Characterization of the correlation between the interfaces and failure behaviors for particle reinforced Mg–Li composites

The interfacial microstructure of SiC_p or YAl_2p reinforced Mg–14Li–3Al matrix composites was comparatively characterized by scanning electron microscopy and electron probe microanalysis. A nanoindentation combined with scanning electron microscopy technique was used to characterize the interfacial mechanical properties between the reinforcements and matrix. The interfacial strength and failure behaviors for the composites were analyzed from the load–penetration curves and corresponding images. In situ tensile tests were used to observe the fracture and deformation processes with the aid of scanning electron microscopy. The results show that both the chemical and mechanical compatibilities between the YAl₂ particles and LA143 matrix are better than those between the SiC particles and LA143 matrix. The interfacial breakage load for the SiC/LA143 composite is lower than that for the YAl₂/LA143 composite because of the worse chemical and mechanical compatibilities between the ceramic particles and metal matrix. Interfacial breakage is the main failure mechanism for the SiC/LA143 composite, while the particle breakage and matrix crack are the main failure mechanism for the YAl₂/LA143 composite. These may be related to the stronger interfacial bonding between the intermetallic particles and metal matrix.     

Pulvermetallurgische Erzeugung von SiC‐ und Al2O3‐verstärkten Al‐Cu‐Legierungen

Powder metallurgical fabrication of SiC and Al₂O₃ reinforced Al‐Cu alloys Based on metallographic studies the states of composite powder formation during high‐energy ball milling will be discussed. Spherical powder of aluminium alloy AA2017 was used as feedstock material for the matrix. SiC and Al₂O₃ powders of submicron and micron grain size (<2 μm) were chosen as reinforcement particles with contents of 5 and 15 vol.‐% respectively. The milling duration amounted to a maximum of 4 hours. The abrasion of the surface of the steel balls, the rotor and the vessel is indicated by the content of ferrous particles in the powder. High‐energy ball milling leads to satisfying particle dispersion for both types of reinforcement particles. Further improvements are intended. The microstructure of compact material obtained by hot isostatic pressing and extrusion was studied in detail by scanning and transmission electron microscopy. For both types of reinforcement the microstructure of composites is similar. The microporosity is low. The interface between reinforcement particles and matrix is free of brittle phases and microcracks. In the case of SiC reinforcement particles, a small interface interaction is detectable which implies a good embedding of reinforcement particles. High‐energy ball milling under air‐atmosphere leads to the formation of the spinel phase MgAl₂O₄ during the subsequent powder‐metallurgical processing. Because of the size, rate and dispersion of the spinel particles, an additional reinforcement effect is expected.     

Effect of volume fraction and particle size of alumina reinforcement on compaction and densification behavior of Al-Al2O3 nanocomposites

Al-Al₂O₃ nanostructured composite powders containing 1, 3 and 7 percent volume fraction (vf%) of submicron/nanometeric alumina particles as reinforcement phase were produced by high energy milling. The powders were consolidated by a uniaxial cold press and sintered for various durations of time. Effects of reinforcement particle size and volume fraction on compaction and sintering behavior of nanocomposite powders were investigated considering relative density as the main criterion. It was found that the nanometeric alumina particles had a more hindering effect on densification of the composite powders as compared to the submicron particles. The hindering effect was found to be aggravated by higher volume fractions of the reinforcement particles.     

Effects of YAl2 particulates on microstructure and mechanical properties of β-Mg–Li alloy

A new β-Mg-12 wt%Li matrix composite reinforced with 15 wt%YAl₂ particulates is produced. Microstructures and mechanical properties of the YAl₂p/β-Mg-Li composite were investigated. The results show that a clean interface is formed between YAl₂ particulate and magnesium-lithium matrix; YAl₂ particulates are dispersively distributed in Mg-12 wt%Li alloy matrix; and mechanical properties of the β-Mg-Li alloy are effectively improved by the addition of YAl₂ particulates.     

