浸渗法制备高铬铸铁/TiC-SiC复合材料及微观组织

采用小颗粒TiC包覆SiC陶瓷颗粒,在惰性气体保护下选用无压浸渗方法制备了高铬铸铁/TiC-SiC复合材料;利用SEM/EDX观察和分析了液态铸铁在SiC预制体中的浸渗情况、组织特征和成分分布;结合高铬铸铁/Ti-SiC复合材料的组织特点和浸渗行为特点,分析了TiC粉体对浸渗行为和复合材料组织的影响。观察结果表明,当TiC加入量≤10%(质量分数,下同)时,Fe/Cr合金无法润湿SiC颗粒,而当加入量≥20%时,Fe/Cr合金和预制体之间润湿性得到改善,增加TiC含量更有利于Fe/Cr合金浸渗;基体中大尺寸SiC颗粒消失,出现了尺寸接近毫米级的条状单质碳,这与高铬铸铁/Ti-SiC复合材料的组织差异较大。对比两种复合材料组织发现,添加Ti粉末在金属液中可与C结合生成TiC,而添加的TiC颗粒在组织中呈鹅卵石状,边缘圆润,出现金属液与陶瓷颗粒之间的互溶。在浸渗过程中,添加TiC和Ti与浸渗金属发生的反应不同,且高质量分数的TiC对金属液浸渗过程有明显的促进作用。     

Dynamic measurement on infiltration process and formation mechanism of infiltration front

An infiltration measurement device was developed to research the infiltration process of molten AZ91D magnesium alloy into the Al2O3 short fibre preform.The variation of relationship between the heights of measuring points and the time for molten alloy to reach the measuring points was illustrated.The effect of infiltration process parameters on the infiltration front was analyzed. It is found that pressure and pouring temperature are the most important factors which affect the infiltration velocity and composite quality.Furthermore,considering the influence of temperature field,an infiltration model of molten AZ91D into the short fibre preform was constructed on the basis of experimental results and Darcy’s Law.The analysis shows that the results predicted by this model are consistent with the experimental results.     

金属诱发无压浸渗技术制备B4C/Mg复合材料的磨损行为与机制

利用金属诱发无压浸渗技术制备的B4C/Mg复合材料为实验材料,研究该材料的磨损行为与磨损机制。在销盘式实验装置上对施加不同载荷(20、40、60和80 N)以及磨损速率为250 r/min实验条件下的磨损行为进行评价。结果表明：B4C/Mg 复合材料在所施加载荷下均比纯 Mg 基体表现出更优异的抗磨性能。作为诱发浸渗剂的金属Ti颗粒,其含量对B4C/Mg复合材料的磨损性能具有一定影响。纯Mg基体的主要磨损机制是磨粒磨损;而对于B4C/Mg复合材料,当施加载荷较低时,主要磨损机制为粘着和层离;当施加载荷较高时,其磨损机制为加热软化熔化或塑性变形。     

Effects of Y211 phase contents on the critical current density Jc and microstructural analysis in YBCO bulk superconductors

YBCO bulk superconductors were prepared by the solid state reaction and top-seed-melt-textured growth(TSMTG) process. By using the AC susceptibility measurement, the critical transition temperature Tc of samples is 91.5 Kfor the highest value, and the transition width △TC is less than 1 K. The highest magnetization critical current densities Jcachieved 106 A/cm2 under 5 T at 10 K and 1.35×104 A/cm2 under 2 T at 70 K (H//c), respectively. The results combining theSEM observation indicate that doping of Y211 particles is more effective in improving the growth quality of melt-texturedYBCO superconductor and in reducing the micro-cracks of specimens. Doping of Y2O3 powder forms the rod-shaped Y211particles, but doping of Y211 particles directly to matrix materials forms the spherical Y211 particles mainly. Combiningthe microstructures with Jc measurements shows that the interfaces are most important on flux bundle pinning, in which thegradient of free energy is larger than that of other place between the Y     

