Materials Science Forum Vol. 1175

Abstract: There are many products that produce sound when external force is applied to metals and alloys, such as wind chimes, golf clubs, and metal bats. Previous studies have investigated the differences between acoustic properties and sound impressions of these products depending on the type of material. Sound is an element that influences the comfort in our daily lives and the sensation of players in sports. Therefore, it is important to clarify the differences in acoustic properties of different materials in order to design and improve products. However, the effects of changes in chemical composition in the same material on acoustic properties have not been sufficiently studied. The purpose of this study is to evaluate the change in acoustic properties due to the chemical composition of metals and to contribute to the acoustic design of products. In this study, six types of brass specimens with varying zinc content from 5% to 40% were prepared, and the differences in frequency and decay time of hitting sound were evaluated. As a result, it was confirmed that the frequency tended to decrease as the zinc content increased, and the decrease in frequency was particularly pronounced for the specimens with a zinc content of 40%. Attenuation time showed an increasing trend but decreased slightly for specimens with 40% zinc content. These results indicate that the chemical composition of brass has a significant effect on acoustic properties.

Abstract: The microstructural characteristics of externally solidified crystals (ESCs) and porosities in a non-heat-treated high-pressure die-cast AlSi9MnVZr alloy are investigated under two distinct process conditions: one with the application of lower intensification pressure and the other with higher intensification pressure. Optical microscopy (OM), scanning electron microscopy (SEM), and computed tomography (CT) are employed to analyze the ESCs and porosity distribution. The alloy's microstructure primarily consists of primary α-Al, ESCs, Al-Si eutectic, and iron-rich phases. ESCs nucleate in the shot sleeve, while α-Al forms within the die cavity. When the lower intensification pressure is applied, larger dendritic ESCs are observed, along with significant gas porosity, shrinkage pores, and numerous smaller dispersed pores, resulting in a high porosity fraction. Conversely, the application of higher intensification pressure results in a notable refinement in ESCs morphology, with a significant reduction in their diameter and area fraction. Additionally, the size and fraction of porosity decrease substantially, indicating a marked improvement in casting quality.

Abstract: The microstructural characterization of a fan blade of an aircraft gas turbine, manufacturing of Ti-6Al-4V alloy, was conducted in order to evaluate the occurrence of internal damage. The blade analyzed was removed from aeronautical service. An analysis was carried out by using X-ray computed microtomography and scanning electron microscopy in three samples obtained from the tip and the root of the blade, as well as from its midsection, along its length. These results were compared with those obtained through the microstructural characterization by optical microscopy of specimens, approximately of 15×5×4 mm. The results show the occurrence of early-stage erosive wear on the component and morphological changes of the alpha-grains of Ti-6Al-4V alloy, in comparison with those reported in literature. These changes were observed in the longitudinal and transverse sections of specimens of the blade, which could be related to the mechanical stresses which these elements are subjected during their aeronautical service. The results obtained by X-ray computed microtomography did not show evidence of internal cracking. Finally, the morphological changes identified in the alpha-grains may be a critical parameter to removing these important components from service. Additionally, the use of the open-source software 3D Slicer for the reconstruction of images from X-ray computed microtomography may become a viable and valuable option for the analysis of data obtained by mean of this technique.

Abstract: The formability of Aluminum 2050 alloy is critical for manufacturing large and thick components while maintaining its outstanding performance. To link the damage development during high-temperature loading with the alloy microstructure evolution, a time resolved tensile loading experiment at 480 °C was performed on this alloy using synchrotron diffraction and tomography, i.e. diffraction contrast tomography (DCT) to provide 3D grain maps and phase contrast tomography (PCT) to characterize pores and intermetallics. The evolution of both was quantified as a function of macroscopic strain up to 20.15%. Three pore formation mechanisms were identified: growth from pre-existing pores, fracture of the intermetallics, and nucleation of new pores. The characteristics of the pore evolution are linked with the grain structure characterized by DCT. Additionally, the grain maps reconstructed for initial and final strained states show newly recrystallized grains, indicating the presence of dynamic recrystallization. To exclude the possible explanation by annealing recrystallization, an extra annealing experiment was performed and no recrystallized grains were observed. A comprehensive insight into linking the damage development with the microstructure evolution under high-temperature deformation has been obtained by using synchrotron grain mapping techniques and tomography.

Abstract: In recent years, high-entropy alloys (HEAs) have attracted significant attention owing to their remarkable physical properties such as high strength. It has also been reported that HEAs have a high potential as biomaterials. Bcc-type bio-HEAs possess high strength and biocompatibility equivalent to those of pure titanium. Bio-metallic materials require a low Young's modulus, similar to that of natural bone, but the Young's modulus of bio-high entropy alloys has not yet been clarified. Therefore, this study elucidates the relationship between microstructure control and Young's modulus in titanium-based bio-HEAs. The TiNbTaZrMo-based bio-HEAs were composed of two bcc phases. These two phases correspond to dendrite and interdendrite structures, respectively. In this study, it was found that by varying the volume fractions of these two phases, it is possible to control the Young's modulus.

