The Study of Thermal Stability of Mechanically Alloyed Al-5 wt.% TiO₂ Composites with Cu and Stearic Acid Additives

In this work, we studied the effect of thermal exposure on the microstructure and mechanical properties of an Al-5 wt.% TiO2 composite material with additions of 5 wt.% Cu and 2 wt.% stearic acid as a process control agent (PCA), obtained by mechanical alloying. The composite was processed in a ball mill for 10 h. Composite granules were consolidated by hot pressing at 400 °C. SEM, XRD, and DSC analyses were used to study the microstructure, phase composition, and thermal behavior, respectively. Studies showed that the hot pressing of the material with copper addition leads to the precipitation of Al2Cu particles from the supersaturated solid solution and a decrease in the microhardness to 233 HV in comparison with the as-milled state (291 HV). In the material with a PCA additive, on the other hand, the microhardness increases from 162 to 187 HV due to the formation of aluminum carbide nanoparticles. In both cases, no reduction reaction products were found. At the same time, the Al-5TiO2-2PCA material after hot pressing shows a more stable grain structure than the Al-5TiO2-5Cu material. In addition, the compressive strength at 300 °C of the former material is 1.7 times higher than that of the latter one

Microstructure and Hot Deformation Behaviour of a Novel Zr-Alloyed High-Boron Steel

A novel corrosion-resistant steel with high boron content is investigated in this paper. Three stages during crystallisation of the steel are revealed. The positive influence of Zr addition on the microstructure and mechanical properties after hot deformation is shown. The Zr-alloyed steel demonstrates hot deformation without fracturing in the temperature range of 1273⁻1423 K, and in the strain rate range of 0.1⁻10 s−1, despite the high volume of brittle borides. The processes of ferrite recrystallisation and boride structure fragmentation occur during hot deformation, promoting the appearance of a peak on stress⁻strain curves

Single track scanning experiment on the hypereutectic aluminium alloy Al-8%Zn-7%Ni-3%Mg

Solidification path, hot tearing susceptibility and processability by L-PBF of the hypereutectic aluminium alloy Al-8%Zn-7%Ni-3%Mg were investigated. It was shown that the alloy has an advantageous hot tearing resistance due to formation of an adequate amount of the [(Al)+Al3Ni] eutectic and a reduced effective solidification range. In that sense, it may be valid for L-PBF. To prepare a feedstock for L-PBF, we produced chips which were subsequently grinded by high-energy ball milling into a 100 µm fine powder batch. The powder contained irregular shape particles that may have led to failure in fabrication of regular single tracks at a laser power of 170-250 W and scanning speed of 200-350 mm/s. Whilst from on-top view all the tracks had defects like balling and irregularity, their cross-sections also revealed a high degree of penetration into 5052 alloy substrate. Most structures showed a level of mixing of 5/1 between the substrate and the experimental alloy. The most successful track obtained at 250 W and 250 mm/s showed an inhomogeneity in distribution of the alloy-rich regions. Meanwhile, no defects and no primary Al3Ni phase were observed. The present study serves as an initial one for further research which may be focused on producing of a finer powder, assessment of different layer thicknesses and fabrication of bulk specimens

Single track scanning experiment on the hypereutectic aluminium alloy Al-8%Zn-7%Ni-3%Mg

Solidification path, hot tearing susceptibility and processability by L-PBF of the hypereutectic aluminium alloy Al-8%Zn-7%Ni-3%Mg were investigated. It was shown that the alloy has an advantageous hot tearing resistance due to formation of an adequate amount of the [(Al)+Al3Ni] eutectic and a reduced effective solidification range. In that sense, it may be valid for L-PBF. To prepare a feedstock for L-PBF, we produced chips which were subsequently grinded by high-energy ball milling into a 100 µm fine powder batch. The powder contained irregular shape particles that may have led to failure in fabrication of regular single tracks at a laser power of 170-250 W and scanning speed of 200-350 mm/s. Whilst from on-top view all the tracks had defects like balling and irregularity, their cross-sections also revealed a high degree of penetration into 5052 alloy substrate. Most structures showed a level of mixing of 5/1 between the substrate and the experimental alloy. The most successful track obtained at 250 W and 250 mm/s showed an inhomogeneity in distribution of the alloy-rich regions. Meanwhile, no defects and no primary Al3Ni phase were observed. The present study serves as an initial one for further research which may be focused on producing of a finer powder, assessment of different layer thicknesses and fabrication of bulk specimens

The Effect of Ce on the Microstructure, Superplasticity, and Mechanical Properties of Al-Mg-Si-Cu Alloy

