Fabrication of titania coatings on stainless steel via laser-induced deposition of colloidal titanium oxide from sol–gel suspension

A novel processing route that exploits the application of laser energy to induce deposition of colloidal titania (TiO₂) from sol–gel suspension was developed to produce titania coatings onto stainless steel (AISI316) substrate. Various laser parameters were investigated in order to establish the feasibility and to work out the key factors and optimal conditions for effectively fabricating these coatings on the substrate. The SEM, EDS, ATR-FTIR, XRD, and contact angle measurement were employed to analyse surface morphology, phase composition, crystalline structure, and the surface properties of the deposited titania coatings. Results show that the laser energy density plays a key role in controlling the deposition process and the deposited coating's properties, whilst traverse speed is also an effective factor. Higher laser energy density delivered to the specific area leads to thicker coatings and higher crystalline phases in the deposited coatings. At lowest energy density of 4.4 J mm⁻² tested in this work, the deposited coating is mainly amorphous, although a small amount of anatase phase is detectable. More crystalline phases are formed including anatase, rutile, substoichiometric titanium oxides, ilmenite and hematite when the laser energy density is increased to 8.7–17.4 J mm⁻². Further increases in laser energy density to 21.7 J mm⁻² results in an increase in the amount of rutile phase and the disappearance of substoichiometric titanium oxide phase. The coated surfaces show an elemental composition very close to the theoretical atomic ratio of TiO₂ which is significantly different from that of the as-dried coating from the same sol. Laser irradiation over a control solution, which has the same composition as the titania sol, but without the titania precursor, was also carried out and the result showed that no change on the solution composition was detected under all laser conditions, but slight oxidation of the substrate was observed at the higher laser energy density.     

Study on tribological property of CrCN coating based on magnetron sputtering plating technique

The influence of carbon doping on tribological properties of CrCN coating was studied through preparation of coatings deposited on single crystal silicon and M2 high-speed steel (HSS) substrate using closed-field unbalanced magnetron sputtering ion plating technique. The friction coefficients were measured by pin-on-disc set-up and the wear traces of the coatings were observed by optical microscope. The microstructure and bond states of the coatings were characterized by atomic force microscope (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that the friction coefficient of coating decreases from 0.75 to 0.38, the micro-hardness increases from 1930 HV to 2300 HV, and the specific wear ratio of the coatings decreases from 8.351 × 10⁻¹⁵ m³/Nm to 3.859 × 10⁻¹⁵ m³/Nm with the increasing of carbon target current (I_C) from 0 A to 1.5 A. The grain size and the roughness of the coatings both decrease with the increasing of carbon target current, at the same time the coatings transform from crystalline state to amorphous state.     

Comparison of high temperature wear behaviour of plasma sprayed WC–Co coated and hard chromium plated AISI 304 austenitic stainless steel

The wear behaviour of plasma sprayed coating and hard chrome plating on AISI 304 austenitic stainless steel substrate is experimentally investigated in unlubricated conditions. Experiments were conducted at different temperatures (room temp, 100 °C, 200 °C and 300 °C) with 50 N load and 1 m/s sliding velocity. Wear tests were carried out by dry sliding contact of EN-24 medium carbon steel pin as counterpart on a pin-on-disc wear testing machine. In both coatings, specimens were characterised by hardness, microstructure, coating density and sliding wear resistance. Wear studies showed that the hard chromium coating exhibited improved tribological performance than that of the plasma sprayed WC–Co coating. X-ray diffraction analysis (XRD) of the coatings showed that the better wear resistance at high temperature has been attributed to the formation of a protective oxide layer at the surface during sliding. The wear mechanisms were investigated through scanning electron microscopy (SEM) and XRD. It was observed that the chromium coating provided higher hardness, good adhesion with the substrate and nearly five times the wear resistance than that obtained by uncoated AISI 304 austenitic stainless steel.     

Microstructural characterisation of nanocomposite nc-MeC/a-C coatings on oxygen hardened Ti-6Al-4V alloy

