TiN/Cr/Al2O3 and TiN/Al2O3 hybrid coatings structure features and properties resulting from combined treatment

New experimental results are presented on the structure and the elemental and phase composition of hybrid coatings, which were deposited on a substrate of AISI 321 stainless steel using a combination of plasma-detonation, vacuum-arc and subsequent High-Current Electron Beam (HCEB) treatment. We found that an increase in energy density intensified mass transfer processes and resulted in changes in aluminum oxide phase composition (γ → α and β → α). Also we observed the formation of a nanocrystalline structure in Al₂O₃ coatings. Electron beam treatment of a hybrid coating surface induced higher adhesion, decreased the intensity of surface wear and increased corrosion resistance in a sulphuric acid solution. The corrosion resistance of the coatings was studied in several electrolytic solutions (0.5 M H₂SO₄, 1 M HCl, 0.75 M NaCl) using electrochemical techniques. In most cases the corrosion resistance was improved, except those in NaCl solutions. The nano-hardness of the protecting coating was 13 GPa before electron beam melting and 9 GPa after it (as a result of TiN and Al₂O₃ sub-layers mixing).     

Wear behavior of Al2O3/Ti(C,N)/SiC new ceramic tool material when machining tool steel and cast iron

Design, fabrication and application of ceramic cutting tools are one of the important research topics in the field of metal cutting and advanced ceramic materials. In the present study, wear resistance of an advanced Al₂O₃/Ti(C,N)/SiC multiphase composite ceramic tool material have been studied when dry machining hardened tool steel and cast iron under different cutting conditions. Microstructures of the worn materials were observed with scanning electronic microscope to help analyze wear mechanisms. It is shown that when machining hardened tool steel at low speed wear mode of the kind of ceramic tool material is mainly flank wear with slight crater wear. The adhesion between tool and work piece is relatively weak. With the increase of cutting speed, cutting temperature increases consequently. As a result, the adhesion is intensified both in the crater area and flank face. The ceramic tool material has good wear resistance when machining grey cast iron with uniform flank wear. Wear mechanism is mainly abrasive wear at low cutting speed, while adhesion is intensified in the wear area at high cutting speed. Wear modes are dominantly rake face wear and flank wear in this case.     

Microstructure and tribological behavior of suspension plasma sprayed Al2O3 and Al2O3-YSZ composite coatings

Several alumina and alumina-zirconia composite coatings were manufactured by suspension plasma spraying (SPS), implementing different operating conditions in order to achieve dense and cohesive structures. Temperatures and velocities of the in flight particles were measured with a commercial diagnostic system (Accuraspray®) at the spray distance as a function of the plasma operating parameters. Temperatures around 2000 °C and velocities as high as 450 m/s were detected. Hence, coatings with high amount of α-alumina phase were produced. The microstructure evolution according to the spray parameters was studied as well as the final tribological properties showing efficient wear resistance.     

Phase formation of Al2O3/Ti(C,N)–NiTi composite

This study investigates the addition of NiTi shape memory alloy into Al₂O₃/Ti(C,N) ceramic as a toughening agent. The reported study is focused on the thermal–chemical interaction between the NiTi additive and the ceramic matrix. It is found that at the sintering temperature of 1673 K, the NiTi alloy is melted and the Ti content of the molten alloy react with the ceramic matrix to form TiC, leaving behind Ni which resolidifies into elliptical inclusions with distinctive mutlizone structures in the matrix of the ceramic. These findings provide useful guidance for NiTi–ceramic composite design.     

Improved oxidation resistance of Ti with a thermal sprayed Ti3Al(O)–Al2O3 composite coating

A Ti₃Al(O)–Al₂O₃ in situ composite was explored as a coating system for Ti using thermal spray. Oxidation tests at 700–800 °C showed that this coating remarkably decreased the oxidation rate and increased the scale spallation resistance compared with Ti. The mechanisms for these improvements were then briefly discussed.     

Microstructure and wear property of laser-clad Co3Mo2Si/Coss wear resistant coatings

Novel wear resistant Co₃Mo₂Si/Co_ss coatings consisting of a microstructure of hard and strong Co₃Mo₂Si intermetallic phases embedded in the ductile Co-base matrix were fabricated on austenite stainless steel by the laser cladding process from the Co-Mo-Si powder blend precursor. The microstructures of the coatings were characterized by optical microscopy (MO), X-ray diffraction (XRD), and scanning electron microscopy (SEM) with an energy-dispersive X-ray analysis (EDX). The wear resistance of the coatings was evaluated in a dry sliding wear test condition at room temperature. Results indicated that the laser-clad Co₃Mo₂Si/Co_ss coatings exhibited very excellent wear resistance against abrasive and adhesive wear.     

