Effect of Si addition on microstructure and mechanical properties of Ti–Al–N coating

Ti–Al–N coatings are widely used to prevent the untimely consumption of cutting tools exposed to wear. Increasing requirements on high speed and dry cutting application open up new demands on the quality of wear-protective quaternary or multinary Ti–Al–N based coating materials. Here, we investigated the microstructure and mechanical properties of Ti–Al–N and Ti–Al–Si–N coatings deposited on cemented carbide by cathodic arc evaporation. The formation of nanocomposite nc-TiAlN/a-Si₃N₄ structure by incorporation of Si into Ti–Al–N coating causes a significant increase on hardness from ∼ 35.7 GPa of Ti–Al–N to ∼ 42.4 GPa of Ti–Al–Si–N. Both coatings behave age-hardening during thermal annealing, however Ti–Al–Si–N coating reveal better thermal stability. Therefore, the improved cutting performance of Ti–Al–Si–N coated inserts is obtained compared to Ti–Al–N coated inserts.     

Effect of Mg addition on mechanical and thermoelectrical properties of Al–Al2O3 nanocomposite

The effects of Mg addition on mechanical thermo-electrical properties of Al–Mg/5%Al₂O₃ nanocomposite with different Mg contents (0, 5%, 10% and 20%) produced by mechanical alloying were studied. Scanning electron microscopy analysis (SEM), X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM) were used to characterize the produced powder. The results show that addition of Mg forms a predominant phase (Al–Mg solid solution). By increasing the mass fraction of Mg, the crystallite size decreases and the lattice strain increases which results from the atomic penetration of Mg atoms into the substitutional sites of Al lattice. The microhardness of the composite increases with the increase of the Mg content. The thermal and electrical conductivities increase linearly with the temperature increase in the inspected temperature range. Moreover, the thermal conductivity increases with the increase of Mg content.     

Mechanical properties of polytypoidally joined Si3N4–Al2O3

Crack-free joining of alumina and silicon nitride has been achieved by a unique approach introducing sialon polytypoids as a functionally graded materials (FGM) bonding layer. The polytypoid compositions are identified in the phase diagram of the Si₃N₄–Al₂O₃ system. The thermal stresses of this FGM junction were analyzed using a finite element analysis program taking into account both coefficient of thermal expansion and modulus variations. From this analysis, the result showed a dramatic decrease in radial, axial and hoop stresses as the FGM changes from three layers to 20 graded layers. Scaling was considered, showing that the graded transition layer should constitute about 75% or more of the total sample thickness to reach a minimal residual stress. Oriented Vickers indentation testing was used to qualitatively characterize the strengths of the joint and the various interfaces. The indentation cracks were minimally or not deflected at the sialon layers, implying strong interfaces. Finally, flexural testing was conducted at room temperature and at high temperature. The average strength at room temperature was found to be 581 MPa and the average strength at high temperature (1200°C) was found to be 262 MPa. Scanning electron microscope observation of fracture surfaces at a different loading rates indicated that the strength loss at higher temperatures was consistent with a softening of glassy materials present at grain junctions.     

Study on microstructures of micron Si3N4 composite ceramic with addition of nano SiC and SiC whisker

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Optimization of friction and wear behaviour of Al–Si3N4 nano composite and Al–Gr–Si3N4 hybrid composite under dry sliding conditions

The tribological behaviour of gravity die stir cast LM6 alloy with graphite (Gr) and silicon nitride nanoparticles was investigated. Al–Gr–Si₃N₄ hybrid composite, Al–Si₃N₄ nanocomposite and Al–Gr nanocomposites were separately fabricated to investigate their frictional and wear characteristics under dry sliding conditions. EDS was used to ensure the uniform presence of nano Si₃N₄ and graphite in the cast. L9 orthogonal array method was chosen to conduct the experiments to study the effect of different applied loads (20, 30 and 40 N) and sliding distances (1, 2 and 3 km). The results showed that the respective wear rate and coefficient of friction (COF) decreased by 25% and 15% for hybrid composite when compared with those of Al–Si₃N₄ nanocomposite whereas the wear rate and COF of Al–Gr was found to be very minimal. The micro Vickers hardness of the hybrid composite was 14% more than that of the simple nanocomposite and there was not much notable variation for Al–Gr and Al–Si₃N₄ nanocomposite materials. Scanning electron microscope was used to analyze the worn surface and subsurface, from which it was noted that the predominant wear mechanisms observed were abrasive for nanocomposite and both abrasive and adhesive mechanism for hybrid composite. Analysis of variance (ANOVA) and F-test were used to check the validity model and to determine the significant parameters affecting the wear rates.     

