结晶力驱动纤维状晶体生长:宁南盆地清水营组背生式纤维状石膏脉体的岩相学证据

背生式纤维状脉体是一种发育在低渗透泥岩中具有明显延长晶体形态的矿物脉体,其成因机制存在争议。通过对宁南盆地清水营组中背生式纤维状石膏脉体详细的野外和岩相学观察,结合脉体开启和延伸的运动学和动力学特征,研究了脉体的成因机制。结果显示,单个背生式纤维状石膏脉体由中间带和纤维状带组成,二者特征明显不同,指示不同的生长机制。中间带是脉体开启的原始位置,充填块状石膏晶体和大量围岩碎片、条带,表明背生式纤维状石膏脉体的中间带是通过裂开-愈合机制形成。纤维状带由平行对齐的纤维状石膏晶体组成,单个晶体具有光学连续性,相邻晶体之间没有明显的生长竞争,表明纤维状晶体生长过程中没有发生破裂。我们推测是结晶力造成了局部应力场扰动,使脉体尖端偏离了脉体延伸方向,并逐渐向相邻脉体弯曲生长,最终导致了脉体相互作用区域围岩变形和脉体纤维状带厚度差异。

新型高再结晶抗力α-Al(MnCr)Si弥散强化Al-Mg-Si-Cu合金研究

Al-Mg-Si-Cu铝合金(6XXX)属于可热处理强化合金,其高比强度、耐腐蚀及优良的成形性能使得它们在各种工业应用中具有吸引力,包括电力传输和交通运输行业;但相对较低的强度和硬度限制了其应用。最新研究表明,在合金中加入Mn/Cr等过渡族元素结合均匀化热处理工艺能够在Al-Mg-Si-Cu铝合金基体中形成纳米级、与基体部分共格的α-Al(MnCr)Si弥散相,从而借助弥散强化作用进一步提升合金的综合力学性能,拓展Al-Mg-Si-Cu铝合金的应用范围。弥散相因其对位错运动和(亚)晶界迁移的钉扎作用而有助于限制动态回复并抑制动态再结晶。此外,弥散相还能够限制合金在固溶处理过程中再结晶晶粒的形核和长大过程,进而抑制静态再结晶的发生。但较少有文献针对弥散相对Al-Mg-Si-Cu合金变形后热处理过程中的微观演变进行量化统计和机理分析,未能建立模型来描述变形条件对微观组织演变的影响。本工作对6061合金和Mn/Cr微合金化的Al-Mg-Si-Cu合金(后者被标记为HSW-1合金)在不同条件下进行热变形处理(变形温度:300、400、500℃;应变速率:0.01、0.1、1、10 s^(-1);真应变:1.2),研究变形合金在固溶和时效热处理过程中的微观结构演变,提出热变形合金经固溶处理后的微观组织调控机制。采用TEM观察证实了HSW-1合金基体中均匀分布着大量纳米级的α-Al(MnCr)Si弥散相。将热变形后的两种合金在560℃下盐浴保温不同时间,应用准原位EBSD技术表征微观结构的演变,统计取向差分布及亚晶粒尺寸的变化。结果表明,热变形条件(变形温度、应变速率)对6061和HSW-1合金在固溶处理过程中的静态再结晶行为有显著影响。两种合金静态再结晶行为随着变形温度的降低、应变量的增加及应变速率的升高而得到强化。相同的变形条件下,尽管6061合金静态软化驱动力低于HSW-1合金,但其在固溶处理过程中的静态再结晶行为明显强于HSW-1合金。这表明,弥散相通过钉扎作用有效抑制变形合金在固溶和时效过程中的静态再结晶行为,在显著提升合金的抗再结晶能力的同时保持变形合金的微观结构,使变形合金获得弥散强化和变形强化的综合效果,进而赋予其高强度。最后,通过理论分析提出了T6热处理后两种变形合金的微观结构控制模型。通过调整变形参数,即变形温度和应变速率,可以精确调节热处理后的微观组织成分,实验数据有效支持了模型的可行性。该结果为开发新型高强韧高性能铝合金提供了实验基础和理论分析。

