Lijia Zhao

Northeastern University (Shenyang, China) | NEU · Key Laboratory of Electromagnetic Processing of Materials

The primary columnar crystal deviates due to forced flow induced by a mold electromagnetic stirrer (M-EMS). On this basis, the flow field can be qualitatively analyzed. As the growth characteristics of primary columnar crystal by double stirrings are still unknown, an electromagnetic swirling flow in the nozzle (EMSFN) approach was applied with M-E...

Directional solidification experiments of eutectic AlFe alloys were carried out under different high magnetic field gradients. High magnetic field gradient changed the microstructure selection during solidification process, induced the solidification microstructure to undergo eutectic instability, cellular transition, single-phase instability, and...

Using Tb0.27Dy0.73Fe1.95 as a model alloy, we generate (Tb, Dy)Fe2 and (Tb, Dy)Fe3 phases with preferred orientations. We study the mechanism that determines the preferred crystal orientation of a peritectic alloy under high magnetic fields. Adjusting the preparation parameters yields four Tb0.27Dy0.73Fe1.95 alloys with respective 〈110〉, 〈111〉, 〈11...

Under the joint action of electromagnetic swirling flow in the nozzle (EMSFN) and mold electromagnetic stirring, Liquid level fluctuation in the mold is investigated to find the optimal combination parameters for the occurrence time of the minimum macrosegregation degree in continuous casting of round billet. When the current intensity of EMSFN dev...

Gas–liquid flow widely exists in industrial processes. Bubble refinement is of importance because smaller bubbles lead to higher efficiency of the gas–liquid interaction. Here, the novel rotating flow is designed for bubble refinement without using invasive parts. The drag force along the flow direction and the additional shear-lift force applied o...

To alleviate macrosegregation, it is the first time that an electromagnetic nozzle swirling flow is applied with a mold electromagnetic stirrer (M-EMS) during continuous casting of square and round billets. Compared with those by only M-EMS, the carbon ranges in square and round billets can be reduced to 0.022 and 0.046 pct, respectively, and the e...

We report evidence of a displacive phase transformation from retained austenite to martensite during preparation of quenched and partitioned steel micro-pillars by using a focused ion beam (FIB) technique. The BCC phase produced by the FIB damage was identified as martensite. The invariant-plane strain surface relief associated with the martensitic...

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...

Nowadays, a new concept of process utilizing dynamic ferrite transformation, which can achieve ultrafine-grained structure with a mean grain size of approximately 1 μm, has been proposed. This paper reports transformation mode of dynamic ferrite transformation and formation mechanism of ultrafine-grained structure revealed by our novel technique of...

Comparison on the kinetics of two different phase transformations, including phase transformation after deformation and phase transformation during deformation (i.e. dynamic transformation, DT), reveals a new discovery that the transformation kinetics can be significantly enhanced in DT even under low driving forces. DT enables continuous generatio...

The present work provides an insight into the phase-specific mechanical properties of the microstructural constituents in a quenching and partitioning (Q&P) processed steel. The mechanical properties of carbon-enriched retained austenite and low-carbon primary martensite were studied by nano-indentation tests. The results show that the hardness of...

Ultrafine grained (UFG) steels with grain sizes around 1 micron exhibit an excellent strength-ductility combination and have been extensively studied worldwide. Among the different grain refinement strategies, thermomechanical controlled processing (TMCP) employing dynamic transformation (DT), that is, ferrite transformation during deformation of a...

Fully recrystallized ultrafine-grained (UFG) pure Cu specimens were fabricated by high-pressure torsion (HPT) and controlled annealing. The recrystallized UFG Cu with a minimum mean grain size of 0.51 μm showed high yield strength, good ductility, obvious yield drop and large Lüders strain during tensile test. The mechanical behavior of the Cu spec...

Hot deformation behavior of an equiatomic CoCrFeMnNi high entropy alloy was investigated. Hot compression tests were carried out at various temperatures ranging from 800°C to 1000°C at different strain rates from 0.001s⁻¹ to 1s⁻¹. Stress-strain curves indicated softening due to dynamic recrystallization (DRX) under most conditions. Flow stress anal...

