Effect of heat treatment on the microstructure and hardness of Al0.3CoCrFeNi high entropy alloy

In this study, the cold-rolled Al0.3CoCrFeNi high entropy alloys were heat treated at 900°C for 30min and 1050°C for 20min, respectively, to investigate the effect of heat treatment on the microstructure of the alloy. The results showed that grain refinement occurred in the 900°C/30min annealed sample, while remarkable equiaxial grains and twins appeared in the 1050°C/20min annealed sample. The hardness of samples showed a decrease trend following: as-rolled sample, 900°C/30min annealed sample, and 1050°C/20min annealed sample, which can be attributed to the dislocation elimination caused by recovery and recrystallization.

The Effects of Annealing at Different Temperatures on Microstructure and Mechanical Properties of Cold-Rolled Al0.3CoCrFeNi High-Entropy Alloy

In this work, cold-rolling was utilized to induce a high density of crystal defects in Al0.3CoCrFeNi high-entropy alloys. The effects of annealing temperature on static recrystallization, precipitation behavior and mechanical properties were investigated. With increasing annealing temperature from 590 °C to 800 °C, the area fraction of recrystallized region increases from 26.9% to 93.9%. Cold-rolling deformation largely promotes the precipitation of B2 phases during annealing, and the characteristics of the precipitates are linked to recrystallization level. The coarse and equiaxed B2 phases exist in the recrystallized region and the fine and elongated B2 phases occupy the non-recrystallized region. Combined use of cold-rolling and annealing can remarkably enhance the strength and toughness. A partially recrystallized microstructure in a cold-rolled sample annealed at 700 °C exhibits a better combination of strength and toughness than a fully recrystallized microstructure in a cold-rolled sample annealed at 800 °C. Finally, related mechanisms are discussed.

Influence of Ageing Time and Different Ni wt.% on Triplex Steel

This paper presents a study of three types of Triples steel, where containing 16 to 28 wt.% manganese, 0.8 to 0.89 wt.% Carbon, 9.9 to 11.21 wt.% Aluminum, and with different Nickel content. We investigated the aging effect on properties of Triplex steel by using an optical microscope, scanning electron microscope (SEM) and X-ray diffraction (XRD). The used temperature in the ageing process is 550°C and we take three different times in that process (1min, 1hr, and 5hrs). The microstructure shows one austenite phase of an as-rolled sample without Ni and shows two austenite phases of an as-rolled sample with Ni content. The k-carbide, intermetallic phase (Ni3Al) and annealing twins formation will appear after adding Ni element. Furthermore, those phases will be increased with aging time. X-ray diffraction shows a competitive formation between the k-carbides and intermetallic phase formation during the aging time. It's confirmed that K-carbides will be formed first after that intermetallic phase, where k-carbides were formed at low temperature. Finally, we can conclude from these results that adding Ni in Triplex steel improves the ductility with 1hr aging time.

EFFECT OF DIFFERENT STRAIN ROUTES ON MECHANICAL PROPERTIES AND MICROSTRUCTURE OF COPPER

In the current paper, the role of change in strain routes was investigated, along with the cold rolling of copper metal. Four different strain routes including, (a) unidirectional rolling, (b) reverse rolling, (C) two-stage cross-rolling, and (d) multi-stage cross-rolling, were utilized to investigate the effect of strain routes change on microstructure, texture evolution, and anisotropy. Tensile strength in the unidirectional rolling sample compared to the cross-rolling sample decreased in the direction of initial rolling from 364 Mpa to 340 Mpa, in the direction of 45˚ to the initial rolling from 359 Mpa to 347 Mpa, and in the direction of perpendicular to the initial rolling from 371 Mpa to 360 Mpa. Texture intensity also decreased from 1413 in the unidirectional rolling sample to 992 in the cross-rolled sample. The results demonstrated that by rolling in different routes, the cross-rolling has led to a more homogeneous microstructure, less anisotropy, and weaker texture.

Degradation Characteristics of Mg-1,6Gd Alloy at Low Thickness Reduction of Warm Rolling

Magnesium has been developed as a biodegradable bone implant material due to its similarity in elasticity modulus of bone. However, magnesium has a higher corrosion rate and a lower strength. Gadolinium is alloyed to magnesium in order to improve the corrosion resistance and then rolled to improve the strength due to grain refinement in rolling. Cold roll produced the finest grain, but magnesium has a poor formability. Due to this fact, warm rolling with temperature 247 – 375 oC is applied. Optical Microscope, Scanning Electron Microscope (SEM), and Energy Dispersive Spectrometry (EDS) are used for characterization. Electrochemical Impedance Spectroscopy (EIS) and Polarization test were carried out to observe the corrosion mechanism of Mg-Gd in SBF Kokubo to replicate a human body condition. The result of polarization test shows that the cross-rolled sample experienced an increase in E corr, with 0,15 and –0,048 V due to a better distribution of Gadolinium. EIS states that the single pass rolled sample has a stronger passive layer with 116 and 126 kΩ value of Rf due to a smaller grain size which resulted a fewer compression stress. The hydrogen evolution was also observed with immersion test. Keywords: uni-directional rolling, cross-directional rolling, corrosion, simulated body fluid, hydrogen evolution.

