Volume 108, Issue 6

The grain growth and thermodynamic stability induced by solute co-segregation in ternary alloys are presented. Grain growth behavior of the single-phase supersaturated grains prepared in Ni–Fe–Pb alloy melt at different undercoolings was investigated by performing isothermal annealings at T = 400 °C–800 °C. Combining the multicomponent Gibbs adsorption equation and Guttmann's grain boundary segregation model, an empirical relation for isothermal grain growth was derived. By application of the model to grain growth in Ni–Fe–Pb, Fe–Cr–Zr and Fe–Ni–Zr alloys, it was predicted that driving grain boundary energy to zero is possible in alloys due to the co-segregation induced by the interactive effect between the solutes Fe/Pb, Zr/Ni and Zr/Cr. A non-linear relationship rather than a simple linear relation between 1/ D * ( D * the metastable equilibrium grain size) and ln( T ) was predicted due to the interactive effect.

The most challenging part, in modelling tailored hot stamping processes, is the variable cooling transformation that occurs in real industrial processes. In this study, analytical equations are first fitted to both experimental isothermal and continuous cooling transformation data. Then, an optimized fitting method with a weight coefficient is introduced that considers two transformation data to provide a more accurate transformation prediction. Finally, the generalized calculated result of incubation time using Rios's proposed method based on optimized continuous cooling transformation curves is contrasted against one calculated with a modified generalized calculated method. The results show that the consideration of the current temperature and cooling rate increases the accuracy of incubation time predictions as the gradient of cooling rate increases.

This study investigates the aging behavior of the recently developed ZnAl15Cu1 alloy and its change of mechanical properties with time. Samples obtained from drawn bars were artificially aged at 80 and 220°C for up to several weeks. The mechanical properties were monitored periodically by hardness testing, until a plateau was reached. The microstructural evolution was studied by optical and scanning electron microscope analyses. Bidimensional X-ray diffraction, transmission electron microscopy and selected area electron diffraction experiments were carried out to study the recrystallization phenomena. Nanoindentation measurements were also performed to determine the hardness of the single constituents. It was demonstrated that the aging causes a drop of about 30% in hardness with time. This reduction was related to the recrystallization of the Zn-rich phase network, occurring at both the studied temperatures.

We report hot deformation behavior of icosahedral quasi-crystalline phase reinforced Mg-1.50Zn-0.25Gd (at.%) alloys fabricated by a traditional gravity casting approach. The exponential law constitutive equation is applied to describe their flow stress behavior and the average activation energy is determined to be 187.70 kJ mol −1 . We also find that I-phase forms and grows in the alloys when the deformation strain is increasingly applied and that twinning contributes to high basal texture at early stage of deformation. Basal texture is weakened when the applied strain is strong owing to the dynamic recrystallization and also to the particle stimulation nucleation (PSN) effects of I-phase at late stage of deformation. High temperature is found to contribute to recrystallization but restrain I-phase precipitation and also weaken PSN effects of I-phase. Moreover, we find that a large strain rate not only promotes non-basal dislocation glide/twinning but also contributes to basal texture randomization, while a moderate strain rate is harmful for deformation due to the generation of strong basal texture. Furthermore, I-phase is found to be more effective for basal texture randomization than other strengthening secondary phases in Mg alloys, which is due to the presence of many orientation relationships and also because the interface between I-phase and Mg matrix is coherent or semi-coherent.

This paper first provides a critical review of experimental and theoretically-predicted diffusivities in both liquid and fcc Al–Si–Mg– RE ( RE = Ce, Sc) alloys as-reported by previous researchers. The modified Sutherland equation is then employed to predict self- and impurity diffusivities in Al–Si–Mg– RE melts. The self-diffusivity of metastable fcc Sc is evaluated via the first-principles computed activation energy and semi-empirical relations. Based on the critically-reviewed and presently evaluated diffusivity information, atomic mobility descriptions for liquid and fcc phases in the Al–Si–Mg– RE systems are established by means of the Diffusion-Controlled TRAnsformation (DICTRA) software package. Comprehensive comparisons show that most of the measured and theoretically-predicted diffusivities can be reasonably reproduced by the present atomic mobility descriptions. The atomic mobility descriptions for liquid and fcc Al–Si–Mg– RE alloys are further validated by comparing the model-predicted differential scanning calorimetry curves for RE -containing A357 alloys during solidification against experimental data. Detailed analysis of the curves and microstructures in RE -free and RE -containing A357 alloys indicates that both Ce and Sc can serve as the grain refiner for A357 alloys, and that the grain refinement efficiency of Sc is much higher.

