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。     

TiB2-TiC复相陶瓷的结构与性能研究

TiB₂-TiC复合粉制备的TiB₂-TiC复相陶瓷的相对密度达99.8%,硬度为 93.2HRA,断裂韧性为5.53MPa·m1/2。显微结构研究表明:TiB₂-TiC烧结体体内的位错和残余气孔影响材料性能。复合粉烧结体晶粒尺寸细小,大小分布均匀,晶粒之间界面干净,无杂质沉积,烧结体中TiB₂和TiC两相界面接合处元素B,C,Ti的含量存在梯度变化,都有利于烧结体性能提高。TiB₂晶粒生长存在取向性。     

纳米晶合金粉芯的超重力渗流制备及磁性能

为了探索粉芯的新制备工艺,以Fe73.5Cu₁Nb₃Si13.5B₉纳米晶合金铁芯为原料,使用机械破碎法制粉,并采用超重力渗流工艺制备了7种不同粒度配比的纳米晶合金粉芯,借助SEM、XRD、VSM分别对纳米晶粉末的形貌、结构和磁性能进行了表征,研究了粉末粒度配比对纳米晶合金粉芯的形貌、密度、有效磁导率、损耗及品质因数的影响。结果表明,机械破碎法制得的粉末虽带尖角,但矫顽力低,利用超重力渗流工艺制备的粉芯其粉末表面基本被树脂完全包覆。同时,通过适当的粉末粒度匹配,发现性能最佳粉芯的粉末粒度配比为:100~200目占60%,200~400目占20%,400~1 000目占20%。该种粉芯的密度为4.46 gcm³,在100~3 000 kHz频率范围内有效磁导率比较稳定,且在3 000 kHz时为28.2。当设定磁感应强度为20 mT,频率为500 kHz时,其损耗为99.1 W/kg。另外,根据实验结果可知,该工艺能够制备出频率在MHz以上具有较低损耗的粉芯。     

SHS/QP制备(TiB2+Fe)/Fe叠层材料的结构与性能分析

采用SHS/QP工艺制备了(TiB₂+Fe)/Fe叠层材料。SEM分析表明TiB₂+Fe金属陶瓷层结构致密。用EPMA研究了TiB₂+Fe金属陶瓷层与Fe基片之间的界面连接机制,结果表明TiB₂从TiB₂+Fe侧向Fe基片侧进行扩散,以及TiB₂+Fe层中的Fe粘结相和Fe基片的粘接完成了(TiB₂+Fe)/Fe叠层材料的界面连接。叠层材料接头断裂时,断裂位置发生在TiB₂+Fe金属陶瓷层,而不是沿着TiB₂+Fe层与Fe基片的界面断裂。     

原位生成TiB2/ZA27复合材料的制备与性能

以Al熔液为载体,采用原位反应生成形状规则、尺寸细小的TiB₂颗粒相,再将TiB₂颗粒传递到ZA27合金中,形成TiB₂颗粒增强的ZA27复合材料。采用合理的熔炼工艺促进了TiB₂颗粒在基体中的均匀分布。实验结果显示,TiB₂颗粒在ZA27复合材料中,分布均匀,平均直径在3 μm以下。TiB₂颗粒的加入使得复合材料的晶粒明显细化,并随着TiB₂颗粒含量增加,复合材料的抗拉强度、硬度明显提高,2.1%TiB₂/ZA27复合材料与基体合金相比室温抗拉强度提高13%、布氏硬度提高21%,弹性模量也有所提高,在强度、硬度及弹性模量提高的同时,材料的塑性并未恶化,延伸率略有提高,另外,材料的热膨胀系数随着TiB₂颗粒的加入有所降低。     

