Surface microstructure of 316L austenitic stainless steel by the salt bath nitrocarburizing and post-oxidation process known as QPQ

Systematic materials characterization of the Quench-Polish-Quench complex salt bath heat-treatment process (QPQ) surface modified 316L steel was investigated. The results reveal that the nitro-carburized sample surfaces consist of Cr₂N/γ´-Fe₄N and CrN/γ-Fe, while the post-oxidized sample surfaces are comprised of CrO₃, (Fe₃O₄)/ε-Fe₂(N,C), γ′-Fe₄N and S(γ_N)/CrN/α-Fe. Nuclei ε-Fe₂N_1 − x accumulates at the interface between oxide layer and nitride compound layer by the help of post-oxidation. The diffraction peak lines of S-phase (γ_N) move gradually towards higher diffraction angles as increasing depth of 15 μm to 35 μm. An increased content of oxygen is recorded in the post-oxidized surface layer down to the depth of approximately 15 μm, a small peak concentration of carbon occurs at the front of the nitrided layer. Micro-hardness of the post-oxidized samples reaches about 1300 HV_0.1 near the surface region and then reduces sharply across the case/substrate interface.     

Structure and electrical conduction behavior of LiZnVO4 ceramic prepared by solution-based chemical route

In the present work, an evaluation of the structural and electrical properties of a compound (LiZnVO₄) has been undertaken. This compound was prepared by solution-based chemical route. The electrical properties were measured using a.c. impedance spectroscopy method in the frequency range of 10³-10⁶ Hz at various temperatures from 28 to 300 °C. X-ray diffraction study indicates a rhombohedral unit cell structure with lattice parameters a = 14.1934 Å, b = 14.1934 Å, c = 9.4926 Å, V = 1656.12 (Å)³, α = 90°, β = 90° and γ = 120°. A field emission scanning electron micrograph reveals a polycrystalline texture of the compound with grains of unequal sizes ∼0.2-2.0 μm. The electrical conduction in the material is a thermally activated process due to the bulk effect. Frequency dependence of a.c. conductivity obeys Jonscher's universal law (σ_ac = σ_dc + Aωⁿ).     

Comparison of hardmetal and hard chromium coatings under different tribological conditions

Electroplated hard chromium and thermal spray hardmetal coatings are widely used in a variety of applications for wear protection of component surfaces. The two protective coating types are tested in direct comparison for tribological conditions of dry abrasive wear (Taber Abraser test) and dry oscillating wear load. Oscillating wear tests are carried out both with hardened 100Cr6 steel and alumina balls as counterbody. Different types of hardmetal coatings are imparted. Besides HVOF sprayed coatings also coatings sprayed by an APS gun with axial powder feed are tested. For HVOF spraying besides standard WC/Co(Cr) feedstock also coarse (d₅₀ = 5 μm) and fine carbide feedstock (d₅₀ = 0.8 μm) and ultrafine powders, i.e. 2 μm < d < 12 μm, are considered. Use of ultrafine powders is particularly interesting from the economical point of view, as belt grinding can be sufficient for finishing in many cases. The optimum coating solution for wear protection depends on the specific tribosystem. The choice of feedstock, spraying process, equipment and processing conditions does not only depend on the resultant tribological properties. Therefore simultaneous influence on corrosion protection capability and thermal conductivity might have to be considered.     

Studies on the power factor of (Ba,Sr)Co2+xRu4−xO11 compounds

We have prepared polycrystalline single-phase ACo_2+xRu_4−xO₁₁ (A = Sr, Ba; 0 ≤ x ≤ 0.5) using the ceramic method and we have studied their structure, electrical resistivity and Seebeck coefficient, in order to estimate their power factor (P.F.). These layered compounds show values of electrical resistivity of the order of 10⁻⁵ Ωm and their Seebeck coefficients are positive and range from 1 μV K⁻¹ (T = 100 K) to 20 μV K⁻¹ (T = 450 K). The maximum power factor at room temperature is displayed by BaCo₂Ru₄O₁₁ (P.F.: 0.20 μW K⁻² cm⁻¹), value that is comparable to that shown by compounds such as SrRuO₃ and Sr₆Co₅O₁₅.     

