Experimental investigation on tribological behaviours of PA6, PA6-reinforced Al<Subscript>2</Subscript><Emphasis Type="Italic">O</Emphasis><Subscript>3</Subscript> and PA6-reinforced graphite polymer composites

This article reports on the preparation, characterization and experimental investigation of polyamide 6 (PA6) reinforced with alumina oxide (Al₂O₃) and graphite composites. The test specimens were prepared in an injection-moulding machine by varying the weight proportions of Al₂O₃ and graphite particles blended with PA6. The tribological properties of the composites were observed by using pin-on-disc wear test rig under dry sliding conditions. The worn surfaces of the composites were examined using scanning electron microscope. The addition of Al₂O₃ and graphite significantly enhanced the tribological properties of PA6. The PA6 containing 30 wt% Al₂O₃ and 20 wt% graphite revealed the best tribological behaviours due to the stronger interfacial bonding characteristics with improved wear resistance. Further, the thermal stability of Al₂O₃ and graphite particles was studied through thermogravimetric analysis test. It was also found that further addition of Al₂O₃ and graphite in PA6 had no significant improvement in wear resistance, the co-efficient of friction and heat generation.     

Effect of magnesium addition on wear behaviour of Al–70 vol.-%Al2O3p composites

Abstract

Inthisstudy, drysliding and abrasive wear behaviour ofAl-70 vol.-%Al₂O₃particulate composite alloyed with Mg was examined. The composites were produced by a pressure infiltration casting technique. The composition of the matrix varied between 0 and 8 wt-%Mg, and the diameter of the Al₂O₃ particulates was 60 μm. Dry sliding wear tests were carried out on an unlubricated M2 quality high speed tool steel disc by a pin on disc type wear tester. Abrasive wear tests were run by rubbing the composites on abrasive Al₂O₃ grains. The results of the wear tests revealed that, both dry sliding and abrasive wear resistance ofthe composites increased with increasing Mg content in the matrix.     

The wear behavior of Al/(Al2O3 + SiC + C) hybrid composites fabricated stir casting assisted squeeze

Economically fabrication and achieving appropriate properties of HMMCs is a challenge. Keeping in view, an oil fired muffle furnace has been designed and developed for melting of Al matrix. Hybrid Al/(Al₂O₃?+?SiC?+?C)MMCs were fabricated by liquid stir with squeeze casting. In addition, an electrochemical micro-machining (ECMM) setup has been developed and utilized for micro-machining of hybrid MMC. The wear tests were carried out on a pin on disc machine at a constant track diameter of 60?mm, by varying speed of disc at 300, 600, and 1200?rpm and applying the varying loads at 4.91, 9.82, and 14.72?N under dry sliding conditions. The HMMC with 20% SiC, 7.5% C, and 10% Al₂O₃ was found to be the best wear resistance under high load and high speed. The wear resistance was improved by 64.28 and 85.29%, when carbon particles reinforcement content increased from 3 to 5% and 3 to 7.5%, respectively. The machined surface texture and decomposition of metallic compounds deposited on workpiece were measured and analyzed through various SEM, EDX, and XRD images.     

Wear behavior of TiB<Subscript>2</Subscript> inoculated 20Cr–3Mo–4C high chromium white cast irons

FeTi, B₂O₃, Al, and FeW particulates, approximately 40–60 μm in size, were mixed in stoichiometric ratio and sintered at 1,200 °C. The sintered particulates were added as 5 wt% to molten high chromium white cast iron over 50 C-deg above the melting temperature, and stirred at 1,000 rpm. The samples were investigated in three groups: (1) high Cr white cast iron inoculated by the particulates sintered from Al–FeTi–B₂O₃ particulates; (2) high Cr white cast iron inoculated by the sintered particulates derived from Al–FeTi, B₂O₃, and FeW particulates; and (3) specimens of the second group that were subsequently homogenized. The microhardness of ceramic particulates was measured as 2,800–3,400 HV₁₀. The effect of sintered particulate volume fraction on the abrasive wear resistance of the high chromium white cast iron was determined. The wear resistance and hardness of the composites improved significantly as a result of particulate inoculation. The application of the homogenization heat treatment to the inoculated samples produced a microstructure having homogeneously distributed particulates.     

