The microstructure and mechanical properties of TiC and TiB2-reinforced cast metal matrix composites

TiC and TiB₂ particles have been spontaneously incorporated into commercial purity aluminum melts through the use of a K-Al-F-based liquid flux that removes the oxide layer from the surface of the melt. The combination of spontaneous particle entry and close crystal structure matching in the Al-TiB₂ and Al-TiC systems, results in low particle-solid interfacial energies and the generation of good spatial distributions of the reinforcing phase in the solidified composite castings. The reinforcement distribution is largely insensitive to the cooling rate of the melt and the majority of the particles are located within the grains. Modulus increases after TiC and TiB₂ particle additions are greater than those for Al₂O₃ and SiC. It is thought that interfacial bonding is enhanced in the TiC and TiB₂ systems due to wetting of the reinforcement by the liquid and particle engulfment into the solid phase. TiC-reinforced composites exhibit higher stiffnesses and ductilities than TiB₂-reinforced composites. This has been attributed to stronger interfacial bonding in the Al-TiC system, due to the increased tendency for nucleation of solid on the particle surfaces.     

原位TiB晶须和TiC颗粒复合增强Ti复合材料的压缩性能及微观结构

采用反应热压方法制备了原位TiB晶须和TiC颗粒复合增强钛复合材料,对复合材料进行了高温压缩试验,对变形前后的微观结构进行了分析。在350-650℃温度范围内,复合材料的强度均明显高于钛基体。原位增强相与钛基体具有良好的界面结合,压缩变形后在钛基体中产生大量的形变孪晶。     

Effects of Sr on the microstructure and mechanical properties of in situ TiB2 reinforced A356 composite

In situ A356–3 wt.% TiB₂ composites were fabricated via a remelting and diluting (RD) approach, to investigate the effect of Sr on the modification of in situ A356–TiB₂ composites with respect to the composite prepared by the conventional flux assisted synthesis (FAS) approach. The tensile properties of the composites were tested to evaluate the modification efficiency of Sr in different approaches. The results demonstrated that the RD composite can achieve fully modified eutectic structures than the FAS one owing to avoidance of the Sr–B interaction, which is commonly encountered in the FAS composites. The addition of Sr greatly improves the mechanical properties (especially the elongation) of thus prepared composites, only when the composites are in a fully modified state. Optimum modification of in situ A356–3 wt.% TiB₂ composite was obtained with Sr addition in the range around 0.03 wt.%. The elongation of the 0.03 wt.% Sr modified RD A356–3 wt.% TiB₂ composite are 6.6% and 5.6%, in as-cast and T6 states, respectively. The improvements in strength and ductility are attributed to the morphology change of Si as well as the improved melt cleanliness.     

Hot deformation behavior of in situ synthesized Ti composite reinforced with 5 vol.% (TiB + TiC) particles

In this paper, 5 vol.% (TiB + TiC)/Ti-1100 composite was fabricated using in situ techniques. Hot-deformation behavior of the composite was studied by hot compression tests in the temperature range 1,000–1,150 °C under different strain rates. It was found that solid solute C element in Ti matrix has obvious effect on the hot-deformation behavior of the composite by increasing the (α + β)/β transus temperature. Variation in the volume ratio of α/β phase and the effect of reinforcements result in a change in hot-deformation behavior of the composite. The effect of reinforcements on hot deformation behavior of the composite is more obvious in the (α + β) phase field than in the β phase field.     

Dry sliding wear behavior of extruded titanium matrix composite reinforced by in situ TiB whisker and TiC particle

The dry sliding wear behavior of titanium matrix composite (TMC) reinforced by in situ TiB whisker and TiC particle was investigated. Compared to the unreinforced pure Ti matrix, the TMC exhibited a markedly improved wear resistance due to the existence of the ceramic reinforcements. The TMC showed lower friction coefficient than the pure Ti. The mean values of steady-state friction coefficient of the TMC and pure Ti against a tool steel were about 0.270–0.330 and 0.385–0.395, respectively, under the loads of 40–100 N. Meanwhile, the TMC showed lower weight loss and its surface wearing was less severe compared to that of the pure Ti. The worn surface of the TMC was covered with mild grooves and some fine wear debris, which exhibited the characteristic of both adhesive and abrasive. TiO₂ was found on the worn surface due to the oxidation behavior of the Ti matrix, which may reduce the wear tendency of the TMC. The results show that the in situ ceramic reinforcements could greatly increase the wear resistance of pure Ti.     

Processing, microstructure and mechanical properties of nickel particles embedded aluminium matrix composite

Nickel particles were embedded into an Al matrix by friction stir processing (FSP) to produce metal particle reinforced composite. FSP resulted in uniform dispersion of nickel particles with excellent interfacial bonding with the Al matrix and also lead to significant grain refinement of the matrix. The novelty of the process is that the composite was processed in one step without any pretreatment being given to the constituents and no harmful intermetallic formed. The novel feature of the composite is that it shows a three fold increase in the yield strength while appreciable amount of ductility is retained. The hardness also improved significantly. The fracture surface showed a ductile failure mode and also revealed the superior bonding between the particles and the matrix. Electron backscattered diffraction (EBSD) and transmission electron microscopy analysis revealed a dynamically recrystallized equiaxed microstructure. A gradual increase in misorientation from sub-grain to high-angle boundaries is observed from EBSD analysis pointing towards a continuous type dynamic recrystallization mechanism.     

