Materials Science Forum Vol. 941

Abstract: The tailoring of mechanical and technological properties of the initial material in sheet metal forming has been widely investigated and successfully applied. The benefits of such an approach can be found in the improvement of both the post-forming performances of the manufactured component and the forming process capabilities. Different strategies can be found and most of them involve a microstructural alteration by a selective heat source (e.g. laser, induction, UV light). The use of aluminium alloys combined with these strategies has been extensively investigated, while magnesium alloys are almost not yet considered from this viewpoint. In this work, we investigated the effect of a selective laser heat treatment on an AZ31 magnesium alloy sheet. After laser heat treating a single track in the centre of a blank with different heat input values, bulge tests at elevated temperatures were conducted. The dome height evolution was continuously acquired during the tests and differences between the untreated specimen and the laser treated ones have been characterized. The effect of the laser treatment was evaluated also in terms of thickness distribution of the formed specimens. A thickness discontinuity was found along the treated specimens in the transition zone between the treated and the untreated material. Results highlighted that an effective change in the forming behaviour can be induced in the treated zone depending on the laser heat input. It has thus been shown that this approach can be employed for tailoring the magnesium alloy blank properties prior to the gas forming at elevated temperatures.

Abstract: Ti-15Mo alloy belongs to metastable β-Ti alloys that are currently used in aircraft manufacturing and Ti15Mo alloy is a perspective candidate for the use in medicine thanks to its biotolerant composition. In this study, Ti15Mo alloy was prepared by advanced techniques of powder metallurgy. The powder of gas atomized Ti-15Mo alloy was subjected to cryogenic milling to achieve ultra-fine grained microstructure within the powder particles. Powder was subsequently compacted using spark plasma sintering (SPS). The effect of cryogenic milling on the microstructure and phase composition of final bulk material after SPS was studied by scanning electron microscopy. Sintering at 750°C was not sufficient for achieving full density in gas atomized powder, while milled material could be successfully sintered at this temperature. Alpha phase particles precipitated during sintering and their size, as well as the size of beta matrix grains, was strongly affected by the sintering temperature.

Abstract: We have focused on shape-memory properties of Cu-Sn based ternary alloys in this study. We have attempted to suppress degradation at room temperature aging and to improve the amount of shape recovery by adding the third element to a binary Cu-Sn alloy. The attempt has successfully conducted in Cu-Sn-Mn alloy, the degradation due to aging at room temperature was suppressed and the thermal stability was improved. Furthermore, the present study revealed that Cu-Sn-Mn alloy exhibited a large super elastic recovery in three point bending tests. We have also investigated the shape-memory properties of Cu-Sn-Si alloys and revealed that the ternary alloy has achieved super-elastic recovery better than the Cu-Sn-Mn alloy in the three-point bending tests.

Abstract: Mercury Marine has used a new alloy, Mercalloy A362, for the manufacturing of a re-designed lower unit transmission gearcase. The enhanced strength of the alloy allowed for a substantial weight reduction in the new design. The purpose of this study was to examine and determine why cracking may develop in the gear casing during in service testing. Two types of material states, (i) as cast and (ii) heat treated were compared. Metallography and neutron diffraction analysis was carried out at locations identified as being areas of high stress by Magma software – which was performed in a separate study. Microstructural characterization at these locations revealed microstructural and the compositional differences. Differences in the porosity, eutectic phase, and volume fraction of the precipitates were observed at various locations of interest in each material state. The residual stress analysis was performed with application of neutron diffraction and revealed that the stresses in the as-cast component reached a maximum value of 120 MPa, which is below the yield strength of the alloy. The heat treatment applied to the castings reduced the stress by approximately 50 MPa. Based on the microstructure and neutron diffraction results, it is likely that performing a heat treatment process extends the lifetime of the component, however, it may not completely eliminate the cracking problem. Farther studies are currently nearing completion, targeting the mass production of the redesigned gearcase.

Abstract: Behavior of hydrogen in tensile-deformed Al-9mass%Mg and Al-5.8mass%Zn-2.4mass%Mg alloys was investigated by means of hydrogen microprint technique, HMPT, a method to visualize the microscopic location of hydrogen evolution from specimen surface as silver particles. Both in the two alloys, surface relief was formed at most grain boundaries by the stretching, while hydrogen evolution was observed at some grain boundaries. The evolution of hydrogen was discussed with parameters such as the angle between grain boundary on the specimen surface and tensile direction, the angle between grain boundary on the surface and slip line inside the grain, the height of the surface relief, and maximum gradient of the surface relief. The results indicated that the shear deformation along grain boundary caused transportation of hydrogen atoms with gliding dislocations to the surface, breakage of surface oxide film. In the Al-Zn-Mg alloy, it was suggested that the preferential deformation in the precipitate free zone was attributed to hydrogen evolution.

