Ti_2AlNb粉末与Ti/Al纳米叠层箔带混合烧结高温微叠层材料的微观结构

为了探索研制一种工作温度700~750℃,而且室温塑性较好的钛基高温合金,使用Ti/Al纳米叠层箔带和Ti_2AlNb合金粉末作为原料,在1 473 K,30 MPa,1.5 h的热压条件下直接混合烧结,制备出新型钛铝系金属间化合物高温微叠层材料(TiAl+Ti_2AlNb)样品,其中,Ti/Al纳米叠层箔带在热压烧结过程中的放热反应促进了样品烧结致密化。采用X射线衍射(X-ray diffraction,XRD)、扫描电子显微镜(Scanning electron microscope,SEM)和能谱仪(Energy dispersive spectroscopy,EDS)研究烧结产物相组成及显微结构的影响,并测试微区的显微硬度。结果表明,不同混合方式配比热压烧结体的相组成结构比较相似,烧结体内部主要形成了组织渐变的Ti_2AlNb/Ti_2Al(Nb)/TiAl显微结构,并且通过XRD也检测到了Ti_3Al相。破碎的Ti/Al纳米叠层材料和Ti_2AlNb合金粉末在热压烧结后,以扩散反应形成的Ti∶Al∶Nb大约为1∶1∶1的TiAl(Nb)相,其硬度最高(605.85 HV),由Ti/Al纳米叠层箔带生成并保留下来的TiAl相,其硬度最低(251.11 HV)。     

激光熔覆原位自生Ti-Al-Si复合涂层的微观组织和高温抗氧化性能

为提高钛合金的高温抗氧化性能,采用激光熔覆原位自生技术,在TC4钛合金表面自行设计并制备了原子百分比为Ti∶Al∶Si=41∶41∶18和Ti∶Al∶Si=35∶35∶30的两种涂层。通过XRD、OM、SEM表征了涂层的微观组织和物相组成;借助管式电阻炉测试了涂层和基体试样在800℃×24h×5次循环氧化条件下的高温抗氧化性能;结合氧化增重和氧化动力学曲线分析了涂层的高温抗氧化机理。结果表明,涂层主要由Ti5Si3、Ti7Al5Si12、Ti3Al、TiAl和TiAl3等物相组成。涂层中没有出现一般激光熔覆所产生的外延生长柱状晶组织,全部为细小等轴晶。在800℃×24h×5次循环氧化条件下,TC4基材单位面积的氧化增重约为35.1mg·cm-2,涂层的约为2.8mg·cm-2和3.3mg·cm-2。两种涂层的高温抗氧化性能较钛合金基材分别提高了12.5倍和10.6倍。激光熔覆原位自生Ti-Al-Si复合涂层能明显改善TC4钛合金的高温抗氧化性能。涂层抗氧化性改善的机理,一方面是表面生成了连续致密的TiO2、Al2O3、SiO2氧化层,阻碍了氧扩散;另一方面是提高了氧化层的黏附性,使氧化层不易从涂层表面剥落,对涂层未氧化部分起到了很好的保护作用。     

激光熔覆Zr基涂层的组织性能研究

在纯Ti(TA2)基体上分别激光熔覆Zr65Al7．5Ni10Cu17．5和Zr65Al7．5Nil0Cu17．5 0．8％C合金粉末，对涂层进行了X射线衍射分析、SEM观察和TEM分析，可知涂层由金属间化合物(其中包括纳米晶)和少量的非晶组成。这种具有高比强度、高硬度和高抗氧化性的金属间化合物与非晶相混合的复合涂层具有较好的性能，两种涂层的最高硬度分别达到1114．4HK和977．8HK。     

Nb对Ti3Al价电子结构及其脆性的影响

应用固体与分子经验电子理论计算了Ti3Al及加入Nb后各相的价电子结构,并从均匀变形因子α、解理能Gc及位错行为等方面分析了Nb对Ti3Al脆性的影响。结果表明,Nb使α2相部分无序化,产生新的韧性相,提高了Ti3Al合金的α和Gc值;同时Nb也减弱了Ti-Ti共价键,增加了基面滑移,从而综合导致Ti3Al脆性有本质改善。     

等离子喷涂制备Al_2O_3/ZrO_2复合结构热障涂层的性能

以NiCrAlY为金属黏结层材料、以Al_2O_3和ZrO_2为陶瓷层材料,采用等离子喷涂技术在304不锈钢表面制备了3种热障涂层,通过扫描电子显微镜(SEM)和X射线衍射仪(XRD)分别对涂层的微观形貌和晶相进行了表征,并研究了涂层的抗高温氧化性能和抗热震性能。结果表明:NiCrAlY/Al_2O_3/ZrO_2复合结构热障涂层表面无孔洞和裂纹等缺陷,高温氧化后该涂层主要包括Mg_2Zr_5O_(12)和(Fe,Mg)(Cr,Fe)_2O_4两种晶相;由于Al_2O_3的阻氧作用,NiCrAlY/Al_2O_3/ZrO_2涂层具有最佳的抗高温氧化性能;NiCrAlY/ZrO_2涂层层间材料的热膨胀系数呈梯度变化,表现出最佳的抗热震性能。     

