Cryogenic Temperature Rolling Research Articles

Fabricating a pure titanium foil with excellent strength-ductility combination via bimodal grain structure coupling with deformation twins

Preparation of pure titanium foil by cold rolling deformation often confronts the strength-ductility trade-off dilemma, how to obtain an excellent strength-ductility combination remains a great challenge. In the present work, we have prepared a pure titanium foil with a bimodal grain (BG) structure consisting of coarse grain (CG) and ultrafine grain (UFG), coupling with high-density deformation twins (DT) via a cryogenic-temperature rolling (CTR) and partial recrystallization annealing (PRA) process. Notably, a high strength-ductility synergy with YS of ∼483 MPa, UTS of ∼517 MPa and elongation of ∼21 % is achieved. The high strength is mainly caused by pronounced fine grain strengthening from the UFG region and twin boundary strengthening from strong interactions between DT and dislocations activated in the CG region. The GND caused by the hetero-deformation between CG and UFG, along with the activation of pyramidal <c+a> dislocation via DT in the CG region endows the pure titanium foil with excellent ductility.

Modulating the thermomechanical processing to optimize strength and ductility in FeCrNi2Nb0.1 medium-entropy alloy

The yield strength of face-centered cubic (FCC) alloy is insufficient, resulting in the limitation in bear-load applications and the reduced competitiveness among advanced structural materials. In this work, by modulating thermomechanical processing, the route combining dual phase and heterogeneous structure of grain is proposed to optimize the balance of strength and ductility in FeCrNi2Nb0.1 medium-entropy alloy (MEA). It is found that the processing method via cryogenic-temperature rolling and following annealing can result in heterogeneous microstructures consisting of fully recrystallized grains with annealing twins, non-recrystallized grains with high-density of dislocation, and small-size dispersive Laves phase. The multi-scale heterogeneous microstructure of MEA exhibits an optimized strength and ductility (yield strength ∼720 MPa, ultimate tensile strength ∼920 MPa and uniform elongation ∼23%), as well as considerable strain-hardening capacity. The harmonized strength and ductility can be attributed to the multiple strengthening mechanisms including grain boundary hardening, dislocation hardening, deformation twinning hardening and hetero-deformation-induced hardening. The results pay a feasible way to design dual-phase MEAs/HEAs with outstanding mechanical properties.

Optimizing heterostructure parameters for enhanced mechanical performance of Al0.1CoCrFeNi high entropy alloy

The Al0.1CoCrFeNi high entropy alloy with different heterostructure parameters, including the volume fraction of recrystallized grains (VRG) and high-angle domain misorientation (VHADM), was fabricated through cryogenic-temperature rolling and partial recrystallizing annealing. With the increase of VRG and VHADM, the yield strength and ultimate tensile strength initially increase and then decrease, while the uniform elongation consistently increases. The results indicate that the Al0.1CoCrFeNi HEA with the optimized heterostructure parameter, characterized by VRG of ∼35.9% and VHADM of ∼48.2%, shows a significant heterogeneous deformation-induced (HDI) strengthening effect. Electron backscatter diffraction results elucidate the discovery of a rapid accumulation of geometrically necessary dislocations in the domain boundary region, resulting in high HDI stress. It is observed that HDI hardening predominates at lower strain levels, while conventional dislocation hardening is more effective at higher strain levels. Higher VRG and VHADM are found to have a more significant impact on the HDI hardening effect. Our research provides valuable insights into tuning heterostructure parameters to fabricate high-performance heterostructured materials.