Rapidly solidified non-equilibrium microstructure and phase transformation of plasma cladding Fe-based alloy coating

The rapidly solidified microstructural and compositional features, the precipitation and transformation of carbides during aging of Fe-based alloy coating prepared by plasma cladding have been investigated. The clad coating materials, whose powder mixture of Fe, Cr, Ni, B, Si and C with a weight ratio of 54.5:35:5:1:2:2.5, is processed using a non-transferred plasma arc. The clad coating adheres with low carbon steel in a good metallurgical bonding and the rate of dilution is 15-20%. Microstructural studies demonstrate that the coating possesses the metastable microstructure comprising the primary dendritic γ-austenite which is a non-equilibrium phase with an extended solid solution of alloying elements and interdendritic eutectic consisting of γ-austenite and (Cr,Fe)₇C₃ carbides. During the high temperature aging at 1253 K for 2 h, the fine spherical (Cr,Fe)₂₃C₆ carbide nucleates within (Cr,Fe)₇C₃ carbide and austenite matrix, and some martensite (α) also forms during cooling. The solidification and evolution sequence of the phase can be represented as follows: L → γ + L → γ + (γ + (Cr,Fe)₇C₃) → (γ + (Cr,Fe)₂₃C₆ + α). Due to the precipitation of (Cr,Fe)₂₃C₆ carbide and uniform distribution of carbide in the as-aged coating, the average hardness becomes higher than that of the as-clad coating.     

Infrared emissivity of Sr doped lanthanum manganites in coating form

The Sr doped lanthanum manganite coatings were prepared using La_0.8Sr_0.2MnO₃ particles and epoxy modified polyurethane as pigment and resin matrix, respectively. The structure, morphology, surface roughness and infrared normal emissivity (?_N) in the 3-5 and 8-14 μm wavebands of the samples were systematically investigated. With the increase of La_0.8Sr_0.2MnO₃ pigment, the ?_N of the coatings decreases and the ?_N values in the 8-14 μm waveband are higher than those in the 3-5 μm waveband. The surface roughness has no significant effect on the infrared emissivity of LSMO coatings. For 50% LSMO coating, the sample shows variable-emissivity property in the 8-14 μm waveband and the emissivity property remains unchanged before and after ultraviolet irradiation.     

A comparative study on titania layers formed on Ti, Ti-6Al-4V and NiTi shape memory alloy through a low temperature oxidation process

For improving the bioactivity and biocompatibility of metals for medical applications, anatase titania layers were synthesized on Ti, Ti-6Al-4V and NiTi shape memory alloy (SMA) using the H₂O₂-oxidation and hot water aging treatment method at 80 °C. The thickness of the titania layers on Ti, Ti-6Al-4V and NiTi SMA was 7.43 ± 0.93 μm, 3.14 ± 0.38 μm and 4.04 ± 0.25 μm, respectively. X-ray diffraction (XRD) and transmission electron microscopic (TEM) analysis indicated that the titania layers formed were poorly crystalline anatase. Fourier transform infrared spectroscopy (FTIR) suggested that abundant Ti-OH functional groups were produced on titania, which could improve bioactivity of the metals. In addition, the titania layer formed on Ti substrate was shown to contain more molecularly chemisorbed water and Ti-OH functional groups than those on Ti-6Al-4V and NiTi SMA. Atomic force microscopic (AFM) results showed that the surface roughness values of metal samples depended on the scanning size and that surface roughness of samples significantly increased after the H₂O₂-oxidation and hot water aging treatment for all three metals. Compared to Ti-6Al-4V and NiTi SMA, the H₂O₂-treated and aged Ti samples exhibited the roughest surface. The wettability of samples was evaluated through water contact angle measurements. After the H₂O₂-oxidation treatment, the three metals exhibited high hydrophilicity. The bonding strength of titania layers on Ti, Ti-6Al-4V and NiTi was also investigated. Potentiodynamic polarization tests indicated that the corrosion resistance of H₂O₂-treated and aged Ti, Ti-6Al-4V and NiTi SMA was significantly improved due to the titania layer formation.     

Numerical and experimental study of post-heat treatment gas quenching and its impact on microstructure and creep in CMSX-10 superalloy

The gas quenching process at the end of solution heat treatment and its influence on microstructure and creep properties of the single crystal superalloy CMSX-10 was studied using numerical and experimental techniques. Computational fluid dynamics was used to model the turbulent flow field in the furnace during quenching. Boundary conditions were obtained by measuring the pressure drop across the chamber. The calculated flow velocities for a range of process conditions were in reasonable agreement with the ones measured using a Pitot tube; differences were mainly attributed to the unsteady nature of the turbulent flow. The resulting cooling rates in the furnace load were quantified with higher cooling rates leading to smaller γ′ precipitates. Asymmetry of the flow field leads to variations in γ′ size. This can be reduced by changing the way turbine blades are placed in the furnace. Creep tests demonstrated that this can have a significant effect on the creep properties of the material. At low temperatures (850 °C), specimens with larger γ′ particles showed better creep performance, with less pronounced primary creep. At high temperatures (1100 °C) small γ′ size showed a slight advantage.     

