Combination Of Cold Rolling Research Articles

Fabrication and characterization of self-supporting and backed 107Ag targets for lifetime measurements using RDM and DSAM

Self-supporting and Au backed 107Ag targets have been fabricated from material in the form of powder at the Inter-University Accelerator Centre (IUAC), New Delhi. The method described in this report (using the combination of cold rolling and e-beam melting technique) is efficient in such a way that targets are fabricated without any significant loss of material and are free from major contamination. Consequently, this method of fabricating targets is useful for materials which are very expensive. Various techniques for thickness measurements and characterizations have been carried out, viz., α-transmission method, Rutherford Backscattering Spectrometry (RBS), X-ray Diffractometry (XRD), Energy Dispersive X-ray Fluorescence (EDXRF), Energy Dispersive X-ray Spectroscopy (EDS) and Scanning Electron Microscopy (SEM). The thickness of self-supporting 107Ag and backed 107Ag is ≈1.43± 0.08 and ≈1.11± 0.07 mg/cm2, respectively. One of the fabricated targets has been used successfully in nuclear physics experiment.

The effect of combined cold rolling and homogenization on the microstructures and mechanical properties of twin-roll casted 8021 aluminum alloy

The microstructures and mechanical properties of the twin-roll casting (TRC) 8021 alloy strip under different homogenization processes (direct homogenization, cold rolling + homogenization) have been systematically investigated by optical microscope, tensile testing, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) technique. It was revealed that due to the severe microstructural gradient throughout the full strip thickness, the coarse grain layer is readily formed in the strip surface due to the high stored energy involved. Although the introduction of cold rolling before homogenization reduces the strain inhomogeneity in the strip, the rather high deformation level produces fully recrystallized structures after homogenization at 580 °C. After cold rolling and final annealing, recrystallized grains are formed in the interior of the sheets for most the homogenization temperatures. Compared with direct homogenized samples, the average recrystallized grain sizes in the “cold-rolled + homogenized” samples are larger due to the small thickness reduction. Therefore, the combination of cold rolling and homogenization can improve the elongation and decrease the strength of the strip. Homogenization at 530 °C is selected as the optimum parameter for both the two homogenization processes as it provides a good combination of strength and elongation.

Effects of Cold Rolling and Annealing Treatment on Microstructure and Properties of CoFeNiMnV High‐Entropy Alloys

Herein, a combination of cold rolling (CR) and annealing treatment is used to investigate the evolution of the microstructure and mechanical properties of CoFeNiMnV high‐entropy alloys (HEAs) fabricated by powder plasma arc additive manufacturing (PPA‐AM). The deposited CoFeNiMnV HEAs exhibit a face‐centered cubic (FCC) structure with a small amount of σ phase precipitation. After 50% CR, the microstructure of CoFeNiMnV HEAs is severely deformed along the rolling direction, and the grain size is obviously refined. Therefore, the hardness and strength of the alloy are significantly improved. The rolled CoFeNiMnV HEAs are annealed at 500, 700 and 900 °C, for 60 min. The results show that annealing at 500 °C has little effect on the microstructure and dislocation density of the alloy, and the alloy still maintains high strength and hardness. With increasing of annealing temperature to 700 and 900 °C, the dislocation density of the CoFeNiMnV HEAs is significantly reduced. Meanwhile the σ phase is gradually dissolved, and the recrystallized grains and annealing twins are significantly coarsened. The analysis suggests that it decreases the strength of the CoFeNiMnV HEAs, but increases the elongation. CoFeNiMnV HEAs annealed at 700 °C for 60 min after CR exhibit an excellent high strength–toughness combination.

Cold Rolling Electrostimulation of Hard-Deform Alloys

On the example of shape memory alloys in coarse-grained and ultrafine-grained states there is demonstrated an influence of pulse current on deformation behavior, microstructure and mechanical properties during cold rolling. The combination of cold rolling with the introduction of a pulsed current stimulates an increase in the deformation ability and strong structural refinement into the region of nanograins in a hard-deformed shape memory TiNi alloy. For both coarse-grained and ultrafine-grained structural states, the maximum achievable one-time and the total degree of deformation are higher in the case of using a pulsed current. Subsequent annealing improves the strength and functional properties. It has been shown that effect of pulsed current on deformability during cold rolling is higher in an alloy with a high content of impurities.