Abstract: This study investigates the effects of different welding and heat treatment sequences on the mechanical and microstructural properties of laser powder bed fusion (PBF-LB) fabricated Inconel 718. Three conditions were examined: laser welding of as-built material (LW-built), welding after heat treatment (HT-LW), and welding followed by post-weld heat treatment (LW-HT). Tensile testing, microscopy, fractography, and finite element simulations were used to evaluate performance. The LW-HT condition exhibited the highest strength (UTS ~1430 MPa) and the most uniform stress distribution, attributed to the re-precipitation of laves/δ phases during post-weld aging. In contrast, the HT-LW condition showed localized softening and early failure due to precipitate dissolution in the fusion zone. Fracture surface analysis confirmed enhanced ductility in LW-built and refined microstructural features in LW-HT. These findings demonstrate that post-weld heat treatment (LW-HT) is the most effective route for optimizing strength and structural stability in welded PBF-LB Inconel 718, with some trade-off in ductility.

Abstract: The design flexibility afforded by additive manufacturing, commonly known as 3D printing, is broadening the industrial applications of high-entropy alloys (HEAs). The 3D-printed CrMnFeCoNi HEA (or Cantor alloy) exhibits a unique combination of strength and ductility, attributed to its multifaceted deformation mechanisms. While the deformation behavior of this alloy under monotonic loading has been extensively studied, its cyclic plasticity, which is crucial for fatigue performance, remains a relatively underexplored area. To address this gap, the current work investigates the deformation microstructure of a CrMnFeCoNi HEA fabricated using laser-beam powder bed fusion. Electron backscatter diffraction (EBSD) is employed to characterize the surface microstructural changes. The results reveal the simultaneous activation of multiple slip systems in the region near the fatigue crack, which induces grain rotation. Additionally, the activation of twinning-induced plasticity plays a significant role in accommodating the cyclic plastic strain.

Abstract: Pre-alloyed powders, which are mainly used in laser powder bed fusion (LPBF), have the disadvantage of being time-consuming and costly to manufacture. To overcome these disadvantages, in-situ alloying, which mixes pure element powders and performs alloying in real time during the LPBF process, has been attracting attention. In particular, it is quite challenging to manufacture high entropy alloy (HEA) containing high melting point refractory elements by in-situ alloying. In this study, we designed a single-phase BCC refractory HEA with a mix of Ti, Nb, Mo, Ta, and W through thermodynamic calculations and fabricated the designed composition by LPBF by mixing powders of each element and performing in-situ alloying. High energy density and remelting effectively suppressed segregation of constituent elements, which caused a decrease in residual stress and increased relative density. Our study represents a pioneering attempt to manufacture in-situ alloyed HEA by LPBF and demonstrates the effectiveness of in-situ alloying using mixed powders.

Abstract: Additive Manufacturing enables the production of intricate geometries and products with improved strength-to-weight ratios, driving its applications in defence, aerospace, and automobile sectors. Maraging steel and Superalloy Inconel 625 are renowned for their excellent mechanical properties and are candidate materials for high performance applications. It is essential to study the fatigue behaviour of additively manufactured samples prior to their deployment in real working environments, as their mechanical properties and fatigue behaviour differ from those of conventionally manufactured materials. In the present study, low cycle fatigue (LCF) behaviour of Maraging steel (M300) and Inconel 625, at different strain amplitudes and heat treatment conditions were evaluated. Fractographic characterization was conducted using scanning electron microscopy (SEM). To understand the effect of build orientation on LCF behaviour, the maraging steel samples were also tested in different build orientations (0^o and 90^o). It was found that build orientation significantly affected the fatigue life of additive manufactured maraging steel samples. The LCF study was also done at different strain amplitudes for Inconel 625 and results indicated that there was drastic decrease in fatigue life at higher strain amplitudes. It was observed that defects introduced due to layer wise processing of additive samples have adverse effect on fatigue life. Ultrasonic shot peening was also applied to the additively manufactured fatigue samples to examine its impact on fatigue life.

Abstract: A test probe is used for continuity test of semiconductor packages with solder balls. The probe material is often damaged due to solder adhesion on it by repeated test. The Pd-42Cu-10Ni (mass%) alloy has been developed as a substitute material for the conventional Pd-30Cu-29.5Ag-0.5Zn (mass%) alloy. The interfacial reaction between Pd-42Cu-10Ni and Sn by aging at 150°C was investigated in this study. Moreover, the obtained data was compared to those of the conventional alloy. As a result, it was confirmed that granular (Cu,Ni)₆Sn₅ forms at the interface between the reaction layer and Sn, and the reaction layer consists of stacked layers of the PdSn₄+PdSn₃ layer and the (Cu,Ni)₆Sn₅+Cu₃Sn+PdSn layer. The reaction layer mainly grew toward the Sn side from the original interface. Furthermore, the thickness of the reaction layer grown by aging was suppressed to approximately one-fourth compared with the conventional alloy.