TC4/TA17异种钛合金激光焊接接头显微组织和力学性能

研究TC4/TA17异种钛合金激光焊接接头的显微组织和力学性能。结果表明,TC4/TA17异种钛合金激光焊接头焊缝的显微组织为片状α′马氏体,TC4侧靠近母材的热影响区和TA17侧靠近母材的热影响区只发生α相向β相转变,TC4侧靠近焊缝的显微组织为残余α相+针状α′马氏体,TA17侧靠近焊缝的显微组织为残余α相+片状α′马氏体。TC4/TA17异种钛合金激光焊接头的显微硬度呈不对称分布,焊缝的显微硬度最高,TA17母材显微硬度最低。TC4/TA17异种钛合金激光焊接接头断裂在TA17母材,断口呈现韧性断裂形貌。     

TC4钛合金窄间隙激光填绞股焊丝焊接接头组织及性能

采用实心绞股焊丝,通过窄间隙激光填丝焊对TC4钛合金进行焊接,分析了激光填丝焊接头各区域的微观组织及形貌,并测试了焊接接头的显微硬度、室温拉伸性能及冲击性能等力学性能。结果表明,焊缝截面整体成形良好,无明显未熔合和气孔等缺陷;母材由等轴α+β相组成,热影响区晶粒比母材稍大,热影响区由针状α′马氏体+初生α相组成,焊缝由粗大的原始β柱状晶和内部网篮状α′马氏体组成;焊接接头的抗拉强度平均值达940 MPa,拉伸断裂在母材,断口韧窝较浅,主要表现为韧性断裂特征;焊缝的显微硬度平均值为375 HV,高于母材及热影响区。 创新点： 采用高熔敷效率的绞股焊丝作为填充金属,对 20 mm 厚 TC4 钛合金板进行激光填丝焊,探究了厚板钛合金焊接接头的组织与性能分布规律,为厚板钛合金焊接结构的实际应用提供基础数据支撑。     

轧制+增材TC4合金电子束焊接接头组织与性能

研究了一种电子束焊接规范对轧制+增材TC4钛合金焊接接头组织影响,分析了焊后钛合金力学性能.结果表明,轧制侧热影响区合金组织变化较大,离焊缝中心距离越近,β转变组织含量增加,晶粒逐渐转变为等轴晶组织,等轴晶内有集束状马氏体α'相析出,越靠近焊缝等轴晶尺寸越大;增材侧热影响区组织形态变化较小,β晶粒形态保持柱状晶形态,无等轴晶区产生,晶内组织转变为马氏体α'相.焊缝两侧热影响区显微硬度变化趋势相同,均为越靠近焊缝中心,显微硬度越高,焊接重熔区硬度最高,达400 HV左右.焊接接头力学性能与TC4钛合金锻件相当,且断裂位置均位于激光沉积母材区域.     

TC4钛合金激光焊接头微观组织和硬度

采用光学显微镜和场发射扫描电镜观察了TC4钛合金激光焊接接头的显微组织,测量了接头焊缝中心到母材的显微硬度。结果表明,母材由α相和其相界上断续分布的粒状β相组成。焊接接头组织由粗大等轴晶区、柱状晶区、细等轴晶区和热影响区过热组织组成。粗大等轴晶区组织形态有层片状α+β、魏氏体α和网篮状α+β3种,其显微硬度略低于柱状晶区和细等轴晶区,但比母材高;柱状晶区和细等轴晶区组织为针状马氏体,柱状晶区显微硬度相对较高。热影响区显微硬度与母材相差不大。     

TC4钛合金电子束焊接接头组织和性能

通过室温拉伸、室温缺口拉伸、显微硬度以及金相分析对TC4钛合金电子束焊接接头的显微组织和性能进行了研究。试验结果表明，用电子束焊接TC4钛合金可获得性能良好的焊接接头，其接头的抗拉强度不低于母材，焊缝的缺口敏感系数均小于1。焊缝区和热影响区的硬度均高于母材，焊缝组织是由较粗大的原始β相转变而成的α′相，即针状马氏体，热影响区组织为均匀且细小的针状马氏体和原始α相的混合物。     