Effect of Heat Treatment on Mechanical Properties of Heavily Cold Rolled Pure Titanium

Stainless steel is known as material with high corrosion resistance, and has excellent mechanical properties, workability, heat resistance. Therefore, it is used in a very wide range of fields such as mechanical parts, building materials, chemical parts, aviation parts, medical equipment, and food supplies. On the other hand, along with stainless steel, pure titanium is also known as material showing extremely high corrosion resistance. It has been used for a long time together with titanium alloys as chemical plant and heat exchanger. Pure titanium, which is widely used as a product, is JIS2 type. However, the problem is that the strength of pure titanium is lower than that of titanium alloys. Therefore, it is expected to use pure titanium having high strength while maintaining purity. Generally, cold working and heat treatment methods are used to increase strength. In the present study, the material properties of pure titanium were improved by a combination of cold rolling and heat treatment. Mechanical properties were examined by tensile testing. The test material was a commercially available pure titanium JIS2 sheet. The thickness of the tensile test workpiece was 0.4 to 0.7 mm. The rolling reduction ranged from 75 to 93 %. An increase in tensile strength was obtained in the heat treatment from 400 to 500 oC while maintaining the ductility. Tensile strength was greatly improved under the condition of 93 % of rolling reduction and heat treatment temperature of 400 oC.

Microstructure evolution of additively manufactured CoCrFeNiAl0.4 high-entropy alloy under thermo-mechanical processing

The microstructure and texture evolution during thermo-mechanical processing (TMP) and their relationship with the mechanical properties in the non-equiatomic CoCrFeNiAl0.4 high-entropy alloy (HEA) were investigated. In this work, a combination of cold rolling and annealing technology was used to investigate the HEA which has been fabricated by powder plasma arc additive manufacturing (PPA-AM) in the deformed and recrystallized states. Microstructure and texture analysis were performed by electron backscatter diffraction. The mechanical properties were evaluated using static tensile testing. It was substantiated that annealing twins facilitates the transition from the cube texture to the shear texture and has a great influence on the evolution of texture after TMP. Based on the research of CoCrFeNiAl0.4 high-entropy alloy, thermo-mechanical processing under appropriate conditions can increase the work hardening rate, but the work hardening rate is relatively stable under 30%–45% plastic deformation. The correlation during TMP between mechanical properties and work hardening, texture evolution, and recrystallization was discussed.

Effect of cold rolling on mechanical and corrosion properties of stabilized Al–Mg–Mn–Er–Zr alloy

Al–Mg–Mn–Er–Zr alloy, produced through a combination of cold rolling and heat treatment process conditions, has been studied on its microstructure evolution, strengthening mechanism, and corrosion properties. The results demonstrated that, the dispersion of coherent Al3 (Er, Zr) nanoscale particles effectively pinned dislocations and increased the strength. The dislocation strengthening was considered as the primary strengthening method for Al–Mg–Mn–Er–Zr alloy. The β phase was preferentially precipitated at the grain boundary and the tip of the Al6Mn phase during annealing. The corrosion resistance of stabilized alloys was degraded after cold rolling, which can be attributed to the increase in the proportion of sub-grain stripe and high-angle grain boundaries. The alloy prepared by the process (50% deformation + 270 °C/4 h annealing + 10% deformation) exhibited a UTS of 434 MPa and a YS of 323 MPa; the degree of sensitization was quantified by the ASTM G67 test and the susceptibility to intergranular corrosion was in unsusceptible categories; this alloy thus achieves excellent mechanical properties and presents sufficient corrosion resistance.