Effect of Nb and Nb2O5 additives on mechano-thermal processing of TiAl/Al2O3 nano-composite

In this research, TiAl matrix nano-composite with Al₂O₃ reinforcement was obtained by mechanical activation of TiO₂ and Al powder mixture and its subsequent heat treatment. Effect of Nb and/or Nb₂O₅ additions on the process was investigated. Structural changes and thermal behavior of the samples were evaluated by X-ray diffraction and differential thermal analysis, respectively. Moreover, the microstructure was characterized by transmission electron microscopy. The results confirmed the partial dissolution of Nb in Al during the milling stage in the Nb-added samples. The reaction mechanism during heat treatment in the sample without any additives was a two-stage process that was quite similar to the sample with Nb addition. However, Nb₂O₅ addition led to the progress of reaction through a single stage and with a higher rate. Both additives promoted formation of the Ti₃Al phase in the final products. The results confirmed the formation of nano-sized Al₂O₃ particles in a nano-crystalline Ti–Al matrix with a mean crystallite size of 30 nm.     

Liquid-phase impact diffusion welding of SiCp/6061Al and its mechanism

Liquid-phase impact diffusion welding (LPIDW) technique was used to join the aluminum matrix composite SiC_p/6061Al. The composite joints welded successfully, gave tensile strength up to 260 MPa and radial deformation below 3%. Analysis of the microstructure and tensile strength of the welded joints showed: (i) the achievement of prominent joint interface between SiC particles and the matrix; (ii) the change of pernicious contact-state from reinforcement (SiC)/reinforcement (SiC) to reinforcement (SiC)/matrix/reinforcement (SiC) of the reinforcement particles; (iii) the disappearance of the harmful microstructure/brittle phase of Al₄C₃ from the welded joint; (iv) the density of dislocation in the matrix next to the interface being higher; (v) the sign of intensively mutual entwisting of dislocation; and (vi) the deformation mainly taking place in the matrix grain. Furthermore, the rapid thermal pressing offered a denser nucleus area for matrix crystal and their deforming matrices around SiC particles engendered intensive aberration, which was favorable for forming nano-grains and for improving the properties of the welded composite joints.     

Effects of reinforcement distribution on low and high temperature tensile properties of Al356/SiCp cast composites produced by a novel reinforcement dispersion technique

A major challenge for full utilization of the potentials of SiC_p reinforced metal matrix composites is the uniform dispersion of very fine SiC particles in the matrix alloys. In this study, a novel method for gradual in situ release of properly wetted SiC particles with average size of less than 3 μm in the liquid metal was employed which greatly overcame this challenge. SiC particles were injected into the melt in three different forms, i.e., untreated SiC_p, milled particulate Al-SiC_p composite powder, and milled particulate Al-SiC_p-Mg composite powder. The resultant composite slurries were then cast in either a fully liquid state (stir casting) or semisolid state (compocasting). Subsequently, the effects of the type of the injected powder and the casting method on the microstructural and mechanical characteristics of the cast composites at room temperature and 300 °C were investigated. The results demonstrated that distribution of SiC particles in the matrix were greatly improved by injecting milled composite powders instead of untreated SiC particles into the melt. Also casting the composite slurries in a semisolid state instead of fully liquid state slightly improved the distribution. The ultimate tensile strength, yield strength and elongation at room temperature of Al356/5 vol.% SiC_p composite manufactured by compocasting of the (Al-SiC_p-Mg)_cp-injected melt were increased by 113%, 90% and 135%, respectively, compared to those of the composite manufactured by stir casting of the untreated-SiC_p injected melt. The improvements in these properties at 300 °C were about 100%, 103% and 129%, respectively. Almost all the composite samples retained more than 90% of their strengths at 300 °C, whereas the monolithic samples lost more than 25% of their strength at this temperature. The composites manufactured by compocasting of (Al-SiC_p-Mg)_cp-injected melts exhibited a typical ductile fracture surface with equiaxed dimples at both room temperature and 300 °C.     

