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The microstructure evolution of Al-Zn-Mg-Cu alloy with erbium was studied by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) during homogenization process. The results showed that there were serious component segregation in the as-cast structure of the alloy, mainly composed of T(AlZnMgCu) , S(Al2CuMg) and a small amount of Al8Cu4Er and Al7Cu2Fe. The overheating temperature of the alloy was 482.5 °C. After homogenized at 470 °C for 24 h, the dissolution of T(AlZnMgCu) phase and S(Al2CuMg) phase reached to a balance, but the residual Al8Cu4Er phase could not be dissolved completely. Compared with single-stage homogenization, Al3(Er,Zr) dispersion phase with smaller grain size and more uniform distribution can be obtained after two stage homogenization process of 400 °C for 8 h followed by 470 °C for 24 h. By comparing the residue of non-equilibrium eutectic phase, two-stage homogenization is the best.

A new type of near α high temperature titanium alloy of Ti-Al-Sn-Zr-Mo-Si-Er was studied. The samples with different primary α phase content were prepared by solid solution at 950 °C/1 h—1010 °C/1 h. The multi-step hot compression experiments were carried out by Gleeble-3500 in a sequence of upper region of α + β phase, then followed by lower region of α + β phase. The effects of primary α phase content and deformation temperature on the microstructure of the alloy were studied by means of true stress-strain curve and optical microscope. The results show that the content of primary α phase gradually decreases from 45.4% at 950°C to 0% at 1010°C. As the deformation temperature decreases from 940°C to 900°C, the content of α phase increases gradually from 65% to 94%, which is changed from dynamic recrystallization to deformed structure elongated along RD direction. It is found that the arrangement of α phase along RD direction is the longest at 920°C. With the increase of the deformation temperature in the multi-step high temperature region from 970°C to 990°C, the width of deformed α phase decreases from 3.64 μm at 970°C to 2.71 μm at 990°C. The optimized microstructure is composed of 20% primary α phase arranged along RD direction. This process has a certain potential in the process of hot deformation of the alloy. Key words: high temperature titanium alloy, primary α phase, multi-step hot deformation

The effects of the heat treatment process parameters on the microstructure and mechanical properties of a selective laser melted (SLMed) AlSi10Mg alloy were systematically investigated. The SLMed AlSi10Mg alloy was treated with T1 (180°C× 4h + air cooling) process, which had the microstructure of fine α-Al grains, fine Si phase, and nano-sized precipitations. The microhardness significantly increased to 150 HV, which is even higher than as-SLMed one (126 HV). The microhardness of SLMed AlSi10Mg alloy treated with T4 (540°C × 2h + water cooling) heat-treatment process significantly decreased to 62 HV due to the growth of α-Al grains, Si phase and the formation of β-AlFeSi phase. However, the microhardness and ultimate tensile strength of AlSi10Mg alloy treated with T6 (540°C × 2 h water cool + 180°C × 4 h air cool) process decreased to 91 HV, although the strengthening precipitation of Mg2Si phase formed. It indicates that the Mg2Si phase cannot compensate for the adverse effect of grain growth. It may provide the best potential heat treatment method for fabricating the high strength SLMed AlSi10Mg alloy.

The effect of the primary α content and precipitate on the creep resistance of a high-temperature titanium alloy with a small amount of Hf addition were studied. The microstructures with different primary α contents were prepared by the heat treatment of 920~1010 °C /1 h+700 °C/5 h, and the creep test (600 °C/150 MPa/100 h) was carried out. The interaction between the precipitation phase and the dislocation configuration was analyzed. The results showed that with the increase of solution temperature, the volume fraction of primary α phase decreased from 44.9% at 920 °C to 0% at 1010 °C, and the steady state creep rate of the alloy decreased from 60.60×10-4%/h to 3.72×10-4%/h, indicating that the creep property was significantly improved with the decrease of solution temperature. The basket structure with optimal creep resistance was obtained under the heat treatment of 1010 °C/1 h+700 °C/5 h. It is believed that during the high temperature creep test, the precipitated α2 phase and the hafnium-containing silicide hinder the dislocation motion in α crystal and the phase boundary, thereby improving the creep resistance of the alloy.

In this paper, an Al-Zn-Mg-Cu alloy with a small amount of Er and Zr added was used as the research object. The homogenization annealing was carried out, and the 7N01 aluminum alloy was used at 300 °C, 350 °C, 400 °C, 450 °C and 0.1 s-1, 1 s-1, 10 s-1 deformation conditions by Gleeble-3500 thermal simulator. Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM) were used for microstructure analysis. The results show that the stress-strain curve of with Er 7N01 aluminum alloy can be divided into micro-strain stage, uniform deformation stage and steady-state flow stage during the thermal compression process. The flow stress of 7N01 aluminum alloy achieved peaks at the initial stage of strain, and then increased with the increase of strain rate and the decrease of deformation temperature. With the increase of deformation temperature and the decrease of deformation rate, the recrystallization process was significantly increased.