Microstructure evolution of directionally solidified Ti-45Al-8.5Nb-(W, B, Y) alloys

Intermetallic Ti-45Al-8.5Nb-(W, B, Y) alloys were directionally solidified at constant growth rates (V) ranging from 10 to 400 μm/s under the temperature gradient G = 3.8 × 10³ K/m. Quenching was performed at the end of directional solidification (DS) experiments. Microstructure evolution was investigated by analyzing the microstructures formed at the quenching interfaces and in the DS regions. The primary dendritic arm spacing (λ) decreases with increasing growth rate according to the relationship λ ∝ V^−0.36. Both the width of columnar grain (λw) and the interlamellar spacing (λ_s) decrease with increasing growth rate according to the relationships λw∝V−1.13 and λ_s ∝ V^−0.32, respectively. Lamellar microstructure initially disappears from the dendrites at the growth rate of 100 μm/s and subsequently from the interdendritic regions when the growth rate is up to 200 μm/s. The B2 particles can precipitate in the interdendritic regions.     

Determination of heat transfer coefficient and ceramic mold material parameters for alloy IN738LC investment castings

Investment casting molds with different numbers of shells and pre-heating temperatures were investigated in this study. The primary layer consists of colloidal silica bound ZrSiO₄ with additions of CoAl₂O₄ to achieve fine grains and to reach a good surface quality, whereas the following layers consist of mullite bound by colloidal silica. Interface temperatures (alloy/mold) that are necessary to determine heat transfer coefficients were obtained by linear extrapolation. Heat transfer coefficients in the range of 300-660 W/(m² K) were obtained. The castings were examined with regard to grain size and secondary dendrite arm spacing. Physical properties of the investment casting mold were examined by differential scanning calorimetry (DSC) and Laserflash methods for temperatures up to 1300 °C. The specific heat capacity was determined to 1.13 J/(g K), thermal diffusivity was found to be in the range of (4-5) × 10⁻⁷ m²/s and the thermal conductivity to be 1 ± 0.1 W/(m K).     

Influence of cluster composition on NLO properties of neutral cubane-like heterothiometallic clusters

A series of new candidates as nonlinear optical materials, tetra-nuclear heterobimetallic clusters [MOS₃M₃′Y(PPh₃)₃] (M = Mo, M′ = Ag, Y = Br 1; M = W, M′ = Ag, Y = I 2; M = Mo, M′ = Cu, Y = I 3; M = W, M′ = Cu, Y = I 4), have been synthesized by newly developed ligand-redistribution reaction for third-order nonlinear optical (NLO) studies. Single-crystal X-ray diffraction shows that clusters [MoX(μ₃-S)₃(μ₃-Br)(AgPPh₃)₃] 1 and [WX(μ₃-S)₃(μ₃-I)(CuPPh₃)₃] 4 (X = O_0.5S_0.51, O 4) adopt an isomorphous neutral cubane-like skeleton. Their optical nonlinearities were measured by Z-scan technique with an 8 ns pulsed laser at 532 nm. These clusters were found to exhibit effective nonlinear absorption, self-focusing effects and large optical limiting capabilities. The effective NLO susceptibilities χ⁽³⁾ and the corresponding second-order hyperpolarizabilities γ of these clusters are also reported. The influence of cluster composition on NLO properties has been discussed accordingly.     

Workpiece surface integrity when slot milling γ-TiAl intermetallic alloy

Slot milling is presented as a potential manufacturing route for aerospace component feature production when machining γ-TiAl intermetallic alloy Ti–45Al–2Mn–2Nb + 0.8 vol.% TiB₂XD using 2 mm diameter AlTiN coated WC ball nose end milling cutters. When operating with flood cutting fluid at v = 88 m/min, f = 0.05 mm/tooth, d = 0.2 mm, maximum flank wear was ∼65 μm after 25 min. SEM micrographs of slot surfaces show re-deposited/adhered and smeared workpiece material to a length of ∼50 μm. Brittle fracture of the slot edges was restricted to <10 μm with sporadic top burr formation observed up to ∼20 μm. Cross sectional micrographs of the slot sidewalls showed bending of the lamellae limited to within 5 μm.     

