Laser surface treatment of high‐speed steel: presence of TiC particles at the surface

Laser treatment of a high‐speed steel surface is carried out and metallurgical and morphological changes in the laser‐treated layer are examined using SEM, EDS and XRD. A carbon film of 50 µm thickness and containing 5% TiC particles is formed at the workpiece surface prior to the laser treatment process. The carbon film formed at the surface enhances the absorption of laser irradiation and retains TiC particles at the workpiece surface. The residual stress formed at the laser‐treated surface is determined using the XRD technique while the indentation tests are carried out to measure microhardness and fracture toughness of the resulting surface. It is found that ε‐Fe₃N, and ε‐Fe₃ (N,C) compounds are formed at the laser‐treated surface, which are attributed to the presence of carbon film and high‐pressure nitrogen‐assisting gas. The fracture toughness of the laser‐treated surface reduces because of the increased hardness and dense layer formed at the surface vicinity. Copyright © 2011 John Wiley & Sons, Ltd.     

Laser embedding of TiC particles into the surface of phosphor bronze‐bearing material

A carbon film containing 5% TiC particles is formed on a pre‐prepared bronze surface prior to laser treatment. The carbon film provides increased absorption of the incident laser beam and hosts TiC particles with a uniform distribution at the workpiece surface. Optical and scanning electron microscopy are used to examine the metallurgical and morphological changes in the laser treated layer. Micro‐hardness of the laser‐treated surface is measured, and the residual stress formed in the surface vicinity is measured using the X‐ray diffraction technique. It was found that a dense layer with fine grains was formed in the laser‐treated layer. The micro‐hardness of the laser‐treated surface increases almost three times compared with the base material hardness. The presence of a dense layer and the formation of Cu₃N in the surface region contribute to the hardness enhancement at the surface. Copyright © 2012 John Wiley & Sons, Ltd.     

Characterization and corrosion resistance of pure Mg modified by micro‐arc oxidation using phosphate electrolyte with/without NaOH

Magnesium and its alloys have been suggested as potential absorbable implant materials due to their excellent biodegradability and biocompatibility. Current researchers focus on reducing the rapid corrosion rate of Mg and its alloys by alloying and surface modification. To improve the corrosion resistance, pure Mg is modified by micro‐arc oxidation (MAO) in phosphate electrolyte containing sodium hydroxide and its properties are compared with those formed using only phosphate or sodium hydroxide as electrolytes. A uniform and stable coating layer is formed on Mg after MAO treatment in phosphate electrolyte containing sodium hydroxide. The corrosion resistance of MAO‐coated Mg is evaluated by potentiodynamic polarization study and immersion test. The results reveal that MAO coating enables a good improvement in corrosion resistance, and among them, coatings treated using phosphate electrolyte containing sodium hydroxide offer the best performance. Copyright © 2013 John Wiley & Sons, Ltd.     

Post‐oxidizing effects on surface characteristics of salt bath nitrocarburized AISI 02 tool steel type

The effect of post‐oxidizing treatment on the characteristics of modified surface layers produced by salt bath nitrocarburizing on the industrial American Iron and Steel Institute (AISI) 02 tool steel types is investigated. Nitrocarburizing treatment is performed for 6 h and 8 h at 570 °C and post‐oxidizing treatment for 30, 60 and 90 min at 520 °C, using argon–steam mixture. Formed layers are characterized by their basic properties such as thickness layer, depth, surface hardness and wear resistance. Detailed estimation of the modified metal surface quality, in terms of chemical composition, formed phases, microstructures and diffusion mechanisms are performed by metallographic techniques, EDX, X‐ray diffraction, scanning electron microscopy (SEM) and glow discharge optical electron spectroscopy (GDOES). The corrosion resistance was investigated in 0.4 M H₂SO₄ solutions, using steady‐state electrochemical polarization methods. The obtained results revealed the existence of a superficial oxide layer which consists of magnetite (Fe₃O₄) and hematite (Fe₂O₃) and the presence of an ε‐phase associated with a small amount of γ′‐phase. Important improvements in wear, microhardness and corrosion resistance occur after these treatments and it is specifically concluded that the sole application of a nitrocarburizing treatment does not significantly ameliorate the corrosion resistance of the as‐received steel. In fact, post‐oxidation treatment contributes to increase corrosion resistance by forming a dense magnetite layer and at the same time, it partially covers the compound layer pores. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of anodic oxidation on corrosion properties of Al coating by arc spraying in seawater

