Ti-22Al-24Nb-0.5Mo粉末合金的制备及电子束焊接

采用预合金粉末热等静压工艺制备了Ti-22Al-24Nb-0.5Mo(原子分数,%)粉末合金,对Ti-22Al-24Nb-0.5Mo粉末合金环坯和板坯进行电子束焊接.采用OM,SEM,EPMA和X射线三维成像技术对焊接接头的微观组织进行表征,研究了焊后热处理对焊接接头显微硬度、拉伸性能和持久性能的影响.结果表明,热等静压温度显著影响Ti-22Al-24Nb-0.5Mo粉末合金的孔隙分布.在1030oC热等静压成型的粉末环坯经980oC,2 h,真空炉冷热处理后表现出较好的可焊性.焊接接头熔合区、热影响区和母材的化学成分均匀,虽然显微组织差异明显,但是显微硬度无明显区别.拉伸及持久性能测试试样皆断裂于熔合区.焊接接头熔合区存在大量的显微孔隙是焊接接头发生断裂的失效机制.焊后热处理可以减少焊缝处的显微孔隙数量,从而提高焊接接头塑性及高温持久寿命.     

热暴露对Ti-24Al-15Nb-1.5Mo/TC11焊接界面显微硬度和元素分布的影响

通过550℃,50h热暴露试验研究了Ti-24Al-15Nb-1．5Mo／TC11焊接界面显微硬度和元素分布的变化规律．结果表明,梯度热处理后Ti-24Al-15Nb-1．5Mo合金基体组织的显微硬度高于双重热处理．梯度热处理条件下,变形30％试样在热暴露期间由于焊缝组织中细针状α相数量的减少,造成显微硬度升高;而在Ti-24Al-15Nb—1．5Mo合金侧由于晶格畸变能的释放,造成显微硬度的降低．而变形量40％,50％＋梯度热处理试样焊缝组织在热暴露期间继续分解、长大,造成显微硬度的降低．热暴露过程中,焊缝界面处的元素继续扩散;Nb元素在焊缝区域中的含量明显增加,增加了品格畸变,也是引起显微硬度升高的原因之一．     

Influence of Welding Thermal Cycle on Microstructure and Properties in Heat-affected Zone of X80 Pipeline Steel

Single welding thermal–cycles with different input linear energies (ILE)(15, 20, 30, 40, 50 kJ/cm) and peak temperatures (PT) (900, 1050, 1200, 1300, 1350 ℃) were simulated by MMS-300 to study the correlation of toughness and microstructure in heat-affected zone (HAZ) of a X80 pipeline. The evolution characteristics of microstructure were investigated by OM, SEM and EBSD. The results show that numerous polygonal ferrites and grain boundary ferrites appear, and the sizes apparently decrease as the heat input decreases. Heat input in single welding should be less than 35 kJ/cm to ensure well Charpy impact toughness. The toughness of course grain zone is the lowest when welding heating temperature is 1350 ℃ and it is the weakness part in welded zone. The uniformity of prior austenite grain is worsened as increasing the heat input. Moreover, the characteristics of M-A constituents and high angle grain boundaries (HAGB) are influenced by heat input and PT. In the case of low heat input and PT, higher density of HAGBs, dispersed and fine M-A constituents were observed. Otherwise, with high heat input (≥40 kJ/cm), the effective grain size is almost the diameter of prior austenite grain, and it will decrease the density of HAGB, moreover, coarse M-A constituents which are prone to crack initiation will be generated, thus, the impact toughness of the coarse grain zone will be worsened obviously in welding HAZ.     

大厚度TC21钛合金电子束焊接试验

对56mm厚TC21钛合金进行了电子束对接试验,对接头显微组织和力学性能进行了研究.结果表明,接头焊缝区组织形态以柱状β晶粒为基体,针状的马氏体弥散其中;热影响区从焊缝到母材分为三个区域,依次为等轴再结晶β晶粒区、片状和针状а相形成的魏氏组织区以及片状α相聚集长大的区域;熔合区内柱状晶与等轴晶联生.接头强度达到母材水平,断裂发生在母材内,接头厚度方向性能一致.接头塑性损失较大,只达到母材的50%左右.接头焊缝区硬度最高,其次是热影响区的等轴晶区和魏氏组织区,而热影响区内片状α相聚集长大的区域硬度值最低.

