Papers by Keyword: Alloy Design

Abstract: The manufacturing of high temperature heat exchangers and precoolers within the aerospace industry often requires the joining of thin-walled components through brazing. Existing commercially available brazing alloys are often relatively hard with brittle failure modes despite ductility and strength being desirable properties of a brazed joint. High entropy alloys have been demonstrated to have desirable material properties such as high ductility and strength. Previous work on CoCrCuFeNi has demonstrated that the addition of melting point depressants such as Boron, are able to beneficially reduce the brazing temperatures sufficiently to allow brazing of steel components while maintaining a strong and ductile joint. The current work has focussed on finding new, non-equimolar, HEA compositions with a lower targeted melting point for a wider range of brazed substrate materials. Alloy compositions were down-selected through empirical thermodynamic classification and CALPHAD simulations. Identified potential compositions were synthesised using induction casting, and solidus and liquidus measured using DSC. Phases were confirmed using a combination of microscopy, hardness and XRD analysis. The best alloy candidates were then modified with the addition of Boron to further reduce the melting point to meet the required manufacturing temperatures of the joint. Finally, shear strength measurements were carried out on the samples which met the brazing temperature requirements.

Abstract: High-entropy alloys (HEAs) are a new and rapidly developing area of materials science, characterized by their high entropy content. High-entropy alloys have received considerable attention in recent years because of their properties, such as high tensile strength, corrosion resistance and excellent heat resistance. These materials have the potential to broaden material utilization in aerospace, automotive, energy, and other industries. There are three main manufacturing technology group to produce high entropy alloys. These groups are melting and casting, powder metallurgy, and deposition techniques. The manufacturing processes is essential to optimize the properties of the final product and meet the requirements of the application. The paper summarizes the four core effects and the production methods for high-entropy alloys.

Abstract: In this paper, a novel lightweight and low-cost Al₃₅Mg₂₀Zn₁₅Cu₁₀Si₂₀ at. % (Al_26.17Mg_13.47Zn_27.18Cu_17.61Si_15.57 wt.%) has been successfully designed, produced, and characterized. The thermophysical parameters were used to understand the phases associated with this alloy that show a low density of 3.42 g/cm³. The designed alloy was manufactured using both the arc and the muffle furnace. The alloy was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer (EDS). The alloy is characterized by a multiphase microstructure with three major phases including Mg₂Si intermetallic phase and eutectic. The volume fraction of the eutectic and the intermetallic phases are 37.83 and 34.99 respectively. The heat capacities of the alloy were also determined by means of differential scanning calorimetry (DSC). The alloy provides a high latent heat of up to 124 J/g, which is one of the highest among the high-temperature metallic materials. The present work provides valuable information for researchers wishing to design and manufacture industrial-grade high-entropy alloys (HEAs).

Abstract: Carbide free bainitic microstructures of steels in hot rolled condition have high potential for automotive and structural applications, where both high elongation and toughness at a high strength level are needed. However, achieving a combination of these properties remains a challenge due to difficulties in ensuring a high stability of retained austenite while maintaining industrial processability. Therefore, an attempt has been made in this work to achieve combined high toughness and high elongation in hot rolled carbide free bainitic steels.

Abstract: Additive manufacturing (AM) provides numerous advantages compared to conventional manufacturing methods, such as high design freedom and low material waste. Among the available materials, precipitation-hardenable aluminum alloys are highly attractive for AM due to their high specific strength and low density. Precise control of the processing conditions during AM and post heat treatment (HT) is required to tailor the final mechanical properties. Consequently, many variables, such as the chemical composition and process and HT parameters, must be considered to design suitable alloys for AM. Experimental investigations are, however, limited in variation of these variables. Therefore, computational alloy design approaches allowing for a faster evaluation of many possible variations must be developed. This work presents a high-throughput approach to determine the precipitation kinetics and thermodynamic properties based on the CALculation of PHAse Diagrams (CALPHAD) method. The developed approach is successfully validated for an Al-Mg-Si-Ti-Fe alloy and is applied to screen 243 combinations of chemical compositions and HT parameters. The results confirm the microstructural stability of the Al-Mg-Si-Ti-Fe system to small composition variations.

Abstract: In this paper, a new metastable Titanium alloy in the Ti-Nb-Ta-Mo system has been successfully produced using both the d-electron and Mo_eq concept. The influence of cold rolling on the microstructure and hardness was investigated. The alloy was fabricated by arc melting, cold rolled up to 90% reduction in thickness and characterized using X-ray diffraction (XRD), optical microscope and Vickers microhardness. The XRD peaks depicted both β and α′′ phases in all the cold rolled specimens. The hardness of the alloy increased with increasing cold rolling reduction thickness. An excellent plasticity (≥ 65%) and compressive strength up to (2.9 GPa) was achieved with low Young’s modulus (31 GPa) and no failure or crack on the alloy. Also, the alloy demonstrated a high compressive true strength coefficient (k ≈1426 MPa) along with improved strain hardening index (n ≈ 0.41). Based on the XRD, optical microscope and microhardness indentation micrographs, the deformation mechanism of Ti-13Nb-1.5Ta-3Mo was found to be a combination of stress induced transformation, mechanical twinning and slipping.