A layer of Al coatings was prepared on the S355 steel by arc spraying, which was conducted by anodic oxidation treatment; the morphologies, chemical element compositions and phases of Al coating, and anodic oxide layer were analyzed with field emission scanning electron microscope (FESEM), energy dispersive spectrometer (EDS) and X‐ray diffraction (XRD), respectively. The corrosion protections of Al coating before and after anodic oxidation were discussed with a seawater immersion test; the corrosion resistance mechanisms of Al coating and anodic oxide layer in the seawater were also investigated. The results show that the thickness of Al coating is about 300 µm by arc spraying, the sample surfaces become loose after seawater immersion corrosion and Cl^? and O^2? penetrate into the substrate from the cracks, destroying the binding properties of coating–substrate, and the coating fails. After anodic oxidation, the oxide layer is formed in the surface of Al coating with the thickness of about 30 µm; the corrosion products are mainly composed of Al(OH)₃, which barraged the holes caused by seawater corrosion. The corrosion cracks are formed during the corrosion, while the number and depth of cracks decrease obviously after anodic oxidation treatment. The corrosion of Al coating becomes the local corrosion after anodic oxidation treatment, and the grains are smaller, which are easily nucleated to form a new corrosion resistance layer. Copyright © 2015 John Wiley & Sons, Ltd.     

非晶态Ni-W-B合金的电沉积及其热处理前后的性能

To strengthen the properties of Ni-W alloy, dimethylamine borane （DMAB） was added to an alloy Ni-W electrolyte solution and a ternary Ni-W-B alloy was electrodeposited. The electrodeposition, crystallographic structure, surface morphology, heat treatment and corrosion resistance, of the alloy were studied by DSC, XRD, SEM and electrochemical techniques. The results showed that the structure of the alloy was greatly affected by the cooperation of boron compound. DSC experiment combined with X-ray diffractometry indicated that the obtained Ni-W-B alloy was still in amorphous structure although W content in the alloy was decreased by the addition of DMAB. After heat treatment at 400 ℃ for 1 h, the microhardness was increased from 612 to 947 kg.mm^-2 that was com- parative to Cr coating. The appearance of the as-plated coating was in f＇me and slice grains and kept almost no change after heat treatment. In w=0.03 NaC1 solution the as-plated coating presented very good corrosion resistance. After the coating was heat-treated its corrosion resistance was enhanced.     

Characterization of the Corrosion of Nanostructured 17-4 PH Stainless Steel by Surface Mechanical Attrition Treatment (SMAT)

Abstract

The corrosion properties of nanostructured 17-4PH stainless steel facilitated by a surface mechanical attrition treatment (SMAT) process were studied using electrochemical measurements in 0.6?M NaCl aqueous solution. The microstructure of the surface layer was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results demonstrated the formation of a nanostructured surface layer on the surface of the material. By the combination of SMAT and low-temperature annealing processes, the potentiodynamic polarization measurements and X-ray photoelectron spectroscopy (XPS) spectra demonstrated an improvement in the corrosion resistance of 17-4PH stainless steel with a reduced corrosion current density of 0.241?mA/cm² and a higher chromium content. The improved corrosion resistance may be attributed to the formation of nucleation sites through which chromium may freely move from the matrix to the upper surface and thereby form a protective oxide layer on the surface of the material.     

激光熔凝处理对纯铁渗稀土层组织与耐蚀性能的影响

通过SEM观察,X射线光电子能谱分析,电化学阻抗谱测定和阳极极化曲线的测试,探讨激光熔凝处理对纯铁渗稀土层组织与耐蚀性能的影响,结果表明,在一定条件下,激光熔凝处理可进一步提高纯铁渗稀土层组织的致密性与均匀性,显著提高稀土渗层的耐蚀性。     

Characterization of laser‐treated Rene 41 surface due to B4C and SiC particles at surface prior to laser treatment

Laser surface treatment of Rene 41 high‐performance alloy is carried out with the presence of hard particles at the surface. B₄C and SiC particles are uniformly distributed within 40 µm carbon film at the workpiece surface prior to laser treatment process. The effect of hard particles on residual stress and microhardness variations is investigated at the treated surface. Morphological and metallurgical changes in the treated layer are examined by using electron microscopy, energy dispersive spectroscopy, and X‐ray diffraction. Residual stress formed at the surface is determined from the X‐ray data. It is found that the treated surface is free from asperities such as large size voids and cracks. A dense layer is formed in the surface region, which causes volume shrinkage while contributing to microhardness and residual stress enhancement at the surface. B₄C hard particles result in the highest residual stress and microhardness at the surface, which is attributed to its high thermal expansion coefficient. Copyright © 2013 John Wiley & Sons, Ltd.     

