Effect of hot rolling and annealing temperatures on the microstructure and mechanical properties of SP-700 alloy

The effect of rolling temperature on both two-and single-phase regions and annealing in a temperature range of 700–950°C on the microstructure and mechanical properties of Ti-5 Al-4 V-2 Fe-1 Mo alloy was investigated. The results indicated that the best balance of strength and ductility is obtained by rolling in the two-phase region due to the globularization of the alpha phase and increase in its volume fraction. After rolling in the two-phase region, the ductility of the specimens annealed at 700 to 800°C increased because of the finer size and globularized alpha phase, while the reduction in strength was attributed to a decrease in the alpha phase volume fraction. However, at 950°C, the strength increased and ductility dropped by the formation of acicular alpha phase due to an increase in the phase boundary area. Annealing and aging after rolling in the beta-phase region increased the strength and decreased the ductility, which is attributed to the formation of a secondary alpha phase. A combination of favorable yield strength(1113 MPa) and elongation(13.3%) was obtained through rolling at 850°C followed by annealing at 750°C and aging at 570°C.     

Microstructure and texture evolution in commercial-purity Zr 702 during cold rolling and annealing

Microstructure and texture evolution in commercial-purity Zr 702 during cold rolling and annealing was investigated by optical microscopy, transmission electron microscopy, and X-ray diffraction. The results showed that crystallographic slip was the predominant deformation mechanism in the early stage of deformation. Deformation twins started to form when the rolling reduction was larger than 38.9%; both the dislocation density and the number of twins increased with increasing rolling reduction. The initial texture of the Zr 702 plate consisted of the basal fiber component. During cold rolling the strength of the basal fiber first decreased and then increased with increasing rolling reduction. The cold-rolled sheets were fully recrystallized after being annealed at 550°C. The recrystallization temperature and the size of recrystallized grains decreased with increasing rolling reduction. A larger rolling reduction resulted in a higher grain growth rate when the annealing temperature increased from 550°C to 700°C. The recrystallization texture was characterized by a major basal fiber and a minor {0113}<2110> component. The strength of the recrystallization texture increased with increasing rolling reduction.     

Improved cold rolling workability of warm rolled Fe?6.5wt%Si electrical steel with columnar grains by annealing

The effects of annealing temperature(with the annealing time being constant at 1 h) on the microstructure, ordering, residual stress, mechanical properties, and subsequent cold rolling workability of Fe?6.5wt%Si electrical steel with columnar grains were investigated, where the steel was warm rolled at 500°C with a reduction of 95%. The results show that recrystallization began to occur in the sample annealed at 575°C and that full recrystallization occurred in the sample annealed at 625°C. When the annealing temperature was 500°C or greater, the extent of reordering in the sample was high, which reduced the room-temperature plasticity. However, annealing at temperatures below 300°C did not significantly reduce the residual tensile stress on the edge of the warm rolled samples. Considering the comprehensive effects of annealing temperature on the recrystallization, reordering, residual stress, and mechanical properties of the warm rolled Fe?6.5wt%Si electrical steel with columnar grains, the appropriate annealing temperature range is 300°C?400°C. Unlike the serious edge cracks that appeared in the sample after direct cold rolling, the annealed samples could be cold rolled to a total reduction of more than 71.4% without the formation of obvious edge cracks, and bright-surface Fe?6.5wt%Si electrical steel strips with a thickness less than 0.1 mm could be fabricated by cold rolling.     

Effect of cryogenic rolling and annealing on the microstructure evolution and mechanical properties of 304 stainless steel

Metastable 304 austenitic stainless steel was subjected to rolling at cryogenic and room temperatures, followed by annealing at different temperatures from 500 to 950℃. Phase transition during annealing was studied using X-ray diffractometry. Transmission electron microscopy and electron backscattered diffraction were used to characterize the martensite transformation and the distribution of austenite grain size after annealing. The recrystallization mechanism during cryogenic rolling was a reversal of martensite into austenite and austenite growth. Cryogenic rolling followed by annealing refined grains to 4.7 μm compared with 8.7 μm achieved under room-temperature rolling, as shown by the electron backscattered diffraction images. Tensile tests showed significantly improved mechanical properties after cryogenic rolling as the yield strength was enhanced by 47% compared with room-temperature rolling.     