The served harsh environment of advanced aircraft engine puts forward higher requirements for high temperature titanium alloy performance. The optimized heat treatment technology provides effective theoretical basis for improving the microstructure and properties of high temperature titanium alloys. In this paper, we study the influence of different heat treatment systems on microstructure and mechanical properties of high temperature alloy with equiaxed structure, in order to obtain the corresponding relationship between the process and the microstructure performance of the alloy and the optimal heat treatment process. Analysis the effect of solution treatment on the primary α phase quantitatively by optical microscope and Image-Pro-Plus 6.0 software based on the forged high temperature titanium alloy in α+β phase region. Observe the precipitation of α2 phase and silicide by TEM, optimize the aging process according to hardness test. The results show that the content of primary a phase decrease from 63.3% at 920°C to 15.3% at 990°C with the increase of solution temperature. When the temperature rises to 980~990°C, the structure changes from equiaxed structure to α+β duplex microstructure. And change into lamellar structure when the solution temperature raise to 1010°C. The secondary α phase precipitates more fully when the aging temperature increases. And with increasing aging time, the trend of α2 phase growth become more significantly. The optimum heat treatment system obtained in this experimental is 990°C/1h/AC+700°C/5h/AC, and the α phase is about 15.3%. Hence, the excellent microstructure and properties match has been obtained.

A triple-microstructure with the precipitation of silicide along the α/β phase boundaries and α2 phase in the Ti-5.8Al-3Sn-5Zr-0.5Mo-1.0Nb-1.0Ta-0.4Si-0.2Er alloy was prepared for improving thermal stability and creep resistance. The alloys were forged at 1050 °C and 1000 °C followed by solution treatment at 1000 °C for 1 h and subsequent ageing at 700 °C for 5 h. The effects of α morphology and precipitation characteristics on the thermal stability and creep performance of high-temperature titanium alloy were investigated. A triple-microstructure with the participation of silicide along the α/β phase boundary and α2 phase was a promising structure with improved thermal stability and creep resistance. The plasticity loss rate was 25.0% after thermal exposure at 650 °C for 100 h due to the participation and coarsening of α2 and silicide. Meanwhile, the plastic creep strain was 0.111% during the creep deformation at 650 °C for 100 h with an applied stress of 100 MPa, which was attributed to the inhibition of silicide and α2 phase for boundary migration and dislocation slipping. Furthermore, the mutual precipitation of coarsening silicide and α2 phase inside α matrix was a significant reason for the dramatic decrease in the thermal ability, which also worsened the inhibition for dislocation climbing of silicon element during the creep deformation.

Dislocation boundary response and characteristic micro-structure were investigated in commercial pure titanium during the penetration impact and dynamic compression. The initial dislocation boundary induced by cold rolling can strengthen the adiabatic shearing sensitivity of commercial pure titanium during the penetration impact, which is consistent with the mechanical response and micro-structure during the dynamic compression. The compression with a loading direction vertical to the initial geometrically necessary boundaries (GNBs) results in the decrease in the spacing between GNBs, while the compression with a loading direction parallel to the initial GNBs attributes to the generation of new dislocation boundary crossed with the initial one. Then, a model of distribution and morphology of dislocation boundary around crater is proposed.

The microstructure and micro-orientation evolution of a novel high-temperature titanium alloy were characterized during a two-step deformation process. In the first step, the specimens were deformed at temperatures of 800, 850, 900 and 950 °C, and subsequently deformed in the same β-phase region of 1050 °C. The specimens pre-strained at 800 °C and 950 °C were fully recrystallized during the β-phase deformation process. By contrast, the specimens pre-strained at 850 and 900 °C were not fully recrystallized during the β-phase deformation process. This indicates that the extent of dynamic recrystallization did not increased monotonically with the pre-strain temperature. The extent of dynamic recrystallization was related to the stored energy accumulated in the α and β-phase during the pre-strain deformation. The change in stored energy was based on the difference in microstructure morphology produced by different pre-deformation temperatures,and stored energy was quantitatively estimated based on the local misorientation distribution. Meanwhile, the generation of dynamically recrystallized grains was beneficial to decreasing the generation possibility of the macro-zone. This decrease was attributed to the refinement of β-grains and randomly distributed orientation, which was also related to the decrease in the typically distributed “two parallel wings” orientation between the α and β phase induced by uncrystallized deformation. Additionally, the two-step deformation process with the pre-strain at the (α + β) middle regime was an effective strategy to promote the dynamic recrystallization and decrease the generation probability of the macro-zone.

