Mo(Si0.95,Al0.05)2价电子结构计算及其性能分析

根据固体与分子经验电子理论（EET）,采用键距差法（BLD）,分析并计算了C11b型金属间化合物MoSi2的价电子结构与理论键能;采用合金元素Al部分取代MoSi2晶格中的Si原子,依据固体与分子经验电子理论在代位式固溶体中的平均原子模型,分析并计算了C11b型Mo(Si0.95,Al0.05)2的价电子结构与理论键能。结果表明：Al微合金化改变了Mo原子和Si原子的杂化状态,从而使相应的价电子结构参数发生变化。与MoSi2相比,Mo(Si0.95,Al0.05)2固溶体中共价电子数在总价电子数中所占的比例（h）由65.87%降至64.28%,因而Al微合金化不利于MoSi2强度的提高;但是晶格电子数由4.7141增至4.9202,所以Al微合金化有利于MoSi2塑性的改善。     

W含量对(Mo_(1-x),W_x)Si_2复合材料力学性能和高温氧化性能的影响

以Mo、W和Si粉为原料,采用自蔓延热爆合成和热压工艺制备不同W含量的(Mo_(1-x),W_x)Si_2复合材料,研究W含量对(Mo_(1-x),W_x)Si_2复合材料的力学性能和高温抗氧化性能的影响.结果表明:随着W含量的增加,(Mo_(1-x),W_x)Si_2复合材料的力学性能逐渐增加,氧化激活能逐渐降低;(Mo_(0.5),W_(0.5))Si_2复合材料的室温抗弯强度、1 200℃高温抗弯强度、硬度和断裂韧性分别为363 MPa、480 MPa、9.28 GPa和3.82 MPa·m~(1/2)与纯MoSi_2比较,分别增加了40.7%、112.4%、12.1%和27.3%;(Mo_(1-x),W_x)Si_2复合材料在1 673～1 873 K空气中能形成致密的氧化层,氧化增量符合抛物线规律.     

Mo(Si_(1-x)Al_x)_2/Al_2O_3复合材料的制备与强韧化

以Mo、Al、Si和Mo O_34种粉末为原料,通过燃烧合成和真空热压烧结工艺原位制备了(Si_(1-x)Al_x)_2/Al_2O_3复合材料,分析了其燃烧模式、产物相结构、微观组织和力学性能。结果表明:添加Al之后坯体的燃烧合成反应更加剧烈,燃烧模式由螺旋模式转入混沌模式。随着合金化Al含量的增加,基体相结构由C11_b型Mo Si_2转变为C40型Mo(Si,Al)_2,并且在所有复合材料中都可以鉴别出Al_2O_3衍射峰,表明通过燃烧合成技术原位制备了Mo(Si_(1-x)Al_x)_2/Al_2O_3复合材料。复合材料的断裂韧性和抗弯强度最高分别达到4.25 MPa·m~(1/2)和346 MPa,比纯Mo Si_2提高了39%和60%。复合材料的强韧化机制主要有Al合金化强韧化、Al_2O_3第二相颗粒弥散强韧化、玻璃相的消除以及断裂方式的转变。     

2％C／MoSi2复合材料的组织结构与性能

采用热压烧结工艺制得了2％C／MoSi2（质量分数）复合材料,并测定了材料的显微组织和结构、室温和高温力学性能、耐磨性能以及电阻率。结果:C／MoSi2复合材料由大量的MoSi2、多量的Mo5Si3和少量的β－SiC组成,其硬度Hv为1060,抗弯强度为470MPa,断裂韧性为5．12MPa.m^1/2,800℃的硬度Hv为750,1200℃的抗压强度为450MPa,1400℃的抗压强度为142MPa;在Al2O3和SiC磨盘上表现出优异的耐磨性能,材料的电阻率为349n.m。与纯MoSi2相比,2％C／MoSi2复合材料在硬度、抗弯强度、断裂性、高温抗压强度、弹性模量和耐磨性能等方面都有较大的提高。     

热循环对SiCp／MoSi2复合材料性能的影响

研究了热循环ＳｉＣｐ／ＭｏＳｉ２复合材料抗弯强度和断裂韧度的影响，并测定了材料的宏观残余应力，实验材料是用热压方法制备了ＭｏＳｉ２和不同体积百分数（１０，２０，３０ｖｏｌ％）ＳｉＣｐ增强ＭｏＳｉ２复合材料，实验结果表明，复合材料的抗弯强度和断裂韧度都随ＳｉＣ含量的增加而增加，经过热循环以后，四种材料的抗弯强度都有不同程度的增加，而断裂韧度则下降约２０％左右，这是由于材料经过热循环以后，造成ＳｉＣｐ     