Optical parameters induced by phase transformation in RF magnetron sputtered TiO2nanostructured thin films

Pure TiO2 thin films were deposited onto quartz substrates using a ceramic TiO2 target at an elevated substrate temperature of 573 K by RF magnetron sputtering, and an analysis of structural, optical and photoluminescence characteristics of the films upon phase transformation is reported in this paper. Structural investigations using X-ray diffraction revealed that the as-deposited film was amorphous in nature. Thermal annealing for 2 h at 873 K in air resulted in the formation of anatase phase, and a phase transformation to rutile was observed at 1073 K.An increase in grain size and an improvement in crystallinity were also observed on annealing. Rod- like rutile crystallites were observed in the SEM images of the film annealed at 1273 K. As-deposited films and films annealed up to 1073 K were highly transparent in the visible region with a transparency 480%. Optical band gap of the films decreased upon thermal annealing which is attributed to phase transformation from amorphous to anatase and then to rutile. Optical parameters such as refractive index, optical conductivity and optical dielectric constant increased with increase in annealing temperature. Since rutile is the optically active phase, the superior refractive index of the film annealed at 1073 K along with its high transparency in visible region suggests the application of this film in antireflective coatings. Photoluminescence emission of maximum intensity was observed for the film annealed at 873 K, which exhibits anatase phase. Intense blue emission observed in this film makes it suitable for use in optoelectronic display devices.     

Effect of cold rolling process on microstructure and mechanical properties of high strength β titanium alloy thin sheets

The microstructure and mechanical properties of Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe high strength titanium alloy sheets prepared by unidirectional cold rolling and two-step cross cold rolling were investigated. Results showed that the β phase grains were refined significantly by cold rolling followed by solution treatment for a short time.Compared to unidirectional cold rolling, the short time solution treatment after two-step cross rolling could significantly reduce the non-uniformity of the microstructure of the alloy sheets. After aging treatment at 550 ℃,the anisotropy of the mechanical properties still existed in the unidirectional rolled sheets, and the tensile strength was highest along the rolling direction. After solution and aging treatment, the anisotropy of the mechanical properties of the two-step cross rolling process sheet was not obvious than unidirectional cold rolling,and alloy had good strength and plasticity matching.     

High Temperature Ductility Loss of 16MnCr5 Pinion Steels

A wide ductility trough covering from 700 to 1100 is observed in the curve of Reduction of Area (RA) vs. tempetature for 16MnCr5 pinion steel. At 750℃, corresponding to the minimum of RA, it is grain boundary sliding that controls its hot ductility rather than usual Deforming Induced Ferrite (DIF), which can only appear just below 750℃ and slightly improve hot ductility. The volume fraction of ferrite is dependent on the strain and strain rate.Firstly a critical strain must be necessary for formation of DIF then with strain rate increasing, the volume fraction of DIF decreases but RA is elevated. In the γ phase region, hot ductility is seriously deteriorated because of grain boundary sliding promoted by oxidcs and sulfides at the grain boundary and recovered because of dynamic recrystallization at higher temperature; when strain rate increases, ductility is improved as there is insufficient time for cracks to propagate along the γ grain boundary as well as dynamically precipitating, and ductility trough becomes narrower because the temperature for onset of dynamic recrystallization decreases. In addition, γ→α phase transformation introduced by temperature drop before the tensile test encourages precipitation of AlN and impairs ductility.     

Microstructure evolution and mechanical properties of a hot-rolled Ti alloy

The microstructure evolution and mechanical properties of a hot-rolled Ti-5.1 Al-2.5 Cr-0.5 Fe-4.5 Mo-1.1 Sn-1.8 Zr-2.9 Zn titanium alloy sheet along the thickness direction were investigated.The results indicated that the hotrolled titanium alloy sheet presented different microstructures along the thickness direction owing to the uneven distribution of stress and temperature during the hot rolling.The grains in central region underwent a larger deformation,leading to relative complete grain fragmentation and the formation of fine grains.During the air cooling process followed by hot rolling,the fraction of a phase precipitated in the central region was lower than that in the regions near the surface of the sheet.During hot rolling process,more deformation energy transformed to thermal energy and lower cooling rate in the central region promoted the α→β phase transformation,resulting in the increasing of the dynamic recrystallization in the β phase.By contrast,the dynamic recrystallization for a phase decreased.Distinct {0001}_α and {001}_β textures were observed,and these textures were markedly strengthened with the increasing distance from the central region.Due to the softening induced by dynamic recrystallization and the strengthening by concentrated dislocations,the surface of the sheet exhibits highest yield strength and lowest elongation.     