7 mm厚TC4钛合金电子束焊接头组织和性能

采用真空电子束焊对7 mm厚TC4钛合金板进行焊接,利用光学显微镜对焊接接头显微组织进行表征,分析不同区域显微组织,通过显微硬度、拉伸试验、冲击试验、弯曲试验对力学性能进行测试,借助扫描电镜对拉伸、冲击断口形貌进行观察,对焊接接头显微组织演变规律和性能进行研究。结果表明,真空电子束焊焊接接头成形良好,TC4钛合金母材组织由α相和β相组成,焊缝区组织由原始的β相转变而成α′相（针状马氏体）,为粗大的柱状晶组织,热影响区组织由均匀且细小的针状马氏体α′相及原始的α相和β相组成;焊缝区显微硬度高于热影响区和母材区,从焊缝顶部到根部显微硬度逐渐下降;焊接接头抗拉强度高于母材抗拉强度;V形缺口在焊缝区的冲击试样具有较好的韧性。     

厚板TC4钛合金电子束焊接头组织和力学性能研究

对30 mm厚TC4钛合金进行电子束焊接试验,通过金相分析以及显微硬度测试对焊接接头的显微组织和力学性能进行了研究。结果表明,TC4钛合金母材由等轴α以及部分β转变组织组成,焊缝区组织在纵向上具有不均匀性。焊缝顶部β柱状晶粗大,沿熔合线向顶部生长,中部和下部柱状晶相对较小,垂直熔合线向焊缝中心对称竞相生长。β晶粒内部微观组织为针状马氏体,马氏体尺寸从焊缝顶部到底部逐渐减小。热影响区显微组织为等轴初生α相和α'针状马氏体,以及未完全转变的β相。焊缝区和热影响区显微硬度值高于母材;在焊缝区纵向上,顶部显微硬度值为340 HV,随着距离焊缝顶部距离的增加,硬度值显著增大,最大值为435 HV。     

焊前热处理对TC4-DT钛合金电子束焊接接头组织的影响

焊前首先对TC4-DT钛合金母材进行不同固溶处理,进而研究电子束焊接对接头显微组织的影响.结果显示,在炉冷条件下960℃固溶处理的母材为双态组织,晶粒细小,焊缝轮廓清晰,热影响区为等轴初生α相和针状马氏体α'相,焊缝为"网篮状"马氏体组织;经1018℃固溶处理的母材为魏氏组织,晶粒粗大,焊缝轮廓模糊,热影响区为板条状α相和针状马氏体α'相,焊缝柱状晶宽度增加;经960℃+1018℃固溶处理的母材,魏氏组织晶粒尺寸最大,焊缝柱状晶宽度也最大.固溶后空冷处理的母材α片层厚度小,热影响区α相也小,但焊缝区的马氏体α相变宽、变粗.     

工艺参数对TC4钛合金电阻点焊接头组织和性能的影响

对TC4钛合金电阻点焊接头进行了试验研究。结果表明,TC4钛合金电阻点焊焊缝区的显微组织为粗大的针状α′,近焊缝HAZ显微组织为细小的针状α′,远焊缝HAZ显微组织为α+β+α′;母材组织为α+β;近焊缝HAZ硬度值最大,远焊缝HAZ硬度值最低;在TC4钛合金薄板厚度为1mm、焊接电流为6kA、焊接时间为0.16s时,接头剪切力达到最大值。     

薄板TC4钛合金TIG电弧和激光焊接接头晶粒尺寸与微观组织

对薄板TC4钛合金进行TIG电弧和激光焊接技术研究,重点分析了TIG焊接电流、焊接速度和激光输出功率对TC4钛合金焊接接头晶粒尺寸、微观组织和显微硬度的影响规律. 试验结果表明,在实现薄板TC4钛合金完全熔透的条件下,激光焊接具有更小热输入,接头焊缝区和热影响区宽度也显著降低. TIG焊接接头晶粒尺寸随热输入增加,呈现增加趋势. 随距焊缝中心位置增加,焊接接头晶粒尺寸均逐渐降低. TC4钛合金激光焊接接头焊缝区呈现魏氏组织特征,针状α'马氏体细小. 近缝热影响区组织为网篮状α'马氏体,而近母材热影响区为未转变α相和针状α'马氏体的双相组织. 随距焊缝中心位置增加,马氏体生成量逐渐减少,焊缝显微硬度值呈现降低趋势;同时相比于TIG焊接,TC4激光焊接接头具有更高的显微硬度.     

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.