放电等离子烧结制备致密TiAl/Ti2AlC复合材料

本研究以Ti／Al/TiC为原料，采用放电等离子烧结工艺制备致密TiAl/Ti2AlC复合材料。制备材料主要由TiA1和Ti2AlC两相组成。当原料中掺人体积分数为7％的TiC时，Ti-A1基体由γ相和层状相所构成，而Ti2AlC颗粒则均匀分布在基体中。经热处理后，则转变为Ti2AlC颗粒均匀分布在由γ相构成的基体中的结构。研究中还测定了所得复合材料的断裂韧性和弯曲强度。     

TA15/Ti2AlNb四层空心舵翼超塑成形/扩散连接工艺研究

目的 研究TA15/Ti2AlNb异种合金四层空心舵翼件成形/扩散连接工艺,获得合理的工艺参数,掌握塑性变形和扩散连接规律,推动异种合金轻量化中空结构件的应用。方法 采用MSC.Marc有限元仿真了TA15/Ti2AlNb异种合金四层空心舵翼超塑成形/扩散连接工艺过程,根据2种材料的高温变形规律优化出气压加载曲线,开展了空心舵翼的超塑成形/扩散连接实验研究,测试了舵翼的壁厚分布,分析了焊缝的金相组织。结果 成功制备了TA15芯板直立筋良好、三角区宽度仅1.1 mm的四层空心舵翼,面板最大减薄率为20.0%,芯板最大减薄率为54.2%,芯板与面板之间扩散连接区域的焊合率为46.8%～98.6%。结论 超塑成形/扩散连接工艺可制造TA15/Ti2AlNb异种合金空心结构,2种合金高温流动应力的显著差别避免了表面沟槽缺陷,但当整形压力和保压时间不足时,四层结构内各处扩散连接焊合率存在不稳定性。     

微量B元素对铸造Ti2AlNb合金组织与力学性能的影响

目的 研究微量B元素对铸造Ti2AlNb合金组织和力学性能的影响,优选出适合铸造工艺的Ti2AlNb合金成分,为推进铸造Ti2AlNb合金的应用提供理论和数据支撑。方法 以Ti–22Al–25Nb(原子数分数,下同)、Ti–22Al–24Nb–0.1B、Ti–22Al–24Nb–0.2B合金为研究对象,采用光学显微镜、扫描电镜研究不同B含量合金铸态、热等静压态的宏、微观组织及析出相形态。采用XRD分析合金的物相组成,室温拉伸性能测试评价力学性能,通过扫描电镜观察拉伸断口,分析微量B元素对力学性能产生影响的原因。结果 添加微量B元素可以明显细化Ti–22Al–25Nb合金的晶粒尺寸,随着B元素原子数分数增加至0.2%,晶粒尺寸由958 μm减小至548 μm。B元素在合金中主要以固溶态、TiB和TiB2针片状析出相形式存在,随着B含量的增加,硼化物长度和厚度尺寸略微增加、体积分数由0.3%增加至0.8%。0.1B合金的室温屈服强度、抗拉强度和伸长率与原合金水平相当,0.2B合金的屈服强度提升,但其抗拉强度和伸长率均降低。断口分析显示,0.2B合金塑性降低是硼化物增多、集中分布引起脆性断裂所致。结论 综合B元素对流动性的改善效果,优选出适合铸造工艺的合金成分为Ti–22Al–24Nb–0.1B。     

TiAl合金与高温合金的扩散焊接头组织及性能

采用直接扩散焊和加中间层的扩散焊方法进行了TiAl合金和高温合金异种材料组合的连接实验。在1000℃/20MPa/1h规范下直接扩散焊获得的TiAl/GH2036接头组织中存在大量未焊合的孔洞,接头室温剪切强度平均值仅有16MPa。采用Ti-Zr-Cu-Ni合金作为中间层在935℃加压3MPa保温10min和1h进行了TiAl/GH3536组合接头的液相扩散焊,获得的扩散焊缝中含有Ti3Al,NiTi等多种物相,中间层合金与两侧母材发生作用形成了具有一定厚度的反应层。在935℃/3MPa/1h规范下获得了与两侧母材结合良好的无缺陷扩散焊接头,室温剪切强度达到125MPa。     

