压下量对WE43镁合金变形机理和孪生行为的影响（英文）

研究最后一道次压下量对铸态WE43镁合金在480℃直接热轧过程中位错滑移和孪生行为的影响。结果表明,在480℃轧制时柱面滑移始终是主要的滑移模式。另外,不同压下量下激活的孪生类型不同。较小的压下量(2%)下激活的主要是{■}拉伸孪生,而在较大的压下量(12%和20%)下激活的主要是{■}压缩孪生和■二次孪生。Schmid因子计算表明,{■}孪晶变体选择遵循Schmid定律,而{■}孪晶变体选择不遵循Schmid定律。即使单道次压下量达到20%也几乎没有发现动态再结晶晶粒,这可能是因为没有达到动态再结晶所需要的变形量。     

Effect of hot deformation on α→β phase transformation in 47Zr-45Ti-5Al-3V alloy

The effect of strain rate and deformation temperature on the α→β phase transformation in 47Zr-45Ti-5Al-3V alloy with an initial widmanstatten α structure was investigated. At the deformation temperature of 550 °C, the volume fraction of α phase decreased with increasing strain rate. At 600 and 650 °C, the volume fraction of α phase firstly increased to a maximum value with increasing strain rate from 1×10^?3 to 1×10^?2 s^?1, and then decreased. At 700 °C, the microstructure consisted of single β phase. At a given strain rate, the volume fraction of α phase decreased with increasing deformation temperature. With decreasing strain rate and increasing deformation temperature, the volume fraction and size of globular α phase increased. At 650 °C and 1×10^?3 s^?1, the lamellar α phase was fully globularized. The variation in the volume fraction and morphology of α phase with strain rate and deformation temperature significantly affected the hardness of 47Zr-45Ti-5Al-3V alloy.     

Effect of heat treatment and exposure on microstructure and mechanical properties of Ti–25V–15Cr–2Al–0.2C (wt%)

The effect of heat treatment and exposure on the microstructure and mechanical properties of extruded, burn-resistant β titanium alloy Ti–25V–15Cr–2Al–0.2C (wt%) has been studied. It has been found that pre-exposure annealing at 600, 700 and 800°C affected the distribution of α phase that precipitated following subsequent exposure at temperatures between 450 and 550°C. Samples annealed at 600°C and subsequently exposed at 450°C showed excellent microstructural and property stability. Although the room-temperature ductility of the alloy decreased and the strength increased slightly with increasing exposure time at 500°C, no further drop in ductility was observed after 500 h. However, a gradual degradation of properties with exposure time was observed in samples exposed at 550°C. The significance of the observations is discussed in terms of the effect of pre-exposure annealing and exposure on α precipitation and tensile properties.     

Precipitation Behavior of α Phase and Mechanical Properties in Severely Plastic Deformed Ti-15-3 Alloy

研究了大变形量冷轧Ti-15-3合金的时效析出行为和时效过程中力学性能的变化。冷变形使Ti-15-3合金中形成部分纳米晶。冷变形合金在450～650℃时效时,从β相纳米晶区析出极为细小的针状α相,而从β相非纳米晶区析出的α相随着时效温度的升高由针状逐渐长大为条状,进而演变为凸透镜状。冷变形合金在450℃时效4h后,硬度达到了峰值,HV为5328MPa。450℃时效时在硬度峰值处同样达到了强度峰值,屈服强度和抗拉强度分别可高达1483和1562MPa。时效温度升高,达到峰值硬度的时间缩短,硬度值大幅度下降。650℃时效后的强度和硬度均低于时效前,粗大的透镜状析出相、纳米晶的长大以及位错密度的急剧下降是650℃时效时硬化效果消失的主要原因。不同时效工艺下的强度和硬度的变化规律相似,性能的变化与时效过程中析出相的状态有关。     

Effect of the quasi-continuous equal-channel angular pressing on the structure and functional properties of Ti–Ni-based shape-memory alloys

The effect of severe plastic deformation by equal-channel angular pressing (ECAP) under normal and quasi-continuous regimes on the structure and the mechanical and functional properties of a Ti–50.2 at % Ni shape-memory alloy (SMA) has been studied. ECAP was carried out at an angle of intersection of channels of 120° in the normal regime with heating between passes at 450°C for 20 passes and in the quasi-continuous regime at the temperature of 400°C for three, five, and seven passes. The hot screw rolling with subsequent annealing at 750°C for 30 min and cooling in water was used as a control treatment (CT). A mixed submicrocrystalline and nanosubgrained structure was formed. The increase in the number of passes from three to seven led to a decrease in the average size of structural elements from 115 ± 5 to 103 ± 5 nm and to an increase in the fraction of grains/subgrains having a size less than 100 nm. After ECAP (seven passes) and post-deformation annealing at the temperature of 400°C for 1 h, a completely recoverable strain was 9.5%; after normal ECAP, 7.2%; after CT, 4.0%.     