2%C/MoSi_2复合材料的组织结构与性能

采用热压烧结工艺制得了 2 %C/MoSi2 (质量分数 )复合材料 ,并测定了材料的显微组织和结构、室温和高温力学性能、耐磨性能以及电阻率。结果表明 :C/MoSi2 复合材料由大量的MoSi2 、多量的Mo5Si3 和少量的 β SiC组成 ,其硬度Hv为 10 6 0 ,抗弯强度为 470MPa ,断裂韧性为 5 .12MPa·m1/ 2 ,80 0℃的硬度Hv为 75 0 ,12 0 0℃的抗压强度为 45 0MPa ,140 0℃的抗压强度为 142MPa ;在Al2 O3 和SiC磨盘上表现出优异的耐磨性能 ,材料的电阻率为 34 9nΩ·m。与纯MoSi2 相比 ,2 %C/MoSi2 复合材料在硬度、抗弯强度、断裂韧性、高温抗压强度、弹性模量和耐磨性能等方面都有较大的提高。     

ZrO2／MoSi2纳米复合陶瓷显微结构和性能

热压合成制备ZrO2/MoSi2纳米复合陶瓷。显微结构和力学性能测试分析表明：复合陶瓷中ZrO2粒子沿着MoSi2晶界偏聚,抑制MoSi2晶粒长大;复合陶瓷断口晶粒细小,裂纹扩展曲折,呈现出沿晶与穿晶的混合型断裂特征。ZrO2/MoSi2纳米复合与MoSi2陶瓷相比综合力学性能较好。     

(SiC_p C)/MoSi_2复合材料的组织结构及力学性能

通过热压烧结工艺制得了 (SiCp C) /MoSi2 复合材料 ,分析了材料的组织结构、室温和高温力学性能。结果表明 :(SiCp C) /MoSi2 复合材料主要由MoSi2 (大量 )、α SiCp(大量 )、Mo5Si3(多量 )和 β SiC(少量 )组成 ,密度为 5 .12g/cm3,相对密度为 91% ;增强相的粒径 <3 0 μm ,体积分数为 3 9%。材料室温硬度、抗弯强度和断裂韧性分别为 12 .2GPa ,5 3 0MPa和 7.2MPa·m1/ 2 ;在 80 0℃的维氏硬度为 8.0GPa ,12 0 0℃和 14 0 0℃的抗压强度分别为 5 60MPa和 160MPa。与非增强MoSi2 相比 ,材料的各种力学性能都有大幅度的提高     

反应熔渗法制备Mo(Si,Al)2-SiC复合材料的研究

通过尝试对MoSi2+C坯体中熔融渗Al制备了Mo(Si,Al)2-SiC复合材料,并对其组织及性能进行了研究.反应熔渗Al法制备Mo(Si,Al)2-SiC复合材料中,反应生成物主要为Mo(Si1-x,Alx)2和SiC相,还有少量Mo5Si3C和Al相.随着x值的增加,Mo5Si3C相和Al相逐渐减少,并消失.其组织为片状Mo(Si,Al)2组织间隙中分布着针尖状SiC颗粒;从断口形貌看,SiC颗粒非常细小,团聚在大的Mo(Si,Al)2颗粒周围.根据断口形貌,部分形成的SiC为晶须状,当x=0.4时,形成的SiC多为晶须状,并且形成的晶须状的SiC和Mo(Si,Al)2连成片.反应熔渗Al法制备复合材料抗弯强度是随着x值先增加后降低,在设计值x=0.237时取得最高值.     

反应熔渗法制备Mo(Si,Al)2-SiC复合材料的研究

通过尝试对MoSi2+C坯体中熔融渗Al制备了Mo(Si,Al)2-SiC复合材料,并对其组织及性能进行了研究.反应熔渗Al法制备Mo(Si,Al)2-SiC复合材料中,反应生成物主要为Mo(Si1-x,Alx)2和SiC相,还有少量Mo5Si3C和Al相.随着x值的增加,Mo5Si3C相和Al相逐渐减少,并消失.其组织为片状Mo(Si,Al)2组织间隙中分布着针尖状SiC颗粒;从断口形貌看,SiC颗粒非常细小,团聚在大的Mo(Si,Al)2颗粒周围.根据断口形貌,部分形成的SiC为晶须状,当x=0.4时,形成的SiC多为晶须状,并且形成的晶须状的SiC和Mo(Si,Al)2连成片.反应熔渗Al法制备复合材料抗弯强度是随着x值先增加后降低,在设计值x=0.237时取得最高值.     

Preparation of Mo(Si,Al)2 feedstock used for air plasma spraying

In order to prepare high quality Mo(Si,Al)₂ feedstock characterized with C40 phase, higher Al doping amount and excellent flowability, Mo(Si_1–x,Al_x)₂ with different Al contents (x=0, 0.1, 0.2, 0.3, 0.4, 0.5) were synthesized by self-propagating high-temperature synthesis first and Mo(Si_0.6,Al_0.4)₂ was confirmed as the suitable material through X-ray diffraction analysis. A series of tests with different parameters of induction plasma spheroidization were applied to improving the flowability of feedstock. Mo(Si,Al)₂ feedstock with excellent flowability (26.2 s/50 g) was prepared through adding hydrogen into sheath gas and decreasing the powder feeding rate. The composition segregation occurred in the spheroidized powder after Al consumption and oxidation. The inhomogeneous structure of the same particle was caused by the asymmetric heating and cooling when particle passed through the plasma jet.     