The effect of the different electromagnetic stirring frequency after low temperature pouring on microstructures and mechanical properties of Al-7Si-0.42 Mg-0.1Cu alloys was studied. It was found that the primary α-Al becomes smaller and tended to be spherical morphology, and the particles were uniformly distributed after electromagnetic stirring. The tensile strength of alloys improved gradually from 193.02 MPa to 212.54 MPa, and the elongation increased from 3.73% to 6.67% when the stirring frequency was 10 Hz. From the fracture morphology, the fracture for alloy stirred at frequency of 10 Hz showed more dimples than that without stirring. When the stirring frequency increased to 15 Hz, the microstructures of primary α-Al appeared to be dendritic structures, and the grains became coarse. As a result, the 10 Hz was the best electromagnetic stirring frequency.

A new high-temperature titanium alloy containing erbium was designed and fabricated. The influence of α+β forging process and β forging process on microstructure and mechanical properties of the alloy was studied. The microstructure, mechanical properties and fracture morphologies of the new high-temperature titanium alloy after different forging processes were characterized. The results showed that the forging process significantly affected the microstructure of the alloy. The alloy exhibits nearly equiaxed microstructure and lamellar microstructure after α+β and β forging, respectively. In addition, there were Er-rich phases in both forged alloys. The alloy with nearly equiaxed microstructure acquired a satisfactory comprehensive performance. However, the alloy with lamellar microstructure had higher strength and less plasticity. The tensile fracture of the alloy after α + β forging had more dimples, while cleavage plane was obvious in the alloy after β forging. Owing to the addition of erbium and the formation of Er-rich phases, forged alloys possess excellent strength. The Er-rich phase might be the main reason for the fracture.

The 6061 aluminum alloys with different content of erbium were prepared. The erbium content was optimized by measurement of grain refining effects and tensile strength. After solid solution treatment of the alloy with optimized erbium content at 505 °C ~ 595 °C for 4 h. and then ageing at –160 °C ~ 200 °C for 3 h., the grain size decreased with the content of erbium, achieving the most effective grain size refinement at the erbium content of 0.15wt.%. The tensile strength of as-cast alloy could reach up to 243 MPa at the erbium content of 0.15%. -Combined with the microstructures and mechanical properties, the erbium content of 0.15% was the optimized content, and heat treatments of ageing at 180 °C for 3 h. followed by solid solution at 565 °C for 4 h were suggested.

The microstructures and mechanical properties of the high temperature titanium alloys containing Er, i.e. Ti-6Al-2.5Sn-4Zr-0.3Mo-1Nb-0.35Si-xEr (x=0, 0.1, 0.3wt%), were investigated. Both the grain size and lamellar structure inside grains were significantly refined with the addition of Er in as-cast alloys. Lamellar and duplex microstructures were obtained after forging and heat treatment. Silicide precipitates were generated in the boundary of lamellar α phase after aging treatment. Meanwhile, a few α2 phase were precipitated in the alloys after aging treatment. After 600°C /100h thermal exposure, the α2 phases with a mean size of 7nm and spacing of 10 nm were precipitated homogeneously in α lamellar. The creep properties were significantly improved by the addition of rare earth Er due to the formation of the second phase containing Er, silicide and α2 phase.

The microstructure and mechanical properties of as-homogenized 6061 aluminum alloy with 0.2wt.% Er were investigated. The microstructures of the as-casted and homogenized alloys were analyzed using optical microscopy (OM) and scanning electron microscopy (SEM). Energy dispersion X-ray spectroscopy (EDS) was used to analyze the phase chemical composition. The results showed that the homogenizing treatment had a significant influence on the precipitate morphology of the alloy. With increasing homogenization temperature, the long strip-like Fe-rich grain distributed on the boundary phase became discontinuous and sparseness, transforming to short rod and granular shape. In addition, the Fe-rich phase with a large fish-bone structure became smaller. During homogenizing treatment, a large number of dispersive Mg2Si phase appeared inside grains, and large number of the phases containing Er were dissolved into the matrix.