A novel cryogenic rolling method for commercially pure titanium sheets featuring high strength and ductility

Commercially pure titanium (CP Ti) has a low yield strength (YS); consequently, its utilization is limited to industrial applications that do not require high load-bearing capabilities. Cryogenic deformation has been regarded as an effective method for strengthening CP Ti. However, this method increases production costs and degrades ductility, thereby hindering the commercialization of cryogenic deformation for industrial production. In this study, we devised a two-temperature rolling method for CP Ti by combining room-temperature rolling (RTR) and cryogenic-temperature rolling (CTR), which can induce significant material strengthening while reducing the number of rolling passes required at cryogenic temperature. The RTR and CTR sequence substantially affected the strengthening degree. Employing CTR for only a part of the total area reduction (AR) induced considerable strengthening comparable to that obtained by employing it for the entire AR. Furthermore, the two-temperature rolling process did not appreciably degrade the ductility, despite inducing considerable strengthening, leading to an excellent strength–ductility combination. We identified microstructural factors for the high strength and ductility in the processed CP Ti. The devised rolling method is highly cost-effective, as it can reduce the proportion of cryogenic-temperature treatment in the whole rolling process; thus, this methodology will contribute considerably to the commercialization of CTR for industrial applications.

On impact of cryogenic temperature rolled 6082 Al alloy by dome- and conical-nosed projectiles

The simultaneous improvement in strength and toughness through cryogenic temperature rolling observed in recent studies is of profound interest for designers in defence, automobile and aerospace domains. The present work discusses the effects of different projectile nose shapes – dome and conical – on the ballistic impact behaviour of the 1 mm thick AA 6082 alloy targets, rolled to different cryogenic strains, using the experimental data for impact velocities ranging from 50 to 250 m/s reported in our earlier work. The cryogenic rolling strains were imparted by providing different thickness reductions, namely, 50%, 66.66%, 75% and 80%. The target performance was also analysed using velocity drop approach. The projectile nose shape influenced the ballistic limit strongly for 50% and 75% thickness reductions. Conical-nosed projectiles were found to be better penetrators than the dome-nosed projectiles within the overall tested velocity range of 50–250 m/s. The observations confirmed the dominance of the samples with 66.66% thickness reduction impacted with both dome and conical-nosed projectiles in the average and maximum velocity drops after the ballistic limits, indicating superior performance.

Effect of Different Cryogenic Rolling Strains on the Impact Properties of 6082 Aluminum Alloy

The demand for light-weight materials, exhibiting superior strength and higher toughness, has increased attention to cryogenic temperature rolling as it produces bi-modal microstructures with improved mechanical properties. The samples were cryorolled to a final thickness of 1 mm after thickness reductions of 50%, 66.66%, 75%, and 80%. The ballistic behavior of cryorolled AA 6082 aluminum alloy with different rolling strains/thickness reductions was investigated in this study. The cryorolled Al alloys were subjected to normal high-speed impact using dome-shaped projectiles at velocities between 50 and 250 m/s. The 66.66% thickness reduced samples exhibited higher impact resistance, especially at higher impact velocities. The maximum energy absorption of 106.43 J was observed for 66.66% thickness reduced sample at an impact velocity of 234.38 m/s. This study suggests the existence of an optimal value of cryogenic rolling strain for superior impact resistance, possibly due to an ideal combination of coarse and fine grains in the resulting bimodal microstructure.

Nanocrystalline structure fabricated by cryogenic temperature rolling of AA 2099 aluminum alloy

Solid solution treated AA 2099 alloy was rolled by a total reduction of 80% at both room and cryogenic temperature. Results show that nanocrystalline grain structure with a size around 20–100 nm was only observed in the cryogenic temperature rolled sample at high rolling strain. The formation of those nanograins related to shear banding behavior. Shear banding behavior was greatly promoted by cryogenic temperature rolling, which had a strong influence on mechanical homogeneity of rolled samples. The width of these high-density shear bands is around 0.2–8 µm. Shear strain partitioning between slip and shear banding was depended on slip behavior in deformed grains. Strain concentration inside shear bands may give rise to an obvious temperature increase, which caused significant grain refinement in or near the shear bands. The growth of nano-grains is retarded due to limited heat and pinning effect of nanosized precipitation.

