Fabrication and mechanical properties of in situ formed carbide particulate reinforced aluminium composite

Stable carbide particles of TiC, ZrC and TaC were in situ synthesized in liquid aluminium by the reaction between Al-Ti, Al-Zr or Al-Ta systems liquid alloy and SiC or Al₄C₃ particles. It was possible to generate TiC particles of nearly 1 m diameter, even utilizing SiC of 14 m. However, the dispersion behaviour of TiC particles in the matrix depended on the size of the raw carbide. Finer SiC made the dispersion of TiC particles more uniform, resulting in a greater improvement of the mechanical properties. Furthermore, although Al-Ti-Si system intermetallic compound was detected in a TiC_p/Al-Si composite fabricated by the melt-stirring method, those compounds considerably decreased in the composite fabricated by the in situ method. The mechanical properties of in situ formed TiC_p/Al-5 wt% Mg and TiC_p/Al-5 wt% Cu composites were better than those fabricated by the melt-stirring method and by T6 heat treatment, the properties of in situ formed TiC_p/Al-5 wt% Cu composite were further improved. The experimental results were analysed by the reaction model based on the assumption that the overall reaction rate was controlled by both the reaction and the diffusion.     

Production and wear characterisation of AA 6061 matrix titanium carbide particulate reinforced composite by enhanced stir casting method

Metal matrix composite (MMC) focuses primarily on improved specific strength, high temperature and wear resistance application. Aluminium matrix reinforced with titanium carbide (Al–TiC_p) has good potential. The main challenge is to produce this composite in a cost effective way to meet the above requirements. In this study Al–TiC_p castings with different volume fraction of TiC were produced in an argon atmosphere by an enhanced stir casting method. Specific strength of the composite has increased with higher % of TiC addition. Dry sliding wear behaviour of AMC was analysed with the help of a pin on disc wear and friction monitor. The present analyses reveal the improved specific strength as well as wear resistance.     

A novel heat-resistant Al–Si–Cu–Ni–Mg base material synergistically strengthened by Ni-rich intermetallics and nano-AlN_p microskeletons

In this work, nano-AlN particle(nano-AlN_p) microskeletons were introduced into an Al–Si–Cu–Ni–Mg alloy by Al–8 AlN master alloy in which the nano-AlN_p reinforcements connect with each other to form three-dimensional networks. It is found that these nano-AlN_p microskeletons mainly distribute in the binary Al–Si eutectic zones resulting in flaky eutectic Si phases being modified to particulates. Meanwhile,the microskeletons strengthen the matrix synergistically with semi-continuous Ni-rich intermetallics in three dimensions. The tensile mechanical properties, micro-hardness and thermal expansion properties of the alloy at different temperatures are significantly improved. Especially, the ultimate tensile strength(UTS) at 350℃ increases from 85MPa to 106MPa, rising by 24.7%, which is ascribed to nano-AlN_p microskeletons assisting intermetallics with undertaking mechanical loading, and to the modification of eutectic Si phases to reduce the stress concentration at elevated temperatures.     

Ductile and strong aluminium-matrix titanium aluminide composite formedin situ from aluminium,titanium dioxide and sodium hexafluoroaluminate

An aluminium-matrix TiAl₃-particle (1–2 m) composite exhibiting high tensile ductility (22%), high tensile strength (235 MPa) and a grain size of 50 m was made by a newin situ method involving reactions between Al, TiO₂ and Na₃AlF₆, which were subjected to stir casting at 900 °C. The strength and ductility were higher than those of an aluminium-matrix TiAl₃-particle Al₂O₃-particle composite madein situ by reacting Al with TiO₂ (without Na₃AlF₆). This is due to the ability of Na₃AlF₆ to enhance the reduction of TiO₂ and Al₂O₃, thus resulting in more TiAl₃ and a smaller grain size.     

Fabrication and Wear Performance of (Cu–Sn) Solution/TiC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Bonded Diamond Composites

The Cu(Sn)–TiC_x bonded diamond composites were prepared by in situ reaction sintering of Cu, Ti₂SnC and diamond powders. Effect of Ti₂SnC content on the phase composition, microstructure and grinding properties were studied. The result shows that Ti₂SnC was decomposed to TiC_x and Sn. And then, Sn atom dissolved into the crystal lattice of Cu and formed Cu(Sn) solution. The rich C formed at the interface between diamond and the matrix. Excess Ti₂SnC inhibited the formation of Cu solid solution and reacted with Cu to form Cu₃Sn. Additionally, its matrix was mainly composed of TiC_x with better wear resistance, which may improve obviously the grinding performance of the composites. The grinding ratio value of copper–diamond composite was only 132. The grinding ratio value of the composite contained higher Ti₂SnC content in the raw materials was 636.     

