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1.
Al–Bi immiscible alloy is of particular interest as potential self-lubricating wear materials with a homogeneous distribution of minority phase. However, it is difficult to obtain a homogeneous microstructure by conventional casting methods due to liquid phase separation of Al–Bi immiscible alloy. We have developed a new strategy to restrain liquid phase separation and improve the properties of Al–Bi immiscible alloy by in situ phases. The in situ AlB2 phase acts as heterogeneous nucleation site to accelerate the nucleation and slow down the velocity of the Bi-rich droplet, resulting in a significant size reduction and a homogeneous microstructure of Al–Bi immiscible alloy. The self-lubricating wear resistance of Al–Bi immiscible alloy can be further enhanced by in situ Al2Cuphase. 相似文献
2.
Al–Li–SiCp composites were fabricated by a modified version of the conventional stir casting technique. Composites containing 8, 12 and 18 vol% SiC particles (40 mm) were fabricated. Hardness, tensile and compressive strengths of the unreinforced alloy and composites were determined. Ageing kinetics and effect of ageing on properties were also investigated. Additions of SiC particles increase the hardness, 0.2% proof stress, ultimate tensile strength and elastic modulus of Al–Li–8%SiC and Al–Li–12%SiC composites. In case of the composite reinforced with 18% SiC particles, although the elastic modulus increases the 0.2% proof stress and compressive strength were only marginally higher than the unreinforced alloy and lower than those of Al–Li–8%SiC and Al–Li–12%SiC composites. Clustering of SiC particles appears to be responsible for reduced the strength of Al–Li–18%SiC composite. The fracture surface of unreinforced 8090 Al-Li alloy (8090Al) shows a dimpled structure, indicating ductile mode of failure. Fracture in composites occurs by a mixed mode, giving rise to a bimodal distribution of dimples in the fracture surface. Cleavage of SiC particles was also observed in the fracture surface of composites. Composites show higher peak hardness and lower peak ageing time compared with unreinforced 8090Al alloy. Macroand microhardness increase significantly after peak ageing. Ageing also results in considerable improvement in strength of the unreinforced 8090Al alloy and its composites. This is attributed to formation of δ' (Al3Li) and S' (Al2CuMg) precipitates during ageing. Per cent elongation, however, decreases due to age hardening. Al–Li–12%SiC, which shows marginally lower UTS and compressive strength than the Al–Li–8%SiC composite in extruded condition, exhibits higher strength than Al–Li–8%SiC in peak-aged condition. 相似文献
3.
《Materials Science & Technology》2013,29(8):1321-1327
AbstractTiC/Ti–6Al–4V composites containing various volume fractions of TiC were produced by induction skull melting and common casting utilising in situ reaction between titanium and carbon powder. The microstructure and room tensile properties of as cast and heat treated TiC/Ti–6Al–4V composites were investigated. Bar-like or small globular eutectic TiC were found in 5 vol.-%TiC/Ti–6Al–4V composite, whereas the equiaxed or dendritic primary TiC particles were found to be the main reinforcements in 10 and 15 vol.-%TiC/Ti–6Al–4V composites. The as cast TiC/Ti–6Al–4V composites have shown higher strength but lower ductility than those of monolithic Ti–6Al–4V alloy. The shape and fracture of TiC particles can strongly influence the fracture and failure of the composites, and so the ultimate tensile strengths and elongations of as cast composites reduce with the increase in volume fraction of TiC. TiC particles appear to be spheroidised, and titanium precipitation can be found within large TiC particles after heat treatment at 1050°C for 8 h, which can promote the resistance to fracture of composites. Therefore, the elongations of the composites increase significantly, and the ultimate tensile strengths also have marginal increase especially for the 10 and 15 vol.-%TiC/Ti–6Al–4V composites after heat treatment. 相似文献
4.
Incorporation of SnO2 into MgO–spinel (M–S) increased mechanical properties significantly. Relationships between the parameters improving mechanical properties and microstructural variables were examined. Basic parameters improving the mechanical properties of M–S–SnO2 composites were identified as follows: (a) when microcracks come across with either Mg2SnO4 particles or pores; crack branching and deviation of interlinked microcracks or crack arresting occurred more effectively than those of spinel particles, (b) fracture type was converted to intergranular fracture with incorporation of spinel into MgO, and transgranular fracture with addition of SnO2 to M–S; additionally with the incorporation of additives, (c) critical defect size, (d) work of fracture values increased, and (e) MgO grain size decreased. Rst thermal shock parameter values of M–S–SnO2 composites were markedly higher than those of M–S materials, associated with low strength loss, high thermal shock damage resistance and thus longer service life of M–S–SnO2 composites for high-temperature industrial applications. 相似文献
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6.