Effects of Mo segregation on Charpy absorbed energy in Ti-12Mo alloys

Beta phase stabilizing elements such as Mo have strong tendency to segregate. We have introduced swirly type segregation of Mo in Ti-12Mo (mass %) alloy through groove bar rolling. After solution treatment and low temperature aging, hard omega phase was precipitated heterogeneously, which improved the room temperature tensile elongation values without sacrificing tensile strength. In this study, the effect of Mo segregation and heterogeneous distribution of omega phase on Charpy absorbed energy was investigated in Ti-12Mo alloy. Samples with two types of segregation were prepared; namely, swirly segregation in bar rolled sample and layered segregation in plate rolled sample. For comparison, we have also prepared Ti-12Mo bar samples with lesser Mo segregation, through high temperature thermomechanical treatment. Charpy impact tests were carried out at room temperature, 373 K and 473 K, respectively, using the samples after aging to introduce isothermal omega-phase. The samples with the segregation exhibited higher Charpy absorbed energy, especially at higher temperature of 473 K, while the sample with the swirly segregation showed higher Charpy absorbed energy than that with the layered segregation. The sample with lesser Mo segregation exhibited brittle intergranular fracture surface after Charpy testing. On the contrary, samples with Mo segregation exhibited ductile transgranular fracture surfaces.

Microstructure Characterization and Mechanical Property of Mg/Al Laminated Composite Prepared by the Novel Approach: Corrugated + Flat Rolling (CFR)

In this paper, Mg/Al laminated composites were successfully prepared at 400 °C by corrugated + flat rolling (CFR) with reduction ratios of 35% and 25% and subsequent annealing treatments were conducted at 200–350 °C for 30 min. A two-dimensional model was established to analyze the strain distribution during the first corrugated rolling process. Simulation results indicated that severe plastic deformation was formed at trough positions, which included more numerous refined grains than in the peak positions. The interfacial microstructure and mechanical property of the flattened composites along the rolling direction (RD) and the transverse direction (TD) were investigated. The results revealed that longitudinal discontinuous and transverse continuous interfacial intermetallic compounds (IMCs) were observed of the flattened as-rolled sample. Spatial distribution was provided for the grain microstructure along the thickness and rolling direction for AZ31B magnesium alloys of the CFR as-rolled composite. Mechanical property results showed that the longitudinal ultimate tensile strength (UTS) and elongation (EL) of the as-rolled sample reached 255 MPa and 4.14%, respectively. The as-rolled UTS along TD reached 325 MPa, about 30% higher than that along the RD. After heat treatment, the anisotropy of mechanical properties remained. The microstructure evolution and mechanical properties were discussed in detail.

Microstructure and Mechanical Properties of Hot- Rolled and Cold-Rolled Medium-Mn TRIP Steels

This study investigated the microstructure and mechanical properties of hot-rolled and cold-rolled medium-Mn transformation-induced plasticity (TRIP) steel. The experimental steel, processed by quenching and tempering (Q & T) heat treatment, exhibited excellent mechanical properties for hot-rolled and Q & T steels (strength of 1050–1130 MPa and ductility of 16–34%), as well as for cold-rolled and Q & T steels (strength of 878–1373 MPa and ductility of 18–40%). The mechanical properties obtained after isothermal holding at 775 °C for one hour for cold-rolled/Q & T steel were superior to that of hot-rolled/Q & T steel. Excellent mechanical properties were attributed to the large amount of retained austenite, which produced a discontinuous TRIP effect. Additionally, the differences in mechanical properties correlated with the morphology, stability and content of retained austenite. The cold-rolled sample, quenched from 650 °C (CR 650°C) had extensive TRIP effects in the middle and late stages of the deformation, leading to better mechanical properties. The fracture modes of the hot-rolled sample, quenched from 650 °C, and the cold-rolled sample quenched from 650 °C, were ductile fractures, resulting in excellent ductility.

EBSD study of microstructure evolution of ferritic stainless steel during cold rolling and annealing

The microstructure and texture of ferritic stainless steels (FSSs), formed during cold rolling and annealing processes, determine the mechanical properties of final sheet, especially the deep drawing formability. In this work, aNb, Ti stabilized17%Cr FSS was cold rolled with the reductions of 20%~70% and annealed for periods at 700°C. EBSD technique was used to characterize the microstructure evolution and inhomogeneous deformation strain distribution of the sheet during cold rolling. Partially annealed sheets were also analyzed to observe the nucleation and growth of recrystallized grains. Special attentions were paid on the crystal orientation of the deformed grains and recrystallzed grains. The results infer that in-grain shear band was formed in the cold rolled sample with the reduction higher than 30%, associated with the formation of high deformation strains. And the recrystallized grains prefer to form at some unique grain boundaries and in-grain shear bands. The orientations of recrystallized grains relates to the deformed grains.

A Dilatometric Study of the Non Isothermal Aging of a Cold Rolled Al-Mg-Si Alloy

In contrast to isothermal aging, few reports document the non-isothermal aging of deformed Al–Mg–Si alloys. The knowledge of non-isothermal aging of pre-deformed Al–Mg–Si alloys is of primary importance to understand the thermal stability as well as to control the microstructure of the final product during industrial processing. Therefore, the present work has been focused to understand the microstructure evolution during the continuous heating of a cold rolled Al–Mg–Si alloy. This has been followed using dilatometry, Differential Scanning Calorimetry, X-Ray Diffraction and microhardness measurement. Based on the results obtained, it is shown that dilatometry is a powerful tool to study phase transformations in deformed Al-Mg-Si alloys, moreover, the microstructural evolution, of the cold rolled sample, can be described as follows: at the earlier stages of the non-isothermal aging, formation and then the reversion of fully coherent GP zones take place. This is followed by the simultaneous occurrence of β” and β’ precipitation and recovery reaction. By continuing aging, the next reactions which will take place are β” and β’ dissolution and recrystallization. Finally, one can observe the formation and then the dissolution of the equilibrium phase β.