Ti40Zr25Ni8Cu9Be18块体非晶合金低温动态压缩性能研究

采用铜模喷铸法制备Ti40Zr25Ni8Cu9Be18块体非晶合金,通过分离式霍普金森压杆装置(SHPB)对Ti40Zr25Ni8Cu9Be18块体非晶合金进行室温(25℃)和液氮温度(–196℃)条件下的高应变率加载动态压缩测试,结合S-4800型扫描电镜(SEM)对压缩试样断口进行观察,对比在室温和液氮温度下Ti40Zr25Ni8Cu9Be18块体非晶合金动态压缩性能及其断口形貌特征的差异。结果表明:Ti40Zr25Ni8Cu9Be18块体非晶合金室温动态压缩时,随应变率提高抗压强度无明显变化,没有应变率硬化效应。在液氮温度动态压缩时,抗压强度随着应变率提高有较大幅度增加,存在应变率硬化效应。液氮温度时的动态抗压强度明显高于室温动态抗压强度。Ti40Zr25Ni8Cu9Be18块体非晶合金室温动态压缩为剪切断裂,微观形貌上出现脉状花样和剪切带,剪切带诱发了裂纹的形成,裂纹沿着剪切带扩展。液氮温度下断口微观形貌有解理台阶和河流花样。室温动态断裂过程中,局域应变集中产生塑性变形;液氮温度下压缩动能转化的热量大部分被抵消,削弱了绝热剪切作用。     

纯锆的动态力学行为及绝热剪切带

使用分离式霍普金森压杆装置(SHPB)对纯锆在室温下进行动态压缩实验,应变速率为800～4000 s-1。采用金相显微镜和Quanta200型扫描电子显微镜对绝热剪切带及压缩断口进行观察。结果表明,纯锆具有较低的应变速率敏感性,由于高应变条件下产生了高密度的孪晶,材料硬化显著增强,真应力-真应变曲线随应变增加呈上升趋势,最大抗压强度为843 MPa。纯锆试样中观察到明显的绝热剪切带,且沿剪切带出现裂纹,压缩断口呈韧性断裂。绝热剪切带的出现和发展是材料失效的主要原因。对剪切带内部的温度进行了估算,结果表明,纯锆剪切带内部最高温度为1564℃。     

低速热变形对挤压态Mg-Zn-Mn合金组织及力学性能的影响

结合光学显微镜(OM)、电子背散射衍射技术(EBSD)、透射电子显微镜(TEM)等，分析了低速热变形对挤压态Mg-Zn-Mn合金显微组织及室温压缩性能的影响。结果表明：Mg-Zn-Mn合金在200～300℃的低速热压缩过程中存在明显的动态再结晶和动态析出，热压后样品组织明显细化且基面织构减弱。对于热压后样品，其抗压强度和断裂应变随变形温度的升高先增大后减小。对于250℃下热压缩的样品，其抗压强度和断裂应变随热压变形量的增大先减小后增大。其中，在250℃下热压缩且变形量为70%时，合金的性能提升最为显著，在不损害塑性的情况下，其屈服强度(σ0.2)和抗压强度分别达到247 MPa和504 MPa，比挤压态时分别提升了63%和19%。     

高应变率下铸造镁合金AZ91的动态压缩性能及破坏机理

利用INSTRON准静态试验机和分离式Hopkinson压杆系统对铸造镁合金AZ91在不同应变率下进行压缩试验,研究AZ91镁合金在高应变率范围内(应变率6×102～1×104 s-1)的动态力学行为,并利用扫描电镜观察试样在不同应变率下破坏断口微观形貌的变化,探索应变率对破坏机理的影响.结果表明:室温下铸造镁合金AZ91具有明显的应变硬化性质;在准静态压缩过程中材料对应变率负敏感,当应变率达到7×103 s-1时,AZ91镁合金表现出明显的应变率敏感性;在准静态破坏和动态破坏下,材料断口的微观形貌具有很大不同.     

304不锈钢热拉伸实验的组织和性能

对304不锈钢在25~600℃进行热拉伸实验,得到了不同温度下的真实应力-应变曲线,并且通过扫描电子显微镜(SEM),X射线衍射仪(XRD)对拉伸断口及断口的形貌变化进行了分析。结果表明:随着实验温度的升高,304不锈钢的强度下降,塑性提高;在实验温度范围内,应变量小于2.5%,在达到同等变形量的条件下,室温下材料变形所需要的应力远高于加热情况下所需应力,这表明只要适当地升高温度,这种材料的塑性就会大为改善。当温度到达600℃时,材料的晶界明显弱化,断口韧窝形态减少,断裂以沿晶断裂为主。     