Ti_3Al和Ti_2AlNb合金扩散连接界面的组织及力学性能

采用直接扩散连接Ti3Al和Ti2AlNb合金,研究了连接压力、连接温度、保温时间等工艺参数对接头界面组织形貌及性能的影响。利用扫描电镜、能谱分析和X射线衍射等方法观察分析了界面组织结构,并测试了接头的力学性能。结果表明:直接固相扩散连接接头的典型组织为Ti3Al/O相+α2相过渡层/富B2层/Ti2AlNb。当连接温度为1000℃,保温时间60min,连接压力为5MPa时获得的接头室温抗剪强度为635MPa,室温抗拉强度为795MPa,均断裂于Ti3Al母材一侧。经1000℃/60min热循环后Ti3Al母材的抗拉强度下降至原始母材的76%。连接温度低于950℃或保温时间小于60min会导致未焊合等缺陷;温度高于1050℃或保温时间超过120min则导致Ti3Al发生相变。     

Ti2AlNb合金与钛基复合材料的低温固相扩散连接机理

Ti2AlNb合金和Ti基复合材料可以使用直接固相扩散的方法进行连接,但较高的扩散温度使得母材发生相变,其接头性能也因此变差。采用Ti箔中间层的方法优化Ti2AlNb合金和Ti基复合材料的固相扩散连接接头性能。结果表明:加入30μm的Ti箔中间层后,扩散连接温度由950℃降低至850℃,变形率由5%降低至1.7%,扩散连接温度的降低有效地改变了接头界面的组织,典型界面组织为Ti2AlNb/富B2相/α+β双相组织/Ti基复合材料,其中接头界面处α+β双相组织的形成提高了接头的强度。最佳扩散连接工艺参数为850℃/60min/5 MPa时,剪切强度达到最大值399MPa,实现了Ti2AlNb和Ti基复合材料在低温下的扩散连接。     

放电等离子烧结工艺合成Ti3SiC2材料

以铝为助剂结合放电等离子烧结工艺,在较低温度下快速制备出高纯致密Ti3SiC2块体材料.掺加适量铝能加快Ti3SiC2的反应合成,提高制备材料的纯度,并促进Ti3SiC2晶体的生长和材料的快速烧结致密.在升温速率为80℃/min,z轴压力为30MPa时,材料制备的最佳温度为1250～1300℃.所制备材料经XRD、SME和EDS分析表明不含TiC和SiC等杂质相,Ti3SiC2为5～15μm的板状结晶,断裂韧性为6.8±0.2MPa·m1/2,弯曲强度为420±10MPa.     

放电等离子合成Ti3AlC2/TiB2复合材料的制备及性能研究

采用放电等离子烧结方法研究了Ti3AlC2/TiB2复合材料的制备和不同TiB2含量(体积百分数)对Ti3AlC2/TiB2性能的影响.研究表明,在1 250℃,30 MPa压力和保温8 min条件下烧结,可以得到相对密度达98%以上的致密Ti3AlC2/TiB2块体材料;在Ti3AlC2中添加TiB2能大幅度提高材料的硬度;Ti3AlC2/TiB2维氏硬度达到10.39 GPa,电导率达到3.7×106 S·m-1当TiB2含量为10%时,抗弯强度为696 MPa,断裂韧性为6.6 MPa·m1/2,但当TiB2含量继续增加时,由于TiB2的团聚和TiB2抑制Ti3AlC2晶体的生长导致了材料的抗弯强度和断裂韧性的下降.     

