熔体反应法制备Ａl—4.5Cu／TiB2复合材料的热力学

用冶金热力学理论计算出TiO2-H3BO3-Na3AlF6-Al-4.5Cu体系的起反应温度,为950℃,并根据溶液热力分析了TiB2颗粒形成的可能性,当熔体中[Ti],[B]的摩尔比为1／2时,在熔体中形成TiB2颗粒,当熔体中[Ti],[B]的摩尔比大于1／2时,熔体中除生成TiB2颗粒外,还形成TiAl3.     

铝晶粒细化剂Al-5Ti-1B合金的晶粒细化机理

分别采用Al-5Ti-1B、Al-10Ti、Al-4B合金和TiB2粉末对纯铝进行细化实验,比较了TiAl3、TiB2和AlB2对纯铝的晶粒细化作用,利用光学显微镜、X射线衍射仪、扫描电镜和透射电子显微镜研究了Al-5Ti-1B合金的晶粒细化机理。结果表明,TiAl3是铝晶粒的有效异质形核相,但Al-5Ti-1B合金中的TiAl3因在铝熔体中会熔化而不是铝晶粒的直接形核相。单独的AlB2和TiB2都不是铝晶粒的有效异质形核相,但TiB2通过表面包覆TiAl3后可成为铝晶粒的有效异质形核相。Al-5Ti-1B合金的晶粒细化机理为TiAl3熔解于铝熔体中释放Ti原子,部分Ti原子通过浓度起伏形成TiAl3,TiAl3再与铝熔体发生包晶转变形成α-Al晶粒直接起到晶粒细化作用;部分Ti原子在TiB2表面偏聚形成TiAl3,TiAl3再与铝熔体发生包晶转变形成α-Al晶粒起到晶粒细化作用。     

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.     

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.     

Al-TiO2-B2O3-C系XD合成铝基复合材料的反应机理及力学性能

研究了Al-TiO2-B2O3-C反应系XD合成铝基复合材料的反应机理.结果表明在Al-TiO2-B2O3-C系中,当B2O3/TiO2摩尔比=0.5,C/TiO2摩尔比=0时,TiO2和B2O3分别与Al结合生成热力学稳定的Al2O3和活性Ti原子、B原子,B原子和Ti原子分别穿过各自反应层结合生成热力学稳定的TiB2,过剩的Ti原子则与Al结合生成棒状物Al3Ti;加入碳粉后,Ti原子将优先与C和C与Al的化合物Al4C3反应生成TiC,Al3Ti逐渐减少,在C/TiO2摩尔比为0.5时,Al3Ti相基本消失,力学性能得到改善,其拉伸强度和延伸率分别从266MPa和3%增加到315MPa和7%.     

Al-TiO2-B系XD合成铝基复合材料的力学性能

本文主要讨论了Al-TiO2-B系XD合成铝基复合材料的力学性能及其增强机理.研究结果表明:当B/TiO2摩尔比从0增加到2时,棒状物Al3 Ti增强相逐渐减少直至消失,Al2O3颗粒分布的均匀性提高,TiB2粒状弥散分布在合金基体中,材料的抗拉强度明显增强,由224.5MPa上升到354.5MPa,延伸率也由3.2%增加到5.6%.Al2O3和TiB2主要以奥罗万机制强化基体,而Al3 Ti则以位错塞积强化基体.     

钛金属熔融Na_2B_4O_7硼化:热力学和动力学过程

以无水硼砂为硼化剂在金属钛表面进行硼化,通过XRD分析样品表面的物相组成。结果表明,当温度为900℃时,钛金属表面主要生成Na0.23TiO,基本没有硼化物生成;当温度升高到950℃时,钛金属表面只生成少量的硼化物;而当温度高于950℃时,钛金属表面有明显的硼化物生成。随着温度的升高,硼化物种TiB2的量增多,而TiB量减少。热力学分析表明,随着温度的升高,生成TiB2和TiB的趋势应该降低,这与实验结果相矛盾。根据Sar-ma的B原子在金属钛中的扩散动力学,由于低温时B原子在TiB中的扩散速度大于其在TiB2和Ti中的扩散速度,故能同时生成TiB2和TiB;而高温时由于B在Ti中的扩散速度大于其在TiB中的扩散速度,主要生成TiB2,而TiB的生成受到抑制。     

