Mechanical behavior of Al-based matrix composites reinforced with Mg58Cu28.5Gd11Ag2.5 metallic glasses

Al-based composites reinforced with Mg₅₈Cu_28.5Gd₁₁Ag_2.5 glassy particles have been synthesized by powder metallurgy. Powder consolidation was carried out by uniaxial hot pressing at temperatures within the super-cooled liquid region of the reinforcement to take advantage of the viscous flow of the glassy particles. The composites have improved yield and compressive strength compared to the unreinforced Al matrix without deteriorating the plasticity of the material. The relationship between mechanical properties and structure of the composites was investigated and described through the modified shear lag and mixture models.     

热轧工艺对20%B4C/Al复合材料显微组织及缺陷的影响

采用热等静压烧结与热轧相结合的方法制备了20%B_4C/Al(质量分数,下同)复合材料,采用排水法及SEM、EDS等手段研究了热轧工艺(道次变形量、总变形量)对复合材料缺陷及显微组织的影响。研究结果表明,热等静压制备的B_4C/Al复合材料坯体密度可达2.66g/cm3(相对密度100%),B_4C颗粒分布均匀且与Al界面处结合紧密;B_4C/Al复合材料轧制道次变形量应控制在10%以内,进一步增加道次变形量复合材料内出现宏观裂纹。复合材料经热轧后,B_4C颗粒仍分布较为均匀,且与Al基体结合紧密,复合材料内部未观察到明显的显微缺陷。     

Synthesis,microstructure and mechanical properties of ZrB2 nano and microparticle reinforced copper matrix composite by in situ processings

Copper matrix composite reinforced with ZrB₂ particles was prepared by in situ reaction in two different ways: by mechanical alloying and subsequent hot pressing, i.e. mechanical alloying and followed by laser melting process. Microstructural changes during mechanical alloying, hot pressing and laser melting of Cu, Zr and B powder mixtures were studied using scanning electron microscopy and X-ray diffraction. In particular, changes in the Cu particle size, structural parameters of the powder mixtures and formation of new ZrB₂ and CuZr phases during hot pressing, i.e. laser melting were investigated. The mechanisms of in situ formation of reinforcement particles and hardening effects in the copper composite were also studied. Large supersaturation which is possible with laser melting process results in homogeneous nucleation of CuZr precipitates and the presence of finer CuZr precipitates and ZrB₂ reinforcements in the Cu matrix. This affected on significantly higher degree of Cu matrix hardening compared to composites obtained by mechanical alloying and hot pressing.     

Effects of particulate reinforcement and heat treatment on the hardness and wear properties of AA 2024-MoSi2 nanocomposites

In this study, nanocomposites of AA 2024 aluminum alloy matrix reinforced with different volume fractions of nanometric MoSi₂ intermetallic particles ranging from 0 to 5%, were produced using mechanical alloying technique. For comparison, samples without reinforcing particles and mechanical alloying and a sample with micrometric MoSi₂ particles were also synthesized. The prepared composite powders were consolidated by cold and hot pressing and then heat treated to solution and aged condition (T6). The effects of MoSi₂ particle size, volume fraction and also heat treatment on the hardness and wear properties of the composites were investigated using Brinell hardness and pin-on-disc wear tests. The results indicated that although T6 heat treatment increases the hardness of all samples compared to as hot-pressed (HP) condition, the age-hardenability (aging induced hardness improvement) decreases after mechanical alloying and with increasing MoSi₂ volume fraction due to the high dislocation density produced during mechanical alloying. With increasing the volume fraction of nano-sized MoSi₂ particles up to 3–4%, the hardness of the composites continuously increases and then declines most probably due to the particle agglomeration. The wear sliding test disclosed that the wear resistance of all specimens in T6 condition is higher than that of HP condition and increases with increasing MoSi₂ content. Scanning electron microscopic observation of the worn surfaces was conducted and the dominant wear mechanism was recognized as abrasive wear accompanied by some adhesive wear mechanism.     

