Papers by Keyword: Microstructure

Abstract: Characterization, classification, and size distribution of non-metallic inclusions (NMIs) in a cast high-Mn TWIP steel (Fe-20Mn-0.6C-1.5Al-0.3V, in wt.%), were studied to explore their interplay with the fracture mode during tensile deformation. NMIs were separated by electrochemical extraction, and subsequent X-ray dispersive analysis was performed to characterize their compositions. Subsequently, 70 % cold rolled TWIP sheets were processed and undergone fast heating annealing (FHA) at a heating rate of 200°C/s to anneal at temperatures 750 - 850 °C for 30 s. The grain structures achieved by FHA were evaluated by EBSD. The mechanical properties were determined by tensile testing. Distinct categories of NMIs, including Al2O3 and Mn (S,Se), and (Ti,V)N nitrides, and intricate combinations of inclusions, were identified. FHA process at low temperatures, 750-800 °C, promoted partially recrystallized microstructures. Fully recrystallized structures were obtained at 850 °C characterized by an average grain size of 2 µm at 850 °C. The structure promoted at FA 850 °C displayed noteworthy elongation of 60% with a yield strength (YS) and tensile strength (TS) of 410 and 830 MPa, respectively. A minimal effect of NMIs in TWIP steel was observed due to activating mechanical twinning mechanism, which overcomes the detrimental impact of NMIs and retard the necking induced by void formation related to NMIs.

Abstract: This study investigates the influence of symmetric and asymmetric hot rolling on the microstructural evolution and mechanical performance of a homogenized Mg–1.5Zn–0.5Ca (ZC1) alloy. X-ray diffraction confirmed phase stability across all processing conditions, with α-Mg as the primary matrix and Mg₆Zn₃Ca₂ as the secondary phase. Scanning electron microscopy revealed progressive fragmentation and redistribution of intermetallic particles upon rolling, with asymmetric rolling introducing higher shear strain and promoting dynamic recrystallization. Mechanical testing showed that symmetric rolling delivered the most favorable strength–ductility combination (UTS: 230 MPa, Elongation: 37%), while asymmetric rolling exhibited the highest yield strength (121 MPa) and microhardness (59 HV). Despite the intensified strain effects in asymmetric rolling, symmetric rolling provided superior mechanical synergy due to more uniform grain refinement and stable phase distribution. The findings highlight symmetric rolling as a robust and scalable deformation route for enhancing mechanical performance in Mg-Zn-Ca alloy systems.

Abstract: Anatase-type TiO₂ films synthesised on quartz glass demonstrated cell adhesion control when illuminated from the backside with a 150 W Xe lamp emitting white light. The UV component was fully absorbed by the TiO₂ film, preventing cell exposure to it. By selectively applying localised light, non-contact control of cell adhesion areas was achieved. If non-toxic films responsive to conventional LED panels could be used, this would enable precise and easy control of cell adhesion areas. The purpose of this study was to synthesise inorganic semiconductor films with a narrower bandgap than TiO₂, responding to visible light from LED, and to investigate their photo-responsive properties. α-Fe₂O₃ films were deposited on borosilicate glass or ITO-coated quartz glass using RF sputtering with the corresponding metallic targets under an Ar or Ar/O₂ mixed atmosphere. XRD analysis showed sharp diffraction peaks, confirming the successful synthesis of the films. The absorption edges of the oxides shifted to longer wavelengths compared to that of TiO₂, corresponding to their bandgap differences. When a tablet device (HUAWEI MediaPad M3 Lite 10wp) displaying a white image was used as a light source, the oxide films showed a noticeable photocurrent. In the photocurrent profile during the on/off cycle of the light, a phenomenon of current flowing in the reverse direction when the light was turned off was observed. Moreover, this current reversal was more pronounced when the grains were fine. This suggests that the grain boundaries acted like a capacitor and induced polarisation behaviour.

Abstract: Laser powder bed fusion (LBPF) is currently the most mature metal additive manufacturing (AM) technology. While it does not have the same flexibility as directed energy deposition techniques to produce compositional gradients, LPBF can still be used to generate bimetallic parts by depositing one metal on a build plate made of another. Here, we print combinations of Ti-6Al-4V with Ta and characterize defects that occur at the interface. We use thermodynamic modeling to explain the formation of keyhole porosity and solidification cracks when Ta is built on a Ti baseplate, and the lack of defects when the materials are reversed. By understanding the mechanisms that lead to defect formation, the methodology demonstrated here can be applied to other material systems to efficiently design bimetallic LPBF processes.

Abstract: This study investigates polymer component manufacturing using fused deposition modeling, specifically focusing on the thermoplastic PLA-Cu in open-source FDM machines. Mechanical characteristics are explored, emphasizing infill density, pattern, and nozzle temperature. FDM-produced PLA-Cu specimens, varying in infill (60%, 80%, 100%) and patterns (TRIANGLE, HEXAGON, LINE), reveal superior mechanical properties in those with 100% density, TRIANGLE pattern, and a 210° nozzle temperature. ASTM-standard tests measure tensile and flexural strength, and scanning electron microscopy examines micro-morphology. Results indicate a correlation between increased strain rate and higher yield stress and elastic modulus in PLA-Cu specimens, emphasizing its engineering potential.

