Assessment of B4C reaction with liquid iron alloys

The degree of reaction achieved when B₄C powders are brought into contact with liquid iron alloys has been assessed by a levitation dispersion test. Reaction occurs rapidly, leading to boron carbide dissolution and iron boride formation. In carbon-free iron alloys borocarbide, Fe₂₃(C, B)₆, also forms and in low-carbon iron alloys free graphite was also formed. Highcarbon alloys reacted to form both Fe₃(C, B) and free graphite. Attempts to provide protection for the B₄C by forming a TiC coating on its surface byin situ reactions with liquid Fe-Ti and Fe-Ti-C alloys proved unsuccessful, with TiC forming as a dispersed phase throughout the iron matrix     

Physical properties of some iron based alloys in liquid and amorphous states

The atomic structure and the physical properties of amorphous ribbons depend strongly on the state of the melt before quench. It is known that slightly above liquidus metallic melts can preserve a non-equilibrium metastable state for a long time. Moreover some structural transformations in liquid metallic alloys, similar to phase transitions in solids, may take place with an increase of the temperature. In this paper we report measurements of the viscosity, magnetic susceptibility and surface tension in some Fe-based melts. Amorphous ribbons of the same alloys were prepared by standard planar method from different states of the melt. The electrical resistivity, the kinetics of crystallization and the magnetic properties of the ribbons were investigated. It was found that the properties depending upon nanoscale inhomogeneities are different for ribbons produced after different heat treatments of the melt before quench.     

Vacuum diffusion bonding of TiB2 cermet to TiAl based alloys

Abstract

Vacuum diffusion bonding of TiB₂ cermet to TiAl based alloys was carried out at 1123 – 1323 K for 0.6 – 3.6 ks under 80 MPa. The microstructural analyses indicate that a compound Ti(Cu, Al)₂ is formed in the interface of the TiB₂ /TiAl joints, and the width and quantity of the Ti(Cu, Al)₂ compound increase with the increase of the bonding temperature and bonding time. The experimental results show that the shear strength of the diffusion bonded TiB₂ /TiAl joint is 103 MPa, when TiB₂ cermet is bonded to TiAl based alloy at 1223 K for 1.8 ks under 80 MPa.     

Microstructure and mechanical behavior of AlSiCuMgNi piston alloys reinforced with TiB2 particles

AlSiCuMgNi piston composites reinforced with in-situ TiB₂ particles were fabricated by mixing salts reaction process successfully. Microstructures of the composites were observed by mean of scanning electron microscope (SEM) and transmission electron microscope (TEM). X-ray diffraction (XRD) was used to identify the phases in the composites. TiB₂ reinforcement grows in equiaxed or near equiaxed shape and the interfaces between reinforcements and matrix are clear. Compared with the matrix alloys, the composites show an obvious aging peak and an incubation time in the hardness. The aging is accelerated in the composites reinforced with TiB₂. At room temperature, the ultimate tensile strength (UTS) of the composites increases as the percentage of TiB₂ reinforcement increases. When the temperature is beyond 250°C, the ultimate tensile strength of the piston composites decreases sharply. The fracture surfaces of the piston composites are analyzed.     

纳米SiO_2粉体在水泥液相中的分散性

针对纳米SiO_2存在颗粒团聚现象,借助LS13320激光粒度仪、SEM和TEM测试手段,研究水泥液相中纳米SiO_2粉体的粒度分布及其分散性。通过超声脉冲技术分散纳米SiO_2粉体,并确定最优超声功率;研究表面活性剂添加顺序对水泥液相中纳米SiO_2粒度分布的影响。结果表明:超声脉冲与表面活性剂协同作用为纳米SiO_2最佳分散方式;获得纳米SiO_2最佳粒度分布的实验条件为超声时间5 min、超声功率360 W;在纳米SiO_2加入到水泥液相之后再加入表面活性剂,这种添加顺序更有利于提高纳米SiO_2分散性。     

SiC晶须对反应合成多孔TiB_2-TiC复合材料的影响

以Ti、B_4C和SiC晶须(SiC_w)为原料,采用自蔓延高温合成法制备了多孔TiB__2-TiC复合材料。讨论了SiC_w含量对TiB__2-TiC复合材料物相、组织形貌、孔隙率和抗压强度的影响。结果表明:不添加SiC_w时,复合材料中主要物相为贫硼相TiB和Ti_3B_4以及TiC和少量TiB__2;在5Ti+B_4C体系中加入SiC_w后,贫硼相TiB和Ti_3B_4逐渐减少直至消失,而出现富硼相TiB__2和TiC的含量增加。随着SiC_w含量的增加,复合材料的孔隙率逐渐增加,由38.46%增加至5_2.78%。当SiC_w含量小于1.0时,随着SiC_w含量的增加,多孔TiB_2-TiC复合材料的抗压强度明显增加,当SiC_w含量为1.0时,复合材料的抗压强度达到最大值56.04MPa。Ti与SiC_w反应会生成TiC、Ti_3SiC_2和TiSi_2等物相,消耗一定量的Ti,使得与B4C反应的Ti量减少,从而促进富硼相TiB_2形成和TiC的增多。并且在SiC_w表面形成颗粒状TiC或者层片状Ti_3SiC_2,增加SiC_w与TiB_2-TiC基体之间的结合,更有利于发挥SiC_w的强化作用。     