Microstructure evolution of TA15 titanium alloy subjected to equal channel angular pressing and subsequent annealing at various temperatures

TA15 titanium alloy was successfully processed for the first time by equal channel angular pressing (ECAP) in the temperature range of 900-1000 °C and annealed in a wide temperature interval from 650 to 800 °C. The investigation was achieved by light microscope (LM), scanning electron microscope (SEM) and transmission electron microscope (TEM) on the microstructure evolution of TA15 alloy subjected to ECAP and subsequent annealing after ECAP. In the present work, equal channel angular pressing (ECAP) was taken as the effective method to acquire severe plastic deformation (SPD). The studies we have performed show that grains have been obviously refined and well globularized after ECAP. When TA15 alloy was pressed at the temperatures of α + β phase region equiaxed microstructure was created. There was an increase in the equilibrium grain size with increasing pressing temperature, while a decrease in the volume fraction of equiaxed α phase. TEM microstructural images illustrate that an amount of deformation twins emerged while pressing TA15 below α-β transformation temperature (T_β), which led to the continued plastic deformation through the restarting of many slip bands. Severe coarsening took place in β grains during ECAP at the temperature above T_β. A larger number of well globularized and more homogeneous equiaxed α phase of TA15 alloy annealed after ECAP has been attained. Furthermore, with annealing at the optimum temperature, grains have not grown significantly.     

Analysis of the solidification and deformation behaviors of twin roll cast Mg-6Al-X alloys

In this study, the solidification and deformation behaviors in twin roll cast (TRC) Mg-6Al-X alloys have been investigated. The TRC simulation results showed that the AX60 alloy tended to have lower segregation while the AZ60 had the highest segregation due to the different solidification behavior and thermal properties. Compared to the as-cast microstructure, the segregation area was well matched with the melt to roll nip distance predicted in simulation. Mg alloys with Ca or Sr elements showed weaker textures when compared to A6 alloys rolled at 350 °C. In addition, there was a significant change in (0002) pole figures from strong basal textures to random textures when the rolling temperature increased from 350 °C to 450 °C. This may be attributed to the non-basal slip system activity at high temperatures. The results of visco-plastic self-consistent simulation revealed that critical resolved shear stress of the tension twin increased with increasing rolling temperature. This led to tension twin suppression in compression, which were associated with enhancing the yield isotropy of Mg alloys. Furthermore, the relative activities of basal <a> slip in AX60 alloy were higher than the other Mg alloys. This means they were responsible for enhancing the formability and yield isotropy of Mg alloys.     

Orientation factor analysis of deformation mechanisms under special processing techniques in AZ31 magnesium alloys

Experiments show that special processing techniques such as asymmetrical rolling(ASR),equal channel angular pressing(ECAP) and equal channel angular rolling(ECAR) can weaken the basal texture of the magnesium alloys and therefore improve their plasticity.However,the deformation mechanisms related are different.In this paper,we determine the deformation mechanisms activated during ASR,ECAP and ECAR by calculation of orientation factors.Analysis shows that during ASR the shear stress σ13 on the rolling plane ...     

Formation of the structure and properties of β-type titanium alloy upon thermomechanical treatment

The rapid quenching of β-type titanium alloy from 800°C and cold deformation by drawing (ε = 24%) leads to the formation of a cellular-banded structure with a cell size of 200 × 400 nm and high density of dislocations (~5 × 10¹⁴ m^–2). During subsequent aging at 450°C, the decomposition of the β-phase occurs with a heterogeneous precipitation (at dislocations) of plates of the α phase with a thickness of 10–30 nm and length of 50–100 nm. The small size and high density of α crystals (5 × 10²¹ m^–3) provide a substantial increase in the strength characteristics of the alloy.     

Effect of heat-treatment conditions on structural and phase transformations in a two-phase α + β titanium alloy subjected to thermomechanical treatment

Effect of heat-treatment parameters (heating temperature in a range of 550 to 700°C and holding time from 0.5 to 2 h) on the occurrence of structural and phase transformations in the Ti-6-4 Eli titanium alloy, which was preliminarily subjected to warm rolling at 550°C after quenching from 945°C, has been studied. During the heating of the rolled alloy to 550°C, the formation of recrystallized nanosized grains in the martensitic matrix was found to occur. The increase in the temperature and time of holding favors the activation of recrystallization processes and increase in the size of arising grains to a micron level. It has been found that the decomposition of the α′ martensite can occur at the expense of both the precipitation of nanosized β-phase particles via a heterogeneous mechanism (T _h = 550–600°C) and through the formation of individual β-phase grains between recrystallized α′ particles at the higher heating temperatures (650–700°C). The prevalence of one of these processes, namely, recrystallization or decomposition, during the heat treatment of the deformed alloy determines the character of changes of microhardness characteristics.     