Effect of mechanical milling on the corrosion behavior of Al–Zn/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite in NaCl solution

Ceramic particle reinforced aluminum metal matrix composites (MMCs) have resulted in potential use in aerospace and automobile industries. The composites have been processed by mechanical milling followed by traditional powder metallurgy route. The Al crystallite size is reduced to 27 nm after 60 h of milling. Results of the corrosion tests, evaluated using the potentiodynamic method in the NaCl solution, indicate that corrosion of the investigated composite materials depends on the weight fraction of the reinforcing particles. It has been found out, based on the determined anode polarization curves, that the investigated materials are susceptible to pitting corrosion. Moreover, experimental results suggest that the milled composite material Al–Zn/Al₂O_3p has higher corrosion resistance in the selected environment compared to unmilled composite Al–Zn/Al₂O_3p. Polarization curves show that the milling procedure improves the composite corrosion resistance in passive conditions. This is illustrated by the corrosion potential, which becomes nobler with milling.     

Effect of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> on the crystallization behavior of SiO<Subscript>2</Subscript>–MgO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

A series of glass comprising of SiO₂–MgO–B₂O₃–Y₂O₃–Al₂O₃ in different mole ratio has been synthesized. The crystallization kinetics of these glasses was investigated using various characterization techniques such as differential thermal analysis (DTA), thermo gravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Crystallization behavior of these glasses was markedly influenced by the addition of Y₂O₃ instead of Al₂O₃. Addition of Y₂O₃ increases the transition temperature, T _g, crystallization temperature, T _c and stability of the glasses. Also, it suppresses the formation of cordierite phase, which is very prominent and detrimental in MgO-based glasses. The results are discussed on the basis of the structural and chemical role of Y³⁺ and Al³⁺ ions in the present glasses.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> on the properties of nanocrystalline ZrO<Subscript>2</Subscript> + 3 mol % Y<Subscript>2</Subscript>O<Subscript>3</Subscript> powder

We have studied the properties of nanocrystalline ZrO₂〈3 mol % Y₂O₃〉 and 90 wt % ZrO₂〈3 mol % Y₂O₃〉-10 wt % Al₂O₃ powders prepared via hydrothermal treatment of coprecipitated hydroxides at 210°C. The results demonstrate that Al₂O₃ doping raises the phase transition temperatures of the metastable low-temperature ZrO₂ polymorphs and that the structural transformations of the ZrO₂ and Al₂O₃ in the doped material inhibit each other.     

Role of Ti diffusion on the formation of phases in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> brazed interface

Diffusivities of Ti, Cu, Al and Ag in the interface of Al₂O₃–Al₂O₃ braze joints using Ag–Cu–Ti active filler alloy, have been calculated by Matano–Boltzman method. The Matano plane has been identified for each elemental diffusion at various brazing temperatures. The diffusivities of Ag, Cu and Al are almost insignificant on formation of interface during brazing, whereas the diffusivity of Ti changes significantly with the brazing temperature and controls the formation of different reaction product in the interface. Presence of TiO and Ti₃Cu₃O phases in the interface has been confirmed by transmission electron microscopy (TEM).     

The effects of various reinforcements on dry sliding wear behaviour of AA 6061 nanocomposites

The present work aims to investigate the dry sliding wear behaviour of AA 6061 nanocomposites reinforced with various nanolevel reinforcements, such as titanium carbide (TiC), gamma phase alumina (γ-Al₂O₃) and hybrid (TiC + Al₂O₃) nanoparticles with two weight percentages (wt.%) prepared by 30 h of mechanical alloying (MA). The tests were performed using a pin-on-disk wear tester by sliding these pin specimens at sliding speeds of 0.6, 0.9 and 1.2 m/s against an oil-hardened non-shrinking (OHNS) steel disk at room temperature. Wear tests were conducted for normal loads of 5, 7 and 10 N at different sliding speeds at room temperature. The variations of the friction coefficient and the wear rate with the sliding distances (500 m, 1000 m and 1600 m) for different normal loads and sliding velocities were plotted and investigated. To observe the wear characteristics and to investigate the wear mechanism, the morphologies of the worn surfaces were analysed using a scanning electron microscope (SEM). The formation of an oxide layer on the worn surface was examined by energy dispersive spectroscopy (EDS). The wear rate was found to increase with the load and sliding velocity for all prepared nanocomposites. Hybrid (TiC + Al₂O₃) reinforced AA 6061 nanocomposites had lower wear rates and friction coefficients compared with TiC and Al₂O₃ reinforced AA 6061 nanocomposites.     

