Attainment of high specific hardness and specific modulus in spark plasma sintered aluminium-copper-silicon carbide-titanium carbide hybrid composite

Aluminium matrix hybrid composites have been consolidated effectively by spark plasma sintering with new combinations of reinforcement and high volume percentage of ceramic particulates to maximize specific hardness and specific modulus through the powder metallurgy route. The aforementioned techno-scientific accomplishment with regard to metal matrix composite aims to meet a continuous increase in the global demand for a material with minimum structural weight and high-modulus for structural (automotive and aerospace) applications. The new aluminium based hybrid composite developed by incorporating ceramic particulate reinforcements (12.5 wt.% silicon carbide and 12.5 wt.% titanium carbide) along with 22.5 wt.% copper as the metallic reinforcement attains significantly high specific hardness (85 HV/gcm⁻³), specific Young's modulus (33.56 GPa/g cm⁻³), specific bulk modulus (27.97 GPa/g cm⁻³) when compared with the reported range of specific hardness (13 HV/g cm⁻³–89 HV/g cm⁻³), specific Young's modulus (24 GPa/g cm⁻³–27 GPa/g cm⁻³) and specific bulk modulus (20 GPa/g cm⁻³–22 GPa/g cm⁻³) possessed by structural steels. This is accredited to the genesis of a novel microstructure that consists of fine copper, silicon carbide and titanium carbide particulates together with a nominal in-situ originated aluminium-copper equilibrium phases distributed in a highly substructured aluminium based matrix with a significant dislocation density (7.56 ⋅ 10¹⁴ m^-2).     

Mechanical properties of squeeze-cast zinc alloy matrix composites containing α-alumina fibres

α-Alumina fibre-reinforced ZA12 alloy matrix composites, with fibre volume fractions ranging from 7.5 to 30%, were manufactured by squeeze casting. The alumina fibres were homogeneously distributed in the matrix and had a planar-random orientation. Mechanical properties of the composites such as hardness, tensile strength, Young's modulus, elongation and wear resistance were measured and the effect of fibre volume fraction on these properties was investigated. At room temperature the hardness, Young's modulus and wear resistance increased with increasing volume fraction of alumina fibres, but the other properties were inferior. At elevated temperature (above 80°C) the tensile strengths of the composites were higher than that of the matrix alloy.     

Nextel™ 610 alumina fibre reinforced aluminium: influence of matrix and process on flow stress

Continuous alumina fibre reinforced aluminium matrix composites are produced using two different liquid metal infiltration methods, namely direct squeeze casting and gas pressure infiltration. Net-shape fibre performs for longitudinal parallel tensile bars are prepared by winding the Nextel™ 610 alumina fibre (3M, St Paul, MN) into graphite moulds. High purity aluminium, two binary (Al–6% Zn and Al–1% Mg) and one ternary (Al–6% Zn–0.5% Mg) aluminium alloys are used as matrix materials. The composite is tested in uniaxial tension–compression, using unload–reload loops to monitor the evolution of Young's modulus. A linear dependence between Young's modulus and strain is observed; this is attributed, by deduction, to intrinsic elastic non-linearity of the alumina fibre. This conclusion is then used to compare on the basis of the in situ matrix flow curve the influence of matrix composition and infiltration process on the composite stress–strain behaviour.     