Pb-free glass frits prepared by spray pyrolysis as inorganic binders of Al electrodes in Si solar cells

Pb-free glass frits prepared by spray pyrolysis for Al electrodes were of fine size, spherical morphology and dense structure. Their mean size and geometric standard deviation when prepared at 1,200 °C were 1.0 μm and 1.4, respectively. Their glass transition temperature (T_g) was 374 °C. An Al electrode formed from Al paste with glass frits had a dense structure and good adhesion to the Si substrate. It had a well-developed back-surface field layer of 17.5 μm thickness. Al electrodes formed from Al paste without glass frits had sheet resistances between 21 and 32 mΩ sq⁻¹ as the firing temperature changed from 600 to 900 °C. This compared with values from electrodes formed with frits that decreased from 20 to 7 mΩ sq⁻¹ over the same range of firing temperatures.     

Supplementary measurements of the primary crystalline phases of the Co-Ni-Sb and the Co-Fe-Sb ternary systems

Some primary crystalline phases of the Co-Ni-Sb and the Co-Fe-Sb systems are studied on the basis of the crystalline structure analysis by X-ray diffraction (XRD), the microstructure observation by scanning electron microscopy (SEM), the composition determination by electron probe microanalysis (EPMA) and the phase equilibrium relations of the constituent binary systems. From the experimental measurements of the present work and the phase equilibrium relations of literature reports, the liquidus projections of the Co-Ni-Sb and the Co-Fe-Sb ternary systems are determined. There exist 6 primary crystalline phases in each of the ternary systems, which are γ(A1)-Fcc_A1, β(Co,Ni)₃Sb-D0₃, γ(Co,Ni)Sb-NiAs, ζ(Co,Ni)Sb₂-FeS₂, η(Co,Ni)Sb₃-CoAs₃ and Sb-Rhombo_A7 in the Co-Ni-Sb system and γ(A1)-Fcc_A1, α(A2)-Bcc_A2, γ(Co,Fe)Sb-NiAs, ζ(Co,Fe)Sb₂-FeS₂, η(Co,Fe)Sb₃-CoAs₃ and Sb-Rhombo_A7 in the Co-Fe-Sb system. Two of invariant reactions are proposed, which are the eutectic reaction L → γ(A1) + β(Co,Ni)₃Sb + γ(Co,Ni)Sb in the Co-Ni rich side of the Co-Ni-Sb system and the transition reaction L + γ(A1) → α(A2) + γ(Co,Fe)Sb in the Co-Fe rich side of the Co-Fe-Sb system.     

Effects of SiC volume fraction and aluminum particulate size on interfacial reactions in SiC nanoparticulate reinforced aluminum matrix composites

The SiC nanoparticulate reinforced Al-3.0 wt.% Mg composites were fabricated by combining pressureless infiltration with ball-milling and cold-pressing technology at 700 °C for 2 h. The effects of SiC nanoparticulate volume fractions (6%, 10% and 14%) and Al particulate sizes (38 μm and 74 μm) on interfacial reactions were investigated by SEM, TEM and X-ray diffraction. The results show that the MgO at the interface between SiC nanoparticulate and molten Al can provide a barrier for the diffusion of Si, C and Al. Using Al particulate (74 μm) as raw material, the Al₄C₃ phase was not found in the composites containing 6 vol.% and 10 vol.% SiC, but presented in the composites containing 14 vol.% SiC. When SiC content up to 14 vol.%, the products of MgO around SiC nanoparticulate are not enough to provide effective protection from the reaction between SiC and molten Al, therefore the diffusion of Si, C and Al can take place to produce Al₄C₃ and Si phases. Using 38 μm Al particulate as raw material, the fine Al particulate possesses the high reaction activity and can easily be embedded into the gap among the big Mg particulate segregated at the interface, resulting in the appearance of exposure surface of SiCp to the Al and the forming of diffusion channels for the atomics C, Si and Al. So, the formations of Al₄C₃ and Si phases were occurred.     

Optical properties of highly Er-doped sodium-aluminium-phosphate glasses for broadband 1.5 μm emission

Erbium-doped Na₃Al₂P₃O₁₂ (NAP) glasses with compositions 92NAP-(8−x)Al₂O₃-(x)Er₂O₃ (where x = 2-8) were prepared and characterized for absorption, visible and NIR emission and decay time properties. Judd-Ofelt analysis has been carried out to predict radiative properties of luminescent levels of Er³⁺ ions. Comparatively larger photoluminescence lifetimes (7.86 ms) and larger quantum efficiencies (74%) for the laser transition, ⁴I_13/2 → ⁴I_15/2 (at 1.54 μm) are observed. The moisture insensitivity, large Er³⁺ ion doping capability and relatively high-gain and broad emission at 1.5 μm are the most notable features of these glasses to realize efficient short-length optical amplifiers.     