Ti2AlNb合金电子束焊接头残余应力及变形的数值模拟

目的 研究平板对接电子束焊接过程中Ti2AlNb合金接头的残余应力及变形规律。方法 采用高斯圆柱体和高斯面组合热源模型模拟了6.6 mm厚的Ti2AlNb合金平板对接电子束焊过程,对比研究了高焊速高束流和低焊速低束流2种工艺参数下焊接接头的残余应力和变形分布规律,并用小孔法测量了焊缝中心及距焊缝中心10 mm位置的残余应力值。结果 在高焊速高束流参数下,获得了熔池体积小、熔池宽度窄(为3.62 mm)、深宽比高的焊缝;在该参数下焊缝横截面上的高应力集中区(应力在900 MPa以上)尺寸较小,其宽度仅为低焊速低束流参数下的89%;同时,在高焊速高束流参数下,焊缝法向变形最大值为0.79 mm,低于低焊速低束流参数下的0.82 mm;模拟计算所得残余应力与实测值的误差在5.64%以内。结论 高束流高焊速工艺具有热输入小、热量集中、加工效率高的特点,有助于获得高应力集中区域小、深宽比高、变形小的焊缝,比低束流低焊速工艺更具优势。     

放电等离子合成Ti3AlC2-TiB2复合材料的相形成研究

采用放电等离子烧结工艺,以Ti,Al,B4C,Tic为原料制备Ti3AlC2/TiB2复合材料.通过X射线衍射分析了从600℃到1 300℃Ti3AlC2/TiB2系统反应过程的相形成规律.用扫描电镜观察了不同温度下试样的显微组织演变.结果表明,在900℃之前,主要的反应是Ti和AJ反应生成Ti-A1金属问化合物,900℃之后,Ti-Al金属问化合物与TiC逐渐生成Ti3AlC2和TiB2相,形成致密Ti3AlC2/TiB2复合材料.     

Effect of post-weld heat treatment on microstructure and properties of electron beam welded joint of Ti2AlNb/TC11

Abstract

The present paper reports the influence of post-weld heat treatment (PWHT) on microstructure and properties of electron beam welded dissimilar joint. Ti₂AlNb and TC11 alloys were used to fabricate the joints. Three PWHTs were applied to the welded joints. The structures were analysed using optical microscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques. The results show that weld metal of the fusion zone is mainly composed of α₂ and β phases. As the energy input increases under different PWHTs, the decomposition degree of metastable phases (α′/β) rises, but the tensile strength and impact toughness of the joint reduce. Under each condition, the tensile strength of the joint is higher than that of the TC11 base metal.     

TiAl/40Cr钢扩散连接界面组织结构对接头强度的影响

扩散连接界面组织结构是影响连接性能的关键因素，不同的界面组织结构及生成相所决定的接合强度不同．本文研究了TiAl/40Cr钢的扩散连接，结果显示：连接温度过高及连接时间过长时，由于界面处形成了过多的TiC脆性层及Ti3Al FeAl FeAl2的金属间化合物混合层，接头拉伸强度低；当连接温度较低及连接时间较短时，界面紧密接触与元素扩散不充分，接头拉伸强度也较低．脆性TiC层的生成导致TiAl与40Cr钢之间的扩散连接性能较差，接头均破断于TiC层或TiC层与Ti3Al FeAl FeAl2的金属间化合物混合层之间．     

Effect of isothermal deformation on microstructure and properties of electron beam welded joint of Ti2AlNb/TC11

Abstract

The present paper reports the influence of hot work (isothermal deformation accompanied with heat treatment) on microstructure and properties of electron beam welded dissimilar joint. Ti₂AlNb alloy and TC11 alloy were used to fabricate the joints. Isothermal deformation and heat treatment were performed under certain conditions. The structures were analysed using optical microscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that the as welded metal of Ti₂AlNb/TC11 joint is mainly composed of α₂ and β phases. The metastable β phase transformed into α+β phases during deformation and heat treatment processes. There are no big differences in tensile strength of joints under different conditions. However, the impact toughness of the weld has improved 72% after hot work.     

