GH742y合金凝固偏析行为

采用组织分析和差热分析相结合的方法系统研究GH742y合金的凝固偏析行为和铸态组织形成规律。GH742y合金枝晶偏析严重,组织析出复杂:Cr、Co、W、V和Al偏析于枝晶干,而Nb、Ti和Mo等元素在枝晶间的富集导致一次和二次γ′相、(γ γ′)共晶、MC碳化物、M6C碳化物、Laves相和δ相的析出;稀土元素La和Ce的偏析导致Ni5Ce相和富氧硫稀土相的枝晶间析出。相分计算表明,严重的元素偏析以及大量富Nb和Ti相的析出是σ相和μ相等有害TCP相析出的主要原因。GH742y合金的凝固顺序为:γ基体、MC碳化物、一次γ′相、(γ γ′)共晶、Laves相、Ni5Ce相和M6C碳化物。     

铸态GH742合金的凝固特点及枝晶偏析

高合金化GH742合金存在严重的枝晶偏析,Nb、Ti大量偏聚于枝晶间,导致MC碳化物、(γ+γ′)共晶、Laves相、δ相等析出;高Mo含量及其枝晶间偏析是析出σ相的重要原因;La、Ce在枝晶间的富集促使含氧硫稀土相和Ni5Ce相的析出。与一般合金凝固特点不同,高含量Al、Ti、Nb导致GH742合金凝固过程中先后发生(γ+γ′)和(γ+Laves)两种类型的共晶反应。结合差热分析技术和凝固组织特点确定了合金的凝固温度区间为1346-1190℃,凝固顺序为γ、MC、(γ+γ′)、Laves、Ni5Ce。     

新型难变形高温合金эк151的组织特征及平衡析出相热力学计算

利用场发射扫描电子显微镜对其铸态组织进行了观察,并通过热力学计算,对该合金中成分对平衡相析出的影响规律进行了研究。结果表明,эк151合金凝固过程中,Mo、Nb和Ti等元素在枝晶间偏析,并形成大量γ′+γ共晶相。合金主要析出相为大量的γ′相、少量的一次、二次碳化物和硼化物以及μ相。其中强化相γ′多成立方状,800℃下平衡态质量分数含量高达50%左右。当成分在规定范围波动时,对熔点影响最大的为Cr、Mo、Nb和Ti;而Al、Ti和Nb含量变化均会影响到γ′相的析出量及析出温度;Cr、Mo含量变化还会影响到二次碳化物的种类,Ti、Nb、C虽然是一次碳化物MC的主要形成元素,但是成分范围内对其析出温度影响并不明显。影响μ相析出温度和析出量的主要成分为Cr、Mo和W。     

GH4169合金铸态组织特征及均匀化处理工艺

通过CLSM、OM和SEM等测试方式,研究了GH4169合金铸态组织和均匀化热处理工艺对晶粒尺寸、析出相、氧化层厚度以及溶质元素均匀性的影响.研究表明,铸态组织枝晶间存在Laves相、δ相、γ′相和MC碳化物等析出相,主要偏析元素Nb在铸锭中心偏析最严重;在第一段1160℃ ×16 h,第二段1190℃ ×30 h均匀...     

Nb含量对GH4169合金钢锭凝固及均匀化过程相演化规律的影响

以不同Nb含量的直径160 mm GH4169合金钢锭为研究对象,利用热力学软件Thermo-Calc的模拟计算及电子探针成分分析,系统研究了Nb元素含量变化对GH4169合金钢锭凝固及均匀化过程相演化规律的影响。结果表明:Nb元素含量的增加会降低合金初熔点和终熔点,扩大凝固区间,增加偏析形成的趋势;Nb元素含量的增加还可以提高GH4169合金钢锭凝固过程Laves相的析出温度,若Nb元素偏析浓度超过7.0%,Laves相的析出温度会高于标准均匀化温度1160℃,导致部分高浓度下生成的Laves相无法回溶。进一步的凝固过程中各相Gibbs自由能变化规律分析表明,GH4169合金凝固过程中,当达到Laves相的析出温度后,Laves相的形成激活能要显著小于MC碳化物,此时高浓度的Nb元素主要用于Laves相的析出和生长,Laves相的大量形成抑制了MC碳化物的进一步形成和长大,导致了Laves相与MC碳化物集合体的产生。上述的热力学分析结果与实际钢锭的相析出回溶实验结果一致。     

