Effect of Si addition on microstructure and mechanical properties of Ti–Al–N coating

Ti–Al–N coatings are widely used to prevent the untimely consumption of cutting tools exposed to wear. Increasing requirements on high speed and dry cutting application open up new demands on the quality of wear-protective quaternary or multinary Ti–Al–N based coating materials. Here, we investigated the microstructure and mechanical properties of Ti–Al–N and Ti–Al–Si–N coatings deposited on cemented carbide by cathodic arc evaporation. The formation of nanocomposite nc-TiAlN/a-Si₃N₄ structure by incorporation of Si into Ti–Al–N coating causes a significant increase on hardness from ∼ 35.7 GPa of Ti–Al–N to ∼ 42.4 GPa of Ti–Al–Si–N. Both coatings behave age-hardening during thermal annealing, however Ti–Al–Si–N coating reveal better thermal stability. Therefore, the improved cutting performance of Ti–Al–Si–N coated inserts is obtained compared to Ti–Al–N coated inserts.     

Corrosion behavior of sintered zinc-aluminum coating in NaCl solution

Sintered zinc-aluminum coating (SZAC) was prepared using zinc flakes,aluminum flakes and CrO3 as main raw materials,The corrosion behavior of SZAC in 3.5NaCl solution was Studied by means of SEM,EDS,EIS and so on.Results indicate that aluminum corroded in advance of zinc to produce speculate or spherical substances,which attaches to SZAC and adds mass to it.Corrosion production passivates metal powders in SZAC.causes Ecorr of SZAC to increase gradually,and causes the arising of the third time constant in EIS,which corresponds to the insulation of corrosion production.     

Corrosion properties of anodic oxide coatings on Ti–6Al–4V in simulated body solution

Abstract

Anodic oxide coatings were synthesised on Ti–6Al–4V substrates using aqueous electrolytes containing dissolved calcium and phosphorus. Different coatings were produced by varying the time of synthesis. Inherent features of the coatings were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Uniform corrosion, electrochemical polarisation and ac impedance tests were performed in simulated body fluid (SBF). Small amounts of calcium and phosphorus are deposited from the electrolyte on to the coating and their levels increase with increasing duration of synthesis. Maximum values of porosity and thickness are obtained for oxides coated for 3 h. Coatings produced from shorter times showed very good resistance to the attack of SBF.     

Corrosion behavior of Cu–Sn bronze alloys in simulated archeological soil media

The corrosion behavior of synthetic Cu–Sn bronze alloys with six different Sn contents was examined through an electrochemical test and a synthetic test in a simulated corrosive medium. The mechanism of corrosion and the morphology of the corroded surfaces were characterized through field emission scanning electron microscopy equipped with energy-dispersive spectroscopy. At the corrosion potential, the corrosion behavior appears to be determined by the charge transfer step and the diffusion process. It was found that the bronze-IV (Cu–26.8Sn) specimen exhibited the best corrosion resistance, as evidenced by a low corrosion current density and a high impedance. This improvement resulted from an increase in the content of the Cu–Sn solid solution in the alloy, which was conducive to forming a relatively more protective passive film on the surface of the bronze alloy. This finding would be valuable in the anticorrosion protection of archeological artefacts after their excavation.     

Electrochemical and Spectroscopic Study on the Corrosion of Ti–5Al and Ti–5Al–5Cu in Chloride Solutions

Metals and Materials International - In this study, manufacturing of Ti–5Al and Ti–5Al–5Cu alloys were accomplished employing mechanical alloying technique. The corrosion...     

Corrosion and wear behavior of an Mg–2Zn–0.2Mn alloy in simulated body fluid

In this work, the corrosion behavior of the ascast and extrusion and aging treatment Mg–2Zn–0.2Mn alloy in simulated body fluid(SBF) were studied. The wear behavior of Mg–2Zn–0.2Mn alloy was investigated using pin-on-disk technique and stainless steel as counterbody under a constant sliding velocity at different loads ranging from 2 to 5 N with deionized water and SBF as lubrication.The results showed that the extrusion and aging treatment Mg–2Zn–0.2Mn alloy exhibited better corrosion resistance compared with the as-cast alloy due to finer average grain size, more homogeneous phase distribution, and decrease in porosity. The friction coefficient of fractional pair under SBF and deionized water lubrication were obviously lower than that of dry sliding condition. However, the wear rate of Mg–2Zn–0.2Mn alloy under SBF lubrication was higher than that of dry sliding and deionized water lubrication due to the corrosiveness of SBF accelerated the wear of the magnesium alloy. The magnesium alloy exhibited different wear mechanisms with the variety of loads and lubrication conditions.     

