Volume 36, Issue 8 -

The directionally solidified eutectic MgAl 2 O 4 -Y 3 Al 5 O 12 crystal was prepared at a pressure of 0.4 MPa of ambient nitrogen gas by the high frequency induction heated floating zone furnace. In order to determine the high temperature characteristics, directionally solidified MgAl 2 O 4 -Y 3 Al 5 O 12 eutectic phase has been analyzed with creep test, tensile strength, young modulus and fracture toughness at the various temperatures and the microstructural variations have been studied according to the analysis results. It has been seen that directionally solidified with zone melting MgAl 2 O 4 -YAG eutectic ceramic which has given the value of 168 MPa below 10 −6 /s strain rate at 1,700 °C temperature has revealed minimum stress.

High temperature powder X-ray diffraction measurements of Ba 3 R B 3 O 9 ( R =Sm–Yb, and Y) were carried out at temperatures ranging from room temperature to just below the corresponding melting temperatures (1,200–1,300 °C). No phase transition was found for the H-type phase ( R 3‾$\overline 3 $) with R =Sm–Tb and the L-type phase ( P 6 3 cm) with R =Tm–Yb. On the other hand, phase transition from the L phase to the H phase was observed for R =Dy–Er, and Y at around 1,100–1,200 °C. The obtained axial thermal expansion coefficient (ATEC) of the a -axis was larger than that of the c -axis for the H phase, and the ATEC of the c -axis was larger than that of the a -axis for the L phase. The observed anisotropic nature of ATEC is attributed to the distribution of the BO 3 anionic group with rigid boron–oxygen bonding in the structures of the H and L phases.

T92 samples were solutionized at 1,050 °C, 1,100 °C and 1,150 °C for 20 min and then tempered at 730 °C, 745 °C and 760 °C for 60 min. Optical microscopy studies were carried out to understand the microstructural evolution due to heat treatment. These heat-treated samples comprised of lath martensite microstructure in all the cases. Prior austenite grain size of the heat-treated samples increased with solutionizing temperature. Tensile properties were evaluated using micro-tensile samples. Hardness values of the heat-treated samples were estimated using Vickers hardness tester. Interestingly, for all the given tempering condition, the hardness values showed an increasing trend with solutionizing temperature while their tensile strength values tend to decrease. Fractograph analysis depicted that increasing the solutionizing temperature led to grain boundary decohesion.

Microwave-absorbing characteristics of the oxidized ilmenite concentrate were measured by the method of microwave cavity perturbation. The effects of particle size, oxidation temperature and oxidation time on the microwave-absorbing characteristics were investigated. The particle size, oxidation temperature and oxidation time have substantial impact on the microwave-absorbing characteristics of the sample and therefore the microwave heating performance during the oxidation processes of the ilmenite concentrate. Results indicated that at the same oxidation time, the microwave absorbing characteristics decreased as the oxidation temperature increased, and at a constant temperature, the microwave absorbing characteristics of the sample decreased as the oxidation time increased. The microwave absorbing characteristics of the ilmenite concentrate with 80–120 mesh particle size was stronger than that of 200 mesh particle size. The microwave absorbing characteristics of products oxidized at 900 °C for 30 min were slightly weaker than those treated at 800 °C for 30 min and 900 °C for 20 min. The sample becomes less efficient in absorbing microwave energy as the oxidation proceeds. It is therefore recommended strong microwave absorbing materials or conventional heating be applied at the late stage of oxidation to aid microwave heating.

Nanoscale FeAl 2 O 4 was successfully synthesized via sol–gel method. The sol constituents containing iron and aluminum cations were formed homogenously in stearic acid gel (formation of organic precursor). The pure structural analysis and the size of the spinels were confirmed by X-ray diffraction (XRD). It was observed that the size of the nanoscale materials obtained at around 30–40nm. The micrographs of FeAl 2 O 4 evidenced the homogenous and nanosize formation of spinel. The semiconducting behavior of this mixed metal oxide was observed at 3.14eV based on the band gap energy ( E g ). The final nanoscale materials exhibited a superparamagnetic behavior with a saturation magnetization of 9.8 emu/g at applied field of 10 kOe.

Low cycle fatigue and creep-fatigue experiments of IC10 Ni-base superalloy plate specimens with multiple holes were performed below 1,000 °C. The average fatigue life is 10 5.4 cycles, while the creep-fatigue life is 10 3.4 cycles, which shows that the life of creep-fatigue is reduced 1–2 times compared with low cycle fatigue life. After tests, the detailed fracture and microscopic structure evolution were observed by scanning electron microscopy (SEM); meanwhile, the constitutive model based on crystal plasticity theory was established and the fracture mechanism was analyzed. Three conclusions have been obtained: First, the load during dwell time leads to the damage accumulation caused by deformation and the interaction of fatigue and creep shortens the service life of materials seriously. Second, in order to maintain the macroscopic deformation, a new slip plane starts to makes the dislocation slide in reverse direction, which leads to fatigue damage and initial cracks. Third, the inner free surface creates opportunities for escape of the dislocation line, which is caused by the cavity. What’s more, the cure dislocation generated by cyclic loading contributes to the formation and growth of cavities.