Current state of Fe-Mn-Al-C low density steels

Fe-Mn-Al-C steels, previously developed in the 1950s for replacing Fe-Cr-Ni steels, are currently generating a lot of interest with potential applications for structural parts in the automotive industry because they are lighter. This paper provides a review on the physical metallurgy, processing strategies, strengthening mechanisms and mechanical properties of Fe-Mn-Al-C steels from the published literature over a period of many years, and suggests avenues for future applications of these alloys in the automotive sector.The addition of Al to Fe-C steels leads to a reduction in both density and Young’s modulus. A 1.3% reduction in density and a 2% reduction in Young’s modulus are obtained per 1 wt% addition of Al. Due to the addition of the high amounts of Al, together with Mn and C, the physical metallurgy, general processing, microstructural evolutions and deformation mechanisms of these steels are largely different from those of the conventional steels.The addition of Al to high-Mn austenitic steels brings two other important effects: increasing the stacking fault energy (SFE) and producing short-range ordering (SRO) and/or κ′-carbide precipitation. Plastic deformation of low-density Fe-Mn-Al-C steels with a high SFE, which involves SRO, is dominated by planar glide. New deformation mechanisms such as the microband induced plasticity (MBIP), the dynamic slip band refinement (DSBR) and the shear band induced plasticity (SIP) are introduced to describe plastic deformation of Fe-Mn-Al-C austenitic steels in addition to the transformation-induced plasticity (TRIP) and the twinning-induced plasticity (TWIP), which are often observed in Mn TWIP steels. These new deformation mechanisms are related to the formation and uniform arrangement of the SRO or nano-sized κ′-carbides which are coherent with the austenitic matrix. The κ′-carbide precipitation is a unique strengthening mechanism in the austenitic Fe-Mn-Al-C steels bearing high amounts of Al and C.The lightweight Fe-Mn–Al-C alloys can produce a variety of microstructures and achieve a wide range of properties. These alloys can be classified into four categories: ferritic steels, ferrite based duplex steels, austenite based duplex steels and austenitic steels. The austenitic steels are the most promising in terms of properties and processing. The tensile properties of the austenitic lightweight steels are similar to those of high Mn TWIP steels. The impact toughness of these steels in the solution treated condition is slightly lower than that of Cr-Ni stainless steels but is higher than that of the conventional high strength steels. The energy absorption at high strain rate is similar to that of high Mn TWIP steels and higher than that of conventional deep drawing steels. The ferrite based duplex low-density steels is another promising alternative. A bimodal microstructure can be obtained here through process control for steels with lower alloying contents, in which the plastic deformation of the ferrite and the TRIP and/or TWIP effects from the retained austenite can be profitably used. This type of Fe-Mn-Al-C steels exhibits an improved combination of strength and ductility compared with the first generation advanced high strength steels. The ferritic Fe-Al steels have tensile properties comparable with HSLA steels of 400–500 MPa strength level. The corrosion behaviour of Fe-Mn-Al-C steels is not improved in comparison with the conventional high strength steels. The application properties such as the fatigue behaviour and formability of Fe-Mn-Al-C steels cannot be properly understood at this stage, because of the limited experimental results so far. Some other application aspects such as weldability, coatability are not well documented.The applications of the Fe-Mn-Al-C steels in the automobiles is still not prevalent due to the lack of knowledge related to application properties so far. Above all, the reduced Young’s modulus of these steels and the processing problems as a result of the high Al and high Mn contents are the main issues. The future developments will therefore have to concentrate on the alloying and processing strategies and also on the methods to increase the Young's modulus. An improved processing strategy and a high value for the Young’s modulus will go a long way towards upscaling these steels to real automotive applications.     

Maximisation of the ratio of microhardness to the Young's modulus of Ti–12Mo–13Nb alloy through microstructure changes

Alloys for orthopaedic and dentistry applications require high mechanical strength and a low Young's modulus to avoid stress shielding. Metastable β titanium alloys appear to fulfil these requirements. This study investigated the correlation of phases precipitated in a Ti–12Mo–13Nb alloy with changes in hardness and the Young's modulus. The alloy was produced by arc melting under an argon atmosphere, after which, it was heat treated and cold forged. Two different routes of heat treatment were employed. Phase transformations were studied by employing X-ray diffraction and transmission electron microscopy. Property characterisation was based on Vickers microhardness tests and Young's modulus measurements. The highest ratio of microhardness to the Young's modulus was obtained using thermomechanical treatment, which consists of heating at 1000 °C for 24 h, water quenching, cold forging to reduce 80% of the area, and ageing at 500 °C for 24 h, where the final microstructure consisted of an α phase dispersed in a β matrix. The α phase appeared in two different forms: as fine lamellas (with 240 ± 100 nm length) and massive particles of 200–500 nm size.     

Microstress distribution in graphite fibre/epoxy composites containing an elastomeric interphase: response to uniaxial and biaxial loading conditions

A micromechanical model based upon the method of cells is introduced to characterize three-phase composites that contain a distinct and homogeneous interphase region. Initially, the performance characteristics of the model are shown to be quite consistent with those of a concentric cylinder model formulation. Subsequently, a parametric study is performed that examines the mechanical response of model graphite/epoxy composites as a function of selected interphase properties. The micromechanical model is utilized to establish an interdependence among the interphase Young's modulus, the interphase thickness and the average stresses within the fibre, interphase and matrix resulting from two external loading conditions: uniaxial longitudinal tension and biaxial transverse shear. Material combinations are considered wherein the interphase Young's modulus is systematically varied above and below the matrix Young's modulus. The simulation indicates that the selected interphase properties significantly influence the stress state within each of the three composite constituents. The manner in which the stress states are modified proves to be non-intuitive in many of the cases considered. In particular, there are material domains encountered where the model predicts that certain stress components in a constituent will exhibit (1) a maximum with respect to variations in the interphase Young's modulus and/or (2) a minimum with respect to variations in the interphase thickness.     

