Time-dependent effects in transient liquid phase bonding of 304L and Cp-Ti using an Ag-Cu interlayer

One of the challenges for bimetal manufacturing is the joining process.Hence,transient liquid phase(TLP)bonding was performed between 304L stainless steel and Cp-Ti using an Ag-Cu interlayer with a thickness of 75μm for bonding time of 20,40,60,and 90 min.The bonding temperature of 860℃ was considered,which is under the β transus temperature of Cp-Ti.During TLP bonding,various intermetallic compounds(IMCs),including Ti_(5)Cr_(7)Fe_(17),(Cr,Fe)_(2)Ti,Ti(Cu,Fe),Ti_(2)(Cu,Ag),and Ti_(2)Cu from 304L toward Cp-Ti formed in the joint.Also,on the one side,with the increase in time,further diffusion of elements decreases the blocky IMCs such as Ti_(5)Cr_(7)Fe_(17),(Cr,Fe)_(2)Ti,Ti(Cu,Fe)in the 304L diffusion-affected zone(DAZ)and reaction zone,and on the other side,Ti_(2)(Cu,Ag)IMC transformed into fine morphology toward Cp-Ti DAZ.The microhardness test also demonstrated that the(Cr,Fe)_(2)Ti+Ti_(5)Cr_(7)Fe_(17) IMCs in the DAZ on the side of 304L have a hardness value of HV 564,making it the hardest phase.The maximum and minimum shear strength values are equal to 78.84 and 29.0 MPa,respectively.The cleavage pattern dominated fracture surfaces due to the formation of brittle phases in dissimilar joints.

Microstructure - properties relationship of transient liquid phase diffusion bonded a third generation single crystal super alloy joint

Microstructure of transient liquid phase( TLP) diffusion bonded a third generation single crystal superalloy joint was investigated using scanning electron microscopy( SEM),and mechanical properties test of joint was carried out,for obtaining relationship between microstructure and mechanical properties of joint. The results showed that the joint contained bonding zone and base metal. The diffusion zone was obviously observed. When it was not finished for isothermal solidification process,the bonding zone would contain isothermal solidification zone and rapid solidification zone. Metallographic examination revealed that isothermal solidification zone was consisted of γ and γ' phase. Rapid solidification zone was consisted of two different structures,which were ternary eutectic of borides,γ and γ' phase developing at the edge of joint,binary eutectic of γ and γ' phase appearing in the portion of joint. When it was not enough for homogenization process under the condition of finishing isothermal solidification process,the bonding zone would contain isothermal solidification zone and borides at the interface. Under the conditions of relatively high welding temperature and long welding time,average tensile strength of joint was equivalent to that of parent material.

A two-step transient liquid phase diffusion bonding process of T91 steels

In this study, a two-step heating process is introduced for transient liquid phase （ TLP） diffusion bonding fo r sound joints with T91 heat resistant steels. At first, a short-time higher temperature heating step is addressed to melt the interlayer, followed by the second step to complete isothermal solidification at a low temperature. The most critical feature of our new method is producing a non-planar interface at the T9／ heat resistant steels joint. We propose a transitional liquid phase bonding of T91 heat resistant steels by this approach. Since joint microstructures have been studied, we tested the tensile strength to assess joint mechanical property. The result indicates that the solidified bond may contain a primary solid-solution, similar composition to the parent metal and free from precipitates. Joint tensile strength of the joint is not lower than parent materials. Joint bend＇s strengths are enhanced due to the higher metal-to-metal junction producing a non-planar bond lines. Nevertheless, the traditional transient liquid phase diffusion bonding produces planar ones. Bonding parameters of new process are 1 260 °C for 0. 5 min and 1 230 °C fo r 4 min.