Development of moderate temperature CVD Al2O3 coatings

Chemically vapor deposited Al₂O₃ coatings, due to their high hardness and chemical inertness, are currently the state of art in the cutting tool industry. The conventional high deposition temperature of about 1050 °C for Al₂O₃ coatings, based on the water–gas shift process, has to a great extend restricted the development of several hybrid coatings, such as TiC/TiN/TiCN/Al₂O₃. To overcome this limitation, alternate systems to deposit Al₂O₃ at moderate temperatures have been investigated. Systems using NO–H₂, H₂O₂, NO₂–H₂ and HCOOH were identified and thermodynamic calculations were performed to evaluate them as potential sources of oxygen donors to form Al₂O₃ in the moderate temperature range of 700–950 °C. Preliminary results have clearly demonstrated that it is possible to grow moderate temperature alumina (using such alternate sources) on the TiC/TiN coated cemented carbide substrates.     

Microstructure and magnetic properties of Co/Al2O3 nanocomposite powders

Nanocomposite powders of magnetic cobalt nanoparticles dispersed by nonmagnetic Al₂O₃ particles have been prepared by planetary ball milling. Ball milling of the CoO and Al mixture powder after a certain milling duration reduces CoO to (fcc and hcp) Co completely and oxidizes Al to -Al₂O₃ simultaneously. The average grain sizes of the nanocomposite powders are 19 nm for Co and 28 nm for -Al₂O₃ after the completion of the reduction reaction. By direct ball milling of the mixture of Co and Al₂O₃, the allotropic phase transformation of Co was observed and the average grain size of Co is reduced to 5 nm. For both the samples of the mechanochemical series and the direct milling series, the saturation magnetizations of the nanocomposite powders decrease with decreasing average grain size of Co. This may be due to the enhancement of the interface effects and the increase of the superparamagnetic particles with decreasing Co grain size. The coercivities of the Co/Al₂O₃ nanocomposite powders increase up to 380 Oe. The increasing grain boundaries with decreasing Co grain size result in the domain wall pinning which predicts the coercivity enhancement. In addition to the grain size effects, the reduction of the particle size toward the size region of single domain also contributes to the increase of coercivity.     

Mechanical and tribological performance of Al2O3-TiO2 coatings elaborated by flame and plasma spraying

Mechanical properties and wear rates of Al₂O₃-13 wt.% TiO₂ (AT-13) and Al₂O₃-43 wt.% TiO₂ (AT-43) coatings obtained by flame and atmospheric plasma spraying were studied. The feed stock was either ceramic cords or powders. Results show that the wear resistance of AT-13 coatings is higher than that of AT-43 and it seems that the effect of hardness on wear resistance is more important than that of toughness. Additionally, it was established that, according to conditions used to elaborate coatings and the sliding tribological test chosen, spray processes do not seem to have an important effect on the wear resistance of these coatings.     

Thermal shock fatigue behavior of TiC/Al2O3 composite ceramics

The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt.% TiC/Al₂O₃ composites were studied. The effect of TiC and Al₂O₃ starting particle size on the mechanical properties of the composites was discussed. Indentation-quench test was conducted to evaluate the effect of thermal fatigue temperature difference (ΔT) and number of thermal cycles (N) on fatigue crack growth (Δa). The mechanical properties and thermal fatigue resistance of TiC/Al₂O₃ composites are remarkably improved by the addition of TiC. The thermal shock fatigue of monolithic alumina and TiC/Al₂O₃ composites is due to a “true” cycling effect (thermal fatigue). Crack deflection and bridging are the predominant reasons for the improvement of thermal shock fatigue resistance of the composites.     

Mechanical properties of the plasma-sprayed Al2O3/ZrSiO4 coatings

The mechanical properties of plasma-sprayed Al₂O₃/ZrSiO₄ coatings were investigated by indentation-based techniques. Two types of feedstock were used to prepare the coatings: spray-dried powders and plasma-spheroidized powders. A 100-kW direct current (d.c.) thermal plasma system was employed. The values obtained were found to exhibit a close relationship with the microstructure of the as-sprayed coatings, which composed of zircon, alumina, amorphous silica and tetragonal zirconia. The coatings produced with plasma-spheroidized powders had higher microhardness, Young's modulus and fracture toughness than that produced with the spray-dried powders. The coatings produced with plasma-spheroidized powders by a 100-kW computerized system at 15 kW of net plasma energy had the best mechanical properties, while those deposited at 19 kW of net plasma energy had the worst properties due to the high density of cracks in the coatings.     