Microstructure tailoring for property improvements of DP steel via cyclic intercritical annealing

Multi-step intercritical annealing treatment was applied on the quenched and cold rolled martesnitic microstructures to unravel the effects of thermal cycling on dual phase (DP) steel. During intercritical annealing of the quenched microstructure, hardness decreased with increasing holding time and reached a plateau. However, during intercritical annealing of the cold rolled microstructure, there was a rapid fall of hardness due to recrystallization. Afterwards, hardness increased as a result of austenitization, and then reached a plateau. A rapid grain growth was observed during repetition of intercritical annealing cycle for the DP steel originated from the quenched microstructure with adverse effects on the tensile properties. Conversely, decreased size of martensite islands and formation of chain like morphology of martensite around ferrite grains was observed during thermal cycling of the DP steel originated from the cold rolled microstructure with the consequent enhanced work hardening behavior. Accordingly, the combination of cold rolling and cyclic intercritical annealing was recommended in this work to enhance the work hardening behavior and mechanical properties of DP steels.

Superior Strength and Ductility of In Situ Nano TiB2/Al–Cu–Mg Composites by Cold Rolling and Post-Aging Treatment

In this work, the combination of cold rolling with post-aging treatment is developed to achieve the optimal strength–ductility for the in situ nano TiB2/Al–Cu–Mg composite. The microstructure and mechanical properties of the composite subjected to 20% thickness reduction of cold rolling at room temperature and their evolutions upon post-aging at different temperatures were investigated by means of a tensile test, differential scanning calorimetry, scanning electron microscopy, and transmission electron microscopy. It was found that the TiB2 particles were effective in dislocation pinning and accumulation during the cold-rolling process. The tensile tests indicated that both the yield and ultimate tensile strengths of the cold-rolling sample increased a lot due to the dislocation strengthening and precipitation strengthening generated by dynamic precipitation during cold rolling in comparison with the conventional T6 sample. After aging at 100 °C/12 h, the elongation to failure reached ~8.4%, which was higher than the conventional T6 sample. Meanwhile, there was also a dramatic increase of strength. The yield and ultimate tensile strengths are ~644 MPa and ~726 MPa, respectively. This remarkable strength–ductility combination was due to the modified microstructure caused prior to artificial aging by the cold-rolling method and the formation of nanosized Guinier–Preston–Bagaryatsky (GPB) zones. The underlying mechanisms related to the superior strength–ductility combination were discussed regarding the microstructural characteristics in the composite.

Effect of Heat Treatment and Combination of Cold Rolling and Heat Treatment on Microstructure and Mechanical Properties of Titanium Alloy Ti6Al2V2Zr1.5Mo

The heat treatment and cold rolling combinations have been carried out on titanium alloy Ti6Al2V2Zr1.5Mo, and microstructure evolution and mechanical behavior have been studied. Solution treatment below the β-transus temperature, followed by air cooling, resulted in higher microhardness/strength as compared to the same with water quenching. A sudden drop in microhardness/strength is observed in sample solution heat-treated above β-transus temperature followed by air cooling. The former is attributed to the additional presence of fine secondary α-phase formed by dynamic aging during air cooling as compared to water-quenched samples which did not have fine secondary α-phase. Solution treatment above β-transus temperature resulted in Widmanstatten microstructure with no significant fine secondary α in air-cooled samples. Among the studied conditions of cold rolling (CR), gain in strength of the alloy from annealed condition is significant with first 15% reduction and thereafter it is marginal for 30% reduction. Initiation of cracks at the edges has been observed in 30% CR. The microstructure of cold-rolled samples confirms the fragmentation of α-plates with the presence of high dislocation density. Heat treatment of cold-rolled samples resulted in significant reduction in strength from the as-cold-rolled conditions. The marginally lower strength than the as-received (annealed) or heat-treated alloy samples is due to the recrystallization in CR samples and the formation of Widmanstatten microstructure in air-cooled samples. The alloy does not have fine secondary α or regions with large dislocation density in this condition. The microstructure in the samples heat-treated (with air cooling) below as well as above β-transus temperature (after CR) is similar to air-cooled samples (without prior CR) with heat treatment above β-transus temperature. This indicates the reduction in recrystallization temperature with cold working, which is substantiated with the reduction in strength as well.