Interfacial reactions and diffusion path in partial transient liquid-phase bonding of Si_3N_4/Ti/Ni/Ti/Si_3N_4

The interfacial reactions in partial transient liquid-phase bonding of Si3N4 ceramics with Ti/Ni/Ti interlayers were studied by means of scanning electron microscopy （SEM）, energy dispersive spectrometry （EDS） and X-ray diffractometry （XRD）. It was shown that the interfacial structure of Si3N4/TiN/Ti5Si3+Ti5Si4 + Ni3Si/ （NiTi ） /Ni3Ti/ Ni was formed after bonding. The activation energies for TiN layer and the mixed reaction layer of Ti5Si3 + Ti5Si4 + Ni3Si are 546. 8 kJ/mol and 543. 9 kJ/mol, respectively. The formation and transition processes of interface layer sequence in the joint were clarified by diffusion path. An important characteristic, which is different from the conventional brazing and soid-state diffusion bonding, has been found, i. e., during the partial transient liquid-phase bonding, not only the reaction layers which have formed grow, but also the diffusion path in the subsequent reaction changes because of the remarkable variation of the concentration on the metal side.

Interfacial Microstructure and Properties of Ti(C, N)/Ni Bonded by Transient Liquid-phase Diffusion

Effects of the main process parameters（temperature and time） on microstructure and properties of Ti（C, N）/Ni interface bonded by （Cu＋Nb） interlayer in a vacuum diffusion bonding device were investigated. The interfacial microstructures consisted initially of Ni3Nb metallic compound and eutectic of Ni3Nb ＋ CuNiss, and finally transformed to （Ti, Nb） （C, N）＋Ni3Nb near Ti （C, N） and NiCuss ＋ Ni3Nb near Ni when diffusion bonding temperature was 1 523-1 573 K. It was clear that Cu was a constituent in the transient liquid phase （TLP） into which Ni was dissolved by forming Cu-Ni transition liquid. Nb was dissolved in Cu-Ni transition liquid rapidly. Ti （C, N） conld be wetted by resultant Ni-Nb-Cu transient liquid phase which was followed by a little （Ti, Nb） （C, N） solid solution formed at interface. This increased the interface combining capability. Ultimately the interface shear strength was able to reach 140 MPa. The theoretle analysis and experimental results show that the growth of interfacial reaction layer Ni3Nb accords with parabola law, and the activation energy of diffusion reaction is 115.0±0.5 kJ/mol, while the diffusion reaction speed constant is 12.53 mm/s^1/2.

Effect of the formation process of transient liquid phase (TLP) on the interface structure of TiAl joints

TiAl has been joined employing the transient liquid phase （TLP） bonding with Ti combined with Cu, Ni or Fe foils. Experimental results showed that though the interface structures of the joints are quite different, all the joined zones are composed of five sublayers, i.e. two diffusion zones, two interfacial zones and an interlayer. It has been convinced that the formation process of the transient liquid phase controls the diffusion behavior of melting point depressant （MPD） Cu, Ni, and Fe atoms, which leads to form different interface structures of the joints.

A study on the two-step transient liquid phase diffusion bonding of K640 superalloy

A new technology, the two-step transient liquid phase diffusion bonding （TLP-DB） technology for cobalt-based K640 superalloy, was investigated. The method consists of a short-time high temperature heating to melt interlayer followed by isothermal solidification of liquid phase at a lower temperature than that of the conventional TLP-DB. The result indicates that the two-step TLP-DB can reliably produce an ideal joint with uniform chemical composition, which is superior to the joint welded by conventional TLP-DB in microstructure and mechanical properties. Bonding parameters of new process are 1 250℃ for 0. 5 h and 1 180℃ for 3 h. The high-temperature tensile strength of the joint by two-step TLP-DB reaches 74% of that of the base material on an equal basis, but the high-temperature tensile strength of the joint by conventional TLP-DB is only 58% of that of the base material.