Abstract：

Electron beam welding of TC21 56 mm titanium alloy was carried out. The microstructure and the mechanical properties of welded joints were analyzed and tested. The results showed that the weld zone consisted of the columnar β gains, and in which the transgranular acicular α' martensite were dispersedly distributed. HAZ can be divided into three parts from base metal to weld zone, which are the equiaxed recrystallized β grain zone, Widmanstaten structure zone formed by lamellar and aeicular α phases and lamellar a phase coarsening zone. Fusion zone consists of the adnate columnar and equiaxed grains. Tensile strength of joints reaches to that of base metal and the failure appears in the base metal. The mechanical properties are uniform along the vertical direction. Plasticity in the welded joint is greatly decreased and only up to 50% of that of the base metal. The microhardness in weld zone is the highest, and that of the equiaxed grain zone and Widmanstaten structure zone in HAZ is higher, and the microhardness in columnar a phase coarsening zone is the lowest.     

Microstructure and properties of SAF2507 superduplex stainless steel welded joints

SAF2507 plates （ 12 mm thickness ） were welded using shield metal arc welding （SMAW） process with E2594 electrode. The microstructure, o-phase, and impact fraetograph of the welded joints were analyzed using optical microscope and scanning electron mieroseope. The results show that the fusion zone consists of ferrite, chromium nitride, and secondary aastenite precipitation when welding is performed at low heat input （0. 5 kJ/mm）. However, the increase in heat input causes precipitation of brittle o＂ phase at the y/c~ interface in weld metal and heat-affected zone, as well as a brittle fracture along the grain boundary. Heat input in the range of O. 5 kJ/mm to 1.5 kJ/mm is suitable for joining SAF2507 plates.     

Effect of welding heat input on HAZ character in ultra-fine grain steel welding

In this essay, we studied how heat input affected the microstructure, hardness, grain size and heat-affected zone (HAZ) dimension of WCX355 ultra-fine grain steel which was welded respectively by the ultra narrow-gap welding (UNGW) process and the overlaying process with CO2 as protective atmosphere and laser welding process. The experimental results show when the heat input changed from 1.65 kJ/cm to 5.93 kJ/cm, the width of its HAZ ranged from O. 6 mm to 2. 1 ram. The average grain size grew up from 2 ~ 5 pln of base metal to 20～70 um and found no obvious soften phenomenon in overheatedzone. The width of normalized zone was generally wide as 2/3 as that of the whole HAZ, and the grain size in this zone is smaller than that in base metal. Under the circumstance of equal heat input, the HAZ width of UNGW is narrower than that of the laser welding.     

Effect of processing parameters on formability,microstructure, and micro-hardness of a novel laser additive manufactured Ti-6.38Al-3.87V-2.43Mo alloy

A novel Ti-6.38Al-3.87V-2.43Mo alloy was designed with a cluster formula of 12[Al-Ti12](V0.75Mo0.25Ti2)+4[Al-Ti12](Al3)by replacing Ti with Mo/V on the basis of the Ti-Al congruent alloy.The effects of laser power and scanning speed on the molten pool size,surface roughness,relative density,microstructure,and micro-hardness of single-track and bulk Ti-6.38Al-3.87V-2.43Mo samples prepared via laser additive manufacturing(LAM)were investigated.The results show that processing parameters significantly affect the formability,microstructure,and micro-hardness of the alloy.With decreasing laser power from 1,900 W to 1,000 W,the relative density is decreased from 99.86%to 90.91%due to the increase of lack-of-fusion;however,with increasing scanning speed,the relative density does not change significantly,but exceeds 99%.In particular,Ti-6.38Al-3.87V-2.43Mo samples of single-track and bulk exhibit a good formability under an input laser power of 1,900 W and a scanning speed of 8 mm·s_-1,and display the lowest surface roughness(Ra=13.33μm)and the highest relative density(99.86%).Besides,the microstructure of LAM Ti-6.38Al-3.87V-2.43Mo alloy coarsens with increasing laser power or decreasing scanning speed due to the greater input energy reducing the cooling rate.The coarsening of the microstructure decreases the microhardness of the alloy.     