The effects of homogenization treatments on the precipitation behavior of Al 3 (Er,Zr) particles and theirs effects on recrystallization resistance in a new type Al-Zn-Mg-Er-Zr alloy have been investigated. Four different homogenization treatments, conventional one-stage homogenization, double-stage homogenization and ramp heating homogenization are carried out. Compared with that in the conventional one-stage homogenization, a finer particle size, higher number density and volume fraction of Al 3 (Er,Zr) particles can be obtained in other three homogenization treatments. In addition, the double-stage homogenization and the ramp heating homogenization can improve the Al 3 (Er,Zr) particles distribution and minimize the width of precipitation free zone in the region near the grain boundary, and provide an additional but nonnegligible strengthening effect for the Al-Zn-Mg-Er-Zr alloy. The difference in precipitation behavior of Al 3 (Er,Zr) particles lead to different recrystallization resistance. The high recrystallization resistance can be attributed to the larger f V /r ratio of Al 3 (Er,Zr) particles, which resulting in a higher Zener drag to effectively resist the recrystallization in Al-Zn-Mg-Er-Zr alloy during hot deformation and the subsequent thermal processing. Therefore, under the same annealing time, the double-stage homogenized and the ramp heating homogenized samples can achieve a significant lower recrystallized fraction compared with the conventional one-stage homogenized samples.

Isothermal compression testing of Ti–5.8Al–3Sn–5Zr–0.5Mo–1.0Nb–1.0Ta–0.4Si–0.2Er titanium alloy is performed on a Gleeble-3500 thermal simulator, and the corresponding microstructures are analyzed to clarify the softening mechanism and participates evolution. A constitutive equation compensated by strain has been established to describe the hot deformation behavior of the alloy. The deformation activation energies are calculated to be 369760.93–699310.86 J/mol in α + β two-phase region and 268030.03–325800.41 J/mol in β single-phase region. At a temperature of 880 °C, the main softening mechanism is the continuous dynamic recrystallization of lamellar α colony, controlled by the mechanical rotation of the sub-grain followed by dislocation climbing and annihilation by diffusion. Meanwhile, the dominant softening mechanism is the discontinuous dynamic recrystallization of β phase during the deformation at temperatures of 920 °C–1080 °C. Silicide containing Er with an average diameter of 20 nm is formed during the water quenching.

The homogeneity of microstructure and microhardness in different parts of as-fabricated selective laser melting (SLM) and as-solutionized Ti-6Zr-5Fe alloy is presented in this paper. The results show that the as-fabricated SLM alloy has a bigger β phase and finer α phase size in the top part than that in the bottom part due to the reheating treatment during SLM process. However, as-solutionized Ti-6Zr-5Fe alloy mainly consists of β phase in the top part, and the bottom part is mainly comprised of β and α phase in the grain boundary. Apart from the change of phase composition, the β phase size in bottom part is smaller than that in the top part, due to the precipitation of α phase at the grain boundary in the bottom part. The fine α phase in the top part of as-fabricated SLM Ti-6Zr-5Fe alloy results in that the top part has a higher microhardness (518 HV) than the bottom part (394 HV). While, the microhardness becomes almost the same in the top part (482 HV) and bottom part (475 HV) after solid solution treatment. The dissolution of fine α phase in the top part and solution strengthening of Fe and Zr element in the bottom part after solution treatment improve the uniformity of microhardness. This research provides an approach for obtaining the gradient microstructure or gradient property for near-β Ti alloy samples by governing the parameters of SLM technology and solution treatment.

A series of ternary Ti–6Zr-xFe (x = 4, 5, 6, 7 wt %) biomedical titanium alloy was designed to develop potential biomedical materials. The effect of the Fe content on microstructure, mechanical properties, Young’s modulus, and electrochemical behavior was studied in depth. The developed Ti–6Zr-xFe (x = 4, 5, 6, 7 wt %) alloys are mainly composed of α and β phases. The results indicated that the grain size of the β phase in Ti–6Zr-xFe alloys decreased with the increase of Fe element. The increase of Fe content also caused the decrease of α phase fraction, increase of β phase fraction and formation of ω phase. Besides, the increase of Fe content improved the microhardness (264, 300, 328, and 348 HV) and ultimate tensile strengths (748, 829, 917, and 994 MPa) of Ti–6Zr-xFe alloys due to the contribution of solid-solution strengthening effect for higher Fe contents, the refined strength of the β phase and the dispersion strength of ω phase. Young’s modulus of Ti–6Zr-xFe alloys was 90, 93, 93, and 94 GPa, which was lower than that of Ti–6Al–4V alloy. Moreover, the Ti–6Zr-xFe alloy with the addition of 4 and 5 wt % Fe displayed excellent corrosion resistance. These results show that Ti–6Zr-xFe alloys are potential biomedical materials.