Eupatorium adenophorum, global exotic weeds, was utilized as feedstock for preparation of activated carbon (AC) via microwave-induced KOH activation. Influences of the three vital process parameters – microwave power, activation time and impregnation ratio (IR) – have been assessed on the adsorption capacity and yield of AC. The process parameters were optimized utilizing the Design Expert software and were identified to be a microwave power of 700 W, an activation time of 15 min and an IR of 4, with the resultant iodine adsorption number and yield being 2,621 mg/g and 28.25 %, respectively. The key parameters that characterize the AC such as the brunauer emmett teller (BET) surface area, total pore volume and average pore diameter were estimated to be 3,918 m 2 /g, 2,383 ml/g and 2.43 nm, respectively, under the optimized process conditions. The surface characteristics of AC were characterized by Fourier transform infrared spectroscopy, scanning electron microscope and Transmission electron microscope.

Vacuum metallurgical processes such as the electron beam melting are highly conducive to volatilization. In titanium processing, it concerns the alloying elements which show a high vapor pressure with respect to titanium matrix, such as Al. Two different experimental approaches using a laboratory electron beam furnace have been developed for the estimation of volatilization rate and activity coefficient of Al in Ti64. The first innovative method is based on the deposition rate of Al on Si wafers located at different angles θ above the liquid bath. We found that a deposition according to a cos 2 ( π /2− θ ) law describes well the experimental distribution of the weight of the deposition layer. The second approach relies on the depletion of aluminum in the liquid pool at two separate times of the volatilization process. Both approaches provide values of the Al activity coefficient at T =1, 860 °C in a fairly narrow range [0.044–0.0495], in good agreement with the range reported in the literature. Furthermore numerical simulation of the Al behavior in the liquid pool reveals (in the specific case of electron beam button melting) a weak transport resistance in the surface boundary layer.

Circle quenching and tempering (CQ&T), intercritical quenching and tempering (IQ&T) and regular quenching and tempering (Q&T) were used to study the influence of heat treatment techniques on the low temperature impact toughness of steel EQ70 for offshore structure. The steels with 2.10 wt. % Ni (steel A) and 1.47 wt. % Ni (steel B) were chosen to analyze the effect of Ni content on the low temperature impact toughness of steel EQ70 for offshore structure. The fracture morphologies were examined by using a scanning electron microscope (SEM, JSM-6480LV), and microstructures etched by 4 vol. % nitric acid were observed on a type 9XB-PC optical microscope. The results show that the impact toughness of steel A is higher than that of steel B at the same test temperature and heat treatment technique. For steel B, the energy absorbed is, in descending order, CQ&T, Q&T and IQ&T, while for steel A, that is CQ&T, IQ&T and Q&T. The effects of heat treatment on the low temperature impact toughness are different for steels A and B, the absorbed energy changes more obviously for steel A. The results can be significant references for actual heat treatment techniques in steel plant.

Calcium aluminate cements (CAC) with 0.21 wt% B 2 O 3 and without B 2 O 3 were used as binders of corundum-based castables. The properties of the castables with and without B 2 O 3 after heat treatment at 110 °C, 1,100 °C and 1,450 °C were investigated, with emphasis on studying the effect of B 2 O 3 in CAC on the volume stability and high temperature strength of the castables. It is found that a very small amount (about 0.01 wt%) of B 2 O 3 introduced by the cement alleviates the expansion of the castables after firing at 1,450 °C and decreases the high-temperature strength of castables as the presence of B 2 O 3 should generate liquid phase.

Nickeliferous limonitic laterite ores are becoming increasingly attractive as a source of metallic nickel as the costs associated with recovering nickel from the sulphide ores increase. Unlike the sulphide ores, however, the laterite ores are not amenable to concentration by conventional mineral processing techniques such as froth flotation. One potential concentrating method would be the pyrometallurgical solid state reduction of the nickeliferous limonitic ores at relatively low temperatures, followed by beneficiation via magnetic separation. A number of reductants can be utilized in the reduction step, and in this research, a thermodynamic model has been developed to investigate the reduction of a nickeliferous limonitic laterite by hydrogen. The nickel recovery to the ferronickel phase was predicted to be greater than 95 % at temperatures of 673–873 K. Reductant additions above the stoichiometric requirement resulted in high recoveries over a wider temperature range, but the nickel grade of the ferronickel decreased.

Microwave-assisted heating technology has become a popular alternative to conventional heating technologies because of its many advantages. However, the matching performance of microwave heating system is of particular concern because it provides an important index of the utilization efficiency of microwave energy. In this work, a new microwave heating system is designed by the theory of optical resonator in first. Then the comprehensive analysis of the mutual coupling of high sensitive geometrical and material parameters were investigated based on this new microwave heating system at 2.45 GHz. It is demonstrated that the thickness of materials dramatically influences microwave energy absorption efficiency and should be carefully considered and perhaps given priority. Moreover, it is shown that matching performance is the best when the titanium concentrates thickness at about 0.075 m.

Effects of heat treatment on the mechanical properties of Ni films on 430 stainless steel substrate were investigated. The Ni films were annealed at heat treatment temperatures ranging from 0 °C to 800 °C for 2 h. The surface morphology, composition, and texture orientation of Ni films were studied by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. The load–indentation depth curves of Ni films before and after heat treatment were measured by using nanoindentation method. In conjunction with finite element modeling and dimensional analysis, the stress–strain relationships of Ni films on 430 stainless steel substrate at different temperatures are successfully obtained by using a power-law hardening model.