Studies of the correlation between wear behaviour and bonding strength in two types of ceramic coating

The plasma-spraying technique is used in this study. Two types of ceramic coating (Al2O3–13 wt% TiO2 and Cr2O3–5 wt% SiO2–3 wt% TiO2) with and without NiAl bonding coating are subjected to bonding strength and wear tests. Determining the most suitable coating and coating technique and solving an industrial problem are the main objectives of this study. © 1998 Kluwer Academic Publishers     

Structure and properties of a moulded carbon derived from rice hull

Rice hull was moulded into a tube (outer diameter: 54 mm; inner diameter: 17 mm, length: c. 170 mm) by use of an extruder and then carbonized in nitrogen atmosphere below 1000 °C. Ash content of the hull was 16 wt%, of which c. 94 and 4 wt% were SiO₂ and K₂O, respectively. Carbon yield and shrinkage of the mould after carbonization at 1000 °C were 42 wt%, and 43 vol%, respectively. The bulk density increased with rising of carbonization temperature to reach to 0.93 g ml^–1 at 1000 °C via 0.82 g ml^–1 at 500 °C. The largest compressive strength of 3.6 MPa was obtained after carbonization at 1000 °C. No micropore was developed after carbonization, and the total pore volume measured by a mercury porosimeter was 0.25–0.31 ml g^–1 after carbonization. These data were compared with those of charcoal.     

On the influence of alloying elements on the bainite reaction in low alloy steels during continuous cooling

The CCT diagrams of a class of Fe-(0.1–0.6)C-(0.4–2.0)Si-(0.4–2.0)Mn-(0.5–2.0)Cr-(0.0–0.8)Mo steels are predicted by an artificial neural network (ANN) model. The model indicates that an increase in carbon concentration (C wt%) gives rise to a decrease in bainite start (BS) temperatures. The rate of decrease depends also on cooling rate. Additions of Si, Mn, Cr and Mo all decrease the bainite start temperature. The dependencies for different alloying elements vary: 32, 100–120, 100–130, and 70–150°C per wt% of Si, Mn, Cr, and Mo, respectively. Mn shifts the whole bainite transformation region to the far right-hand side of the CCT diagram, while C, Cr, and Mo have considerable, and Si has minor effects on the incubation period of bainite. Mn and Cr significantly decrease the MS temperature, while Si only has a minor influence. When Mo < 0.5 wt% it has a minor influence, whilst when Mo > 0.5 wt%, it increases MS temperature. Quasi-isochronal and quasi-isothermal methods have been used to analyze the influence of the proportion of Mo and C upon the BS and incubation period. Attempts, for qualitative explanations using the shear and diffusion mechanism, as well as a certain amount of thermodynamic analysis, have been made to interpret the influence of alloying elements on the nucleation of the bainite reaction. The results support that bainite reaction takes place utilizing a diffusion-controlled mechanism.     

Predicting of mechanical properties of Fe–Mn–(Al, Si) TRIP/TWIP steels using neural network modeling

In this work, an artificial neural network (ANN) model was established in order to predict the mechanical properties of transformation induced plasticity/twinning induced plasticity (TRIP/TWIP) steels. The model developed in this study was consider the contents of Mn (15–30 wt%), Si (2–4 wt%) and Al (2–4 wt%) as inputs, while, the total elongation, yield strength and tensile strength are presented as outputs. The optimal ANN architecture and training algorithm were determined. Comparing the predicted values by ANN with the experimental data indicates that trained neural network model provides accurate results.     

A fine cobalt-toughened Al2O3-TiC ceramic and its wear resistance

Mechanical ball milling is the most common method for mixing ceramic powders with a ductile phase such as metal particles. In this paper, a new powder processing way is presented. Al2O3 and TiC powders are coated with a layer of metal cobalt using the chemical deposition process. The thickness of the metal cobalt film can be controlled by adjusting the deposition conditions. The Co-coated Al2O3 (Al2O3–Co) and TiC (Tic–Co) powders are mixed at the rate of 7:3 and hot-press sintered into a fine Al2O3–TiC–Co (ATC) ceramic. The main properties, erosion behaviour, abrasion behaviour, wear mechanism and wear resistance of Al2O3-TiC-Co and Al2O3–30 wt% TiC (AT30) ceramics are determined by transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, etc. It is shown that the ATC ceramic possesses improved mechanical properties. Because of the existence of metal cobalt in the grain boundaries, the bonding strength between grains is increased, and this prevents spalling of grains during wear. Experimentation indicates that ATC is more resistant to wear than Al2O3–TiC ceramic. The relationship between their mechanical properties and wear resistance is also discussed in this paper.     