Wetting of Ti-6Al-4V alloy by two industrial grade Al alloys (i. e., Al 6061 and 4043 alloys) was studied using the sessile drop method at 600–700 °C under high vacuum. Al/Ti-6Al-4V is a typical reactive wetting system with good final wettability accompanied by the formation of precursor film which is actually an extended reaction layer. The formation mechanism for the precursor film is “subcutaneous infiltration”. The small amount of alloying element Si in the alloys can cause significant segregation at the liquid/solid interface which satisfies the thermodynamic condition. The wetting behavior can be described by the classic reaction product control models, and Ti 7 Al 5 Si 12 decomposition and Al 3 Ti formation correspond to the two spreading stages. The small difference in alloying elements in Al 6061 and 4043 resulted in distinctly different interface structures, formation of precursor film and spreading dynamics, especially for the Si segregation at the interface.

In this study, Co 2 B nanocrystals, which were synthesized in a planetary type mill by using the mechanochemical method, were pre-coated on the surface of S235JRC low carbon steel substrates, and then the surfaces were clad using a CO 2 laser. In the experiments, laser scan speed was kept constant and laser power was specified as the variable parameter. The microstructure and phases of the coatings were investigated by using X-ray diffractometry, scanning electron microscopy, and optical microscopy. The mechanical properties of the coatings were characterized using micro-hardness, ball-on-disc wear, and scratch testing. The thickness of the coatings depending on the laser power was measured in the range 35–71 μm. The hardness and the wear resistance of the coatings were approximately 3 times higher compared to the base metal due to FeN 0.0760 , Fe 15.1 C, FeCo, and B 2 C 5 N 2 phases of the coatings. The most durable coatings against wear were obtained at 174 W and 220 W laser powers.

The paper analyses stress distribution in mono/multi-layers of coated tools. It presents an analysis performed on mono-layer, double-layer and multi-layer coatings using numerical models to detect the developed stress distribution and the most stressed zones in these mostly 1–10 micron layers. With such thin layers, experimental detection of stress distribution would be very difficult. Moreover, coating thickness is distributed differently on flat surfaces from on shaped features in coated tools. This non-uniform coating results solely from the technology applied and such uneven deposition of the coating is critical in terms of how the tools themselves function. The paper provides an analysis of stresses in thinner or accumulated layers of coating on the rounded edge, for example in cutting. This analysis was initiated by ProTech Coating Service, Ltd., which manufactures physical vapour deposition coatings for cutting and forming tools.

The responses of a cryolite-based bath to shifts in heat input/output balance have been investigated in previous work. The effect of such heat balance shifts on bath superheat and on the frozen ledge, protecting the cell walls, is of most interest and has been investigated primarily in an experimental analogue to a smelting cell. In this paper, the microstructure and morphology of the freeze itself, as a function of the applied heat balance shift is investigated. Different layers were detected in the freeze, showing that both the freeze morphology and the phases present vary depending on bath conditions. The phase composition change was also analysed and compared with the bulk bath in different thermal states, created when the heat balance was shifted. Based on the investigation, a freeze growth mechanism is proposed.

Shape memory polyurethanes have been prepared from polycaprolactone diol, 1,6-hexanediol and 4,4′-dicyclohexylmethane diisocyanate. The structural identification of the final polymer was confirmed by Fourier transform infrared spectroscopy. The thermo-mechanical history was studied using thermo-gravimetric analysis, differential scanning calorimetry, dynamic mechanical thermal analysis and shape memory testing by tensile cyclic loading using a temperature controlled chamber. The absence of any peak corresponding to functional groups of monomers confirmed the completion of reaction. The thermo-grams showed a gradual decrease in the thermal transition with increasing crystallinity, with corresponding increase in the molecular weight of macrodiol used as soft segments. The highest value of shape recovery of the sample (PCL, 4 000 g mol −1 ) obtained was 96%, and retention up to 85%.