Simulated and experimental investigation on discontinuous dynamic recrystallization of a near-α TA15 titanium alloy during isothermal hot compression in βsingle-phase field

A cellular automaton（CA） modeling of discontinuous dynamic recrystallization（DDRX） of a near-α Ti-6Al-2Zr-1Mo-1V（TA15） isothermally compressed in the β single phase field was presented.In the CA model,nucleation of the β-DDRX and the growth of recrystallized grains（re-grains） were considered and visibly simulated by the CA model.The driving force of re-grain growth was provided by dislocation density accumulating around the grain boundaries.To verify the CA model,the predicted flow stress by the CA model was compared with the experimental data.The comparison showed that the average relative errors were10.2%,10.1%and 6%,respectively,at 1.0,0.1 and 0.01 s^-1 of 1020 ℃,and were 10.2%,11.35%and 7.5%,respectively,at 1.0,0.1and 0.01 s^-1 of 1050 ℃.The CA model was further applied to predicting the average growth rate,average re-grain size and recrystallization kinetics.The simulated results showed that the average growth rate increases with the increasing strain rate or temperature,while the re-grain size increases with the decreasing strain rate;the volume fraction of recrystallization decreases with the increasing strain rate or decreasing temperature.

Dynamic recrystallization kinetics of as-cast AZ91D alloy

The flow behavior and dynamic recrystallization（DRX） behavior of an as-cast AZ91 D alloy were investigated systematically by applying the isothermal compression tests in temperature range of 220-380 ℃ and strain rate range of 0.001-1 s^-1.The effect of temperature and strain rate on the DRX behavior was discussed.The results indicate that the nucleation and growth of dynamic recrystallized grains easily occur at higher temperatures and lower strain rates.To evaluate the evolution of dynamic recrystallization,the DRX kinetics model was proposed based on the experimental data of true stress-true strain curves.It was revealed that the volume fraction of dynamic recrystallized grains increased with increasing strain in terms of S-curves.A good agreement between the proposed DRX kinetics model and microstructure observation results validates the accuracy of DRX kinetics model for AZ91 D alloy.

Effect of minor Zr and Sc on microstructures and mechanical properties of Al-Mg-Si-Cu-Cr-V alloys

The effects of minor contents of Zr and Sc on the microstructures and mechanical properties of Al-Mg-Si-Cu-Cr-V alloy were studied. The results show that the effects of minor Zr and Sc on the as-cast grain refinement in the ingots, the improvement in the strength of the as-extruded alloys and the restriction of high angle grain boundaries in the aged alloys can be sorted as Al3ScAl3 （Zr,Sc）Al3Zr. None of them could stop the nucleation of recrystallization, but Al3 （Zr,Sc） phase is a more effective inhibitor of dislocation movement compared to Al3 Sc in the aged alloys. Compared with the mechanical properties of the aged alloy added only 0.15% Sc, the joint addition of Zr and Sc to the alloy leads to a very slight decrease in strength with even no cost of ductility. Taking both the production cost and the little bad influence on mechanical properties into consideration, an optimal content of Zr and Sc in the Al-Mg-Si-Cu-Cr-V alloy to substitute 0.15% Sc is 0.13% Zr＋0.03% Sc.

Arrhenius-type constitutive model and dynamic recrystallization behavior of V-5Cr-5Ti alloy during hot compression

To clarify the high temperature flow stress behavior and microstructures evolution of a V-5Cr-5Ti （mass fraction, %） alloy, the isothermal hot compression tests were conducted in the temperature range of 1423-1573 K with strain rates of 0.01, 0.1, and 1 s-1. The results show that the measured flow stress should be revised by friction and the calculated values of friction coefficient m are in the range of 0.45-0.56. Arrhenius-type constitutive equation was developed by regression analysis. The comparison between the experimental and predicted flow stress shows that the R~ and the average absolute relative error （AARE） are 0.948 and 5.44%, respectively. The measured apparent activation energy Qa is in the range of 540-890 kJ/mol. Both dis-continuous dynamic recrystallization （DDRX） and continuous dynamic recrystallization （CDRX） mechanisms are observed in the deformed alloy, but dynamic recovery （DRV） is the dominant softening mechanism up to a true strain of 1.5.