The low temperature magnetic properties of austenitic Fe---Cr---Ni alloys. 3. The effect of chromium concentration in Fe---Cr-17wt% Ni alloys

The magnetic properties of ternary Fe---Cr---Ni alloys containing 17 wt% Ni and 18–24% Cr have been studied over a range of temperature from 4.2–35 K by both ac and dc techniques in fields from 5 Am⁻¹ − 6 MA m⁻¹. At room temperature, the matrix of all the alloys was the paramagnetic fcc austenite phase (with an unavoidable 0.1 – 0.5 wt% δ ferrite) and on cooling all the alloys showed distinct peaks in ac susceptibility, though equivalent peaks in dc susceptibility were only observed at low fields in the alloy containing 18 wt% Cr. An analysis of the magnetization/field/temperature results showed that all the alloys were superparamagnetic at low temperature, due to the formation of ferromagnetic clusters in the disordered antiferromagnetic matrix, and that the chromium atoms make no measureable contribution to the magnetization of these clusters. Appropriate susceptibility values are tabulated for use as design data.     

Dry sliding wear behaviour of Al–12Si–4Mg alloy with cerium addition

The purpose of this work is to understand the effect of cerium addition on wear resistance behaviour of as-cast alloys. Al–12Si–4 Mg alloys with 1–5 wt% cerium addition were prepared using the casting technique. A sliding wear test was carried out under applied loads of 10 N, 30 N and 50 N at a fixed sliding speed of 1 m/s using a pin-on-disc configuration. The wear test was conducted in dry conditions at room temperature of 25 °C. Detailed analysis of the microstructure, worn surface, collected debris and microhardness was undertaken in order to investigate the differences between the as-cast alloys with different levels of cerium addition. The addition of 1–5 wt% cerium was found to lead to the precipitation of intermetallic phases (Al–Ce), resulting a needle-like structures. Increasing cerium content up to 2 wt% improved both wear resistance and microhardness of as-cast alloys. Addition of more than 2 wt% cerium, however, led to a decrease in microhardness, resulting in lower wear resistance of the alloys. Moderate wear was observed at all loads, with specific wear rates (K′) ranging from 6.82 × 10⁻⁵ with 2 wt% Ce at applied load of 50 N to 21.48 × 10⁻⁵ mm³/N m without added Ce at an applied load of 10 N. Based on K′ ranges, the as-cast alloys exhibited moderate wear regimes, and the mechanism of wear is a combination of abrasion and adhesion. Alloy containing 2 wt% Ce, with the highest hardness and lowest K′ value, showed the greatest wear resistance.     

Effects of fly ash additions on the mechanical and other properties of porcelainised stoneware tiles

The effect of fly ash additions on the mechanical properties of porcelainised stoneware tile composition has been investigated. Fly ash additions in the range of 0–40 wt% have been added in to the tile body composition, wet milled, spray dried, shaped and fired at 1250°C. The MOR strength improved with increasing fly ash content and reached maximum when 25–30 wt% fly ash used, and with greater additions it decreased. A linear correlation between strength development and mullite formation was found. The tiles with 25 wt% fly ash had improved bending strength, abrasion resistance and hardness compared to the conventional tiles and conform to all other properties at an EN standard specification.     

