Volume 32, Issue 6

Improved designs, mostly for lightweight component manufacturer, have been made for improvement of forging and heat-treatment techniques. Low temperature precipitation strengthening and resistance to austenite grain size coarsening at reheat temperature for forging have been property improvement technique in these microalloyed steels. Studies of peak strain and flow stress at 1123–1423 K have shown increase in peak strain, peak stress and increment in mean flow stress in austenite phases in presence of vanadium. Partial vanadium alloying (1 part V substitute for 2 parts Mo) by substituting molybdenum has improved hardenability properties of conventional steels. Ultrafine grained steels have shown strain hardening effects from severe deformation by equal channel angular pressing (ECAP) followed by annealing. The strain induced precipitation of nano-metric sizes have pinned dislocations for strain hardening. Estimation of remaining life for reactor components have been done by simulated experiments under similar conditions as the service exposure. Vanadium in ferritic stainless steel has shown competitive performance, e.g. chloride environment. This has shown equivalent effects like nickel. In welding of microalloyed steel inter-critical grain coarsened heat affected zone (IC GC HAZ) has martensite austenite (M-A) blisters to yield poorest toughness.

High temperature creep and useful creep life behavior of Al-Cu-Mg (2124-T851 aluminum) alloy was investigated by conducting constant stress uniaxial tensile creep tests at different temperatures (473–563 K) and at stresses ranging from 80 to 200 MPa. It was found that the stress and temperature dependence of minimum creep rate could be successfully described by the power-law creep equation. The power-law stress exponent, n  = 5.2 and the activation energy for secondary creep, Q  = 164 kJ mol −1 , which is close to that observed for self diffusion of aluminum (~140 kJ mol −1 ). The observed values of n and Q suggest that the secondary creep of 2124-T851 aluminum alloy is governed by the lattice diffusion controlled dislocation climb process. A Monkman-Grant type relationship between minimum creep rate and time for reaching 1.5% creep strain is proposed and could be employed for predicting the useful creep life of 2124-T851 aluminum alloy.

According to the ion and molecule coexistence theory (IMCT) for molten slags and corresponding phase diagrams, a thermodynamic model for the evaluation of mass action concentrations (designated by N i for structure unit i) for La 2 O 3 -Al 2 O 3 , La 2 O 3 -Al 2 O 3 -CaF 2 , La 2 O 3 -Al 2 O 3 -CaF 2 -CaO, La 2 O 3 -Al 2 O 3 -CaF 2 -MgO and La 2 O 3 -Al 2 O 3 -CaF 2 -CaO-MgO slag systems for electroslag remelting (ESR) has been formulated. The influencing factors for the mass action concentration of La 2 O 3 , such as mass fraction of Al 2 O 3 , CaF 2 , CaO and MgO and temperature, were investigated. The results show that when the mole fraction of La 2 O 3 is at 0.495, the mass action concentration of La 2 O 3  · Al 2 O 3 achieves its maximum value 0.946 in the La 2 O 3 -Al 2 O 3 binary slag. In a composition area of La 2 O 3 : 10wt% ∼ 45wt%, Al 2 O 3 : 0wt% ∼ 50wt% and CaF 2 : 20wt% ∼ 70wt% of the La 2 O 3 -Al 2 O 3 -CaF 2 ternary slag at 1873 K, the results show that the calculated values of N La 2 O 3 are in good agreement with the reported measured values of a La 2 O 3 . The iso-curves of N La 2 O 3 is also drawn from the calculated results, which reveals that the mass action concentration of La 2 O 3 decreases with the increasing of the Al 2 O 3 and CaF 2 content, and Al 2 O 3 is stronger than CaF 2 in decreasing the mass action concentration of La 2 O 3 . However, in La 2 O 3 -Al 2 O 3 -CaF 2 -CaO, La 2 O 3 -Al 2 O 3 -CaF 2 -MgO and La 2 O 3 -Al 2 O 3 -CaF 2 -CaO-MgO slag systems, the mass action concentration of La 2 O 3 increases with the increasing of the MgO and CaO content, and CaO is stronger than MgO in increasing the mass action concentration of La 2 O 3 . In addition, the mass action concentration of La 2 O 3 increases with the increasing temperature at the composition of 30wt%La 2 O 3 , 10wt%Al 2 O 3 , 40wt%CaF 2 , 10wt%MgO and 10wt%CaO.

The effect of the addition of a small amount of CuO on the microstructure, hardness, fracture toughness and electrical conductivity properties of 8YSZ were investigated using 8 mol% yttria-stabilized cubic zirconia (8YSZ). The addition of 1 wt% CuO to 8YSZ powders were doped using a colloidal process. Undoped and CuO doped 8YSZ specimens were pressureless sintered at 1400 °C for 10 h. The grain size measurement results showed that the presence of CuO as a intergranular second phase at the grain boundaries of the 8YSZ gave rise to a decrease in the grain size. The fracture toughness values for undoped and 1 wt% CuO-doped 8YSZ specimens were obtained as 1.79 and 2.20 MPa.m 1/2 , respectively. The decrease in the grain size of the 8YSZ with CuO addition caused an increase in the fracture toughness. The electrical conductivity of the undoped and 1 wt% CuO-doped 8YSZ specimens was measured using a frequency response analyzer in the frequency range of 100 mHz–13 MHz and at the temperature range of 300–800 °C. The electrical conductivity results showed that there was a decrease in the grain interior, and specific grain boundary conductivity, with the addition of a small amount of CuO to 8YSZ. The presence of a second phase layer with high resistance at the grain boundaries of the 8YSZ caused a decrease in the specific grain boundary conductivity.