Synthesis and mechanical properties of Ti3AlC2 by spark plasma sintering

In this paper, spark plasma sintering (SPS), after hot isostatically pressing (HIP) method was reported as a new approach to prepare bulk polycrystalline samples of Ti₃AlC₂. The ternary carbide was fabricated by spark plasma sintering (SPS) at a pressure of 22 MPa and temperature of 1250°C. The raw materials, elemental powders of Ti, Al and activated carbon, were pretreated in the following different ways prior to SPS: one way was to obtain porous Ti₃AlC₂ by self-propagating high-temperature synthesis (SHS) from mixture of Ti, Al and C, and then densify the product by SPS; the second way was to synthesize Al₄C₃ from Al and C firstly, and then mix powders of Ti and C with synthesized Al₄C₃ to fabricate bulk Ti₃AlC₂ by SPS. Obtained polycrystalline Ti₃AlC₂ ceramics had excellent mechanical properties: density was 4.24 ± 0.02 g/cm³, flexural strength was 552 ± 30 MPa and fracture toughness (K _IC) was 9.1 ± 0.3 MPa · m^1/2. It could be concluded that SPS method was a useful method to synthesize bulk Ti₃AlC₂ with excellent properties in a very short time and easily sintering process. The optimal conditions to synthesize Ti₃AlC₂ were also discussed.     

Ti_2AlC-TiB_2对TiAl基复合材料组织及力学性能的影响

以Ti、Al和B4C为原料,采用真空电弧熔炼的方法制备了含Ti_2AlC-TiB_2增强相的TiAl基复合材料;分析了添加不同含量的Ti_2AlC-TiB_2对复合材料的物相组成、组织结构及力学性能的影响,并探讨了微观组织结构的形成机制。结果表明:Ti_2AlC-TiB_2/TiAl复合材料主要由TiAl、Ti3Al、TiB_2和Ti_2AlC等物相组成,TiB_2和Ti_2AlC分布在层片状的TiAl+Ti3Al基体中;随着原料中B4C含量的增多,复合材料组织中Ti_2AlC-TiB_2含量增多,且TiAl基体的晶粒被明显细化,TiB_2和Ti_2AlC分布于基体晶界或晶内。Ti_2AlC主要为层片状和板条状,尺寸5~15μm,而TiB_2颗粒形态与其含量有关,当Ti_2AlC-TiB_2含量小于20wt%时,TiB_2颗粒呈针棒状,尺寸为0.5~5μm,当Ti_2AlC-TiB_2含量增加到30wt%时,TiB_2颗粒主要呈块状,尺寸为5~20μm。Ti_2AlC由TiC与Ti-Al熔体发生包晶反应生成,Ti_2AlC和TiB_2的形成提高了Ti_2AlC-TiB_2/TiAl复合材料的硬度、塑性和抗压强度。当4Ti+Al+B4C的加入量为10wt%时,复合材料的变形量比纯TiAl提高14%,而抗压强度达到最高值1 591 MPa。Ti_2AlC和TiB_2通过裂纹偏转、颗粒钉扎、拔出等机制对Ti_2AlC-TiB_2/TiAl复合材料起到增强增塑的作用。     

热处理对铸造Ti15-3合金显微组织和力学性能的影响

借助光学显微分析、ＴＥＭ和ＳＥＭ分析手段研究了不同热处理工艺对Ｔｉ１５－３合金显微组织和力学性能的影响。结果表明：合金在铸态时的组织特征为粗大的β相,由于合金中没有析出相的弥散强化作用,因而合金的强度低,在不同温度时效处理后,在晶内和晶界析出α相,随着时效温度和时效时间的增加,析出相不断粗化,与铸态相比,合金时效后强度大幅度提高而处伸率大幅度下降,在变形过程中,合金中的位错在析出相周围形成缠结,合     

Investigation into the microstructure and mechanical properties of diffusion bonded TiAl alloys