Transient liquid phase bonding of Al 2024 to Ti-6Al-4V alloy using Cu-Zn interlayer

Transient liquid phase bonding of two dissimilar alloys Al 2024 and Ti?6Al?4V using Cu?22%Zn interlayer was carried out at 510 °C under vacuum of 0.01 Pa for various bonding time. In order to characterize the microstructure evolution in the joint zone, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were applied. The results show that joint formation is attributed to the solid-state diffusion of Cu and Zn into Ti?6Al?4V and Al 2024 alloys followed by eutectic formation and isothermal solidification along the Cu?Zn/Al 2024 interface. The hardness of the joints at the interface increases with an increase in bonding time which can be attributed to formation of intermetallic compounds such as Al2Cu, TiCu3, Al4.2Cu3.2Zn0.7, Al0.71Zn0.29, Ti2Cu, TiAl3 and TiZn16 in the joint zone. Moreover, shear strength of the joint reaches the highest value of 37 MPa at bonding time of 60 min.

Effect of gap size on microstructure of transient liquid phase bonded IN-738LC superalloy

In order to investigate the microstructure evolution and gain complete isothermal solidification time, transient liquid phase （TLP） bonding of IN-738LC superalloy was carried out using powdered AMS 4777 as the filler metal. The influence of gap size and bonding time on the joints was investigated. For example, complete isothermal solidification time for 40μm gap size was obtained as 45 min. In the case of lack of completion of isothermal solidification step, the remained molten interlayer cooled in the bonding zone under non-equilibrium condition andγ–γ′ eutectic phase formed in that area. The relationship between gap size and holding time was not linear. With the increase in gap size, eutectic phase width became thicker. In the diffusion affected zone, a much larger amount of alloying elements were observed reaching a peak. These peaks might be due to the formation of boride or silicide intermetallic. With the increase in gap size, the time required for bonding will increase, so the alloying elements have more time for diffusion and distribution in farther areas. As a result, concentrations of alloying elements decreased slightly with the increase in the gap size. The present bi-phasic model did not properly predict the complete isothermal solidification time for IN-738LC-AMS 4777-IN-738LC TLP bonding system.

Improvement of Joint Strength of SiCp/Al Metal Matrix Composite in Transient Liquid Phase Bonding Using Cu/Ni/Cu Film Interlayer

The compact oxide on the surface of SiCp/Al metal matrix composite （SiCp/Al MMC） greatly depends on the property of the joint. Inlaid sputtering target was applied to etch the oxide completely on the bonding surface of SiCp/Al MMC by plasma erosion. Cu/Ni/Cu film of 5μm in thickness was prepared by magnetron sputtering method on the clean bonding surface in the same vacuum chamber, which was acted as an interlayer in transient liquid phase （TLP） bonding process. Compared with the same thickness of single Cu foil and Ni foil interlayer, the shear strength of 200 MPa was obtained using Cu/Ni/Cu film interlayer during TLP bonding, which was 89.7% that of base metal. In addition, homogenization of the bonding region and no particle segregation in interfacial region were found by analysis of the joint microstructure. Scanning electron microscopy （SEM） was used to observe the micrograph of the joint interface. The result shows that a homogenous microstructure of joint was achieved, which is similar with that of based metal.

Microstructural evaluation of Hastelloy-X transient liquid phase bonded joints:Effects of filler metal thickness and holding time

Transient liquid phase(TLP)bonding was investigated in Hastelloy-X samples with different filler metal thicknesses(20,35,50,65,and 100μm)and holding time(5,20,80,320,and 640 min)to obtain optimum bonding parameters.Microstructural evaluations using electron probe microanalysis(EPMA)and electron backscattered diffraction(EBSD)show that the central eutectic phases present in the athermally solidified zone(ASZ)are Ni_(3)B,Ni_(2)Si,and CrB,and the precipitates formed in the diffusion-affected zone(DAZ)are MoB,CrB_(2),and Mo_(2)B_(5).According to the results,decreasing the filler thickness as well as increasing the holding time helps realize the completion of isothermal solidification and reduction in the density of precipitates in the DAZ,leading to a joint with more uniform properties.Diffusion of boron and silicon to longer distances with increasing holding time causes the removal of Cr-rich borides in the DAZ and the formation of Mo-rich silicide at the joint interface.Decrease in hardness of ASZ and DAZ due to the elimination of brittle phases in these zones during long holding time causes more uniform hardness distribution in the joint area.The best results are obtained for the sample joined with the 35μm-thick filler metal for 640 min holding time.