Dissolution kinetics and mechanism of gibbsitic bauxite and pure gibbsite in sodium hydroxide solution under atmospheric pressure

The crystal structure, morphology, dissolution kinetics and mechanism of gibbsitic bauxite and pure gibbsite in Na OH solution under atmospheric pressure were systematically investigated by XRD and SEM. The results show that the size of single crystal of gibbsite in gibbsitic bauxite is smaller than that in pure gibbsite, but the interplanar distance is larger than that of pure gibbsite, which result in more defects in the crystal and less energy needed to dissolve in alkaline solution for the gibbsitic bauxite. The dissolution kinetic equations of gibbsitic bauxite and pure gibbsite were established, and the corresponding activation energies were calculated to be 99.144 and 115.149 k J/mol, respectively.

Hot deformation behavior of Al-Zn-Mg-Cu-Zr aluminum alloys during compression at elevated temperature

The hot compression tests of Al-Zn-Mg-Cu-Zr aluminum alloys （7056 alloy and 7150 alloy） were performed in a temperature range from 300 to 450 °C and at strain rate range from 0.01 to 10 s-1. The results show that the true stress-true strain curves exhibit a peak stress at a critical strain, then the flow stresses decrease monotonically until high strains, showing a dynamic flow softening. The peak stresses depend on the temperature compensated strain rate, which can be represented by the Zener-Hollomon parameter Z in the hyperbolic-sine equation with hot deformation activation energy of 244.64 kJ/mol for 7056 alloy and 229.75 kJ/mol for 7150 alloy, respectively, while the peak stresses for the former are lower than those for the latter under the similar compression condition. The deformed microstructures consist of a great amount of precipitates within subgrains in the elongated grains at high Z value and exhibit well formed subgrains in the recrystallized grains at low Z value. The smaller subgrains and greater density of fine precipitates in 7150 alloy are responsible for the high peak stresses because of the substructural strengthening and precipitating hardening compared with 7056 alloy.

Deformation behaviors and processing maps of CNTs/Al alloy composite fabricated by flake powder metallurgy

Deformation behaviors of CNTs/Al alloy composite fabricated by the method of flake powder metallurgy were investigated by hot compression tests, which were performed in the temperature range of 300?550 °C and strain rate range of 0.001? 10 s?1 with Gleeble?3500 thermal simulator system. Processing maps of the CNTs/Al alloy at different strains were calculated to study the optimum processing domain. Microstructures before and after hot compressions were characterized by electron backscattered diffraction (EBSD) method. Stress?strain curves indicate that the flow stress increases with the increase of strain rate and the decrease of temperature. The processing maps of the CNTs/Al alloy at different strains show that the optimum processing domain is 500?550 °C, 10 s?1 for hot working. EBSD analysis demonstrates that fully dynamic recrystallization occurs in the optimum processing domain (high strainrate 10 s?1), whereas the main soften mechanism is dynamic recovery at low strain rate (0.001 s?1).

Effects of geometric parameters and axial magnetic field on buoyant-thermocapillary convection during detached solidification

In order to understand the effect of geometric parameters and axial magnetic field on buoyant-thermocapillary convection during detached solidification, a series of threedimensional numerical simulations were conducted by the finite-difference method. The results indicate that the stable flow is observed when the Marangoni number （Ma） is small; however, when the value of Ma increases and exceeds a threshold value, the stable steady flow transits to be unstable flow. As the height of the melt increases, the flow is enhanced at first and then gets weakened. As the width of gap decreases gradually, the strength of flow is enhanced. The approach of using axial magnetic field is an effective way to suppress the buoyant-thermocapillary convection. As the magnetic field strength increases, the inhibition is enhanced. The critical Marangoni number increases slightly with a greater melt height, a narrower width of gap, and a more strength of magnetic field.