Microstructure and Mechanical Properties of Rapidly Solidified Hypereutectic Al–Si and Al–Si–Fe Alloys

The microstructure and mechanical properties of rapidly solidified Al–18 wt% Si and Al–18 wt% Si–5 wt% Fe alloys were investigated by a combination of optical microscopy, scanning electron microscopy, transmission electron microscopy, x-ray diffraction, tensile testing, and wear testing. The centrifugally atomized binary alloy powder consisted of the -Al (slightly supersaturated with Si) and Si phases and the ternary alloy powder consisted of the -Al (slightly supersaturated with Si), silicon, and needle-like metastable Al–Fe–Si intermetallic phases. During extrusion the metastable -Al₄FeSi₂ phase in the as-solidified ternary alloy transformed to the equilibrium -Al₅FeSi phase. The tensile strength of both the binary and the ternary alloys decreased with a high-temperature exposure, but a significant fraction of the strength was retained up to 573 K. The specific wear gradually increased with increasing sliding speed but decreased with the addition of 5 wt% Fe to the Al–18 wt% Si alloy. The wear resistance improved with annealing due to coarsening of the silicon particles.     

Studies on mechanical and wear properties of alloyed hypereutectic gray cast irons in the as-cast pearlitic and austempered conditions

The mechanical and wear behavior of a series of as-cast gray iron alloys were compared with properties obtained after austempering at 360 °C. The austempered alloys showed equivalent or moderately enhanced mechanical strength than the as-cast pearlitic gray irons. The specific wear rates of all the austempered alloys decreased significantly by 7–15 times and friction coefficient reduced by 30–50% compared to pearlitic alloyed gray irons. The dry sliding wear studies of as-cast alloys against high carbon 1%Cr through-thickness hardened steel shows that the specific wear rate ranged from 5.6 to 19.1 (×10⁻⁷) g/Nm with friction coefficient from 0.55 to 0.7. While, the austempered alloys showed wear rates from 0.5 to 2.6 (×10⁻⁷) g/Nm with friction coefficient ranging from 0.23 to 0.4. The improved wear resistance was attributed to the layer wise surface phase transformation associated with strain induced martensite formation of the stabilized austenite in the austempered matrix, lubrication of the interface by the flake graphite and better heat conduction from the rubbing interface by higher volume fraction of the graphite. Cast iron alloyed with Ni shows enhanced mechanical properties and wear resistance. The tensile strength shows decreasing trend with increase in carbon equivalent and graphite volume. The specific wear rate and friction coefficient shows decreasing trend with increase in hardness and graphite flake volume.     

Effect of silicon on microstructure and stress rupture properties at 1100°C of yttrium modified Ni-Al-Mo-B alloy IC6

The effect of adding 0.10–0.30 wt%Si on microstructure of the yttrium modified alloy IC6 was examined by scanning electron microscope (SEM), energy dispersive spectrum(EDS) technique of electron probe micro-analyzer (EPMA) and transmission electron microscope (TEM). The results show that two bulk shape phases, Mo_1.24Ni_0.76 and Mo₆(Ni_0.75Si_0.25)₇ are formed in the interdendritic area in the alloy with addition of 0.10–0.20 Siwt% and 0.12 wt%Y, and that a needle like phase named Y-NiMo precipitates in the interdendritic area in the alloy with addition of 0.30 wt% silicon and 0.12 wt% yttrium besides the formation of the bulk shape phases mentioned above. The stress rupture properties under 1100°C/80 MPa were improved by adding 0.12 wt%Y but decreased by adding 0.10–1.30 wt%Si and 0.12 wt%Y.     

On the creep and phase stability of advanced Ni-base single crystal superalloys

The present article examines microstructure stability and creep resistance of a 5th generation superalloy, which has Cr content at 4.6 wt%, 6.4 wt% Re and 5.0 wt% Ru, in comparison with that of a 4th generation superalloy (3.2 wt% Cr, 5.8 wt% Re and 3.6 wt% Ru). The aim is to elucidate the implication of increasing Cr, Re and Ru contents for future alloy developments. Experimental results have concluded that high Re + Ru content could promote formation of hexagonal δ phase at 900 °C; additional Cr and Re could enhance the precipitation of TCP phase at 1100 °C. Although an increase in lattice misfit between γ and γ′ in the 5th generation superalloy could strengthen the alloy against creep deformation under conditions at high temperatures (≥1000 °C) and low stresses (≤245 MPa) whilst the microstructural stability remained, the tendency to raft should be avoided during creep at lower temperatures and higher stresses.     