Preparation of in situ TiCP/LY12 composite and its microstructure and mechanical properties

Mechanical properties of TiC_P/LY12 Al-based composites prepared by an in situ synthesis method were studied. The micro-structure, morphology, and distribution of TiC_p particles in the LY12 Al alloy matrix were also investigated by XRD, SEM, and HRTEM. The phase composition of the TiC_P/LY12 composites, interfacial structure of TiC particle-to-particle and TiC particle-to-Al matrix, and structure of triple phase among TiC particle, Al₂Cu phase, and Al matrix were also studied. There are no detectable Al₃Ti phases in TiC_P/LY12 composites, and a strong cohesive interface between TiC particles and Al-based alloy matrix was observed in the in situ synthesized TiC_P/LY12 composites. After heat treatment using T6 procedure, it was found that ultimate strength (σ_b), yield strength (σ_s), and Young's modulus (E) of TiC_P/LY12 composites increased but the elongation ratio decreased with increasing of the mass fraction of TiC particles.     

脉冲磁场下原位合成TiB2/7O55铝基复合材料的组织和力学性能

脉冲磁场下,采用7055-(Al-3％B)-Ti剂体系熔体原位反应法成功制备TiB2/7055铝基复合材料.利用XRD、OM和SEM等测试技术研究了复合材料的相组成和微观组织,同时在电子拉伸试验机上测试了复合材料的拉伸性能.结果表明,磁场作用下,原位反应更快更充分,颗粒分布更均匀,生成的TiB2颗粒呈六边形或多边状,平均尺寸约为600nm,α-Al晶粒细化到约10～20μm,第二相由连续网格状分布转变为非连续性分布.复合材料的抗拉强度从310MPa提高到333MPa,延伸率从7.5％提高到了8.0％.     

铝基材料TIG焊填充材料对接头组织性能的影响

采用TIG焊方法焊接铝基复合材料,讨论了填充材料钛对焊缝综合性能的影响及填充材料的厚度与焊缝中生成物之间的关系.研究表明:填充材料的加入,提高了熔池的流动性,使得焊缝中的孔洞、未熔合明显减少;在高温下钛优先与增强颗粒SiC发生原位反应,从而抑制了有害相Al4C3,的生成,而且生成的TiC颗粒在焊缝中起增强作用;接头的机械性能与填充材料的厚度有着密切关系,填充材料的厚度过小,抑制有害反应的作用减弱,填充材料的厚度过大,则焊缝的脆性增大,本实验条件下填充材料厚度为0.45mm时获得最佳接头.     

微合金化对TiB2颗粒增强铝基复合材料微观组织和力学性能影响的研究进展

微量添加合金元素是改善铝基复合材料综合性能的有效方法,是基于电磁搅拌、超声振动等物理工艺,双峰结构、仿生层状材料等制备技术之外改善增强相/基体界面结构、调控强度-韧性力学性能的一种行之有效的低成本技术.近年来,合金元素在TiB2颗粒增强铝基复合材料中的研究备受关注,取得了一定的成果,对其作用机理的理解也向纳米层级甚至原子层级迈进.本文归纳了国内外微量添加合金元素对TiB2/Al复合材料中TiB2颗粒形貌、微观组织、力学性能的一系列最新进展,阐述了微合金化机制,并展望了其在调控复合材料裂纹萌生与扩展、发挥微纳尺度本征力学性能、协调材料强度和韧性矛盾中的潜在价值,以期为制备高性能铝基复合材料提供借鉴和参考.     

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.     

The mechanical properties and microstructure of SiC–AlN particulate composite

Silicon carbide (SiC) and aluminium nitride (AlN) were found to form a solid solution at temperatures above 1800°C. Based on this interesting result, the composite was fabricated by mechanical mixing of the SiC and AlN powders, and hot pressed under 40 MPa at 1950°C in an argon atmosphere. The objective was to achieve full density and minimize solid solution formation. During the sintering process, the SiC–AlN system passed through three steps to form the solid solution at the end. First, the AlN particle is vaporized from its surface; next, the evaporated AlN is deposited on the surface of the SiC grains and the AlN particle, accompanied by a reduction in its size, and finally, partial SiC and AlN solid-solution formation on the boundary of the SiC grains. Because of the AlN deposition and solid-solution formation at the boundary of SiC grains, a barrier layer was present on the surface of SiC grains. This leads to the formation of fine grains. The toughening mechanism is thought to be by thermal residual stresses, due to the difference between the coefficients of thermal expansion of the matrix SiC and that of the dispersed AlN particles, and crack deflection around the SiC grains. Therefore, it is that which improves the mechanical properties of the SiC–AlN composite. © 1998 Chapman & Hall     

Effect of Mo addition on the microstructure and wear resistance of in situ TiC/Al composite

In this work, Mo was investigated as an additive for in situ preparation of TiC/Al composite using a casting route assisted by self-propagating high-temperature synthesis (SHS). Experimental results show Mo improves the wettability between TiC phase and aluminium melt due to the formation of a Mo-rich shell around the formed TiC particles, which is a kind of good modificator. Compared with the composite without added Mo, 1.0 wt.% Mo addition developed finer matrix structure, significant refinement of TiC particles and more uniform distribution of TiC particles in the matrix. Meanwhile, both wear and tensile properties of TiC/Al composite were improved with 1.0 wt.% Mo addition and then deteriorated with the further increase of Mo content due to the formation of fragile phase Al₅Mo.     