Enhancing low-cycle fatigue life of commercially-pure Ti by deformation at cryogenic temperature

In this study, the low-cycle fatigue behavior of a cryogenic-rolled commercially pure titanium alloy was investigated, and compared with those of undeformed and room-temperature rolled ones. The amounts of deformation twins increased to >69.8% after cryogenic temperature rolling, and to 27.5% after room temperature rolling. Strain-controlled low-cycle fatigue tests were performed at total strain amplitudes 0.4%≤Δεt2≤ 1.2%. The Coffin-Manson and hysteresis energy-based models confirmed that low-cycle fatigue resistance was remarkably improved with increasing the volume fraction of deformation twins by pre-deformation. As the proportion of deformation twins in the microstructure increased, the hysteresis loop area decreased, the striation spacing decreased, and the severity of crack-deflection behavior increased. At low Δεt2 = 0.4%, dislocation recovery was suppressed in the pre-deformed microstructure, so cyclic behavior was stable. However, at Δεt/2 ≥ 0.8%, the recovery became the predominant mechanism, so well-defined cell structures formed and cyclic softening occurred. The smaller dislocation cells formed in RTR and CTR were considered to cause more severe crack arrest than in AR.

Microstructure and strength–ductility balance of pure titanium processed by cryogenic rolling at various rolling reductions

In this study, we examined the microstructure and strength–ductility balance of pure Ti processed by cryogenic-temperature rolling (CTR) at various rolling reductions (RRs). The strength–ductility balance of the processed materials was evaluated by multiplying the yield strength by the fracture elongation, which were measured by tensile testing. Generally, the strength–ductility balance deteriorates as metallic materials are strengthened, but remarkably, CTR enhanced the strength–ductility balance while significantly strengthening pure Ti by adjusting the amount of RR. CTR formed numerous thin twins in the grains of the material with suppressed dislocation generation due to the increased twinning activity and relatively decreased slip activity at a low temperature, which cannot be achieved in typical processes performed at or above room temperature. This unique microstructure enhanced the strength–ductility balance of the processed material by intensifying grain refinement and improving resistance to necking instability. However, the strength–ductility balance deteriorated when a large RR was imposed due to the significant changes in the microstructure as the deformation proceeded. Therefore, it is important to adjust the amount of RR for CTR to impart its exceptional ability. We discuss the effects of microstructural factors on the strength–ductility balance in terms of possible strengthening mechanisms and strain-hardening capacity. The present findings could guide the design of optimized CTR for the production of pure Ti plates or sheets with excellent tensile properties and extend their use in industrial applications.

Grade-4 commercially pure titanium with ultrahigh strength achieved by twinning-induced grain refinement through cryogenic deformation

The yield strength of commercially pure (CP) Ti of ASTM grade 4, the strongest among all the CP-Ti grades, is too low for structural applications that require high-strength materials. Here, we demonstrate the strengthening of grade-4 CP Ti by cryogenic-temperature rolling (CTR), which enables deformation twinning in grade-4 CP Ti to achieve twinning-induced grain refinement. CTR activated 112-2 twinning and 101-2 twinning, which are the most common twinning systems in pure Ti, whereas room-temperature rolling (RTR) did not activate any twinning system. CTR with imposing an area reduction of just 30% significantly increased the yield strength of the CP Ti to 946 MPa, which is not achievable through typical processes performed at or above room temperature and is comparable to that of commercial Ti-6Al-4V. The significant increase in strength was due to microstructural strengthening caused by twinning-induced grain refinement, combined with dislocation accumulation. In contrast to RTR, CTR greatly increased the stress concentration at grain boundaries (GBs), which caused the unusual activation of twinning in the grade-4 CP Ti by facilitating twin nucleation at GBs. The stress concentration increased because CTR activated the <c+a> slip to a lesser extent compared to RTR, thereby reducing the strain compatibility between neighboring grains. These results will contribute to development of ultrahigh-strength CP Ti and may thereby extend its use to structural applications that require high-strength materials.