高能球磨及热挤压对Al-Ti-B细化剂纳米TiB2颗粒分散性与细化性能的影响

为获得高晶粒细化性能的Al-Ti-B细化剂,本文利用高能球磨法在微米Ti粉上负载纳米TiB₂颗粒制备了Ti/TiB₂粉末细化剂,并采用热挤压工艺制备了杆状Al-Ti-B细化剂,对比分析了两种细化剂的晶粒细化性能及机理。研究表明:高能球磨可将纳米TiB₂颗粒均匀负载分散在微米Ti粉表面,使工业纯铝的平均晶粒尺寸细化至74.6 μm;热挤压则使细化剂致密化,微米Ti粉及纳米TiB₂颗粒在铝基体中分布更加均匀,可将工业纯铝的平均晶粒尺寸进一步细化至58.4 μm,获得最佳细化效果,并使细化剂的抗衰退性能提高。机理分析表明,随着细化剂中纳米TiB₂颗粒的分散性提高、团聚现象减缓,其在铝熔体中的沉降速度缓慢,对晶粒的形核促进作用、长大抑制作用更充分,是热挤压Al-Ti-B细化剂对工业纯铝有优异晶粒细化效果的关键。     

TiAl-B合金片状TiB2晶体表面结构及生长机理

用原位自生法制备了Ti-54Al-xB (at%)合金并利用XRD,SEM对合金的相组成和微观组织进行了研究。结果表明:片状TiB₂基面存在与[0001]晶向平行的细棒状分枝,表面存在与[0001]晶向垂直的薄片凸耳状分枝,它们的晶体学取向与母体的取向一致。片状TiB₂厚度一般小于0.3μm,表面上的凸耳状分枝厚度一般小于0.1 μm。分析表明,在不平衡凝固条件下,片状TiB₂固-液界面前沿产生的富Al边界层和随着片状TiB₂晶体的长大导致固-液界面上B原子过饱和度不均匀性增加的共同作用使固-液界面失稳,从而形成了片状TiB₂的这种表面结构。     

电场激活燃烧合成( TiB2)PNi/Ni3Al/ Ni功能梯度材料

采用电场激活压力辅助合成技术(FAPAS)制备了(TiB₂)_PNi/(TiB₂)_PNi₃Al/Ni₃Al/Ni梯度材料,主要研究电场激活燃烧合成过程中电场对材料合成及层界面扩散连接的作用。分析了梯度材料各层的界面微观组织及相组成和材料的硬度分布。结果表明,采用FAPAS 技术结合机械合金化工艺制备的(TiB₂)_PNi/(TiB₂)_PNi₃Al/Ni₃Al/Ni 功能梯度材料具有快速、简便和组织均匀密实的特点。梯度材料的陶瓷复合层、Ni₃Al层和Ni板的界面区产生成分的互扩散,形成了良好的冶金结合。从Ni板到陶瓷复合层的硬度呈梯度分布。     

热压自蔓延高温合成制备TiB2/NiAl金属间化合物基复合材料

采用热压自蔓延高温合成技术(SHS+HP)制备了TiB₂/NiAl颗粒复合材料。采用X-射线衍射、扫描电镜和图像分析等方法研究了材料的微观结构,结果表明:SHS+HP工艺特别适合制备颗粒增强的复合材料,采用该工艺制备的TiB₂/NiAl材料,其残余孔隙率约为1%。这种材料中增强颗粒是自生长的。晶粒细小,平均粒径约为0.8μm。力学性能研究表明:材料的强度和硬度随TiB₂量的增加而提高。     

烧结温度对(Ti5Si3+TiC+TiB)/Ti复合材料组织和力学性能的影响

为了获得性能优异的钛基复合材料和解决单一增强相对性能提升有限等问题,以Ti粉、SiC粉、TiB₂粉、C粉为原料,采用粉末冶金法,在不同烧结温度下原位自生制备了(Ti₅Si₃+TiC+TiB)/Ti复合材料。通过XRD、SEM、万能试验机等设备表征了复合材料的微观组织和力学性能。结果表明:随烧结温度的升高,复合材料的致密度提高,平均晶粒尺寸逐渐增大;烧结温度的升高使增强相数量增加的同时减少了较低烧结温度下的团聚现象。复合材料的洛氏硬度、屈服强度、抗拉强度随烧结温度的升高先增大后减小,断裂应变下降不显著。在1 300 ℃下,(Ti₅Si₃+TiC+TiB)/Ti具有最佳的综合力学性能,烧结态试样的抗压强度达到最高2 435 MPa,屈服强度1 649 MPa,洛氏硬度49.1HRC,断裂应变28.7%。分析可知,微米尺寸的TiC、TiB和亚微米尺寸的Ti₅Si₃增强相的协同作用在显著提高复合材料强度的同时也保持了一定的塑性。(Ti₅Si₃+TiC+TiB)/Ti复合材料的增强方式以细晶强化、弥散强化和载荷传递强化为主。     