Corrosion behavior of B30 Cu-Ni alloy and anti-corrosion coating in marine environment

The corrosion behavior of B30 Cu-Ni alloy in a sterile seawater and a SRB solution was investigated. The results show that the corrosion potential of specimen in the SRB solution is much lower than that in the sterile seawater. The polarization resistance of specimen in the SRB solution decreases quickly after a period immersion and becomes much lower than that in the sterile seawater. It is concluded that the SRB accelerates the corrosion process of B30 Cu-Ni alloy greatly. An anti-corrosion electroless Ni-P coating was produced and applied to the alloy. The results show that specimens coated with Ni-P plating exhibit favorable corrosion resistance property in SRB solution. Severe pitting corrosion appears on the uncoated specimens in the SRB solution when the coated specimens are still in good condition. The anti-corrosion mechanism of Ni-P plating was analyzed. It is concluded that coating the B30 Cu-Ni alloy with electroless Ni-P plating is an effective technique against the attack of SRB in marine environment.     

Corrosion and electrochemical evaluation of an Al–Si–Cu aluminum alloy in ethanol solutions

The corrosion of aluminum alloy AlSi8Cu3Fe(Zn) in ethanol and ethanol solutions containing 10 vol.% water and 10 vol.% acetic acid, respectively, was investigated by means of electrochemical impedance spectroscopy (EIS), polarization curve, immersion, optical microscopy, scanning electron microscopy and element mapping. The Al alloy in the ethanol and its solutions exhibited a capacitive loop in the measured Nyquist EIS spectra at high frequencies, which can be attributed to the ethanol’s dielectric response. Addition of 10 vol.% acetic acid increased the ethanol corrosivity more significantly than the same amount of water addition. The Al–Si–Cu–Mg precipitated zones in the alloy were susceptible to corrosion attack due to the micro-galvanic effect by the Cu-containing precipitates.     

Corrosion behavior of novel Cu–Ni–Al–Si alloy with super-high strength in 3.5% NaCl solution

A novel Cu–6.5Ni–1Al–1Si–0.15Mg–0.15Ce alloy with super-high strength was designed and its corrosion behavior in 3.5% NaCl solution at 25 °C was investigated by the means of SEM observation, TEM observation and XPS analysis. The alloy after solution treatment, 80% cold rolling and aging at 450 °C for 1 h had the best comprehensive properties with hardness of HV 314, electrical conductivity of 19.4% IACS, tensile strength of 1017 MPa, and average annual corrosion rate of 0.028 mm/a. The oxides and chloride products formed at first, followed by the formation of dyroxides products. The alloy showed super-high strength, good electrical conductivity and corrosion resistant because Ni₂Si hindered the precipitation of large NiAl at the grain boundary and the denickelefication of the alloy.     

Glass forming ability and crystallization behavior of Al–Ni–RE metallic glasses

Atomic size may change due to the interaction between different elements when pure metals are synthesized into alloys. In present paper, the effective atomic radii instead of the nominal radii were introduced in the cluster line method to predict the optimum glass forming compositions in Al-based Al–Ni–RE (RE = La, Y, Ce, Gd, Dy) systems. Wedge-shaped samples of the alloys were suction cast under well-controlled condition to experimentally determine the dependence of the glass forming ability (GFA) on the composition. It is found that such a modification to the method makes the prediction very close to the experimental results. When the effective atomic radii are used to calculate the topological instability parameter originally proposed by Egami and Waseda, λ′, the λ′ corresponding to the best GFA in each Al–Ni–RE system linearly changes with the radius of the RE element. Meantime, the onset temperature of crystallization and mixing enthalpy linearly increase with the λ′.     

The formation mechanism of the O phase in a Ti3Al–Nb alloy

It is reported that there are several different transformation mechanisms of the O phase in different heat treatment conditions in the Ti₃Al based alloys. However, very little work has been carried out on the α₂→O phase transformation in the Ti₃Al–Nb alloys of Nb amounts exceeding 12 at%. In this paper, the formation mechanism of the O phase in the Ti–24Al–14Nb–3V–0.5Mo (at%) alloy has been carried out by means of TEM and HRTEM. The results show that the O phase is directly derived from the primary equiaxed α₂ grains with a fine streak contrast, and exists in multivariant forms owing to its different orientations after the alloy is solution treated at 1000°C for 1 h followed by water quenching (WQ) and aged at 650°C for 24 h. The O plates in the primary equiaxed α₂ grains exist not only in the form of a single variant, but also in the form of fine α₂+O mixtures. The analysis indicates that the formation of the O phase is the result of a phase decomposition, that is the introduction of niobium as the preferred β stabilizer makes the supersaturation of niobium in the primary α₂ grains, and the α₂ phase containing Niobium separates into Niobium lean and Niobium rich regions through the Niobium diffusion: α₂→α₂(Nb-lean)+O(Nb-rich). Niobium rich regions transform to the ordered orthorhombic phase (O phase) with a lattice distortion and only a very small composition change. It appears, therefore, that the transformation involves nucleation, growth and coarsening of the O phase by a diffusion mechanism.     