Plasticity improvement for dendrite/metallic glass matrix composites by pre-deformation

The mechanical properties of in-situ metallic glass matrix composites (MGMCs) are investigated by tensile pre-deformation, followed by compression. The pre-deformation is utilized to exploit notable increases in plasticity, accompanied by slight increases in the compressive strength, and the deformation mechanisms are explored. The increased free volumes in the glass matrix after tensile pre-deformation contribute to the decrease of the Young's modulus of the glass matrix and lead to the increase in the stress concentration, promoting multiplication of shear bands. When the Young's modulus of the glass matrix matches that of the dendrites, the plasticity of in-situ dendrite-reinforced MGMCs is the optimized. Matching Young's modulus opens a door to design the MGMCs with excellent plasticity and remarkable work-hardening capability.     

Recent Advances in Research on Carbon Nanotube–Polymer Composites

Carbon nanotubes (CNTs) demonstrate remarkable electrical, thermal, and mechanical properties, which allow a number of exciting potential applications. In this article, we review the most recent progress in research on the development of CNT–polymer composites, with particular attention to their mechanical and electrical (conductive) properties. Various functionalization and fabrication approaches and their role in the preparation of CNT–polymer composites with improved mechanical and electrical properties are discussed. We tabulate the most recent values of Young's modulus and electrical conductivities for various CNT–polymer composites and compare the effectiveness of different processing techniques. Finally, we give a future outlook for the development of CNT–polymer composites as potential alternative materials for various applications, including flexible electrodes in displays, electronic paper, antistatic coatings, bullet‐proof vests, protective clothing, and high‐performance composites for aircraft and automotive industries.     

Preliminary studies of mesophase-pitch-based carbon fibres: Structure and microtexture

Four different Union Carbide mesophase-pitch-based carbon fibres were studied by transmission electron microscopy after thin sectioning (transverse and longitudinal sections). Three phases were distinguished, viz. graphite, a microporous turbostratic phase and a phase similar to high-modulus polyacrylonitrile-based fibres (layers smoothly curved and entangled parallel to the fibre axis). The Young's modulus increases with the average degree of graphitization, i.e. as the percentage of graphite increases, the percentage of microporous phase decreases and the radius of curvature and the diameter of the layers of the third phase increase.     

Processing,microstructure, and physical properties of interpenetrating Al2O3/Ni composites

Abstract

Alumina/nickel composites have been fabricated by hot pressing powder blends of various volume fractions of nickel and alumina. The electrical resistivities and Young's moduli of these composites have been measured and their dependence on the volume fraction of reinforcement has been investigated. Microstructural parameters such as contiguity were measured to quantify the distribution of the phases in these composites, and existing property models based on these data were used to predict the properties of the composites. The percolation threshold of nickel was found to occur at between 7.5 and 15 vol.-%Ni. The Young's modulus decreases as the volume fraction of nickel increases and is dependent on the contiguity of alumina. Composites containing 25, 35, 50, and 65 vol.-%Ni display microstructures with interpenetrating networks of alumina and nickel. The property models were found to fit both the resistivity and modulus data well, although the percolation threshold was predicted at a lower volume fraction than measured experimentally.     

Einfluss elastischer Kennwerte auf die Eigenschaften von Blechformteilen

Influence of elastic material characteristics on the properties of forming parts Trends in the automotive industry tend towards safety, fuel saving and reduction of exhaust gas result in an increased application of high strength steels in the car body production. The sheet thickness can be reduced when using high strength steels but without reducing the load capacity. The forming of these steels is more difficult due to the special springback behaviour. Furthermore the dent resistance shows an important role especially for outer panel parts. One influencing factor on the material behaviour is the Young's modulus, which will be discussed in this paper.     

Computational study of the effect of carbon vacancy defects on the Young's modulus of (6, 6) single wall carbon nanotube

Most molecular dynamics (MD) simulations for single wall carbon nanotubes (SWCNT) are based on a perfect molecular material structure. The presence of vacancy defects in SWCNTs could lead to deviations from this perfect structure thus affecting the predicted properties. The present paper investigates the effect of carbon vacancy defects in the molecular structure of SWCNT on the Young's modulus of the SWCNT using MD simulations performed via Accelrys and Materials Studio. The effect of the position of the defects in the nanotube ring and the effect of the number of defects on the Young's modulus are studied. The studies indicate that for an enclosed defect with the same shape in a SWCNT structure, its position did not cause any change in the Young's modulus. However, as the number of defects increased, the predicted Young's modulus was found to decrease. For a 10 ring (6, 6) SWCNT, six vacancy defects (corresponding to a defect percentage of 2.5%) reduced the Young's modulus by 13.7%.     