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。     

The Ti-B-N system: nanocomposite nc-TiN/a-(TiB2, BN) and nano-multilayer nc-TiN/a-TiBN thin films

The nanostructures and mechanical properties of nanocomposite nc-TiN/a-(TiB2, BN) and nanostructured multilayers nc-TiN/a-TiBN were investigated using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), microindentation, and stress measurements. It was found that the monolayer Ti-B-N thin films consisted of nanometer-sized crystalline (nc-) Ti(N, B) embedded into amorphous (a-) (TiB2, BN) matrix. When B content was below approximately 16 at.%, two different-sized nanocrystallites with mean grain sizes of approximately 3 and 9 nm respectively were embedded in a-TiB2. With increasing B incorporation (> approximately 27 at.%), more uniform nanograins was embedded a-(TiB2, BN). Incorporation of B not only decreased the size of nanocrystallites, but also gave rise to twinning deformation in nanocrystallites. A maximum hardness of approximately 44 GPa was achieved at B content of 19 at.%. It was also found that the nanostructure and mechanical behaviors of nc-TiN/a-TiBN multilayers was dependent on the modulation length (bilayer thickness A). Decrease of Lambda made the preferred orientation of nc-TiN gradually transform from (200) to (111). A maximum hardness of approximately 30 GPa was achieved at Lambda = 1.8 nm. Deflection from this Lambda value decreased hardness. By contrast, the residual compressive stress value monotonically increased with decrease of A. The enhancement of the hardness was due to the coherent stresses and the structural barriers to dislocation motion in the interface.     

Effect of silicon content in grain refining hypoeutectic Al–Si foundry alloys with boron and titanium additions

Abstract

The effect of Si content on the grain refinement of hypoeutectic Al–Si alloys was investigated. Alloying with Si refines the grain structure, which tends to be coarse and columnar in commercially pure aluminium. The smallest grain size occurs at ～2 wt-%Si, where the solidification interval of hypoeutectic Al–Si alloys is the largest. Grains become increasingly coarser with increasing Si starting from this point. The grains of Al–Si alloys with 500 ppm Ti are smaller than those cast without Ti regardless of the Si content of the alloy. The fivefold reduction in grain size in commercially pure aluminium upon Ti addition is gradually reduced with increasing Si. Finally, the grain refinement provided by Ti fails to meet the expectations once Ti starts to be removed from the melt via the formation of Ti–Si compounds above 5 wt-%Si. The B addition relies on the formation of AlB₂ particles to offer grain refinement. Analysis of the Al rich corner of the calculated Al–Si–B liquidus surface suggests that the primary AlB₂ is formed at a Si concentration of ～4 wt-%. While a perfect grain refiner for hypoeutectic Al–Si alloys with at least 4 wt-%Si, B fails to refine the grain structure when the Si content is less.     

非晶态Ti—B—N薄膜的制备及晶化研究

采用双靶轮流溅射技术，以Ｔｉ和六方氮化硼反应合成了Ｔｉ－Ｂ－Ｎ薄膜，并采用ＸＲＤ，ＴＥＭ和显微硬度计研究薄膜的微结构及其力学性能。结果表明，镀态Ｔｉ－Ｂ－Ｎ薄膜为非晶体Ｔｉ（Ｎ，Ｂ）化合物，其硬度达到ＨＫ２４７０；薄膜经过热处理晶化形成ＴｉＮ结构类型的Ｔｉ（Ｎ，Ｂ）晶体，硬度略有降低。     

Microstructure Evolution of Ti/BN Powder Blend during Ball Milling and Heat Treatment

Ball milled Ti/BN composite powder was prepared by high energy ball milling for 40 h, using Ti and BN (the molar ratio of Ti/BN is 3:2) as starting materials. The as-milled composite powder consists of TiN, Ti and amorphous phase. TiN formed while the milled powder was annealed at 400℃. The heat treatment at 700℃ led to the formation of TiB2 and TiB. The nanocrystalline Ti and amorphous phase converted to TiN and TiB2 when the powder was heated to 1300℃.     