Investigation of the microstructure and properties of Al–Si–Mg/SiC composite materials produced by solidification under pressure

Composite materials based on alloys of the Al–Si–Mg system have been obtained via the introduction of 5, 10, and 15 wt % of SiC particles into the alloy melt and the solidification under a pressure. As a result of solidification under pressure, the porosity of the composite materials decreased substantially. An increase in the content of SiC particles in the composites enabled a smaller size of dendritic cells to be obtained. It has been shown by the X-ray diffraction method that, in the process of solidification under pressure, an interaction occurred between the matrix and reinforcing SiC particles. The presence of SiC particles in the structure of composites led to the acceleration of the aging process and to an increase in the peak hardness in comparison with the matrix alloy.     

Synthesis of ZrO2-SiC composite powder and effect of its addition on properties of Al2O3-C refractories

ZrO2-SiC composite powder was synthesized by carbothermal reduction of zircon in argon atmosphere, and it was used as the additive to prepare Al2O3-C refractories. The effects of heating temperature on the synthesis process and the addition of the synthesized composite powder on the properties of the Al2O3-C refractories were investigated. The results show that the synthesized composite powder can be easily obtained by heating the mixture of zircon and carbon black at 1 873 K for 4 h in argon atmosphere, and the relative contents of ZrO2 and SiC in sample reach about 83.7% and 16.3%, respectively. The bulk density, crushing strength and thermal shock resistance of the Al2O3-C refractories can be improved obviously by the addition of the synthesized ZrO2-SiC composite powder.     

Effect of Al addition on properties of TiNiFe shape memory alloys

A little amount of aluminum substituting for Ni was added to Ti50Ni48Fe2 and Ti50Ni47.5Fe2.5 alloys to improve the mechanical properties, especially the yield stress of the TiNiFe alloys. The martensitic transformation temperature and mechanical properties of Ti50Ni48-xFe2Alx and Ti50Ni47.5-xFe2.5Alx （x=0, 0.5, 1） alloys were examined, and it was revealed that 0.5% and 1%（mole fraction） aluminum addition lead to about 10℃ and 60-80℃ martensitic transformation temperature （Ms） decrease, respectively, 1%（mole fraction） aluminum addition enhances remarkably the yield stresses of Ti50Ni47Fe2Al1 and Ti50Ni46.5Fe2.5Al1 to 560 and 580 MPa, respectively. The systemic microstructure analysis indicates that the second phase Ti2Ni at the grain boundaries plays an important role in improving the mechanical properties of TiNiFe shape memory alloys.     

Mechanical and wear properties of Mo5Si3–Mo3Si–Al2O3 composites

Mo₅Si₃ and Mo₅Si₃–Mo₃Si–Al₂O₃ composite were synthesized use MoO₃, Mo, Si and Al as raw materials by mechanically induced self propagating reaction and then consolidated by hot-pressing. The microstructure of the materials was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with X-ray energy dispersive spectroscopy (EDS). The effects of the Al₂O₃ on the mechanical and tribological properties of Mo₅Si₃–Mo₃Si–Al₂O₃ composite have been studied. It was found that benefits associated with the addition of the Al₂O₃ to Mo₅Si₃ and Mo₃Si include finer microstructure, higher strength, higher fracture toughness and higher hardness. The dry sliding wear properties of the composite were investigated using against GCr15 bearing steel in ball-on-disk system at room temperature. The results indicated that the friction coefficients and specific wear rates of Mo₅Si₃–Mo₃Si–Al₂O₃ composite were significantly reduced by the addition of Al₂O₃, and its specific wear rates decreased by an order of magnitude compare with the monophase Mo₅Si₃. The friction coefficients of test materials decrease with an increasing load. The dominant wear mechanism of the composites was interpreted by several different wear models involving plastic deformation, adhesion, brittle fracture and reaction to form a tribo-oxidation layer.     

