Solid State Phenomena Vol. 353

Abstract: In this paper, two types of W-Zr alloy with different proportions were prepared. The dynamic and quasi-static compression mechanical properties of Zr-25%W alloy and Zr-50%W alloy at various strain rates were obtained. The results showed that the tungsten component could improve the mechanical strength of the alloy, while the zirconium component could significantly improve the plasticity of the alloy. The JC constitutive models of two types of W-Zr alloys and the KHL constitutive model of Zr-25%W alloy were proposed. The fitting parameters of JC model and KHL model were determined by the dynamic and quad-static compression tests. Dynamic impact tests of two types of W-Zr alloys were carried out in argon atmosphere at various velocities. The power law distribution theory for brittle materials could also describe the high-speed impact of W-Zr alloy.

Abstract: The microstructure and mechanical properties of Al-Zn-Mg alloys with low Zn/Mg ratios have been studied.According to various researchers, the major strengthening is due to η-phase and T phase. There are many briefly research on the microstructure and interface of the η-phase types but not briefly information about the T-phase That’s why now our aim to work on T-phase. In actual our aim is to observe the T-phase interface. The MgZn₂ phase (η phase) and its metastable phase (η′ phase) were the most prominent precipitates. Another study revealed various Mg₃₂(Al, Zn)₄₉ phases (T phase) and their metastable phase (T′ phase) in Al-Zn-Mg alloys with low Zn and high Mg content. Al-Zn-Mg alloys with a Zn/Mg ratio of 0.71 were explored for this study. The alloy with a Zn/Mg ratio of 0.71 aged at 473k for 2000 minutes exhibited the highest hardness, according to the observations. The strengthening precipitates in the investigated alloy were totally T′ phase, according to TEM observation.

Abstract: As aerospace engines advance to obtain higher thermal efficiencies, it is imperative to develop high temperature materials. Inconel 718 is a nickel-based superalloy that has been used for decades in aero-engine parts as it allows for use in high temperature applications. ATI 718Plus is a newer nickel-based superalloy that has been developed with a 55°C higher temperature capability over Inconel 718. ATI 718Plus components are manufactured by forging a wrought billet in stages to obtain the desired geometry and microstructure. Parts are heat treated to optimised proportions of γ’ and η phases. η phase is an acicular phase that precipitates on the grain boundaries, whereas γ’ is the primary strengthening phase. η phase is an important phase to understand as it is utilised in controlling the grain size during hot working processes at temperatures below its solvus temperature. When η phase is fully solutioned, the grain size is free to increase and hence the material mechanical properties can become detrimental. The short-term precipitation kinetics of η phase in strain-free ATI 718Plus is still not completely understood. In this study, the aims and objectives were to study the η precipitation kinetics in strain-free material as well as studying η phase precipitation in equilibrium conditions. TTT diagrams were produced for the η phase in strain-free material and compared to the limited data available in the open literature. In addition, the equilibrium η phase content, aspect ratio, length and width were determined and compared to the very little data that is currently published.

Abstract: Magnesium alloys have the advantages being lightweight and high recyclability. On the other hands, it is thought that magnesium has the disadvantage of poor plastic workability at room temperature due to its crystal structure. Especially, in pipe materials, winkles occur on the compressed side during bending. We aim to improve the bending workability in magnesium alloy pipe by torsion and back-torsion. In this study, tensile and compressive tests using specimens of pipes processed by torsion and back-torsion showed reduction the difference of yield stress. Microstructural observation of processed pipes revealed reducing crystal grain size and forming deformation twinning. Vickers hardness tests shows increasing hardness by torsion and back-torsion. Moreover, bending tests showed decreasing flatting ratio by torsion and back-torsion. These results demonstrated that torsion and back-torsion have effect of improvement in bending workability for magnesium alloy pipes.

Abstract: Severe plastic deformation processing and subsequent aging treatment have been known to be effective for achieving higher strength than the conventional aging treatment in aluminum alloys. This study prepared the Al-Cu-Mg-based alloy sample, Al-5.3Cu-2.8Mg (mass%). The alloys were solution treated at 480, 495 and 505°C, and cold-rolled by 90%. The effect of process condition and test environment on tensile properties in cold-rolled Al-Cu-Mg alloys was investigated. Results confirm that strength and ductility were improved with increasing the solution heat treatment temperature regardless of test environment. 0.2% proof stress and ultimate tensile strength were higher than aging treatment specimens, but elongation to failure was lower than aged one. Hydrogen embrittlement susceptibility increased with increasing solution treatment temperature. Ductile fracture with many dimples is observed in both cold-rolled and aged specimens. Second-phase particles were observed at the bottom of the dimples. There was no significant difference in fracture surface between the different test environments.