Dry sliding wear of TiB2 particle reinforced aluminium alloy composites

Abstract

Al–4 wt-%Cu alloy and composites reinforced with 10 and 20 vol.-% of TiB₂ particles were prepared by powder metallurgy followed by hot isostatic pressing. The dry sliding wear behaviour of specimens of these materials was investigated. Pin-on-disc measurements showed that the wear resistance of Al–4Cu alloy can be improved dramatically by the addition of 20 vol.-%TiB₂ particles. This was due to the high hardness of the TiB₂ particles, and to strong particle–matrix bonding. The wear data were found to correlate with SEM observations.     

20vol%体积分数纳米Al2O3颗粒增强铝基复合材料的高温压缩性能

为提高铝基材料的高温力学性能以满足其在573 K以上用于航空航天装备结构件的性能需求,采用高能球磨结合真空热压烧结工艺制备了体积分数高达20vol%的纳米Al₂O₃颗粒(146 nm)增强铝基复合材料,对其微观结构和高温压缩性能进行了研究。结果表明：纳米Al₂O₃颗粒均匀分散于超细晶铝基体中,且复合材料完全致密;该复合材料具有优异的高温压缩性能：应变速率为0.001/s时,473 K时压缩强度高达380 MPa,即使673 K时依然高达250 MPa,比其他传统铝基材料提高至少1倍;通过对其流变应力进行基于热激活的本构模型拟合可以发现,该复合材料具有高的应力指数(30)和表观激活能(204.02 kJ/mol)。这是由于高体积分数纳米颗粒能够有效钉扎晶界,并与铝基体形成热稳定的界面结合,显著提高复合材料的组织热稳定性,而且在变形过程中与晶界有效阻碍位错运动,显著提高复合材料的热变形门槛应力(在473～673 K时为190.6～328.4 MPa),其热变形过程可以由亚结构不变模型进行解释。     

Pressure infiltration casting process and thermophysical properties of high volume fraction SiCp/Al metal matrix composites

Abstract

SiC_p/Al composites containing high volume fraction SiC particles were fabricated using a pressure infiltration casting process, and their thermophysical properties, such as thermal conductivity and coefficient of thermal expansion (CTE), were characterised. High volume fraction SiC particulate preforms containing 50–70 vol.-%SiC particles were fabricated by ball milling and a pressing process, controlling the size of SiC particles and contents of an inorganic binder. 50–70 vol.-%SiC_p/Al composites were fabricated by high pressure infiltration casting an Al melt into the SiC particulate preforms. Complete infiltration of the Al melt into SiC preform was successfully achieved through the optimisation of process parameters, such as temperature of Al melt, preheat temperature of preform, and infiltration pressure and infiltration time after pouring. Microstructures of 50–70 vol.-%SiC_p/Al composites showed that pores resided preferentially at interfaces between the SiC particles and Al matrix with increasing volume fraction of SiC particles. The measured coefficients of thermal expansion of SiC_p/Al composites were in good agreement with the estimated values based on Turner's model. The measured thermal conductivity of SiC_p/Al composites agreed well with estimated values based on the 'rule of mixture' up to 70 vol.-% of SiC particles, while they were lower than the estimated values above 70 vol.-% of SiC particles, mainly due to the residual pores at SiC/Al interfaces. The high volume fraction SiC_p/Al composite is a good candidate material to substitute for conventional thermal management materials in advanced electronic packages due to their tailorable thermophysical properties.     

Microstructure evolution and mechanical properties of Nb-alloyed Cu–Zr–Al–Ni large-sized metallic glass composites

The effects of Nb on the microstructures and mechanical properties of large-sized (Cu_0.47Zr_0.47Al_0.06)_99???xNi₁Nb_x (x?=?0, 0.5, 1, 2?at.-%) bulk metallic glass composites were investigated. It is verified that the liquidus temperature (T_l) of the Nb-added alloys decreases to cause the increase of glass-forming ability (GFA). The addition of Nb adjusts the distribution and the volume fraction of B2-CuZr phase in the Cu–Zr–Al–Ni large-sized composites by changing the GFA of the alloys. The mechanical properties of the composites strongly depend on the volume fraction and distribution of B2-CuZr phase in the glassy matrix. The alloy with 0.5?at.-% Nb addition exhibits the high mechanical properties, which should be attributed to the uniform distribution and the proper volume fraction of B2-CuZr phase in the glassy matrix.     

