真空钎焊工艺对Al_2O_3陶瓷/304不锈钢接头成形的影响

采用Ag-Cu-Ti钎料对Al_2O_3陶瓷与304不锈钢进行了不同工艺参数下的真空钎焊连接试验。通过SEM、EDS、XRD方法分析了钎焊接头的显微组织和界面反应产物,研究了钎焊温度和保温时间对钎焊接头组织和裂纹的影响。结果表明,Al_2O_3/304接头钎缝分为3个反应区,分别是靠近陶瓷的反应层,由Ti O反应层和Ti3Al反应层组成;钎缝区,由Ag(Cu)固溶体、Cu(Ag)固溶体和Ti Fe_2组成;靠近不锈钢的Ti Fe_2+Ti O反应层。随着钎焊温度升高,保温时间的延长,接头钎缝中Ti Fe_2数量增加,尺寸增大,这降低了通过塑性变形缓解接头残余应力的能力,同时陶瓷侧界面反应层增厚。这些使得接头陶瓷的裂纹现象越严重。     

Al2O3/Cu基复合材料与Nb的钎焊

采用Ag—20Cu—5Ti对Al2O3／Cu基复合材料与Nb的钎焊性进行了初步探讨。研究表明,通过在钎料中加入活性元素Ti,可以减少和消除钎缝中的Al2O3,颗粒,避免Al2O3颗粒在钎缝中的聚集,实现离子共价键Al2O3向类金属键TiO转化,从而提高钎缝基体与颗粒相之间的匹配性。     

Al2O3P／Cu基复合材料与Nb钎焊研究

采用Ag-20Cu-5Ti对Al2O3P／Cu基复合材料与Nb的钎焊性进行了初步探讨。研究表明，通过在钎料中加入活性元素Ti，可以减少和消除钎缝中的Al2O3P颗粒，避免Al2O3P颗粒在钎缝中的聚集，实现离子共价键Al2O3P向类金属键TiO转化，从而提高钎缝基体与颗粒相之间的匹配性。     

采用复合钎料加压钎焊70%SiCp/Al复合材料

采用机械球磨的方法制备了Al-Si-xSiC(x为体积分数)复合钎料,采用复合钎料实现了70%SiCp/Al复合材料的加压钎焊连接. 利用SEM和EDS确定了钎缝是由α-Al,Si,SiC,Al₂O₃等相组成. 结果表明,在压力作用下SiC颗粒被固定在钎缝区而使得钎缝区的组织类似于复合材料,钎缝中一定的SiC颗粒可以缓解母材与金属钎料之间的热膨胀系数之差,从而减小了焊接残余应力,可以提高接头的强度,而钎焊施加一定的压力则可促进钎料与SiC颗粒的润湿性. 工艺适当时,接头最高强度达到125.7 MPa.     

金属/陶瓷发热体直接钎焊接头的应力分析

采用热弹塑性有限元方法,在考虑了材料性能参数随温度变化的情况下,分析了采用Ag-Cu-Ti钎料钎焊Al2O3陶瓷与镍金属丝的钎焊接头,在钎焊和随后再次加热过程中产生的应力大小和分布情况,计算中着重考虑了钎料对接头残余应力的影响.结果表明,在钎料与陶瓷的界面处存在着较大的残余拉应力,影响了钎焊接头的连接强度,并可能在界面的陶瓷侧产生裂纹.通过试验对比,认为在此类连接结构中,钎料是造成接头形成较大残余应力的主要因素.并指出钎料性能参数是决定有限元计算精度的主要因素,要使计算结果与实际情况尽量符合,钎料性能参数的正确选择是关键.     

