基于计算机仿真镍基单晶高温合金再结晶过程分析（英文）

再结晶是影响高温合金高温蠕变性能的重要因素。以DD6镍基单晶高温合金为研究对象,建立了再结晶过程中形核生长、储能分布、晶粒长大的数学模型,利用计算机模拟技术分析了材料热处理过程中再结晶的整个过程和动力学曲线。该研究为镍基单晶高温合金生产过程中的蠕变性能优化提供了参考。     

镍基单晶高温合金再结晶过程仿真分析

以DD6镍基单晶高温合金为对象,建立了合金再结晶过程中晶粒形核长大、储能分布的数学模型,利用计算机模拟技术分析了材料热处理过程中再结晶的动力学曲线。模拟结果和文献实验结果具有很高的吻合度,为镍基单晶高温合金蠕变性能的优化提供了参考。     

镍基单晶高温合金蠕变行为研究进展

从镍基单晶高温合金蠕变中γ'相定向粗化和筏化、蠕变各向异性、蠕变寿命预测及Re和Ru元素对蠕变性能的影响方面,综述了镍基单晶高温合金蠕变行为的研究进展,并对镍基单晶高温合金的发展方向进行了展望。     

镍基单晶高温合金中Ru元素作用的研究进展

具有优异的高温抗蠕变、抗疲劳、抗氧化和耐热腐蚀等综合性能的先进镍基单晶高温合金，是当代先进航空发动机热端部件的首选材料。研究者发现，Ru元素的引入对镍基单晶高温合金的组织稳定性和高温蠕变性能有重大影响。但是相关研究开始较晚，不够充分，因此Ru元素具体作用机制尚不明晰。此外，Ru的添加提高了镍基单晶高温合金的制造成本，所以高代次单晶合金目前仍处于试验阶段，并未在实际生产中实现大规模应用。本文从Ru元素对镍基单晶高温合金铸态组织、热处理态组织、组织结构稳定性和蠕变性能的影响4个方面出发，总结了Ru元素在单晶高温合金中具体作用的研究进展。     

纵向静磁场对单晶高温合金DD483组织及蠕变性能的影响

在静磁场下进行高温合金DD483的定向凝固实验,研究了不同磁场强度对单晶镍基高温合金DD483凝固组织枝晶形貌、合金元素偏析系数、析出相和蠕变性能的影响.结果表明:纵向静磁场的施加使高温合金DD483单晶生长性受到破坏,强的磁场使得枝晶定向生长形态受到破坏,形成“雀斑组织”,对一次枝晶间距影响不大.施加磁场使得该单晶合金中合金元素的偏析降低;也使单晶高温合金DD483凝固态组织中γ’析出尺寸降低、碳化物和共晶组织尺寸和含量显著减小.同时磁场对该合金的单晶性和枝晶的定向生长行为的破坏使得合金的蠕变性能降低.     

镍基单晶高温合金的小角度偏离[001]取向对蠕变性能的影响

小角度偏离[001]取向的镍基单晶高温合金的蠕变性能受温度、γ?尺寸的大小和应力条件的影响。本文综述了镍基单晶高温合金的[001]取向小角度偏离对蠕变性能的影响。不同程度的偏离引起的不同蠕变性能变化,源于不同的蠕变变形机制。不同的蠕变变形机制对应着引起蠕变率发生的不同临界应力。在中温(760℃-850℃),合金的蠕变性能对[001]取向的角度偏离很敏感,即使角度有一点变化也会引起蠕变性能的很大的差异,但是在温度高于850℃以上小角度的取向偏离对蠕变性能影响不大。γ?尺寸的大小对小角度偏离的合金的蠕变性能的影响受温度的制约。在中温,γ?尺寸的大小变化影响着不同的小角度偏离是否引起蠕变性能的变化,但是在高温γ? 相快速伐化,变形机制和γ?尺寸变化无关。     

镍基单晶高温合金的小角度偏离[001]取向对蠕变性能的影响（英文）

小角度偏离[001]取向的镍基单晶高温合金的蠕变性能受温度、γ'尺寸和应力条件的影响。本文综述了镍基单晶高温合金的[001]取向小角度偏离对蠕变性能的影响。不同程度的偏离引起的不同蠕变性能变化,源于不同的蠕变变形机制。不同的蠕变变形机制对应着引起蠕变发生的不同临界应力。在中温(760～850°C),合金的蠕变性能对[001]取向的角度偏离很敏感,即使角度有轻微变化也会对蠕变性能有明显影响,但是温度高于850°C时,小角度的取向偏离对蠕变性能影响不大。γ'尺寸对小角度偏离的合金蠕变性能的影响受温度制约。在中温,γ'尺寸的变化影响着小角度偏离引起的蠕变性能变化,但是在高温γ'相快速伐化,变形机制和γ'尺寸变化无关。     

加载速率和峰值载荷对DD407镍基单晶高温合金纳米压痕蠕变行为的影响

在加载速率500～6000 uN/s和峰值载荷4000～12000 uN的条件下进行纳米压痕蠕变实验,研究DD407镍基单晶高温合金在室温下的蠕变行为.结果表明:DD407镍基单晶高温合金具有良好的蠕变抗力性能,但其蠕变性能对加载速率和峰值载荷敏感.依据Findley模型,得到拟合的蠕变参数随着加载速率和峰值载荷的增加...     

W和Re对固溶态镍基单晶高温合金变形和再结晶的影响

镍基单晶高温合金固溶处理后,分别经过Brinell硬度计压痕和吹砂引入变形,热处理后观察再结晶,研究了W和Re元素对固溶态镍基单晶高温合金变形和再结晶的影响.结果表明,加入W和Re后,单晶高温合金变形后位错密度增大,位错缠结增多,再结晶形核时间滞后,即再结晶孕育期延长,再结晶深度明显减小.单晶高温合金经吹砂后,表面显微硬度明显增加,加入W和Re后,变形深度减小,再结晶晶界迁移速率最大值降低,且沿着再结晶深度方向,晶界平均迁移速率的变化与显微硬度变化趋势一致.     

定向凝固和单晶高温合金的再结晶

本文系统分析了定向凝固和单晶高温合金再结晶的特点、危害以及影响再结晶的主要因素,阐述了再结晶的物理本质.再结晶行为受合金元素、变形程度、热处理温度及时间、变形速率、变形工艺等的影响.再结晶的物理本质是由铸态γ'相溶解控制的高能态畸变组织向低能态无畸变组织转变的过程.镍基定向凝固高温合金再结晶开始温度在1050℃左右,钴基定向凝固高温合金在1100℃左右.定向凝固和单晶高温合金的动态再结晶行为主要与高温氧污染和自由表面有关.再结晶对高温持久、疲劳性能影响较大,含再结晶层的断口源区表现为沿晶断裂.目前定向凝固构件上的再结晶检测普遍采用金相方法.     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.