Effect of short carbon fiber addition on pressureless densification and mechanical properties of ZrB2–SiC–Csf nanocomposite

In the present paper, ZrB₂–SiC–C_sf composites were produced by pressureless sintering method. Carbon fiber and SiC nanoparticles with different weight percentages were added to the milled ZrB₂ powder. The mixed powders were formed by hot pressing and cold isostatic press (CIP) and after the pyrolysis, were sintered at 2100 °C and 2150 °C. In order to compare the microstructure and mechanical properties of samples scanning electron microscopy (SEM) equipped with EDS spectroscopy, XRD analysis, hardness and toughness tests were used. The results show that with the increase in weight percentage of carbon fiber, the porosity increases but the hardness, fracture toughness and density decrease. On the other hand, with the increase in weight percentage of SiC nano-particles, the porosity decreases and fracture toughness, hardness and density increase. The results indicate that in an optimal percentage of both additives, the hardness and toughness increase. Additionally, with the increase in sintering temperature, the values of hardness and fracture toughness increase and porosity decreases.     

Thermal shock and thermal fatigue resistance of Sialon–Si3N4 graded composite ceramic materials

Sialon–Si₃N₄ graded composite ceramic materials were fabricated by hot press sintering. The mechanical properties and microstructure of the composites were examined. The thermal shock and thermal fatigue resistance of the Sialon–Si₃N₄ graded composite ceramic materials were investigated by means of the water quenching method. The microstructure of the composites was characterized with transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results showed that the graded ceramic exhibited higher retained flexural strength under all thermal shock temperature differences compared to the homogeneous reference one, indicating the higher thermal shock resistance of the graded ceramic. The highest critical temperature difference of the graded composites was 600 °C. The crack growth (∆c) of graded ceramic materials was much lower than that of homogeneous ceramic materials, which revealed the higher thermal fatigue resistance of the graded ceramics. The improvement of the thermal shock and thermal fatigue resistance was attributed to the formation of compressive residual stress in the surface layer and the enhanced mechanical properties induced by the graded compositional structure.     

Effect of heat treatment on mechanical and wear properties of Zn–40Al–2Cu–2Si alloy

In order to determine the effect of heat treatment on the mechanical and wear properties of Zn–40Al– 2Cu–2Si alloy, different heat treatments including homogenization followed by air-cooling (H1), homogenization followed by furnace-cooling (H2), stabilization (T5) and quench–aging (T6 and T7) were applied. The effects of these heat treatments on the mechanical and tribological properties of the alloy were studied by metallography and, mechanical and wear tests in comparison with SAE 65 bronze. The wear tests were performed using a block on cylinder type test apparatus. The hardness, tensile strength and compressive strength of the alloy increase by the application of H1 and T6 heat treatments, and all the heat treatments except T6, increase its elongation to fracture. H1, T5 and T6 heat treatments cause a reduction in friction coefficient and wear volume of the alloy. However, this alloy exhibits the lowest friction coefficient and wear volume after T6 heat treatment. Therefore, T6 heat treatment appears to be the best process for the lubricated tribological applications of this alloy at a pressure of 14 MPa. However, Zn–40Al–2Cu–2Si alloy in the as-cast and heat-treated conditions shows lower wear loss or higher wear resistance than the bronze.     

