Densification and mechanical properties of fine-grained Al2O3-ZrO2 composites consolidated by spark plasma sintering

Alumina matrix composites containing 5 and 10 wt% of ZrO₂ were sintered under 100 MPa pressure by spark plasma sintering process. Alumina powder with an average particle size of 600 nm and yttria-stabilized zirconia with 16 at% of Y₂O₃ and with a particle size of 40 nm were used as starting materials. The influence of ZrO₂ content and sintering temperature on microstructures and mechanical properties of the composites were investigated. All samples could be fully densified at a temperature lower than 1400 °C. The microstructure analysis indicated that the alumina grains had no significant growth (alumina size controlled in submicron level 0.66-0.79 μm), indicating that the zirconia particles provided a hindering effect on the grain growth of alumina. Vickers hardness and fracture toughness of composites increased with increasing ZrO₂ content, and the samples containing 10 wt% of ZrO₂ had the highest Vickers hardness of 18 GPa (5 kg load) and fracture toughness of 5.1 MPa m^1/2.     

Effect of applied current on the electrodeposited Ni-Al2O3 composite coatings

Nano-sized Al₂O₃ ceramic particles (50 nm) were co-deposited with nickel using electrodeposition technique to develop composite coatings. The coatings were produced in an aqueous nickel bath at different current densities and the research investigated the effect of applied current on microstructure and thickness of the coatings. The variation in some mechanical properties such as hardness, wear resistance, and the adhesive strength of the composite coatings is influenced by the applied current and this was also studied. The morphology of the coatings was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The hardness, wear resistance, and bond strength of the coatings were evaluated by Vickers micro-hardness test, pin-on-disc test, and tensile test, respectively. Results showed that the Al₂O₃ particles were uniformly distributed in the coatings, and the coatings deposited at a current density of 0.01 A/cm² was most favorable in achieving a maximum current efficiency which causes the co-deposition of a maximum amount of Al₂O₃ particles (4.3 wt.%) in the coatings. The increase in Al₂O₃ particles in the coatings increased the mechanical properties of the Ni-Al₂O₃ composite coatings by grain refining and dispersion strengthening mechanisms.     

The effect of particle size,sintering temperature and sintering time on the properties of Al–Al2O3 composites,made by powder metallurgy

Al₂O₃ is a major reinforcement in aluminum-based composites, which have been developing rapidly in recent years. The aim of this paper is to investigate the effect of alumina particle size, sintering temperature and sintering time on the properties of Al–Al₂O₃ composite. The average particle size of alumina were 3, 12 and 48 μm. Sintering temperature and time were in the range of 500–600 °C for 30–90 min. A correlation is established between the microstructure and mechanical properties. The investigated properties include density, hardness, microstructure, yield strength, compressive strength and elongation to fracture. It has been concluded that as the particle size of alumina is reduced, the density is increased followed by a fall in density. In addition, at low particle size, the hardness and yield strength and compressive strength and elongation to fracture were higher, compared to coarse particles size of alumina. The variations in properties of Al–Al₂O₃ composite are dependent on both sintering temperature and time. Prolonged sintering times had an adverse effect on the strength of the composite.     

Machining performance and decomposition of TiAlN/TiN multilayer coated metal cutting inserts

The wear resistance of metal cutting inserts coated with metastable Ti_0.34Al_0.66N/TiN multilayers was tested in continuous turning of an AISI 316L stainless steel. The multilayers had periods of 25 + 50, 12 + 25 and 6 + 12 nm (Ti_0.34Al_0.66N + TiN) with a total multilayer stack thickness of 2 μm. Inserts coated with monolithic TiN and Ti_0.34Al_0.66N deposited under similar conditions were used as references. The multilayer coated inserts show a decrease of wear with decreased multilayer period, both on the rake and flank face. The wear on the rake face was lower on all the multilayer coated tools compared to the references. Scanning transmission electron imaging and energy dispersive spectroscopy elemental mapping of a worn multilayer coating show decomposition of the Ti_0.34Al_0.66N to domains rich of Al and Ti. High resolution transmission electron micrography shows preserved epitaxy between the TiN and Ti_0.34Al_0.66N layers. The improved wear resistance of the multilayer coated inserts is discussed in terms of an improved thermal stability of the multilayer stacks.     