Abstract: Additive Manufacturing (AM) processes are becoming more and more important for production of parts with increasing geometrical complexity and functionality. However, to draw on the full potential of AM technologies, alloys that exploit process inherent particularities such as extremely high cooling rates (ca. 10⁶ K/s) have to be developed. One of most important AM-processes is Laser Powder Bed Fusion (LPBF), a batch-wise process. This complicates experimental alloy development and increases the use of powder resources since only one chemical composition can be tested within one test job and the process chamber has to be cleaned carefully in between. The process Extreme High-Speed Laser Material Deposition (EHLA) has been found to have similar cooling rates as LPBF, however it uses an in situ supply of powders which allows an easy switching between materials and has potential for rapid alloy development methods. Since the mechanical properties of materials primarily depend on chemical composition and microstructure, which in turn depends heavily on the cooling rates in the production process, the EHLA-process could be used as a means for an accelerated alloy development for LPBF. However, to explore this possibility, a thorough comparison of the two processes has to be performed.In this work, EHLA and LPBF processes are compared and evaluated regarding the following characteristics: process parameters, laser intensities and volume energy densities, resulting microstructure (primary dendrite arm spacing, DAS), melt pool size and shape. The reference samples were manufactured using one set of LPBF process parameters and EHLA samples were manufactured using three different sets of process parameters.The volume energy densities E_v [J/mm³] of the processes were found to differ by a factor 2.4 with higher E_v observed in LPBF. However, considering that approximately 2 to 3 layers are remelted with each pass of the laser beam, the introduced E_v per pass approximates the E_v introduced in the EHLA process. The melt pool size as seen in a cross section in the EHLA-manufactured samples is approximately 25 times larger than in the LPBF-manufactured samples and its depth to width ratio (d/w ratio) can be attributed to a heat conduction welding process while the d/w ratio observed in the LPBF-manufactured sample suggests a transition process between heat conduction welding and deep welding. The observed DAS is in the same order of magnitude for both processes ranging from 0.55 to 1.15 µm in EHLA-manufactured samples and 0.73 µm in the LPBF-manufactured reference sample. Since the resulting microstructures of samples manufactured with both processes show this common feature and EHLA process parameters can be adjusted to control the cooling rates, the transferability between EHLA- and LPBF-processes is supported in this first investigation. Research for a more efficient alloy development for LPBF using EHLA will be continued by e.g. examining chemical compositions and performing mechanical testing.

Abstract: Rina Consulting Centro Sviluppo Materiali (CSM) has been involved in the study and development of powder metallurgy for different applications, thanks to its participation in many research industrial and funded projects. The entire metal powder production chain takes place within the company's own researcher and facilities. This allows to produce high quality powders starting from alloy design, VIGA atomization and chemical, rheological and particle size analysis. In recent years, the development has mainly concerned manufacturing processes. Currently only a limited number of metal alloys can be processed by AM. For that reason, the alloy design becomes a really important topic to enlarge AM capabilities to other materials and applications. Starting from commercial Thermodynamic and Kinetic codes and proprietary models on solidification and micro-segregation, the alloy chemical composition can be fine-tuned to optimize the microstructure, considering the target properties of the material and the relevant AM processing windows, taking into account also the post process treatment conditions. Moreover, the knowledge of the production plants allows CSM to have a wide vision on the realization and the characterization of the metal powders focusing to achieve the best powder quality suitable for AM applications. Finally, AM is a relatively “new” process, standardization is still an ongoing activity involving several communities and organizations like ASTM, AWS and ISO; in this contest CSM has already designed the guidelines for qualification and certification processes and has created a dedicated laboratory to qualify powders of AM players.

Abstract: In the present study, two newly developed non-equiatomic high entropy Al₁₀Cr₁₂Mn₂₈Fe_(50-x)Ni_(x) alloys (x= 20 & 15 at%, namely: Ni₂₀ & Ni₁₅, respectively) are investigated. The studied HEAs were designed based on thermodynamic principles to maintain high ductility and improve strength. Ingots were prepared using arc-melting then microstructure examinations and mechanical properties for the as-cast alloys were done. The mechanical properties were enhanced for the as-cast material, compared with previously introduced HEAs of the same system, namely Al₅Cr₁₂Mn₂₈Fe₃₅Ni₂₀, (Al₅) and Al₁₀Cr₁₂Mn₂₃Fe₃₅Ni₂₀, (Al₁₀). Al₁₀Cr₁₂Mn₂₈Fe₃₀Ni₂₀ (Ni₂₀) HEA generally shows the highest compressive yield strength which was improved by ∼7% when compared with previously introduced Al₁₀.

Abstract: This paper provides a comprehensive review of developments and progress made in martensitic heat-resistant steels, especially, with the emphasis on strengthening mechanisms used in elevated temperatures. We desired to elucidate the correlation between high creep resistance at elevated temperatures and thermal stability of nano-sized particles precipitated from martensite matrix. Finally, future prospective strengthening methods for martensitic heat-resistant steels were discussed.