含h-BN 的钛合金激光熔覆自润滑耐磨涂层的摩擦学行为

为提高Ti6Al4V合金的摩擦学性能,采用激光熔覆技术在钛合金表面制备以TiC、TiB2、CrB等为增强相、γ-Ni基固溶体为增韧相、h-BN为固体润滑相的自润滑耐磨复合涂层;分别在不同载荷下测试复合涂层和Ti6Al4V合金基体的干滑动磨损性能。结果表明,该复合涂层的摩擦因数及磨损率随着载荷的增大呈现先减小后略增大的趋势,并且摩擦因数和磨损率均比Ti6Al4V合金基体显著降低;在中等载荷下,复合涂层中的润滑颗粒被挤出磨损表面形成润滑膜,因而具有较好的自润滑耐磨性能,磨损后表面光滑平整。     

原位反应制备Ti_2AlNb/TiC+Ti_3SiC_2梯度材料的激光熔覆组织及成形机理

设计从基体到Ti连接层、Ti+SiC混合过渡层、陶瓷复合层的结构,通过激光熔覆原位反应成功制备Ti_2AlNb/TiC+Ti_3SiC_2体系梯度材料。通过扫描电子显微镜、能谱分析和X射线衍射仪分析了梯度复合层的微观组织。结果表明,层与层之间结合良好,实现了成分与显微结构的梯度过渡。梯度复合层共有6层,总厚度约1.5 mm,在Ti+SiC的混合过渡层中,Ti与SiC反应生成TiC和Ti_5Si_3,并保留了残余的富Ti相,在Ti+Si+C的陶瓷复合层中,Ti、Si、C元素反应生成Ti_5Si_3、TiC和Ti_3SiC_2。梯度材料从基体、Ti连接层、Ti+SiC混合过渡层再到陶瓷复合层,显微硬度逐渐升高,最高硬度达到1 341 HV,最外层由于三元陶瓷相Ti_3SiC_2的生成,硬度比起TiC、Ti_5Si_3明显降低,因此复合层硬度有所下降。反应产物TiC、Ti5Si3和Ti_3SiC_2均是高熔点化合物,有利于提高材料的耐高温性能。     

采用(Ti/Ni/Cu)_f多层箔钎焊C/C复合材料与TiAl合金

采用(Ti/Ni/Cu)_f多层箔状钎料进行C/C复合材料与TiAl合金的钎焊,实现了良好的界面结合,保证了接头的高温力学性能。研究结果表明:钎焊过程中,首先在Ti/Ni界面处接触反应形成低熔共晶液相,Cu元素的溶解促进了钎料的完全熔化和扩散,接头组织一般为C/C/TiC/Al_2(Cu,Ni)Ti_3C/Ti(Cu,Ni)+Al(Cu,Ni)_2Ti/Al(Cu,Ni)Ti+Ti_3Al/TiAl,Ti(Cu,Ni)基体相和球状弥散分布的Al(Cu,Ni)_2Ti相是钎缝的主要组成部分。当钎焊温度较低或者保温时间较短时,由于钎缝中生成了大量的脆性Ti2Ni相,降低了接头的力学性能;当钎焊温度较高或保温时间较长时,C/C复合材料母材界面处开裂,且TiC层从母材脱落,也削弱了接头的抗剪强度。当钎焊温度为980℃,保温时间为10 min时,C/C复合材料与TiAl合金的接头室温抗剪强度达到最大值18 MPa,600℃时接头的高温抗剪强度达到22 MPa。     

激光气体氮化原位合成制备TiN/Ti_3Al复合涂层及其抗高温冲蚀性能

通过在氮气中加入铝粉,采用激光气体氮化技术在Ti-6Al-4V钛合金表面原位制备了TiN/Ti_3Al复合涂层,研究了涂层的微观形貌、物相组成、硬度分布以及抗含SiC和SiO_2颗粒的高温高速水蒸气冲蚀的能力。结果表明:涂层的表面硬度为(1 400±50)HV,是Ti-6Al-4V钛合金的4倍;用SiC颗粒冲蚀较短时间或用SiO_2颗粒冲蚀后,涂层的冲蚀质量损失随冲蚀角度的增大而增加,Ti-6Al-4V钛合金的则减小;在相同冲蚀角度下,涂层的冲蚀质量损失随冲蚀颗粒硬度的增加而增大,Ti-6Al-4V合金的冲蚀质量损失在较小冲蚀角度时也遵循此规律,但在较大冲蚀角度下,质量损失的变化不大。     