Effect of heat input on microstructure and properties of welded joint in magnesium alloy AZ31B

Using the optical microscope, tensile test machine and micro-hardness meter, the effect of heat input on the microstructure and mechanical properties in fusion welding joints of AZ31B wrought alloys was investigated systematically, the mechanism on joint properties losing was analyzed, and a valid method to improve joint properties of the magnesium alloy fusion welding was explored. The results show that the heat input has an obvious effect on the microstructure and properties. Under the condition of penetration, with the heat input decreasing, the crystal grain in the weld and heat-affected zone (HAZ) becomes fine, the width of HAZ becomes obviously narrow, and the molding of the weld is improved, so the tensile strength and elongation are increased and the hardness of joints is improved. When the heat input reaches 60 J/mm, the high quality joints can he gained.     

Microstructure and interface reaction of investment casting TiAl alloys

In order to research the microstructure of TiAI alloy and TiAl-mould reaction between TiAI and ceramic mould shells prepared with the low cost binder in investment casting, the ceramic mould shells were prepared with low cost binder and refractory materials. Using two kinds of casting methods （gravity casting and centrifugal casting）, the titanium aluminum alloys with rare earth element （Ti-47.5Al-2Cr-2Nb-0.3Y and Ti-45Al-5Nb-0.3Y） were cast into the mould shells. The microstructures of investment casting titanium aluminum alloys were observed by optical microscope （OM）. The distributions of elements of topping investment on the surfaces of titanium aluminum alloys castings were analyzed by the means of electron probe micro-analysis （EPMA）, and the mechanical properties were studied. The results show that the microstructures of two kinds of titanium aluminum alloys are both lamella shape, and lamella is thin. The thickness of reaction and diffusing layer of Ti-47.5Al-2Cr-2Nb-0.3Y alloy is about 80 μm, and that of Ti-45Al-5Nb-0.3Y is less than 30 μm.     

Effects of minor yttrium addition on hot deformability of lamellar Ti-45Al-5Nb alloy

The effects of 0.3%(molar fraction,the same below)yttrium addition on hot deformability of lamellar Ti-45Al-5Nb alloywere investigated by simulated isothermal forging tests.The ingots with the nominal compositions of Ti-45Al-5Nb andTi-45Al-5Nb-0.3Y were prepared by induction skull melting.Simulated isothermal forging tests were conducted on Gleeble 1500Dthermo-simulation machine using a 6 mm in diameter and 10 mm in length compressive specimen at the deformation temperatures of1 100,1 150,1 200℃and strain rates of 1.0,0.1,0.01 s-1.The results show that yttrium addition remarkably improves hotdeformability of Ti-45Al-5Nb alloy.An appropriate hot deformation processing parameter of Ti-45Al-5Nb-0.3Y alloy is determinedas 1 200℃,0.01 s-1.The flow stresses are decreased by yttrium addition under the same compressive conditions.The activationenergies of deformation Q are calculated as 448.6 and 399.5 kJ/mol for Y-free and Y-containing alloys,respectively.The deformedmicrostructure observation under 1 200℃,0.01 s-1condition indicates that Ti-45Al-5Nb-0.3Y alloy shows more dynamicrecrystallization.The improvement of hot deformability of Ti-45Al-5Nb-0.3Y alloy induced by yttrium addition should be attributedto that the smaller the original lamellar colonies,the lower the deformation resistance and activation energy of deformation are,andthe more the dynamic recrystallization is.     

热输入对双光束激光焊接Ti-6Al-4V合金T型接头焊接过程、焊缝成形、组织及力学性能的影响

采用双光束同步激光填丝焊接的方法制备了Ti-6Al-4V合金T型接头,使用高速摄像机拍摄了焊接过程图像并研究了热输入对焊接过程稳定性、焊缝成形、组织及力学性能的影响。试验结果表明,热输入显著影响熔池行为和填丝焊接熔滴过渡,进而影响T型接头焊缝形貌及质量。随着热输入的增加,T型接头组织发生变化,晶粒尺寸变大。热影响区及焊缝处的马氏体使得这2个区域的显微硬度高于母材。另外,沿蒙皮方向及筋条方向的抗拉伸强度随着热输入的增加而增大。由于接头处马氏体增强作用,拉伸断裂均发生于母材处。     

