Microstructure of Laser Remelted Ni-base Alloy Coating on Stainless Steel

A 5 kW CW CO2 gas laser was used to produce NiCrBSi superalloy coatings. Powders were preplaced by plasma-spraying. The microstructure and chemical composition of the coating have been studied by SEM, XRD and HREM. The results show the coating microstructure is fine dendrites, composed of γ matrix, γ' and boride (NiB) eutectic, the lattice parameter of the γ matrix is 0.3572 nm and there is a metallurgical bonding in interface.     

Influence of Structural Modification on Work-hardening Behaviour of Type 316 Stainless Steel

Work-hardening behaviour of type 316 austenitic stainless steel having difFerent initial dislocation structures introduced by swaging to various levels is analysed by a simplified Kock's model which takes into account the structural changes through the dislocation accumulation and annihilation process during deformation. The dislocation accumulation and annihilation factors show a temperature and structure dependence. The dislocation annihilation factor shows a plateau or decreasing tendency in the dynamic strain ageing (DSA) temperature range. This is attributed as either due to dislocation accumulation being more pronounced than dislocation annihilation or as due to precipitates being formed at DSA temperatures acting as obstacles to dislocation motion in the DSA temperature range.     

Nanosecond Laser “Pulling” Patterning of Micro–Nano Structures on Zr-Based Metallic Glass

Flexible and controllable fabrication of micro–nano structures on metallic glasses (MGs) endow them with more functional applications, but it is still challenging due to the unique mechanical, physical, and chemical properties of MGs. In this study, inspired by a new physical phenomenon observed in the nanosecond laser–MG interaction (i.e., the surface structure is transformed from the normally observed microgroove into the micro–nano bulge at a critical peak laser power intensity), a nanosecond laser “pulling” method is proposed to pattern the MG surface. The formation mechanism and evolution of the micro–nano bulge are investigated in detail, and accordingly, various micro–nano structures including the unidirectional stripe, pillar, cross-hatch patterns, “JLU”, circle, triangle, and square, are derived and created on the MG surface, which affects the surface optical diffraction. Overall, this study provides a highly flexible and controllable method to fabricate micro–nano structures on MGs.     

Influence of Hydrogen on Dislocation Structure in a Duplex Stainless Steel

The dislocation structure of specimens of aduplex stainless steel with precharged hydrogen hasbeen investigated by transmission electronmicroscopy.The result showed the hydrogen acti-vated dislocation source on phase boundaries offerrite/austenite and makes certain dislocations inaustenite grains move.The dislocation appearancesin each phase in specimens uncharged withhydrogen have been given for comparison.     

Effects of Forging and Heat Treatments on the Microstructure and Oxidation Behavior of 316LN Stainless Steel in High Temperature Water

Microstructure of 316 LN stainless steel(ss),including the as-received material and samples processed by solution anneal treatment and stress relief treatment after forging,was characterized by Vickers hardness(HV) testing and electron back scattering diffraction(EBSD).The oxide film formed on samples after immersion in borated and lithiated water at 583.15 K was investigated by scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS).Results showed that the grain size of samples was largely reduced after forging.Higher fraction of coincidence site lattice(CSL) boundaries and lower residual strain were observed in samples with either solution anneal treatment or stress relief treatment.The proportion of CSL boundaries was largely enhanced by solution anneal treatment after forging,due to the recrystallization occurring during solution anneal treatment.The oxide film grown on 316 LNss with solution anneal treatment after forging exhibited more strong protectiveness,as compared to the oxide film grown on samples with stress relief treatment after forging and the oxide film grown on asreceived samples without forging.The mechanisms of oxidation were then discussed.     

Fabrication and Evaluation of a Bioactive Sr–Ca–P Contained Micro-Arc Oxidation Coating on Magnesium Strontium Alloy for Bone Repair Application

Considering the compatibility between degradation and bioactivity of magnesium-based implants for bone repair, micro-arc oxidation is used to modify the magnesium alloy surface in aqueous electrolytes,allowing strontium, calcium, and phosphorus to be incorporated into the coating. The thickness, composition, morphology and phase of this Sr–Ca–P containing coating are characterized by scanning electron microscopy equipped with energy dispersive X-ray spectrometer and X-ray diffraction. The in vitro and in vivo degradation of the coating is evaluated by immersion test, electrochemical test and implantation test. Moreover, the cytocompatibility is tested with osteoblast cell according to ISO 10993. The results show that Sr, Ca and P elements are incorporated into the oxide coating, and a refined structure with tiny discharging micro-pores is observed on the surface of the coating. The Sr–Ca–P coating possesses a better corrosion resistance in vitro and retards the degradation in vivo. Such coating is expected to have significant medical applications on orthopedic implants and bone repair materials.     

Failure Analysis of Authentic Stainless Steel Tubes in a Vertical Fixed Shell–Tube Heat Exchanger

Journal of Failure Analysis and Prevention - The vertical fixed shell–tube heat exchanger failed to work in one chemical plant, and the leakage of the heat exchanger tubes were found after...     