TiAl alloys are potential candidates for replacing conventional Ti-alloys in gas turbine applications in the relatively lower temperature sections, owing to their low density and excellent high temperature properties. However, their intolerable ambient temperature brittleness hinders their use in such applications. Recently, TiAl alloys with some room temperature ductility were developed through alloy development programmes using special production routes such as powder metallurgy. However, the room temperature brittleness of these alloys could not be overcome. Sound joining of these alloys is a fundamental prerequisite for their successful integration into high temperature aerospace applications. It has been well demonstrated that diffusion bonding, a commonly used joining technology in conventional Ti-alloys, can successfully be used in joining of TiAl alloys both in as-cast or special-rolled conditions. In this study, diffusion bondability of a recently developed C containing TiAl alloy with a duplex microstructure using bonding parameters in the range of commercially available equipments was studied. Microstructural investigations in the joint area of the bonds were conducted to observe the presence of any weld defect. Additionally, the mechanical behaviour of the bonds was determined by shear testing to find out the optimum bonding parameters. Furthermore, the effect of post-bond heat treatment on the mechanical properties was investigated.     

Diffusion bonding of TiAl intermetallic and Ti3AlC2 ceramic: Interfacial microstructure and joining properties

TiAl intermetallics and Ti₃AlC₂ ceramics were jointed through diffusion bonding using Ti/Ni interlayer. The effect of bonding temperature and holding time on interfacial microstructure and mechanical properties of the bonded joints were investigated. The typical interfacial microstructure of the joint from TiAl to Ti₃AlC₂ side could be divided into τ₃-Al₃NiTi₂, α₂-Ti₃Al, α-Ti + δ-Ti₂Ni, δ-Ti₂Ni, β₂-TiNi, η-TiNi₃, γ-(Ni)_ss, γ′-Ni₃(Al, Ti), γ′-Ni₃(Al, Ti) + Ti₃AlC₂, respectively. The value of the microhardness in the reactive zones increased due to the formation of intermetallcs. Lower or higher bonding temperature and longer or shorter holding time both resulted in low strength owing to the insufficient diffusion of atoms or excessive formation of intermetallics. A high bonding strength can be obtained when bonding at 920 °C for 60 min. Fracture occurred through the intermetallic layer adjacent to the Ti₃AlC₂ substrate during shear test, showing brittle intergranular and transgranular characteristic.     

Formation process of the bonding joint in Ti/Al diffusion bonding

The process of the formation of Ti/Al diffusion bonding joints was studied by means of scanning electron microscopy (SEM), X-ray diffractometry (XRD) and shear strength measurement. Pure titanium and pure aluminum were used as bonding couples. The results show that the process of joint formation can be separated into four stages, and the product of the diffusion reaction is only TiAl₃ under a particular range of holding time. There is a delay time t_D before TiAl₃ is generated, which is mainly affected by temperature. The joint strength depends on the metallurgical combination percentage and the interface structure in the diffusion zone, and it can reach or even exceed the strength of pure aluminum after TiAl₃ forms a layer. The position where shear fracture occurs depends on interface structure in the diffusion zone.     

Effect of heat treatment on mechanical properties and microstructure of CrN/AlN multilayer coatings

Polycrystalline CrN/AlN multilayer coatings were deposited by RF magnetron sputtering on silicon (001) substrates. The bilayer periods of CrN/AlN were controlled from 4 nm to 20 nm by the use of shutters, which were adjusted by a programmable logic control (PLC). To evaluate the thermal stability, the films were annealed at 500 °C, 600 °C, 700 °C, 800 °C, and 850 °C, for 1 h in both vacuum and air environments. The phase transformation during thermal evolution was studied by X-ray diffraction (XRD). The microstructure of CrN/AlN multilayer coatings as-deposited and after annealing was observed by transmission electron microscopy (TEM). The hardness of as-deposited CrN/AlN coating with a period of 4 nm was 28.2 GPa, which was 60% higher than that predicted by the rule of mixtures. The hardness of CrN/AlN multilayer coatings annealed at 850 °C in vacuum remained similar to the as-deposited state, and the nano-layered structure still persisted. The thermal stability of CrN/AlN coatings was better than that of CrN coating. The hardness degradation ratio of CrN/AlN coating with modulation period of 4 nm was only 8.1% at 700 °C, which was superior to that of a simple CrN coating.