Selective laser melting (SLM) process belongs to a layer-by-layer additive manufacturing technology, which has different temperature gradients, cooling rates, and reheating treatment in different regions due to the variation of the thermal histories for different layers during SLM process. This work aims to study the microstructural homogeneity evolution of β phases, such as size, morphology, distribution, crystallographic orientation, and phase composition in different regions of the SLM Ti-6Zr-5Fe near β titanium alloy. The results indicate that the microstructure in different regions of SLM Ti-6Zr-5Fe alloy sample is quite different. The β phase in the bottom area had the smallest size about 7.25 μm, the β phase in the side-top area had the largest size about 20.56 μm. The β phase in the side-middle and middle part had a lower aspect ratio of 1.52 and 1.59, the β phase in the side-bottom and top part had a larger aspect ratio of 1.93 and 1.92. Most of the β phase in the side-bottom and top part had the 〈001〉 crystal orientation towards build direction and laser moving direction, the texture type in other regions was random. The α phase in the top of the SLM Ti-6Zr-5Fe sample had a smaller size than that in the middle and bottom of the sample. Meanwhile, the microhardness in the top of SLM Ti-6Zr-5Fe sample was higher than that in the middle and bottom of the sample. The temperature gradients, cooling rates, and reheating treatment play different leading roles in different regions of the SLM Ti-6Zr-5Fe alloy sample.

In this paper, effects of initial micro-structures on deformation behaviors of commercial pure titanium were elaborated by investigating the evolution of dislocation boundary and its adiabatic shear sensitivity. At the low to medium stain rates, the main plastic deformation mechanism of as-annealed commercial pure titanium is dislocation slipping. Meanwhile, geometrically necessary boundaries (GNBs) with different directions are generated and crossed with each other. However, new dislocation boundaries are formed in as-cold rolled plates, which are parallel to the initial ones induced by cold rolling. When the strain rate is up to 1000 s-1, the initial dislocation boundary playes an adverse role in the adiabatic shear sensitivity of commercial pure titanium. The adiabatic shear band is the high-speed deformation characteristic micro-structure in commercial pure titanium. In addition, dynamic recrystallized grains are generated in the center of an adiabatic shear band, which is consistent with the sub-grain rotation mechanism.

Al-Si alloy was widely applied in automobile engine parts to realize weight reduction. The influence of casting temperature on the microstructure of die casting Al-Si-Cu-Mg alloy was studied in this paper. Based on ZL 101 alloy, the strength was improved with addition of 0.8% Cu element. The influence of pouring temperature on microstructure was investigated using optical microscope and electron probe micro-analysis (EPMA), and T1 heat treatment was optimized. The primary α-Al was more coarsened when the pouring temperature rose from 660 ̊C to 690 ̊C. The solid solubility of Cu in α-Al was 0.2406 wt%, analyzed by EPMA. Considering the solid solubility of Cu and avoiding porosity at high-temperature, T1 heat treatment was reasonable and affective. The micro-hardness reached to a peak value of 114 HV during aging at a temperature of 175 ̊C after 10 h. Therefore, 175 ̊C×10h aging was the most appropriate heat treatment process.

As-annealed commercial pure titanium was selected as a model material with hexagonal close-packed (hcp) crystalline structure. Dislocation boundaries with different spacing values were prepared by cold rolling at various reductions. The influence mechanism of the initial dislocation boundaries on the adiabatic shear sensitivity of commercial pure titanium was investigated from two aspects: related dynamic mechanical response and dislocation boundary configuration. The geometrically necessary dislocation boundaries (GNBs) with spacing values of 550 nm, 340 nm and 107 nm were induced by cold rolling. The narrower the spacing of the GNBs was, the more sensitive the adiabatic shearing behavior was, which was attributed to the shear stress and adiabatic temperature rise. A narrow spacing of GNBs shortened the mean free path of dislocation slipping; as a result, the deformed resistance and accumulated plastic deformation work became larger. Therefore, the adiabatic temperature rise that was converted from plastic deformation work increased, thereby strengthening the material's adiabatic shear sensitivity.

The commercial pure titanium plate was shot vertically by the projectile with a diameter of 7.62mm at impact velocities ranging from 782m/s to 825m/s. The microstructure around the crater of commercial pure titanium plate was analyzed by optical microscopy (OM) and electron backscatter diffraction (EBSD) methods. It was found that different microstructures were observed along the depth of cater. In upper region of the crater, grains were deformed and fragmented. Adiabatic shear bands (ASBs) were observed in the middle of the crater, and some ASBs were bifurcated. At the bottom of the crater, the grains were less deformed, and the deformation twins were formed. The microstructures in the center of adiabatic shear band were mainly consisted of the dynamic recrystallization grains and sub-grains. The microstructure in the transition region was elongated grains along the shear stress distribution.