Abstract: Additive manufacturing (AM) technology has been dramatically attracted attention because of advantages in building free-shaped parts and simplification of manufacturing process. Recently the most relevant alloys, such as TiAl6V4, Inconel 718, AlSi10Mg and so on, are able to manufacture the parts using metal AM technology. However high-strength 2024, 6061 and 7075 aluminum alloys are difficult to fabricate using selective laser melting (SLM) owing to solidification cracking during solidification. In this research, the melting and solidification behaviors of AlSi10Mg alloy during SLM process were observed under various fabrication conditions of laser power and scan speed using a high-speed camera. It was found that the melting and solidification behavior of the alloy is greatly different by the fabrication conditions. And also the mechanism of solidification cracking in 2024 and 6061 aluminum alloys is investigated by the observation of the surface morphology and microstructure of the alloys using OM, SEM and EDS, comparing with Al10SiMg alloy. As a result, crack-free 2024 and 6061 aluminum alloy parts can be obtained by fabrication at the higer enrgy density.

Abstract: Aluminium alloys are somehow the workhorse among light metals: spreading from castable, work hardenable to age-hardenable alloys, a wide panel of alternatives is available for the users. Nevertheless, continuous improvement of these alloys is ongoing, looking for higher strength, wider service temperature ranges, and suitability for new manufacturing processes.Likewise, a better knowledge of microstructure and ‘finer’ effects have to be encompassed.A proper multiscale approach and competent preparation are advisable for the best interpretation of the performances of new or ‘revised’ alloys.In this work a case study is presented in which multiscale approach has been used in order to explain the behavior of relatively widely used alloys, and also the problems and solution adopted in order to obtain the best results from microstructural analyses.Wrought age hardenable alloys were analyzed to have a better comprehension of ‘high temperature’ evolution of microstructure. The overall appearance of the microstructure was first identified by optical microscopy. Scanning Electron Microscopy (SEM) was involved to analyze grain size, type and size of secondary phases and texture. The results supported modeling studies related to the effect of grain size and texture. Finally, High Resolution Transmission Electron Microscopy (HR-TEM) investigations helped to understand the modification in the decay of mechanical properties upon extended overaging.

Abstract: Already, there are several processes to produce intermetalic alloy parts from powder , ex. metal injection molding (MIM) or additive manufacturing (AM). For these processes, pre-alloyed powder made by gas atomized powder is used because of their quality. As other way, intermetallic alloy can be produced combustion reaction process. On this process, ingredient metal powders are mixed and reacted by combustion. However, powders are fused by reaction heat, and they are difficult to keep the powder condition. There for, we are developed the process to produce intermetallic alloy precursor by slow combustion reaction. On this process, temperature of mixed powders increases slower than 0.2K/sec. while the combustion reaction, and powders are reacted without fusing. Using this process, TiAl presursor is synthesized. Relation of reacting condition and quality of the precursor is evaluated, and researched the practical usage of this precurser.

Abstract: The fast and spontaneous hydrogen diffusion in HCP structures leads to the hydride precipitation. It is often pointed as causing embrittlement and rupture in zirconium alloys for applications in the nuclear industry. In our previous works TEM, DSC, SEM-EBSD and XRD were used to study the hydride stability after many precipitation-dissolution thermal cycles as well as the crystallographic hydride phase nature and the hydride-substrate crystallographic orientation relationships as a function of the hydrogen content. Results showed that the evolution of the dissolution and precipitation energies is correlated to the concentration of hydrogen atoms available to reprecipitate, which is submitted to a diffusion controlled by the misfit dislocation migration. In the present work in-situ TEM thermal cycling was performed in order to locally investigate the crystallographic stability of zirconium hydrides of different structures after many dissolution-reprecipitation cycles.

Abstract: Numerous studies have been conducted to develop next-generation recording technology in spintronics. Because ultrafine magneitc particles are vital components of the technology, the interplay between the microsturcture and magnetic properties has attracted attention extensively in recent years. We focused on the relationship between the microstructure and magnetic properties of Cu-Ni-X (X=Fe, Co, FeCo) alloys comprising nanogranular magnetic particles. In this work, we prepared Cu-20 at% Ni-5 at% (FeCo), Cu-20 at% Ni-5 at% Fe, Cu-20 at% Ni-5 at% Co and examined the changes of microstructure and magnetic properties associated with heat treatments and composition. To examaine microstructural evolution of the alloy specimens, we conducted transmission electron microscope observations (TEM) with the as-quenched specimens and those aged at at 773-1073 K. We also carried out magneto-thermo gravimetry (MTG) measurements, superconducting quantum interference device (SQUID) measurements, magnetoresistance (MR) measurements and first-principles calculations based on the Koster-Korringa-Rostker (KKR) method with the Coherent Potential Approximation (CPA), to investigate the magnetic properties. The present work confirmed that the microstructure significantly changed, depending on the composition and heat treatment conditions. The present work also revealed that the magnetic properties closely correlated with the microstructure of samples.