Polyaniline (PANI) is one of the most studied conductive polymer with several unique properties and good conductivity. In this study it was aimed to prepare Polyaniline (PANI)/Hexagonal boron nitride (h-BN) composites. Chemical structures of the composites were characterized by FTIR analysis. Thermal properties of these novel composites were analyzed by TGA and DSC measurements. Glass transition temperatures and char yields of the composites increased with increasing h-BN percentage. FTIR, XRD and UV measurements indicated that the boron atoms in h-BN particles interact with the unpaired electrons in nitrogen atoms of PANI. Dielectric measurements revealed dipolar polarization behavior of the composites.

Ferritic heat-resistant steels are commonly used for automotive exhaust systems and have replaced cast iron, the traditional material for this application. Efforts to improve the efficiency of engines, reduce weight, and minimize toxic ingredients by increasing the gas temperature have shifted the requirement for ferritic heat-resistant steels to a higher hot strength. Methods of improving the high-temperature strength are solid-solution strengthening, precipitation hardening, and grain refinement. In this work, the influence of MX precipitates on the high-temperature mechanical properties of three different ferritic Fe-Cr stainless steels was investigated and compared to a reference material. Investigations were performed with uniaxial compression tests of samples aged isothermally at 900 °C for up to 1440 h. The most effective method of increasing the high-temperature strength is to alloy the steel with 2 mass% tungsten. Grain growth during annealing at 900 °C was decelerated by solid-state formation of MX carbonitrides. Microstructural investigations also revealed a slow coarsening rate of the MX precipitates.

This paper deals with the effect of thermal shock treatment on grindability and grinding characteristics of zircon minerals and the overall energy saving achieved. This attempt is made due to a fine dry grinding of zircon minerals to produce zircon flour is an energy intensive operation. The effect of grinding time on grinding of zircon minerals in a continuously agitated rod mill indicate that the time required is 170 minutes for obtaining 75% of particles passing 45 µm size for natural zircon mineral whereas for thermally treated zircon it is only 100 minutes to achieve the same. Hence, 70 minutes of grinding time is saved. The work index test results show that 13.3% of the total energy can be saved when a sample is preheated to 850 °C and subjected to thermal shock treatment. The effect is due to the development of numerous micro-cracks and fractures in samples subjected to thermal shock.

The electrochemical impedance spectra was employed to investigate corrosion behavior of porous Cu-35mass%Ni-5mass%Cr and Cu-35mass%Ni-10mass%Cr alloys in molten (0.62Li,0.38K) 2 CO 3 at 650 °C in air. The results show that the Nyquist plots for the corrosion of two alloys are composed of two capacitive loops which indicate that localized corrosion occur for the total immersion time. The differential potential between Cu-rich phase and Cu-depleted phase contributes to galvanic corrosion of the alloys. As compared to porous Cu-35mass%Ni-5mass%Cr, porous Cu-35mass%Ni-10mass%Cr is more corrosion resistant, which is related with its smaller area fraction of the cathodic Cu-rich phase. In addition, crevice corrosion in the pores of the alloys promotes the micro-crack generation and expansion.

The effects of moisture content and temperature on the dielectric property of sodium chloride were investigated by using open-ended senor dielectric measurement system at the frequency of 2.45 GHz. Moisture content is a major influencing factor in the variation of dielectric properties. Dielectric constant, loss factor and loss tangent all increase linearly with moisture content increasing. Three predictive models were developed to obtain dielectric constant, loss factor, loss tangent and of sodium chloride as linear functions of moisture content. Temperature between 20 °C and 100 °C has a positive effect on dielectric constant and loss factor. Penetration depth decreased nonlinearly with moisture and temperature increasing. A predictive model was developed to calculate penetration depth for sodium chloride as a fifth function of moisture content. In addition, the measurements indicate that the particles temperature increases linearly with microwaving heating time at different power levels. The knowledge gained from these results is useful in developing more effective applications of microwave drying and designing better sensors for measuring moisture content of sodium chloride.

The microstructure, morphologies of precipitates in directional solidified 50W600 non-oriented silicon steel with three cooling rates (0.095, 0.33 and 4.28 °C/s) were investigated. The results showed that the morphology of solid-liquid interface evolved from cellular to cellular dendritic, and then to dendritic with an increase of cooling rate. The grain size of specimen in the steady-state growth region decreased with increasing cooling rate. The precipitates in the steel were mainly four types as follows: AlN, MnS, AlN-MnS and Fe 3 C. The amount and volume fraction of precipitates firstly increased and then decreased with increasing cooling rate, and reached maximum values in the specimen with a cooling rate of 0.76 °C/s. The average size of precipitates decreased gradually with increasing cooling rate. The relationship between the average size of precipitates and cooling rate was D  = 75.762· R −0.190 .