自生复合Al11La3/Al共晶材料的轴向拉伸性能及其断裂机制

本文研究了自生复合Al₁₁La₃/Al共晶材料从室温到673K时的轴向拉伸性能和轴向拉伸断裂机制.结果表明:在G=700K/cm、R=11.1μm/s的定向凝固条件下,该材料轴向拉伸性能在室温时为260MPa、在673K时为265MPa.对拉伸过程的动态观察和断口形貌的分析表明:自生复合Al₁₁La₃/Al共晶材料在室温到673K温度范围内,其轴向拉伸断裂机制相同:纤维相Al₁₁La₃的断裂是整个共晶体断裂的控制机制:其轴向拉伸的断裂模型为:弹性变形、裂纹萌生、界面脱粘、搭桥过程、宏观断裂.     

Influences of Friction Stir Welding and Post‐Weld Heat Treatment on Al–Cu–Li Alloy

In this paper, the influences of friction stir welding (FSW) and post‐weld heat treatment (PWHT) on the microstructures and tensile properties of Al–Cu–Li alloy are investigated. After FSW, strengthen loss occurred in the welding area. Remarkable softening occurs in the thermo‐mechanically affected zone (TMAZ) resulting from dissolution of Al₃Li (δ′) phases. Recrystallization and precipitation of ultra‐fine δ′ phases take place in the nugget zone (NZ) that lightens the softening degree of this zone. A noteworthy enhancement in the hardness and tensile strength of the joint is achieved after T8 re­aging treatment (3% ? pre‐deformation, 30 h at 152 °C). However, re‐solution treatment coupled with re‐aging treatment leads to ductility deterioration in the joint because coplanar slip of coarse Al₃Li phases induces severe stress concentration during plastic deformation.

     

Accumulative press bonding; a novel manufacturing process of nanostructured metal matrix composites

A new manufacturing process for metal matrix composites has been invented, namely accumulative press bonding (APB). The APB process provided an effective method to produce bulk Al/10 vol.% WC_p composite using tungsten carbide (WC) powder and AA1050 aluminum sheets as the raw materials. The microstructural evolutions and mechanical properties of the monolithic aluminum and Al/WC_p composite during various APB cycles were examined by scanning electron microscopy, X-ray diffractometry, X’pert HighScore software, and tensile test equipment. The results revealed that by increasing the number of APB cycles (a) the uniformity of WC particles in aluminum matrix improved, (b) the porosity of the composite eliminated, (c) the particle free zones decreased and (d) the cluster characteristics improved. Hence, the final Al/WC_p composite processed by 14 APB cycles showed a uniform distribution of WC_p throughout the aluminum matrix, strong bonding between particles and matrix, and a microstructure without any porosity and undesirable phases. The X-ray diffraction results also showed that nanostructured Al/WC_p composite with the average crystallite size of 58.4 nm was successfully achieved by employing 14 cycles of APB technique. The tensile strength of the composites enhanced by increasing the number of APB cycles, and reached to a maximum value of 216 MPa at the end of 14th cycle, which is 2.45 and 1.2 times higher than obtained values for annealed (raw material, 88 MPa) and 14 cycles APBed monolithic aluminum (180 MPa), respectively. Though the elongation of Al/WC_p composite lessened during the initial cycles of APB process, it increased at the final cycles of the mentioned process by 78%. Role of WC particles, uniformity of reinforcement, porosity, bonding quality of the reinforcement and matrix, grain refinement, and strain hardening were considered as the strengthening mechanisms in the manufactured composites.     

Effect of Zr on microstructure and mechanical properties of the Al–Cu–Er alloy

ABSTRACT

The microstructure and mechanical properties of the Al–4Cu–2.7Er–0.3Zr alloy were investigated. The precipitates of the L1₂ structured phase with sizes 37?±?12?nm were formed in lines and homogenously distributed inside the aluminium matrix after annealing at 605°C for 1?h. The as-rolled Al–4Cu–2.7Er–0.3Zr alloy developed an increased hardness after 1?h annealing at 100–550°C and 0.5–6?h annealing at 150–250°C due to precipitation of the Al₃(Er,Zr) phase. Addition of Zirconium improved the tensile properties relative to those of the Zr-free alloy by approximately 20?MPa: yield strength?=?273–296?MPa and ultimate tensile strength?=?296–328?MPa in the alloys annealed at 100–150°C.     

