Papers by Keyword: Microstructure

Abstract: In this work, Fe₃₅Cr₃₅Ti₁₀Ni₁₀Zr₁₀ (at%) is a new light-weight medium entropy alloy subjected to different annealing conditions (at 700 - 1000°C for different durations) to examine its thermal stability, microstructural evolution, and microhardness change. The developed alloy was characterized by Optical light microscopy, X-ray diffraction (XRD), and Vickers microhardness. It was observed that the alloy demonstrated high microhardness value of ~707and high thermal stability with minor changes in its microstructures after different annealing treatments. These excellent properties displayed by the alloy highlight its promise for high-temperature applications.

Abstract: This study investigates the influence of the thermal cycle induced by the multipass weld bead when double-pulsed Gas Metal Arc Welding (GMAW-DP) is used to join duplex stainless steel (DSS) with Lean Duplex Stainless Steel (LDSS) welds, with emphasis on microestructure evolution. The microstructures of the heated affected zone (HAZ) and weld metal (WM) were analysed by light optical micorscopy (LOM), scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS) and high-energy synchrotron X-ray diffraction (HEXRD) in the different passes. They are formed by austenite and ferrite with different morphologies and fractions, associated to the dilution and thermal cycle experienced. The ferrite content was between 50 and 80%, considering the consumable used. Mechanical behaviour was evaluated by Vickers microhardness profiles. These results provide experimental data that contribute to the understanding of dissimilar welding of duplex stainless steels through GMAW-DP process.

Abstract: 17-4 Precipitation hardenable (PH) stainless steel (SS) is useful for applications that require a combination of high strength and corrosion resistance. However, when produced through selective laser melting (SLM), it has a distinct microstructure with significant composition and phase variations based on the process parameters and post processing heat treatment conditions. Therefore, the present study examines how process parameters, such as scanning speed and hatch distance, affect the microstructural, and corrosion characteristics of additively manufactured (AM) 17-4 PH stainless steel samples. Post-processing heat treatment resulted in a uniform and reproducible microstructure in SLM samples. Heat-treated AM samples were assessed in a 3.5 wt. % NaCl solution using electrochemical impedance spectroscopy (EIS). The specimen with an energy density of 39.06 J/mm³ exhibited the lowest open circuit potential value, indicating a favorable tendency to form a passive film. The sample with 66.96 J/mm³ exhibits enhanced corrosion resistance attributed to robust protective performance facilitated by a dense network of precipitates and finer grain size. This heightened resistance is further supported by the sample's highest corrosion layer resistance and charge transfer resistance.

Abstract: The promotion of green and low-carbon initiatives has spurred the application of lightweight materials in steel/Al car bodies. The development and utilization of large Al alloy die-casting (DCAA) materials and thermo-formed steel plates (TFSS) impose higher demands on joining technologies of the steel/Al dissimilar material. Taking the innovative body with DCAA and TFSP as a case, this paper systematically investigates the principles, characteristics and forming progress of force-self-piercing riveting(FSPR) joining technology for two-layer and three-layer plates with DCAA and TFSP. The types of test samples, the combination of plates and the test methods of mechanical properties are designed. Using the TL4225/C611/CR5 plate combination, the riveting and forming processing, the microstructures and morphologies were studied. Based on it, the methods to achieve high-quality joints were obtained. For the joining of two-layer plates containing DACC and TFSP, better joint forming and higher joint strength can be obtained for the ideal arc gap filling. For the joining of three-layer plates, TFSP will affect the filling effect for the elastic-plastic deformation of the middle layer during the forming. Although the joint can meet the product design, but the strength index is significantly lower than that of the two-layer plates. Based on the relevant data in the course of this experiment, general rules of product design for FSPR joining, such as joining space, flange edge size, plate strength and plate thickness, were analyzed and summarized combining plate characteristics, plate combination, die structure, joining method, joint strength and weld accessibility. The study will provide the technical support for the application of DCAA parts and TFSP in car bodies.

Abstract: In the field of ballistic protection systems, Wire Arc Additive Manufacturing (WAAM) technology represents an innovative approach. WAAM offers a novel solution for producing complex components in ballistic protection systems. The process involves using an electric arc to melt metal wire, which is deposited layer by layer to form the desired structure. This method enables the creation of intricate geometries, presenting new possibilities for enhancing the ballistic resistance of protective systems. In this study, WAAM technology was employed to manufacture strike face layers for ballistic protection, with two types of welding wires selected to fabricate bimetallic composites. The produced components were evaluated in three configurations (COW, MCH, and Bim), which were subjected to ballistic testing with 7.62 mm FMJ M80 projectiles in accordance with the NATO AEP-55 STANAG 4569 standard. The results revealed that configuration II (MCH) exhibited complete ballistic resistance, meeting NATO AEP-55 STANAG 4569 level 1, while configuration III (Bim) demonstrated a higher velocity reduction compared to configuration I (COW).