The influence of Al2O3 reinforcement on the properties of stainless steel cold spray coatings

The effect of Al₂O₃ additions to type 316 austenitic stainless steel cold spray coatings was studied. Adding Al₂O₃ to the feedstock powder increased the overall deposition efficiency, though the Al₂O₃ itself deposited less efficiently than the stainless steel. Shear testing of the coatings using a shear lug test revealed a change in fracture from cohesive to adhesive with increasing alumina addition. The corrosion behaviour, assessed using anodic polarisation tests of the coatings, showed a shift towards the polarisation behaviour of bulk stainless steel with Al₂O₃ additions. All of these changes in coating behaviour with Al₂O₃ additions suggest an improved degree of metallurgical bonding, likely due to increased plasticity in the stainless steel particles.     

Fabrication and wear characteristics of MoSi2 matrix composite reinforced by WSi2 and La2O3

MoSi₂ matrix composites (RWM) reinforced by the addition of both WSi₂ and La₂O₃ were fabricated by mechanical alloying and self-propagating high-temperature synthesis (SHS) technique. This composite was analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is difficult to synthesize RWM composite by mechanical alloying with Mo–W–Si–La₂O₃ powder mixture, and suitable by self-propagating high-temperature synthesis. The hardness and toughness of MoSi₂ was improved significantly by the addition of both, WSi₂ and La₂O₃ more than by only WSi₂. By adding 0.8 wt.% La₂O₃ and 50 mol.% WSi₂ into the MoSi₂ matrix, this composite has the highest hardness and toughness and exhibits more wear resistance than monolithic MoSi₂ during the sliding wear test under oil lubrication, in this case, the material removal mechanism has been observed to be micro-cutting and micro-fracture.     

Improvement in hydrogen sorption properties of Mg by reactive mechanical grinding with Cr2O3, Al2O3 and CeO2

We tried to improve the hydrogen sorption properties of Mg by mechanical grinding under H₂ (reactive mechanical grinding) with oxides Cr₂O₃, Al₂O₃ and CeO₂. The hydriding rates of Mg are reportedly controlled by the diffusion of hydrogen through a growing Mg hydride layer. The added oxides can help pulverization of Mg during mechanical grinding. A part of Mg is transformed into MgH₂ during reactive mechanical grinding. The Mg+10wt.%Cr₂O₃ powder has the largest transformed fraction 0.215, followed in order by Mg+10wt.%CeO₂ and Mg+10wt.%Al₂O₃. The Mg+10wt.%Cr₂O₃ powder has the largest hydriding rates at the first and fifth hydriding cycle, followed in order by Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. Mg+10wt.%Cr₂O₃ absorbs 5.87wt.% H at 573 K, 11 bar H₂ during 60 min at the first cycle. The Mg+10wt.%Cr₂O₃ powder has the largest dehydriding rates at the first and fifth dehydriding cycle, followed by Mg+10wt.%CeO₂ and Mg+10wt.%Al₂O₃. It desorbs 4.44 wt.% H at 573 K, 0.5 bar H₂ during 60 min at the first cycle. All the samples absorb and desorb less hydrogen at the fifth cycle than at the first cycle. It is considered that this results from the agglomeration of the particles during hydriding–dehydriding cycling. The average particle sizes of the as-milled and cycled powders increase in the order of Mg+10wt.%Cr₂O₃, Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. The quantities of hydrogen absorbed or desorbed for 1 h for the first and fifth cycles decrease in the order of Mg+10wt.%Cr₂O₃, Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. The quantities of absorbed or desorbed hydrogen increase as the average particle sizes decrease. As the particle size decreases, the diffusion distance shortens. This leads to the larger hydriding and dehydriding rates. The Cr₂O₃ in the Mg+10wt.%Cr₂O₃ powder is reduced after hydriding–dehydriding cycling. The much larger chemical affinity of Mg than Cr for oxygen leads to a reduction of Cr₂O₃ after cycling.     

Thermal shock behavior of nanostructured and conventional Al2O3/13 wt%TiO2 coatings fabricated by plasma spraying

The thermal shock behavior of three kinds of Al₂O₃/13 wt%TiO₂ coatings fabricated by plasma spraying was studied in this paper. One kind of those coatings was derived from conventional fused and crushed feedstock powder available commercially; the other two kinds of coatings were derived from nanostructured agglomerated feedstock powders. These two nano coatings possess moderate pores and pre-existing microcracks, they were composed of fused structure and three-dimensional net or skeleton-like structure. For conventional coatings, the pores and pre-existing cracks were bigger, sharp-point and mostly distributed between splats. Thermal shock tests for the three coatings were performed by water quenching method. Testing result showed the two kinds of nano coatings had much higher thermal shock resistance than the conventional coatings. The improved thermal shock resistance for nano coatings could attribute to their improved microstructure and crack propagation mode. The damage evolution and failure mechanism of coatings was quite different at thermal shock temperature of 650 °C and 850 °C, which was explained by a simple model. Different crack propagating modes in nanostructured and conventional coatings during thermal shock tests were due to their different microstructures in these two kinds coatings. The stress state of coating surfaces during the thermal cycles was also discussed in this paper.     