Growth and optical properties of Er,Yb:YAl3(BO3)4 crystal

Single crystal of erbium, ytterbium-codoped yttrium aluminum tetraborate Er,Yb:YAl₃(BO₃)₄(Er,Yb:YAB) has been grown by the flux method. The absorption spectrum in the visible and NIR regions of Er,Yb:YAl₃(BO₃)₄ crystal are measured at room temperature and fluorescence spectrum of Er,Yb:YAl₃(BO₃)₄ crystal are also measured at room temperature, excited by 976 nm laser. Not only the strong NIR emission peaks located at 1548 nm was observed, but also the visible up-conversion luminescence has been found. The specific heat of the Er/Yb:YAB crystal at room temperature is 0.81 J/g °C.     

Refinement of microstructure and improvement of mechanical properties of Al/Al2O3 cast composite by accumulative roll bonding process

Some important problems associated with cast metal matrix composites (MMCs) include non-uniformity of the reinforcement particles, high porosity content, and weak bonding between reinforcement and matrix, which collectively result in low mechanical properties. Accumulative roll bonding (ARB) process was used in this study as a very effective method for refinement of microstructure and improvement of mechanical properties of the cast Al/10 vol.% Al₂O₃ composite. The average particle size of the Al₂O₃ was 3 μm. The results revealed that the microstructure of the composite after eleven cycles of the ARB had an excellent distribution of alumina particles in the aluminum matrix without any noticeable porosity. The results also indicated that the tensile strength and elongation of the composites increased as the number of ARB cycles increased. After eleven ARB cycles tensile strength and elongation values reached 158.1 MPa and 7.8%, which were 2.54 and 2.36 times greater than those of the as-cast MMC, respectively.     

Fabrication of thermochromic composite using monodispersed VO2 coated SiO2 nanoparticles prepared by modified chemical solution deposition

Monodispersed thermochromic VO₂ particles were fabricated by VO₂ coating onto monodispersed SiO₂ nanoparticles with the modified chemical solution deposition technique using vanadium isopropoxide solution and monodispersed SiO₂ particle suspension solution. The average size of the resultant VO₂–SiO₂ particle was 57 nm and the coating thickness of the VO₂ layer was 6 nm. A thermochromic composite was fabricated using the VO₂–SiO₂ particles and a poly lactose acid polymer as a transparent matrix, and the transmittance of the composite at a high temperature was 10% less than that at a low temperature.     

Evaluation of microstructure and mechanical properties of Al/Al2O3/SiC hybrid composite fabricated by accumulative roll bonding process

In this investigation, a new kind of metal matrix composites with a matrix of pure aluminum and hybrid reinforcement of Al₂O₃ and SiC particles was fabricated for the first time by anodizing followed by eight cycles accumulative roll bonding (ARB). The resulting microstructures and the corresponding mechanical properties of composites within different stages of ARB process were studied. It was found that with increasing the ARB cycles, alumina layers were fractured, resulting in homogenous distribution of Al₂O₃ particles in the aluminum matrix. Also, the distribution of SiC particles was improved and the porosity between particles and the matrix was decreased. It was observed that the tensile strength of composites improved by increasing the ARB passes, i.e. the tensile strength of the Al/1.6 vol.% Al₂O₃/1 vol.% SiC composite was measured to be about 3.1 times higher than as-received material. In addition, tensile strength of composites decreased by increasing volume fraction of SiC particles to more than 1 vol.%. Scanning electron microscopy (SEM) observation of fractured surfaces showed that the failure mechanism of broken hybrid composite was shear ductile rupture.     

Evolution of manufacturing parameters in Al/Ni3Al composite powder formation using blending and mechanical milling processes

Aluminu–matrix composites produced by Ni₃Al intermetallic particles are increasingly used in aerospace and structural applications because of their outstanding properties. In manufacturing of metal–matrix composites using powder metallurgy blending and milling are important factors. They control the final distribution of reinforcement particles and porosity in green compacts which in turn, strongly affect the mechanical properties of the produced PM materials. This paper studies different conditions for producing composite powders with uniform dispersion of Ni₃Al particles in aluminum powders and improved physical and mechanical properties. The results indicated that an intermediate milling time for fabrication of composite powder, better than prolonged and shortened ones, causes better microstructure and properties. It was shown that addition of 5 vol.% Ni₃Al particles, produced by 15 h mechanical alloying to aluminum powders, and then 12 h blending operation provides an appropriate condition for producing Al–Ni₃Al composite powder.     