Effect of cyclic treatment on the formation of a fragmented structure in a sparingly alloyed martensitic steel

Methods of metallography and transmission electron microscopy were used to study the structure of a high-alloy low-carbon steel of martensitic VKS-10 class subjected to cyclic treatment according to different regimes. It has been found that the warm deformation in the α state at 700°C causes the fragmentation of the structure; however, the decomposition of the α solid solution and the precipitation of coarse carbides leads to a significant decrease in the strength. It has been shown that 12 cycles of treatment, including austenitizing at 1000°C, rolling at 700°C, and subsequent γ → α transformation during rapid cooling do not lead to a noticeable fragmentation of the structure. It has been found that the deformation of the overcooled austenite by rolling carried out using 12 cycles in the range of temperatures of 700–500°C and subsequent γ → α transformation lead to the formation of a fragmented structure with a large fraction of fine grains with a size less than 0.5 μm. This treatment and the subsequent tempering at 530°C for 1 h allow us to increase the strength and hardness of the VKS-10 steel at an insignificant decrease in the plasticity.     

60NiTi合金的热压缩变形与显微组织演变（英文）

采用Gleeble-3500热模拟试验机对在变形温度500～650℃和应变速率0.001～1 s^-1条件下的60NiTi合金进行热压缩变形,分析其热变形行为和显微组织,建立变形本构模型,绘制热加工图。结果表明,当压缩温度升高或应变速率降低时,峰值应力减小。合金的热变形激活能为327.89 k J/mol,热加工工艺参数为变形温度600～650℃和应变速率0.005～0.05 s^-1。当变形温度升高时,合金的再结晶程度增大;当应变速率增大时,位错密度和孪晶数量增大,Ni₃Ti相易于聚集;Ni₃Ti析出相有利于诱发合金基体的动态再结晶。动态回复、动态再结晶和孪生是60NiTi合金热变形的主要机制。     

Structure formation during thermomechanical processing of Ti-Nb-(Zr,Ta) alloys and the manifestation of the shape-memory effect

The formation of structure during thermomechanical processing by the regime of cold plastic deformation by rolling and postdeformation annealing (PDA) and its influence on the mechanical properties of Ti-Nb-(Zr, Ta) shape-memory alloys (SMAs) have been investigated. A moderate strain (e ≈ 0.3) leads to the formation of a developed dislocation substructure in the β phase. With going to severe plastic deformation (e ≈ 2), a nanocrystalline structure can locally be formed without the amorphization of the structure. There are also present α″-, α-, ω phases in the deformed alloys. When the PDA (1 h) is performed below 450°C, the structure of the β phase changes only slightly. Above 450°C, a polygonized substructure is formed in the β phase, which is nanosubgrained at an annealing temperature of 500°C and transforms completely into a submicron one at 600°C. In the case of severe plastic deformation to e ≈ 2, in this range of annealing temperatures, high-angle misorientations of blocks are also observed. The recrystallization of the β phase in the Ti-Nb-(Zr, Ta) SMAs develops at temperatures above 600°C. The presence of the ω phase is detected at temperatures of up to 550°C. The lattice parameters of the strain-induced α″ martensite formed in the Ti-Nb-Ta alloy are independent of the PDA temperature in the range from 600 to 900°C, where the polygonized substructure transforms into the recrystallized structure of the β phase. The range of PDA temperatures that are most favorable for the manifestation of the effect of superelasticity in the Ti-Nb-(Zr, Ta) alloys is in the vicinity of 600°C.     

Subtransus deformation mechanisms of TC11 titanium alloy with lamellar structure

Isothermal compression tests are applied to study the deformation mechanisms of TC11 titanium alloy with lamellar structure under the deformation temperature range of 890-995 oC and strain rate range of 0.01-10 s-1.According to the flow stress data obtained by compression tests,the deformation activations are calculated based on kinetics analysis of high temperature deformation,which are then used for deformation mechanism analysis combined with microstructure investigation.The results show that deformation mechanisms vary with deformation conditions:at low strain rate range,the deformation mechanism is mainly dislocation slip;at low temperature and high strain rate range,twinning is the main mechanism;at high temperature and high strain rate range,the deformation is mainly controlled by diffusion of β phase.     