GH3230合金TLP扩散连接动力学实验研究

过渡液相(TLP)扩散连接能够获得与母材组织性能相似的焊缝,因而成为航空发动机热端部件镍基高温合金结构的重要连接技术而被广泛应用。TLP扩散连接过程中液相的等温凝固形成不含析出物的固溶体组织是TLP扩散连接机制与过程动力学的核心环节,采用自行研制的镍基非晶态中间层针对GH3230合金的TLP扩散连接过程进行了研究试验,重点分析了不同连接时间条件下TLP扩散连接焊缝区域的元素扩散和分布特征,以中间层中Co元素为示踪原子,根据GH3230合金与中间层材料中的Co元素的含量分布状态判定等温凝固阶段前的液相最大宽度及等温凝固完成时间等重要参数,结果表明:液相最大宽度为72μm,GH3230合金在1180℃的焊接温度下TLP扩散连接等温凝固完成时间大于4 h。

Ti/Ni/Ti复合层TLP扩散连接Si_3N_4陶瓷与接头质量控制

研究了Ti/Ni/Ti复合层TLP扩散连接Si3 N4 陶瓷。结果表明 ,Ni Ti过渡液相存在时间短 ,在此期间形成的界面结合强度低 ;必须进一步固态扩散反应才能形成高强度接头 ,相应的接头显微结构为 :Si3 N4 /TiN/Ti5Si3+Ti5Si4 +Ni3 Si/NiTi/Ni3 Ti/Ni。连接时间、连接温度、连接压力及Ti和Ni的厚度影响接头组织和强度 ,其最佳值为 6 0min ,10 5 0℃、2 .5MPa、2 0 μm和 40 0 μm ,所得接头室温和 80 0℃剪切强度分别为 142MPa和 6 1MPa。

扩散时间对DD6单晶高温合金TLP接头界面组织的影响

采用厚度30μm的商用BNi2钎料为中间层,在钎焊温度1 100℃,保温时间20 min条件下实现了DD6单晶高温合金的TLP连接.研究了在温度1 180℃不同扩散时间对DD6单晶高温合金TLP接头界面组织的影响规律,重点分析了接头区域合金元素随扩散时间的分布规律.结果表明,随着扩散时间的延长,接头界面处形成的针棒状硼化物逐渐溶解并消失;长时间扩散后,DD6母材中γ′相不断长大并相互连接,形成网状组织;Al,Si元素经16 h扩散处理后在焊缝和母材中基本实现均匀化,Co,Cr元素由于扩散速度较小,均匀化程度较差,而W,Re是难熔合金元素,由于其扩散速率最小,很难实现其在接头区域的均匀化.

连接温度对GH4169合金TLP接头界面组织和性能的影响

采用50μm厚的Ni82CrSiB非晶箔片为中间层,通过瞬时液相扩散连接(TLP)方法实现GH4169合金的连接。研究TLP接头的界面组织结构,重点分析连接温度对接头界面组织和力学性能的影响规律。结果表明:GH4169合金TLP接头由等温凝固区(ISZ)和扩散区(DZ)组成。等温凝固区为单相镍基固溶体,B元素向母材的扩散导致在扩散区内晶界处形成大量的针棒状硼化物。随着连接温度的升高,扩散区厚度逐渐增加,而等温凝固区厚度基本保持不变。当连接温度为1 120℃、连接时间为2 h时,接头室温及高温(600℃)抗拉强度最高,分别为692和599 MPa,为母材强度的82%和71%。断口分析结果表明:随连接温度的升高,室温拉伸时接头断裂位置由等温凝固区逐渐转向扩散区,而高温拉伸时接头均在等温凝固区发生断裂。

