌水平连铸,破碎铸造组织并通过高温退火细化铸造组织中的析出物"Ni-P"化合物,经过20辊轧机的成品轧制,生产的QBD-6高性能铜合金板带材具有高强度、高弹性、高导电和高光洁度等特性,可替代进口合金,如:MF202、CAC5以及部分低强度的C7025。成功应用于引线框架材料、连接器、端子以及电动工具中的电机电刷部件。     

Cu含量对Al—Mg—Si合金析出及烤漆硬化行为的影响

采用DSC、硬度测试及TEM研究A16016铝合金中Cu含量对淬火及淬火预时效样品的人工时效析出和硬化行为的影响。结果表明,微量Cu有利于形成较大且稳定性较好的GPI,能在随后的人工时效过程中进一步向GPII转化,从而提高合金的烤漆硬化能力。但是,当Cu含量为0．3％时,烤漆硬化能力没有得到显著增加。对于含Cu合金,预时效热处理也能有效地抑制合金的自然时效行为。     

酶澄清绿茶饮料研究

研究了不同种类酶对绿茶茶汤抗沉淀效果,并采用HPLC分析了经单宁酶处理后茶汤中酯型儿茶素的变化。结果表明,单宁酶、果胶酶、木瓜蛋白酶对绿茶茶汤抗沉淀影响达极显著水平。多酚类和咖啡碱都有不同程度地减少,但没有达到显著水平。经木瓜蛋白酶处理的茶汤蛋白质含量减少,氨基酸含量同其他处理样相比有一定的增加。结合方差分析和感官审评结果表明,单宁酶对绿茶茶汤抗沉淀效果最好,单宁酶最佳作用时间为2h。在一定范围内,随着单宁酶作用时间的延长,茶汤中酯型儿茶素的总量在不断减少,茶汤的透光率随着酯型儿茶素的减少在不断增大。     

Arsenic association and stability in long-term disposed arsenic residues

Long-term stability of arsenic residues is investigated by determining arsenic phases remaining in gold mining residues after two decades of impoundment. The residues, generated by arsenic coprecipitation with iron and lime, were disposed of in-lined sites for 9-16 years (pit C) and 16-23 years (pits A and B). Arsenic is present in the residues as As(V) species, predominantly in the form of amorphous iron arsenate (55-75% As_total, pits A and B; 55-70% As_total, pit C) and sorbed onto amorphous iron-oxyhydroxides (20-33% As_total, pits A and B; 22-37% As_total, pit C). The presence of minor Ca-arsenate phases (undefined composition) and Al-arsenate coprecipitates is also indicated. The passive enrichment of iron in pits A and B, and the relative low concentration of calcium, sulfur and arsenic if compared to those of pit C, suggest that a soluble Ca-arsenate phase (e.g. CaHAsO₄.H₂O), a fraction of gypsum and As(III) were dissolved along 16-23 years of residue disposal. The presence of As(V) only and excess iron demonstrates the importance of the oxidation state and high Fe/As ratio on long-term stability of arsenic residues.     

Hydrothermal synthesis of magnetite nanoparticles via sequential formation of iron hydroxide precipitates

A novel method for preparing fine magnetite nanoparticles without using any additives and organic solvents has been developed. In this method, a sequential precipitates formation method, ferrous and ferric hydroxides are not coprecipitated but sequentially formed in an alkaline solution, and then the resulting suspension is subjected to a hydrothermal treatment. The obtained magnetite nanoparticles were characterised through scanning electron microscopy observation and X-ray diffraction analysis, and the particle size and magnetic properties were measured with a dynamic light scattering particle size analyser and a superconducting quantum interference device magnetometer, respectively. In order to prepare fine magnetite nanoparticles with a uniform size, both the formation sequence of ferrous and ferric hydroxide precipitates and the supersaturation of ferric hydroxide in the solution were essential. The ferromagnetic magnetite nanoparticles with a median size 8.5?nm were relatively easily obtained in the formation process in which a ferric sulphate solution was rapidly poured into a suspension of ferrous hydroxide particles prepared beforehand using ferric chloride and sodium hydroxide, whereas the median size of magnetite nanoparticles prepared via conventional coprecipitation route was 38.6?nm.