Surface characteristics of AZ91D alloy anodized with various conditions

Anodic oxidation of an AZ91D magnesium alloy was carried out in an attempt to increase the corrosion resistance. The alloy was placed in an electrolyte containing 0.1 M sodium silicate (Na₂SiO₃), 2.0 M sodium hydroxide (NaOH) and 0.1 M sodium phosphate (Na₃PO₄), and treated with a current density of 100–400 mA/cm² for 1 to 4 min. After the anodic oxidation treatment, the surface characteristics were analyzed by SEM, X‐ray diffraction (XRD) and a surface roughness tester. The corrosion resistance was determined by measuring the corrosion potential and corrosion current density using potentiodynamic polarization in a 3.5 wt% NaCl electrolyte solution. Although the anodic oxidation treatment with the base electrolyte resulted in an arrival voltage ranging from 60 to 70 V, the addition of silicate tended to reduce this arrival voltage by approximately 10–20 V and decrease the critical voltage required for the formation of a porous oxide film. The pore size and film thickness increased with increasing applied current and treatment time. The addition of silicate to the electrolyte resulted in films with a homogeneous pore size and a film thickness increasing with the increasing applied current and treatment time. XRD showed the formation of a new MgO and Mg₂SiO₄ phase. The formation of Mg₂SiO₄ was attributed to the presence of SiO₄^4? in the film. After the addition of silicate, the corrosion potential increased and corrosion current decreased, resulting in improved corrosion resistance. Copyright © 2008 John Wiley & Sons, Ltd.     

Laser surface treatment of high‐speed tool steel (AISI M2)

High‐speed tool steel (AISI M2) surface is pre‐prepared to form a thin carbon film containing 5% B₄C particles prior to laser treatment process. Morphological and metallurgical changes are examined in the treated layer using electron microscope, energy dispersive spectroscopy, and X‐ray diffraction. The microhardness and the residual stress formed at the treated surfaces are measured for samples with and without B₄C particles. It is found that the micro‐stresses formed in the neighborhood of B₄C particles at the treated surface contributed to the microhardness enhancement at the surface. This is associated with the mismatch of thermal expansion coefficients between B₄C particles and the base alloy. The nitride phases are formed at the treated surface, which also contribute to the microhardness increase at the surface. Copyright © 2012 John Wiley & Sons, Ltd.     

Nitrogen uptake of nickel free austenitic stainless steel powder during heat treatment—an XPS study

In austenitic stainless steel nitrogen stabilizes the austenitic phase, improves the mechanical properties and increases the corrosion resistance. Nitrogen alloying enables to produce austenitic steels without the element nickel which is high priced and classified as allergy inducing. A novel production route is nitrogen alloying of CrMn‐prealloyed steel powder via the gas phase. This is beneficial as the nitrogen content can be adjusted above the amount that is reached during conventional casting. A problem which has to be overcome is the oxide layer present on the powder surface which impedes both the sintering process and the uptake of nitrogen. This study focuses on whether heat treatment under pure nitrogen is an appropriate procedure to enable sintering and nitrogen uptake by reduction of surface oxides. X‐ray photoelectron spectroscopy (XPS) in combination with scanning electron microscopy (SEM) and energy dispersive X‐ray spectrometry (EDS) are used to investigate the surface of powdered FeMn19Cr17C0.4N heat treated under nitrogen atmosphere. The analyses showed reduction of iron oxides already at 500 °C leading to oxide‐free metallic surface zones. Mn and Cr oxides are reduced at higher temperatures. Distinct nitrogen uptake was registered, and successful subsequent sintering was reached. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of thermal treatment on hydrophilicity and corrosion resistance of Ti surface

Surface treatment of titanium (Ti) surface has been extensively studied to improve its properties for biomedical applications, including hydrophilicity, corrosion resistance, and tissue integration. In this present work, we present the effects of thermal oxidation as surface modification method on metallic titanium (Ti). The Ti foils were oxidized at 300°C, 400°C, 500°C, and 600°C under air atmosphere for 3 hours, which formed oxide layer on Ti surface. The physicochemical properties including surface chemistry, roughness, and thickness of the oxide layer were evaluated in order to investigate how these factors affected surface hydrophilicity, microhardness, and corrosion resistance properties of the Ti surface. The results revealed that surfaces of all oxidized samples were modified by formation of titanium dioxide layer, of which morphology, phase, and thickness were changed according to the oxidized temperatures. Increasing oxidation temperature led to the formation of thicker oxide layer and phase transformation of anatase to rutile. The presence of the oxide layer helped the improvement of corrosion resistance and microhardness. The most improvement in surface roughness was found in the specimens treated at 400°C, which significantly improved surface hydrophilicity. But both surface roughness and hydrophilicity reduced when oxidized at 500°C and 600°C, suggesting that hydrophilicity was dominated by the surface roughness. In addition, this surface treatment did not reduce the biocompatibility of the metallic Ti substrates against murine osteoblasts (MC3T3).     