Microstructures and mechanical properties evaluation of TiAlN/CrSiN multilayered thin films with different bilayer periods

The Ti_0.45Al_0.55N/Cr_0.75Si_0.25N nanoscale multilayered coatings were deposited periodically by a bipolar asymmetric pulsed DC reactive magnetron sputtering technique. The structures and bilayer period of multilayer coatings were characterized by an X-ray diffractometer. The surface and cross-sectional morphologies of thin films were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The surface roughness of thin films was explored by atomic force microscopy (AFM). A nanoindenter, a micro Vickers hardness tester and pin-on-disk wear tests were used to evaluate the hardness, fracture toughness and tribological properties of the thin films, respectively. Six coatings with bilayer period ranges from 6 nm to 40 nm were produced in this work. It was observed that the hardness increased with increasing bilayer period and reached the maximum at 12 nm and then leveled off at periods larger than 12 nm. An optimal hardness, and plastic deformation resistance, as well as adequate tribological behaviors were found on the coating with a critical bilayer period of 12 nm.     

Sintering of translucent alumina

Alumina (Al₂O₃) specimens were made via powder injection moulding and then sintered, respectively, at three different temperatures, 1800 °C, 1850 °C and 1900 °C, for 30 min in a vacuum condition to achieve a desirable translucent level. The Al₂O₃ samples with different transparency were fabricated. The sintered polycrystalline alumina samples with desirable and undesirable transparency were characterized using an X-ray diffractometer (XRD) and a scanning electron microscope (SEM) attached with an energy dispersive X-ray microanalyzer (EDX). The relationship between the degree of transparency and the microstructure was investigated. It was found that the undesirable transparency was due to the presence of second phase along the grain boundaries, porosity and the range of pore sizes. Other properties of the samples, such as density, porosity, and Vickers hardness, were also measured. The optimum sintering temperature and time, that is 1850 °C for 30 min, were given for the fabrication of translucent alumina to achieve the highest density and minimum porosity.     

Fabrication of A356 composite reinforced with micro and nano Al2O3 particles by a developed compocasting method and study of its properties

Aluminum/alumina composites are used in automotive and aerospace industries due to their low density and good mechanical strength. In this study, compocasting was used to fabricate aluminum-matrix composite reinforced with micro and nano-alumina particles. Different weight fractions of micro (3, 5 and 7.5 wt.%) and nano (1, 2, 3 and 4 wt.%) alumina particles were injected by argon gas into the semi-solid state A356 aluminum alloy and stirred by a mechanical stirrer with different speeds of 200, 300 and 450 rpm. The microstructure of the composite samples was investigated by Optical and Scanning Electron Microscopy. Also, density and hardness variation of micro and nano composites were measured. The microstructure study results revealed that application of compocasting process led to a transformation of a dendritic to a nondendritic structure of the matrix alloy. The SEM micrographs revealed that Al₂O₃ nano particles were surrounded by silicon eutectic and inclined to move toward inter-dendritic regions. They were dispersed uniformly in the matrix when 1, 2 and 3 wt.% nano Al₂O₃ or 3 and 5 wt.% micro Al₂O₃ was added, while, further increase in Al₂O₃ (4 wt.% nano Al₂O₃ and 7.5 wt.% micro Al₂O₃) led to agglomeration. The density measurements showed that the amount of porosity in the composites increased with increasing weight fraction and speed of stirring and decreasing particle size. The hardness results indicated that the hardness of the composites increased with decreasing size and increasing weight fraction of particles.     

Mechanical property of Fe-base metallic glass coating formed by gas tunnel type plasma spraying

Metallic glass has excellent functions such as high toughness and corrosion resistance. Therefore it is one of the most attractive materials, and many researchers have conducted various developmental research works. However, the metallic glass material is expensive and a composite material is preferred for the industrial application. Thermal spraying method is one of potential candidates to produce metallic glass composites. The gas tunnel type plasma system, which has high energy density and efficiency, is useful for smart plasma processing to obtain high quality ceramic coatings such as alumina (Al₂O₃) and zirconia (ZrO₂) coatings. Also, the gas tunnel type plasma spraying can produce metallic glass coatings. In this study, the Fe-base metallic glass coatings were formed on the stainless-steel substrate by the gas tunnel type plasma spraying, and the microstructure and mechanical property were investigated. The Fe-base metallic glass coatings of about 200 μm in thickness were dense with a Vickers hardness of about Hv = 1100 at plasma current of 300 A. The abrasive wear resistance of Fe-base metallic glass coating was higher than the SUS substrate.     