原位合成(TiB_2+TiC)/Ti_3SiC_2复相材料及其性能研究

在热力学分析的基础上,以TiH2粉、Si粉、石墨粉与B4C粉为原料,采用热压烧结法原位合成制备了(TiB2+TiC)/Ti3SiC2复相材料.采用X射线衍射、扫描电镜与透射电镜对材料的物相组成和显微结构进行了表征,研究了烧结温度对材料物相组成、烧结性能、力学性能与显微结构的影响.结果表明,1400～1600℃烧结温度范围内均能获得致密的(TiB2+TiC)/Ti3SiC2复合材料.随着烧结温度的升高,复合材料的强度、断裂韧性与显微硬度均逐渐提高,1500～1600℃烧结所得复合材料具有优化、微细的显微结构,抗弯强度与断裂韧性均分别高于700MPa与9MPa·m1/2,显微硬度为7.33～8.31GPa.原位合成的柱状TiB2与等轴状TiC协同作用,通过颗粒增强、裂纹偏转、晶粒拔出、晶粒细化等机制对Ti3SiC2基体起到了显著的补强增韧效果.     

Al-TiO2-C系XD合成铝基复合材料的反应机理及拉伸性能

本文讨论了热扩散反应法制备Al-TiO2-C系铝基复合材料的反应机理及拉伸性能.热力学分析表明Al-TiO2-C系的合成反应是放热并可自发进行,反应产物中α-Al2O3生成自由能最低,热力学最稳定,当温度高于500K时,TiC优先于Al4C3生成.实验结果表明,当C/TiO2摩尔比为零时,增强体由α-Al2O3和Al3Ti组成,α-Al2O3为细小颗粒,呈偏聚状态,Al3Ti呈棒状,分布相对均匀.随着C/TiO2摩尔比的增加,Al3Ti逐渐减少,在C/TiO2摩尔比等于1时,Al3Ti基本消失,反应产物中未见Al4C3相,其拉伸性能也随之得到改善,拉伸强度和延伸率分别从273.4MPa和3%上升到350.7MPa和6%.     

Cu/Ti3SiC2/TiB2复合材料的研究

采用化学镀Cu的TiB2粉和Ti3SiC2粉与cu粉进行湿混,通过真空无压烧结法制备TiB2增强的Cu-Ti3SiC2复合材料.研究了其致密度、硬度随TiB2含量变化的规律.因为TiB2镀Cu和Ti3SiC2镀Cu改善了它们与Cu的湿润性而提高了相互之间的结合强度,从而提高了TiB2增强cu-Ti3SiC2复合材料的效果.结果表明,在Ti3SiC2含量为20%(体积分数),烧结温度为950℃时制备Cu/Ti3SiC2/TiB2的复合材料致密性最好,硬度最高.     

原位自生TiB2/Al-4.5Cu复合材料微观组织和力学性能

采用混合盐反应法制备TiB2含量分别为0%,2%,5%,8%(质量分数,下同)的TiB2/Al-4.5Cu复合材料,T6热处理后,采用XRD,ICP,OM,SEM,EDS等测试手段和室温拉伸实验进行微观组织观察和力学性能测试。XRD和ICP测试证实,合金体系中仅含α-Al,Al2Cu及TiB2,无Al3Ti,Al2B等反应中间产物。OM和SEM发现,基体材料中α-Al平均晶粒尺寸为167.5μm,而在2%,5%,8%的TiB2/Al-4.5Cu中,其平均晶粒尺寸依次为110.4,87.2,75.2μm,晶粒细化效果显著。TEM观察发现,TiB2颗粒主要分布在晶界处,呈四方和六方结构。室温拉伸实验表明,随着TiB2含量的增加,强度、显微硬度值均呈增加趋势,但伸长率不断下降。当加入8%TiB2时,屈服强度、抗拉强度、弹性模量和显微硬度分别达到356 MPa,416 MPa,92.5GPa和96.5HV,但其伸长率从10.3%降低到4.3%。载荷传递强化、细晶强化、位错增殖强化是TiB2/Al-4.5Cu复合材料力学性能得以大幅提升的影响因素,尤其是在位错增殖强化作用下,TiB2颗粒周边致密分布的位错胞、位错环对强度的提升起到了决定性作用。     

