TiAl基合金高温变形行为研究

通过对Ｔｉ－３３Ａｌ－３Ｃｒ－０．５Ｍｏ（ｗｔ％）合金在９００℃高温拉伸时的变形特性、显微组织变化及断口形貌的研究。发现ＴｉＡｌ基合金高温变形主要是通过等轴γ相晶粒内的位错滑移、晶界滑移和层片晶团中层片间的相对滑移来进行的；γ相晶粒在变形过程中发生周期性的动态再结晶并引起流变应力周期性波动；层片状晶团与γ晶粒变形的非协调性导致孔洞在Ｌ／γ界面形核，长大并相互连通使合金最后断裂。     

大晶粒FeAl合金超塑性变形的显微组织演变和变形激活能

本文对大晶粒ＦｅＡｌ金属间化合物塑性变形的微观组织演变进行了研究，并测定了其超塑性变形激活能，显微组织分析表明，合金的超塑性变形是一个晶粒变形，内部形成亚晶界，进而亚晶界向晶界转换，从而使晶粒得以细化的过程，Ｆｅ－３６．５Ａｌ，Ｆｅ－３６．５Ａｌ－１Ｔｉ和Ｆｅ－３６．５Ａｌ－２Ｔｉ合金变形激活能的测定值分别为３７０，２９０和２６０ｋＪ．ｍｏｌ＾－１大大低于其他的ＦｅＡｌ基合金蠕变激活能，表明超塑性     

TiAl基合金固态焊接

研究了各种显微组织ＴｉＡｌ基合金材料之间自体固态焊接,实验结果表明,粗晶ＴｉＡｌ基合金与粗晶ＴｉＡｌ基合金作焊接对偶件时,在结合面上形成与基体组织不同的再结晶细晶组织。这种显微组织的差异及结合面上微孔隙的残存,导致焊接构件的断裂主要发生在结合面上,如采用粗晶ＴｉＡｌ合金与细晶双态组织ＴｉＡｌ基合金对焊时。由于细晶ＴｉＡｌ基合金具有较好超塑性变形能力。在热压力作用下此部分材料可镶嵌入焊接对偶另一侧,     

γ－TiAl基合金的显微组织与机械性能

简要介绍了γ－ＴｉＡｌ基合金性能与其显微组织的关系以及该合金的变形、断裂、韧化机制，由此归纳出了γ－ＴｉＡｌ基合金的塑化、初化途经。指出，合金化和显微组织的控制是改善该合金性能的重要方法。文章还探讨了γ－ＴｉＡｌ基合金今后的研究工作重点。     

TiAl基合金高温变形行为研究￣ 

通过对Ｔｉ－３３Ａｌ－３Ｃｒ－０．５Ｍｏ（ｗｔ％）合金在９００℃高温拉伸时的变形特性、显微组织变化及断口形貌的研究，发现ＴｉＡｌ基合金高温变形主要是通过等轴相晶粒内的位错滑移、晶界滑移和层片晶团（Ｌ）中层片间的相对滑移来进行的；相晶粒在变形过程中发生周期性的动态再结晶并引起流变应力周期性波动；层片状晶团与晶粒变形的非协调性导致孔洞在Ｌ／界面形核、长大并相互连通使合金最后断裂。     

Nb和A1对γ—Tial基合金高温强度的影响

研究了Ｎｂ对γＴｉＡｌ基合金性能的影响。结果表明,高Ｎｂ合金化能大大提高γ－ＴｉＡｌ基合金的高温强度,合金含Ｎｂ量越高,强度就越高。ＴＥＭ观察表明,Ｎｂ对γ－ＴｉＡｌ性能的影响类似于氧元素。增强ｄ－ｄ键的６方向性,增加普通位错的Ｐ－Ｎ力,提高普通位错开动的临界分切应力和滑移阻力。Ａｌ对γ－Ｔ合金性能的影响是通过影响合金中的ａ２相含量来影响其性能的。随俣金中Ａｌ含量升高,ａ２相含理减少,位错运动非热     

粉末冶金TiAl基合金显微组织及力学性能的研究

采用粉末冶金方法制备多种成分的ＴｉＡｌ基合金,并研究其显微组织及室温、高温力学性能,结果表明,采用粉末冶金方法能制备成分均匀、显微组织细小的Ｔｉ－Ａｌ－Ｃｒ－Ｎｂ系列合金。添加合金元素对粉末冶金ＴｉＡｌ基合金的显微组织具有显著影响。粉末冶金ＴｉＡｌ基合金的力学性能与其显微组织有密切的关系,显微组织越细小,其室温强度及延性越高,但在高温下,其屈服强度随晶粒尺寸增加而增加。所制备出的Ｔｉ－４７Ａｌ－３     

Fe3Al—Ti超塑性变形过程中晶粒形态演化规律

对Ｆｅ３Ａｌ－Ｔｉ合金超塑性变形中不同应变量下的晶粒形态进行了研究，发现Ｆｅ３Ａｌ－Ｔｉ行为与连续再结晶有关，随变形量增大，晶粒逐渐细化，但晶粒形状变化不大，并沿拉伸方向有所伸长。ＴＥＭ分析表明，晶粒细化过程与超塑性过程中亚晶界向大角晶界的演化有关。本文对Ｆｅ２Ａｌ－Ｔｉ合金超塑性变形机理进行了初步的探讨。     

Fe_3Al－Ti超塑性变形过程中晶粒形态演化规律

对Ｆｅ_３Ａｌ－Ｔｉ合金超塑性变形中不同应变量下的晶粒形态进行了研究。发现Ｆｅ_３Ａｌ－Ｔｉ超塑性行为与连续再结晶有关，随变形量增大，晶粒逐渐细化，但晶粒形状变化不大，并沿拉伸方向有所伸长。ＴＥＭ分析表明，晶粒细化过程与超塑性过程中亚晶界向大角晶界的演化有关。本文对Ｆｅ３Ａｌ－Ｔｉ合会超塑性变形机理进行了初步的探讨。     

TiAl基合金热处理显微组织缺陷

研究了等温锻造和热处理后ＴｉＡｌ基合金显微组织中晶粒尺寸不均匀参数，讨论了这种缺陷对ＴｉＡｌ基合金室温抗拉笥能的影响，提出了这种显微组织缺陷形成机理。     

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.     

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.     

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.