Influence of the sintering temperature on Young's modulus and the shear modulus of tricalcium phosphate – fluorapatite composites evaluated by ultrasound techniques

The mechanical properties of the tricalcium phosphate sintered between 1100 °C and 1450 °C for 1 h with different percentages of fluorapatite (13.26 wt%; 19.9 wt%; 26.52 wt%; 33.16 wt% and 40 wt%) have been characterized and evaluated using the ultrasound techniques. Young's modulus and the shear modulus were calculated from the point of the longitudinal and the transversal ultrasonic velocities. Young's modulus and the shear modulus of tricalcium phosphate increased with the sintering temperature and with the addition of the fluorapatite additive into the tricalcium phosphate matrix. At 1300 °C, the shear modulus and Young's modulus of the tricalcium phosphate – 40 wt% fluorapatite composites registered optimum values: 26 GPa and 66.2 GPa, respectively. Above 1300 °C, the mechanical properties of the tricalcium phosphate – fluorapatite composites were hindered by the tricalcium phosphate allotropic transformation and the formation of both the intragranular porosity and the cracks.     

Thermo-mechanical properties of randomly oriented carbon/epoxy nanocomposites

The thermo-mechanical properties of epoxy-based nanocomposites based on low weight fractions (from 0.01 to 0.5 wt%) of randomly oriented single- and multi-walled carbon nanotubes were examined. Preparation methods for the nanocomposites, using two types of epoxy resins, were developed and good dispersion was generally achieved. The mechanical properties examined were the tensile Young's modulus by Dynamic Mechanical Thermal Analysis and the toughness under tensile impact using notched specimens. Moderate Young's modulus improvements of nanocomposites were observed with respect to the pure matrix material. A particularly significant enhancement of the tensile impact toughness was obtained for specific nanocomposites, using only minute nanotube weight fractions. No significant change in the glass transition temperature of SWCNT/epoxy nanocomposites was observed, compared to that of the epoxy matrix. The elastic modulus of the SWNT-based nanocomposites was found to be slightly higher than the value predicted by the Krenchel model for short-fiber composites with random orientation.     

Transition in flexural microbuckling mechanisms in unidirectional glass fibre-reinforced thermoplastics

A transition in the mechanism of flexural failure previously observed in low matrix modulus unidirectional glass fibre composites is semi-quantitatively explained by considering the criterion for each of the failure modes. The failure strength for cooperative fibre microbuckling is controlled by the shear modulus of the composite which is linearly related to the Young's modulus of the matrix, while the failure strength for delamination splitting microbuckling is controlled by the composite shear strength which is not as strongly dependent on the Young's modulus of the matrix. Because the critical failure stresses have different dependencies on the matrix modulus, a transition from cooperative fibre microbuckling to delamination splitting microbuckling occurs as the matrix modulus increases. Due to the stress gradient in the beam, the compressive failure behaviour in bending is not the same as in uniform compression. When the failure mode is cooperative fibre microbuckling, the bending strength is higher than expected, especially in the thin beams. In bending, the delamination splitting microbuckling mode does not lead to abrupt splitting of the entire beam, but rather occurs by gradual accumulation of surface damage.     

Bio‐Inspired,Self‐Toughening Polymers Enabled by Plasticizer‐Releasing Microcapsules

A new concept for the design of self‐toughening thermoplastic polymers is presented. The approach involves the incorporation of plasticizer‐filled microcapsules (MCs) in an intrinsically rigid and brittle matrix polymer. The intriguing adaptability that this simple tactic enables is demonstrated with composites composed of a poly(lactic acid) (PLA) matrix and 5–20% w/w poly(urea‐formaldehyde) (PUF) MCs that contained hexyl acetate as plasticizer. At low strain (<1.5%), the glassy PLA/MC composites remain rigid, although the intact MCs reduce the Young's modulus and tensile strength by up to 50%. While the neat PLA shows brittle failure at a strain of around 2.5%, the composites yield in this regime, because the MCs rupture and release their plasticizing cargo. This effect leads up to 25‐fold increase of the elongation at break and 20‐fold increase of the toughness vis‐à‐vis the neat PLA, while the impact on modulus and ultimate stress is much smaller. Ballistic impact tests show that the self‐toughening mechanism also works at much higher strain rates than applied in tensile tests and the operating mechanism is corroborated through systematic thermomechanical studies that involved dynamic mechanical testing and thermal analysis.     