Modeling of strain hardening and dynamic recrystallization of ZK60 magnesium alloy during hot deformation

The flow stress behavior of ZK60 alloy at elevated temperature was investigated. The strain hardening and dynamic recrystallization of the alloy were modeled by Kocks-Meching model and Avrami equation, respectively. A new constitutive equation during hot deformation was constructed to predict the flow stress considering the dynamic recrystallization. The results show that the flow stress curves predicted by the proposed equation have high correlation coefficients with the experimental data, which confirms that the developed model is accurate and effective to establish the flow stress equation of ZK60 magnesium alloy during hot deformation. Microstructure observation shows that dynamic recovery occurs in the initial stage of hot deformation. However, the microstructure turns to recrvstallization structure as the strain increases.

Rate controlling mechanisms in hot deformation of 7A55 aluminum alloy

The hot deformation behavior of 7A55 aluminum alloy was investigated at the temperature ranging from 300 ℃ to 450 ℃ and strain rate ranging from 0.01 s-1 to 1 s-1 on a Gleeble-3500 simulator. Processing maps were established in order to apprehend the kinetics of hot deformation and the rate controlling mechanism was interpreted by the kinetic rate analysis obeying power-law relation. The results indicated that one significant domain representing dynamic recrystallization （DRX） existed on the processing maps and lying in 410-450 ＆#176;C and 0.05-1 s-1. The conclusions of kinetic analysis correlated well with those obtained from processing maps. The apparent activation energy values calculated in the dynamic recrystallization （DRX） domain and the stability regions except dynamic recrystallization （DRX） domain were 91.2 kJ/mol and 128.8 kJ/mol, respectively, which suggested that grain boundary self-diffusion and cross-slip were the rate controlling mechanisms.

Microstructure and mechanical properties of cryo-rolled AA6061 Al alloy

The microstructure and mechanical properties of the age hardening AA6061 Al alloy subjected to cryo-rolling（CR） and room temperature rolling（RTR） treatments were investigated. The rolled and aged alloys were analyzed by using DSC, EBSD, TEM, Vickers hardness analysis and tensile test. The results show that the cryo-rolled treatment has an effect on the precipitation sequence of AA6061 Al alloy. The ultrafine grain structures are formed to promote the fine second phase particles to disperse in the aluminum matrix after the peak aging, which is attributed to lots of dislocations tangled in the rolling process. Therefore, the strength and ductility of AA6061 Al alloy are simultaneously modified after the cryo-rolling and aging treatment compared with room temperature rolled one.

Effects of static magnetic fields on melt flow in detached solidification

A series of three-dimensional numerical computations were conducted to understand the effects of different static magnetic fields on thermal fluctuation and melt flow during the detached solidification of CdZnTe. Numerical calculations were carried out by three different configurations of magnetic field: without magnetic field, with an axial magnetic field (AMF) and with a cusp-shaped magnetic field (CMF). The results reveal that the magnetic fields can effectively suppress the melt flow and thermal fluctuation and the suppression effect of the AMF is stronger than that of the CMF. Besides, the physical mechanism of thermocapillary?buoyancy convection instability was discussed and the effects of magnetic field on the critical Marangoni number were also obtained.

Effect of consolidation parameters on mechanical properties of Cu-based bulk amorphous alloy consolidated by hot pressing

Cu50Zr40Ti10 bulk amorphous alloys were fabricated by hot pressing gas-atomized Cu50Zr40Ti10 amorphous powder under different consolidation conditions without vacuum and inert gas protection. The consolidation conditions of the Cu50Zr40Ti10 amorphous powder were investigated based on an L9（34） orthogonal design. The compression strength and strain limit of the Cu50Zr40Ti10 bulk amorphous alloys can reach up to 1090.4 MPa and 11.9 %, respectively. The consolidation pressure significantly influences the strain limit and compression strength of the compact. But the mechanical properties are not significantly influenced by the consolidation temperature. In addition, the preforming pressure significantly influences not the compression strength but the strain limit. The optimum consolidation condition for the Cu50Zr40Ti10 amorphous powder is first precompacted under the pressure of 150 MPa, and then consolidated under the pressure of 450 MPa and the temperature of 380 °C.