Microstructure and mechanical properties of in situ synthesised (TiC+TiB)/Ti–6Al–4V composites prepared by powder metallurgy

Abstract

Titanium matrix composites (TMCs) reinforced with hybrid reinforcements were synthesised by blending Ti–6Al–4V, Ti, B₄C and C powders followed by reactive hot pressing. The phases were identified by X-ray diffraction, and the microstructures were examined by optical microscopy and scanning electron microscopy (SEM). Mechanical properties were tested at room temperature (RT), 400, 450 and 500°C respectively. The results show that Ti–6Al–4V produced by hot pressing has higher strength and better plasticity than by casting; there are four kinds of reinforcements in TMCs, and the TMCs’ strength increases significantly with the addition of reinforcements both at RT and elevated temperature; the TMCs with 5 vol.-% of reinforcements have higher strength than that with 10 vol.-% at high temperature. The fracture surfaces were examined by SEM. It shows that the bond between the reinforcements and matrix is not so well that reinforcements’ debonding occurs even at RT.     

Fabrication process and thermal properties of SiCp/Al metal matrix composites for electronic packaging applications

The fabrication process and thermal properties of 50–71 vol% SiC_p/Al metal matrix composites (MMCs) for electronic packaging applications have been investigated. The preforms consisted with 50–71 vol% SiC particles were fabricated by the ball milling and pressing method. The SiC particles were mixed with SiO₂ as an inorganic binder, and cationic starch as a organic binder in distilled water. The mixtures were consolidated in a mold by pressing and dried in two step process, followed by calcination at 1100 °C. The SiC_p/Al composites were fabricated by the infiltration of Al melt into SiC preforms using squeeze casting process. The thermal conductivity ranged 120–177 W/mK and coefficient of thermal expansion ranged 6–10 × 10^–6/K were obtained in 50–71 vol% SiC_p/Al MMCs. The thermal conductivity of SiC_p/Al composite decreased with increasing volume fraction of SiC_p and with increasing the amount of inorganic binder. The coefficient of thermal expansion of SiC_p/Al composite decreased with increasing volume fraction of SiC_p, while thermal conductivity was insensitive to the amount of inorganic binder. The experimental values of the coefficient of thermal expansion and thermal conductivity were in good agreement with the calculated coefficient of thermal expansion based on Turner's model and the calculated thermal conductivity based on Maxwell's model.     

Microstructure and Mechanical Properties of B4C/6061Al Nanocomposites Fabricated by Advanced Powder Metallurgy

In this study, B₄C/6061Al nanocomposites reinforced with various volume fractions of nano‐sized B₄C particles (B₄C/6061Al NCs) are successfully fabricated by a powder metallurgy route consisting of spark plasma sintering (SPS) and hot extrusion and rolling (HER). The microstructure evolution, phase composition, and mechanical properties of B₄C/6061Al NCs are experimentally investigate. The results show that nearly fully dense (maximum ≈99.21%) as‐SPSed NCs can be fabricated, and this can be attributed to joule heating at the particle contacts and tip spark plasma at the gaps. Nanosized B₄C particles mainly distributed in the 6061Al particles boundaries and formed inhomogeneous network materials in as‐SPSed NCs, while B₄C particles distributed relatively homogeneously in the 6061Al matrix after HER. No new phases are found in the B₄C/6061Al NCs over three deformation stages. The pin effect of the nanosized B₄C can suppress dynamic recovery and improve the driving force for dynamic recrystallization. The mechanical properties are further improved after HER, and the maximum ultimate tensile strength and yield strength for as‐rolled NCs are 305 and 168 MPa. The strengthening mechanisms mainly included load transfer strengthening, dislocation strengthening, Orowan strengthening, and fine‐grain strengthening.