送丝速度对Ti-3Al-6Mo-2Fe-2Zr钛合金激光填丝焊接头组织与性能的影响

采用Ti-6Al-4V(TC4)焊丝对2 mm厚的Ti-3Al-6Mo-2Fe-2Zr钛合金进行激光填丝焊接,利用光学显微镜、扫描电子显微镜、X射线能谱仪等分析测试方法研究了送丝速度对接头显微组织和力学性能的影响. 结果表明,由于从熔合线至母材受到焊接热作用逐渐递减,热影响区组织依次为单一β相、基体β相 + 初生α_p相、基体β相 + 初生α_p相 + 少量次生α_s相. 焊缝中有针状α'相生成,且分布不均匀. 随着送丝速度的增加,针状α'相的数量增加,尺寸增大. 激光填丝焊接头的抗拉强度及断后伸长率均低于母材,随送丝速度的增加,接头抗拉强度上升,断后伸长率下降.其原因在于TC4焊丝的加入,促使针状α'相在焊缝中析出,送丝速度加快,造成焊缝中钼当量[Mo]_eq降低,析出的针状α'相数量进一步增多,尺寸增大. 针状α'相的析出提高了焊缝强度,当送丝速度大于1.0 m/min时,接头的断裂位置为热影响区.     

TC4合金TIG焊接头组织转变与力学性能分析

针对TC4合金TIG焊接头微观组织特征以及焊接过程中的组织转变规律进行了研究,并对接头力学性能进行了分析.经历TIG焊接热循环之后,焊缝及热影响区粗晶区晶粒严重粗化,热影响区晶粒尺寸具有突变特征,过渡区组织呈带状分布,不存在明显的细晶区.升温过程中(α+β)→β转变过程包括两个阶段:原始β→高温β转变和原始α→高温β转变,而且在原始α→高温β转变开始之前,原始β→高温β转变已经完成.冷却过程中在β→α'转变区间冷速较慢时,α'相首先在高温β晶界上形核,并向晶内生长,生成针状α';在快速冷却时,α'相在晶内大量形核,形成"筐篮"组织.硬度测量结果表明,粗晶区部位存在一个软化区;接头抗拉强度与母材接近,接头性能优异.

Abstract：

The microstructure and phase transformation of TC4 alloy weld joints during TIG welding were investigated. The mechanical properties of the welded joints were also tested. When the TC4 alloy was heated by TIG arc, grains in the weld bead and heat affected zone (HAZ) were badly coarsening. The grain size in HAZ has mutant character. The microstructure in the transition region presented zonal distribution. There was no obvious fine grained region. In temperature-rise period, the transformation of (α + β)→β was divided into two processes which included the original β→ high-temperature β and the original α→ high-temperature β. And the previous phase transformation was finished before the next starting. In the cooling process, slowly cooling rate introduced α' phases nucleating at the high-temperature β grain boundary in the β→α transform temperature range. The α' martensite grew up into the center of the β grains and generated acicular martensite. With quicker cooling rate, large numbers of α' phase nucleated in the high-temperature β grains and generated orthogonally oriented martensites. Hardness measurements show there is a softened zone in HAZ. Tensile strength of welded joint was approximate with the base metal. And the properties of the welded joints were good.     

Ti-22Al-27Nb合金线性摩擦焊接头组织与显微硬度分析

对Ti-22Al-27Nb合金进行了线性摩擦焊及热处理试验,并对热处理前后焊接接头的微观组织和显微硬度进行测量分析. 结果表明,利用线性摩擦焊方法焊接Ti-22Al-27Nb合金得到的接头无焊接缺陷. 焊态下,焊缝区形成了B2单相区组织. 热力影响区为B2 + O + α₂相三相区,出现等轴α₂相,针状O相几乎消失. 热处理后在焊缝区析出板条状O相和针状O相,热力影响区为O相均匀分布的两相区. 母材处的显微硬度值最低约为300 HV,随着向焊缝靠近,显微硬度值逐渐增加,焊缝中心达到最大值354 HV. 热处理后,由于板条O相和针状O相的沉淀析出,使焊缝中心显微硬度急剧增加.     

The MPAW of Ti-3Al-2.5V Thin Sheets and Its Effects on Mechanical and Microstructural Properties

This research work deals with joining of Ti-3Al-2.5V titanium alloy thin sheets by means of microplasma arc welding (MPAW). An experimental set-up was developed to produce specimens welded in butt joint under controlled welding parameters, such as voltage, current, travel speed, and shielding gas flow rate. The performance of MPAW process was examined by mechanical properties tests and microstructural characterization. Results show that tensile strength and elongation of the welded specimens for a range of specific input heat are comparable to those of the base material (BM). Scanning electron microscopy (SEM) images of the fracture surface presented characteristics of ductile rupture. Studies on microstructure morphology of the specimens at the fusion zone (FZ) and heat-affected zone (HAZ) reveal occurrence of phase transformation from high temperature β phase to acicular $ \alpha^{\prime} $ phase, while the BM is of equiaxed α with intergranular β. An increasing variation in hardness was measured at the HAZ and FZ, which can be attributed to the presence of acicular $ \alpha^{\prime} $ phase and decreasing the amount of β phase at these regions. Based on the experimental results, it can be stated that MPAW process is an effective method for joining Ti-3Al-2.5V thin sheets provided appropriate welding parameters are used.     