Corrosion behavior of Zr–Cu–Ni–Al bulk metallic glasses in chloride medium

Polarization and passivation behavior of three Zr-based BMGs, i.e. Zr_58.3Al_14.6Ni_8.3Cu_18.8, Zr₅₈Al₁₆Ni₁₁Cu₁₅ and Zr_57.5Al_17.5Ni_13.8Cu_11.3 were investigated in 3% NaCl aqueous solution. Electrochemical investigations were carried out by potentiodynamic polarization method at room temperature. The corroded sample surfaces were examined using scanning electron microscope having energy dispersive spectroscopy (EDS) attachment. The results of the present investigation revealed that Zr₅₈Al₁₆Ni₁₁Cu₁₅ and Zr_57.5Al_17.5Ni_13.8Cu_11.3 BMGs having relatively larger supercooled liquid region (ΔT_x) and pitting overpotential (η_pit) values exhibit low corrosion current density (i_corr) and corrosion penetration rate (CPR) values.     

Effect of pre-straining on structure and formation mechanism of precipitates in Al–Mg–Si–Cu alloy

The effect of pre-straining on the structure and formation mechanism of precipitates in an Al–Mg–Si–Cu alloy was systematically investigated by atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Elongated and string-like precipitates are formed along the dislocations in the pre-strained Al–Mg–Si–Cu alloy. The precipitates formed along the dislocations exhibit three features: non-periodic atomic arrangement within the precipitate; Cu segregation occurring at the precipitate/α(Al) interface; different orientations presented in one individual precipitate. Four different formation mechanisms of these heterogeneous precipitates were proposed as follows: elongated precipitates are formed independently in the dislocation; string-like precipitates are formed directly along the dislocations; different precipitates encounter to form string-like precipitates; precipitates are connected by other phases or solute enrichment regions. These different formation mechanisms are responsible for forming different atomic structures and morphologies of precipitates.     

Formation and growth mechanism of a manganese phosphate coating on an as-cast Zr–Al binary alloy

The preparation of a manganese phosphate coating on an as-cast Zr–Al alloy is described. The alloy consisted of an α phase (α-Zr) and a β phase (Zr₂Al), where α-Zr is the matrix and Zr₂Al spreads along the grain boundaries discontinuously. The coating was divided by cracks to exhibit a network structure. The manganese phosphate coating showed a combination of crystalline and amorphous structure. The film consists of small particles densely packed. It is uniform and compact. The formation of the phosphate coating on substrates treated for short periods was investigated. Mn₅(PO₄)(OH)₂·H₂O and MnZr(PO₄)₂·4H₂O phases were found in the manganese phosphate coatings. The grain particles are preferentially deposited on the β phase rather than on the α phase.     

The mechanical behavior of a cryomilled Al–10Ti–2Cu alloy

The mechanical behavior of a cryomilled Al–10Ti–2Cu (wt.%) alloy has been studied by performing uniaxial tension tests at temperatures ranging from room temperature to 525°C. Elastic–nearly perfectly plastic stress–strain behavior is observed at all temperatures. Tension–compression asymmetry of the room temperature yield stress is also observed. These characteristics are in agreement with those recently reported in the literature for single-phase NC materials. The flow stress (700 MPa at room temperature) decreases dramatically with increasing temperature. Testing of material following thermal exposures suggests that microstructural coarsening alone cannot account for the decrease in strength with increasing temperature. From a coarsening standpoint, this material appears to be very thermally stable. The ductility is influenced by several factors. Low levels of internal porosity along with the presence of fine oxide and carbide dispersoids contribute to lower ductility. The absence of work hardening exhibited by the Al–10Ti–2Cu also leads to reduced strain to failure. The features observed on fracture surfaces suggest that fracture occurs by the nucleation and growth of voids at particle–matrix interfaces. Evidence of fracture along prior powder particle boundaries is present as well. The microstructure consists primarily of regions containing grains measuring in the range 30–70 nm. Large grained regions consisting of nominally pure Al ranging in size from 300 to 500 nm are also present. No evidence of dislocation activity within either the fine or large grained regions can be found in the as extruded material. Specimens deformed at room temperature and 93°C reveal evidence of dislocation activity within the large grain regions. Dislocation configurations suggest an Orowan bypass mechanism. No dislocations are found within the 30–70 nm size grains following tensile deformation.     