Nanocomposite coatings are novel, important systems composed of two or more nanocrystalline, or nanocrystalline and amorphous, phases. Such coatings offer a possibility of tailoring the coating microstructure and achieving new improved properties of coated materials. In this work a duplex surface treatment, consisting of an oxygen diffusion treatment and deposition of low friction nanocomposite nc-MeC/a-C (Me = transition metal, Ti, W or Cr) coatings, was applied for improvement of the Ti-6Al-4V alloy properties. The coatings composed of nanocrystallites of transition metal carbides (TiC or Cr_xC_y or WC) embedded in hydrogen-free amorphous carbon (a-C) matrix were deposited onto the surface of an oxygen hardened Ti-6Al-4 V alloy substrate by means of a simple DC magnetron sputtering. A nano/microstructure of the substrate material and coatings has been examined by scanning- and transmission electron microscopy complemented with the results of X-ray diffraction analyses.It was found that the nanocomposite coatings are composed of different carbide nanocrystals (with sizes of a few nanometres) embedded in an amorphous carbon matrix. The results of qualitative and quantitative analyses of the nanocrystalline phase in the coatings with use of high-resolution transmission electron microscopy combined with image analysis are given in the paper.An effect of the nano/microstructure parameters of the coated alloy onto its micro-mechanical (nanohardness and Young's modulus) and tribological properties (wear resistance and friction coefficient) is discussed in the paper.     

pH值对Cu-Co合金镀层结构及中温氧化行为的影响

为探索适合用作铁素体不锈钢表面的保护涂层,在不同pH值条件下,通过电沉积法在SUS430铁素体不锈钢表面共沉积Cu-Co合金镀层,并在750℃下进行中温氧化试验,利用X射线衍射(XRD)、扫描电镜(SEM)、能谱分析(EDS)等手段,分析镀层及氧化膜的形貌和组成,结合增重法研究Cu-Co合金镀层的中温抗氧化性能。结果表明:随着pH值的增加,镀层中Co元素的含量逐渐增大,Cu元素含量逐渐减小;在750℃中温氧化时,pH=6试样氧化速率最小;经400 h氧化后,基体表面的氧化物为Cr_2O_3和Fe_3O_4,pH=4镀层的氧化物主要为CuO,pH=5镀层的氧化物开始形成(Cu,Co)_3O_4尖晶石氧化物,pH=6镀层的氧化物中(Cu,Co)_3O_4和CuO成为主相;随着氧化时间的延长,pH=4,5镀层的氧化物晶粒缓慢长大,pH=6镀层的氧化物颗粒逐步细化;Cu-Co合金镀层氧化后的氧化层与SUS430钢的热匹配性较好,且镀层中Co含量较高时,其抗氧化性也较好,因此,pH=6镀液中获得的合金镀层适合用作铁素体不锈钢表面保护涂层。     

离子束溅射沉积羟基磷灰石涂层钛种植体材料的制备和表征

采用Ａｒ＾＋离子束溅射沉积技术和钛基体上沉积羟基磷灰石薄膜涂层,Ａｒ＾＋离子束的能量分别为０．９ｋｅＶ、１．２ｋｅＶ和１．５ｋｅＶ。利用Ｘ射线衍射（ＸＲＤ）、扫描电（ＳＥＭ０、透射电镜（ＴＥＭ）和红外光谱（ＦＴＩＲ）等检测方法,对制备的羟基磷灰石薄膜涂层进行了表征。Ｘ射线衍射和透射电结果表明该薄膜涂层为非晶态;红外光谱中无羟基（ＯＨ）特征峰存在,ＣＯ３根吸收峰的出现说明制备过程中会引入ＣＯ３根;扫     

The effect of PVD coatings on the corrosion behaviour of AZ91 magnesium alloy

In this study, multilayered AlN (AlN + AlN + AlN) and AlN + TiN were coated on AZ91 magnesium alloy using physical vapour deposition (PVD) technique of DC magnetron sputtering, and the influence of the coatings on the corrosion behaviour of the AZ91 alloy was examined. A PVD system for coating processes, a potentiostat for electrochemical corrosion tests, X-ray difractometer for compositional analysis of the coatings, and scanning electron microscopy for surface examinations were used. It was determined that PVD coatings deposited on AZ91 magnesium alloy increased the corrosion resistance of the alloy, and AlN + AlN + AlN coating increased the corrosion resistance much more than AlN + TiN coating. However, it was observed that, in the coating layers, small structural defects e.g., pores, pinholes, cracks that could arise from the coating process or substrate and get the ability of protection from corrosion worsened were present.     

Study of the characteristics and corrosion behavior for the Zr-based metallic glass thin film fabricated by pulse magnetron sputtering process

Two sets of source target which consist of ZrCuAlNiV and ZrTiAlNiV, respectively were selected as the target materials for preparing a series of thin film coatings on the 304 stainless steel substrate by DC pulse magnetron sputtering process. The microstructures of these as-prepared ZrCuAlNiV and ZrTiAlNiV thin films were examined by X-ray diffraction and TEM observation. In parallel, the characteristic analysis of these ZrCuAlNiV and ZrTiAlNiV alloy thin films including surface roughness, and corrosion resistance were analyzed by atomic force microscopy (AFM), and tested by electrochemical method as well as salt spray testing, respectively. The results showed that the ZrCuAlNiV thin film exhibits a typical amorphous microstructure and smooth surface with average roughness about 1 nm. The ZrCuAlNiV thin film performs similar corrosion resistance to 304 stainless steel according to the result of salt spray testing in 5% NaCl solution. Additionally, the AC impedance value of ZrCuAlNiV is 20 times than 316L stainless steel and 4 times than ZrTiAlNiV, implying that the ZrCuAlNiV thin film has better corrosion resistance than the others owing to its amorphous state.     