Effect of rolling temperatures on mechanical and fracture behavior of AA 3003 alloy and pure Cu

Ultrafine-grained materials have an enormous scope of structural and functional applications owing to their higher mechanical properties compared to that of coarse-grained materials. The influence of room temperature and cryogenic temperature rolling of AA 3003 alloy and pure Cu on its mechanical properties and fracture behavior has been investigated in the present study. Both the materials are rolled to a thickness of 2 mm and 1 mm with a true plastic strain of 0.40 and 1.09, respectively. The deformed samples are characterized by tensile test, hardness test, and X-ray diffraction analysis. It has been observed that tensile strength and hardness of cryorolled (CYR) samples are higher than cold rolled (CR) samples and it is due to the fact that rolling at an extremely low temperature (− 196 °C) suppresses the dynamic recovery and hence mobility of dislocations becomes difficult as a result dislocation density increases. In CYR, low stacking fault energy material (Cu) has higher tendency to increase strength and work hardened compared to higher stacking fault energy materials (AA 3003) without much loss of ductility. SEM pictorial view of fractography revealed that CYR samples have mix mode of failure compared to CR samples. The dimple size is gradually decreased with increasing plastic strain and that is due to severe strain hardening and grain refinement.

High Speed Impact Behaviour of Thermo-Mechanically Processed AA 6082-T6 Thin Plates

Thermo-mechanically processed AA 6082-T6 aluminium alloy was investigated for its dynamic failure properties by subjecting it to normal high speed impact using a gas gun arrangement to fire nosed projectiles. Two processing routes viz. cryogenic temperature rolling and room temperature rolling were employed to make samples of 150×150 mm2 containing ultra-fine grains with 0.5 mm final thickness after 50% and 90% thickness reductions. The impact and residual velocities for both processing routes and both thickness reductions are reported. The perforation surfaces were studied using optical and scanning electron microscopy (SEM) along with X-Ray Diffraction (XRD). The results from the microstructural characterization are related with the impact results to identify the inherent mechanisms and phenomena in this study.

Second phase formation in the CoCrFeNiMn high entropy alloy after recrystallization annealing

There is a strong belief that the CoCrFeNiMn alloy is an example of high entropy alloy with single disordered solid solution structure. Recently it was challenged by the demonstration of second phases in the alloy after low-temperature annealing; however, specific processing conditions (prolonged annealing or severe plastic deformation prior to annealing) were used to cause their formation. In this letter, we report the formation of Cr-rich second phases with tetragonal (sigma phase) and bcc structures in the CoCrFeNiMn alloy after room or cryogenic temperature rolling to 80% strain thickness and further annealing at 600–800°C for 1h.

The effects of cold rolling temperature on corrosion resistance of pure iron

The effects of cold rolling temperature on grain size and grain orientation of pure iron were investigated. Comparing with sample rolled at room temperature, the grain refinement was facilitated in sample obtained by cryogenic cold rolling at liquid-nitrogen temperature. However, the grain orientation changed little for two samples. It was shown that cathodic hydrogen evolution reaction could govern the corrosion reaction for pure iron in sulfuric acid solution. The grain refinement obtained by rolling improved the corrosion resistance of iron in sulfuric acid solution, borate buffer solution and borate buffer solution with chloride ion. However, comparing with iron rolled at room temperature, the corrosion resistance of iron obtained by cryogenic temperature rolling was lower. Comparing with iron rolled at room temperature, higher dislocation density in iron rolled at cryogenic temperature reduced its corrosion resistance.

Producing Nanostructured 304 Stainless Steel by Rolling at Cryogenic Temperature

Effect of rolling temperature on deformation-induced α′-martensite and reverted austenite was investigated. Rolling experiments were carried out at room temperature (without inter-pass cooling) and at liquid nitrogen temperature, respectively. The phase components, orientations, and microstructures are characterized by X-ray diffraction, electron backscattered scattering detection, and transmission electron microscopy. The (200)α′ martensite was found to be of the preferred orientation in sample rolled at cryogenic temperature. An average grain size of about 300 nm combined with high yield strength (∼1500 MPa) and good elongation (∼35%) was obtained by the cryogenic temperature rolling and 240 s annealing treatment.

The influence of room temperature and cryogenic temperature rolling on the aging and wear behaviour of Al–4Cu–5TiB 2in situ composites

The effect of ambient and cryogenic temperature rolling on the microstructure, aging and wear behaviour of Al–4Cu–5TiB 2 in situ composite was studied. The results indicate significant increase in aging kinetics and improvement in hardness and wear resistance of the cryo-rolled and room temperature rolled composite in comparison with as-cast composite.