顶部籽晶熔渗法单畴YBCO的制备及其显微结构分析

采用顶部籽晶熔渗工艺(Seeded infiltration and growth technique简称SIG)成功制备出了单畴的YBCO超导体,并对样品的显微结构进行了分析。整个SIG样品的超导相显微组织比较均匀,Y123片层的厚度很薄且连接性很好,但Y211粒子在样品中的分布并不均匀,如相对于c-GS区域而言,a-GSs区域Y211粒子的浓度较大且平均尺寸较小,这种不均匀性与Y211粒子的尺寸有关。本文比较详细的讨论了影响顶部籽晶熔渗法制备单畴YBCO超导体显微组织的因素。     

温度对TFA-MOD制备YBCO薄膜的影响

采用TFA-MOD方法在YSZ单晶基底上制备YBCO薄膜,主要研究高温热处理阶段温度对薄膜微结构和超导电性的影响。采用X射线衍射和扫描电镜分别对相组成与形貌进行分析。结果显示在800～830℃之间,能够获得纯的YBCO相,同时随着晶化温度的降低,薄膜面内a轴晶粒减少,有利于薄膜超导电性的改善。     

Characteristic reaction products in the AZ91/SiC composite fabricated by pressureless infiltration technique

Since the spontaneous infiltration of molten AZ91 Mg alloy into a powder bed containing SiC particles occurred at 700 °C for 1 h under a nitrogen atmosphere, it was possible to fabricate Mg alloy composites reinforced with SiC particles. Since the fabrication conditions (e.g. temperature, time, and atmosphere) of the composite are different from those of the other fabrication route, reaction products formed during the composite fabrication were investigated in detail using field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HRTEM). From the analysis results, we could identify the formation of MgAl₂O₄ and AlN, as well as MgO in fabricated composite.     

Mg对无压自浸渗制备SiCp/Al复合材料组织与性能的影响

采用无压自浸渗法制备SiCp/Al复合材料。研究了Mg含量对SiCp 与Al之间浸润性的影响 ;探讨了Mg含量对SiCp/Al复合材料的组织与性能的影响及其作用机理。结果表明 ,加入的Mg与SiCp 表面的氧化物薄膜和铝基体发生反应 ,生成物会阻止SiCp 与Al基体反应生成Al4 C3 脆性相 ,同时SiCp 表面的微反应也增加了基体与SiCp 的结合强度 ,改善了基体与SiCp 之间的浸润性 ,从而使复合材料的耐磨性提高了 3～ 4倍。     

稀土Y对Al-10Mg合金显微组织和性能的影响

研究了添加少量稀土Y及固溶处理对Al-10Mg合金显微组织、力学性能和耐蚀性能的影响.结果表明,Y的加入能细化铸态合金的晶粒,形成Al4MgY相,沿晶界不连续分布,起到很好的晶界强化作用,从而提高合金的抗拉强度和伸长率.当Y的含量为0.4%时合金具有最佳的综合力学性能,抗拉强度达到261.8 MPa,伸长率为4.3%.当Y含量超过0.4%时,Al4MgY相开始沿晶界连续分布,降低了晶界的结合强度,合金的强度和韧性下降.不含Y的合金拉伸测试时,出现典型的枝晶间脆性断裂,加Y后断裂机制转变为韧性断裂,因此合金韧性大大提高.固溶处理后合金的耐蚀性能好于铸态的,随着Y含量的增加,合金的腐蚀倾向变大,Y对合金的耐蚀性能是不利的.     

熔渗法制备C/C-Cu复合材料的力学性能

以炭纤维(Cf)针刺整体毡为预制体,分别采用化学气相渗透(Chemical vapor deposition,CVI)和浸渍炭化(Impregnation and carbonization,I/C)制备不同密度和基体炭的C/C坯体;通过添加Ti元素改善熔融Cu与C/C坯体的润湿性.采用真空熔渗法制备C/C-Cu复合材料.对复合材料的力学性能及其与坯体之间的关系进行研究,并与常用滑板材料的力学性能进行比较.结果表明:随着坯体密度的增加,复合材料的抗弯强度下降,而坯体密度为1.4 g/cm3的复合材料的冲击韧性达到最大值.与用I/C坯体制备的复合材料相比,用CVI坯体制备的复合材料具有更高的强度和韧性,其弯曲曲线呈“假塑性”断裂特征,断裂时纤维从热解炭层或熔渗金属相中拔出,熔渗金属相呈“韧窝状”的塑性断裂形貌.冲击断裂时,复合材料倾向于沿TiC/熔渗金属界面断裂.C/C-Cu复合材料的抗弯强度为180～300 MPa、冲击韧性高于3.5 J/cm2,优于常用滑动电接触材料的性能,是一种极具潜力的新型滑动电接触材料.     