Microstructure and Mechanical Properties of Pulsed Laser Beam Welded Ti-2Al-1.5Mn Titanium Alloy Joints

The microstructure and mechanical properties in the pulsed laser beam welded joints of Ti-2Al-1.5Mn titanium alloy thin sheet were investigated in this study. The results show that the original α + β-phases and the transformed α + α′-phases are found in the partially transformed heat-affected zone (HAZ) together with the remaining β-phase, and the microhardness gradually enhances in the region as the result of the increase of α′-phase. The martensitic α′-phase and the remaining β-phase are detected in the fully transformed HAZ and the fusion zone (FZ), and the highest microhardness is found in these regions in virtue of the dominant α′-phase structure. The fine α′-phase appeared in the FZ results in higher average microhardness at high welding speed. Moreover, similar to the results of microhardness test, the tensile test results mean that the HAZ and FZ are stronger than the base metal (BM). Therefore, pulsed laser beam welding is feasible for joining thin sheet of Ti-2Al-1.5Mn titanium alloy.     

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。     

热处理对100mm厚TC4钛合金电子束焊接接头性能的影响

针对100mm厚TC4钛合金板进行电子束对接,焊后对接头分别进行850℃再结晶退火和920℃+2 h和500℃+4 h固溶时效热处理,观察接头的微观形貌,测试其硬度和拉伸性能。结果表明,经过再结晶退火后,焊缝中部开始出现β相晶界,热影响区熔合线附近的针状α′相变少,β相等轴晶界开始出现。经过920℃+2 h和500℃+4 h固溶时效处理后,焊缝中部和底部都出现明显的β相晶界,热影响区熔合线附近的β相等轴晶界明显可见,为细片层β转变组织。力学性能测试表明,经过固溶时效热处理的接头焊缝区、热影响区及母材区的显微硬度明显高于焊态,其接头拉伸强度比焊态提升11.3%,屈服强度比焊态提升17.2%,但接头延伸率比焊态降低近59%。     

热力因素对合金元素在Ti-24Al-15Nb-1．5Mo／TC4焊接界面上扩散规律的影响

研究了2种状态的金属间化合物基合金Ti-24Al-15Nb-1．5Mo与TC4钛合金毛坯经真空电子束焊接后，锻造温度、热处理制度、变形量等热力因素以及它们的交互作用对合金元素Al，Nb，V在焊接界面上扩散规律的影响。研究发现：增加变形和提高热处理温度，可以增大原子迁移的动能，有利于提高合金元素的扩散速度，均匀焊缝显微硬度：加大变形量，有利于提高品格畸变能并细化晶粒、改变相的形态、减小相的尺寸，缩短合金元素的扩散路程。Nb在重新凝固区Ti-24Al-15Nb-1．5Mo一侧浓度高于合金的名义成分是由于在焊缝区α2→α变化时，Nb从DO19结构点阵中扩散出来，填补Al，Mo扩散后的空位，造成局部堆积所致。变形后热处理规范的不同，导致焊缝区的显微硬度不同，这与热处理过程中显微组织变化有关。     

热加工历史对Ti-24A1-15Nb-1.5Mo/TC11双合金盘焊接界面组织与性能的作用

采用电子束焊连接,随后近等温锻造+梯度热处理的工艺加工Ti-24Al-15Nb-1.5Mo/TC11双合金盘,通过OM、SEM、TEM、XRD等研究双合金盘的焊接界面状况.结果表明,经此工艺加工的Ti-24A1-15Nb-1.5Mo/TC11双合金盘的高温拉伸性能较优,焊缝的高温强度大于TC11钛合金,但室温拉伸性能分散度较大.采用梯度热处理不能消除经50%变形的双合金盘的焊缝到TC11侧热影响区的晶界α相.焊缝区簇状α_2相的形成与在近等温锻造、梯度热处理加热保温过程中Al、Nb元素从α_2相中分离出来有关.