Tensile Strength Evolution and Damage Mechanisms of Al–Si Piston Alloy at Different Temperatures

The Al–Si piston alloys always bear different temperatures because of its peculiar component structure and service condition. Therefore, the tensile strength, elongation to fracture, and corresponding damage mechanisms of Al12SiCuNiMg piston alloys (ASPA) have been investigated with in situ technique at different temperatures. The tensile properties show two‐stage tendencies: the former stage (25–280 °C) is determined by easily broken phases with inherent brittleness (such as primary Si), and the fracture behavior presents rapid brittle fracture after reaching the critical stress (about 430 MPa, based on in situ technique and the elastic stress field model). The later one (280–425 °C) is dominated by particles debonding and θphase coarsening. The plastic deformation behavior, dynamic recovery, and flow process become more significant on account of thermal activation. The Considère criterion h = K indicates that the transition of damage behaviors from insufficient local strength to insufficient matrix strength and the corresponding failure model shifts from brittle to ductile fracture. Based on the damage mechanisms, the elastic field model and thermal activation relation model have been established to characterize the strength of the ASPA at different temperature ranges.

     

A functionally gradient coating on carbon fibre for C/Al composites

A functionally gradient coating on carbon fibre for casting C/Al composites with an ultimate tensile strength up to 1250 MPa (V _f=0.35) has been produced. The coating consisted of three layers: an inner pyrocarbon layer, an outer silicon layer and an intermediate gradient layer C/SiC/Si, and their optimum thicknesses were 0.1–0.15, 0.1 and 0.2 m, respectively. This coating was fabricated by chemical vapour deposition and the C/Al composite was performed by pressure-regulated infiltration. Auger electron spectroscopy and X-ray diffraction analyses confirmed that the structure of the coating was in keeping with its design. The excellent ultimate tensile strength of the C/Al composite also proves that the functionally gradient coating has many functions, including wetting agent, diffusion and reaction barrier, releaser of residual thermal stresses, and tailor of interfacial shear strength. According to the mechanical, physical and chemical coordination between fibre and matrix, the functionally gradient coating can solve nearly all the problems of the interface during fabrication and service.     

Effect of reduced pressure on oxidation and thermal stability of polycarbosilane-derived SiC fibers

To clarify the effects of reduced pressure on the thermal stability of polycarbosilane-derived SiC fibers (Nicalon, Hi-Nicalon and Hi-Nicalon S), the heat-treatments were conducted at 1623 and 1723 K under total pressures (p _T) of 1–10⁵ Pa. The oxidation behavior and thermal stability of the fibers were investigated through examinations of mass change, grain growth, specific resistivity, fiber morphology and tensile strength. All the fibers were definitely oxidized in the active-oxidation regime at p _T 10² Pa and T = 1723 K. Nicalon and Hi-Nicalon S were subjected to serious degradation of fiber strength. Hi-Nicalon had a strength of 1.2 GPa even after heat-treatment at p _T = 1 Pa.     

Evolution of nickel-rich phases in Al–Si–Cu–Ni–Mg piston alloys with different Cu additions

Evolution of nickel-rich phases (Ni-phases) in Al–Si–Cu–Ni–Mg piston alloys is investigated. The qualitative results show that, with the increasing of Cu content, Ni-phases translate from Al₃Ni (ε-phase) or Al₃CuNi (δ-phase) to Al₇Cu₄Ni (γ-phase), and their morphologies change from short-strip to reticular and then annular or semi-annular shape. Moreover, the quantitative calculations by Thermo-Calc software are in accordance with that of experiments’. The evolutions have a great effect on the mechanical properties. The tensile strength at room temperature decreases from 263.8 MPa to 229.6 MPa, and then increases to 278.9 MPa. Otherwise, the elevated temperature tensile strength increases about 19.7%. But the coefficient of linear expansion decreases constantly.     

Elevated temperature tensile properties of squeeze-cast Al-Al2O3-MgO particulate MMCs up to 573 K