真空热处理对Al2O3陶瓷化学镀Ni-P膜及金属钎焊接头的影响

采用化学镀Ni-P膜法金属化Al2O3陶瓷,并用63Sn-34Pb-2Ag-1Bi钎料膏实现了95%Al2O3陶瓷与45钢之间的低温钎焊.为提高镀膜结合强度并最终提高钎焊接头强度,钎焊前对镀膜陶瓷进行真空热处理.研究了钎焊前真空热处理对Ni-P膜显微组织、钎焊接头显微结构及其强度的影响.结果表明,150～650 ℃高真空热处理会改变Ni-P膜的显微组织,且适当热处理可显著提高钎焊接头强度,在350℃保温1 h可使接头剪切强度到达最高值38 MPa.接头显微结构一般为Al2O3陶瓷/Ni-P镀层/扩散层Ⅰ/富Sn层/钎缝金属层/扩散层Ⅱ/45钢.剪切断裂主要发生在Al2O3陶瓷/Ni-P镀层界面附近,少量扩展到钎缝金属中.     

Al-Al_2O_3结构件钎缝处的剪切应力分布与热膨胀匹配

采用有限元数值模拟方法研究了冷却过程在Al Al2 O3 异种材料结构件钎缝处导致的剪切应力分布。计算结果表明 :最大剪切应力位于钎缝圆角处和靠近钎缝圆角的Al2 O3 陶瓷 /Cu镀层金属界面处 ,同时中间层合金的热膨胀系数与Al的热膨胀系数相匹配时 ,可以最大限度减小剪切应力     

颗粒增强复合钎料钎焊TiAl合金接头界面结构及性能

采用纳米Si3N4颗粒增强的AgCuTi复合钎料(AgCuTiC)实现了TiAl合金的钎焊连接.利用SEM,EDS及XRD等分析方法确定了TiAl/AgCuTiC/TiAl接头的典型界面结构为TiAl/AlCu2Ti/Ag(s,s)+TiN+ Al4Cu9+Ti5Si3.结果表明,钎焊过程中从TiAl母材溶入液相钎料的活性钛与复合钎料中纳米Si3N4颗粒发生反应,在钎缝中形成了细小的颗粒状TiN,Ti5Si3及Al4Cu9化合物增强的银基复合材料组织.银基复合材料的形成不仅提高了钎缝自身的强度,而且通过降低钎缝的线膨胀系数缓解了接头残余应力,并最终改善了钎焊接头的性能.当采用增强相含量为3％的AgCuTiC钎料在880℃保温5min条件下钎焊时,接头室温平均抗剪强度最高为278 MPa,比采用AgCuTi钎料提高40％.     

Al—Al2O3结构件钎缝处的剪切应力分布与热膨胀匹配

采用有限元数值模拟方法研究了冷却过程顺Al-Al2O3异种材料结构件钎缝处导致的剪切应力分布。计算结果:了大剪切应力位于钎缝圆角处和靠近钎缝圆角的Al2O3陶瓷／Cu镀层金属界面处，同时中间层合金的热膨胀系数与Al的热膨胀系数相匹配时，可以最大限度减少剪切应力。     

AgCu+nano-Al_2O_3复合钎料钎焊TC4合金与Al_2O_3陶瓷:界面结构及接头性能

通过向Ag Cu共晶钎料中添加nano-Al2O3增强相(2%,质量分数)并采用高能球磨的方法获得了Ag Cu+nano-Al2O3复合钎料(Ag Cu C钎料)。采用Ag Cu C钎料实现了TC4合金与Al2O3陶瓷的高质量钎焊连接,确定了TC4/Ag Cu C/Al2O3钎焊接头的典型界面组织结构为:TC4/α-Ti+Ti2Cu扩散层/Ti3Cu4层/Ag(s,s)+Ti3Cu4+Ti Cu/Ti3Cu4层/Ti3(Cu,Al)3O层/Al2O3。Nano-Al2O3的添加抑制了钎缝中连续的Ti-Cu化合物层的生长,同时在钎缝中形成了颗粒状Ti-Cu化合物相增强的Ag基复合材料,改善了钎焊接头的界面组织。随着钎焊温度的升高,各反应层厚度逐渐增加,颗粒状Ti-Cu化合物不断长大,Ag基复合材料组织逐渐细小。当钎焊温度T=920℃,保温时间t=10 min时接头抗剪强度达到最大为67.8 MPa,典型断口分析表明:压剪过程中,裂纹起源于钎角处并沿钎缝扩展后转入Al2O3陶瓷,最终在Al2O3陶瓷母材侧发生断裂。     