In the present study, the microstructure, mechanical and wear properties of AXJ530 alloy under different solidification condition were investigated. AXJ530 alloys were cast in a multi-step permanent mould casting (PMC) with five different cooling rates, and also in high pressure die casting (HPDC). The effect of cooling rate was determined for the room temperature mechanical properties and the dry sliding wear resistance of the AXJ530 alloys. The results showed that grain size of AXJ530 alloy was refined and thinner lamellar eutectic phase formed at higher cooling rate. It was concluded that these changes led to the observed concurrent increases in ultimate tensile strength (σuts), yield strength (σ0.2) and elongation (δ) of the AXJ530 alloy. The relationship between grain size and yield strength/hardness agreed with Hall–Patch behavior. The dry sliding wear rate of the PMC specimens decreased with increasing of cooling rate, but micro-porosity/inclusion in the HPDC specimen decreased its wear resistance properties. Abrasion was determined to be the dominant wear mechanism for the AXJ530 alloys. 相似文献
7.
《Materials Science & Technology》2013,29(7):823-832
AbstractIn the present study, elemental magnesium and magnesium–silicon carbide composites were synthesised using the methodology of fluxless casting followed by hot extrusion. Microstructural characterisation studies revealed low porosity and a completely recrystallised matrix in every material. The average size of the recrystallised grains was found to decrease with an increasing presence of SiC particulates. For the reinforced magnesium, fairly uniform distribution of SiC particulates and good SiC–Mg interfacial integrity was realised. The results of X-ray diffraction studies indicated the absence of oxide phases and no evidence of interfacial reaction products except in the case of Mg–26.0 wt-%SiC sample. Results of physical and mechanical properties characterisation revealed that an increase in the amount of SiC particulates incorporated leads to an increase in macrohardness and elastic modulus, which does not affect the 0.2% yield strength and reduces the ultimate tensile strength, ductility, and coefficient of thermal expansion. The weight percentage of SiC particulates when plotted against hardness and 0.2% yield strength revealed a linear correlationship. An attempt is made to investigate the effect of increasing amount of SiC particulates on the microstructural features, and physical and mechanical properties of the magnesium matrix. 相似文献
8.
At present, the mechanical properties of the Mg–3Sn–2Ca magnesium alloy are not satisfying and further enhance needs to be considered via further alloying/microalloying additions. The effects of Zr addition on the as-cast microstructure and mechanical properties of the alloy were investigated by using optical and electron microscopies, differential scanning calorimetry (DSC) analysis, and tensile and creep tests. The results indicate that adding 0.41, 0.76 or 1.18 wt.% Zr can refine the grains of the alloy, and the primary CaMgSn phases in the Zr-containing alloys are changed from coarse needle-like net to relatively fine short block and/or particle-like shapes. As a result, the tensile and/or creep properties of the Zr-containing alloys are improved. Among the Zr-containing alloys, the alloy with the addition of 0.76 wt.% Zr exhibits the relatively optimum mechanical properties. 相似文献
9.
《Materials Science & Technology》2013,29(12):1295-1300
AbstractComposites with an Al–Mg–Si alloy matrix containing 20 vol.-% of either Si3N4 whiskers or Si3N4 particulates were extruded at 773 K with a reduction ratio of 100: 1, and tensile experiments were performed under conditions of constant true strain rate. Recrystallisation and dynamic precipitation occurred during hot extrusion so that very small grain sizes of less than ~ 3 ;amp;#x03BC;m were produced. The extruded composites showed superplastic behaviour at high strain rates (above 10?1 S?1). The high strain rate superplasticity of the composites is attributed to the very small grain sizes. Internal cavities developed during straining and density studies revealed that the rate of increase of the extent of cavitation was lower at a temperature slightly above the partial melting temperature than at a temperature lower than the partial melting temperature. It is concluded that the presence of a liquid phase restricts the development of cavities because the liquid phase serves to relax the stress concentrations.MST/3139 相似文献
10.
《Composites Part B》2000,31(5):383-390
NiAl–Al2O3 functionally gradient composites (FGCs) have been fabricated by reactive hot compaction of Ni and Al powders in which one or both were partially preoxdized. The FGCs consisted of four or five layers with alumina content increasing up to about 35 vol.%. The gradient in the composition was obtained by stacking powder mixtures of desired compositions. It was found that the technique resulted in a gradual transition of the microstructure and microhardness from NiAl to NiAl–35 vol.%Al2O3. In contrast, the NiAl– (NiAl–35 vol.%Al2O3) bilayer compact showed a much steeper microhardness change with pronounced residual stress at the boundary. The FGCs were found to have higher fracture toughness values than the corresponding composites. 相似文献
11.