等离子喷涂NiAl/Al2O3梯度陶瓷涂层的结构与组织特征

利用等离子喷涂方法制备了NiAl/Al2O3梯度陶瓷涂层,并对涂层的组织分布、相结构、硬度和孔隙率进行了研究.结果表明:梯度涂层的组织表现出宏观不均匀性和微观连续性的分布特征,是由α-Al2O3、γ-Al2O3、δ-Al2O3、Ni、NiO以及镍铝金属间化合物等多种相组成的复合材料;梯度涂层中NiAl合金层的孔隙最少,表面纯陶瓷层孔隙率最高;随着Al2O3含量的增加,涂层的硬度逐渐增大.     

Improving of interfacial microstructure of Ti/Al joint during GTA welding by adopting pulsed current

Butt welding of titanium alloy TA15 to aluminum alloy Al2024 dissimilar lightweight metals was conducted using gas tungsten arc welding. Pulsed current was adopted in the welding process. Influence of pulsed current on morphologies and microstructure of Ti-Al intermetallics near the Ti/Al interface was investigated. Microstructure characteristics and phase constitution of weld zone near the Ti/Al interface were analyzed. In top surface and upper region of the joint, Ti base metal was partially melted, and continuous intermetallic layers with Ti₃Al, TiAl, and TiAl₃ were formed in the fusion zone. In middle and bottom regions of the joint, Ti base metal was not melted and a thin TiAl₃ layer was formed near the Ti/Al-brazed interface. Most of the Ti-Al intermetallics formed into discrete TiAl₃ precipitations in the weld metal in upper and middle regions of the joint. No precipitation was observed in bottom region of the joint. Thickness of continuous Ti-Al intermetallic layers in the fusion zone was controlled at a low degree by adopting pulsed current in the welding. Crack sensitivity of weld zone near the Ti/Al interface was decreased.     

Wear characteristic of in situ synthetic TiB2 particulate-reinforced Al matrix composite formed by laser cladding

In order to improve the wear resistance of an aluminum alloy, an in situ synthesized TiB₂ particulate-reinforced metal matrix composite coating was formed on a 2024 aluminum alloy by laser cladding with a powder mixture of Fe-coated boron, Ti and Al was successfully achieved using a 3-kW CW CO₂ laser. The chemical composition, microstructure and phase structure of the composite clad coating were analyzed by energy dispersive X-ray spectroscopy (EDX), SEM, TEM and XRD. The nanohardness and the elastic modulus of the phases of the coating have been examined. The dry sliding wear behaviour of the coating was investigated using a pin-on-ring machine under four loads, namely 8.9, 17.8, 26.7, and 35.6 N. It has been found that the wear characteristics of cladding were completely dependent on the content and morphology of the TiB₂ particulate and intermetallic in the microstructure and the applied load. At the lowest load (8.9 N), with increasing content of TiB₂ particulate and intermetallic, the wear weight loss of the laser cladding was decreased. At higher loads (17.8, 26.7, and 35.5 N), the 2024 Al alloy exhibited superior wear resistance to the particle-reinforced metal matrix composite cladding.     

Scanning and transmission electron microscopy microstructure characterization of mechanically alloyed Nb–Ti–Al alloys

Results are presented of an investigation of the microstructure development during mechanical alloying and following consolidation of an Nb15Ti15Al alloy. The alloy was synthesized from elemental as well as pre‐alloyed powders. The microstructure of this material was examined by transmission electron microscopy, scanning electron microscopy and X‐ray diffraction. The use of pre‐alloyed TiAl powder for synthesis of the Nb15Ti15Al alloy meant that a much shorter time was required to complete the mechanical alloying process compared with the synthesis of elemental powders. The investigation indicates that three phases were present in the consolidated materials: the Nb solid solution, the Nb₃Al intermetallic phase and the dispersoid.     