The current study focuses on the influence of Ce on the superplastic behavior, microstructure, and mechanical properties of the Al-Mg-Si-Cu-Zr-Sc alloy. The multilevel microstructural analysis including light, scanning electron, and transmission electron microscopies was carried out. The simple thermomechanical treatment including the hot and cold rolling resulted in fragmentation of the eutectic originated particles of the Ce-bearing phases. The two-step annealing of the ingots provided the precipitation of the L12-structured Al3(Sc,Zr) phase dispersoids with 10 nm mean size and a high number density. Due to the particle stimulated nucleation (PSN) effect caused by the particles of eutectic origin, and Zener pinning effect provided by nanoscale dispersoids of L12-structured phases, the studied alloy demonstrated good superplastic properties

Investigation of Hot Deformation Behavior and Microstructure Evolution of Lightweight Fe-35Mn-10Al-1C Steel

The deformation behavior of lightweight Fe-35Mn-10Al-1C steel with an elevated concentration of Mn was investigated. Hot compression tests at temperatures of 950–1150 °C and strain rates of 0.1–10 s−1 were carried out using the thermomechanical simulator, Gleeble 3800. Strain compensated constitutive model of hot deformation behavior with high accuracy (error was 4.6%) has shown significant increases in the effective activation energy (410–460 kJ/mol) in comparison with low Mn steels. The significant influence of the strain rate and temperature on the grain size was shown. The grain size decreases from the initial value of 42 ± 6 μm to the value of 3.5 ± 0.7 μm after the deformation at 1050 °C and 10 s−1. The model of the microstructure evolution of the investigated steel was constructed. The average error of the constructed model was 8.5%. The high accuracy of the constructed models allows for their application for the optimization of the hot deformation technologies using finite element simulation

Investigation of Hot Deformation Behavior and Microstructure Evolution of Lightweight Fe-35Mn-10Al-1C Steel

The deformation behavior of lightweight Fe-35Mn-10Al-1C steel with an elevated concentration of Mn was investigated. Hot compression tests at temperatures of 950–1150 °C and strain rates of 0.1–10 s−1 were carried out using the thermomechanical simulator, Gleeble 3800. Strain compensated constitutive model of hot deformation behavior with high accuracy (error was 4.6%) has shown significant increases in the effective activation energy (410–460 kJ/mol) in comparison with low Mn steels. The significant influence of the strain rate and temperature on the grain size was shown. The grain size decreases from the initial value of 42 ± 6 μm to the value of 3.5 ± 0.7 μm after the deformation at 1050 °C and 10 s−1. The model of the microstructure evolution of the investigated steel was constructed. The average error of the constructed model was 8.5%. The high accuracy of the constructed models allows for their application for the optimization of the hot deformation technologies using finite element simulation

The Effect of Isothermal Multi-Directional Forging on the Grain Structure, Superplasticity, and Mechanical Properties of the Conventional Al–Mg-Based Alloy

The current study observed a grain structure evolution in the central part and periphery of the sample of an Al–Mg–Mn-based alloy during isothermal multidirectional forging (IMF) at 350 °C with a cumulative strain of 2.1–6.3 and a strain per pass of 0.7. A bimodal grain size distribution with areas of fine and coarse grains was observed after IMF and subsequent annealing. The grain structure, mechanical properties, and superplastic behavior of the samples subjected to IMF with a cumulative strain of 6.3 and the samples exposed to IMF with subsequent cold rolling were compared to the samples exposed to a simple thermo-mechanical treatment. The micro-shear bands were formed inside original grains after the first three passes. The fraction of recrystallized grains increased and the mean size decreased with an increasing cumulative strain from 2.1 to 6.3. Significant improvements of mechanical properties and superplasticity were observed due to the formation of a homogenous fine grain structure 4.8 µm in size after treatment including IMF and subsequent cold rolling

Decrease in the Starting Temperature of the Reaction for Fabricating Carbides of Refractory Metals When Using Carbon Nanoparticles as Precursors

Metal matrix composites with a matrix of refractory metals (niobium, tungsten) and reinforcing nanodiamond particles were prepared for studying the possibility of decreasing the starting temperature of carbide synthesis. The size of primary nanodiamond particles was 4–6 nm, but they were combined in large-sized agglomerates. Mechanical alloying was used for producing the composites by crushing agglomerates and distributing nanodiamonds evenly in the metal matrix. The initial and fabricated materials were investigated by X-ray diffraction, differential scanning calorimetry, and transmission and scanning electron microscopy. Thermal processing leads to the reaction for carbide synthesis. Studies have found that the usage of carbon nanoparticles (nanodiamonds) as precursors for fabricating carbides of refractory metals leads to a dramatic decrease in the synthesis temperature in comparison with macro-precursors: lower than 200 °C for tungsten and lower than 350 °C for niobium