Abstract: High entropy alloys (HEAs) are a novel type of material with distinct features caused by their atypical compositions. However, their microstructure and mechanical qualities are greatly dependent on processing parameters. Laser cladding is a versatile method for producing HEA coatings, but optimizing the process to achieve the required microstructure and hardness remains a difficulty. Therefore, this work analyses the impact of laser processing parameters, especially laser power and scan speed, on the microstructure and hardness of AlCrFeNiMn HEAs manufactured via laser cladding. The AlCrFeNiMn HEA was successfully created utilizing the laser metal deposition process and several analyses were conducted. Columnar grains were discovered on alloy samples produced with 1500W laser power. As the laser power rose to 2200W coarse columnar dendritic microstructures were discovered. Samples processed with 2400W laser power showed the fewest visible fractures with an increase in scanning speed. As the laser power increased, the hardness of samples decreased from 427 Hv to 382 Hv.

Abstract: A dilute Al-0.083Sc-0.21Zr-0.07Y-0.025Co-0.063Ni-0.10Si (in wt.%) alloy is investigated by hardness and conductivity tests and phase obervation via TEM, HREM and STEM-EDS analysis. The results showed that the alloy achieved a peak hardness of 54.5 HV after annealing at 400°C for 36h while electrical conductivity also reached a plateau. Al₃(Sc,Zr,Y) phase, AlFeNi phase and AlScNiSi phase co-exist in the alloy. Al₃(Sc,Zr,Y) phase possessed spherical shape with a dense distribution and a size range of 6-13nm, the average size, volume fraction and number density were 9.0nm, 0.38% and 6.07×10²¹, respectively. The quantity of AlFeNi phase and AlScNiSi phase are quite small and they had a sparse distribution. Thereinto, the former one possessed rod shape and was coherent with the matrix. Co did not participiate phase formation. This provided a new thought for heat-resistant alloy design.

Abstract: Resistance spot welding (RSW) is a key body-in-white welding technique. The copper alloy (CA) electrode cap (EC) is the most important factor that affects the quality and cost of welding. It is difficult for the existing CrZr EC to meet the high quality and low cost of welding new materials, such as thermoformed steel (TFS) plates. The microstructural and physicochemical characteristics and electrode cap service life of Al₂O₃ and rare earth (RE) copper alloy ECs under welding heat-pressure cycle during their service life were studied to find new EC materials to solve the problems mentioned above. The results show that the Al₂O₃ EC has high hardness, and Al₂O₃ is distributed in the form of spherical or elliptical particles. Under the action of heat-pressure cycle, they are constantly broken and refined, which further improves the creep resistance at high temperature and the life of the EC. Under the same conditions, the microstructures of the RE EC gradually changed from regular twins to fine grid-shaped twins, which played an active role in preventing dislocation movement and improving creep resistance. Al₂O₃ and RE can change the microstructures and interfacial behaviors via different mechanisms to improve the high-temperature creep resistance. Al₂O₃ EC is suitable for welding AlSi-coated plates, such as TFS plate, and prevents further erosion of the surface owing to its ceramic properties. RE EC is suitable for welding galvanized plates because of its special twin microstructures, which can change the properties and structure of the erosion layer and reduce the interfacial tension. The study of the microstructures and interface layer characteristics of the two ECs provided a theoretical basis and research direction for the development and life improvement of ECs.

Abstract: Advanced High-Strength Steel (AHSS) grade 980 is essential in industries demanding superior mechanical performance, such as automotive and aerospace engineering. This study investigates the laser surface hardening (LSH) process as a method to enhance surface properties, emphasizing the influence of varying laser power levels on microstructural and mechanical outcomes. Key microstructural zones, i.e. melting zone (MZ), hardening zone (HZ), and heat-affected zone (HAZ), were analyzed, and each contributes distinctively to the improved surface characteristics. The findings demonstrated significant enhancements in surface hardness, achieving peak values of 591 HV under optimized conditions. Additionally, the process enabled precise control over microstructural refinement and the depth of hardening. These results underscore LSH as an effective and adaptable technique for optimizing AHSS 980, providing enhanced wear resistance and long-term durability for high-performance applications.

Abstract: Developing titanium aluminides (Ti-Al) based alloys by means of Laser Engineered Net Shaping (LENS) in-situ manufacturing presents attractive properties as compared to other fabrication methods. Ti-Al alloys have attracted much attention for high-temperature performance in gas turbine and automobile applications because of their attractive properties such as low density, high strength, high stiffness, and good oxidation resistance. In this work, laser in-situ fabricated Ti-Al-Nb-Cr quaternary alloys were developed. The samples were exposed to 1350°C and cooled in air for stress relief and for homogenizing phase distribution before characterization, corrosion behaviour and oxidation properties were investigated. From the electrochemical performance results, sample QT1 and QT2 displayed high potential and high current densities with the values of-0.33931V, -0.36934V and 5.77E-05A/cm², 4.89E-05A/cm², respectively and the corroded SEM proves that the samples had minimal structural damage. The minimum mass gain was observed during oxidation test proving that Ti-Al-Nb-Cr alloys have outstanding oxidation properties for potential high temperature application.