International Journal of Minerals, Metallurgy and Materials

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Mineral sulphide-lime reactions and effect of CaO/C mole ratio during carbothermic reduction of complex mineral sulphides

Yotamu Stephen Rainford Hara

2014, 21(1): 1-11. doi: 10.1007/s12613-014-0858-0

中文摘要(380) PDF(10) SpringerLink

摘要:
Mineral sulphide (MS)-lime (CaO) ion exchange reactions (MS + CaO = MO + CaS) and the effect of CaO/C mole ratio during carbothermic reduction (MS + CaO + C = M + CaS + CO(g)) were investigated for complex froth flotation mineral sulphide concentrates. Phases in the partially and fully reacted samples were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The primary phases during mineral sulphide-lime ion exchange reactions are Fe₃O₄, CaSO₄ Cu₂S, and CaS. A complex liquid phase of Ca₂CuFeO₃S forms during mineral sulphide-lime exchange reactions above 1173 K. The formation mechanisms of Ca₂CuFeO₃S liquid phase are determined by characterising the partially reacted samples. The reduction rate and extent of mineral sulphides in the presence of CaO and C increase with the increase in CaO/C ratio. The metallic phases are surrounded by the CaS rich phase at CaO/C > 1, but the metallic phases and CaS are found as separate phases at CaO/C < 1. Experimental results show that the stoichiometric ratio of carbon should be slightly higher than that of CaO. The reactions between CaO and gangue minerals (SiO₂ and Al₂O₃) are only observed at CaO/C > 1 and the reacted samples are excessively sintered.

Gas-solid reduction kinetic model of MgO-fluxed pellets

Qiang-jian Gao, Feng-man Shen, Xin Jiang, Guo Wei, Hai-yan Zheng

2014, 21(1): 12-17. doi: 10.1007/s12613-014-0859-z

中文摘要(343) PDF(8) SpringerLink

摘要:
The reduction process of MgO-fluxed pellets was investigated and compared with traditional acidic pellets in this paper. Based on the piston flow concept and experimental data, a kinetic model fitting for the gas-solid phase reduction of pellets in tubular reactors (blast furnace, BF) was built up, and the equations of reduction reaction rate were given for pellets. A series of reduction experiments of pellets were carried out to verify the model. As a result, the experimental data and calculated result were fitted well. Therefore, this model can well describe the gas-solid phase reduction process and calculate the reduction reaction rate of pellets. Besides, it can give a better explanation that the reduction reaction rate (reducibility) of MgO-fluxed pellets is better than that of traditional acidic pellets in BF.

Effects of calculation approaches for thermal conductivity on the simulation accuracy of billet continuous casting

Zun Peng, Yan-ping Bao, Ya-nan Chen, Li-kang Yang, Cao Xie, Feng Zhang

2014, 21(1): 18-25. doi: 10.1007/s12613-014-0860-6

中文摘要(243) PDF(11) SpringerLink

摘要:
An unsteady, two-dimensional, explicitly solved finite difference heat transfer model of a billet caster was presented to clarify the influence of the thermal conductivity of steel on model accuracy. Different approaches were utilized for calculating the thermal conductivity of solid, mushy and liquid steels. Model results predicted by these approaches were compared, and the advantages of advocated approaches were discussed. It is found that the approach for calculating the thermal conductivity of solid steel notably influences model predictions. Convection effects of liquid steel should be considered properly while calculating the thermal conductivity of mushy steel. Different values of the effective thermal conductivity of liquid steel adopted could partly be explained by the fact that different models adopted dissimilar approaches for calculating the thermal conductivity of solid and mushy steels.