The as-casted Al-Si-Mg alloy was treated by solution and aging process of 545°C/10h/water cooling plus 175°C/6h /air cooling. The effect of heat treatment on the microstructure and mechanical property of Al-Si-Mg was investigated by metallographic analysis, scanning electron microscopy, energy dispersion spectrum analysis and mechanical testing. The experimental results showed that the alloy had the ultimate tensile strength (UTS) of 317MPa and the elongation of 2%, and suitable for squeezing cast. During solution treatment, the plate-like eutectic Si particles became small granular or short bacilliform morphology, and the non-uniformly distributed eutectic phase was eliminated substantially. In addition, Si particles distributed uniformly and finely in the matrix. The tensile strength of as-casted alloy was 180 MPa, while it was up to 317 MPa after solution and aging treatment process, and the elongation increased from 2% to 3%, which is consistent with the microstructure. Fracture surface analysis showed that fracture mode of the alloy transformed from brittle fracture into co-existence of ductile fracture and brittle fracture during T6 treatment.

At present, the extensive research on laser protective materials is mainly focused on ensuring the linear transmittance and improving the optical limiting ability. Phthalocyanine has become a promising optical limiting material because of its special large π electronic conjugated structure, which makes it has excellent nonlinear optical properties and fast optical-electron response. Here, we synthesized a sulfonyl-containing hyperbranched lanthanum phthalocyanine (HLaPc) and covalently linked the anthraquinone groups (HLaPc-HAQ) in its axial direction. Since a donor-acceptor system is formed between phthalocyanine and the anthraquinone in HLaPc-HAQ, the electron transfers can effectively enhance the nonlinear optical properties of HLaPc-HAQ. According to the “like dissolves like” theory, two kinds of homogeneous films have been obtained by blending HLaPc and HLaPc-HAQ with yellow polyphenylene sulfoxide containing anthraquinone groups (YPPSU). The films obtained by solution casting method have high transmittance and excellent optical limiting properties. Especially, the Z-scan results show that the lowest incident intensity threshold (Ilim) of HLaPc-HAQ/YPPSU can reach 0.012 J cm-2, and the linear transmittance can still maintain above 57%. This means that the materials obtained in this work surpassed much previously reported work in terms of comprehensive linear transmittance and optical limiting performance. In addition, the energy level model was drawn by the results of the cyclic voltammogram of the solution and the solid films. And from the perspective of the energy level transition, it was confirmed that there are a larger proportion of molecules in the solid films for intersystem crossing, thereby improving optical limiting performance.

The deformation twins of commercial pure titanium were investigated under the split Hopkinson pressure bar compression with different strain rates. It was demonstrated that the types of twins induced by high-speed compression included 11 2 ¯ 2 , 11 2 ¯ 4 contraction twins and 10 1 ¯ 2 , 11 2 ¯ 1 extension twins. Furthermore, the quantities of the deformation twins at the high strain rates were more pronounced than those at the low to medium speed deformation. The content of 11 2 ¯ 2 twin increased with the strain rate, while 11 2 ¯ 1 twin's quantity decreased slightly with the increasing strain rate. The semi-quantitative relationship between twin density and strain rates was derived and discussed, which indicated that twin density was nonlinearly proportional to the strain rate.

The high temperature strength of aluminum can be improved by forming thermal stable precipitates of microalloying elements such as Er, Sc and Zr. Our previous research indicates that composite addition of Er and Zr can improve the amount of precipitations, but the aging time to approach the peak hardness is relatively long. In this paper, we will focus on the deformation behavior of the Al-Er-Zr alloy during hot deformation process and the corresponding microstructure evolution. The results show that the strain can induce rapid precipitation in Al-Er-Zr alloy during hot working conditions. The mechanism of the rapid precipitation and its effect on thermomechanical processing are discussed.

Our former experimental study showed that the addition of Er to Al-Zn-Mg alloys speeded up the aging precipitation, accelerated the precipitation of and enhanced the effect of aging strengthening distinctively. In this paper, the Monte Carlo method was applied to simulate the microstructural evolution of Al-2.6Zn-(2.3Mg)-(0.07Er), Al-2.6Zn-2.3Mg-(0.12Er), and Al-2.6Zn-2.3Mg-0.1(Er,Zr) alloys during aging. The effects of Er addition to Al-Zn-Mg alloys on the clustering of Zn and Mg atoms are studied through analysis of the simulation results and the effects on the subsequent aging process are discussed as well. The results show that the Zn/Mg/Er clusters appear beside the Zn clusters, Mg clusters and Zn/Mg clusters in the Er addition Al-Zn-Mg alloys. The Zn clusters and Zn/Mg clusters are finer in the Al-2.6Zn-2.3Mg-xEr alloys than that in the Al-2.6Zn-2.3Mg alloys without Er addition. The size of the Zn clusters and Zn/Mg clusters in the Al-2.6Zn-2.3Mg-0.07Er is eight percent and nineteen percent smaller than that in the Al-2.6Zn-2.3Mg alloys without Er addition respectively. This precipitation refinement effect of Er addition to the Al-2.6Zn-2.3Mg alloys is enhanced with the increment of Er content. These above results are consistent with the experimental results that the precipitation in the Al-Zn-Mg alloys with Er is finer and denser than that in the Al-Zn-Mg alloys without Er. The Er addition changes the clusters distribution in the Al-Zn-Mg alloys by its interaction with the main solute atoms and the vacancy, and thus influences the precipitations during subsequent aging processing.