Characterization of mechanical properties of FeCrBSiMnNbY metallic glass coatings

This article investigates mechanical characteristics of Fe-based metallic glass coatings. A series of the coatings were fabricated by conventional wire-arc spray process. The microstructure of the coating was characterized by means of X-ray diffraction, scanning election microscopy equipped with energy dispersive X-ray analysis, transmission electron microscopy, and differential scanning calorimeter. The coating is very dense smooth, adhering well and with no cracking. The microstructure of the coating consists of amorphous phase and α(Fe,Cr) nanocrystalline phase. The nanocrystalline grains with a size of 30 to 60 nm are homogenously dispersed in the amorphous phase matrix. The crystallization temperature of the amorphous phase is about 545 °C. The mechanical properties, such as porosity, adhesive strength, microhardness, elastic modulus, and abrasive wear resistance, were analyzed in detail. The experimental results indicate that the coating has high microhardness (15.74 GPa), high elastic modulus (216.97 GPa), and low porosity (1.7%). The average adhesive strength value of the coating is 53.6 MPa. The relationship between abrasive wear behavior and structure of the coating is discussed. The relatively wear resistance of metallic glass coating is about 7 and 2.3 times higher than that of AISI 1045 steel and 3Cr13 martensite stainless steel coating, respectively. The main failure mechanism of metallic glass coating is brittle failure and fracture. The Fe-based metallic glass coating has excellent wear resistance.     

Dry sliding wear behavior and corrosion resistance of NiCrBSi coating deposited by activated combustion-high velocity air fuel spray process

NiCrBSi is a Ni-based superalloy widely used to obtain high wear and corrosion resistant coatings. This Ni-based alloy coating has been deposited onto 0Cr13Ni5Mo stainless steel using the AC-HVAF technique. The structure and morphologies of the Ni-based coatings were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS). The wear resistance and corrosion resistance were studied. The tribological behaviors were evaluated using a HT-600 wear test rig. The wear resistance of the Ni-based coating was shown to be higher than that of the 0Cr13Ni5Mo stainless steel because Fe₃B, with high hardness, was distributed in the coating so the dispersion strengthening in the Ni-based coating was obvious and this increased the wear resistance of the Ni-based coating in a dry sliding wear test. Under the same conditions, the worn volume of 0Cr13Ni5Mo stainless steel was 4.1 times greater than that of the Ni-based coating. The wear mechanism is mainly fatigue wear. A series of the electrochemical tests was carried out in a 3.5 wt.% NaCl solution in order to examine the corrosion behavior. The mechanisms for corrosion resistance are discussed.     

Growth morphology and mechanism of primary TiC carbide in laser clad TiC/FeAl composite coating

TiC-reinforced FeAl intermetallic matrix composite (IMC) coatings were fabricated on substrate of 1Cr18Ni9Ti stainless steel using laser cladding. X-ray diffraction (XRD) was used to identify the phases in the laser clad composite coating and the growth morphologies of TiC carbide were observed by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that there are two phases in the laser clad composite coating: TiC and FeAl intermetallic matrix alloy. The primary TiC carbide in laser clad coating nucleates heterogeneously on the surface of oxide particles; its growth morphology is found to be in a unique radial-branching dendrite with strongly faceted feature. The growth mechanism of TiC is confirmed to be lateral growth from the ledges or steps existing on the growing fronts.     

Formation of hydroxyapatite coating on titanium at 200°C through pulsed laser deposition followed by hydrothermal treatment