稀土Y对AZ31镁合金金相组织和力学性能的影响

研究了稀土元素Y对AZ31镁合金金相组织和力学性能的影响.结果表明当稀土添加量为0.6 %～0.9 %时,α(Mg)基体晶粒变细,并且加入量为0.9 %时得到更细化的组织,β相(Mg17Al12)在晶界由连续网状变为断续弥散状分布,由于α (Mg)基体晶粒的细化和β相形貌的改善,合金的力学性能有提高;当稀土添加量为1.2 %时,α(Mg)基体晶粒显著粗化,β相(Mg17Al12)内部出现针状和圆盘状的第二相,力学性能下降.     

Microstructure and mechanical properties of B<Subscript>4</Subscript>C-TiB<Subscript>2</Subscript>-Al composites fabricated by vacuum infiltration

B_4C-TiB_2-Al composites were fabricated by infiltrating aluminum into porous B_4C-TiB_2 preforms in vacuum. The microstucture and mechanical properties of the B_4C-TiB_2-Al composites were investigated. The hardness decreased, the flexurai strength increased, and the fracture toughness first increased and then decreased slightly with an increase in TiB_2 content. The B_4C-TiB_2-Al composite with 40wt.% TiB_2 showed the optimized properties. The infiltrated aluminum addition was the leading reason for the fracture toughness improvement of the composites. The tear ridges and dimples on the fracture surface of the composites increased gradually with the increase of infdtrated alu-minum content showing inter/transgranular fracture mode. The relationships between the microstructures and the mechanical properties of the composites were discussed.     

Y对Mg-2％Mn合金显微组织和力学性能的影响

用光学显微镜、力学万能试验机和显微硬度仪等分析了Mg-2%Mn-x%Y合金的显微组织和力学性能.结果表明,Y加人到Mg-2%Mn合金中,以Mg24Y5相形式弥散分布在α(Mg)晶内和晶界处.一定量Y(≤1.5wt%)的加入可起到细化晶粒的效果,达到提高合金室温力学性能的目的;但过量Y(>1.5wt%)的加入使合金晶粒粗大,降低了合金的力学性能.     

Y含量对Mg-Zn-Zr合金组织和性能的影响

研究了Y含量(质量分数分别为0、0.93%、2.25%、3.50%)对Mg-0.8Zm-0.35Zr合金组织和力学性能的影响.结果表明,在Mg-008Zn-0.35Zr合金中添加Y,能够有效的细化晶粒,而且随着Y含量的增加,晶界上的第二相和晶粒内部的层片状组织增多;合金的室温和高温抗拉强度提高,合金的室温伸长率呈现先增后降的趋势(Y含量为0.93%时达到峰值26.0%),合金的高温伸长率降低;合金的高温抗蠕变性能得到了明显的提高.     

Microstructure and mechanical properties of B_4C-TiB_2-Al composites fabricated by vacuum infiltration

B4C-TiB2-Al composites were fabricated by infiltrating aluminum into porous B4C-TiB2 preforms in vacuum. The microstucture and mechanical properties of the B4C-TiB2-Al composites were investigated. The hardness decreased, the flexural strength increased, and the fracture toughness first increased and then decreased slightly with an increase in TiB2 content. The B4C-TiB2-Al composite with 40wt.% TiB2 showed the optimized properties. The infiltrated aluminum addition was the leading reason for the fracture toughness improvement of the composites. The tear ridges and dimples on the fracture surface of the composites increased gradually with the increase of infiltrated aluminum content showing inter/transgranular fracture mode. The relationships between the microstructures and the mechanical properties of the composites were discussed.     