Compositional factors affecting the establishment and maintenance of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> scales on Ni–Al–Pt systems

The beneficial role played by platinum addition in promoting the formation of a protective Al₂O₃ scale on representative γ′-Ni₃Al+γ-Ni coating compositions during high-temperature oxidation is discussed. This beneficial effect can be primarily ascribed to the fact that Pt is non-reactive, and its addition decreases the chemical activity of aluminum in γ′. Related to the latter, Pt partitions almost solely to the Ni sites in the ordered L1₂ crystal structure of γ′, which has the effect of amplifying the increase in the Al: Ni atom fraction on a given crystallographic plane containing both Al and Ni. Such an effective Al enrichment at the γ′surface kinetically favors the formation of Al₂O₃ relative to NiO. A further contributing factor is that the Pt-containing γ′-based alloys show subsurface Pt enrichment during the very early stages of oxidation. This enrichment reduces Ni availability and can increase the Al supply to the evolving scale, thus kinetically favoring Al₂O₃ formation. This observed benefit of Pt addition promoting exclusive Al₂O₃-scale growth is inferred to be a special form of the third-element effect.     

Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticle reinforced Fe-based alloys synthesized by thermite reaction

It is very difficult to manufacture oxide nanoparticle strengthened alloys through the conventional casting in the gravity field or even in the space microgravity environment. A thermite reaction process was used to produce molten metal that was then solidified in a graphite mold in super gravity field caused by centrifugal force; we were able to obtain Al₂O₃ nanoparticle reinforced Fe-based alloys. The formation of Al₂O₃ nanoparticles was related to the addition of TiO₂ xerogel to the thermite mixture, and their uniform distribution in the alloy can be explained by their assembly in (Ni, Fe)Al intermetallics during solidification owing to the low interfacial energy between them.     

A novel method for producing open-cell Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> ceramic foams with controlled cell structure

A novel method was introduced to prepare open-cell Al₂O₃–ZrO₂ ceramic foams with controlled cell structure. This method used epispastic polystyrene (EPS) spheres to array ordered templates and centrifugal slip casting in the interstitial spaces of the EPS template to obtain cell struts with high packing density. Aqueous Al₂O₃–ZrO₂ slurries with up to 50 vol.% solid contents were prepared and centrifuged at acceleration of 2,860g. The effect of the solid contents of slurries on segregation phenomena of different particles and green compact uniformity were investigated. In multiphase system, the settling velocities of Al₂O₃ and ZrO₂ particles were calculated. Theory analysis and calculated results both indicated segregation phenomenon was hindered for slurries with 50 vol.% solid content. The cell struts of sintered products had high green density (61.5%TD), sintered density (99.1%TD) and homogeneous microstructures after sintered at 1,550 °C for 2 h. The cell size and porosity of Al₂O₃–ZrO₂ ceramic foams can be adjusted by changing the size of EPS spheres and the load applied on them during packing, respectively. When the porosity increased from 75.3% to 83.1%, the compressive strength decreases from 3.82 to 2.07 MPa.     

Hollow biomorphic Al<Subscript>2</Subscript>O<Subscript>3</Subscript> fibers produced from sisal

Al₂O₃ fibers with a hollow morphology were produced by Al-vapor infiltration-reaction and subsequent oxidation from pyrolysed fibers of natural sisal. Following pyrolysis, the bio-fiber template was reacted with gaseous Al at 1,400 °C–1,600 °C in vacuum to form Al₄C₃. After an oxidation/sintering process at 1,550 °C, the biomorphic Al₄C₃ fibers were fully converted into Al₂O₃, maintaining the microstructural features of the native sisal. Phase and microstructural characterization during processing were evaluated by high temperature X-ray diffractometry and scanning electron microscopy, respectively. Thermo-analyses were performed in the Al₄C₃ samples in order to estimate the reactions and the weight change during the oxidation step.     

Fabrication of TiC and TiB<Subscript>2</Subscript> locally reinforced steel matrix composites using a Fe–Ti–B<Subscript>4</Subscript>C–C system by an SHS-casting route

Steel matrix composites locally reinforced by in situ TiC and TiB₂ particulates were successfully fabricated using self-propagating high-temperature synthesis (SHS) in a Fe–Ti–B₄C–C system during casting. The locally reinforced steel matrix composites consist of three distinct regions: (i) a TiC and TiB₂ particulate-reinforced region, (ii) a transition region, and (iii) a steel matrix region. The TiC and TiB₂ particulates in the locally reinforced regions display a relatively uniform distribution, and their sizes decrease with the increase in Fe content from 10 wt.% to 40 wt.%. The wear resistance of the locally reinforced region of the steel matrix composites is much higher than that of the unreinforced steel matrix.     

