Reza Gholizadeh

Kyoto University | Kyodai · Dept. of Materials Science & Engineering

Ultrafine-grained (UFG) high-Mn austenitic steel exhibited unusual discontinuous yielding on its stress-strain curve, characterized by a yield drop followed by a stress plateau, indicative of Lüders deformation. Utilizing the digital image correlation (DIC) technique, a strain-localized region known as a Lüders band was observed to propagate during...

Medium-entropy alloys (MEAs) have recently emerged as potential replacements for traditional alloys in high-performance applications. Among the various MEAs developed, equi-atomic CoCrNi MEA stands out for its excellent mechanical performance. Nevertheless, the yield strength of this MEA having a single-phase FCC structure is not exceptionally high...

Microstructural evolution and changes in hardness and electrical conductivities of a cast hypoeutectic Cu-2.7at%Zr alloy processed by high-pressure torsion (HPT) were investigated. The cast alloy had a net-like microstructure composed of a primary Cu phase and a eutectic consisting of layered Cu and Cu5Zr phases. The Cu and Cu5Zr phases in the eute...

Grain boundary α A B S T R A C T The coarse lamellar microstructure of as-cast α+β titanium alloys can be effectively refined by boron additions, which has mainly been attributed to the precipitation of TiB whiskers that pin the growth of prior β grains. Here, we report an alternative mechanism of colony refinement in Ti-6Al-4V alloy containing tra...

Interstitial oxygen embrittles titanium, particularly at cryogenic temperatures, which necessitates a stringent control of oxygen content in fabricating titanium and its alloys. Here, we propose a structural strategy, via grain refinement, to alleviate this problem. Compared to a coarse-grained counterpart that is extremely brittle at 77 K, the uni...

A number of recent studies have investigated deformation behavior of CoCrFeMnNi (Cantor) alloy at elevated temperatures by using plastic deformation to relatively small strains such as tensile testing. Therefore, little has been known about the deformation behavior of this typical FCC high-entropy alloy (HEA) in case that the material is subjected...

In this study, we systematically investigated the influences of nitrogen content and grain size on the tensile properties and deformation behaviors of titanium at room temperature. By high-pressure torsion and annealing, we obtained ultrafine-grained (UFG) Ti-0.3wt.%N alloy with a fully recrystallized microstructure, which combined an unprecedented...

Changes in the microstructure and mechanical properties during annealing at 800 °C have been characterized in a 90% cold-rolled AlCoCrFeNi2.1 eutectic high-entropy alloy containing the FCC and B2 (ordered BCC) phases. In the as-rolled condition, the FCC phase is found to contain a high frequency of finely spaced deformation-induced boundaries, whic...

In contrast with pseudo-elasticity, martensite induced by plastic straining is known to exhibit limited further transformability and reversibility. The mechanistic and atomistic nature of a face-centered cubic (FCC)-hexagonal close-packing (HCP)-FCC sequential martensitic transformation pathway is investigated. Both transformations exhibit in the p...

Ultrafine β grain structures with recrystallized morphologies were fabricated by severe plastic deformation and subsequent annealing in Ti-10Mo-8 V-1Fe-3.5Al alloy. The minimum mean β grain size of 480 nm was obtained for the first time as a recrystallized structure in Ti alloys. Precipitation behavior of α in subsequent aging significantly changed...

An interstitial free (IF) steel having single-phase bcc-structure (<∼900 °C) and a SUS-304 stainless steel having single-phase fcc-structure were deformed to high strains by torsion at different temperatures and strain rates. Various grain sizes ranging from 0.6 μm to 46 μm in the IF steel and those from 0.4 μm to 44 μm in the SUS-304 steel were pr...

Single-phase bcc-ferrite in an interstitial free (IF) steel was deformed to different strains in a wide range from low to high strains (ε = 1–7) by torsion under different Zener-Hollomon (Z) conditions. The specimens were rapidly quenched after the torsion to preserve microstructures formed under different deformation conditions. The results showed...

In this study, the hot deformation behavior and microstructural evolution of Ti–6Al–4 V alloy having a lamellar initial microstructure were systematically investigated within a wide range of deformation temperatures (700–950 °C). Flow softening was commonly observed in the true stress–strain curves and the amount of flow softening gradually decreas...

Severe plastic deformation (SPD) have had a revolutionary impact in fabricating ultrafine grained (UFG) or nanostructured metallic materials with bulky dimensions. It is, however, difficult to understand from a viewpoint of conventional metallurgy why UFG microstructures form in the as-deformed (as-SPD-processed) state without annealing process. Th...

Single-phase ferrite of an interstitial free (IF) steel was continuously deformed by torsion to high strains (>5.5) at various temperatures and strain rates; i.e., under various Zener–Hollomon parameter (Z) conditions (Z = 10^30 s−1–10^15 s−1). Accordingly, different microstructures composed of ultrafine, fine, and coarse grains (0.6 µm–46 µm) were...

The dynamically evolved microstructure under high strain deformation condition does still have many debatable aspects, particularly in the case of easy-recovery metals like bcc-iron. In this research, microstructural evolution in high strain deformation by hot torsion of Ti-added interstitial free (IF) steel was systematically investigated. Torsion...

In this study, the effect of cooling rate on the microstructure, solidification parameters, and mechanical property of LM13 alloy has been investigated. To obtain different cooling rates, an air-cooled graphite mold, 3 sand molds with different moisture content, a water-cooled graphite mold, and a water-cooled steel mold were used. The cooling rate...

Multicomponent Al-Si-Ni-Cu-Mg alloys are widely used as automotive piston materials. The aim of the present work is to study the complicated formation of different intermetallic compounds during the solidification of two types of piston alloys: LM13 alloy with 0.9Ni-0.9Cu-1Mg and 3HA alloy containing 2.6Ni-3Cu-0.2Mg. Solidification events were dete...

Dense precipitation of various intermetallic compounds is a common feature in the microstructure of Al-Si piston alloys. In this investigation, microstructure of LM13 alloy and three high Cu-containing Al-Si piston alloys with different amounts of Ni, Fe, and Mn were studied by means of optical microscopy (OM) and scanning electron microscopy (SEM)...

The aim of this work is to partially substitute Fe and Mn for Ni in the 3HA piston alloy and to study the consequences through microstructural evaluation and the thermal analysis technique. Three types of near-eutectic alloys containing (2.6wtpct Ni-0.2wtpct Fe-0.1wtpct Mn), (1.8wtpct Ni-0.75wtpct Fe-0.3wtpct Mn), and (1wtpct Ni-1.15wtpct Fe-0.6wtp...