Influence of deformation and annealing twinning on the microstructure and texture evolution of face-centered cubic high-entropy alloys

The influence of the physical mechanisms activated during deformation and annealing on the microstructure and texture evolution as well as on the mechanical properties in the equiatomic CoCrFeMnNi high-entropy alloy (HEA) were investigated. A combination of cold rolling and annealing was used to investigate the HEA in the deformed, recovered, partially recrystallized, and fully recrystallized states. Detailed microstructure and texture analysis was performed by electron backscatter diffraction, transmission electron microscopy, and X-ray diffraction. The mechanical properties were evaluated using uniaxial tensile testing. A specific focus of this investigation was put on studying the influence of deformation and annealing twinning on the material behavior. It was substantiated that during cold rolling deformation, twinning facilitates the transition from the Cu-type to the Brass-type texture, whereas annealing-twinning leads to a strong modification of the texture formed during recrystallization. The formation of specific twin orientations and the randomization of the recrystallization texture were proven by experiments as well as by cellular automaton simulations. During tension of the cold-rolled and annealed material high work-hardenability was observed. We attribute this behavior primarily to the dominance of planar dislocation slip and reduced tendency for dynamic recovery, since deformation twinning was observed to activate only in the non-recrystallized grains and thus, contributed minimally to the overall plasticity. The correlation between deformation/annealing twinning and the microstructure evolution, texture development, and mechanical properties was discussed in detail.

Low temperature superplastic-like deformation and fracture behavior of nano/ultrafine-grained metastable austenitic stainless steel

We describe here the low temperature superplastic-like deformation in a nano/ultrafine-grained metasable austenitic stainless steel tensile tested at a strain rate of 2.5×10−4s−1 and temperature of 600°C (~0.43 of the absolute melting point). The nano/ultrafine-grained structure was obtained via a combination of cold rolling (~93% in reduction), followed by reversion annealing treatments at 650°C for 10min, 30min, and 700°C for 2min, 5min, respectively, an approach previously adopted by Misra's group (references 11–16). The reversion of martensite to austenite was dominated by diffusional mechanism. The nano/ultrafine-grained steel exhibited superplastic-like behavior with maximum elongation approaching ~153% and strain rate sensitivity of ~0.22. Furthermore, tensile deformation behavior at 20°C and 600°C, and the corresponding fracture characteristics are discussed. Observations of fracture surface indicated that the fracture was characterized by line-up of voids along the striations, when tensile tested at 20°C. Whereas, the fracture surface at 600°C mainly consisted of uniform distribution of dimples. To further study the fracture mechanism during superplastic-like deformation, deformed structures from the longitudinal region close to the tip of the fracture surface were studied. The fracture surface of superplastic-like deformed steel was characterized by interlinkage of cavities.

Recrystallisation mechanism during friction stir welding of ultrafine- and coarse-grained AISI 304L stainless steel

Ultrafine-grained (UFG) and a coarse-grained (CG) 304L stainless steels were produced by a combination of cold rolling and annealing. Friction stir welding (FSW) was applied at the same welding conditions to study the effects of the grain size of the base metal on the grain structure of the weld nugget and its recrystallisation mechanism. The results showed that the recrystallisation mechanism changes with the grain size of the base metal. Continuous dynamic recrystallisation (CDRX) was found to be dominant at the FSW of the UFG sample while discontinuous dynamic recrystallisation is the main recrystallisation mechanism in the FSW of the CG sample. Although the weld nugget grain size of the UFG welded sample is slightly higher than that of the CG welded sample, its nanohardness was found to be higher. This behaviour is attributed to the higher dislocation densities of the austenite grains in the UFG welded sample produced through CDRX.

