镍基单晶合金高温蠕变变形与损伤行为

通过蠕变性能测试和组织观察,研究了镍基单晶合金在高温蠕变期间的变形和损伤行为.结果 表明,该合金在1040℃/137 MPa条件下的蠕变寿命为556 h,表现出优异的蠕变抗力.合金在稳态期间的蠕变特性是位错在γ基体中滑移和攀移越过筏状γ'相.在蠕变后期,合金的变形特征是位错剪切进入筏状γ'相,剪切γ'相的位错可以交滑移...     

预压缩镍基单晶合金拉伸蠕变期间的组织演化

采用预压应力处理使镍基单晶合金中的γ'相转变成P-型筏状结构,通过拉伸蠕变曲线测定和组织形貌观察,研究了该合金拉伸蠕变中的组织演化.结果表明:在拉伸蠕变初期,合金中的P-型筏状γ'相转变为N-型筏状结构.由于高温拉应力导致γ'/γ两相中元素平衡浓度发生变化及P-型筏状γ'相的不均匀粗化,促使P-型筏状γ'相发生分解出现沟槽;沟槽区域溶质元素化学位的提高引起的元素定向扩散是γ'相逐渐溶断成类立方体结构的主要原因.切应力分量使立方,γ'相与应力轴垂直界面的晶格收缩可排斥较大半径的Al和Ta原子,拉伸张应力使平行于应力轴界面的品格扩张可诱捕较大半径的Al和Ta原子,是促使γ'相定向生长成为N-型筏状的主要原因.其中,在拉应力作用下类立方,γ'相不同界面的应变能密度变化是元素扩散及γ'相定向粗化的驱动力.     

含Mo单晶镍基合金的高温蠕变及损伤行为

通过蠕变性能测试及组织形貌观察,研究含3%和5%(质量分数)Mo无Re单晶镍基合金的高温蠕变和损伤行为。结果表明:与3%Mo单晶合金相比,5%Mo无Re单晶合金具有较好的蠕变抗力和较长的蠕变寿命,测定出5%Mo单晶合金在1040℃、137 MPa的蠕变寿命为556 h。在施加的温度和应力范围内,测定出合金在稳态蠕变期间的表观蠕变激活能Q=484.7 kJ/mol。合金在稳态蠕变期间的变形机制是位错在基体中滑移和攀移越过筏状γ′相;合金在蠕变较后阶段的变形机制是位错剪切进入筏状γ′相。随蠕变进行,位错的交替滑移致使合金中筏状γ′相发生扭曲,并在筏状γ′/γ两相界面发生裂纹的萌生和扩展,直至断裂,是合金在高温蠕变后期的损伤与断裂机制。     

单晶镍基高温合金超高温蠕变期间的变形机制

通过蠕变性能测试及组织形貌观察,研究了6％Re-5％Ru(质量分数)单晶镍基高温合金的超高温蠕变行为和变形机制.结果 表明,该合金在1160℃/120 MPa条件下的蠕变寿命为206 h.稳态蠕变期间,位错在基体中滑移和攀移越过筏状γ'相是合金的变形特征,基体中溶解的高浓度难熔元素可增加位错运动阻力.蠕变后期,切入筏状...     

6%Re/5%Ru单晶镍基合金的超高温蠕变行为和影响因素EI北大核心CSCD

通过对6%Re/5%Ru单晶镍基合金(质量分数)进行蠕变性能测试和组织观察,研究了合金的超高温蠕变行为和影响因素。结果表明:测定出合金在(1160℃,120 MPa)的蠕变寿命为206 h。中期稳态阶段,位错在基体中滑移和攀移越过γ′相是合金的变形特征,γ基体中溶解的难熔元素可增加位错在基体中运动的阻力。超高温蠕变期间,随温度提高γ′相发生溶解,可减小筏状γ′相的尺寸,提高位错攀移越过γ′相的速率,特别是当温度大于1170℃时,合金的施加温度敏感性使筏状γ′相的尺寸减小,应变速率提高,这是合金蠕变寿命大幅度降低的主要原因。蠕变后期,基体位错可在位错网破损处切入γ′相,其中,切入γ′相的位错可由{111}面交滑移至{100}面形成K−W锁,抑制位错的滑移和交滑移,可改善合金的蠕变抗力。而在颈缩区域较大的有效应力可开动位错的双取向滑移,致使筏状γ′相扭折,并在扭折区域发生裂纹的萌生和扩展,直至断裂,这是合金在超高温蠕变期间的变形和损伤机制。     