Effect of acicular ferrite on banded structures in low-carbon microalloyed steel

The effect of acicular ferrite (AF) on banded structures in low-carbon microalloyed steel with Mn segregation during both isothermal transformation and continuous cooling processes was studied by dilatometry and microscopic observation. With respect to the isothermal transformation process, the specimen isothermed at 550°C consisted of AF in Mn-poor bands and martensite in Mn-rich bands, whereas the specimen isothermed at 450°C exhibited two different morphologies of AF that appeared as bands. At a continuous cooling rate in the range of 4 to 50°C/s, a mixture of AF and martensite formed in both segregated bands, and the volume fraction of martensite in Mn-rich bands was always higher than that in Mn-poor bands. An increased cooling rate resulted in a decrease in the difference of martensite volume fraction between Mn-rich and Mn-poor bands and thereby leaded to less distinct microstructural banding. The results show that Mn segregation and cooling rate strongly affect the formation of AF-containing banded structures. The formation mechanism of microstructural banding was also discussed.     

A β-type TiNbZr alloy with low modulus and high strength for biomedical applications

The effect of thermo-mechanical treatment on the mechanical properties of a novel β-type Ti–36Nb–5Zr(wt%) alloy has been investigated.The solution treated alloy consists of β and α″ phases and exhibits a two-stage yielding with a low yield stress(around 100 MPa). After cold rolling at a reduction of 87.5% and subsequent annealing treatment at 698 K for 25 min, a fine microstructure with nanosized α precipitates distributed in small β grains as well as high density of dislocations was obtained to achieve a yield strength of 720 MPa and a ultimate tensile strength of 860 MPa. In spite of the formation of α precipitates, the β-stabilizers are not enriched in the parent β matrix due to the short duration and low temperature of the thermal treatment, resulting in a low chemical stability of β phase. The low stability of β phase and the small volume fraction of α precipitates produce a low Young’s modulus of 48 GPa. Such an excellent combination of low elastic modulus and high strength in mechanical properties indicates great potential for biomedical applications.     

Preparation of high-strength Al-Mg-Si-Cu-Fe alloy via heat treatment and rolling

An Al-Mg-Si-Cu-Fe alloy was solid-solution treated at 560°C for 3 h and then cooled by water quenching or furnace cooling. The alloy samples which underwent cooling by these two methods were rolled at different temperatures. The microstructure and mechanical properties of the rolled alloys were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, and tensile testing. For the water-quenched alloys, the peak tensile strength and elongation occurred at a rolling temperature of 180°C. For the furnace-cooled alloys, the tensile strength decreased initially, until the rolling temperature of 420°C, and then increased; the elongation increased consistently with increasing rolling temperature. The effects of grain boundary hardening and dislocation hardening on the mechanical properties of these rolled alloys decreased with increases in rolling temperature. The mechanical properties of the 180°C rolling water-quenched alloy were also improved by the presence of β″ phase. Above 420°C, the effect of solid-solution hardening on the mechanical properties of the rolled alloys increased with increases in rolling temperature.     

Peculiar aging response of near b Ti–25 Nb–2Mo–4Sn alloy for biomedical applications

In this paper,aging response of a recently developed near β Ti-25Nb-2Mo-4Sn(wt%) alloy with high strength and low modulus was investigated intensively.The experimental results from X-ray diffraction and transmission electron microscopy showed that the aging production of the Ti-2524 alloy was(β+ω) or(β+α) even under the same aging treatment condition,depending on the pre-treatments prior to the aging.Solid evidence confirmed the competition between stable α phase and metastable ω phase during the decomposition of β phase on aging.Different aging response of Ti-2524 alloy can be attributed to high-density dislocations and grain boundaries which suppress the formation of ω,and alternatively promote a phase formation.This provides a thermo-mechanical approach to inhibit deleterious ω phase formation and assist fine α phase precipitation.Upon an appropriate aging treatment,superior mechanical properties of high ultimate tensile strength(1233 MPa) and low elastic modulus(77 GPa) were achieved in Ti-2524 alloy.     

Mechanical properties of fine-grained dual phase low-carbon steels based on dynamic transformation

The fine grained dual phase (FG-DP) steel with ferrite grains of 2-4.5 μm and martensite islands smaller than 3 μm was obtained through the mechanism of deformation-enhanced ferrite transformation (DEFT). Mechanical properties of the steel were tested at room temperature. The results indicated that with a similar volume fraction of martensite (about 20vol%),FG-DP steel exhibited a superior combination of higher strength and more rapid strain hardening at low strains compared with the coarse-grained dual phase (CG-DP) steel obtained by critical annealing. The combination of higher strength,large elongation,and more rapid strain hardening of FG-DP steel can be attributed to the fine ferrite grain and finely dispersed martensite islands. In addition,the uniformly distributed martensite islands in FG-DP steel have smaller interspacing compared with that of CG-DP steel. So,at the initial plastic deformation stage,the plastic deformation of ferrite was restrained and more pronounced load was transferred from ferrite to martensite. The plastic deformation of martensite in FG-DP steel started earlier.     

