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。     

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体系的起始反应温度,为950℃,并根据溶液热力学分析了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组织.     

Low-cycle fatigue behavior of in situ TiB2/Cu composite prepared by reactive hot pressing

Copper-based composite reinforced with in situ TiB₂ particulates was prepared through reactive hot pressing of Ti, B and Cu powders. The formation of in situ TiB₂ particulates was verified by the X-ray diffraction technique. Tensile test showed that fine TiB₂ particulates were very effective to increase the tensile and yield strengths of copper at the expense of tensile ductility. Strain-controlled low-cycle fatigue measurements demonstrated that the in situ TiB₂/Cu composite exhibited essentially stable cyclic stress response behavior under small total strain amplitudes of 0.1–0.3%. However, this composite exhibited slight cyclic hardening under strain amplitude of 0.4%. Such cyclic hardening was more pronounced at a total strain amplitude to 0.6% due to the formation of dislocation cells and networks. Finally, the fatigue life data of the in situ TiB₂/Cu composite can be described by the Coffin–Manson equation.     

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.     

Preparation of Al-20Si-4.5Cu alloy and its composite from elemental powders

Hypereutectic Al-Si-Cu alloys with a low thermal expansion coefficient and good wear resistance are commonly prepared from pre-alloyed powders using atomization. In the present work, an attempt was made to explore the possibility of fabricating the materials from cheaper elemental powders through sintering the compacts of the mixture of a silicon powder and an Al-4.5Cu elemental powder in the liquid state. Another advantage of taking this fabrication route is that it gives an additional flexibility to incorporate Al₂O₃ particles into the alloys to form aluminium matrix composites with a further improved Young's modulus, dimensional stability and wear resistance. Due to the change in the phase constitution brought about by the silicon addition, the sintering scheme for the Al-Cu elemental powder must be modified. The results show that it is well possible to take advantage of the good sinterability of the Al-4.5Cu elemental powder, to maintain the dimensions of the Al-20Si-4.5Cu compacts and to hold their shape during liquid-phase sintering. After consolidation with hot extrusion and heat treatment, the materials show an improved Young's modulus and a lowered thermal expansion coefficient at the sacrifice of strength and ductility. The success in using the elemental powders to produce the hypereutectic Al-Si-Cu alloys and their composites opens up a new flexible and economic way to tailor the properties of the materials.     

Cold spraying of in situ produced TiB2–Cu nanocomposite powders

The goal of this work was to study the development of microstructure of the coatings cold sprayed from nanocomposite powders TiB₂–43 vol.%-Cu containing titanium diboride particles 50–100 nm in size. Titanium diboride phase was in situ produced in a copper matrix using high-energy mechanical milling of Ti, B and Cu powders and self-propagating high-temperature synthesis. The coatings were fabricated on a copper substrate. The microstructure of the coatings was studied by scanning electron microscopy and energy dispersive spectroscopy. Due to low-temperature conditions of spraying, nanostructured coatings were produced retaining the microstructure of the nanocomposite powder being sprayed. Despite the high content of titanium diboride and the difference in plasticity of the phases, the coatings were fully dense and composed of closely packed powder particles. Considering the results of this study, cold spraying of nanocomposite mechanically milled powders can be recommended as a promising way for fabrication of nanostructured coatings.     

Wear behaviour of aluminium matrix TiB2 composite prepared by in situ processing

Abstract

The wear behaviour and microstructure of aluminium and Al-12Si alloy (A413) matrix composites containing 1 and 5 vol.-%TiB₂ particles have been investigated. The composites were prepared by an in situ reactive slag technique. The wear surfaces and wear products were studied after reciprocating and rolling - sliding tests. Wear resistance increased with increasing particle content, and the Al-12Si composites were more wear resistant than those with Al matrixes. The wear mechanisms are briefly discussed.     

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.     

Study on squeeze casting of an in situ 5 vol.-% TiB2/2014 Al composite

Abstract

An in situ 5 vol.-% TiB₂/2014 composite was prepared by an exothermic reaction of K₂TiF₆, KBF₄ and Al melts. The effect of introduction of in situ formed TiB₂ particles on the squeeze-casting formability of the composite was discussed. The microstructural evolution and changes in the mechanical properties of the composite at different squeeze pressures were investigated. The results showed that a pouring temperature of 710°C, a die temperature of 200°C and a squeeze pressure of 90 MPa were found to be sufficient to get the qualified squeeze cast and maximum mechanical properties for an Al 2014 alloy. However, the pouring temperature, die temperature and squeeze pressure need to be increased to 780°C, 250°C and 120 MPa for the composite to get the qualified squeeze cast and maximum mechanical properties as a result of the effect of introduction of in situ formed TiB₂ particles on the solidification process, plasticity and fluidity of the composite. The microstructural refinement, elimination of casting defects such as shrinkage porosities and gas porosities and improved distribution of TiB₂ particles in the case of the composite result when pressure was applied during solidification. Compared with the gravity-cast composite, the tensile strength, yield strength and elongation of the squeeze-cast composite at 120 MPa increased by 21%, 16% and 200%.     