TiB2-TiC复合粉的自蔓延高温还原合成

热分析结果表明,对于B₂O₃-TiO₂-Mg-C体系,可利用SHS还原技术合成出TiB₂-TiC陶瓷复合粉。其化学反应机理为:Mg先还原B₂O₃和TiO₂,新生的Ti与B和C反应生成TiB₂和TiC; TiO₂的还原经历了TiO₂→TiO→Ti的逐步过程。采用一定的酸洗工艺得到了纯净的TiB₂-TiC陶瓷复合粉。复合粉中包含六方片状TiB₂和圆球状TiC;复合粉中1μm以下颗粒质量百分数超过45%,87%以上的颗粒大小在3μm以下。在TiB₂-TiC中,TiC_<em>y以一种贫碳结构存在,物料中Ti被B或C结合形成TiB₂和TiC_<em>y,y的值为0.7483。     

Synthesis of boride and nitride ceramics in molten aluminium by reactive infiltration

The infiltration of solid powder mixtures with molten aluminium has been investigated as a potential route for the synthesis of ceramic/metal composites. Either titanium or tantalum powder was mixed with boron nitride flakes for the reaction powder mixture. The infiltration occurred spontaneously at 1473K for both [Ti+BN] and [Ta+BN] powder mixtures. Owing to reactions between the starting materials, both boride and nitride ceramics were produced in molten aluminium. TiB2 and AlN were produced from the [Ti+BN] powder mixture, and TaB2 and AlN were produced from the [Ta+BN] powder mixture. When the [Ti+BN] powder mixture was used, a reaction producing Al3Ti took place immediately after the infiltration of the molten aluminium, and a subsequent reaction producing TiB2 and AlN proceeded gradually. The time required to convert BN flakes to TiB2 and AlN particles at 1473K was in the range of 1800–3600 s. On the other hand, when the [Ta+BN] powder mixture was used, there was an initial incubation period to allow the tantalum and molten aluminium to react with each other. The reaction between tantalum, BN and aluminium took place after this incubation period. This revised version was published online in November 2006 with corrections to the Cover Date.     

Fabrication of (TiB/Ti)-TiAl composites with a controlled laminated architecture and enhanced mechanical properties

The(TiB/Ti)-TiAl composites with a laminated structure composing of alternating TiB/Ti composite layers,α₂-Ti₃Al interfacial reaction layers of andγ-TiAl layers were successfully pre pared by spark plasma sintering of alternately stacked Tib₂/Ti powder layers and TiAl powder layers.And the influence of thickness ratio of Tib₂/Ti powder layers to TiAl powder layers on microstructure evolution and mechanical properties of the re sulting(TiB/Ti)-TiAl laminated composites were investigated systemically.The results showed that the thickening ofα₂-Ti₃Al layers which originated from the reaction of Ti and TiAl was significantly hindered by introducing Tib₂particles into starting Ti powders.As the thickness ratio of Tib₂/Ti powder layers to TiAl powder layers increased,the bending fracture strength and fracture toughness at room temperature of the final(TiB/Ti)-TiAl laminated composites were remarkably improved,especially for the(TiB/Ti)-TiAl composites prepared by Tib₂/Ti powder layers with thickness of 800μm and TiAl powder layers with thickness of 400μm,whose fracture toughness and bending strength were up to 51.2 MPa·m^1/2and 1456 MPa,respectively,293%and 108%higher than that of the monolithic TiAl alloys in the present work.This was attributed to the addition of high-performance network TiB/Ti composite layers.Moreover,it was noteworthy that the ultimate tensile strength at 700℃of(TiB/Ti)-TiAl composites fabricated by 400μm thick Tib₂/Ti powder layers and 400μm thick TiAl powder layers was as high as that at 550℃of network TiB/Ti composites.This means the service temperature of(TiB/Ti)-TiAl laminated composites was likely raised by 150℃,meanwhile a good combination of high strength and high toughness at ambient tempe rature could be maintained.Finally,the fracture mechanism of(TiB/Ti)-TiAl laminated composites was proposed.     