Effects of incorporation of Si or Hf on the microstructure and mechanical properties of Ti-Al-N films prepared by arc ion plating (AIP)

Ti-Al-N, Ti-Al-Si-N and Ti-Al-Hf-N films were deposited on 1Cr11Ni2W2MoV stainless steel by arc ion plating (AIP) with a Ti₇₀Al₃₀, a Ti₆₀Al₃₀Si₁₀ and a Ti₆₈Al₃₀Hf₂ cathode, respectively. The effects of Si or Hf addition on the composition, microstructure and mechanical properties of the Ti-Al-N films were investigated by EPMA, TEM, SEM, XRD, micro-hardness and wear tests. The results show that all the deposited films possessed B1 structure. With the incorporation of Si or Hf, the texture of Ti-Al-N films remarkably changed from preferred orientation of (220) to mixture broadened orientations of (111), (200) and (220), the mean crystallite size of Ti-Al-N decreased from ~ 90 nm to ~ 30 and ~ 15 nm and no peaks of crystalline Si₃N₄ were detected from XRD analyses. Due to the addition of Si or Hf, the micro-hardness of Ti-Al-N films increased remarkably from 23.5 Gpa to 33.6 or 29.5 GPa, and the wear resistance was also enhanced. The effects of incorporation of Si or Hf on the microstructure and mechanical properties of Ti-Al-N films are discussed.     

The effects of heat treatments on hardness and wear resistance in Ni-W alloy coatings

The relationship of processing parameters, microstructure, and mechanical responses of the electrodeposited nickel-tungsten alloys exposed to elevated temperatures in the range 700-1100 °C are investigated. Reverse pulse electrodeposition technique is employed to control the tungsten content and nanocrystalline grain size of the deposits. The application of heat treatment at 700 °C on the alloy with high tungsten content (22 at.%) and small grain size (3 nm) gives hardness enhancement and a small decrease in wear resistance. Prolonging annealing duration and increasing annealing temperature promote more grain growth and reductions of both hardness and wear resistance, despite the formations of secondary phases. For alloys with lower tungsten contents (6% and 13%) and larger grain sizes (13 and 56 nm), higher degrees of grain growth coupled with monotonic decline of hardness are observed. The study indicates that the electrodeposited nickel-tungsten alloys with a high tungsten content potentially serve as strong candidates for high temperature applications.     

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.     

High temperature tribological characterisation of TiAlSiN coatings produced by cathodic arc evaporation

This study reports on the wear properties at medium-high temperatures of TiAlSiN films deposited by cathodic arc evaporation on hot work steel substrates. The chemical composition and microstructure of the coatings were characterised by glow discharge optical emission spectroscopy, scanning electron microscopy and X-ray diffraction. The mechanical properties, i.e. hardness and elastic modulus were evaluated by nanoindentation, and the adhesion of the coatings was tested by scratch tests. Coatings with stoichiometries of Ti_0.31Al_0.1Si_0.06N_0.53 and Ti_0.23Al_0.12Si_0.09N_0.55 exhibit microstructures consisting of solid solutions of (Ti,Al,Si)N, where Al and Si replace Ti atoms. These films show high hardness and good adhesion strength to the hot work steels. Conversely, coatings with a stoichiometry of Ti_0.09Al_0.34Si_0.02N_0.55 show a wurtzite-like microstructure, low hardness and poor adhesion strength.The wear rates of the coatings were investigated by ball-on-disc experiments at room temperature, 200 °C, 400 °C and 600 °C, using alumina balls as counter surfaces. At room temperature, the films show wear rates of the same order of magnitude of TiN and TiAlN coatings. On the other hand, the wear rates of solid solution (Ti,Al,Si)N coatings measured at 200, and 400 °C are one order of magnitude smaller than those measured at room temperature due to the formation of oxide-containing tribofilms on the wear tracks. At 600 °C the wear rates increase but still keep smaller than those measured at room temperature, although this effect can be influenced by the softening of the steel substrates by over-tempering. EDS analyses revealed that, between 200 °C and 400 °C, the oxidation of the coating occurs only at the contact zone between the film and the counterpart body due to the sliding process.     

A356 Reinforced with Nanoparticles: Numerical Analysis of Mechanical Properties

Commercial casting Al-Si (A356)-based composites reinforced with different volume fractions of alumina (Al₂O₃) nanoparticulates (average particle size 50 nm) were synthesized in this study. Particle distribution, hardness, and tensile properties in the as-cast condition were experimentally investigated. The A356 alloy composite showed an increase in hardness, elastic modulus, and tensile strength compared with monolithic alloys. Finally, a combination of an artificial neural network and the finite element method (FEM) was implemented to predict the microstructure and mechanical properties including grain size, length of silicon rods, amount of porosity, hardness, tensile yield stress, ultimate tensile stress, and elongation percentage.     