The effect of grain size on the twin initiation stress in a TWIP steel

The influence of grain size on the twinning stress of an Fe–15Mn–2Al–2Si–0.7C Twinning Induced Plasticity (TWIP) steel has been investigated. Five grain sizes were obtained using a combination of cold rolling and annealing. Electron backscatter diffraction (EBSD) analysis revealed that the material exhibited a typical cold rolled and annealed texture. Tensile testing showed the yield stress to increase with decreasing grain size, however, the ductility of the material was not substantially affected by a reduction in grain size. Cyclic tensile testing at sub-yield stresses indicated the accumulation of plastic strain with each cycle, consequently the nucleation stress for twinning was determined. The twin stress was found to increase with decreasing grain size. Furthermore, the amount of strain accumulated was greater in the coarser grain material. It is believed that this is due to a difference in the twin thickness, which is influenced by the initial grain size of the material. SEM and TEM analysis of the material deformed to 5% strain revealed thinner primary twins in the fine grain material compared to the coarse grain. TEM examination also showed the dislocation arrangement is affected by the grain size. Furthermore, a larger fraction of stacking faults was observed in the coarse-grained material. It is concluded that the twin nucleation stress and also the thickness of the deformation twins in a TWIP steel, is influenced by the initial grain size of the material. In addition grain refinement results in a boost in strength and energy absorption capabilities in the material.

The effect of grain size and martensitic transformation on the wear behavior of AISI 304L stainless steel

In the present study, a combination of cold rolling and subsequent annealing was used to produce an AISI 304L stainless steel with different grain sizes (650nm, 3μm and 12μm). Wear behavior of the steel was subsequently examined using dry sliding wear test under different loads of 10N, 20N and 30N. Different microstructural characterizations were conducted on the samples. The results demonstrated that the ultra-fine grained steel (650nm grain size) had better wear resistance under normal loads of 10N and 20N, whereas under the normal load of 30N, it showed weak wear resistance as compared to the steel with larger grain size (3μm and 12μm). This behavior can be attributed to the amount of induced martensitic transformation formed during the wear test. This transformation was evaluated using XRD analysis and quantified by Ferritescope measurements. Wear mechanism was recognized as delamination in the early stages of the wear test and the mixture of delamination and abrasion for higher distances.

Mechanical properties of aluminium–copper–lithium alloy AA2195 at cryogenic temperatures

Tensile testing was performed on a 4mm thick sheet of the aluminum–lithium alloy AA2195 in T87 (solution treatment+water quenching+7% cold work+peak aging) temper which was subjected to 7% cold working by combination of cold rolling and stretching, over a temperature range from ambient to liquid hydrogen (20K) conditions. Properties were evaluated in longitudinal as well as transverse directions to characterize anisotropy with respect to strength and ductility. Strength and ductility were compared to the conventional aluminum alloy AA2219-T87, developed for similar cryogenic applications. Decreases in test temperature led to higher strengths with little or no change in ductility. As the temperature decreases, the differences between ultimate tensile strength as well as yield strength for two different combinations of cold roll and stretch studied in the present work, narrows down and become equal at 20K.

Study on the Wear Behavior of Ultrafine Grained 304L Stainless Steel

An ultrafine grained 304L stainless steel with average grain size of 650±100 nm was produced by a combination of cold rolling and annealing. Wear behavior of the steel was examined by dry sliding wear tests under different loads. Different microstructural characterizations were conducted on the ultrafine grained structure after thermomechanical processing and wear tests. The results demonstrated that the steel had yield strength of 720 MPa and total elongation of 47%, which is almost twice higher than typical coarse grained strength. Also, wear tests results showed a good linear relation between the cumulative wear loss and distance in each normal load. Wear rate was about 0.024, 0.043 and 0.093 mg/m for normal loads of 10, 20 and 30N, respectively. Wear mechanism was also recognized as delamination (in the early stage) and mixture of delamination and abrasion in higher distances.