Microstructure evolution and mechanical properties of ZK60 magnesium alloy produced by SSTT and RAP route in semi-solid state

The microstructure evolution and mechanical properties of a ZK60 magnesium alloy produced by the semi-solid thermal transformation （SSTT） route and the recrystallization and partial melting （RAP） route were studied, respectively. The microstructure evolution during partial remelting was studied at different temperatures for different time. The tensile mechanical properties of thixoformed components by the two routes at room temperature were examined. The results show that coalescence is dominant in the SSTT alloy and Ostwald ripening is dominant in the RAP alloy. Compared with the SSTT route, the RAP route can produce finer semi-solid microstructure under the similar isothermal holding condition. The microstructure of the RAP alloy is much more spheroidized compared with the SSTT alloy. Thixoforming for the ZK60 magnesium alloy produced by the SSTT and RAP route results in successful filling of the die, and the thixoforming process improves the mechanical properties of ZK60 magnesium alloy. The RAP alloy shows significantly advantageous mechanical properties over that of the SSTT alloy.

Kinetics and microstructural evolution during recrystallization of a Ni_3Al-based single crystal superalloy

The recrystallization kinetics and microstructural evolution of a Ni3Al-based single crystal superalloy were presented, especially the different recrystallization behaviors between the dendrite arm and the interdendritic region. The single crystal alloy was deformed by grit blasting. A succeeding annealing under inert atmosphere at 1280 ℃ for different time led to the formation of recrystallized grains close to the grit blasting surface. It was found that the recrystallization depth and velocity in the dendrite arm were respectively deeper and faster than those in the interdendritic region where the Y-NiMo phase existed. The recrystallization process in the interdendritic region was significantly inhibited by the Y-NiMo precipitates. However, the pinning effect gradually weakened with the annealing time due to the dissolution of the Y-NiMo phase, and the recrystallization depth in the dendrite arm was deeper than that in the interdendritic region.

两种方法制备的纳米水滑石晶体结构与热稳定性的比较研究

分别采用共沉淀法和机械力化学/原位结晶法制备纳米水滑石,通过X射线衍射(XRD)、场发射扫描电镜(FE-SEM)、热重-差示扫描量热分析(TG-DSC)及红外光谱(IR)等方法对比分析了两种纳米水滑石在表观形貌、晶体结构和热稳定性等方面的差异。结果表明,与共沉淀法制备的纳米水滑石相比,机械力化学/原位结晶法制备的纳米水滑石结晶度更高、晶粒呈规则的六边形片状形貌、晶粒粒径约为40 nm、粒度分布均匀,且在TG-DSC曲线上的吸热峰面积、失重量和失重速率较小,热稳定性更好。

Effects of melt overheating degree on undercooling degree and amorphous forming of Nd_9Fe_(85-x)Ti_4C_2B_x(x=10, 12) magnetic alloys

The effectsof melt overheating degree on the undercooling degree and resultant solidification structures of Nd9Fe85-xTi4C2Bx（x=10, 12） glass-forming alloyswerestudied by differential thermal analysis combining with solidification structure analysis. The results indicate that the undercooling degree of Nd9Fe85-xTi4C2Bx（x=10, 12） alloys significantly increaseswith the rise of melt overheating degree, and two overheating degree thresholds corresponding to the drastic increase of the mean undercooling degree are found for each of the alloys. The existence of two turning points of the mean undercooling degreescan be linked to the structure transitions inside the overheated melts, which result in the evident increase of volume fraction of amorphous phasein the solidified structures.

Evolution of twins and texture and its effects on mechanical properties of AZ31 magnesium alloy sheets under different rolling process parameters

In order to investigate the dependence of microstructure and mechanical properties on the rolling process parameters, AZ31 magnesium alloy sheets with different grain sizes, basal texture intensities and twinning types were obtained using hot rolling at various temperatures and reductions. The volume fractions of the extension, contraction and secondary twins in the as-rolled sheets depend on the grain size. The highest volume fractions of three types of twins are obtained at 523 K under the reduction of 10% when the average grain size value is the maximum. The critical reductions for complete dynamic recrystallization are 30% at 523 K and 40% at 473 K. The increase of yield strength is ascribed to both grain-refinement strengthening and basal texture strengthening at the first stage. When the grain size does not decrease with increasing the reduction, the yield strength is mainly influenced by the texture weakening.