Microstrucmre and mechanical properties of Al2O3/TiAl composite

Al2O3/TiAl composites were fabricated by PAXD （pressure-assisted exothermic dispersion） method. The effects of Nb205 content on the microstructure and mechanical properties of the composites were investigated. The results show that the ultimate phases of the composite consist of TiAl, Ti3Al, Al2O3 and a small amount of NbA13. SEM reveals that a submicron γ＋（α2/γ） dual phases structure can be presented after sintered at 1 200 ℃, Furthermore, with the increase of Nb205 content, the ratio of TiAl to Ti3Al phase decreases correspondingly, the grains of the corflposites are remarkably refined, and the produced Al2O3 particles are uniformly dispersed. When 6% Nb205 is added, the composite has the best comprehensive properties. It exhibits a Vickers hardness of 4.77 GPa and a bending strength of 642 MPa. Grain-refinement and dispersion-strengthening are the main strengthening mechanisms.     

Effect of heat-treatment on microstructure and properties of SiC particulate-reinforced aluminum matrix composite

The effects of solid solution and aging processing on the microstructures and mechanical properties of the multi-layer spray co-deposited 7090Al/SiCp composite were investigated. The experimented results show that fine grains and homogeneous microstructures can be obtained, the average grain size of the as-solid solution treated and as-aged composites after extrusion is under 3.0μm. A large amount of the Cu-rich phase particles form in the as-extruded samples, and solve into the matrix after solid solution treatment. After aging, the size of the precipitate phases, mainly MgZn2 and CuAl2 is less than 1.0 μm, which homogeneously distribute inside the grains and at the grain boundaries. The ultimate tensile strength of the composite treated at T6 state, i.e. solid solution treated at 475 ℃for 1 h then aged at 120 ℃ for 24 h, is up to 765 MPa.     

The influence of powder characteristics on mechanical properties of Al2O3–TiC–Co ceramic materials prepared by Co‐coated Al2O3/TiC powders

Ultrafine Al₂O₃–TiC–Co (ATC) ceramic is prepared in order to improve the bending strength and fracture toughness of ceramic materials. The ultrafine Co‐coated Al₂O₃ and TiC powders have been synthesized by electroless plating at room temperature, and the composite powders were sintered by hot‐pressing to compact ATC samples. The average bending strength, average hardness and average fracture toughness values of ATC ceramic with different particle sizes and Co contents were investigated. The toughening mechanism of the ultrafine ATC ceramic was studied by transmission electron microscopy (TEM) and ceramic performance testing methods. The results show that the relative density, bending strength and fracture toughness values increase remarkably with the increase of Co content. The ultrafine grain of original powders is beneficial to improve the relative density, strength and toughness values of ATC ceramic. The Co phase hinders the growth of ATC ceramic grains during sintering. The Co phase forms a three‐dimensional mesh skeleton structure during sintering, improving the fracture toughness and strength of the composite ceramic.     

Effect of Nb addition on microstructure evolution and nanomechanical properties of a glass-forming Ti–Zr–Si alloy

The glass-forming Ti₇₅Zr₁₀Si₁₅ alloy is regarded as a potential material for implant applications due to its composition of non-toxic, biocompatible elements and some interesting mechanical properties. The effects of partial substitution of 15 at.% Ti by Nb on the microstructure and the mechanical behaviour have been investigated by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray analysis, transmission electron microscopy and nanoindentation techniques. Copper mold casting and melt-spinning methods have been applied to study the influence of the cooling rate on the properties of both alloys, Ti₇₅Zr₁₀Si₁₅ and Ti₆₀Zr₁₀Nb₁₅Si₁₅. As a result of different cooling rates, significant microstructural variations from multiphase crystalline states in cast rods to nanocomposite structures in ribbons were observed. The limited glass-forming ability (GFA) of the Ti₇₅Zr₁₀Si₁₅ alloy results for melt-spun ribbons mainly in nanocomposite structures with β-type nanocrystals being embedded in a glassy matrix. Addition of Nb increases the glass-forming ability. Raising the overheating temperature of the melt prior to melt-spinning from 1923 K to 2053 K yields for both alloys a higher amorphous phase fraction. The mechanical properties were investigated using compression tests (bulk samples) and the nano-indentation technique. A decrease of hardness (H), ultimate stress and reduced Young's modulus (E_r) is observed for Ti₆₀Zr₁₀Nb₁₅Si₁₅ rods as compared to Ti₇₅Zr₁₀Si₁₅ ones. This is attributed to an increase of the fraction of the β-type phase. The melt-spun ribbons show an interesting combination of very high hardness values (H) and moderate reduced elastic modulus values (E_r). This results in comparatively very high H/E_r ratios of >0.075 which suggests these new materials for applications demanding high wear resistance.     