On-line spheroidization process of medium-carbon low-alloyed cold heading steel

Yu Fu, Hao Yu, Pan Tao

2014, 21(1): 26-35. doi: 10.1007/s12613-014-0861-5

中文摘要(235) PDF(9) SpringerLink

摘要:
Conventionally manufactured 35CrMo cold heading steel must undergo spheroidization annealing before the cold heading process. In this paper, different types of deformation processes with various controlled cooling periods were operated to achieve on-line spheroidal cementite using the Gleeble-3500 simulation technique. According to the measured dynamic ferrite transformation temperature (A_d3), the deformation could be divided into two types: low temperature deformation at 810 and 780℃; “deformation-induced ferrite transformation” (DIFT) deformation at 750 and 720℃. Compared with the low temperature deformation, the DIFT deformation followed by accelerated cooling to 680℃ is beneficial for the formation of spheroidal cementite. Samples subjected to both the low-temperature deformation and DIFT deformation can obtain granular bainite by accelerated cooling to 640℃; the latter may contribute to the formation of a fine dispersion of secondary constituents. Granular bainite can transform into globular pearlite rapidly during subcritical annealing, and the more the disperse phase, the more homogeneously distributed globular cementite can be obtained.

Dynamic recrystallization and precipitation in high manganese austenitic stainless steel during hot compression

Amir Momeni, Shahab Kazemi, Golam Ebrahimi, Alireza Maldar

2014, 21(1): 36-45. doi: 10.1007/s12613-014-0862-4

中文摘要(351) PDF(14) SpringerLink

摘要:
Dynamic recrystallization and precipitation in a high manganese austenitic stainless steel were investigated by hot compression tests over temperatures of 950–1150℃ at strain rates of 0.001 s⁻¹-1 s⁻¹. All the flow curves within the studied deformation regimes were typical of dynamic recrystallization. A window was constructed to determine the value of apparent activation energy as a function of strain rate and deformation temperature. The kinetics of dynamic recrystallization was analyzed using the Avrami kinetics equation. A range of apparent activation energy for hot deformation from 303 kJ/mol to 477 kJ/mol is obtained at different deformation regimes. Microscopic characterization confirms that under a certain deformation condition (medium Zener-Hollomon parameter (Z) values), dynamic recrystallization appears at first, but large particles can not inhibit the recrystallization. At low or high Z values, dynamic recrystallization may occur before dynamic precipitation and proceeds faster. In both cases, secondary phase precipitation is observed along prior austenite grain boundaries. Stress relaxation tests at the same deformation temperatures also confirm the possibility of dynamic precipitation. Unexpectedly, the Avrami’s exponent value increases with the increase of Z value. It is associated with the priority of dynamic recrystallization to dynamic precipitation at higher Z values.

Influence of cryogenic treatment on the wear characteristics of 100Cr6 bearing steel

R. Sri Siva, D. Mohan Lal, P. Kesavan Nair, M. Arockia Jaswin

2014, 21(1): 46-51. doi: 10.1007/s12613-014-0863-3

中文摘要(341) PDF(12) SpringerLink

摘要:
A series of reciprocating wear tests were performed on the deep cryogenically treated and conventionally heat-treated samples of 100Cr6 bearing steel to study the wear resistance. The worn surfaces as well as the wear debris were analyzed by scanning electron microscopy. The improvement in wear resistance of the deep cryogenically treated samples ranges from 49% to 52%. This significant improvement in wear resistance can be attributed to finer carbide precipitation in the tempered martensitic matrix and the transformation of retained austenite into martensite. X-ray diffraction analysis shows that the volume fraction of retained austenite in the conventionally heat-treated samples is 14% and that of the deep cryogenically treated samples is only 3%.

Influence of Al on the magnetostriction of Fe-Ga polycrystal alloys under compressive stress

Long-long Liao, Mei-ling Fang, Jie Zhu, Ji-heng Li, Jian Wang

2014, 21(1): 52-57. doi: 10.1007/s12613-014-0864-2

中文摘要(262) PDF(8) SpringerLink

摘要:
Fe₈₀Ga_20−xAl_x (x = 0, 6, 9, 14) ingots were prepared from high purity elements using a vacuum induction system. X-ray diffraction patterns show that the alloys are A2 disordered structures. The influence of the partial substitution of Ga in Fe-Ga alloys with Al on their magnetostrictive properties was investigated, and the effects of different heat treatment conditions on the magnetostriction and microstructure of the alloy rods were also examined. The saturation magnetostriction value of Fe₈₀Ga₂₀ can reach to 240·10⁻⁶ under a compressive stress of 20 MPa. The Fe₈₀Ga₁₁Al₉ alloy has many good properties, such as low hysteresis, high linearity of the magnetostriction curve, and low saturated magnetic field, which make it a potential candidate for magnetostrictive actuator and transducer applications. It is found that subgrains have little influence on the magnetostriction of Fe-Ga alloys.