高能球磨工艺对B4C/Al复合粉体结构演变及分布均匀性的影响

制备B4C增强Al基复合材料存在的难点主要是B4C颗粒在Al基体中的均匀分布及界面结合。本研究采用卧式搅拌高能球磨法制备了B4C/Al复合粉体,研究了搅拌轴转速和球磨时间对B4C/Al复合粉体结构演变及分布均匀性的影响。结果表明,随搅拌轴转速的提高,复合粉体受磨球碰撞时所获能量增大,增强体颗粒瞬间被破碎同时使Al粉发生较大的塑性变形,随球磨时间的延长,破碎的B4C颗粒逐渐在Al基体中分散均匀并与基体焊合,利于粉体实现均匀分布和良好的界面结合。球磨过程中B4C沿颗粒棱边脆性断裂,在Al粉的冷焊变形过程中被嵌入,形成一种片状化的Al粉基体包裹B4C增强相的复合粉体。在搅拌轴转速为600/800r/min(交变转速,交变频率为1min),球磨时间为2h时,B4C/Al复合粉体的粒度得到细化,B4C颗粒在Al基体中分布均匀、界面结合紧密。     

Mechanochemical synthesis of ultrafine ZrO2 powder

The synthesis of ultrafine zirconia powders by mechanochemical reaction of ZrCl₄ with CaO has been investigated using x-ray diffraction, TEM and DSC measurements. Mechanical milling resulted in a nanoscale mixture of CaO and amorphous ZrCl₄. with no evidence of any reaction having occurred. Subsequent heat treatment at temperatures above 300 °C resulted in the formation of separated particles of cubic ZrO₂,5–10 nm in diameter, within an CaCl₂ matrix. Measurements of the effect of particle size on the crystal structure of ZrO₂ are also reported.     

Effect of powder characteristics on Cr internal oxidation for preparation of Cr2O3/Cu composite

Abstract

Cr O₃/Cu composite was prepared by the internal oxidation of Cu–Cr pre-alloyed powders formed by high energy milling. Effects of milling time on the internal oxidation characteristics of Cu–Cr pre-alloyed powders were also discussed in this paper. The results indicate that the degree of the internal oxidation continually increases with prolonged milling time. At the initial stage, external oxidation rather than internal oxidation occurs, resulting in coarse Cr₂O₃ particles. With further milling, the internal oxidation becomes more complete and the sizes of Cr₂O₃ particles also become finer and well distributed. The properties of the composite are therefore improved. A high quality composite specimen from Cu–1·0Cr pre-alloyed powders after 40 h milling was prepared by the internal oxidation process. The Cr₂O₃ particles with an average size of 2–5 μm in diameter and about 5–10 μm in particles space were found by a microstructure examination, and they were uniformly dispersed in the Cu matrix.     

Preparation and investigation of Al–4 wt % B<Subscript>4</Subscript>C nanocomposite powders using mechanical milling

Boron carbide nanoparticles were produced using commercially available boron carbide powder (0·8 μm). Mechanical milling was used to synthesize Al nanostructured powder in a planetary ball-mill under argon atmosphere up to 20 h. The same process was applied for Al–4 wt % B₄C nanocomposite powders to explore the role of nanosize reinforcements on mechanical milling stages. Scanning electron microscopy (SEM) analysis as well as apparent density measurements were used to optimize the milling time needed for completion of the mechanical milling process. The results show that the addition of boron carbide particles accelerate the milling process, leading to a faster work hardening rate and fracture of aluminum matrix. FE-SEM images show that distribution of boron carbide particles in aluminum matrix reaches a full homogeneity when steady state takes place. The better distribution of reinforcement throughout the matrix would increase hardness of the powder. To study the compressibility of milled powder, modified heckel equation was used to consider the pressure effect on yield strength as well as reinforcing role of B₄C particles. For better distribution of reinforcement throughout the matrix, r, modified heckel equation was used to consider the pressure effect on yield strength as well as reinforcing role of B₄C particles.     