Abstract: Since the first synthesis of bulk metallic glasses (BMGs) by copper mold casting in 1990, much effort has been devoted to the searching of new BMG composition, the clarification of fundamental and engineering properties for BMGs and their industrialization. At present, BMGs have been formed in a large number of multicomponent alloy systems where the empirical three component rule is satisfied. Nowadays, commercialized BMGs are classified to Zr-based and Fe-based alloy groups. When we look at the industrialization of Zr-Al-Ni-Cu-based BMGs, the first commercialization was made for golf clubs in Japan in 1998, followed by watch parts etc. Since then, Zr-based BMGs have been used continuously up to 2013, though their application scale was in a limited state. Since 2014, the application scale was significantly extended in collaboration with the rapid developments of smartphones and electric vehicles. At present, the mass production facilities for Zr-based BMGs have been significantly developed and variety of BMG products have been produced. On the other hand, Fe-based soft magnetic BMGs were found in 1995. Their BMGs have also been used on a huge number of pieces in various kinds of electronic-magnetic instruments. These recent application states for Zr- and Fe-based BMGs are introduced together with new nanocrystalline Fe-based soft magnetic alloys developed through the derivation of alloy composition from Fe-based BMGs.

Abstract: In order to get the insights about microstructural changes that occurs under the thermo-mechanical processing conditions, the physics based modelling approach is very useful. Therefore, the flow curves of alloy 718 are theoretical simulated using a dislocation density dependent constitutive model for different conditions. Presented model considers the microstructural ingredients that are immobile dislocation density, effective grain size and dislocation cell size as the variables to address the creep. The simulated flow curves show a good agreement with the experimental flow curves. The magnitude of immobile dislocation density and dislocation cell size in between 3.87× 10¹⁴ - 3.87× 10^14­ m^-2 and 8.29-8.45 μm, respectively, at the completion of the simulation. Furthermore, this approach also provides the possibility to quantify and depict the variation in each strengthening contributions.

Abstract: A systematic study has been made on a Cu-40%Zn alloy treated by an electric current pulse (ECP) and by the examination of the microstructure and the crystallographic features of both the parent and the product phases. The β precipitates under ECP show a Kurdjumov Sachs Orientation Relation (K-S OR) in the vicinity of the grain boundaries (GBs), but a Nishiyama Wasserman (N-W) OR within the grains. Along the GBs the {111}_α /<110>_α dislocation arrays were spotted, whereas the {111}_α /<112>_α stacking faults were observed in the grain interiors. A closer examination of the lattice strain required for the phase transformation revealed that the maximum lattice deformation under the K-S OR is a shear on the {111}_α plane in the <110>_α direction. The dislocations arrays existing along the GBs offer the pre-strain that favors the precipitation of β particles obeying the K-S OR. Oppositely, the stacking faults within the grains provide pre-stains for the formation of the β precipitates respecting the N-W OR. This study sheds some light on the mechanisms by which crystal defects initiate phase transformation in a Cu-40%Zn alloy.

Abstract: Titanium and its alloys are the 5th most common metallic materials used world wide but the markets volume of titanium materials, is difficult to expand due to associated production costs, and the decrease of those costs are critical in order to expand their markets. A possible option is the alloy design, i.e. using low price alloying element, such as iron, chromium, manganese and oxygen, and the selection of other raw materials, i.e. grade of sponge titanium. In beta titanium alloy, Ti-Mo system alloy using ferro-molybdeum was developed by USA company or Ti-Cr-Fe-Al beta alloy were also developed by Japan company. In this paper, those developed alloys were explained. Furthermore, substitution of Ti-10V-2Fe-3Al near beta alloy, presenters are studying about Ti-Mn-Fe-Al alloy.

Abstract: Magnesium and its alloys display a non-usual relationship between flow stress and grain size at room temperature. Breaks in the Hall-Petch relationship have been reported in the literature. Inverse Hall-Petch behavior in which flow stress reduces with grain size decreasing has also been reported in pure magnesium and magnesium alloys with ultrafine and nanocrystalline structures. The present overview discusses these effects in terms of controlling deformation mechanisms. The distinct strength observed in pure magnesium and magnesium alloys with ultrafine grained structure is also discussed. It is shown that experimental data for fine and ultrafine grained magnesium alloys agree with a model suggested recently based on the mechanism of grain boundary sliding. It is also exhibited that the stability of the grain structure might control the strength of ultrafine grained samples.