Al2O3陶瓷Ti+Nb/Mo金属化对其与Kovar合金钎焊连接的组织和力学性能的影响

采用磁控溅射在Al₂O₃陶瓷表面沉积了Ti+Nb/Mo金属层,实现了氧化铝陶瓷的金属化,并通过电镀镍提高了金属化效果.采用AgCu28钎料,实现了金属化Al₂O₃陶瓷与Kovar合金的可靠连接.通过扫描电子显微镜和能谱观察了钎缝的微观组织.结果表明,钎料与母材发生了明显的界面反应.Cu元素扩散进入Kovar合金,同时Ni元素扩散进入钎料的富铜区,从而促进AgCu/Kovar连接界面的形成;金属化层在Al₂O₃/AgCu钎料界面处,起到了关键作用,其中铌可以抑制脆性化合物形成,缓解残余应力.金属化层镀镍后,钎缝中AgCu共晶区明显,且钎缝较宽,对提高镀镍试样的钎焊接头强度有一定作用.     

Al2O3/SUS304 Brazing via AgCuTi-W Composite as Active Filler

Alumina ceramic (α-Al₂O₃) was brazed to stainless steel (SUS304) using an Ag-Cu-Ti + W composite filler and a traditional active brazing filler alloy (CuSil-ABA). Then, the effects of the presence of W particles and of the brazing parameters on the microstructures and mechanical properties of the brazed joints were investigated. The maximum tensile strength of the joints obtained using Ag-Cu-Ti + W composite filler was 13.2 MPa, which is similar to that obtained using CuSil-ABA filler (13.5 MPa). When the joint was brazed at 930 °C for 30 min, the tensile strengths decreased for both kinds of fillers, although the strength was slightly higher for the Ag-Cu-Ti + W composite filler than for the Ag-Cu-Ti filler. The interfacial microstructure results show that the Ti reacts with W to form a Ti-W-O compound in the brazing alloy. When there are more W particles in the brazing alloy, the thickness of the Ti _X O _Y reaction layer near the alumina ceramic decreases. Moreover, W particles added to the brazing alloy can reduce the coefficient of thermal expansion of the brazing alloy, which results in lower residual stress between the Al₂O₃ and SUS304 in the brazing joints and thus yields higher tensile strengths as compared to those obtained using the CuSil-ABA brazing alloy.     

Ti活度对Al2O3/AgCuTi/Fe-Ni-Co钎焊接头机械性能和微观组织结构的影响

采用AgCuTi钎料实现了Al₂O₃陶瓷与Fe-Co-Ni合金的钎焊连接,并调查了不同钛含量的钎料对Al₂O₃/AgCuTi/Fe-Ni-Co钎焊接头机械性能和微观组织结构的影响。扫描电子显微镜(SEM), X射线能量色散光谱仪(EDS), X射线衍射仪(XRD)及电子万能试验机用于分析钎焊接头的机械性能和微观组织结构,结果表明:钛含量的增加明显提高AgCuTi钎料与Al₂O₃陶瓷的相互作用,在Al₂O₃/Ag-Cu-Ti界面生成一层由Ti-Al 和 Ti-O化合物组成的反应层。Al₂O₃/AgCuTi/Fe-Ni-Co钎焊接头的抗拉强度随钛含量的增加而增加,当钛含量提高到8wt.%时,抗拉强度达到最大值78Mpa。通过微观组织结构分析发现,采用AgCu4Ti在890℃保温5min的条件下可以获得较好的钎焊接头,典型接头的微观组织结构为Al₂O₃/TiAl+Ti₃O₅/NiTi+Cu₃Ti+Ag(s,s)/Ag(s,s)+Cu(s,s)+(Cu,Ni)/Fe-Ni-Co。采用AgCu8Ti获得的钎焊接头的界面反应层与AgCu4Ti差异不大,但反应层稍微增厚,并伴有TiO和Ti3Al在Al₂O₃/Ag-Cu-Ti界面生成。     