无压反应烧结Mo（Si，Al）2-SiC复合材料的研究

利用MoSi2，Al，C之间的原位反应无压烧结制备了Mo（Si1-x，Alx）2-SiC复合材料。随着烧结温度从1400℃升高到1650℃，MoSi2相消失，反应产物为Mo（Si，Al）2和SiC及Mo5Si3C相。由于固溶体及Nowotny（Mo5Si3C）相的形成，使得原位反应中化学计量法则变得困难。原位生成的SiC相随着温度的升高由颗粒状变为晶须状，并由于它的强韧化作用使得复相材料的性能较单相材料成倍提高。     

Al2O3/Mo复合材料的制备与性能

采用溶胶-凝胶法制备氧化铝颗粒增强的钼基复合材料.测定了钼基体的显微硬度;用SEM,TEM及XRD分别对混合粉体与坯体进行了微观分析;用销盘式摩擦磨损试验机测定了复合材料的滑动磨损性能.结果表明:在复合粉体及其材料中,Al2O3作为分散相具有细化晶粒的作用,随氧化铝体积分数增加,钼基体显微硬度增加,复合材料摩擦系数缓慢降低,磨损量先增加后减少,一定程度上改善了材料的磨损性能.     

The role of microstructure on pesting during oxidation of MoSi2 and Mo(Si,Al)2 at 773 K

The pesting behavior of MoSi₂ and Mo(Si,Al)₂ has been examined in air at 773 K to clarify the origin and mechanism of pesting phenomena and the effect of aluminum on pesting phenomena. The initial cracks play a much more important role than the grain boundaries and the initial oxide layer in pesting. Mo and Si oxidize to amorphous Mo-Si-O simultaneously with about a 200% volume expansion. Therefore, large stress appears at the cracktips and induce many new cracks. MoO₃ vaporizes from the Mo-Si-O layer on the external surface and crack surfaces causing the oxides in the initial cracks to become porous. Oxygen has a short-circuit path to enter the sample in the cracks. Therefore, the partial pressure of oxygen is sufficiently high to allow oxidation of Mo in the materials. The platelet-like MoO₃ grows on the external surface and also in the cracks. Finally, the sample distintegrates into powder. Pesting of Mo(Si,Al)₂ occurs in the same way, however, its rate is much lower than that of MoSi₂. The role of Al is to decrease the initial crack density of the samples from the melt. Other effects of Al might be to decrease the oxygen flux toward the oxide-intermetallic interface and to increase the plasticity of the amorphous oxide being formed in the cracks.     

(Mo1-x,Wx)Si2固溶体的价电子结构及其性能研究

根据固体与分子经验电子理论(EET),利用平均原子模型对(Mo1-x,Wx)Si2固溶体进行价电子结构分析,并分别与MoSi2和WSi2基体进行比较。结果表明,随着x值的增加,(Mo1-x,Wx)Si2固溶体的主干键络键能、最强键上共价电子数和共价电子总数百分比均逐渐增加,表明固溶体的熔点、硬度和强度均逐渐增加。     

Oxidation behavior of MoSi2 and Mo(Si,Al)2 coated Mo–0.5Ti–0.1Zr–0.02C alloy

MoSi₂ and Mo(Si, Al)₂ coatings were prepared on Mo–0.5Ti–0.1Zr–0.02C alloy using pack cementation process. Oxidation studies revealed that Mo(Si, Al)₂ coating had a much superior oxidation resistance in the temperature range from 400 to 900 °C, where pest disintegration of MoSi₂ occurs due to internal oxidation. The growth kinetics of Al₂O₃ layer formed on Mo(Si, Al)₂ coating was much slower than that of SiO₂ layer formed on MoSi₂ coatings during oxidation.     

Temperature dependence of single-crystal elastic constants of Mo(Si,Al)2

The temperature dependence of single-crystal elastic constants of Mo(Si,Al)₂ with the hexagonal C40 structure has been measured by the rectangular parallelepiped resonance method over the temperature range from room temperature to 1373 K. The silicide has the largest value of Poisson's ratio among transition-metal silicides with the C40 structure. This is interpreted in terms of the reduced directionality in atomic bonding due to the partial substitution of Al for Si atoms. The expression of the elastic constants on the basis of simple interatomic interactions cannot reproduce the elastic anisotropy of crystal with the C40 structure. The disagreement is considered to be a consequence of the occurrence of internal displacements during elastic deformation in crystals with the non-centrosymmetry.