难变形高温合金GH4175铸态组织及均匀化工艺

采用热力学计算、光学显微镜、扫描电镜和能谱分析等方法对GH4175合金铸锭进行显微组织、析出相和元素偏析情况分析,并研究了均匀化处理过程中合金组织演变和元素再分配的变化规律.结果 表明:GH4175合金铸锭枝晶偏析严重,Nb、Mo、Ti元素偏聚于枝晶间,Nb元素的偏析最为严重,主要析出相为γ'相、M23C6、MC、Laves相及针状8相.合金铸锭在1150℃时出现低熔点相熔化现象,在1200℃时出现枝晶初熔.合金铸锭均匀化应采用低温预处理加高温扩散的两段式,经1140℃×10 h+1190℃×30 h均匀化处理后,合金中的有害低熔点相回溶,枝晶偏析基本消除,是比较合理的均匀化工艺.     

钒微合金化对718合金中铌元素偏析行为的影响

利用金相显微镜、电子探针、能谱仪等分析了含钒元素（V）0.066%的718合金铸锭凝固组织,对其微观组织和析出相特征进行分析,研究其中易偏析铌元素（Nb）的分布状态及偏析规律。结果表明,V元素的微合金化使718合金铸锭枝晶组织得到细化,二次枝晶间距及Nb元素的偏析系数均有所降低;由于Nb元素主要分布在Laves相及碳化物中,通过对二者体积分数的定量表征,V元素的加入大大降低Laves相及碳化物的析出,体积分数降低;线扫描分析表明,距Laves相越远,Nb元素含量越低,而含V样品中,这种含量降低的趋势有所减缓。所有分析结果均表明,V元素的合金化改善了718合金中Nb元素的偏析状态,细化了枝晶组织,对降低718合金均匀化热处理难度、提高合金成分和组织均匀性有利。含V碳化物在凝固过程中成为异质形核点,减小了凝固形核的驱动力,使得二次枝晶间距变小,表现出更小的Laves相体积分数和较细的枝晶组织。     

718Plus合金铸锭的元素偏析及均匀化工艺

采用光学显微镜(OM)、扫描电镜(SEM)和能谱仪(EDS)等研究了镍基718Plus合金铸锭的组织特点、元素偏析规律及均匀化过程中枝晶间低熔点偏析相的回溶情况.结果 表明:在合金非平衡凝固过程中,Nb和Mo为易偏析元素,在枝晶间形成γ+Laves的共晶相.合金经1150℃×48 h的均匀化工艺处理后,偏析元素扩散均匀,Laves相的回溶情况较为理想,实验结果与利用残余偏析指数6的计算结果基本一致.     

铌在一种高合金化高温合金中的偏析与扩散行为

研究铌在一种高合金化镍基高温合金凝固过程中的偏析和均匀化过程中的扩散行为。铌严重偏析于枝晶间区域,其偏析系数高达4.30。许多富铌相,包括Laves相、δ相、（γ＋γ′）共晶、MC和M6C碳化物等在枝晶间析出。利用差热分析和在不同温度、时间的均匀化处理确定各种富铌相的溶解温度和枝晶偏析的消除程度。元素扩散计算表明：铌的扩散速率随着均匀化温度的提高而显著增加,从而有效地缩短均匀化时间。提出一种无初熔的三步均匀化制度,可以完全消除铌的枝晶偏析,获得均一的组织。     

新型低钴铸造镍基高温合金的相析出行为研究

利用热力学计算软件JMatPro和差示扫描量热实验,研究新型低钴铸造镍基高温合金的相析出行为,并与实际铸锭的组织、成分进行对比。结果表明,低钴合金铸态组织主要包括γ（基体）、γ′、碳化物（MC、M6C）和γ+γ′共晶组织（体积分数约13.9%）,凝固过程中Ta和Hf出现正偏析。DSC测试得出合金初熔点、终熔点和γ′相回溶温度分别为1349.6℃、1300.1℃和1272.1℃,理论计算与实验结果基本一致。热力学计算显示Al、W含量增加能够分别提高γ′和M6C型碳化物的析出量与回溶温度,Hf、Ta元素能增大MC型碳化物的液析倾向,新型低钴合金的预期持久性能优于现有商用镍基多晶铸造高温合金。     

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.