Surface treatment of zinc by Schiff’s bases and its corrosion study

The zinc metal surface is chemically modified by newly synthesized Schiff’s bases and its corrosion protection is investigated. The influence of concentration of Schiff’s bases on modification of zinc surface and immersion time in treatment bath are investigated and optimized for maximum corrosion protection efficiency. The electrochemical studies of treated zinc specimens are performed in aqueous acid solution using galvanostatic polarization technique. The treated zinc samples show good corrosion resistance. The recorded electrochemical data of chemically treated samples indicate a basic modification of the zinc surface. The protection efficiency of organic layer formed on zinc surface is tested by varying the acid concentration and temperature of the corrosive medium. The corrosion protection efficiency increases with the concentration of Schiff’s bases and immersion time. This is due to a strong interaction between zinc and the organic molecules, which results in the formation of a protective layer. This layer prevents the contact of aggressive medium with the zinc surface. The surface modification is confirmed by the scanning electron microscopy images. The interaction between metal atoms and Schiff’s bases is also established by IR studies. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 7, pp. 886–892. The text was submitted by the authors in English.     

Effect of TiO2–Ti and TiO2–TiN composite coatings on corrosion behavior of NiTi alloy

Two kinds of biocompatible coatings were produced in order to improve the corrosion resistance of nickel titanium (NiTi) alloy. A titanium oxide–titanium (TiO₂–Ti) composite was coated on NiTi alloy using electrophoretic method. After the coating process, the samples were heat‐treated at 1000 °C in two tube furnaces, the first one in argon atmosphere and the second one in nitrogen atmosphere at 1000 °C. The morphology and phase analysis of coatings were investigated using scanning electron microscopy and X‐ray diffraction analysis, respectively. The electrochemical behavior of the NiTi and coated samples was examined using polarization and electrochemical impedance spectroscopy tests. Electrochemical tests in simulated body fluid demonstrated a considerable increase in corrosion resistance of composite‐coated NiTi specimens compared to the non‐coated one. The heat‐treated composite coating sample in nitrogen atmosphere had a higher level of corrosion resistance compared to the heat‐treated sample in argon atmosphere, which is mainly due to having nitride phases. Copyright © 2014 John Wiley & Sons, Ltd.     

Study of the effect of laser treatment on the initial oxidation behaviour of Al‐coated NiCrAlY bond‐coat

In this study, the initial oxidation behaviour of laser‐treated Al/NiCrAlY bond‐coat is investigated. Two approaches, (i) Al film sputtering on the surface of bond‐coat and (ii) laser treatment, have been taken to enhance the oxidation resistance of NiCrAlY bond‐coat. Experimental results showed that after laser treatment, the Al/NiCrAlY bond‐coat exhibited a columnar dendritic microstructure without cracks and voids. A dense and continuous α‐Al₂O₃/Cr₂O₃ multilayer was found to form on the bond‐coat surface. Results on the cyclic oxidation at 1200 °C (for time ≤ 204 h) revealed that the laser‐treated Al/NiCrAlY bond‐coat exhibited better oxidation resistance compared to as‐sprayed NiCrAlY, Al/NiCrAlY and laser‐remelted NiCrAlY bond‐coat. The formation of θ‐Al₂O₃, NiO, Cr₂O₃ and NiCr₂O₄ spinel oxides was observed to be suppressed due to the preformed α‐Al₂O₃ scale during initial oxidation on the surface of laser pre‐oxidized Al/NiCrAlY bond‐coat. Copyright © 2013 John Wiley & Sons, Ltd.     