Mechanical properties, corrosion resistance, and microstructure of Al alloys with trace element erbium were studied. Systemic studies in the pure aluminum and 5xxx series Al alloys showed that the tensile strength was significantly improved by above 20% with little loss of elongation by Er alloying. The 5xxx series Al alloys with erbium also exhibited excellent corrosion resistance. Erbium improved the aging hardness response of 7xxx series Al alloys and the addition of 0.4%Er to Al-Zn-Mg alloys increases the hardness by 35MPa. In all experiment Al alloys, a small addition of 0.1wt% Er induced a quick increase of the tensile strength and the amount of 0.4%Er shows optimized balance of the strength and ductility. The Er addition improved the thermal stability, with increasing the starting Rex temperature about 50°C in all investigated Al alloys. With regard to the microstructure mechanisms, in all experimental Al alloys Er addition has significantly refined the microstructure, which mainly attributed to presence the Al3Er particles. In the 7xxx series Al alloys, no observable PFZ after addition of 0.4% Er was found. The fatigue property, the fracture toughness and the thermal stability of microstructure and properties are on the way.

The microstructure and microstructural evolution were investigated near crater wall in Al–Cu–Mn alloy using optical and transmission electron microscopy (TEM) after projectile impaction. The results show that three characteristic zones around the crater can be classified based on the different microstructure, i.e. deformation bands, dynamic recovery zone and adiabatic shear bands (ASBs). The TEM observation indicates that the dislocation glide plays a crucial role in the formation of that microstructure during projectile impact. The adiabatic shear bands were formed near the crater wall and extend into matrix. It can be found that fine grains were formed within the adiabatic shear bands by dynamic recrystallization occurring during projectile impact. The micro-cracks have been developed along the adiabatic shear bands. However, It is demonstrated that the formation of deformation bands are favorable for improving anti-impact property of Al–Cu–Mn alloy, but adiabatic shear bands are easily to initiate micro-cracks, leads to the failure of target material.

TC21 titanium alloy was hot compressed isothermally at temperatures ranging from 880 °C to 950 °C and strain rates ranging from 0.01 to 10 s −1 . Microstructures were investigated by electron backscatter diffraction (EBSD) technique and transmission electron microscopy (TEM), and processing maps were developed at different strains. It is found that strain rate is a key factor for the formation of hot deformation microstructure. The stress–strain curves were exhibited flow softening behavior at high strain rate above 1 s −1 , while equiaxed grains were found at lower strain rates. There is no large instability zone besides two peak-areas of 880–900 °C, 1–10 s −1 and 925–950 °C, 10 −0.5 to 10 s −1 .

The hot deformation behavior of an Al–5.7 wt.%Mg alloy with erbium has been investigated. Compression tests are performed in the temperature range of 300–500 °C and in the strain rate ranging from 0.001 s−1 to 50 s−1 up to a true strain of 0.7. The processing maps are developed at different strains and the standard kinetic analysis has been applied to evaluate the rate controlling mechanisms. The processing maps have exhibited two domains of 350–450 °C at 0.001–0.03 s−1 and 450–500 °C at 0.01–1 s−1, representing dynamic recovery of Al–5.7 wt.%Mg with erbium. The apparent activation energies estimated in these two domains are 180 kJ/mol and 163 kJ/mol respectively, which suggests that cross-slip of dislocation and lattice self-diffusion are the deformation mechanisms. At strain rates higher than 10 s−1, the flow curves demonstrate flow softening behavior, and the flow instability regions reveal mixed microstructure of local deformation and dynamic recrystallization.