Ti-48Al-2Cr-2Nb钛铝化合物的韧化和氧化抗力研究

在ＴｉＡｌ合金中添加过渡族合金元素，观测了其微观组织和结构，测定了室温弯曲性能和高温氧化性能，研究了改善塑性及提高其高温氧化抗力的因素。试验结果表明，与单相γ－ＴｉＡｌ不同，添加过渡族元素Ｃｒ、Ｎｂ的Ｔｉ－４８Ａｌ－２Ｃｒ－２Ｎｂ钛铝化合物所形成的双相或等轴γ和α２／γ片层状双态组织，改善了脆性γ－ＴｉＡｌ合金的室温塑性，使弯曲强度达４９０ＭＰａ，弯曲挠度为０．３９ｍｍ；；大量层错带和变形孪晶的形成是室温变形的主要机制。另外，在高温下，钛铝化合物的表面由表及里形成了不易剥落的ＴｉＯ２、Ａｌ２Ｏ３及ＴｉＯ２＋Ａｌ２Ｏ３三层氧化层，连续、致密的Ａｌ２Ｏ３层是提高氧化抗力的重要原因     

Tribological behavior of CrCoNiAlTiY coating synthesized by double-glow plasma surface alloying technique

A dense CrCoNiAlTiY coating was deposited onto the γ-TiAl alloy by double-glow plasma surface alloying technique to improve its wear resistance. Microstructure analysis showed that the coating consisted of AlCr₂, σ-NiCoCr, γ-TiAl and γ׳-Ni₃Al phase, and was well diffusion bonded to the substrate. In terms of the H/E and H³/E² ratios, the CrCoNiAlTiY coating was nearly 3.5 times better than the γ-TiAl substrate. Dry wear test results indicated that the specific wear rate of γ-TiAl substrate was 3.8×10⁻⁴ mm³N⁻¹ m⁻¹, which was about 4 times greater than that of the CrCoNiAlTiY coating. The improvement in wear resistance of the CrCoNiAlTiY coating may be attributed to the increased H/E and H³/E² ratios and to good adhesion strength between CrCoNiAlTiY coating and γ-TiAl substrate.     

Microstructure and joining mechanism of Ti/Al dissimilar joint by pulsed gas metal arc welding

Butt joining of titanium alloy Ti–2Al–Mn to aluminum 1060 using AlSi5 filler wire was conducted using pulsed gas metal arc welding. Joining mechanism of Ti–2Al–Mn/Al 1060 dissimilar joint with different welding heat input was investigated. Formations of precipitation and Ti/Al interface were discussed in detail. Fusion zone near aluminum is composed of α-Al dendrites and Al–Si hypoeutectic structures. A few TiAl₃ precipitations appear in the weld metal owing to metallurgical reactions of Al with dissolved Ti. When the welding heat input was in the range of 1.87–2.10 kJ/cm, titanium alloy Ti–2Al–Mn and Al 1060 were joined together by the formation of a complex Ti/Al interface. With a low welding heat input, a serrate TiAl₃ interfacial reaction layer was formed near Ti/Al interface. With the increasing of the welding heat input, α-Ti, Ti₇Al₅Si₁₂, and TiAl₃ layers were formed orderly from Ti–2Al–Mn to weld metal.     

铌及其合金高温抗氧化涂层研究

主要介绍了铌及其合金的氧化机理和铌合金高温表面涂层保护的3方面技术—抗氧化金属与合金涂层、金属间化合物涂层、复合防护涂层以及目前存在的主要问题,并简要的提出了高温抗氧化涂层的发展方向。     

Microstructure and tribological properties of laser clad γ/Cr7C3/TiC composite coatings on γ-TiAl intermetallic alloy

In order to improve the wear resistance of the γ-TiAl intermetallic alloy, microstructure, room- and high-temperature (600 °C) wear behaviors of laser clad γ/Cr₇C₃/TiC composite coatings with different constitution of NiCr–Cr₃C₂ precursor-mixed powders have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS), block-on-ring (room-temperature) and pin-on-disk (high-temperature) wear tests. The responding wear mechanisms are discussed in detail. Results show that microstructures of the laser clad composite coatings have non-equilibrium solidified microstructures consisting of primary hard Cr₇C₃ and TiC carbides and the inter-primary γ/Cr₇C₃ eutectic matrix, about three to five times higher average microhardness compared with the TiAl alloy substrate. Higher wear resistance than the original TiAl alloy is achieved in the clad composite coatings under dry sliding wear conditions, which is closely related to the formation of non-equilibrium solidified reinforced Cr₇C₃ and TiC carbides and the positive contribution of the relatively ductile and tough γ/Cr₇C₃ eutectics matrix and their stability under high-temperature exposure.     

The use of a single fibre test technique to investigate interfacial phenomena in SiC/Ti3Al-based composites

A study of the chemical compatibility of a Ti₃ Al-based alloy (Ti–24Al–10Nb, at.%) with two silicon carbide continuous fibres (SCS-6, SM 1240) has been conducted. Owing to the difficulty in processing intermetallic matrix composites, this type of material has been simulated in the present work by sputtering a thin titanium aluminide layer onto fibres and heat treating at temperatures representative of fabrication conditions. The degradation of the fibre strength due to its interaction with the matrix was correlated with analytical studies of the fibre/matrix interface using a combination of SEM, TEM, EELS and a submicrometre ion probe.