Nitrogen Addition to an O-1 Tool Steel

A new processing technique makes nitrogen alloying possible by adding nitrogen under elevated nitrogen pressure to prealloyed Fe-C ingots during continuous casting, producing a whole new class of precipitation-free, iron–carbon–nitrogen alloys. When both carbon and nitrogen bulk concentration levels exceeded 0.5 wt%, a duplex fcc-/(bcc-bct-) Fe microstructure resulted that is iron carbide- and nitride-free. With increasing carbon and nitrogen concentrations, there was an increase in the retained fcc-Fe phase. In cooling rate studies, increasing carbon and nitrogen concentrations shifted the knee of the fcc-Fe-to-bcc-Fe phase time–temperature–transformation (T–T–T) curve to longer times. Hardness, compression strength, and wear resistance increased with increasing carbon and nitrogen concentrations and were superior to iron–carbon alloys without the nitrogen addition.     

Wear and mechanical properties of epoxy/SiO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> composites

Preparation of epoxy/SiO₂-TiO₂ composites is investigated in this paper. The products are characterized by FT-IR spectroscopy. Results of FT-IR spectroscopy and atom force microscope (AFM) demonstrated that epoxy chains have been covalently bonded to the surface of the SiO₂-TiO₂ particles. The particles sized of SiO₂-TiO₂ are about 20–50 nm, which characterized by AFM. The properties of composites such as impact strength, flexural strength, tensile strength and ring-on-block wear are also investigated. Dry sliding wear tests showed that the SiO₂-TiO₂ particles could improve the wear resistance of the epoxy matrix even though the content of the SiO₂-TiO₂ particles was at a relatively low level (1.95–2.65 wt%). This makes it possible to develop novel type of epoxy-based materials with improved wear resistance for various applications. The worn surface was observed by scanning electron microscopy (SEM), and mechanisms for the improvement are discussed in this paper     

The effect of high-velocity oxygen fuel, thermally sprayed WC–Co coatings on the high-cycle fatigue of aluminium alloy and steel

Thermally sprayed WC–Co coatings are currently used in numerous contact wear applications in the aircraft, automotive and paper industries. High-cycle fatigue tests were performed at room temperature and 370 °C on SAE 12L14 low-carbon steel and aluminium alloy 2024-T4 thermally sprayed with WC–17 wt% Co using the high-velocity oxygen fuel process. The fatigue life distributions of specimens in the polished, grit-blasted, peened and coated conditions are presented as a function of the probability of failure. Composite beam theory was applied to the coated beam to evaluate the stresses and elastic modulus.The stress–strain curves for the coated and uncoated specimens were used to evaluate the stiffness factor for the aluminium alloy and steel. It is concluded that (i) the coated specimens exhibited significantly high fatigue lives compared with the uncoated specimens, (ii) the mechanisms of deformation for the coated and uncoated aluminium alloy specimens are quite different and (iii) the elastic modulus of the coating plays a significant role in determining the fatigue strength of the coated component. © 1998 Kluwer Academic Publishers     

Diphasic mullite gel pressed at 1.5 GPa: Mechanical properties and microstructure of ceramics

Mullite gels containing 72–85 wt% Al2O3 were prepared by mixing commercial boehmite and silica sols and gelled by heating. Powdered gels were either dried at 60°C or calcined at 550°C, and cold isostatically pressed under 0.5, 1.0 or 1.5 GPa. The effect of pressure is greater for the calcined gels than for the dried gels. The bulk density and room-temperature flexural strength of ceramics increased with increasing compacting pressure, while the fracture toughness is independent of the pressure. Mullite containing 75 wt% Al2O3 and sintered at 1500°C for 3 h has a density which is about 99% of the theoretical density, a flexural strength of 523±40 MPa and a fracture toughness of 3.5 MPa m1/2.     