Effect of equal channel angular pressing on aging treatment of Al-7075 alloy

The effect of aging treatment on microstructure and mechanical properties of equal channel angular pressed Al-7075 alloy was examined.Commercial Al-7075 alloy in the solid solution heat-treated condition was processed by equal channel angular pressing through route BCat both the room temperature and 120 1C. Only three passes of equal channel angular pressing was possible due to the low ductility of the alloy at both temperatures. Followed by equal channel angular pressing, the specimens have been aged at 120 1C for different aging times. Mechanical properties were measured by Vickers microhardness and tensile tests and microstructural observations were undertaken using transmission electron microscopy, X-ray diffractometer as well as optical microscopy. Microstructural investigations showed that ultrafine-grained materials with grain size in the range of 200–350 nm and 300–500 nm could be obtained after three passes of equal channel angular pressing at room temperature and 120 1C, respectively. Equal channel angular pressing of solid solution heat-treated Al-7075 alloy accelerates precipitation rate and subsequently leads to a significant decrease in aging time to attain maximum mechanical properties. Furthermore, it is possible to achieve maximum mechanical properties during equal channel angular pressing at 120 1C as a result of dynamic aging and formation of small η′ phase.     

Microstructure evolution and mechanical properties of Ti-8Nb-2Fe-0.2O alloy with high elastic admissible strain for orthopedic implant applications

A Ti-8Nb-2Fe-0.2O(wt.%) alloy with high strength,high elastic admissible strain(δ) and low cost was designed using d-electron theory combined with electron-to-atom ratio(e/a) approach.Interstitial oxygen was introduced to strengthen the matrix of the alloy.The β-solution treated alloy was mainly composed of α " martensite with internal {111}_(α") type Ⅰ nano-twins.The α " martensite with hexagonal-like crystal structure caused by interstitial oxygen showed a high strength of 1.1 GPa but limited ductility.The alloy generated equiaxed fine-grained a phase embedded by β matrix via hot rolling and subsequent annealing in α+β phase field.The obtained alloy indicated a good combination of mechanical properties with ultimate tensile strength,Young's modulus,ductility and δ value of 1029 MPa,74 GPa,21% tensile elongation and 1.32%,respectively.These findings demonstrate that interstitial oxygen and martensitic nano-twins can be used to strengthen the soft α" martensite and high elastic admissible strain can be obtained by formation of equiaxed fine-grained α phase embedded by βmatrix in this Ti-8Nb-2Fe-0.2O alloy for orthopedic implant.     

Mechanical properties and constitutive behaviors of as-cast 7050 aluminum alloy from room temperature to above the solidus temperature

The mechanical properties and constitutive behaviors of as-cast AA7050 in both the solid and semi-solid states were determined using the on-cooling and in situ solidification approaches, respectively. The results show that the strength in the solid state tends to increase with decreasing temperature. The strain rate plays an important role in the stress–strain behaviors at higher temperatures, whereas the influence becomes less pronounced and irregular when the temperature is less than 250°C. The experimental data were fitted to the extended Ludwik equation, which is suitable to describe the mechanical behavior of the materials in the as-cast state. In the semi-solid state, both the strength and ductility of the alloy are high near the solidus temperature and decrease drastically with decreasing solid fraction. As the solid fraction is less than 0.97, the maximum strength only slightly decreases, whereas the post-peak ductility begins to increase. The experimental data were fitted to the modified creep law, which is used to describe the mechanical behavior of semi-solid materials, to determine the equivalent parameter f_GBWL, i.e., the fraction of grain boundaries covered by liquid phase.     