The effect of microstructure and texture on mechanical properties of Ti6-4

The widely used titanium alloy, Ti6-4, is available in several different microstructural conditions, with variations being due to a number of factors including processing route and subsequent heat treatments. These differing microstructures can produce significant variations in the fatigue life of the material and as such it is essential that predictions can be made about the fatigue performance based on the microstructural condition. The paper examines six microstructural variations of Ti6-4 and seeks to identify trends within strain control data, and the subsequent effect on notched specimen behaviour, used to characterise the effect of stress raising features in engineering applications.     

微合金化对Ti基非晶复合材料的组织和力学性能的影响

采用悬浮熔炼-水冷铜模吸铸法制备了(Ti0.5Ni0.5-xZrx)80Cu20(x=0,0.02,0.04,0.06和0.08)。通过对Zr的添加量的控制制备具有组织连续梯度的非晶复合材料,研究其组织和力学行为及微量Zr的添加对此非晶复合材料的组织和力学性能的影响。结果表明,凝固过程的温度梯度决定了复合材料的组织梯度,由表及里,主要为非晶相、马氏体相和奥氏体树枝晶相。铸态非晶基体上析出了B2-Ti(Ni,Cu)过冷奥氏体相和B19’-Ti(Ni,Cu)热诱发马氏体相,加载断裂后应力诱发马氏体相变,马氏体衍射峰比铸态增强且马氏体择优取向。随着Zr的不断添加,此系列非晶合金非晶形成能力先提高后降低,奥氏体含量不断下降,相变诱发塑性减弱,从而塑性逐级递减,强度先升高后降低。     

Investigation of the Young''s modulus of TiB needles in situ produced in titanium matrix composite

In situ Ti/TiB composites with different volume fractions of discontinuous TiB reinforcements were produced by powder metallurgy. After compacting Ti+TiB₂ powders by hot unidirectional pressure, heat treatments led to the in situ formation of distinctive needles of TiB, randomly distributed in the titanium matrix. The Young's modulus of TiB was evaluated using the ASW computation method and experimental Vickers micro-indentation. Three point bend tests were performed on Ti/TiB composites as a function of the TiB volume fraction in order to extract the Young's modulus of TiB from the elastic properties of the composite. The different values obtained according to these three methods were discussed and compared with the literature.     

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。     

Investigation on microstructure and mechanical properties of reactively synthesized TiAlN/AlON nanomultilayers

The novel TiAlN/AlON nanomultilayers with different AlON layer thickness were synthesized by reactive magnetron sputtering. The microstructure and mechanical properties were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM) and nano-indentation techniques. The results indicated that, under the template effect of fcc (face-centered cubic) TiAlN layers, originally amorphous AlON layers were crystallized and grew epitaxially with TiAlN layers when AlON layer thickness was below 0.7 nm. Accordingly, the hardness and elastic modulus of the nanomultilayers increase and reach the maximum values of 36.2 and 385.6 GPa, respectively. With further increase of AlON layer thickness, AlON layers transformed back into amorphous state and broken the coherent growth of nanomultilayers, leading to the decrease of hardness and elastic modulus. The strengthening mechanism of TiAlN/AlON nanomultilayers was further discussed.     

The microstructure and mechanical properties of Al-Si-B4C metal matrix composites

B₄C particles have been added to molten Al- 7wt% Si- 0.3 wt% Mg alloys, at levels of 5 and 10 wt%, using a propriatory K-Al-Ti-F flux. The resulting composites were examined metallographically and mechanically tested in the as-manufactured condition and after heat treatment for 48 hours at 500°C and 700°C. During incorporation into the melt, a complex Ti-B-C reaction layer was formed on the particle surfaces. The reaction layer remained intact during heat treatment and the stable, protective nature of this layer gave rise to a significantly reduced rate of particle degradation compared to other Al-B₄C composites. Significant increases in stiffness were observed; modulus increases per volume percent of particles added were similar to those for the Al-TiC system where strong interfacial bonding occurs. Improved adhesion between the solidified matrix and the B₄C reinforcement was encouraged by the enhanced metallic character of the reaction layer. Solid state reaction at 500°C produced little change in mechanical properties. Heat treatment and reaction at 700°C resulted in an increase in the volume fraction of stiff, brittle reinforcing phases, leading to an increase in stiffness and a decrease in ductility.