一种含4.2%Re单晶镍基合金在蠕变期间的组织演化与变形特征(英文)

通过组织形貌观察及蠕变曲线测定,研究了一种含Re镍基单晶合金的高温蠕变行为。结果表明:含4.2%Re单晶合金在1060-1100℃温度区间具有较好的承温能力,但表现出较强的施加应力敏感性。经高温蠕变断裂后,在试样不同区域γ′相具有不同的组织形貌,在远离断口区域γ′相形成的筏状组织与施加应力轴方向垂直,而在近断口区域,筏状γ′相的粗化及扭曲程度的增大为该区域发生较大塑性变形所致。在蠕变后期,合金的变形机制是迹线方向为[011]和[011]的滑移位错切入筏状γ′相,主、次滑移系交替开动,使筏状γ′相发生扭折形成不规则的扭曲形态,直至发生断裂是合金的蠕变断裂机制。     

预压缩处理对镍基单晶高温合金蠕变变形机制的影响

对[001]取向镍基单晶合金进行预压缩处理,获得P-型筏状结构后进行拉伸蠕变实验,测定P-型γ'合金(预压缩态)与立方γ'合金(热处理态)的相对蠕变性能.结果表明:在800 ℃,600 MPa条件下,P-型γ'合金的初期蠕变应变及稳态蠕变速率相对较高,而持久寿命相对较短.TEM观察显示,P-型γ'合金在蠕变初始阶段除了基体中的{111}<110>多滑移启动外,位错还以层错和超位错的形式切入γ'相.在980-1020℃温度区间及恒定载荷200 MPa条件下,P-型γ'合金的稳态蠕变速率相对较低,持久寿命相对较高.在稳态蠕变初期,合金中的γ'相有效地抑制了位错沿垂直γ/γ'界面的攀移运动;而在稳态蠕变中期,γ'相被稠密的位错网包围,位错难以切入,合金的蠕变抗力提高.     

热处理对4.5%Re单晶镍基合金高温蠕变行为的影响

通过对一种4.5%Re(质量分数)镍基单晶合金进行不同工艺热处理、蠕变性能测试及组织形貌观察,研究了固溶时间对该合金组织结构与高温蠕变行为的影响。结果表明:铸态合金中各元素存在较大的成分偏析,经高温长时间固溶及时效处理后,合金中各元素在枝晶间/臂的偏析程度明显降低;将固溶时间由10 h延长至24 h后,合金在1100℃、137 MPa的蠕变寿命由101 h提高至164 h;其中,10 h固溶处理合金中仍存在较大程度的元素偏析,并且在蠕变期间,析出针状TCP相。合金在高温蠕变期间的变形机制是位错在基体中滑移和剪切筏状γ′相;蠕变后期,大量位错剪切筏状γ′相,致使近断口区域的筏状γ′相扭曲,在筏状γ/γ′两相界面发生裂纹的萌生,并沿垂直于应力轴方向扩展,直至发生蠕变断裂。这是合金的高温蠕变断裂机制。     

含Re/Ru镍基单晶合金的高温蠕变行为和损伤特征

通过蠕变性能测试和组织观察,研究4.5％Re/3％Ru镍基单晶合金在高温的蠕变行为和损伤特征.结果表明:测定出该合金在(1100℃,140 MPa)下的蠕变寿命为476 h.合金在高温稳态蠕变期间的变形机制是位错在γ基体中滑移和攀移越过筏形γ′相,在蠕变后期的变形机制是位错在基体中滑移和剪切筏状γ′相.其中,剪切进入γ...     

镍基单晶合金在压缩蠕变期间的组织演化与有限元分析

通过[001]取向镍基单晶合金压缩蠕变性能测试及组织形貌观察,确定出合金经压应力蠕变后的组织结构是γ'相沿平行于应力轴方向形成P-型筏状组织。采用三维应力应变有限元方法计算出立方γ/γ'两相共格界面的Von Mises应力分布,研究了施加应力对应力分布及γ'相定向粗化规律的影响。结果表明,施加压应力可改变立方γ/γ'两相的应力分布,γ'相的定向粗化取向与γ基体通道的Von Mises应力分布密切相关,其中,在施加压应力作用下,立方γ'相的(001)晶面产生较大的Von Mises应力及应变能密度变化是使其发生组织演化的主要原因。并进一步提出压应力蠕变期间,合金中发生元素定向扩散和γ'相定向生长的驱动力。     

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.