Recrystallization behavior of SPD processed high purity iron was studied. The 99.95% iron sheet was deformed by the accumulative roll-bonding (ARB) process up to 8 cycles (equivalent strain of 6.4) at ambient temperature. Subsequently, the ARB-processed specimens were annealed for 1.8ks at various temperatures from 300°C to 500°C. The microstructures of these specimens were characterized by TEM and SEM/EBSP. The microstructure of the as-ARB-processed specimens showed the lamellar boundary structure elongated along RD, which was the typical microstructure of the ARB-processed materials. The mean interval of the lamellar boundaries was about 100 nm. After annealing at 400°C, the ARB specimen showed a partially recrystallized microstructure composed of equiaxed grains with grain size larger than 10 5m and the recovered lamellar boundary structure. After annealing above 500°C, the microstructures were filled with equiaxed recrystallized grains. These results suggest that conventional discontinuous recrystallization characterized by nucleation and growth occurs during annealing at annealing temperature above 400 °C. In previous work reported about the annealing behavior of the low carbon IF steel ARB processed, the continuous recrystallization occurred during annealing at annealing temperature above 600 °C. The recrystallization temperature of the pure iron was much lower than the IF steel and the recrystallization process were significantly different. This difference was suggested to be caused by inhomogeneous microstructure in the pure iron ARB-processed.

We have systemically studied the effect of the erbium on the microstructure and the mechanical properties in the 5xxx series aluminum alloys by using optical microscope, transmission electron microscope (TEM) and by tensile testing. The results demonstrate that the tensile strength increased quickly at the beginning of small contents of 0.1%Er both in the hot and cold rolled states, then slowly increased with increasing the contents of Er until 0.4%, at which the best balance of the strength and ductility (438MPa and 9.6%) were obtained. Microstructure observation in the hot rolled state was indicated that the grain structure in the Er free Al-5Mg alloy revealed fully recrystallized grain structure, while in the Al-5Mg containing Er was demonstrated deformation structure, indicating the Er addition delayed the recrystallization behavior by the formation of the precipitation of the Al3Er, which confirmed by means of the X-ray diffraction analysis. Furthermore in the TEM microstructure observation the precipitation of Al3Er was distributed both in the grain interior and subgrain or grain boundaries, which could be pinning the subgrain or grain boundary migration and dislocation movement as well. Consequently the beginning of the recrystallization temperature in the Al-5Mg containing Er was elevated about 50°C than in Al-5Mg without Er. This could be explained that the strength increased without the deterioration of the ductility was attributed to the microstructure refinement by the Er addition.

Ultra-low carbon steel (ferritic steel), commercial purity aluminum and high purity copper were heavily deformed by the accumulative roll bonding (ARB) process, and the microstructural evolution during the ARB was analyzed. Significant grain refinement by grain subdivision mechanism was confirmed in all three kinds of materials. On the other hand, microstructure refinement slowed down with increasing strain and the grain size stayed in nearly a constant value in the ultrahigh strain region. The mechanism of the grain size saturation was discussed.

A 36mass% Ni austenitic steel was deformed to equivalent strains of 0.8 to 4.8 by the accumulative roll-bonding (ARB) process at 500°C, with slight lubrication. We analyzed the microstructure and crystallographic analysis by employing the electron back-scatter pattern (EBSP) technique in a field emission gun (FEG) SEM. After several ARB cycles, ultrafine lamellar boundary structures elongated in the rolling direction (RD) formed uniformly in the material. Observations indicated that the mean spacing of high-angle lamellar boundaries determined from the EBSP results decreased exponentially as a function of equivalent strain. The fraction of high-angle boundaries (HABs) increased, thus the average misorientation of the boundaries increased with increasing strain. In the six-cycle ARB-processed specimen, the mean spacing of the uniform lamellar boundaries was 150 nm, the fraction of HABs was 75%, and the average misorientation was 32°. The ultrafine lamellar boundary structure in the 36%Ni austenitic steel was finer and straighter than in ferritic steel (IF steel) deformed under similar conditions, probably because recovery occurs more easily in ferritic steel than austenitic steel.

An oxygen free high conductivity (OFHC) copper (99.99%) was intensely deformed by the accumulative roll-bonding (ARB) process up to equivalent strain of 4.8 at ambient temperature. The microstructure evolution during the ARB process was explained by grain subdivision. The deformed specimens revealed dislocation cell structures at low strain and elongated ultra fine grains separated by high angle boundaries at high strain. The spacing of the high angle lamellar boundary exponentially decreased as a function of strain. The fractions of high angle boundaries (HAB) and the low angle boundaries (LAB) were nearly equal even at strain of 3.2, which was significantly different from the ARB processed Al alloys and ferritic steel where the HAB fraction was above 70% at the same strain. TEM observations indicated a mixed microstructure of dislocation boundaries and cell walls with dislocation tangle at low strain of 1.6, and small recrystallized grains partly appeared above strain of 3.2. As a result, the LAB fraction due to partial recrystallization was high even at strain of 4.8. The occurrence of recrystallization is attributed to high purity of the OFHC copper, the accumulated dislocation density, and the adiabatic heating during the ARB process of one-pass large reduction without lubrication.