Microstructure, mechanical and electrochemical properties evaluation of pulsed DC reactive magnetron sputtered nanostructured Cr-Zr-N and Cr-Zr-Si-N thin films

Cr-Zr-Si-N thin films with various Zr contents were deposited by a bipolar asymmetric pulsed DC reactive magnetron sputtering system. In addition, a Cr-Zr-N film without Si addition was fabricated as a reference. The influence of Zr on the constitution, microstructure, mechanical, tribological and electrochemical properties of Cr-Zr-Si-N films was investigated. The microstructure of thin films was determined by a glancing angle X-ray diffractometer (GA-XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. A nanoindenter, a Vickers micro hardness tester and pin-on-disk wear tests were adopted to evaluate the hardness, toughness and tribological properties of thin films, respectively. The electrochemical properties of thin films were also evaluated in 3.5 wt.% NaCl aqueous solution. In case of the Cr-Zr-Si-N films, the Si content was fixed around 6-8 at.% and various Zr contents ranging from 0.5 to 13.6 at.% were achieved by changing the Zr target power density. In comparison to the Cr-Zr-N reference film, the addition of ~ 7.0 at.% Si in Cr-Zr-Si-N films resulted in a refined columnar structure and enhanced mechanical and anti-corrosion properties. A lattice constant expansion of these films was observed with increasing Zr content. A nanostructured thin film with around 5-10 nm grain size was obtained in case of a Cr-13.6 at.% Zr-6.8 at.% Si-N film. In general, the hardness, plastic deformation resistance and corrosion resistance increased also with increasing Zr content in the Cr-Zr-Si-N films. The Cr-Zr-Si-N film containing 13.6 at.% Zr exhibited a combination of high hardness, good mechanical properties, adequate tribological performance and excellent corrosion resistance in this study.     

Influence of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Particle Size on Microstructure,Mechanical Properties and Abrasive Wear Behavior of Flame-Sprayed and Remelted NiCrBSi Coatings

The influence of micrometric alumina (low surface area-to-volume ratio) and nanometric alumina (high surface area-to-volume ratio) on microstructure, hardness and abrasive wear of a NiCrBSi hardfacing alloy coating applied to an AISI 304 substrate using flame spraying (FS) combined with surface flame melting (SFM) is studied. Remelting after spraying improved the mechanical and tribological properties of the coatings. Microstructural characterization using XRD, SEM and EDS indicated that alumina additions produced similar phases (NiSi, Ni₃B, CrC and Ni₃₁Si₁₂) regardless of the alumina size, but the phases differed in morphology, size distribution and relative proportions from one coating to another. The addition of 12 wt.% nanometric Al₂O₃ increased the phases concentration more than five- to sixfold and reduced the hard phases size about four-to threefold compared with NiCrBSi + 12 wt.% micrometric Al₂O₃. Nanoalumina led to reduced mass loss during abrasive wear compared to micrometric alumina and greater improvement in hardness.     

TiBCN:CNx multilayer coatings deposited by pulsed closed field unbalanced magnetron sputtering

In this study, a combination of nanocomposite and multilayer coating design was investigated in an effort to reduce the coefficient of friction (COF) while maintaining good mechanical properties of the TiBCN coatings. The TiBCN:CN_x coatings consist of TiBCN and CN_x nanolayers which were deposited alternately by reactive sputtering a TiBC composite target (80 mol% TiB₂ + 20 mol% TiC) and a graphite target in an Ar:N₂ mixture using a pulsed closed field unbalanced magnetron sputtering system. Low angle X-ray diffraction and transmission electron microscopy characterizations confirmed that the coatings consist of different bilayer periods in a range of 3.5 to 7.0 nm. The TiBCN layers exhibited a nanocomposite structure, whereas the CN_x layers were in an amorphous state. The mechanical properties and wear resistance of the TiBCN:CN_x multilayer coatings were investigated using nanoindentation and ball-on-disk wear test. The TiBCN:CN_x coatings exhibited high hardness in a range of 20-30 GPa. The highest hardness of 30 GPa was achieved in the coating with a bilayer period of 4.5 nm. A low COF of 0.17 sliding against a WC-Co ball was obtained at a bilayer period of 4.5 nm, which is much lower than those of the single layer TiBCN and TiBC nanocomposite coatings (0.55-0.7).     