Microstructure and stress rupture properties of polycrystal and directionally solidified castings of nickel-based superalloys

Bao-ping Wu, Lin-han Li, Jian-tao Wu, Zhen Wang, Yan-bin Wang, Xing-fu Chen, Jian-xin Dong, Jun-tao Li

2014, 21(1): 58-64. doi: 10.1007/s12613-014-0865-1

中文摘要(312) PDF(7) SpringerLink

摘要:
A new directionally solidified Ni-based superalloy DZ24, which is a modification of K24 alloy without rare and expensive elemental additions, such as Ta and Hf, was studied in this paper. The microstructure and stress rupture properties of conventionally cast and directionally solidified superalloys were comparatively analyzed. It is indicated that the microstructure of K24 alloy is composed of γ, γ′, γ/γ′ eutectics and MC carbides. Compared with the microstructure of K24 polycrystalline alloy, γ/γ′ eutectic completely dissolves into the γ matrix, the fine and regular γ′ phase reprecipitates, and MC carbides decompose to M₆C/M₂₃C₆ carbides after heat treatment in DZ24 alloy. The rupture life of DZ24 alloy is two times longer than that of K24 alloy. The more homogeneous the size of γ′ precipitate, the longer the rupture life. The coarsening and rafting behaviors of γ′ precipitates are observed in DZ24 alloy after the stress-rupture test.

Characterization of Cu₃P phase in Sn3.0Ag0.5Cu0.5P/Cu solder joints

Jian-xun Chen, Xing-ke Zhao, Xu-chen Zou, Ji-hua Huang, Hai-chun Hu, Hai-lian Luo

2014, 21(1): 65-70. doi: 10.1007/s12613-014-0866-0

中文摘要(231) PDF(9) SpringerLink

摘要:
This article reports the effects of phosphorus addition on the melting behavior, microstructure, and mechanical properties of Sn3.0Ag0.5Cu solder. The melting behavior of the solder alloys was determined by differential scanning calorimetry. The interfacial microstructure and phase composition of solder/Cu joints were studied by scanning electron microscopy and energy dispersive spectrometry. Thermodynamics of Cu-P phase formation at the interface between Sn3.0Ag0.5Cu0.5P solder and the Cu substrate was characterized. The results indicate that P addition into Sn3.0Ag0.5Cu solder can change the microstructure and cause the appearance of rod-like Cu₃P phase which is distributed randomly in the solder bulk. The Sn3.0Ag0.5Cu0.5P joint shows a mixture of ductile and brittle fracture after shear testing. Meanwhile, the solidus temperature of Sn3.0Ag0.5Cu solder is slightly enhanced with P addition.

Production of ultra-transparent glass-ceramics via controlled crystallization of nanocrystals in the glassy matrix of LAST

Mohammad Sadegh Shakeri

2014, 21(1): 71-76. doi: 10.1007/s12613-014-0867-z

中文摘要(183) PDF(8) SpringerLink

摘要:
Microstructural variation in glass-ceramics encompasses the range from nanocrystalline transparent materials to microcrystalline tough materials. In this investigation, the crystallization process was controlled for the development of ultra transparent Li₂O-Al₂O₃-SiO₂ glass-ceramics containing TiO₂ as a nucleating agent (LAST). Results of UV-Vis absorption spectra were compared with the expected theoretical values calculated by the Rayleigh scattering method for the determination of ultra transparency. Results of the investigation illustrate that the control of crystallization increases the range of ultra transparency by the reduction of crystal size and their uniformity in the glassy matrix. Last but not the least, the optimized samples are ultra transparent approximately in the whole light wavelengths.