Preparation and electrical erosion resistance of TiB2/Cu nanocomposites

A procedure is described for producing nanocomposite TiB₂/Cu powders containing up to 57 vol % TiB₂. Using shock compression of composite powders, we have prepared electrode materials offering enhanced electrical erosion resistance at high arc discharge currents. The effect of titanium diboride nanoparticles embedded in the copper matrix on the erosion behavior of the nanocomposites is examined. The nanoparticles are shown to suppress the copper droplet entrainment during the service of the electrode. TiB₂/Cu nanocomposite electrodes containing more than 10 vol % TiB₂ retain their shape and dimensions in the course of electrical erosion tests and offer enhanced service life.     

TiB2/Cu金属基复合材料的研究

重点介绍了非原位复合法与原位复合法制备TiB2/Cu复合材料的过程及材料性能,归纳总结了纳米弥散强化铜合金的结构特点.     

Interfacial reactions in a Ti-6Al-4V based composite: role of the TiB2 coating

The characterization of TiB₂/C-coated SiC fibres and their interface region in a Ti-6Al-4V based composite has been performed by using scanning electron microscopy (SEM), energy-dispersion X-rays (EDX) and Auger electron spectroscopy (AES). The features of the as-received fibre and the reactivity between fibre and matrix occurring during preparation of the composite have been studied in this paper. The interaction of the TiB₂ external coating of the fibre with both the adjacent carbon layer and the titanium-based matrix is already appreciable in the as-received composite: TiB needles grow from TiB₂ towards the matrix and a new layer containing C, Ti and B appears between TiB₂ and C. The thicknesses of the original carbon and TiB₂ fibre coatings decrease in the composite from 1000 nm to 400 and 800 nm, respectively. The TiB₂ inhibits the reaction between SiC and Ti: there is no evidence of Si _x Ti _y brittle phases.     

The structure of stircast Al-6Cu

A series of batch-type stirring experiments have been performed to investigate the morphological changes in the growth of the primary solid phase in Al-6Cu(Al-6 wt% Cu), as a function of the cooling rate and the rotational speed of the stirrer. The experiments show, that the cell-spacings of primary particles in stircast microstructures increase as a result of stirring, when compared to secondary dendrite arm spacings in the unstirred alloy. This result can be explained regarding heat transport during solidification. It is suggested that the solid-liquid interface of floating crystals in bulk metal liquids is cellular.Al-6Cu refers to the alloy Al-6 wt% Cu, which may also be written as AlCu6.     

Microstructural characterization and ablation mechanism of TiB2/(Cu,Ni) melt-infiltrated ceramic composite

In this study TiB₂/(Cu,Ni) melt-infiltrated composites with the TiB₂ volume content of 81.6% were prepared by mean of pre-sintering of the as-pressed TiB₂ preform and melt-infiltration processing. The thermal ablation behavior of TiB₂/(Cu,Ni) composite was conducted by plasma arc heater. The microstructure, interfacial bonding and ablation behavior were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) pattern. The ablated morphology of cross-section includes three parts: ablated region, transition region and matrix region. The microstructure analysis after ablation experiment reveals a clue of redistribution of infiltrated (Cu,Ni) phase so as to analyze and explain the functioning of transpiration cooling.     

温度梯度对定向凝固Al-4.5%Cu合金一次枝晶间距的影响

使用5kg坩埚下拉式定向凝固设备,对Al-4.5%Cu合金进行定向凝固试验,研究Al-4.5%Cu合金在不同温度梯度下一次枝晶间距的变化规律。结果表明:在其他凝固参数不变时,随着温度梯度的增大,一次枝晶逐渐变小,细密,挺直,基本呈平行状分布,同时计算的一次枝晶间距值与Hunt模型计算值接近,实验测得的一次枝晶间距的回归曲线为:y=2843478.3x2-70217.4x+543.8。用温度梯度较高的实验值来模拟时,可得到1λ=26.7G-0.5-135.9,一次枝晶间距λ1与G-0.5基本呈线性关系,这和Hunt模型分析结果一致。