Papers by Keyword: Microstructural Refinement

Abstract: In this study, the impact of heat treatment and Equal Channel Angular Pressing (ECAP) processing routes on refining the microstructure, hardness, and corrosion resistance of Al-7.5% S alloy in a 3.5% NaCl solution was examined. The alloy underwent T5 and T6 heat treatments, followed by ECAP processing via routes A and Bc in a mold with a channel angle of 120° at room temperature. The results indicate that dendritic α-Al grains transformed to globular and fiber shapes after processing routes Bc and A, respectively. Both processing routes fragmented coarse and brittle Si particles into smaller sizes in the eutectic phase. The use of a combination of heat treatment and the Equal Channel Angular Pressing (ECAP) process significantly improved the hardness and corrosion resistance of the samples. The hardness of the heat-treated samples increased considerably from 68 to 116 and 129 HV after three and four passes, respectively. Reducing the area ratio between the noble silicon particles and the less noble eutectic aluminum phase greatly enhances the resistance of alloy to pitting corrosion.

Abstract: This article presents an investigation into the impact of High Pressure Torsion Extrusion (HPTE) on the microstructural features, hardness and hydrogen storage, focusing on pure magnesium. HPTE is a modern mechanical nanostructuring technique that can refine the microstructural properties and subsequently affects the mechanical and functional properties of the materials. Two HPTE regimes were used in this study: (1) Direct Extrusion without rotation (DE), and (2) an extrusion speed of 6 mm/min along with a rotational speed of 1.8 rpm (v6w1.8). One sample in as-received conditions was also tested as a reference. Results showed increased hardness in the material after HPTE processing, with the DE sample reaching 60 HRB and the v6w1.8 sample exhibiting a gradient distribution of hardness from 71 to 83 HRB. X-ray diffraction analysis revealed significant microstructural refinement in the v6w1.8 sample. Results of hydrogenation kinetics showed that the DE sample absorbed up to 1.2 wt.% of hydrogen, while the v6w1.8 sample displayed 7.2 wt.% of hydrogen absorption, approaching the theoretical hydrogen storage capacity for magnesium (7.6 wt.%). These findings highlight the positive effects of HPTE on microstructural refinement and hydrogen storage, showcasing its potential for advancements in materials science and hydrogen-based energy technologies.

Abstract: This study aimed to evaluate the effects of extrusion process and subsequentheat-treatment on microstructural evolution and mechanical properties of Mg-4%Y alloy. Theresults showed that the dynamic recrystallization occurred during extrusion, the microstructure istiny equiaxial grains, the shearing stripes and parallel streamlines which distribute along theextrusion direction are especially obvious. The tensile curve has obvious yield phenomenon. Afterannealing, parallel streamlines disappear, the yield phenomenon of tensile curve eliminates, theyield strength(σ0.2) and the tensile strength(σb) decrease, the plasticity increases. The underneathmechanism for mechanical properties can be ascribed to the weak pining effect of second-phaseparticles on the movement of dislocation and release of the pile-up dislocations.

Abstract: The surface of body-centred cubic Fe-7Al (mass%) alloy plate was successfully modified by friction stir processing with SiC particles addition. The stir zone with SiC addition had an average grain size of 5.9 μm, smaller than that of 10.1 μm in the stir zone without SiC addition. SiC particles introduced by friction stir processing were converted to fine Fe₃AlC_x particles by reaction with the ferrite matrix. The hardness near the surface of the stir zone was significantly increased to 351 HV by introduction of particles, compared to the hardness of 200 HV in the stir zone without particles addition. The dispersed particles also contributed to suppression of grain growth of the matrix at elevated temperature.

Abstract: A novel β-type, Ti-29Nb-13Ta-4.6Zr, referred to as TNTZ has been developed for biomedical applications. Its fatigue strength is one of the most important mechanical biocompatibilities of TNTZ because, in surgical applications, it will be used under cyclic loading conditions. The effect of the microstructural refinement by high-pressure torsion (HPT) on the fatigue behaviour of TNTZ is systematically investigated in this study. TNTZ subjected to HPT processing where the rotation number (N) is 20 (TNTZ_AHPT) after aging treatment (AT) shows a unique microstructure having ultrafine elongated grains (285 nm in length and 36 nm in width) with high-density dislocations, a large fraction of blurred and wavy boundaries consisting of non-uniform subgrains with high misorientation and nanostructured precipitated α phase. Remarkably, a good combination of high mechanical strength (1375 MPa) and low Young’s modulus (87 GPa), compared to that of Ti-6Al-4V (Ti64) ELI, is achieved for TNTZ_AHPT at N = 20. TNTZ_AHPT a great fatigue strength, which is comparable to those of (Ti64) ELI.

Abstract: Modification of AISI D2 tool steel was conducted by friction stir processing (FSP). Effects of tool rotational speed on microstructural evolution and mechanical properties were investigated. Though coarse primary carbides in the size of 10-50 m were observed before FSP, fine carbides smaller than 20 m and martensitic matrix with fine grains were obtained after FSP. High hardness of over 900 HV, higher than the hardness in conventional D2 tool steel, was achieved under the condition of moderate rotational speed.

Abstract: In this study, a TMCP was attempted to obtain a low carbon high strength Nb-Ti microalloyed dual phase with low yield ratio at Baosteel. Optical and scanning electron microscopy was utilized to analyze microstructures. A mixed fine microstructures consisting of acicular ferrite and martensite/austenite was observed. The austenite maintained a small grain size during reheating in the temperatures ranging from 1100°C to 1250°C. The growth of austenite was strongly retarded by Nb and Ti nitride and carbide. The higher end cooling temperature (650°C) had much influence on the refinement of microstructures, especially the length of ferrite packets, whereas the lower temperatures (600-500°C) had little effect on the microstructure refinement.

Abstract: The objective of this work is to present the results of the comparative analysis of YAG:Ce3+ microstructural parameters obtained from x-ray powder diffraction (XRPD) data using Rietveld based Koalariet and Fullprof programs. YAG:Ce3+ powder is obtained via low temperature aerosol route at 3200C followed by post annealing treatment. The chosen technique of synthesis, i.e. ultrasonic spray pyrolysis, provides the generation of spherically shaped and submicronically sized particles having composite nanostructure. Since the targeting garnet phase represents a very promising host phosphor material being doped with rare-earth ions, the most important criteria determining its applicability in various optical devices is the uniform distribution of the luminescent center in the host lattice as well as the cubic YAG phase crystallinity. Comparison of the data obtained for the same samples by the above mentioned XRPD analyses gives us an insight into the validity of the refined parameters.

Abstract: Mechanical behavior and microstructure evolution of Ti and Ti-64 titanium alloy during warm “abc” deformation has been studied. The “abc” deformation was consisted of successive compression of a sample along three orthogonal directions. Mechanical behavior of each material was described by set of successive σ-ε curves combined into cumulative σ-Σε curve. Microstructure of Ti was found to be refined to a grain size of about 0.4 μm due to formation of deformation-induced boundaries within initial grains. Although a stage like steady state flow was observed at the cumulative σ-Σε curve such mechanical behavior was hardly associated with superplastic flow. In two-phase Ti-64 alloy the structure was found to be refined to a grain size of about 0.4 μm after warm “abc” deformation due to globularization α- and β-particles following breaking down of α-lamellar and β- layers. Microstructure refinement of the alloy was associated with softening and superplastic flow.