Studies on the development of aluminium alloy–mild steel reinforced composite

With a view to developing a new metal–metal cast composite material as a possible substitute for ferrous materials in wear resistant applications, Al alloy (LM11) is reinforced with mild steel (ms) wires and it is heat treated to get ‘reaction interface’ (RI). Microhardness, tensile properties and wear characteristics of the matrix, as-cast and heat treated composites have been determined. While microhardness of the composite showed variation from 150 to 45 VHN across the interface in the as-cast composite, annealed (500–525°C) composite showed a microhardness of 350–420 VHN at the interface indicating the effectiveness of the heat treatment. It is seen that the % improvement in wear resistance increased with increase in number of wires when embedded in the aluminium alloy matrix. Further imrpovement of about 30% was observed when heat treated at 500°C for 15 h. These results have been discussed in terms of wetting between ms wires and the matrix, particularly the increase of hardness and tensile strength to the formation of ‘reaction interface’ due to annealing. The width of the interface increased with annealing time and temperature and the kinetics of reaction followed logarithmic and parabolic growth rate. The activation energy for the formation of intermetallics constituting the reaction interface is found to be 20.7 KJ mol⁻¹. From the measured hardness and ultimate tensile strength of the constituents and composites an empirical relation was deduced.     

Characteristics of a continuous Si-Ti-C-O fibre with low oxygen content using an organometallic polymer precursor

A continuous Si-Ti-C-O fibre with 12 wt% oxygen content, which is lower than the usual 18 wt% found in the normal fibres, was synthesized by using polytitanocarbosilane which has fewer Si-Si bonds than the usual precursor polymer. The density, tensile strength, tensile modulus and thermal conductivity were found to be 2.37 g cm^–3, 3.4±0.3 GPa, 190±10 GPa and 1.40 W m^–1 K^–1, respectively. Amongst these properties, the tensile modulus was improved by 20 GPa and the thermal conductivity had a higher value in comparison with that of the ordinary Si-Ti-C-O fibre with 18 wt% oxygen content. The Si-Ti-C-O fibre with a 12 wt% oxygen content has a better heat resistance above 1400 °C in an argon atmosphere and 1300 °C in air, than the usual fibre. About 60 and 40% of its tensile strength at room temperature were retained in air at respectively, 1500 and 1600 °C. This improved ceramic fibre is considered to be useful as a reinforcing material for advanced composites such as high-temperature ceramic matrix composites and metal matrix composites.     

Thermal behaviour of a polytitanocarbosilane-derived fibre with a low oxygen content: the Tyranno Lox-E fibre

The chemical composition, microstructure and mechanical properties of Tyranno Lox-E fibre were studied in the as-received state and after annealing in inert atmosphere. The fibre consists of SiC nanocrystals of 2–3 nm, free carbon aggregates of 4–5 distorted aromatic layers and 1–3 nm in length and an amorphous silicon (titanium) oxycarbide phase. Except for evolution of residual hydrogen and a slight densification, the fibre is chemically and structurally stable and retains a high strength up to 1300°C. Beyond 1300°C, superficial degradation resulting from decomposition of the oxycarbide into SiO(g) and CO(g) induces a decrease of strength. Compared with bulk polycrystalline SiC, the fibre has a low creep resistance at high temperature, mainly because of the nanometric size of the SiC crystals but also because of the presence at the grain boundary of the oxycarbide phase (viscous and chemically unstable) and of the poorly organized free carbon phase (chemically and structurally unstable). © 1998 Chapman & Hall     

Superplastic deformation of Al-Li-Cu-Mg alloy sheet

Al-2.5 Li-1.2 Cu-0.6 Mg-0.12 Zr (wt%) alloy sheet was cold-rolled, solution heat-treated for 20 min at 510° C, prestrained by 3% and superplastically deformed at 450 to 540° C at strain rates between 1×10^–4 and 2.8×10^–1 sec^–1. The maximum elongation obtained was 300%. Significant cavitation occurred above about 0.5 strain at a rate (void volume/unit strain) of 4% at 540° C and 6% at 500° C. The onset of cavitation coincided with a reduction in the room-temperature tensile properties after reheat-treatment. During annealing at 500 to 540° C, grain coarsening near the sheet surface was associated with magnesium and lithium depletion. Superplastic deformation produced a fine equiaxed microstructure by dynamic recrystallization.