Al-Al₂O₃-MgO squeeze-cast composites were prepared using a modified “MgO-coating” technique and their tensile behaviour up to 300°C (573 K) evaluated. In each case, 10 wt% total powder mixture (Al₂O₃ + MgO) containing 15% MgO was stirred into well-superheated Al melt and the stirred slurry was squeezed in the pressure range 80–140 MPa using a 60t semi-automatic hydraulic press and alloy-cast iron dies. The tensile behaviour at 100, 200 and 300 °C (373, 473 and 573 K) of the squeezed composites (70 mm diameter, 60 mm long) was then examined. It was found that the composite squeezed at 140 MPa and ambient die temperature displayed the best tensile properties up to 573 K, the ultimate tensile strength (UTS) values being 207.9, 197.8, 179 and 160.4 MN m⁻² at ambient, 373, 473 and 573 K, respectively. Compared to ordinary gravity chill-cast composite, the UTS of the above composite was higher by 52% at 373 K. This value rose to 161% and 162% at 473 and 573 K, respectively. The above composite retained about 77% of its ambient UTS value at 573 K, while the ordinary gravity chill-cast composite retained only 44% of its ambient UTS value. The performance of the squeezed composite with regard to 0.2% offset yield strength (YS) was distinctly superior to the gravity chill-cast composite. The YS values for the squeezed composite were 119.5, 117.3, 115 and 112.8 MN m⁻² at ambient, 373 K, 473 K and 573 K, respectively. The squeezed composite retained 94.4% of its ambient YS value at 573 K, while the gravity chillcast composite retained only 47.6% of its ambient YS value at the same test temperature. The YS of squeezed composite was higher by 105% compared with the YS value of gravity chillcast composite at 573 K. The performance of the squeezed composite progressively improved compared to gravity chill-cast composite as the test temperature was systematically raised to 573 K. Squeezed composites also exhibited fully ductile fracture features compared to semiductile to brittle fracture features of the gravity chill-cast composites; they also perform better because of the virtual absence of porosity and some degree of grain refinement obtained upon squeezing. Increasing the squeeze pressure in the range 160–240 MPa is likely to improve the properties of the composite further.     

Cu<Superscript>2+</Superscript> and Al<Superscript>3+</Superscript> co-substituted cobalt ferrite: structural analysis,morphology and magnetic properties

Cu–Al substituted Co ferrite nanopowders, Co_1?x Cu _x Fe_2?x Al _x O₄ (0.0 ≤ x ≤ 0.8) were synthesized by the co-precipitation method. The effect of Cu–Al substitution on the structural and magnetic properties have been investigated. X-ray diffraction (XRD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM) are used for studying the effect of variation in the Cu–Al substitution and its impact on particle size, magnetic properties such as M _s and H _c . Cu–Al substitution occurs and produce a secondary phase, α-Fe ₂ O ₃. The crystallite size of the powder calcined at 800 ^°C was in the range of 19–26 nm. The lattice parameter decreases with increasing Cu–Al content. The nanostructural features were examined by FESEM images. Infrared absorption (IR) spectra shows two vibrational bands; at around 600 (v ₁) and 400 cm ^?1 (v ₂). They are attributed to the tetrahedral and octahedral group complexes of the spinel lattice, respectively. It was found that the physical and magnetic properties have changed with Cu–Al contents. The saturation magnetization decreases with the increase in Cu–Al substitution. The reduction of coercive force, saturation magnetization and magnetic moments are may be due to dilution of the magnetic interaction.     

Interfacial reaction and its effect on strength of Al18 B4O33 /Al composites

Abstract

Aluminium alloy 6061, AC8A, Al–1Mg, Al–9Cu and pure aluminium composites reinforced with aluminium borate whiskers were fabricated by a squeeze casting process. The interfacial reaction in the composites and its effect on the bending strength are discussed, together with the results from SEM, TEM, and X-ray diffraction. A slight interfacial reaction is favourable for composite strength as it has the effect of anchoring the whiskers. A T6 treatment can enhance the strength of an Al–9Cu matrix composite, but is not efficient for magnesium containing 6061 and AC8A matrix composites. Furthermore, if heated at temperatures higher than 793 K for a long time, the composite strength drops rapidly owing to whisker damage and shortening during the interfacial reaction. It is suggested that the interface in an Al₁₈ B₄O₃₃ /Al alloy composite is stable below 623 K which is the temperature requirement for automobile engine components.     

Effect of stress ratio on fatigue behaviour in SiC particulate-reinforced aluminium alloy composite

Axial fatigue tests have been performed at three different stress ratios, R, of ?1, 0 and 0.4 using smooth specimens of an aluminium alloy composite reinforced with SiC particulates of 20 μm particle size. The effect of stress ratio on fatigue strength was studied on the basis of crack initiation, small crack growth and fracture surface analysis. The stress ratio dependence of fatigue strength that has been commonly observed in other materials was obtained, in which fatigue strength decreased with increasing stress ratio when characterized in terms of stress amplitude. At R=?1, the fatigue strength of the SiC_p/Al composite was the same as that of the unreinforced alloy, but at R= 0 and 0.4 decreased significantly, indicating a detrimental effect of tensile mean stress in the SiC_p/Al composite. The modified Goodman relation gave a fairly good estimation of the fatigue strength at 10⁷ cycles in the unreinforced alloy, but significantly unconservative estimation in the SiC_p/Al composite. At R= 0 and 0.4, cracks initiated at the interfaces between SiC particles and the matrix or due to particle cracking and then grew predominantly along the interfaces, because debonding between SiC particles and the matrix occurred easily under tensile mean stress. Such behaviour was different from that at R=?1. Therefore, it was concluded that the decrease in fatigue strength at high stress ratios and the observed stress ratio dependence in the SiC_p/Al composite were attributed to the different fracture mechanisms operated at high stress ratios.     