Ambient and cryogenic tensile properties of AA2195T87 sheets with pre-aging cold work by a combination of cold rolling and stretching

Al–Cu–Li–Mg–Ag–Zr alloy AA2195, in the form of 4mm thick sheets, was heat treated to T87 temper with the pre-aging cold work provided by a combination of 5% cold rolling followed by 2% stretching. The tensile properties of the material were evaluated at ambient and cryogenic temperatures (i.e. −196°C and −253°C). Transmission electron microscopy of the heat treated (i.e. T87 treated) material revealed that the major strengthening precipitate is indeed the T1 (Al2CuLi) phase nucleated on the {111}Al planes. In addition, θ′ [metastable Al2Cu (θ)] precipitates on {100}Al planes, and “plate like features” lying on {111}Al planes were further observed. The one atom layer thick “plate like features” have the same crystal structure as that of the matrix Al. The possibility of such “plate like features” being either the early stages of the Ω phase (i.e. a chemically modified coherent form of θ-Al2Cu phase) in the constituent Al–Cu–Mg–Ag system or the evolutionary stages of the T1 phase itself is discussed.

MgH2 as dopant for improved activation of commercial Mg ingot

Abstract In this paper, we propose a method to decrease the activation time (first hydrogenation) of commercial Mg. This new alternative processing route uses a combination of cold rolling and short time ball milling to obtain full hydrogen capacity quickly in the first hydrogenation. As ball milling of ductile materials leads to particle agglomeration, brittle Mg plates produced by repetitive cold rolling were used as starting material. These rolled plates were then ball milled for 30 min with and without the addition of 5 wt% Mg or MgH2 powders. All the synthesized samples were investigated for hydrogen storage, absorption–desorption behavior and microstructure using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and pressure-composition temperature (PCT) methods. Results showed slow activation behavior for cold rolled Mg plates, which was slightly improved after milling. Further improvement was obtained by adding 5 wt% of Mg powder during ball milling. In contrast, when the plates were ball milled with 5 wt% of MgH2 powder a drastic improvement in activation behavior was observed with hydrogen capacity reaching up to 6.2 wt% in comparison to 2.74 wt% for undoped and 3.57 wt% for Mg doped samples. These results reveal that ball milling with ductile Mg powder deforms only the surface of Mg plates while brittle MgH2 powders causes fracturing and cracks, increasing the surface area and generating heterogeneous nucleation sites within the bulk material.

Development of Ni–Fe–Al-based alloys precipitating cubic γ′ for fabrication of nanoporous membranes

During this study, new Ni-base alloys precipitating cubic γ′ were developed which shall be used for the production of polycrystalline nanoporous membranes. The polycrystalline nanoporous membranes are produced through a combination of cold rolling and heat treatment in order to get directional coarsening of the γ′-phase which is selectively dissolved afterwards. Conventional Ni-based superalloys have a γ/γ′ -microstructure with cubic γ′-precipitates and show the needed etching behaviour but their high strength and limited ductility at room temperature do not allow to produce the polycrystalline nanoporous membranes by means of the before mentioned method. Thus, the new alloys with simpler composition were developed which have a γ/γ′ microstructure. The alloy Ni–13Fe–8Al–4Ti (composition in atomic percent) which was produced by Schmitz (Cullivier, ISBN 978-3-86955-523-2, 16) served as basis and showed the promising characteristics. To obtain cubic γ′-precipitates, the misfit was estimated to values of at least |0.2| % by a method presented by Mishima (Acta Metall 33:1161–1169, 23). Further, the phase compositions as well as phase volume fractions of γ-matrix and γ′-phase were calculated by means of Thermocalc® simulations (database: TTNi7). The etching behaviour of the new alloys was adjusted by adding chromium and molybdenum which passivate the γ-matrix so that the γ′-precipitates dissolve during the leaching process. The well-aligned cubic γ′-precipitates were obtained by partially replacing titanium by niobium. Furthermore, the hardness could be significantly lowered compared to conventional superalloys by reduction of alloying elements. Hence, the promising alloys were found to get directional coarsening of the γ′-precipitates in a combined process of cold rolling and heat treatment.