Carbon nanotubes were blended into a Ti–6Al–4V matrix to synthesize titanium carbide (TiC) in situ, via spark plasma sintering. The microstructure and mechanical properties of both the monolithic Ti–6Al–4V alloys and the TiC/Ti–6Al–4V composites were studied to evaluate the strengthening effects of TiC on the Ti–6Al–4V matrix. The morphologies obtained by scanning electronic microscopy and optical microscopy indicated that the grain size of both the Ti–6Al–4V alloy and the TiC/Ti–6Al–4V composite decreased with increasing planetary ball-milling (PBM) speed, leading to an increase in the hardness of the investigated materials. The compressive yield strength of the monolithic Ti–6Al–4V alloys and the TiC/Ti–6Al–4V composites initially increased and then decreased with increasing PBM speed. The strengthening and fracture mechanisms were studied. 相似文献
12.
《Materials Science & Technology》2013,29(11):1653-1656
AbstractMetal matrix composites are considered as a distinct category of the advanced materials, which have low weight, high strength, high modulus of elasticity, low thermal expansion coefficient and high wear resistance. Among them, Al–Al2O3 composites have achieved significant attention due to their desired properties. In the present research, Al–Al2O3 composites with 5 vol.-% alumina were produced by stir casting at a temperature of 800°C. Two different particle sizes of alumina were used as 53–63 and 90–105 μm. The microstructure of the samples was evaluated by SEM. In addition, the mechanical properties of the samples were measured, and hence, the optimum temperature and particle size of alumina to be added to the Al matrix were determined. The results demonstrated the positive effect of alumina on improving the properties of Al–Al2O3 composites. 相似文献
13.
Heguo Zhu Yinglu Ai Jianliang Li Jing Min Da Chu Jun Zhao Jie Chen 《Advanced Powder Technology》2011,22(5):629-633
α-Al2O3 ceramic particles and Ni2Al3 intermetallic compound reinforced aluminum matrix composites were successfully fabricated via exothermic dispersion (XD) reaction in an Al–Ni2O3 system. Thermodynamic analysis indicated that the reaction between Al and Ni2O3 could occur spontaneously due to its negative Gibbs free energy. The reaction characteristic was discussed by using X-ray diffraction (XRD) method and differential scanning calorimetry (DSC) analysis. The results showed that the reactions of the Al–Ni2O3 system consisted of two steps as following: (1) the Al firstly reacted with Ni2O3 to form the stable α-Al2O3 particles and active Ni atoms; (2) the active Ni atoms further reacted with Al to form Ni2Al3. The values of activation energy of the two step reactions were around 457.3 and 282.4 kJ/mol, respectively. The scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) revealed that the Ni2Al3 blocks were uniformly distributed throughout the matrix, while the α-Al2O3 particles were slightly segregated in the matrix. The strength of the composite is controlled by the strength of Ni2Al3 phase, and the tensile strength and the elongation rate of the composite with 30 vol.% reinforcement volume fraction are 210 MPa and 8%, respectively. 相似文献
14.
Xinjiang Zhang Yibin Li Guangping Song Yue Sun Qingyu Peng Yuxin Li Xiaodong He 《Materials & Design》2011,32(8-9):4327-4332
(TiC + Nd2O3)/Ti–4.5 wt.%Si composites were in situ synthesized by a non-consumable arc-melting technology. The phases in the composites were identified by X-ray diffraction. Microstructures of the composites were observed by optical microscope and scanning electron microscope. The composite contains four phases: TiC, Nd2O3, Ti5Si3 and Ti. The TiC and Nd2O3 particles with dendritic and near-equiaxed shapes are well distributed in Ti–4.5 wt.%Si alloy matrix, and the fine Nd2O3 particles exist in the network Ti + Ti5Si3 eutectic cells and Ti matrix of the composites. The hardness and compressive strength of the composites are markedly higher than that of Ti–4.5 wt.%Si alloy. When the TiC content is fixed as 10 wt.% in the composites, the hardness is enhanced as the Nd2O3 content increases from 8 wt.% to 13 wt.%, but the compressive strength peaks at the Nd2O3 content of 8 wt.%. 相似文献
15.
Er-Jun Li Kai Xia Shuang-Feng Yin Wei-Li Dai Sheng-Lian Luo Chak-Tong Au 《Materials Chemistry and Physics》2011,125(1-2):236-241
A series of Bi2O3–MgO composites were synthesized by solvent-thermal method. It was found that the Bi2O3–MgO composites perform much better than TiO2 (P25), Bi2O3 and MgO in the photocatalytic degradation of rhodamine B (RhB) in the presence of HCl and under irradiation of visible light (λ > 400 nm). The effects of Bi/Mg molar ratio, crystallization temperature of Bi2O3–MgO and reaction conditions on photocatalytic activity were studied. The best performance was observed over the composite with Bi:Mg molar ratio equal to 2:1 that had been subject to crystallization at 120 °C for 20 h. In addition, the photocatalytic efficiency of the composite can be significantly enhanced by the presence of hydrochloric acid. The prepared samples were characterized by XRD and UV–vis DRS techniques. The relationships between the structure and photocatalytic performance of the as-prepared Bi2O3–MgO samples were also investigated. 相似文献
16.