Effect of nano-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> doping on formation and superconductivity of bulk MgB<Subscript>2</Subscript>

Bulk materials of MgB₂ have been prepared with the stoichiometry of MgB₂(Al₂O₃) _x (x = 0, 2, 5, 10 and 20% nano-Al₂O₃ powders), by using solid-state reaction route. All samples were sintered at 750 °C for 30 min in a calorimeter to monitor the sintering reaction process. It is found that the onset temperatures of reaction between Mg and B powders increase significantly with increasing the amount of Al₂O₃. However, the reaction time is shortened for the nano-Al₂O₃ powders can effectively activate the reaction as a catalyst. The critical transition temperature decreases from 38.5 to 31.6 K, and the corresponding temperature window becomes narrow (less than 2.6 K). Furthermore, the amount of MgO impurity was found to increase with the increase of Al₂O₃, which probably indicates that partial Mg was replaced by Al.     

Microstructure and high-temperature strength of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Er<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>/ZrO<Subscript>2</Subscript> ternary melt growth composite

A new Al₂O₃/Er₃Al₅O₁₂(EAG)/ZrO₂ ternary MGC (Melt Growth Composite) with a novel microstructure has been fabricated by unidirectional solidification. This ternary MGC has a microstructure consisting of continuous networks of single-crystal Al₂O₃, single-crystal EAG and fine cubic-ZrO₂ phases without grain boundaries. The ternary MGC has also characteristic dimensions of the microstructure of around 2–4 m for EAG phases, around 2–4 m for Al₂O₃ phases reinforced with around 0.4–0.8 m cubic-ZrO₂ phases. No amorphous phases are formed at interfaces between phases in the ternary MGC. The ternary MGCs flexural strength at 1873 K is approximately 700 MPa, more than twice the 330 MPa of the Al₂O₃/EAG binary MGC. The fracture manner of the Al₂O₃/EAG/ZrO₂ ternary MGC at 1873 K shows the same intergranular fracture as the Al₂O₃/EAG binary MGC, but is significantly different from the transgranular fracture of the sintered ceramic.     

Microstructure evolution and mechanical properties of Al<Subscript>2</Subscript>O<Subscript>3sf</Subscript>/AZ91D magnesium matrix composites fabricated by squeeze casting

The squeeze casting process was used to fabricate Al₂O_3sf/AZ91D magnesium matrix composites before thixoforging. The microstructural evolution process in Al₂O_3sf/AZ91D was investigated during partial remelting. Tensile mechanical properties of thixoforged automotive component were determined and compared with those of squeeze casting formed composites. The results show that the microstructural evolution during partial remelting exhibited four stages: the formation of liquid, structural fragmentation, the spheroidization of solid particles, and final coarsening. As the holding time increases, the size of solid particles decreases initially and then increases. However, the size of solid particles decreases monotonously as the temperature increases. Increasing holding time or temperature promotes the degree of spheroidization. It is also shown that the cylindrical feedstock of the Al₂O_3sf/AZ91D composites can be thixoforged in one step into intricate shapes in the semi-solid state. The tensile tests indicate that the yield strength and ultimate tensile strength for Al₂O_3sf/AZ91D thixoforged from starting material fabricated by squeeze casting and partial remelting are better than those of Al₂O_3sf/AZ91D fabricated by squeeze casting. This research confirms that thixoforging is a practical method for the near net shape forming of magnesium matrix composites.     

Mechanical properties and microstructure of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/mullite composite

An Al₂O₃/5 vol.% mullite composite was synthesized by using reaction sintering of Al₂O₃/0.78 wt.% SiC at 1,600 °C for 2 h in air. The phase analysis of the Al₂O₃/mullite composite was carried out using X-ray diffraction (XRD). There were two kinds of mullite in alumina/mullite composite, namely, 3Al₂O₃·2SiO₂ and Al_5.65Si_0.35O_9.175. The microstructure of the Al₂O₃/mullite composite was investigated using scanning electron microscope (SEM) and transmission electron microscope (TEM). The mechanical properties such as Young’s modulus, Poisson’s ratio, hardness, toughness and strength of the Al₂O₃/mullite composite were investigated. The influence of mullite on the composite is discussed.     

Effect of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> coating on interfacial wettability and tensile properties of Al<Subscript>18</Subscript>B<Subscript>4</Subscript>O<Subscript>33</Subscript>w/Al composite

A pure aluminum matrix composite reinforced by Bi₂O₃-coated Al₁₈B₄O₃₃ whisker was fabricated by squeeze casting method. The effects of Bi₂O₃ coating on the whisker/matrix wettability and the ultimate tensile strength and elongation to fracture of the composite are investigated. The results show that Bi₂O₃ coating can react with aluminum matrix during casting process, which improves the whisker/matrix wettability. Moreover, the ultimate tensile strength and elongation to fracture of the composite attain the maximum values at the mass ratio of 40:1 between whisker and Bi₂O₃ coating.     

Effect of alumina particle size and thermal condition of casting on microstructure and mechanical properties of stir cast Al–Al2O3 composites

Abstract

Metal 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.