Ti_3Al基合金TLP扩散连接界面的组织演变

以Ti-37.5Zr-15Cu-10Ni(质量分数,%)非晶箔带为中间层,研究了TLP扩散连接Ti-23Al-17Nb(质量分数,%)合金的界面组织演变过程.结果表明,Ti元素和Nb元素向中间层扩散而Ni,Cu和Zr元素向母材扩散驱动了界面组织演变;在扩散初始阶段即930℃,保温5 min时,界面已形成冶金结合;随保温时间延长至15 min,界面析出条形TiNi3(Cu,Zr)化合物,其随保温时间延长更加细小呈弥散分布;直至保温时间延长至120～200 min,界面组织转变为均一、粗大的针状魏氏组织.保温时间是影响TiNi3(Cu,Zr)化合物析出形态和分布的主要因素,控制保温时间可有效改变界面化合物状态,该方法是优化此类界面组织以提高接头强度的有效途径.

N5单晶高温合金TLP扩散连接头的组织与性能

采用自制镍基非晶箔片KNi3A对N5单晶高温合金进行过渡液相扩散连接,连接工艺为真空环境中1513 K保温0.25~24 h,对性能样品进行标准热处理。利用扫描电镜对接头的组织结构进行观察和分析,研究焊缝组织随保温时间延长的变化规律,阐述焊缝和母材中γ’相长大和球化机制,并对接头进行高温持久性能测试。结果表明,接头区域由连接区、扩散区和母材区组成;随保温时间的延长,上述3区的界线由于等温凝固过程而逐步变得不明显,并最终得到趋于一致的微观组织,热处理后接头1000℃在125 MPa持久寿命可达母材的90%以上。

IC10合金TLP扩散焊接头组织与强度分析

IC10合金是Ni3Al基金属间化合物材料,对该材料的过渡液相(TLP,transient liquid phase)扩散焊试验进行分析。结果表明,采用合适的中间层和焊接工艺,IC10合金TLP扩散焊接头组织与基体相同,由γ+γ′网状组织和少量碳化物组成,接头980℃持久强度超过128MPa,达到基体强度的80%以上。TLP扩散焊接头经过高温长时间使用后,接头室温、高温抗拉强度与基体更接近;室温抗拉断口以准解理形貌为主,高温抗拉断口以韧窝形貌为主。

K640合金TLP连接接头组织及力学性能

为考察瞬时液相(TLP)连接方法对钴基高温合金K640合金的适用性,采用非晶态中间层进行连接试验,观察接头区显微组织,测试接头的力学性能并进行断口分析。结果表明:瞬时液相连接能够实现K640合金的良好结合,接头组织致密,成分均匀,组织与成分均与母材接近;接头高温拉伸强度达到等条件下母材强度74%,断口具有明显的韧窝形貌;高温持久强度达到等条件下母材强度的70%以上。

DD3单晶合金TLP扩散焊接头的高温拉伸性能和持久性能

为了实现DD3单晶合金叶片的优质连接,采用专为DD3设计的XH4A中间层合金,对DD3进行了TLP扩散焊试验。在1240℃/4h的规范下扩散焊,并在焊后按母材热处理制度进行固溶时效处理,可获得致密完整的DD3合金扩散焊接头,焊缝组织与母材类似,接头760℃和900℃拉伸强度达到母材性能指标,760℃和1040℃持久强度分别达到母材性能指标的90%和80%。还研究了扩散焊热循环对母材组织性能的影响,结果表明,DD3合金经1240℃/4h热循环后,再按母材标准热处理制度进行固溶时效处理,其组织和性能与标准热处理态完全相同。研究的DD3合金TLP扩散焊工艺可用于DD3合金实际叶片构件的连接。