Experimental Investigations to Study the Effects of Microwave Treatment Strategy on Tool Performance in Turning Operation

In the present study, microwave treatment has been used to enhance the tribological properties of single-point tungsten carbide (WC) cutting tool inserts such as wear resistance and hardness. The tool hardness and cutting parameters were considered to evaluate the performance of microwave-treated WC inserts in turning operation. The optimum cutting parameters were identified using response surface method (RSM)-based desirability approach. The relationship between cutting parameters and output responses, viz. flank wear, cutting force and surface roughness, was developed using the RSM. The investigations revealed that the increase in tool hardness due to complex carbide formation results in a significant reduction in tool wear, cutting forces and improvement in the surface finish of workpiece. Further, the statistical models results were validated with the experimental results. Metallurgical properties of treated and untreated tool inserts were analyzed using scanning electron microscope, x-ray diffraction method and Vickers microhardness tests. The results highlighted the importance of microwave treatment in enhancing the machining performance in turning operation.     

Preparation, microstructure and sliding-wear characteristics of brush plated copper-nickel multilayer films

Cu/Ni multilayer films with sublayer thickness (h) ranging from 10 to 1000 nm were prepared on ANSI 1045 steel by brush plating of periodically changing layers of Cu and Ni. The microstructure, composition, microhardness and sliding wear properties against standard SiC ball under unlubricated condition were examined. It was found that the brush plated multilayer films are highly dense and free from porosity. A decrease in h results in smaller grain size and lower coefficient of friction. Both microhardness and wear resistance reach the maximum value when h = 20 nm. Although found with lower hardness compared with brush plated Ni monolayer coating, multilayer films with h ranging from 20 to 80 nm showed improved wear resistance. The increase in the wear resistance was attributed to the combined effect of strengthening of the layer structure and the lubricating of Cu.     

Aluminum-rich TiAlCN coatings by Low Pressure CVD

Ti_1 − xAl_xN is a well established material for cutting tool applications exhibiting a high hardness and an excellent oxidation resistance. A main route for increasing the performance of Ti_1 − xAl_xN is the incorporation of further elements. Therefore the main objective of this work is to improve the properties and wear resistance of aluminum-rich CVD-TiAlN coatings by incorporating carbon. A new Low Pressure CVD process was employed for the deposition of a very aluminum-rich TiAlCN layers. The process works with a gas mixture of TiCl₄, AlCl₃, NH₃, H₂, N₂, Ar and ethylene as carbon source. In this work microstructure, composition, properties and cutting performance of CVD-TiAlCN coatings were investigated.Hard aluminum-rich TiAlCN coatings were obtained at 800 °C and 850 °C consisting of a composite of fcc-Ti_1 − xAl_xN and minor phases of TiN, h-AlN and amorphous carbon. WDX analysis indicates only a low carbon content < 2 at.%. Lattice constant calculations suggest that carbon atoms should not be incorporated in the Ti_1 − xAl_xN lattice. From TEM analysis and Raman spectroscopy it is evident that carbon is mainly located at the grain boundaries as a-C phase. Therefore these fcc-Ti_1 − xAl_xN(C) coatings with low carbon content are rather a composite of fcc-Ti_1 − xAl_xN and an amorphous carbon phase (a-C). At 900 °C the metastable fcc-Ti_1 − xAl_xN nearly disappears and co-deposition of TiN and h-AlN occurs. The layers deposited at 800 °C and 850 °C possess a high hardness around 3000 HV and compressive stress. CVD-TiAlCN coatings prepared at 850 °C shows also an amazing thermal stability under high vacuum conditions up to 1200 °C. Aluminum-rich composites fcc-Ti_1 − xAl_xN/a-C with x > 0.8 exhibit a superior cutting performance in different milling tests.     

Cutting wear,microstructure and mechanical properties of (Ti0.5,W0.5)C-based cermet inserts containing Mo2C

(Ti_0.5,W_0.5)C-15 wt%Co cermets containing Mo₂C were prepared and used for cutting tool inserts. The microstructure and mechanical properties were characterized, and cutting wear was compared during machining VDEH 90CrSi5 alloy steel. Tool wear mechanism was analyzed by SEM and EDS. The Mo₂C-added inserts possess refined ceramic grains and solid-solution strengthened binder, and further they have higher coercive force, hardness, fracture toughness, and transverse rupture strength. Owing to these factors, obvious superiority for them is displayed on the flank wear over non-Mo₂C one in continuously machining VDEH 90CrSi5 alloy steel. It is also found that wearing of the inserts is the integrated results of abrasive wearing, adhesive wearing, oxidative wearing and diffusive wearing. After introducing Mo₂C to the inserts, the abrasive wear resistance, adhesive wearing and diffusive wearing are all hindered effectively, still oxidative wearing is not reduced yet.