Microstructure and graphitization behavior of diamond/SiC composites fabricated by vacuum vapor reactive infiltration

To inhibit the graphitization of diamond under high temperature and low pressure, diamond/Si C composites were firstly fabricated by a rapid gaseous Si vacuum reactive infiltration process. The microstructure and graphitization behavior of diamond in the composites under various infiltration temperatures and holding time were investigated. The thermal conductivity of the resultant materials was discussed. The results show that the diamond-to-graphite transition is effectively inhibited at temperature of as high as 1600 °C under vacuum, and the substantial graphitization starts at 1700 °C. The microstructure of those ungraphitized samples is uniform and fully densified. The inhibition mechanisms of graphitization include the isolation of the catalysts from diamond by a series of protective layers, high pressure stress applied on diamond by the reaction-bonded Si C, and the moderate gas–solid reaction. For the graphitized samples, the boundary between diamond and Si C is coarse and loose.The graphitization mechanism is considered to be an initial detachment of the bilayers from the diamond surfaces, and subsequently flattening to form graphite. The ungraphitized samples present higher thermal conductivity of about 410 W·m~(-1)·K~(-1)due to the fine interfacial structure. For the graphitized samples, the thermal conductivity decreases significantly to 285 W·m~(-1)·K~(-1)as a result of high interfacial thermal resistance.     

反应合成Ni-Al金属间化合物的组织及形成机理(英文)

以Ni粉和Al粉为原料,通过热爆反应合成制备Ni-Al系金属间化合物,研究了反应物摩尔比对生成物物相、组织结构和显微硬度的影响。结果表明:当Ni、Al摩尔比为1:1时,反应生成物为单一的NiAl相;当Ni、Al摩尔比为2:1时,生成物相组成为NiAl+Ni3Al相,因为非平衡冷却,NiAl含量多,呈不规则块状形态分布,Ni3Al相析出量少,主要沿初生NiAl晶界分布,当进一步提高Ni含量,且Ni、Al摩尔比为3:1时,生成物组织形态复杂,除枝晶状的β-NiAl、粗大块状和网状的γ-Ni3Al外,还有板条状和针片状的M-NiAl和不规则的块状或者尖条状的γ′-Ni3Al,这主要是由非平衡冷却和β-NiAl内的成分差异而引起的。     

Y、Nd对Mg-5Al合金组织和性能的影响

通过微观分析和力学性能测试等方法.研究了Y、Nd对Mg-5Al合金时效组织和性能的影响.结果表明,加入少量Y、Nd后,合金中Al-RE相以粒状(Al2Y,Al2Nd)、棒状和针状(Al2Nd)分布于基体上,Mg17Al12相数量减少,形态弥散细小.研究表明,Mg-5Al合金中加入0.5%的Y、0.5%的Nd及0.5%的Y+0.5%的Nd后,合金的晶粒尺寸由104.5 μm分别降为86.1、83.5、78.6μm;随着Y、Nd的加入,合金的抗拉强度提高、伸长率增加,其中Mg-5Al-0.5Y-0.5Nd合金具有最高的强度和伸长率,分别为225.2 MPa和13.92%.     

超重力燃烧熔渗钨铜合金绝热温度计算及其显微组织

根据燃烧合成体系绝热温度的热力学基本理论,通过计算机编程,对CuO/Al铝热剂体系的绝热温度进行了数值计算.结果表明,在考虑产物Cu的汽化焓情况下,体系绝热温度为2846 K(Cu的沸点温度),同时还有52.9 at％的Cu产物以气相形式存在,而该体系中钨粉添加量超过30 mass％时,绝热温度低于1800 K而不能自蔓延燃烧.采用超重力燃烧熔渗方法制备出组织致密,钨颗粒体积分数呈梯度分布(沿超重力方向70％～80 at％)的钨铜合金.进一步检测结果表明,该方法与传统烧结方法制备的钨铜合金其相结构及显微组织形貌相同,并对其成型机制进行了初步分析讨论.