Microstructures of ultra-fine grained FeCoV alloys processed by ECAP plus cold rolling and their evolutions during tempering

A new processing method,equal channel angular pressing(ECAP)plus cold rolling(CR),was applied to producing ultra-fine grained FeCoV alloy.The microstructures of ultra-fine grained FeCoV alloy after ECAP,ECAP plus CR,and the effect of tempering treatment on the microstructure of FeCoV alloy produced by ECAP plus CR were investigated.The results show that an elongated substructure with a width of about 0.3μm is obtained after four-pass ECAP using Route A.Cold rolling after ECAP cannot change the morphologies of elongated substructure,and it results in higher fraction of high-angle boundaries and higher dislocation density compared with the identical ECAP without rolling.Subsequent tempering for 30 min at 853 K brings about many nano-phases precipitating at subgrain boundaries and insides the grains,and the size of precipitated phase is measured to be about 10 nm.Nano-phases grow up with increasing tempering temperature and equiaxed structure forms at 883 K.     

扩展路径低温ECAP及时效热处理对Cu0.6Cr合金的组织和性能影响

采用光学显微镜和X射线衍射仪对Cu0.6Cr合金经低温扩展路径等通道转角挤压（ECAP）后的组织演变规律进行了研究。采用扫描电子显微镜和能谱仪研究了Cu0.6Cr合金经不同时效热处理条件后的晶粒大小、析出相分布规律和断裂特征。并且分别测试了合金经低温ECAP和低温ECAP+时效热处理后的抗拉伸强度、硬度和导电率。结果表明,Cu0.6Cr合金经低温ECAP变形后形成明显细化且相互交割的纤维组织,并且合金在变形中始终保持（111）面的择优取向。时效热处理的合金变形量越大,析出相的数目和尺寸就越大,第二相析出速率也越快。5道次合金经450 ℃时效2 h后的抗拉伸强度为568.1 MPa,维氏硬度为1624.8 MPa,导电率为82%IACS。     

Influence of B2 ordered structure on deformation texture

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Microstructure and Precipitate's Characterization of the Cu-Ni-Si-P Alloy

Microstructure of the Cu-Ni-Si-P alloy was investigated by transmission electron microscopy (TEM). The alloy had 551 MPa tensile strength, 226 HV hardness, and 36% IACS electrical conductivity after 80% cold rolling and aging at 450 °C for 2 h. Under the same aging conditions, but without the cold rolling, the strength, hardness, and electrical conductivity were 379 MPa, 216 HV, and 32% IACS, respectively. The precipitates identified by TEM characterization were δ-Ni₂Si. Some semi-coherent spherical precipitates with a typical coffee bean contrast were found after aging for 48 h at 450 °C. The average diameter of the observed semi-coherent precipitates is about 5 nm. The morphology of the fracture surface was observed by scanning electron microscopy. All samples showed typical ductile fracture. The addition of P refined the grain size and increased the nucleation rate of the precipitates. The precipitated phase coarsening was inhibited by the small additions of P. After aging, the Cu-Ni-Si-P alloy can gain excellent mechanical properties with 804 MPa strength and 49% IACS conductivity. This study aimed to optimize processing conditions of the Cu-Ni-Si-P alloys.     

Microstructure evolution of 7050 aluminum alloy during hot deformation

Hot compression of 7050 aluminum alloy was performed on Gleeble 1500D thermo-mechanical simulator at 350 ℃ and 450 ℃ with a constant strain rate of 0.1 s-1 to different nominal strains of 0.1, 0.3 and 0.7. Microstructures of 7050 alloy under various compression conditions were observed by TEM to investigate the microstructure evolution process of the alloy deformed at various temperatures. The microstructure evolves from dislocation tangles to cell structure and subgrain structure when being deformed at 350 ℃, of which dynamic recovery is the softening mechanism. However, continuous dynamic recrystallization (DRX) occurs during hot deformation at 450 ℃, in which the main nucleation mechanisms of DRX are subgrain growth and subgrain coalescence rather than particle-simulated nucleation (PSN).     

The effect of β phase on microstructure and texture evolution during thermomechanical processing of α + β Ti alloy

Microstructure and texture evolution have been investigated in both α and β phases during the hot rolling of β-quenched Ti–6Al–4V at 800 and 950 °C, followed by annealing at 950 °C and air cooling using detailed electron backscattered diffraction mapping. The textures of primary and secondary α in the bi-modal microstructure were analysed separately, and the high-temperature β orientations were calculated by a variant based reconstruction from the inherited α_s orientations. Crystal plasticity finite element modelling has been employed to predict the rolling texture based on common α phase slip systems and compare with the measured α texture. It was found that despite the severe deformation during rolling, a large proportion of the primary α grains retain a Burgers relationship with the β phase. Consequently, the β phase in combination with a variant selection mechanism seems to control the α texture, which explains the discrepancy between predicted and measured rolling textures. The consequence of this mechanism for macrozone formation is also discussed.