Fabrication of nano-macroporous glass–ceramic bioscaffold with a water soluble pore former

Recently, several methods have been reported for fabricating tailored amorphous multi porosity bioscaffolds for bone regeneration and tissue engineering. In particular, the melt-quench-heat-etch method appears attractive for making large and/or complex shape structures or fibers for flexible products. However, often the macropore size has been limited to <100 μm. In this paper we report an improved method for fabricating nano-macroporous soda lime phosphosilicate glass using sucrose as a macropore former. The composite compact consisting of soda lime phosphosilicate glass and sucrose powders is pressed in a die at room temperature. 3D interconnected macroporous structure is formed first by dissolving the sucrose part in water at room temperature, and then sintering the compact at temperatures above the glass transition temperature. Thus, interconnected macropores with controlled size (≥100 microns) are formed readily. The sintering heat-treatment also induces nanoscale phase separation, which is then exploited for introducing nanoscale porosity. For the latter goal, the sample is leached in HCl under optimized conditions to yield desired nano-macroporous glass for bone scaffold or other applications.     

Fabrication of Ni60–SiC coating on carbon steel for improving friction,corrosion properties

The Ni60 and SiC–Ni60 composite coatings were successfully obtained by high-frequency inductive cladding on the AISI 1045 steel surface. The influence of SiC nanoparticles on the morphologies, phase composition, micro-hardness, wear resistance and corrosion resistance of the coatings were investigated systematically. An ultrasonic-assisted method was pre-treated for homogenising coating. The performance tests of coatings indicated that high-quality metallurgical bonding was formed under the optimised parameters. The average micro-hardness of Ni60 and SiC–Ni60 coatings was 765.6 and 1072.4?HV, respectively. The corresponding wear resistance was also measured, and the composite coating showed a much lower friction coefficient and wear rate. The corrosion resistance of the coatings was evidently improved by the addition of SiC nanoparticles.     

Influence of solution treatment temperature on mechanical properties of a Fe–Ni–Cr alloy

Influence of solution treatment temperature on mechanical properties of a Fe–Ni–Cr alloy was studied in this work. The results indicate that the strength and the ductile properties are optimum after solution treatment at 1000 °C followed by conventional two-step aging, but decrease markedly with the increase of solution temperature. Microstructure analyses show that TiC phase particles in the microstructure partly dissolves into the matrix when the solution treatment temperature is higher than 1100 °C, resulting in the coarsening of austenitic grain. Flake-like M₃B₂ phase precipitates at the grain boundary in the specimens solution-treated at temperatures higher than 1050 °C and its formation induces the mechanical properties to be worse.     

Effects of Cr Content on the Microstructure and Properties of 26Cr–3.5Mo–2Ni and 29Cr–3.5Mo–2Ni Super Ferritic Stainless Steels

By using scanning electron microscopy,energy-dispersive spectrometry,X-ray diffraction,strength and hardness measurements,the microstructure,precipitation,mechanical properties,and corrosion resistance have been investigated for two super ferritic stainless steels,26Cr–3.5Mo–2Ni and 29Cr–3.5Mo–2Ni,with the aim to consider the effect of Cr content.The results showed that with the addition of Cr content,the recrystallization temperature was increased;the precipitation of Laves and Sigma(σ)phases was promoted and the mechanical properties of super ferritic stainless steel were modified.Furthermore,the pitting corrosion resistance and corrosion resistance to H_2SO_4 of the two super ferritic stainless steels were improved.In addition,suitable annealing processing is a key factor to maintain integrated performance by optimizing microstructure and removing detrimental precipitation phases.     

The characteristics of a Pd–Ni/Pd–Cu double coating on 316L stainless steel and the corrosion resistance in stirred boiling acetic and formic acids mixture

A Pd–Ni/Pd–Cu double coating was deposited on stainless steel surface by electroplating. The microstructure and corrosion resistance of the double coating in strong reducing corrosive media were studied. In boiling 90 wt% acetic acid +10 wt% formic acid mixture containing 0.005 mol L⁻¹ NaCl with 900 r min⁻¹ stir, the corrosion rate of the double coating coated 316L stainless steel is one order of magnitude lower than that of Pd–Cu coated samples. The double coating shows lower porosity, higher hardness and elasticity modulus as well as higher adhesive strength, which may explain the better corrosion resistance in the testing environments.     

Pitting Corrosion Behavior of Cr–Mn Austenitic Stainless Steel with Addition of Molybdate and Tungstate Under Stagnant and Flow Condition in NaCl Solution

Journal of Failure Analysis and Prevention - Molybdate and tungstate inhibitors were introduced in stagnant and flowing conditions for determining pitting corrosion resistance of Cr–Mn SS in...     

Effect of mechanical coating with Ni and Ni–5% Al on the structure and electrochemical properties of the Mg–50% Ni alloy

The Mg–Ni metastable alloys (with amorphous or nanocrystalline structures) are promising candidates for anode application in nickel–metal hydride rechargeable batteries due to its large hydrogen absorbing capacity, low weight, availability, and relative low price. In spite of these interesting features, improvement on the cycle life performance must be achieved to allow its application in commercial products. In the present paper, the effect of mechanical coating of a Mg–50 at.% Ni alloy with Ni and Ni–5 at.% Al on the structure, powder morphology, and electrochemical properties is investigated. The coating additives, Mg–Ni alloy and resulting nanocomposites (i.e., Mg–Ni alloy + additive) were investigated by means of X-ray diffraction and scanning electron microscopy. The Mg–Ni alloy and nanocomposites were submitted to galvanostatic cycles of charge and discharge to evaluate their electrode performances. The mechanical coating with Ni and Ni–5% Al increased the maximum discharge capacity of the Mg–Ni alloy from of 221 to 257 and 273 mA h g⁻¹, respectively. Improvement on the cycle life performance was also achieved by mechanical coating.