     

Dry sliding tribological behavior and mechanical properties of Al2024–5 wt.%B4C nanocomposite produced by mechanical milling and hot extrusion

In this paper, tribological behavior and mechanical properties of nanostructured Al2024 alloy produced by mechanical milling and hot extrusion were investigated before and after adding B₄C particles. Mechanical milling was used to synthesize the nanostructured Al2024 in attrition mill under argon atmosphere up to 50 h. A similar process was used to produce Al2024–5 wt.%B₄C composite powder. The milled powders were formed by hot pressing and then were exposed to hot extrusion in 750 °C with extrusion ratio of 10:1. To study the microstructure of milled powders and hot extruded samples, optical microscopy, transmission electron microscopy and scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) were used. The mechanical properties of samples were also compared together using tension, compression and hardness tests. The wear properties of samples were studied using pin-on-disk apparatus under a 20 N load. The results show that mechanical milling decreases the size of aluminum matrix grains to less than 100 nm. The results of mechanical and wear tests also indicate that mechanical milling and adding B₄C particles increase strength, hardness and wear resistance of Al2024 and decrease its ductility remarkably.     

Effects of Sip size and volume fraction on properties of Al/Sip composites

Al–12 wt.% Si alloy matrix composites reinforced with high volume fraction of Si_p were fabricated by squeeze infiltration. The effects of the compacting pressure on the volume fraction of Si_p in preforms, and the influences of Si_p size and volume fraction on the properties of Al/Si_p composites were examined through this study. Si particles were compacted at different pressure of 40–130 MPa followed by sintered at 1000 °C for 7 h to obtain preforms containing 60–70 volume fraction (vol.%) of Si_p. The sintered preforms were then infiltrated with Al–12 wt.% Si alloy at 750 °C under a 75 MPa squeeze infiltration pressure. It was found that lower coefficient of thermal expansion (CTE) and smaller density may be obtained with higher Si_p volume fraction, yet increasing Si_p volume fraction leads to higher amount of porosities in the composites and thus lowers the thermal conductivity (TC) and flexural strength. Besides, with the same Si_p volume fraction, coarse Si particles result in higher CTE and TC, while finer Si particles may lower CTE and enhance the flexural strength of the composites effectively. From the results obtained in this study, it is expected that the high volume fraction Si_p reinforced Al/Si_p composites posses good potential in electronic packaging applications.     

Fracture behaviour and microstructure of MoSi2 reinforced with ductile ellipsoidal Nb particles

A MoSi₂/Nb composite with ellipsoidal reinforcements has been produced by uniaxial forging of a sample manufactured by hot isostatic pressing (HIP). The final aspect ratio of the reinforcing Nb particles as a function of strain has been predicted. Reaction products at the interface have been identified by means of energy dispersive X-ray analysis, electron diffraction, high resolution electron microscopy and image simulations. Substantial improvements have been obtained in the fracture toughness compared to the unreinforced matrix and MoSi₂ reinforced with identical volume fraction of spherical Nb reinforcements. The increase has been interpreted on the basis of a reduced number of particles that totally debond.     

Preparation of Fe-aluminide reinforced in situ metal matrix composites by reactive hot pressing

In situ Fe-aluminide and alumina reinforced aluminium matrix composite was prepared by hot pressing a powder mix of aluminium and Fe₂O₃ powders containing nanosized crystallites. The reinforcements were formed in situ by exothermal reaction between the Fe₂O₃ nanoparticles and the host aluminium matrix. The thermal characteristics of the in situ reaction were studied with the aid of differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) along with the energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques were employed to study the microstructural architecture of the composites as a function of hot pressing temperature and volume percent reinforcement. Micro-hardness measurements on the as-prepared in situ aluminium matrix composites show significant increase in hardness with increase in hot pressing temperature and volume fraction of reinforcement.     

Isothermal nanocrystallisation behaviour of melt spun Al86Ni9 Mm5 (Mmmischmetal)amorphous alloy

Abstract

The structure and mechanical properties of melt spun Al₈₆Ni₉Mm₅ alloy ribbons in both as solidified amorphous and heat treated nanocomposite conditions were investigated using DSC, XRD, TEM, and Vickers microhardness techniques. Primary crystallisation of the amorphous alloy resulted in the formation of fine nanocrystalline fcc-Al particles embedded in an amorphous matrix forming a nanocomposite. The growth behaviour of the primary fcc-Al particles under isothermal conditions was investigated. The hardness ofthe composite varied with the solute content in the amorphous phase and the microstructure after heat treatment. The hardening in these nanocomposites was quantitatively explained using a rule of mixtures model based on the volume fraction of the amorphous matrix and the Al particles. The nanometre sized particles were treated as perfect materials and the matrix was treated as an amorphousmaterial, in which the solute concentration increased as the volume fraction of the Al particles increased. The calculated results for the heat treated specimens using the rule of mixtures based on the isostress model have been found to be in good agreement with the experimentally obtained results.     