Pulsed laser deposition (PLD) has emerged as an acceptable technique to coat hydroxyapatite on titanium-based permanent implants for the use in orthopedics and dentistry. It requires substrate temperature higher than 400°C to form coatings of good adhesion and crystallinity. As this range of temperatures is likely to affect the bulk mechanical properties of the implant, lowering the substrate temperature during the coating process is crucial for the long-term performance of the implant. In the present study, hydroxyapatite target was ablated using a pulsed Nd:YAG laser (355 nm) onto commercially pure titanium substrates kept at 200°C. The coating thus obtained has been subjected to hydrothermal treatment at 200°C in an alkaline medium. The coatings were analysed using microscratch test, optical profilometry, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and infrared spectroscopy (FTIR). XRD, EDS and FTIR showed that the as-deposited coating contained amorphous calcium phosphate and the hydrothermal treatment converted it into crystalline hydroxyapatite. The micro-morphology was granular, with an average size of 1 micron. In the micro-scratch test, a remarkable increase in adhesion with the substrate was seen as a result of the treatment. The plasma plume during the deposition has been analysed using optical emission spectroscopy, which revealed atomic and ionic species of calcium, phosphorous and oxygen. The outcomes demonstrate the possibility of obtaining adherent and crystalline hydroxyapatite on titanium substrate at 200°C through pulsed laser deposition and subsequent hydrothermal treatment.     

Effect of the Oxidation Time on Properties of Ceramic Coatings Produced on Ti-6Al-4V by Micro-Arc Oxidation

Ceramic coatings were prepared on Ti-6AI-4V alloy using ac micro-arc oxidation (MAO) in silicate-hypophosphate solution. Growth regularity and formation mechanism of ceramic coatings were discussed. It was found that during the first stage the growth rate of coatings toward the external surface was larger than that toward substrate and then the coating began to grow mainly towards Ti alloy. When the total coating thickness reaches a certain value, it would no longer increase. In addition, the variations of the composition and microstructure of ceramic coatings according to the depositing time were also investigated with X-ray diffraction (XRD) and scanning electron microscope (SEM). The amount of rutile TiO2 gradually increased, whereas the amounts of the anatase TiO2 and amorphous phases first increased and then decreased slightly.     

Growth of permanganate conversion coating on 2024-Al alloy

The growth of permanganate conversion coating on aluminum 2024-T3 alloy has been studied by characterizing, with scanning Auger microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy, the coatings formed by immersion of the alloy in the coating bath (containing KMnO₄ and Na₂B₄O₇, pH 9.1) for different periods of time and at different temperatures. At room temperature, during the first 1-5 min of immersion, MnO₂ deposits are formed only on the second-phase intermetallic particles (of Al-Cu-Mg and Al-Cu-Fe-Mn types), but the coating starts to develop on the Al matrix surface after 5-10 min. The coating slows down and stops after about 150 min, with a thinner deposit over the alloy matrix. The process is accelerated at higher temperatures, for example at 68 °C it self-limits after about 3 min. The electrochemical growth process appears to follow that established for the chromate conversion coatings, although XPS does not detect significant MnO₄⁻ incorporation into the permanganate coatings.     

Electroless deposition of Ni–W–P–B4C nanocomposite coating on AZ91D magnesium alloy and investigation on its properties

In the present work, electroless deposition of quaternary Ni–W–P–B₄C composite coatings on AZ91D magnesium alloy was investigated. The coatings were characterized to study their microstructure, crystallite size, morphology, microhardness and corrosion resistance and compared with Ni–P and Ni–P–B₄C composite coatings, prepared with the same method. The hardness of the Ni–W–P–B₄C composite coatings was around 1290 MPa which was more than that of the Ni–P and Ni–P–B₄C coatings (about 700 and 1200 MPa, respectively). According to polarization test results, the Ni–W–P–B₄C composite coating exhibits less and more corrosion rates with respect to the Ni–P–B₄C and the Ni–P coatings, respectively. X-ray diffraction (XRD) analysis results for the Ni–W–P–B₄C coating showed that the Ni–W–P–B₄C coating has a combination of amorphous and nanocrystalline structures. Also, Williamson–Hall analysis on the X-ray patterns revealed that the Ni–W–P–B₄C coating has an average crystallite size of 1.5 nm.     

Laser surface modification of titanium substrate for pulsed laser deposition of highly adherent hydroxyapatite

Biomedical implant devices made out of titanium and its alloys are benefited by a modified surface or a bioactive coating to enhance bone bonding ability and to function effectively in vivo for the intended period of time. In this respect hydroxyapatite coating developed through pulsed laser deposition is a promising approach. Since the success of the bioactive ceramic coated implant depends mainly on the substrate-coating strength; an attempt has been made to produce micro patterned surface structure on titanium substrate for adherent hydroxyapatite coating. A pulsed Nd-YAG laser beam (355 nm) with 10 Hz repetition rate was used for surface treatment of titanium as well as hydroxyapatite deposition. The unfocussed laser beam was used to modify the substrate surface with 500–18,000 laser pulses while keeping the polished substrate in water. Hydroxyapatite deposition was done in a vacuum deposition chamber at 400°C with the focused laser beam under 1 × 10⁻³ mbar oxygen pressure. Deposits were analyzed to understand the physico-chemical, morphological and mechanical characteristics. The obtained substrate and coating surface morphology indicates that laser treatment method can provide controlled micro-topography. Scratch test analysis and microindentation hardness values of coating on laser treated substrate indicate higher mechanical adhesion with respect to coatings on untreated substrates.     