Strengthening of alloy 8090 and its fracture mechanics parameters

An investigation has been made of the tensile properties, impact-, initial fracture toughness and fracture mode of an aluminium-lithium 8090 alloy at room temperature and 77 K, depending upon the heat treatment and orientation. The peak-aged material exhibited an excellent combination of strength and toughness, equal to or exceeding that shown by the high-strength aluminium alloys of the 2000 and 7000 series. The superior strength and toughness of peak-aged plates, including that of 3% stretched material, compared to underaged material seems to be associated with the lower content of coarse insoluble precipitates, a higher density of S-precipitates in a matrix ligament (grain) which promote ductile fracture. The impact toughness of the peak-aged specimens increased at 77 K only in the L-T plate orientation, while in the T-L orientation it was somewhat lower or remained the same. The toughness increase at 77 K is discussed in terms of the role of the matrix and (sub)grain-boundary precipitates, freezing of low-melting point impurities of sodium and potassium alkaline metals at (sub)grain boundaries and the occurrence of the fine crack divider delamination toughening. The yield strength, R _o.2, increase on ageing was accompanied by a corresponding increase in initial crack divider fracture toughness, K _lc, opposite to the trends obtained for some traditional high-strength aluminium alloys. Changes of K _lc versus R _o.2 depending on orientation are discussed using models for ductile fracture toughness behaviour of aluminium alloys, based on the criterion that a critical width of the heavily strained zone at the crack tip approximates the average ligament width, d _p, i.e. the thickness of the elongated grain in the L-T and T-L plate orientations. It was also found that, for constant chemical composition and fabrication practice of the alloy, a critical plate thickness exists B 0.1 6 t _i, where _i is the initial thickness of the rolling ingot, for which the tensile strength properties in the L-T orientation are the same as that in the T-L orientation, while the plasticity (measured by elongation to failure) of the plate is a maximum. Two types of laminated cracks were observed on fracture surfaces of the specimens: large, >1 mm deep (the number of these cracks remains the same as the number of hot-rolling passes), and fine <0.4 mm (shallow laminated cracks, the number of which significantly increases with decreasing temperature, 77 K).     

Effect of in situ synthesized TiB whisker on microstructure and mechanical properties of carbon–carbon composite and TiBw/Ti–6Al–4V composite joint

Carbon–carbon composite (C–C composite) and TiB whiskers reinforced Ti–6Al–4V composite (TiB_w/Ti–6Al–4V composite) were brazed by Cu–Ni + TiB₂ composite filler. TiB₂ powders have reacted with Ti which diffused from TiB_w/Ti–6Al–4V composite, leading to formation of TiB whiskers in the brazing layer. The effects of TiB₂ addition, brazing temperature, and holding time on microstructure and shear strength of the brazed joints were investigated. The results indicate that in situ synthesized TiB whiskers uniformly distributed in the joints, which not only provided reinforcing effects, but also lowered residual thermal stress of the joints. As for each brazing temperature or holding time, the joint shear strength brazed with Cu–Ni alloy was lower than that of the joints brazed with Cu–Ni + TiB₂ alloy powder. The maximum shear strengths of the joints brazed with Cu–Ni + TiB₂ alloy powder was 18.5 MPa with the brazing temperature of 1223 K for 10 min, which was 56% higher than that of the joints brazed with Cu–Ni alloy powder.     

In situ TiB2 particulate reinforced near eutectic Al–Si alloy composites

In situ TiB₂ particulate reinforced near eutectic Al–Si alloy composites fabricated by the melt reaction composing (MRC) methods have been investigated. It has been shown that minute TiB₂ particles (less than 1 μm) uniformly distribute in the eutectic structure and they are interlaced with the coralline-like eutectic Si, while there are very few TiB₂ particles in α-Al. It has been also shown that in situ TiB₂ particles can enhance the tensile strength of the Al–Si alloy matrix. The strengthening effect increases with increasing TiB₂ content. The ultimate tensile strength (UTS) at room temperature of as-cast 6%TiB₂/Al–Si–Mg composite is 296 MPa, that is a 14.7% increase over the matrix, and its elongation at fracture is 5.5%. After heat-treatment (T6), the UTS of the composites reaches 384 MPa. The strengthening mechanism has been discussed.