Al2O3-ZrO2 mixed oxide composite incorporated aluminium rich zinc coatings for high wear resistance

Corrosion resistance and wear resistance are the two important parameters for high performance of zinc galvanic coating. In the present work, the improvement of these two characteristics was achieved by the incorporation of Al₂O₃-ZrO₂ mixed oxide composite in the coating. Al₂O₃-ZrO₂ mixed oxide composite was synthesized from ZrOCl₂·8H₂O. Aluminium rich zinc coatings with high sliding wear resistance was developed from a galvanic bath containing the mixed oxide. Based on the performance of the coating during physicochemical and electrochemical characterization, the concentration of mixed oxide composite in the bath was optimized as 0.50 wt% Al₂O₃-0.50 wt% ZrO₂. While rich in Al-metal content in the coating caused high corrosion resistance, the incorporation of the mixed oxide improved structural characteristics of the coating resulting in high wear resistance also. The coating was nonporous in nature and even the interior layers had high stability. The coatings have potential scope for high industrial utility.     

An investigation of laser-assisted machining of Al2O3 ceramics planing

Laser-assisted machining (LAM), an alternative method of fabricating difficult-to-machine materials, uses primarily laser power to heat the local area (without necessarily evaporating or melting any material) before the material is removed. It not only efficiently reduces the cutting force during the manufacturing process but also improves the machining characteristics and geography with regard to difficult-to-machine materials, especially structural ceramics.This study on the application of laser-assisted machining to Al₂O₃ ceramics examines the measurements of cutting force and workpiece surface temperature as well as surface integrity and tool wear. Specifically, it uses the lattice Boltzmann method (LBM) to calculate the temperature distribution inside the ceramic workpiece during the LAM process and ensure that the laser energy causes no subsurface damage. The experimental results reveal that the LAM process efficiently reduces the cutting force by 22% (feed force) and 20% (thrust force) and produces better workpiece surface quality than conventional planing.     

TiN/Ti(C,N)涂层的显微组织与力学性能

采用磁控溅射在TNMG120408型号的硬质合金刀片上沉积了TiN/Ti(C,N)单层与多层涂层,通过XRD、SEM、纳米压痕、划痕仪与冲击测试等方法,比较分析了TiN/Ti(C,N)涂层的显微组织与力学性能。结果表明,TiN单层涂层的晶粒形貌为典型的喇叭口结构,Ti(C,N)单层涂层为平直的柱状晶结构;而TiN/Ti(C,N)多层涂层为柱状晶结构,形成了TiN、Ti(C,N)交替排列的结构。TiN与Ti(C,N)单层涂层均呈(220)生长织构,而TiN/Ti(C,N)多层涂层呈(111)生长织构。Ti(C,N)单层涂层表现出较好的硬度,而TiN/Ti(C,N)多层涂层则表现出与基体更好的结合力。     

Al2O3/Ti生物相容连接接头微观组织及力学性能

文中对Al₂O₃陶瓷和金属Ti表面磁控溅射Mo和Ti金属层,以纯Au箔钎料,研究连接工艺及Ti金属化层厚度对连接接头微观组织和力学性能的影响.结果表明,焊缝主要由Au钎料和（Au,Mo） ss构成,（Au,Mo） ss中含有少量（Ti,Mo） ss和TixAuy金属间化合物.另外,在Al₂O₃/钎料界面处及焊缝中存在少量呈条状分布的TiO₂和Ti_xAl_y金属间化合物.连接工艺及Ti金属化层厚度主要影响各物相的数量及分布状态,通过影响焊缝中固溶体的分布均匀性及金属间化合物的数量而影响接头抗剪强度.当连接温度为1 080℃、保温时间为5 min、Ti金属化层厚度为0.2 μm时,接头的抗剪强度达到最大值138 MPa.     

Magnetic and photoluminescence properties of Fe3O4@SiO2@YP1−xVxO4:Dy nanocomposites

In this paper, we report on the bifunctional Fe₃O₄@SiO₂@YP_0.1V_0.9O₄:Dy³⁺ nanocomposites were prepared by the solvothermal method and sol-gel method. The structure, photoluminescence (PL) and magnetic properties of the nanocomposites were characterized by means of X-ray diffraction, scanning electron microscope, transmission electron microscope, PL excitation and emission spectra and vibration sample magnetometry. It is shown that Fe₃O₄@SiO₂@YP_0.1V_0.9O₄:Dy³⁺ nanocomposites with a core-shell structure present excellent fluorescent and magnetic properties. Additionally, the effects of the magnetic field on the luminescence properties of nanocomposites were discussed.