高温熔体反应法制备Al-5Ti-1B细化剂

利用高温熔体反应法成功制备Al-5Ti-1B细化剂。通过热力学计算,确定Al-5Ti-1B细化剂的起始反应温度,研究熔体温度对细化剂组织形貌及吸收率的影响。利用X射线衍射,扫描电子显微镜和X射线能谱仪观察细化剂的相组成和形貌,同时对Al-5Ti-1B细化剂铸锭进行高温挤压,并对挤压出的Ф9.5mm丝材进行微观组织分析和细化实验。结果表明:细化剂主要由TiB_2,TiAl_3,α-Al相组成;850℃制备的细化剂铸锭组织形貌最佳,且Ti和B吸收率达到最佳匹配。挤压后TiAl3相呈细小的块状和TiB_2弥散分布在基体内。添加0.2%(质量分数)细化剂后,纯铝的晶粒尺寸由3.99mm细化到0.45mm。     

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。     

原位合成TiB_2/ZL205A复合材料的组织及流动性

采用原位合成法制备了TiB_2/ZL205A复合材料,对所合成复合材料的物相、TiB_2颗粒形貌及分布、流动性进行了研究。结果表明:TiB_2/ZL205A复合材料主要由α-Al、Al_2Cu和TiB_2组成,TiB_2颗粒呈多边形或卵圆形,平均颗粒尺寸500nm左右,大部分沿晶界分布,少量分布在晶粒内部。TiB_2/ZL205A复合材料的流动性与浇铸温度及TiB_2质量分数的关系均可用指数阻尼模型进行描述。当浇铸温度由710℃提高到750℃时,7wt%TiB_2/ZL205A复合材料的流动性提高了30.4%;当浇铸温度在750℃以上时,7wt%TiB_2/ZL205A复合材料的流动性随浇铸温度的提高而提高的速率降低。与基体合金相比,在730℃浇铸时,3wt%TiB_2/ZL205A复合材料的流动性降低了21.8%,7wt%TiB_2/ZL205A复合材料的流动性降低了36.4%。     

Ti合金插层厚度对反应连接TiB_2基陶瓷/Ti-6Al-4V梯度复合材料的影响

将Ti合金插层引入(Ti+B_4C)反应原料和Ti合金底板之间,研究Ti合金插层厚度变化对超重力反应连接TiB2基陶瓷/Ti-6Al-4V梯度复合材料界面显微组织与力学性能的影响。热力学计算表明:合成反应的绝热温度远超Ti合金的熔点,可以保证不同厚度的Ti合金插层全部熔化。XRD、FESEM及EDS分析结果表明:在陶瓷和Ti合金底板之间形成梯度界面区,且随着Ti合金插层厚度的增加,梯度界面区的厚度也不断增大。自陶瓷基体至Ti合金底板,TiB_2和TiC_(1-x)的体积分数不断减少,而TiB的体积分数先增加而后减少,最终形成以TiB_2、TiC_(1-x)及TiB陶瓷相尺寸和分布为特征的梯度复合结构。而梯度连接区的硬度分布趋势更加平缓,其剪切强度不断提升。     

In situ synthesis of TiB whisker reinforcements in the joints of Al2O3/TC4 during brazing

Al₂O₃ ceramic has been successfully joined to Ti-6Al-4V alloy with Ag-Cu-Ti-B mixed powder. The TiB whiskers in the brazing layer were in situ synthesized during brazing. The effects of B content in reactant on the phase composition, microstructure and shear strength of the joints were investigated using SEM, EDS, and shear test. Results indicate that B content in the filler has a great impact upon the microstructure of the joints via exerting an influence on the volume fraction of in situ synthesized TiB whiskers. When the TiB content is 40 vol.%, the shear strength reaches the maximum value of 77.9 MPa. The higher content of TiB (≥40 vol.%) depresses the shear strength of the joints due to the interfacial thermal stress cannot be relaxed. Reaction phases (Ti₃Cu₂AlO, Ti₂Cu, Ti₂(Cu, Al), Ti(Cu, Al) and Ti₃Al) appear in the joint, moreover, as the volume fraction of TiB increase, Ag (s.s) and Ti(Cu, Al) distribute more uniform and fine in the brazing layer, as well as TiB whiskers mainly distribute in them. Eventually, Ti₃Cu₂AlO, TiB and TiB₂ firstly generate based on the thermodynamic analysis, and in excessive Ti circumstances, TiB whiskers remain in the brazing alloy.