Synthesis of nanocrystalline nickel-zinc ferrite (Ni0.8Zn0.2Fe2O4) thin films by chemical bath deposition method

The nickel-zinc ferrite (Ni_0.8Zn_0.2Fe₂O₄) thin films have been successfully deposited on stainless steel substrates using a chemical bath deposition method from alkaline bath. The films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), static water contact angle and cyclic voltammetry measurements. The X-ray diffraction pattern shows that deposited Ni_0.8Zn_0.2Fe₂O₄ thin films were oriented along (3 1 1) plane. The FTIR spectra showed strong absorption peaks around 600 cm⁻¹ which are typical for cubic spinel crystal structure. SEM study revealed compact flakes like morphology having thickness ∼1.8 μm after air annealing. The annealed films were super hydrophilic in nature having a static water contact angle (θ) of 5°.The electrochemical supercapacitor study of Ni_0.8Zn_0.2Fe₂O₄ thin films has been carried out in 6 M KOH electrolyte.The values of interfacial and specific capacitances obtained were 0.0285 F cm⁻² and 19 F g⁻¹, respectively.     

Preparation of hydrophobic surface on steel by patterning using laser ablation process

Currently there is an increasing demand for the application of hydrophobic surface in industrial and biological processes. It has been found that the contact angle with liquid, closely related to hydrophobicity of a solid surface, is largely determined by micro-geometrical structure and chemistry of the said surface. In this investigation, the hydrophobicity of steel surface was achieved by implementing micro-patterns on substrate using laser ablation process, and depositing amorphous carbon (a-C) thin film using magnetron sputtering technique. For the patterning, a short pulse excimer laser with a wavelength of 248 nm was used to etch the substrate surface to form different controlled patterns. Based on the models built by Wenzel and Cassie-Baxter, the depth of etched grooves, d, the clearance between two grooves, a, and the width of grooves, b, were optimized to obtain the largest contact angle. It was found that when a pattern was set at a = 25 μm, b = 50 μm and d = 8 μm, the contact angle of the surface could be increased to about 130°, compared to the 68.5° found from a plain smooth steel surface (R_a ≤ 0.01 µm). As a preliminary investigation, an amorphous carbon (a-C) coating was deposited on the patterned surface. It shows that the contact angle was increased further by about 10°-20° on a patterned surface.     

Synthesis, thermal stability and properties of [(Fe1−xCox)72Mo4B24]94Dy6 bulk metallic glasses

A series of [(Fe_1−xCo_x)₇₂Mo₄B₂₄]₉₄Dy₆ (x = 0.1, 0.2, 0.3, 0.4 and 0.5 at.%) bulk metallic glasses (BMGs) in rod geometries with critical diameter up to 3 mm were fabricated by copper mold casting method. This alloy system exhibited good thermal stability with high glass transition temperature (T_g) 860 K and crystallization temperature (T_x) 945 K. The addition of Co was found to be effective in adjusting the alloy composition deeper to eutectic, leading to lower liquidus temperature (T_l). The [(Fe_0.8Co_0.2)₇₂Mo₄B₂₄]₉₄Dy₆ alloy showed the largest supercooled liquid region (ΔT_x = T_x − T_g = 92 K), reduced glass transition temperature (T_rg = T_g/T_l = 0.622) and gamma parameter (γ = T_x/(T_g + T_l) = 0.424) among the present system. Maximum compressive fracture strength of 3540 MPa and micro-Vickers hardness of 1185 kg/mm² was achieved, resulting from the strong bonding structure among the alloy constituents. The alloy system possessed soft magnetic properties with high saturation magnetization of 56.61-61.78 A m²/kg and coercivity in the range of 222-264.2 A/m, which might be suitable for application in power electronics devices.     

Influence of rotating magnetic field on the microstructure and phase content of Ni-Al alloy

Rotating magnetic field is introduced in the production process of Ni-Al precursor alloy of skeletal Ni catalyst. The results showed that the big dendrites of Al₃Ni₂ disappeared, the size of Al₃Ni₂ decreased from 64.5 μm to 37.2 and 35.5 μm, phase content of Al₃Ni₂ decreased while Al₃Ni increased after applying field current of 80 A and 140 A, respectively. The change of phase content is probably caused by the increase of surface area between the Al₃Ni₂ phase and fluid which is favorable to the peritectic reaction.