Effects of hydrolysis on dodecyl alcohol modified β-CaSiO3 particles and PDLLA/modified β-CaSiO3 composite films

In this research, β-CaSiO₃ particles were surface modified with dodecyl alcohol, and Poly-(DL-lactic acid) (PDLLA)/modified β-CaSiO₃ composite films were fabricated with a homogenous dispersion of β-CaSiO₃ particles in the PDLLA matrix. The aim of the study was to investigate the properties of the composite films before and after hydrolytic treatment. SEM images showed retained homogenous dispersion of β-CaSiO₃ particles after hydrolysis and tensile test also showed maintained mechanical property. Simulated body fluid (SBF) incubation experiment suggested that hydrolytic treatment did not affect the formation of hydroxyapatite on the surface of the composite films. The hydrophilicity of the composites was greatly recovered (from 69.82° to 50.28°) after hydrolysis. In addition, cells cultured on composite films after hydrolysis presented the highest cell proliferation rate and differentiation level. All of these results suggested that the surface modification of silicate particles with dodecyl alcohol along with reversible hydrolytic treatment was an effective and feasible approach to fabricate polymer/silicate composite materials with improved properties.     

High-temperature shear strength of lead-free Sn-Sb-Ag/Al2O3 composite solder

The lead-free Sn-1.7Sb-1.5Ag solder alloy and the same material reinforced with 5 vol.% of 0.3-μm Al₂O₃ particles were synthesized using the powder-metallurgy route of blending, compaction, sintering, and extrusion. The mechanical properties of both monolithic and composite solders were studied by shear punch testing (SPT) at temperatures in the range of 25-130 °C. Depending on the test temperature, the shear yield stress (SYS) increased by 4.8-8.8 MPa, and ultimate shear strength (USS) increased by 6.2-8.8 MPa in the composite material. The strength improvement was mostly due to the CTE mismatch between the matrix and the particles, and to a lesser extent to the Orowan strengthening mechanism of the submicro-sized Al₂O₃ particles in the composite solder. The contribution of each of these mechanisms was used in a modified shear lag model to predict the total composite-strengthening achieved.     

In situ Al3Ti and Al2O3 nanoparticles reinforced Al composites produced by friction stir processing in an Al-TiO2 system

Al and TiO₂ powders were selected to fabricate in situ Al composites via multiple pass friction stir processing (FSP) based on the thermodynamic analysis. The microstructural investigations indicated FSP would induce reaction between Al and TiO₂. Al₃Ti and Al₂O₃ particles were formed after 4 pass FSP with 100% overlapping. The in situ particles were about 80 nm in size at various FSP conditions, and ultrafine matrix grains 602 nm in size were obtained when water cooling was applied during FSP. Tensile tests indicated that the in situ nanocomposites exhibited pronounced work hardening behavior and a good combination of strength and ductility.     

Impact behavior of in situ TiB2/Al composite at various temperatures

The impact behavior of the in situ TiB₂/Al composite was investigated at temperatures varying from −50 to 200 °C. The effects of the reinforcement, heat treatment as well as temperature on the impact toughness and failure mechanism were discussed. Results showed that the impact toughness of the composite decreases significantly due to the presence of the stiff TiB₂ reinforcements. The precipitations caused by aging play the same role as TiB₂ reinforcements, which constrain the deformation of the matrix and reduce the impact toughness. The TiB₂/Al composite is more endurable in suffering the impact load at subzero and high temperatures compared to that at room temperature. The fractography of the TiB₂/Al composite is a cleavage-and-dimple morphology. The eutectic silicon is the preferred site for catastrophic cracking. There is no cracking in the in situ TiB₂ reinforcement because of the small size and near spherical shape. However, the “pulled-out” failure occurs for the TiB₂ reinforcement, which is due to the relative weaker interfacial strength than the strength of reinforcement.