Al_2O_3/MoS_2复合涂层的制备及摩擦磨损性能

以大气等离子喷涂工艺制备的Al_2O_3陶瓷涂层为模板,利用陶瓷涂层中存在的孔隙和微裂纹,采用水热反应在其内部原位合成具有润滑特性的MoS_2,制备出Al_2O_3/MoS_2的复合涂层。结果表明,通过水热反应在陶瓷涂层原有的微观缺陷中成功合成了MoS_2,合成的MoS_2固体粉末呈类球形状,并且这球状的粉末是由纳米片层状的MoS_2搭建组成的。摩擦试验结果表明,与纯Al_2O_3涂层相比,复合涂层中由于MoS_2润滑膜的形成,其摩擦因数和磨损率都显著降低,且载荷越大,复合涂层的摩擦性能越好。     

Effect of applied current on the electrodeposited Ni-Al2O3 composite coatings

Nano-sized Al₂O₃ ceramic particles (50 nm) were co-deposited with nickel using electrodeposition technique to develop composite coatings. The coatings were produced in an aqueous nickel bath at different current densities and the research investigated the effect of applied current on microstructure and thickness of the coatings. The variation in some mechanical properties such as hardness, wear resistance, and the adhesive strength of the composite coatings is influenced by the applied current and this was also studied. The morphology of the coatings was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The hardness, wear resistance, and bond strength of the coatings were evaluated by Vickers micro-hardness test, pin-on-disc test, and tensile test, respectively. Results showed that the Al₂O₃ particles were uniformly distributed in the coatings, and the coatings deposited at a current density of 0.01 A/cm² was most favorable in achieving a maximum current efficiency which causes the co-deposition of a maximum amount of Al₂O₃ particles (4.3 wt.%) in the coatings. The increase in Al₂O₃ particles in the coatings increased the mechanical properties of the Ni-Al₂O₃ composite coatings by grain refining and dispersion strengthening mechanisms.     

Investigation of residual stress effects in an alloy reinforced ceramic/metal composite

This study aims at investigating the thermal expansion behavior and internal residual strains in metal reinforced ceramic matrix composites (CMCs). A variety of Al₂O₃/A356 CMCs composites with an interpenetrating network structure and varying metal content, ranging from 10 to 40 vol.%, were produced using the pressure infiltration technique of Squeeze casting. Values of coefficients of thermal expansion (CTEs) were found to vary significantly with temperature, indicating an influence of the flow characteristics of the metal. Comparisons are made with well known methods for predicting CTEs values of metal/ceramic composites. The overall strain was found to increase with temperature and scaled proportionally with the metal content of the composite. Comparisons were also made with non-infiltrated porous ceramic preforms and a pure metallic sample. The uniform heating and cooling curves for the composite samples were found to exhibit hysterisis. Residual stress analysis and failure simulation were performed based on thermomechanics and the finite element method (FEM). This analysis is often utilized for the analysis of stress distribution or deformation of a structure. High angle X-ray and CTEs mismatch equation analysis were utilized to analyze the residual stresses at the ceramic/metal interface of the Al₂O₃/A356 composites. The relationship of residual stresses and the contact area of the ceramic/metal interface are also discussed.     