ZrTiNiCuBe块体非晶合金剪切带内温升与断裂温升

在室温环境下(25℃)对某ZrTiNiCuBe块体非晶合金材料进行不同应变率条件下的静态与动态压缩实验。并采用扫描电镜技术(SEM)对试样断口、侧面等进行表征,对比静、动态条件下的应力-应变曲线形貌的差异。结果表明:静态压缩时为剪切断裂,微观形貌上出现脉状花样与剪切带;剪切带诱发裂纹的形成,裂纹随着剪切带扩展。动态压缩时为脆性解理断裂,断面粗糙且发现大量熔滴;断口处出现解理台阶,塑性阶段出现明显的锯齿流变现象。从能量守恒定律出发,利用变形过程中弹性应变能的变化规律推测剪切变形区域内温升的变化规律,温升的变化规律揭示锯齿流变与试样的断裂机制。     

时效态Mg-Gd-Y-Zr镁合金压缩性能和组织演变

采用Gleeble-3500热模拟机对时效态Mg-10Gd-3Y-0.5zr (GW103)和Mg-12Gd-3Y-0.5Zr(GW123)稀土镁合金在变形温度为25～350℃、应变速率为0.01 s~(-1)、最大变形程度为1的条件下进行压缩模拟试验,利用金相显微镜和扫描电镜观察组织变化.结果表明:GW103和GW123合金的室温抗压强度分别为419MPa和460MPa;150-200℃时GW123合金的抗压强度大干GW103合金;当温度高于250℃时,两种合金的抗压强度相近.分析表明250℃以下压缩时,孪生变形是影响压缩力学性能的主要因素;300～350℃压缩时,晶界和变形带处发生动态再结晶是影响压缩力学性能的主要因素.     

V-N微合金化Q420B大规格角钢连铸坯高温热塑性的研究

通过Gleeble-3500热模拟试验机研究了不同应变速率下V-N微合金化Q420B钢连铸坯的高温热塑性,利用扫描电镜观察高塑性区和第Ⅲ脆性温度区拉伸试样的断口形貌及断口处组织形貌,分析了试验钢在高温下的强度和塑性随温度变化的关系,动态再结晶、相变和析出物对高温热塑性的影响。结果表明:在应变速率为ε觶=5×10-3/s时,存在第Ⅲ脆性区(700~900℃),在1000℃时断面收缩率(RA)达到最大值92.16%;当应变速率为ε觶=5×10-2/s时,存在第Ⅲ脆性区(600~862℃),在1100℃时RA达到最大值90.39%;当应变速率为ε觶=5×10-1/s时,不存在塑性凹槽;3个应变速率下均没有出现第Ⅱ脆性区;在第Ⅲ脆性区,随着应变速率的增大,断面收缩率提高;在1000~1200℃出现高塑性的主要原因是发生了动态再结晶;第Ⅲ脆性区塑性低主要是由于晶界处有析出物和夹杂物,同时也是由于沿奥氏体晶界析出的铁素体抗拉强度低。     

30ZrCp／W复合材料的高温压缩变形流变应力行为

在Gleeble-1500D热模拟实验机上对30ZrCp/W复合材料进行高温压缩实验,变形温度和应变速率分别为800℃～1 200℃和10-3 s^-1～1 s^-1,研究其高温压缩变形的流变应力行为.研究表明:随变形温度升高,复合材料的流变应力下降,在10-3s^-1和1200℃下,抗压强度为948.7 MPa.在800℃下发生伪塑性变形,未达到预设变形量,真应力-真应变曲线上表现出的塑性为伪塑性,其是由微裂纹的萌生-钝化引起的.随变形温度升高,复合材料发生动态回复再结晶.随应变速率升高,真应力-真应变曲线形状从“锯齿”型向“平滑”型转变.复合材料对应变速率不敏感,随应变速率升高,复合材料的流变应力略有升高.在800℃和1s^-1下,复合材料的抗压强度为1176.9MPa.用Arrhenius方程描述复合材料在1000℃～1200℃的热变形行为,变形激活能为811.4 kJ/mol.     

700℃超超临界锅炉用Inconel 740H合金的热塑性

研究了不同温度对Inconel 740H合金热塑性的影响。结果表明:Inconel 740H合金在1050~1200℃范围内具有良好的热塑性,拉伸断口处均有明显颈缩现象,为塑性断裂,断面收缩率均在80%以上,且在1150℃左右达到最大值;随着温度的升高,合金断口韧窝增多,塑性越来越好,当温度超过1150℃后断口韧窝减少,塑性开始缓慢下降;随着变形温度的提高,合金的动态再结晶率增大,在1125~1200℃时,可发生完全动态再结晶,当温度超过1150℃后,细小的再结晶晶粒开始缓慢长大。对于Inconel 740H合金热挤压管,在应变速率为1 s~(-1)时,较合适的热变形温度范围为1125~1175℃。     

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.