Mechanical properties of polymer matrix composites at 77 K and at room temperature after irradiation with 60Co γ-rays

Ten different polymer matrix composites were irradiated with ⁶⁰Co γ-rays at room temperature, and were examined with regard to the mechanical properties at 77 K and at room temperature. The radiation-induced degradation of these composites is observed much more significantly in the ultimate strength and in the shear modulus than in the Young's modulus. The radiation resistance of these composites depends primarily on the radiation resistance of matrix resins, which increases in the order diglycidyl ether of bisphenol A < tetraglycidyl| diaminodiphenyl methane < Kerimid 601. Comparison of the mechanical properties tested at 77 K and at room temperature demonstrates that the extent of radiation-induced decrease in the composite strength is appreciably greater in the 77 K test than in the room temperature test. Interpretation of these results is based on the competition between the two opposing effects due to the hardness and brittleness of matrix resins.     

Effect of NiCrAlY platelets inclusion on the mechanical and thermal shock properties of glass matrix composites

NiCrAlY platelets modified glass matrix composites were prepared. Their microstructures were characterized, their Young's modulus, fracture strength in bending, Vickers hardness, and indentation toughness were measured, and their thermal shock resistance was studied using quenching-strength and indentation-quench methods. With increasing NiCrAlY content, evident enhancements of the Young's modulus and indentation toughness were obtained. The NiCrAlY alloy inclusion could exert significant influences on the retained bending strength of the samples after quench tests, from 9.6 MPa for NiCrAlY-free glass to 32.0 MPa for 30 wt.% NiCrAlY-containing composites. The indentation-quench tests showed that NiCrAlY alloy inclusion elevated the critical quenching temperatures for propagation of pre-crack, from 150 °C for NiCrAlY-free glass to 225 °C for 30 wt.% NiCrAlY-containing composites. Inclusion debonding and intersection, crack deflection and bridging were observed, and are likely the micromechanisms accounted for the improvement of fracture resistance.     

超顺排碳纳米管/硅橡胶复合材料各向异性的电学性能和力学性能

采用直接浸润法制备了具有不同层数的超顺排碳纳米管(SACNT)薄膜与硅橡胶的复合材料,使碳纳米管薄膜能够在硅橡胶基体表面均匀分散。测量了SACNT薄膜/硅橡胶复合材料在各个方向的导电性能和力学性能,研究了影响复合材料导电性和力学性能的因素。实验结果表明:SACNT薄膜/硅橡胶复合材料的导电性和杨氏模量都随着碳纳米管薄膜厚度的增加而增加,且具有显著的各向异性。垂直于碳纳米管排列方向的电阻率平均比平行方向的大一个数量级。当碳纳米管层数为240层时,平行于碳纳米管排列方向的杨氏模量为116.9 MPa(比纯硅橡胶基体增加了142倍),而垂直方向的杨氏模量仅为1.23 MPa(比纯硅橡胶基体增加50%),两者之间相差近100倍。结果表明,可以通过选择不同的参数,获得具有特定导电性和杨氏模量的SACNT薄膜/硅橡胶复合材料,并在实际中加以应用。     

Prediction of Young's modulus of particulate two phase composites

Abstract

A new approach for predicting the Young's modulus of two phase composites has been proposed based on a topological transformation and the mean field theory. The new approach has been applied to Co/WC_p,Al/SiC_p, and glass filled epoxy composites. It is shown that the new theoretical predictions are well within the Hashin and Shtrikman lower and upper bounds (the HS bounds) and are in closer agreement with the experimental results for the corresponding composite systems than both the HS bounds and the predictions of the mean field theory. An advantage of the present approach over other continuum approaches is that it can predict not only the effect of volume fraction of the reinforcing phase, but also the effects of microstructural parameters such as grain shape and phase distribution on the stiffness of composites. It is also shown that the classical linear law of mixtures is a specific case (where the reinforcing phase is continuous and perfectly aligned) of the present approach. In contrast to the classical linear law of mixtures, the present approach can be applied to a two phase composite having any volume fraction, grain shape, and phase distribution. It is shown that in a particulate composite having a given volume fraction of reinforcement, the Young's modulus of the composite increases with increasing contiguity of the constituent phases and this increment is dependent on the stiffness ratio of the constituent phases. Furthermore, the present approach can provide a simple and effective solution to the problem of interaction between particles of the same phase.

MST/1587