Effects of aging treatment on the microstructure and superelasticity of columnar-grained Cu<Subscript>71</Subscript>Al<Subscript>18</Subscript>Mn<Subscript>11</Subscript> shape memory alloy

The effect of aging treatment on the superelasticity and martensitic transformation critical stress in columnar-grained Cu₇₁Al₁₈Mn₁₁ shape memory alloy (SMA) at the temperature ranging from 250°C to 400°C was investigated. The microstructure evolution during the aging treatment was characterized by optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results show that the plate-like bainite precipitates distribute homogeneously within austenitic grains and at grain boundaries. The volume fraction of bainite increases with the increase in aging temperature and aging time, which substantially improves the martensitic transformation critical stress of the alloy, whereas the bainite only slightly affects the superelasticity. This behavior is attributed to a coherent relationship between the bainite and the austenite, as well as to the bainite and the martensite exhibiting the same crystal structure. The variations of the martensitic transformation critical stress and the superelasticity of columnar-grained Cu₇₁Al₁₈Mn₁₁ SMA with aging temperature and aging time are described by the Austin–Rickett equation, where the activation energy of bainite precipitation is 77.2 kJ·mol?1. Finally, a columnar-grained Cu₇₁Al₁₈Mn₁₁ SMA with both excellent superelasticity (5%–9%) and high martensitic transformation critical stress (443–677 MPa) is obtained through the application of the appropriate aging treatments.     

Fe–0.3C–9Mn–2Al中锰钢的热塑性行为

The hot ductility of a Fe–0.3C–9Mn–2Al medium Mn steel was investigated using a Gleeble3800 thermo-mechanical simulator. Hot tensile tests were conducted at different temperatures (600–1300°C) under a constant strain rate of 4 × 10?3 s?1. The fracture behavior and mechanism of hot ductility evolution were discussed. Results showed that the hot ductility decreased as the temperature was decreased from 1000°C. The reduction of area (RA) decreased rapidly in the specimens tested below 700°C, whereas that in the specimen tested at 650°C was lower than 65%. Mixed brittle–ductile fracture feature is reflected by the coexistence of cleavage step, intergranular facet, and dimple at the surface. The fracture belonged to ductile failure in the specimens tested between 720–1000°C. Large and deep dimples could delay crack propagation. The change in average width of the dimples was in positive proportion with the change in RA. The wide austenite–ferrite intercritical temperature range was crucial for the hot ductility of medium Mn steel. The formation of ferrite film on austenite grain boundaries led to strain concentration. Yield point elongation occurred at the austenite–ferrite intercritical temperature range during the hot tensile test.     

Effects of annealing temperature on the microstructure and hardness of TiAlSiN hard coatings

TiAlSiN hard coatings were synthesized on high-speed steel using an arc ion enhanced magnetic sputtering hybrid system.The microstructure and hardness of the coatings at different annealing temperatures were explored by means of XRD,TEM,EDAX and Vickers indentation.The as-deposited TiAlSiN coatings were confirmed to be amorphous due to high depositing rate and low deposition temperature during the film growth.The transformation from amorphous to nanocomposites of nano-crystallites and amorphousness were observed after the annealing treatment,the microstructure of TiAlSiN coatings annealed at 800°C and 1000°C were consisted of crystalline hcp-AlN,fcc-TiN and amorphous phase,however,the coatings were only consisted of fcc-TiN and amorphous phase when annealing at 1100°C and 1200°C.Meanwhile,the formation of Al2O3 was detected on the coating surface after annealing at 1200°C and it indicated the excellent oxidation resistance of the TiAlSiN coatings under the present experimental conditions.Furthermore,the average grain size of the TiAlSiN coatings after high temperature annealing even at 1200°C was less than 30 nm and the size increased with the increasing temperature.However,the hardness of the so-deposited coatings with HV0.2N=3300 dramatically decreased with the increase of temperature and reached nearly to the hardness of TiN coatings with HV0.2N=2300.     

Solidification,microstructure, and mechanical properties of the as-cast ZRE1 magnesium alloy with different praseodymium contents

The influence of praseodymium (Pr) content on the solidification characteristics, microstructure, and mechanical properties of ZRE1 magnesium (Mg) cast alloy was investigated. The obtained solidification parameters showed that Pr strongly affected the solidification time, leading to refinement of the microstructure of the alloys. When the freezing time was reduced to approximately 52 s, the grain size decreased by 12%. Mg₁₂Zn (Ce,Pr) was formed as a new phase upon the addition of Pr and was detected via X-ray diffraction analysis. The addition of Pr led to a substantial improvement in mechanical properties, which was attributed to the formation of intermetallic compounds; the ultimate tensile strength and yield strength increased by approximately 10% and 13%, respectively. Pr addition also refined the microstructure, and the hardness was recovered. The results herein demonstrate that the mechanical properties of Mg alloys are strongly influenced by their microstructure characteristics, including the grain size, volume fraction, and distribution of intermetallic phases.