《Materials Science & Technology》2013,29(8):672-677
AbstractAn investigation was made into the influence of a retrogression and reaging treatment on the microstructure, tensile properties, and stress corrosion cracking resistance of 8090 Al–Li alloy. The results show that retrogression of the material at 230°C for 40 min or 325°C for 1·5 min, and then reaging to the peak aged condition, can result in an improved combination of tensile strength and stress corrosion cracking resistance. Through retrogression and reaging treatment, the alloy almost achieves the strength of the peak aged state and the stress corrosion cracking resistance of the overaged state. Transmission electron microscopy indicates that the δ′ phase dissolves during retrogression and reprecipitates during reaging, thus increasing the strength. The T2 phase precipitates and grows during both retrogression and reaging, which results in the increase of stress corrosion cracking resistance.MST/1670 相似文献
17.
The dielectric properties of unreinforced Lanxide Al2O3/Al composites have been investigated over a wide range of temperatures and frequencies. These composites were formed by the directed oxidation of suitably doped aluminium-based alloy melts, with no filler or reinforcing material in the reaction path. As-grown composite materials were good electrical conductors in all directions owing to the presence of an interconnected metallic constituent. As the metallic phases were partially removed (in favour of porosity) by continuing the oxidation reaction to completion, the composites remained electrically conducting parallel to, and became insulating transverse to, the original growth direction of the composite. This anisotropy apparently was caused by different connectivity of the metal phase between the two directions. Thermal treatments at 1600°C in argon resulted in volatilization of the residual metal in the composite, thus further increasing the porosity. As the metal content was decreased, the composites changed from conducting to insulating along the growth direction. When the metallic phase was removed completely, the porous alumina ceramic maintained anisotropic dielectric properties, due to c-axis alignment of the alumina (corundum) phase along the growth direction. The dielectric constants were 8.0 and 6.4, respectively, parallel and perpendicular to the c-axis aligned directions of the porous alumina ceramic. A dielectric relaxation phenomenon was observed in some samples of both as-grown and thermally treated material, and was attributed to an unidentified impurity effect. 相似文献
18.
Yonggang Zhang Shunhua Wu Baolin Zhang Xiaogang Wu 《Journal of Materials Science: Materials in Electronics》2014,25(7):3085-3089
The effect of Li2O3–B2O3–SiO2 (LBS) liquid-phase additives on the sintering, microstructures, and dielectric properties of MgO–TiO2–ZnO–CaO (MTZC) ceramics was investigated. It was found that the sintering temperature could be lowered easily, and the dielectric properties of MTZC ceramics could be greatly improved by adding a small amount of LBS solution additives. With the addition of 10 wt% LBS, the ceramics sintered at 900 °C showed favorable dielectric properties with εr = 21.7, Qf = 5.0 × 104 GHz, and TCF = ?21.6 ppm/ °C. The distructive physical analysis showed an excellent co-firing interfacial behavior between the MTZC ceramic and the Ag electrode. It indicated that MTZC ceramics with LBS solution additives have a number of potential applications on passive integrated devices based on the low-temperature co-fired ceramics technology. 相似文献
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20.
《Materials Letters》2003,57(22-23):3543-3548
The preparation of ZnCr2O4 was carried out by the high-temperature solid-state method with the reaction of Cr2O3 and ZnO at 900 °C. Experimental results on the composites made from different mole ratios of ZnCr2O4 and ZnO for electrical and humidity-sensing properties are described. The sintered polycrystalline disks of the composites were subjected to DC electrical conductivity measurements over the temperature range 330–500 K from which the activation energies were determined. The composites were identified by powder X-ray diffraction (XRD). The scanning electron microscopy (SEM) studies were carried out to study the surface structure of the sensor materials. The composites were subjected to DC resistance measurements as a function of relative humidity in the range of 5–98% RH, achieved by different water vapor buffers thermostated at room temperature. The sensitivity factor Sf (R5%/R98%) measured at 298 K revealed that ZCZO-21 has the highest humidity sensitivity, greater than 6.5×103; however, ZCZO-11, ZCZO-32, and ZCZO-14 have lower sensitivity but better linear trend. The response and recovery characteristics for ZCZO-21 and ZCZO-11 were assessed. 相似文献