Abstract: The superplastic deformation behavior, microstructure evolution in the volume and on the FIB-milled surface of the samples of fine-grained AA5083-type alloy with an initial grain size of ~5 µm were investigated, and the role of deformation mechanisms was discussed for two superplastic deformation regimes (1) a strain rate of 1×10^-3 s^-1 and a temperature of 0.87T_i.m. and (2) a strain rate of 5×10^-3 s^-1 and a temperature of 0.97T_i.m.. The m values were ~0.45-0.55 and elongations to failure were ~300% and ~600% for the first and second regimes, respectively. According to the shifts of the marker grid lines after straining to e=0.41, GBS contributed ~33% and ~23% to the total strain in the low-temperature and high-temperature deformation, respectively. The dislocation-induced intragranular deformation provided ~30% for the low temperature regime and ~20 % for the high temperature regime, and remaining 30-50% of strain was localized in the striated zones formed at the across grain boundaries due to both GBS and diffusion creep deformation mechanisms. Considering the strain induced by grain elongation for the low and high temperature deformation regimes, it was concluded that diffusion creep contributed 23% and 34% of the total deformation, and the recalculated GBS contribution, including both FIB grid shifts and a portion of the strain localized in the striated regions, was 43% and 38%, respectively.

Abstract: Nickel-based coatings are a vital technology in industrial applications, offering protection to metallic objects against high temperatures, wear, corrosion, and erosion. The current research work examines the deposition of NiCrBSi powder in Stainless steel (AISI SS 304) using the high-velocity oxy-fuel (HVOF) thermal spray coating technique. The effects of HVOF-deposited NiCrBSi coatings on the microstructure, morphology, and mechanical and physical properties of the coated stainless steel. Microstructural and morphological analyses were performed using scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), and X-ray diffraction (XRD) to characterize the coating. The coatings were systematically assessed for surface roughness, deposition efficiency, coating thickness, and porosity. Adhesion strength was measured using a pull-off adhesion tester to ensure robust bonding. The results demonstrate that HVOF-sprayed NiCrBSi coatings possess low porosity (2-3%), strong adhesion (45–55 MPa), and increased hardness, making them highly suitable for high-temperature, anti-wear applications, with improved durability and performance under harsh operating conditions.

Abstract: Mg-Al-Zn alloy, an Mg alloy having Al and Zn as the major constituents, is exceptionally lightweight and has potential to become an essential component of modern engineering applications and healthcare systems. This paper presents valuable insights to the friction stir processing (FSP) applied to Mg-Al-Zn alloy in dry conditions. FSP induced extreme plastic deformation in the metal alloy which causes substantial microstructural alterations. These changes were investigated using optical microscope. Microstructural evaluation of FSP-processed zone indicated that average grain diameter of the FSP-processed zone increased in proportion to tool rotating speed. This is attributed to the frictional zone's degree of plastic deformation. In alignment with results obtained from optical microscopy, morphological study conducted using scanning electron microscope (SEM) also demonstrated the synthesis of refined grains. In addition, the study includes evaluation of the FSP-processed alloy's micro-hardness and tensile characteristics in contrast to the base (unprocessed) alloy.

Abstract: ZnO thin films were deposited on borosilicate glass substrates by confocal radio frequency (RF) magnetron sputtering and subsequently annealed in air at 300 °C and 500 °C for 60 min. The influence of thermal treatment on the structural, morphological, optical, and electrical properties was systematically investigated. X-ray diffraction (XRD) confirmed the formation of a hexagonal wurtzite phase with a pronounced (002) preferential orientation. Rietveld refinement analysis revealed that annealing led to a decrease in the lattice parameter c from 5.344 Å to 5.220 Å, an increase in crystallite size from 9.3 nm to 34.1 nm, and a reduction in microstrain from 0.0265 to 0.0027. Raman spectroscopy exhibited a sharper E₂^high mode at 438 cm^-1 and a suppressed defect-related A₁(LO) mode (583 cm^-1), evidencing enhanced crystallinity and defect passivation. Scanning electron microscopy (SEM) observations revealed grain coalescence and densification with increasing annealing temperature. The average optical transmittance improved from 70.8% to 82.2%, accompanied by a slight widening of the optical band gap from 3.22 eV to 3.27 eV. Hall measurements indicated a marked decrease in resistivity from 2.7 × 10^-2 Ω·cm to 5 × 10^-3 Ω·cm, yielding a maximum figure of merit of 1.68 × 10^-3 Ω^-1 at 500 °C. Overall, post-deposition annealing is shown to significantly enhance crystallinity, reduce structural defects, and improve the optoelectronic performance of ZnO thin films, confirming their suitability for transparent electronics and photovoltaic applications.

Abstract: This study investigates how heat treatment affects the mechanical properties and microstructure of extruded AA2017 aluminum alloy. Quenching (icy water vs. liquid nitrogen) and tempering (T6: 120–160°C; T7: 240°C) significantly alter hardness, tensile strength, and fatigue life. T6 promotes fine, coherent precipitates, enhancing strength and fatigue resistance, while T7 leads to over-aging and property degradation [X]. Icy water quenching improves fatigue life over liquid nitrogen by refining precipitates [Y]. Microstructural analysis reveals elastic adaptation (T6) and plastic shakedown (T7) as fatigue stabilization mechanisms, with fracture modes shifting from ductile (T6) to mixed ductile-brittle (T7) [Z]. These results optimize heat treatment for AA2017 in high-strength, fatigue-critical applications.