Relationships of diboride phases in Al–Ti(Zr)–B alloys

Abstract

The relationships of diboride phases in Al–Ti(Zr)–B alloys with a variable Ti/B ratio close to the stoichiometry of TiB₂ were studied. The formation of diboride solid solutions was confirmed. A grain refinement mechanism is proposed as that diboride particles in the Al–Ti–B master alloys reacting with aluminium upon adding into an aluminium melt and release titanium into the melt through forming a (Ti,Al)B₂ solid solution and maintain a thin dynamic Ti rich layer on the surfaces of the (Ti,Al)B₂ particles, which nucleates α-Al grains in solidification. The poisoning effect of zirconium on grain refinement of aluminium by Al–Ti–B master alloys is also discussed.     

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.     

泡沫碳化硅陶瓷的导电性能

采用高分子热解和反应烧结方法制备出泡沫碳化硅陶瓷，研究了泡沫碳化硅陶瓷的体积分数变化和钛的掺杂对泡沫碳化硅陶瓷骨架导电性能的影响．结果表明：随着泡沫碳化硅陶瓷的体积分数提高，泡沫碳化硅陶瓷的电阻率降低，这是泡沫碳化硅陶瓷筋中部碳化硅的面积增加所引起的；掺杂的钛转变成TiSi2导电相改善了泡沫碳化硅陶瓷的导电性能．TiSi2呈现离散和团聚两种形态分布，以不规则的形状位于碳化硅晶界之间，在碳化硅中作为施主杂质．泡沫碳化硅陶瓷表现出的正或负温度系数取决与掺杂的钛量的多少．     

Performance of AlTi5B1, AlTi3B3 and AlB3 master alloys in refining grain structure of aluminium foundry alloys

Abstract

The capacity of AlTi5B1, AlTi3B3 and AlB3 grain refiners to refine the grain structures of AlSi7Mg and AlSi11Cu2 foundry alloys was investigated. The performance of AlTi5B1, well established to be the best grain refiner for wrought aluminium alloys, is not nearly as good with the AlSi7Mg and AlSi11Cu2 alloys. Relatively smaller grains are obtained with the AlTi3B3 grain refiner in both alloys. The AlB3 grain refiner, on the other hand, improves the grain structure only as much as the AlTi5B1 grain refiner does. With as much as 0·04–0·1 wt-%Ti, the commercial alloys cannot enjoy the outstanding potency of the AlB₂ particles since the B supply is readily transformed to TiB₂ particles. However, the grains of the Ti free AlSi7Mg and AlSi11Cu2 alloys (～0·005 wt-%Ti) are very small and nearly globular for the entire range of holding times when inoculated with AlB3, implying not only a remarkable grain refining capacity but also a strong resistance to fading of the grain refinement effect. The lack of Ti in the melt allows the entire B to form AlB₂ particles, the perfect substrates to promote the nucleation of α-Al crystals. Aluminium castings can enjoy grain sizes well below 200 μm, with an addition of 0·02 wt-%B, provided that they are Ti free. That the potent substrates are made available just before the nucleation of α-Al crystals avoids fading effects and is a further advantage of the AlB3 grain refiner in recycling operations.     

HN2154非调质钢中Ti、Nb的控制

文章研究了加Ti、Nb对HN2154非调质钢的组织、力学性能和晶粒大小的影响。研究结果表明,随着Ti、Nb的加入,HN2154钢的强度和硬度出现较明显下降,塑性略有提高,加Ti和加Nb对HN2154钢热轧状态下钢材的晶粒大小没有明显影响;但加Ti、Nb能细化HN2154钢经常规加热正火后的晶粒。加Ti和Nb对感应加热锻造后锻件的晶粒大小影响很小。根据研究结果,确定了HN2154钢中Ti、Nb的控制。