Improving the strength of brazed joints with in situ synthesized TiB whiskers

TiB whiskers have been in situ synthesized as reinforcements in 73Cu-27Ti (wt.%) active brazing filler alloy used for the joining of Al₂O₃ and Ti-6Al-4V alloy. The results show that TiB whiskers served as an effective reinforcement phase aid to decrease the residual stress and increase the shear strength of joints. The shear strength of the joint, containing 30 vol.% TiB whiskers was about 239% higher than that of the joint brazed without TiB whiskers.     

Simulation design for the composition of zirconia composite ceramic tool

The relationship between the fracture toughness increment (ΔK _IC) resulting from toughening mechanisms, such as phase transition, residual stress, geometry effect, and grain bridging, and the volume fraction of zirconia was established to simulate and design the composition of a zirconia-matrix composite tool, thereby avoiding “trial-and-error” experiments. The composition of the ZrO₂/Al₂O₃ ceramic tool was simulated in accordance with the requirement for fracture toughness. It was shown that the simulated result was in agreement with experiment and that the established simulation model was to some extent valid in predicting the composition of the zirconia-matrix composite ceramic tool with dispersed α-Al₂O₃. Thus, a new type of ceramic tool material, a ZrO₂/Al₂O₃ composite, was developed by adding α-Al₂O₃ to ZrO₂ on the basis of the results of the computer simulation.     

A facile method for fabrication of nano-structured Ni-Al2O3 graded coatings: Structural characterization

Powder charges of micron-size Ni and Al₂O₃ were utilized to deposit nano-structured Ni-Al₂O₃ composite coatings on an aluminum plate fixed at the top end of a milling vial using a planetary ball mill. Composite coatings were fabricated using powder mixtures with a wide range of Ni/Al₂O₃ mass ratio varying from 1:1 to plain Ni. XRD, SEM and TEM techniques were employed to study the structural characteristics of the coatings. It was found that the composition of the starting mixture strongly affects the Al₂O₃ content and the microstructure of the final coating. Mixtures containing higher contents of Al₂O₃ yield higher volume fractions of the Al₂O₃ particles in the coating. Though Ni-Al₂O₃ composite coatings with about 50% of Al₂O₃ particles were successfully deposited, well-compacted and free of cracks and/or voids coatings included less than 20% (volume fraction) of Al₂O₃ particles which were deposited from powder mixtures with Ni/Al₂O₃ mass ratios of 4:1 or higher. Moreover, mechanical and metallurgical bondings are the main mechanisms of the adhesion of the coating to the Al substrate. Finally, functionally graded composite coatings with noticeable compaction and integrity were produced by deposition of two separate layers under identical coating conditions.     

Failure mechanisms of TiB2 particle and SiC whisker reinforced Al2O3 ceramic cutting tools when machining nickel-based alloys

In this paper, Al₂O₃/TiB₂/SiC_w ceramic cutting tools with different volume fraction of TiB₂ particles and SiC whiskers were produced by hot pressing. The fundamental properties of these composite tool materials were examined. Machining tests with these ceramic tools were carried out on the Inconel718 nickel-based alloys. The tool wear rates and the cutting temperature were measured. The failure mechanisms of these ceramic tools were investigated and correlated to their mechanical properties. Results showed that the fracture toughness and hardness of the composite tool materials continuously increased with increasing SiC whisker content up to 30 vol.%. The relative density decreased with increasing SiC whisker content, the trend of the flexural strength being the same as that of the relative density. Cutting speeds were found to have a profound effect on the wear behaviors of these ceramic tools. The ceramic tools exhibited relative small flank and crater wear at cutting speed lower than 100 m/min, within further increasing of the cutting speed the flank and crater wear increased greatly. Cutting speeds less than 100 m/min were proved to be the best range for this kind of ceramic tool when machining Inconel718 nickel-based alloys. The composite tool materials with higher SiC whisker content showed more wear resistance. Abrasive wear was found to be the predominant flank wear mechanism. While the mechanisms responsible for the crater wear were determined to be adhesion and diffusion due to the high cutting temperature.