Stress relaxation behavior of an Al–Zn–Mg–Cu alloy in simulated age-forming process

The stress relaxation behavior of age-forming for an Al–Zn–Mg–Cu alloy was studied using a designed device that can simulate the age forming process. The mechanism of stress relaxation was also revealed through calculating thermal activation parameters and analyzing the microstructures. The results suggested that the stress relaxation behavior of the Al–Zn–Mg–Cu alloy in the simulated age-forming process can be divided into three stages according to the stress level. The three stages of stress relaxation are: (i) the initial high stress stage, (ii) the subsequent middle stress transition stage and (iii) the last low stress equilibrium stage, respectively. The deformation activation energies are 132 kJ/mol in the initial high stress stage, 119 kJ/mol in the subsequent middle stress transition stage and 91 kJ/mol in the last low stress equilibrium stage, respectively. The analysis of the thermal activation parameters and microstructures revealed that dislocation creep was the dominant deformation mechanism in the initial and subsequent stages of the stress relaxation; whereas diffusion creep is the mechanism in the last stage of the stress relaxation. Additionally, a special threshold stress phenomena was present in the stress relaxation of the age-forming process, which was scribed to the interaction between precipitation and dislocation in the Al–Zn–Mg–Cu alloy     

Corrosion behavior of LY12CZ aluminum alloy in simulated acid rain solution

The variations of corrosion potential,electrochemical impedance and surface morphology of LY12 aluminum alloy with pH of simulated acidic rain solutions were investigated with EIS and SEM.It is found that corrosion potential shifts to less noble value with increasing pH in the solutions of pH lower than 3.1 and shifts to more noble value in the solutions of pH higher than 3.1.In the solutions of pH lower than 3.1,the electrochemical impedance diagram has a capacitive loop at higher frequency and an inductive loop at lower frequency and the magnitude of high frequency loop decreases with decreasing pH and increasing period of immersion.However,in the solutions of Ph higher than 3.4 two capacitive loops appear and the magnitude of high frequency loops increases with pH ad period of immersion.Observation of SEM shows that the pitting intensity increases with decreasing pH in the range of pH2.0-3.4,no evident pits are observed at pH higher than 3.4.The experiment results were discussed from resistance of oxide film and adsorption processes of anions in simulated acid rain solution.     

Oxidation protection and behavior of C/C composites with an in situ SiC nanowire–SiC–Si/SiC–Si coating

An in situ SiC nanowire–SiC–Si/SiC–Si protective coating was prepared on C/C composites by pack cementation and heat treatment. SiC nanowires suppressed the cracking of the coating by nanowire pullout and bridging and microcrack deflection, avoiding the oxidation of C/C composites. Results showed that the oxidation of the samples was a continuous weight gain process. The oxidation behavior was fitted to the parabolic–linear model and the final weight gain was 1.8% during thermogravimetric analysis from 50 to 1600 °C. The oxidation behavior was fitted to the parabolic model and the final weight gain was 0.51% during isothermal oxidation at 800 °C.     

Corrosion fatigue behavior of epoxy-coated Mg–3Al–1Zn alloy in NaCl solution

The corrosion fatigue behavior of epoxy-coated Mg–3Al–1Zn alloy was investigated in air and 3.5 wt%NaCl solution. Epoxy coating as a new method was used to improve the corrosion fatigue property of the material.Results show that the fatigue limit(FL) of the coated specimens is higher than that of the uncoated specimens in3.5 wt% NaCl solution because of the strengthening and blocking functions of the epoxy coating. The FL of the coated specimens in 3.5 wt% NaCl solution is as high as that in air. It implies that the coated specimens are not as sensitive to the environment as the magnesium alloy. The low tensile strength and the short elongation of the pure epoxy coating lead to that the fatigue crack of the coated specimen is always initiated from the epoxy-coating film Pores and pinholes accelerate the fatigue crack initiation process. Pinholes are caused by the corrosion reactions between the epoxy coating and the NaCl solution.     

Corrosion behavior of Cu–Al–Be shape memory alloys with different compositions and microstructures

The corrosion behavior of Cu–Al–Be shape memory alloys with different microstructures and Be content in a 3.5% NaCl solution was studied by weight loss, cyclic anodic polarization and chronoamperometric measurements. The beryllium has a beneficial effect in β alloys. A pitting potential of −100 mV/SCE was found by anodic polarization tests for all the studied alloys, corresponding to the formation of pits produced by severe dealuminization. Samples with precipitates were more susceptible to pit formation. The corrosion behavior is strongly affected by the alloy microstructural conditions, and the β samples present higher pitting resistance and repassivation ability.