Cu-based metallic glass particle additions to significantly improve overall compressive properties of an Al alloy

We report the development of a novel light-weight Al (520) alloy-based composite reinforced with particles of a Cu-based (Cu₅₄Zr₃₆Ti₁₀) metallic glass by mechanical milling followed by induction heated sintering. The consolidation of the composite is performed at a temperature in the super-cooled liquid region of the metallic glass just above its glass-transition temperature (T_g). Metallic glasses are a promising alternative reinforcement material for metal-matrix composites capable of producing significant strengthening along with a «friendly» sintering behavior. The mechanical milling procedures were properly established to allow reduction of the size of the metallic glass particles and their uniform distribution in the matrix. Microstructural observation of the composite did not reveal any porosity. The interface between the glassy particles and the matrix remained free of such defects. The fully dense consolidated composite showed a drastic gain in specific yield strength under compression relative to the matrix alloy and appreciable plasticity at fracture.     

Formation mechanism of in situ Al3Ti in Al matrix during hot pressing and subsequent friction stir processing

In situ Al₃Ti/Al composites were fabricated by a combination of vacuum hot pressing (VHP) and friction stir processing (FSP). The formation mechanism of the Al₃Ti and the effect of VHP and FSP parameters on the resultant microstructure and mechanical properties were investigated. The Al₃Ti formed due to the reactive diffusion between Al and Ti during VHP, and the number of Al₃Ti particles increased with increasing the temperature and holding time of the VHP. FSP not only induced the Al–Ti reaction, but also resulted in significant refining of the Al₃Ti, thereby creating a homogeneous distribution of Al₃Ti particles in the Al matrix. These microstructural changes led to significant improvement in the tensile properties of the in situ Al₃Ti/Al composite. However, the change trends of the tensile properties of the FSP samples were dependent on the extent of the Al–Ti reaction during VHP.     

A nanostructural design to produce high ductility of high volume fraction SiCp/Al composites with enhanced strength

High ductility and increased strength of SiC_p/Al composites are highly desirable for their applications in complicated components. However, high ductility and high strength are mutually exclusive in high volume fraction SiC_p/Al composites. Here, we report a novel nanostructuring strategy that achieves SiC_p/Al–Sc–Zr composites with superior maximum tensile strain and enhanced tensile strength. The new strategy is based on combination of grain refinement down to ultra-fine scale with nanometric particles inside the grain through adding distinctive elements (Sc, Zr) and refining nucleation centers to nanoscale under the action of high volume fraction reinforcement during the fabrication process. The nanostructured SiC_p/Al–Sc–Zr composites had an increase of ∼300% in maximum tensile strain and a 21% increase in tensile strength. This thought provides a new sight into enhancement of both strength and ductility of particle reinforcement metal matrix composites.     

Production and mechanical properties of metallic glass-reinforced Al-based metal matrix composites

Al-based metal matrix composites were synthesized through powder metallurgy methods by hot extrusion of elemental Al powder blended with different amounts of metallic glass reinforcements. The glass reinforcement was produced by controlled milling of melt-spun Al₈₅Y₈Ni₅Co₂ glassy ribbons. The composite powders were consolidated into highly dense bulk specimens at temperatures within the supercooled liquid region. The mechanical properties of pure Al are improved by the addition of the glass reinforcements. The maximum stress increases from 155 MPa for pure Al to 255 and 295 MPa for the samples with 30 and 50 vol.% of glassy phase, respectively. The composites display appreciable ductility with a strain at maximum stress ranging between 7% and 10%. The mechanical properties of the glass-reinforced composites can be modeled by using the iso-stress Reuss model, which allows the prediction of the mechanical properties of a composite from the volume-weighted averages of the components properties.