We have found a new strategy for ultra grain refinement without high strain deformation by combining dynamic transformation (DT) and dynamic recrystallization (DRX) mechanisms. Through simple thermomechanical processes using a total plastic strain of 0.92 at elevated temperatures, ultrafine grained microstructures having mean grain sizes down to 0....

The grain refinement mechanism of ferrite dynamically transformed (DT) from austenite is investigated in a 10Ni–0.1C steel. For decades, it has been debated whether dynamic recrystallization (DRX) contributes to the grain refinement of DT ferrite. Here, the authors show that the role of DRX has been previously underestimated in grain refinement of...

A fully recrystallized ultrafine-grained (UFG) Fe22wt.%Mn0.6wt.%C twinning-induced plasticity (TWIP) steel with mean grain size of 576 nm was fabricated by cold rolling and annealing process. Tensile test showed that this UFG steel possessed high yield strength of 785 MPa, and unprecedented uniform elongation of 48%. The Hall-Petch relationship was...

Steel rods are hot-rolled at high strains and strain rates with a subsequent controlled cooling process to influence the microstructure. The microstructure and mechanical properties of the hot-rolled rods are controlled to produce high-strength fasteners in the cold heading process without subsequent heat treatment. In the present study, simulation...

Dynamic recrystallization (DRX) is an important grain refinement mechanism to fabricate steels with high strength and high ductility (toughness). The conventional DRX mechanism has reached the limitation of refining grains to several microns even though employing high-strain deformation. Here we show a DRX phenomenon occurring in the dynamically tr...

Two novel two-step thermomechanical routes were developed to produce ultrafine-grained ferrite microstructures in a 10Ni–0.1C steel without high-strain deformation. Homogeneous ultrafine ferrite (UFF) structures having mean grain sizes down to 460 nm were fabricated by a total equivalent strain of 0.92 and exhibited high yield strength of 820 MPa w...

Fully recrystallized Cu-4 at.%Al alloy and Cu-11 at.%Al alloy with grain sizes ranging from 0.5 μm to 80 μm were fabricated by cold rolling and annealing. Tensile tests showed that yield strength, ultimate tensile strength and uniform elongation of the two Cu–Al alloys had linear relationships with the inverse square root of the grain size, and bot...

It is commonly accepted that twinning can induce an increase of strain-hardening rate during the tensile process of face-centered cubic (FCC) metals and alloys with low stacking fault energy (SFE). In this study, we explored the grain size effect on the strain-hardening behavior of a Cu-15 at.%Al alloy with low SFE. Instead of twinning, we detected...

A single-phase Cu–Al alloy with a low stacking fault energy was processed by cold rolling and subsequent annealing. Fully recrystallized microstructures composed of ultrafine grains were obtained after isothermal annealing at different temperatures. The minimum mean grain sizes achieved were below 1 μm. It was found that the microstructures were ho...

Metastable austenite in a Fe-24Ni-0.3C (wt.%) alloy was processed by high-pressure torsion and subsequently heat-treated. The HPT-processed material had lamellae structures composed of highly deformed austenite and deformation-induced martensite. The reverse transformation of the deformation-induced martensite and recovery/recrystallization of the...

Phase transformation from austenite to ferrite is an important process to control the microstructures of steels. To obtain finer ferrite grains for enhancing its mechanical property, various thermomechanical processes followed by static ferrite transformation have been carried out for austenite phase. This article reviews the dynamic transformation...

The effect of strain on the microstructural evolution of ferrite grains during dynamic transformation was investigated using a 10Ni-0.1C steel uniaxially compressed at a strain rate of 10-2 s-1 and temperature of 520 °C. The deformation of the ferrite formed at relatively early stages of dynamic transformation led to the formation of subgrains insi...

The effect of strain on the microstructural evolution of ferrite grains during dynamic transformation was investigated using a 10Ni-0.lC steel uniaxially compressed at a strain rate of 10−2 s−1 and temperature of 520 ℃. The deformation of the ferrite formed at relatively early stages of dynamic transformation led to the formation of subgrains insid...

A mechanical analysis is done to find the evolution of the interface profile between binary immiscible fluids induced by a three-dimensional orthogonal magnetic field gradient. In the experiments, the changes of the interface profile between four groups of binary immiscible fluids are investigated under the same horizontal magnetic field gradients....