Microstructure and mechanical properties of (Ti,Al,Zr)N/(Ti,Al,Zr,Cr)N films on cemented carbide substrates

Shi-lu Zhao, Jun Zhang, Zhen Zhang, Shuang-hong Wang, Zheng-gui Zhang

2014, 21(1): 77-81. doi: 10.1007/s12613-014-0868-y

中文摘要(316) PDF(10) SpringerLink

摘要:
(Ti,Al,Zr)N/(Ti,Al,Zr,Cr)N bilayer films were deposited on cemented carbide (WC-8%Co) substrates by multi-arc ion plating (MAIP) using two Ti-Al-Zr alloy targets and one pure Cr target. To investigate the composition, morphology, and crystalline structure of the bilayer films, a number of complementary methods of elemental and structural analysis were used, namely, scanning electron microscopy (SEM), energy disperse X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Adhesive strength and mechanical properties of the films were evaluated by scratch testing and Vickers microindentation, respectively. It is shown that the resulting films have a TiN-type face-centered cubic (FCC) structure. The films exhibit fully dense, uniform, and columnar morphology. Furthermore, as the bias voltages vary from −50 to −200 V, the microhardness (max. Hv_0.01 4100) and adhesive strength (max. > 200 N) of the bilayer films are superior to those of the (Ti,Al,Zr)N and (Ti,Al,Zr,Cr)N monolayer films.

Structural characteristics, dispersion, and modification of fibrous brucite

Xi Cao, Xiu-yun Chuan

2014, 21(1): 82-88. doi: 10.1007/s12613-014-0869-x

中文摘要(274) PDF(14) SpringerLink

摘要:
Fibrous brucite has very unique structure and physical properties. Brucite fibers were exfoliated into single nanofibers by using dioctyl sodium sulfosuccinate (AOT) as a dispersant through mechanical agitation and ultrasonic dispersion; and then, the nanofibers were modified by stearic acid and (3-aminopropyl)triethoxysilane (γ-APS) compound modification agent. The nanofibers were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and thermal gravimetric analysis. It is found that AOT has good effect on the dispersion. The single fiber has a consistent morphology, and fibrous brucite is dispersed and modified without destroying the crystal structure. Infrared and thermal analysis shows that the surface modification of fibrous brucite is achieved by forming chemical bonds between the coupling agent and magnesium hydroxide.

Fabrication and properties of foam geopolymer using circulating fluidized bed combustion fly ash

Ze Liu, Ning-ning Shao, Dong-min Wang, Jun-feng Qin, Tian-yong Huang, Wei Song, Mu-xi Lin, Jin-sha Yuan, Zhen Wang

2014, 21(1): 89-94. doi: 10.1007/s12613-014-0870-4

中文摘要(288) PDF(16) SpringerLink

摘要:
In recent years, circulating fluidized bed combustion fly ash (CFA) is used as a raw material for geopolymer synthesis. Hydrogen peroxide was employed as a foaming agent to prepare CFA-based foam geopolymer. The particle distribution, mineral composition, and chemical composition of CFA were examined firstly. Geopolymerization products were characterized by mechanical testing, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray fluorescence (XRF). The CFA-based foam geopolymer was successfully fabricated with different contents of hydrogen peroxide and exhibited uncompleted alkali reaction and reasonable strength with relative low atomic ratios of Si/Al and Si/Na. Type-C CFA in this research could be recycled as an alternative source material for geopolymer production.

Influence of sulfides on the tribological properties of composites produced by pulse electric current sintering

Seung Ho Kim

2014, 21(1): 95-103. doi: 10.1007/s12613-014-0871-3

中文摘要(240) PDF(8) SpringerLink

摘要:
Self-lubricating Al₂O₃-15wt% ZrO₂ composites with sulfides, such as molybdenum disulfide (MoS₂) and tungsten disulfide (WS₂) serving as solid lubricants, were fabricated by using the pulse electric current sintering (PECS) technique. The coefficient of friction (COF) of the Al₂O₃-15wt% ZrO₂ composite without/with sulfides was in the range of 0.37–0.48 and 0.27–0.49, respectively. As the amount of sulfides increased, the COF and the wear rate decreased. The reduction in COF and wear rate of the sulfide-containing composite is caused by a reduction in shear stresses between the specimen and the tribological medium due to the formation of a lubricating film resulting from the lamellar structure of sulfides located on the worn surface.

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