CeO2 induced dispersive distribution of TiB2 particles in in situ TiB2/Al composite

Abstract

The roles of CeO₂ additive during preparation of in situ TiB₂/Al composite, alleviating particle settlement in composite melt and significantly improving particle dispersion in final microstructure, are studied in this paper. It is evidenced that the CeO₂ additive reacts with Al melts to release Ce solute into the melts, and the released surface active Ce is absorbed in the Al/TiB₂ interfaces without any other reaction products. First principles calculations show that the interfacial energy of Al/TiB₂ interfaces is reduced owing to the presence of Ce in Al/TiB₂ interfacial area. Therefore, the wettability of molten Al on TiB₂ surface is increased and the dispersion of TiB₂ particles in Al matrix is eventually improved.     

Thermal expansion of TiAl + TiB2 alloys and model calculations of stresses and expansion of continuous fiber composites

Thermal expansion values for three TiAl alloys with different additions of TiB₂ can be represented using a third-order equation at temperatures between 20 and 800°C. Expansion values were obtained on both heating and cooling temperature cycles. The total expansion at 800°C is between 0.917 and 0.931% for three different samples. The expansivity increases from about 10×10^–6°C^–1 at 80°C to 14×10^–6°C^–1 at 750°C. A five-coaxial cylinder elastic model for multizone-coated continuous fiber composites is developed for predicting stresses and thermal expansion of composites. Either isotropic or transversely isotropic material properties can be assigned to the various cylinder zones.Paper presented at the Tenth International Thermal Expansion Symposium, June 6–7, 1989, Boulder, Colorado, U.S.A.     

Dispersion of iron aluminide with polyelectrolyte in water

A stable dispersion of iron aluminide (FeAl) intermetallic powders was achieved in water using ammonium salt of poly(methacrylic acid) (PMAA-NH₄). The electrosteric stabilization was identified to be the prevailing mechanism. pH value correlates inversely with the amount of PMAA-NH₄ adsorbed onto the surface of FeAl particle. The aqueous FeAl solution stabilized by PMAA-NH₄ displays a Newtonian behavior as revealed by rheological measurements.     

Temperature dependence of fracture toughness in cleavage fracture of iron and iron alloys

In order to examine the temperature dependence of fracture toughness in cleavage fracture, exploratory work was carried out. Then effects of alloying elements and micro-structure on the low temperature fracture toughness were studied quantitatively in iron and iron alloys.The results indicate that (1) the relationship between fracture toughness G_ic and testing temperature T at low temperatures is G_ic = G_o exp (T/T_e), where G_e and T_o are the material constants; (2) G_o exhibits a stro dependence on solute carbon and nitrogen contents but is independent of micro-structure and other elements; (3) G_o values increases with increasing solute carbon and nitrogen contents; (4) T_o depends on the structure; (5) $\text{1}\text{T}{}_{\mathrm{o}}$ values increase with increasing nickel and manganese contents, to the contrary, decrease with increasing carbon, silicon and phosphorus contents; and (6) $\text{1}\text{T}{}_{\mathrm{o}}$ values increase with decreasing grain size.     

Solid-solution hardening and softening in binary iron alloys

Six dilute (0.2, 0.5 and 1 at %) binary iron-base alloys with Co, Cr, Al, Si, Mn and Ni were prepared after scavenging inherent carbon with Ti. From tensile and stress relaxation tests in the temperature range of 77 to 450 K, stress-strain behaviours and thermal activation parameters were analysed as functions of solute content and temperature. In the four alloys containing Ni, Mn, Al and Si, solid-solution softening occurs below 250 K while solid-solution hardening occurs above 250 K. In the alloys containing Co or Cr, neither softening nor hardening due to solute additions occurs at any temperature. Detailed analysis of thermal activation parameters leads one to conclude that the solid-solution softening in the above mentioned four alloys is due to a decrease in kink energy with increasing solute content, while in the latter two alloys no change in kink energy occurs. On the other hand, there exists a strong solute concentration dependence of the athermal component, suggesting that the solid-solution hardening is due to the interaction of dislocations with groups of substitutional solute atoms that create lattice and modulus misfits.     

TiB2材料的研究现状

TiB2材料作为一种新型先进材料,由于具有强度高、硬度高、耐磨损、耐腐蚀、熔点高、蒸气压低、导电性良好等优点而被广泛研究。介绍了TiB2材料的晶体结构与性质及其制备方法,包括直接合成法、碳热法、镁热法、溶胶-凝胶法、化学气相沉积法等,并分析总结了TiB2材料的致密化、涂层、复相陶瓷、微纳米结构等应用研究热点。其中,将两种或多种方法结合起来制备TiB2,已成为降低成本、减少污染、优化性能的重要途径。