Formation of amorphous and nanocrystalline phases in high velocity oxy-fuel thermally sprayed a Fe–Cr–Si–B–Mn alloy

High velocity oxy-fuel (HVOF) thermal spray was used to deposit a Fe–Cr–Si–B alloy coating onto stainless steel (1Cr18Ni9Ti) substrate. Microstructures of the powder and the coating were investigated by X-ray diffraction (XRD), scanning election microscopy (SEM), transmission election microscopy (TEM) and differential scanning calorimeter (DSC). The coating had layered morphologies due to the deposition and solidification of successive molten or half-molten splats. The microstructures of the coating consisted of a Fe–Cr-rich matrix and several kinds of borides. The Fe–Cr-rich matrix contained both amorphous phase and nanocrystalline grains with a size of 10–50 nm. The crystallization temperature of the amorphous phase was about 605 °C. The formation of the amorphous phase was attributed to the high cooling rates of molten droplets and the proper powder compositions by effective addition of Cr, Mn, Si and B. The nanocrystalline grains could result from crystallization in amorphous region or interface of the amorphous phase and borides by homogeneous and heterogeneous nucleation.     

Mechanical behaviour of Zn–Fe alloy coated mild steel

Zinc alloy coatings containing various amounts of Fe were deposited by electrodeposition technique on a mild steel substrate. The concentration of Fe in the produced alloy coatings ranged from 0 to 14 wt.%, whereas the thickness of the coatings was about 50 μm. Structural and metallurgical characterization of the produced coatings was performed with the aid of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques. This study aims in investigating the mechanical behaviour of Zn–Fe coated mild steel specimens, as no research investigation concerning the tensile behaviour of Zn alloy coated ferrous alloys has been reported in the past. The experimental results indicated that the ultimate tensile strength of the Zn–Fe coated mild steel was lower than the bare mild steel. In addition, the ductility of the Zn–Fe coated mild steel was found to decrease significantly with increasing Fe content in the coating.     

Microstructures and bond strengths of the calcium phosphate coatings formed on titanium from different simulated body fluids

Calcium phosphate (Ca-P) coatings were deposited on Ti substrates by a biomimetic method from m-SBF and 10× SBF, respectively. Comparative study of microstructures and bond strengths of the Ca-P coatings deposited from those different SBFs was carried out. Effect of the surface roughness of the substrates on the bond strength of the Ca-P coatings was also studied. Scanning electron microscopy (SEM), X-ray diffractometry (XRD), Fourier transformed infrared spectroscopy (FTIR), inductive coupled plasma spectrometry (ICP) and thermogravimetry (TG) were used to characterize the Ca-P coatings. The bond strengths between the coatings and Ti substrates were measured using an adhesive strength test. Results indicated that the ionic concentrations of the SBFs and the surface roughness of the substrate had a significant influence on the formation, morphology and bond strength of the Ca-P precipitates. The induction period of time to deposit a complete Ca-P layer from the m-SBF is much longer, but the Ca-P coating is denser and has higher bond strength than that formed from the 10× SBF. The Ti with a surface roughness of R_a 0.64 µm and R_z 2.81 µm favoures the formation of a compact Ca-P coating from the m-SBF with the highest bond strength of approximately 15.5 MPa.     

双向脉冲快速电沉积非晶态Ni-P/Al_2O_3复合镀层

采用双向脉冲电沉积法制备出高P非晶态Ni-P/Al_2O_3复合镀层,利用扫描电镜(SEM)和能谱分析(EDS)方法考察镀层的微观形貌和化学组成,采用X射线衍射技术(XRD)表征镀层的相结构,并通过分析金属镀层和复合镀层的电化学测试结果,评价不同种类镀层的耐腐蚀能力。结果表明:与直流电沉积法相比,双向脉冲电沉积法可将镀层中的P含量提高至12.06%(质量分数),有利于非晶态Ni-P合金镀层的形成。采用双向脉冲法制备的Ni-P/Al_2O_3复合镀层比直流电沉积法制备的Ni-P/Al_2O_3复合镀层更平整、结晶更致密。脉冲电沉积法制备的非晶态Ni-P合金镀层具有更好的耐蚀性,而且复合微粒Al_2O_3的加入,对进一步提高非晶态Ni-P合金镀层的耐蚀性有积极作用。