Surface characteristics of Ti‐10Ta‐10Nb alloy modified by hydrogen peroxide treatment for dental implants

The use of titanium‐based alloys as biomaterials is becoming more common because they have a reduced elastic modulus, superior biocompatibility, specific strength, good corrosion resistance, superior strain control, and fatigue resistance compared to conventional stainless steel and Co? Cr alloys. However, when implanted into the human body these metals are problematic because they do not directly bond with living bone. Surface treatments play an important role in nucleating calcium phosphate deposition on a surgical titanium alloy implant. The purpose of this study is to examine whether the precipitation of apatite on Ti? 10Ta? 10Nb alloy is affected by surface modification in H₂O₂ solution. Specimens were chemically treated with a solution containing 30 wt% H₂O₂ at 80 °C for 1 h, and subsequently heat treated at 400 °C for 1 h. All specimens were immersed in SBF (Simulated Body Fluid) with a pH of 7.4 at 36.5 °C for seven days, and the surfaces were examined with XRD, SEM, EDX and in vitro testing. The microstructure analysis of the Ti? 10Ta? 10Nb alloy after etching with Keller's etchant showed a Widmanstatten pattern. The micro‐Vickers hardness number was 236.44 ± 4.99, and surface roughness was increased by the surface treatment. The wettability after surface treatment was better than on the nontreated surface. Resistance to cytotoxicity was decreased by the chemical surface treatment (P < 0.05). Copyright © 2011 John Wiley & Sons, Ltd.     

Synergetic effect of sol–gel silica coating and physical/chemical pre-treatment on the oxidation behavior of Ti-6Al-4V alloy

The Ti-6Al-4V alloy was treated in concentrated phosphoric acid solution and by powder blasting, respectively, subsequently coated by silica using sol–gel dip-coating technique. A barrier layer of titanium pyrophosphate (TiP₂O₇) was synthesized at the Ti-6Al-4V substrate surface after the heat treatment. XRD and SEM/EDS analysis revealed that an amorphous silica coating was formed on the alloy. The isothermal and cyclic oxidation behavior of the treated alloy with silica coating and the corresponding bare alloy was investigated at 600 °C in static air to investigate the synergetic effect of the SiO₂ coating and surface treatment on the oxidation resistance of the alloy by thermogravimetry. The average parabolic rate constants of the treated specimens with silica coating were greatly reduced. The stratified oxide layer formed on the bare alloy, while thinner oxide layer formed on the treated alloys with silica coating. The oxidation resistance of the present alloy was improved. The effect of silica coating on the microhardness of the substrate was investigated.     

EIS investigation of a Ce-based posttreatment step on the corrosion behaviour of Alclad AA2024 anodized in TSA

In the aircraft industry, anodizing and posttreatment steps use Cr (VI) compounds, which, despite offering good corrosion resistance and self-healing properties, are highly toxic and carcinogenic. Ce compounds are recognized as efficient corrosion inhibitors for Al alloys, and several works report self-healing ability for these chemicals. In this investigation, the corrosion resistance of Alclad AA2024-T3 alloy anodized in tartaric-sulphuric acid (TSA) bath and posttreated in a solution comprising cerium nitrate without and with hydrogen peroxide was evaluated. The purpose is to investigate the potentiality of using hydrothermal treatment in Ce nitrate solution as candidate to replace Cr (VI) posttreatment. The aim is to provide a posttreatment step which, while improving the corrosion resistance, does not plug the mouths of the pores maintaining the adhesion properties of the porous anodic layer. Microstructural characterization was carried out by SEM-EDS whereas corrosion resistance was evaluated by EIS. The surface analysis showed that the posttreatments, all performed at 50°C, kept the open structure of the pores. EIS analysis showed that the posttreatments performed in the H₂O₂ solution for short immersion times were the most effective in improving the corrosion resistance of the samples, whereas electrical equivalent circuit (EEC) fitting of the data indicated sealing of the porous layer during the immersion of the different samples in the test solution. SEM-EDS analysis of the samples posttreated in the H₂O₂ containing solution, prior and after the corrosion test, showed the presence of Ce oxy-hydroxide randomly deposited on the sample surface, indicating that Ce could be incorporated/stored in the anodic layer.     

Corrosion resistance of zinc electrodeposited from acidic and alkaline electrolytes using pulse current

Corrosion resistance of zinc coatings was investigated in an accelerated corrosion test in a condensation chamber. Zinc was electrodeposited from alkaline and acidic electrolytes using direct current (DC) or pulse current (PC). The zinc coating was subsequently protected against corrosion with a chrome (III) layer. Morphology and structure of the coatings was investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction analysis (XRD) before and after the corrosion test. Corrosion resistance of alkaline zinc coatings electrodeposited with DC and PC under test conditions was found to be comparable. The corrosion resistance of zinc coatings deposited from acidic electrolytes by PC was lower in comparison with corrosion resistance of zinc coatings deposited using DC. Presented at the 8th Conference on Solid State Chemistry, Bratislava, Slovakia, 6–11 July 2008.