Effect of Al addition on formation and mechanical properties of Mg-Cu-Gd bulk metallic glass

The effect of partial substitution of Al for Cu on the glass forming ability（GFA） and mechanical properties of Mg65Cu25-xAlxGd10 （x=0, 1, 3 and 5, molar fraction, %） alloys were studied by X-ray diffi-actometry（XRD）, differential scanning calorimetry（DSC） and uniaxial compression test. The result reveals that GFA of the alloys changes slightly with increasing x from 0 to 3, and then abruptly decreases with x increasing up to 5. The plasticity can be greatly improved with appropriate substitution of Cu by A1 （3%, molar fraction） in Mg65Cu25Gd10 bulk metallic glass, and the resultant fracture strength, total strain to failure, and plastic strain are 898 MPa, 2.19% and 0.2%, respectively.     

Effect of Cu addition on microstructural evolution and hardening of mechanically alloyed Al−Ti−O in-situ composite

The microstructure formation and strengthening of an Al−5wt.%TiO₂ composites with additions of 5 wt.% Cu and 2 wt.% stearic acid (as a process control agent, PCA) during mechanical alloying and subsequent thermal exposure were studied. The powder composites were prepared by high-energy ball milling for up to 10 h. Single line tracks of the powders were laser melted. Optical and scanning electron microscopy, XRD analysis and differential scanning calorimetry were used to study microstructural evolution. The results showed that the Cu addition promotes an effective mechanical alloying of aluminum with TiO₂ from the start of milling, resulting in higher microhardness (up to HV 290), while the PCA, on the contrary, postpones this process. In both cases, the composite granules with uniform distribution of TiO₂ particles were formed. Subsequent heating of mechanically alloyed materials causes the activation of an exothermic reaction of TiO₂ reduction with aluminum, the start temperature of which, in the case of Cu addition, shifts to lower values, that is, the transformation begins in the solid state. Besides, the Cu-added material after laser melting demonstrates a more dispersed and uniform structure which positively affects its microhardness.     

Fabrication and behaviour of Al–Si/SiC composite in cavitation conditions

Aluminium matrix composite (AMC) specimens were prepared using the compocasting technique. The reinforcements used were silicon carbide (SiC) particles with an average size of 30 μm. The influence of reinforced ratio of 10 wt-%SiC on cavitation behaviour was examined. The cavitation resistance of an AMC with SiC (AlSi/SiC) was evaluated using an ultrasonically induced cavitation test method. The mass loss of specimens was measured by an analytical method. The morphology of the damaged surface of tested composite was examined using scanning electron microscopy (SEM). It is shown that the cavitation rate of an AMC with SiC is almost the same as the CA6NM stainless steel, which is largely used in the production of hydraulic machinery components. Because the results show that the composites exhibited very good resistance to the cavitation erosion, this material can be successfully used under conditions where the cavitation resistance is needed.     

In-situ sintering reaction of Al2O3–LaAl11O18–ZrO2 composite

Al₂O₃–LaAl₁₁O₁₈–ZrO₂ composites were prepared by in situ sintering reaction of different proportions of Al₂O₃ and La₂Zr₂O₇. The studied batches were uniaxially pressed and pressureless sintered at 1600 °C up to 1725 °C for 1 h. Phase composition study reveals that the only present phases are alumina, lanthanum hexaluminates and zirconia. No other intermediate phases are present. Rodlike LaAl₁₁O₁₈ was observed in the sintered bodies containing more than 25 wt.% LaAl₁₁O₁₈. The effect of rodlike particles on the densification and mechanical behavior was discussed. It was found that increasing the LaAl₁₁O₁₈ content more than 25 wt.% enhances the fracture toughness, but reduces both the bending strength and the hardness of the sintered composites.