温度及应变速率对NZ31镁合金锯齿流变类型转变的影响（英文）

将固溶处理后的NZ31镁合金在不同温度及应变速率下进行拉伸实验,研究温度及应变速率对锯齿流变(Portevin-Le Chatelier效应)特征的影响。合金的锯齿流变行为出现在温度为150到250℃之间,在250℃时表现最剧烈,并且在晶粒内部可以发现特定取向的滑移带。随着温度的升高或应变速率的降低,锯齿流变类型由A型逐渐转变成C型。单个A型锯齿可划分为局部钉扎、完全钉扎和脱钉三个阶段。当温度升高或者应变速率降低时,溶质原子钉扎能力的增强会促进完全钉扎阶段的形成或者抑制脱钉阶段的发生,从而引起锯齿类型的转变。     

钨对铸态Ti-45Al-8Cr-2Nb合金的高温性能影响

采用高温拉伸测试及显微组织观察,研究了微量钨对铸态Ti-45Al-8Cr-2Nb(原子百分比)合金的高温性能影响。结果表明,在基体合金中添加2%W,能使铸态合金的最大伸长率降低,而最大伸长率相应的温度向高温方向移动;高温变形过程中,晶粒滑动的协调过程由晶界扩散转化为体扩散;含钨的合金在800℃时的伸长率从0.62%提高到90%。     

一种奥氏体铁镍基合金中的锯齿流变现象

采用3种应变速率在不同温度下对一种奥氏体铁镍基合金进行拉伸实验,结果发现在300—700℃范围内发生锯齿流变现象;锯齿流变现象在300—600℃范围内表现为凸起式锯齿,而在700℃时表现为下凹式锯齿;此锯齿流变具有热激活性,即较高的拉伸温度使锯齿易于发生,较大的拉伸速率则抑制其发生.对比分析室温(不发生锯齿流变)及400℃(显著发生锯齿流变)拉伸试样的微观组织,发现在400℃拉伸后的孪晶界上存在明显的位错塞积,说明孪晶界可以有效地阻碍滑移变形,引起孪晶界附近应力积累,从而导致了凸起式锯齿流变的发生.孪晶界数量对锯齿波形的影响证实了此观点.     

挤压工艺对6013铝合金组织和力学性能的影响

以半连续铸造、挤压获得的6013铝合金为研究对象,通过金相显微镜、扫描电镜、室温拉伸以及硬度等组织性能检测手段,对比研究不同挤压温度和挤压速度对6013铝合金组织与性能的影响。结果表明,挤压温度和挤压速度对6013铝合金的组织和力学性能均有显著影响,挤压温度越高、挤压速度越快,越有利于获得再结晶组织。在速度较低时,抗拉强度在500℃时获得最大值;在不同的速度下,6013铝合金的伸长率以及硬度均随着温度的升高而降低。断口分析表明,断口韧窝尺寸较大、较深,且伴有大量撕裂棱,说明合金具有较好的塑性。     

Si相对铸造Al-Si合金低温拉伸断裂行为的影响

对Al-1Si-0.3Mg和Al-7Si-0.3Mg合金在-80~20℃拉伸过程中的断裂行为进行研究。结果表明:随着温度的降低Al-1Si-0.3Mg合金的抗拉强度、屈服强度及伸长率均呈上升趋势;Al-7Si-0.3Mg合金的抗拉强度和屈服强度上升,伸长率却明显下降;拉伸过程中Al-1Si-0.3Mg合金中位错在晶界塞积,易使相邻晶粒内位错源启动,使合金具有较高的塑性;Al-7Si-0.3Mg合金的位错在Si相边界塞积,使相邻晶粒内位错源难以启动,从而造成合金具有较高的强度。     

铁素体/马氏体钢P92的正常和反常锯齿流变行为

对经过正火和回火处理的P92钢在573~623 K的温度区间和5×10~(-5)~1×10~(-3)s~(-1)的应变速率范围内进行了拉伸试验,研究了温度和应变速率对铁素体/马氏体钢P92锯齿流变的影响。结果表明:在应变速率为5×10~(-5)~1×10~(-3)s~(-1)及温度为573~623 K这两个区间内进行拉伸试验,P92钢产生锯齿流变时的临界应变均表现出正常和反常的行为。经计算,正常锯齿流变激活能为134 k J/mol。结合透射电镜观察结果,表明铬原子等置换原子可能是产生锯齿流变的原因,而反常行为则可能是由于位错对析出相产生切割作用引起。     

Al—Li单晶体锯齿流变的形态特征

研究了Ａｌ－Ｌｉ单晶体在不同温度和应变速率范围内产生的锯齿流变及其形态特征。开始产生锯齿流变的临界应升高先减小再增加。锯齿的频率和应力变化幅度受温度和应变速率的影响，但不随应变单调变化。     

热处理对Ti-Ni合金显微组织和力学性能的影响

研究了冷加工变形量为48%的Ti-Ni合金经中温退火(350～600 ℃)处理后退火温度对合金显微组织及室温力学性能的影响.结果表明,变形后获得部分非晶的纳米组织,400 ℃退火后合金发生再结晶;500 ℃退火后完成再结晶,晶粒开始长大;600 ℃退火后合金组织完全粗化,室温下为粗大的自协调马氏体.退火温度升高,合金的抗拉强度大大下降,当退火温度高于500 ℃时,伸长率大大增加,伸长率大于50%.室温下合金拉伸变形时应力诱发马氏体相变的临界应力值σs受退火温度和相变温度的制约.     

热处理制度对6013和6061合金拉伸性能的影响

研究了自然时效（T4）、人工时效（T6）及室温停放对6013和6061合金常温拉伸性能的影响。结果表明：6013合金具有快速时效特性;经热处理后,6013合金的拉伸强度高于6061合金的且两者延伸率均大于10%。研究还表明：6013和6061合金常温拉伸性能的纵、横向差别很小,说明该合金拉伸性能各向异性不明显。文中还就不同热处理制度影响两种合金拉伸性能的原因进行了分析。     

溶质浓度对Al-Cu合金中PLC效应的影响

在不同温度下对Al-Cu合金试件进行固溶处理,以改变溶质原子在固溶体中的浓度及析出相在合金中的含量．对所得到的Al—Cu合金试件进行常应变率拉伸实验,观察其应力一时间关系曲线．由拉伸实验现象分析溶质原子及析出相对位错运动的影响,从而探究Portevin-Le Chatelier（PLC）效应产生的微观机制．结果表明,当固溶处理温度由500℃逐步降低,应力-时间曲线上的锯齿幅值逐渐减小,并在300℃时达到最小值;继续降低固溶处理温度至100℃,锯齿幅值又逐渐增大．固溶处理温度高于300℃时,溶质原子对PLC效应的影响强于析出相的影响而起主要作用;反之,固溶处理温度低于300℃时,析出相对PLC效应的影响强于溶质原子的影响而起主要作用．     

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).     

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.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

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.