Niobium boride coating on AISI M2 steel by boro-niobizing treatment

In this study, niobium boride coating was applied on pre-boronized AISI M2 steel by the thermo-reactive deposition technique in a powder mixture consisting of ferro-niobium, ammonium chloride and alumina at 950 °C for 1-4 h. The coated samples were characterized by X-ray diffraction, scanning electron microscope and micro-hardness tests. Niobium boride layer formed on the pre-boronized AISI M2 steel was smooth, compact and homogeneous. X-ray studies showed that the phases formed on the steel surfaces are NbB, Nb₃B₂, FeB and Fe₂B. The depth of the niobium boride layer ranged from 0.97 μm to 3.25 μm, depending on treatment time. The higher the treatment time the thicker the niobium boride layer observed. The hardness of the niobium boride layer was 2738 ± 353 HV_0.01.     

Diffusion kinetics of borided AISI 52100 and AISI 440C steels

In this study, the case properties and diffusion kinetics of AISI 440C and AISI 52100 steels borided in Ekabor-II powder were investigated by conducting a series of experiments at temperatures of 1123, 1173 and 1223 K for 2, 4 and 8 h.The boride layer was characterized by optical microscopy, X-ray diffraction technique and micro-Vickers hardness tester. X-ray diffraction analysis of boride layers on the surface of the steels revealed the existence of FeB, Fe₂B and CrB compounds.The thickness of boride layer increases by increasing boriding time and temperature for all steels. The hardness of the boride compounds formed on the surface of steels AISI 52100 and AISI 440C ranged from 1530 to 2170 HV_0.05 and 1620 to 1989 HV_0.05, respectively whereas Vickers hardness values of untreated steels AISI 440C and AISI 52100 were 400 HV_0.05 and 311 HV_0.05, respectively. The activation energies (Q) of borided steels were 340.426 kJ/mol for AISI 440C and 269.638 kJ/mol for AISI 52100. The growth kinetics of the boride layers forming on the AISI 440C and AISI 52100 steels and thickness of boride layers were also investigated.     

Formation of carbide layers on AISI H13 and D2 steels by treatment in molten borax containing dissolved both Fe–Nb and Fe–Ti powders

In this work, AISI H13 and D2 tool steels were treated in molten borax, containing dissolved ferro-niobium, ferro-titanium and aluminum, at 1020 °C for 4 h. Samples were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD) and Vickers microhardness. Well defined layers were obtained with excellent thickness regularity. For the AISI H13 steel the layer measured 9 μm and for the AISI D2 steel the layer thickness was 18 μm. Their microhardness values were at about 2600 HV_0.050. The layers consisted of niobium carbide according to XRD analysis. EDS results showed the predominance of niobium and absence of iron in the layers on both steels. The presence of titanium was detected, just in small amounts, in the region of the layer next to substrate.     

Formation of chromium nitride layers on AISI 1010 steel by nitro-chromizing treatment

In this study, chromium nitride coating was realized on AISI 1010 steels by nitro-chromizing treatment. Steel samples were tufftrided at 575 °C for 2 h in the first step of the coating process, and then chromized by pack method in the powder mixture consisting of ferro-chromium, ammonium chloride and alumina at 1000 °C for 1-4 h. Samples were characterized by scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy, X-ray diffraction (XRD) analysis and Vickers micro-hardness tests. Coating layer formed on the steel samples is smooth and compact and well bonded to the steel matrix. The thickness of chromium nitride layer formed on the steel samples ranged from 5.16±1.48 to 13.45±1.73 μm, depending on the treatment time. The average micro-hardness value of the layer was 1789±59 HV_0.05. The layer consisted of Cr₂N and (Cr,Fe)₂N_(1−x) phases, according to XRD. EDS results showed that coating layer includes chromium and nitrogen.     

Microstructural investigations of XW-42 and M2 tool steels in semi-solid zones via direct partial remelting route

A suitable microstructure for thixoforming consists of spheroidal grains in a liquid matrix. In order to achieve this, some processing routes have been established. In this study, microstructural evolution of XW-42 and AISI M2 steels via direct partial remelting from the as-annealed condition was examined. Both steels were found to possess certain types of carbides that dissolved when subjected to heating inside the semi-solid zones. The types of carbides were MC-M₆C for AISI M2 steel (fully dissolved between 1280 and 1300 °C) and M₇C₃ for XW-42 steel (fully dissolved between 1250 and 1270 °C). The dissolution of these grain boundary carbides during partial remelting helps with the grain spheroidisation and also with providing grain lubrication for the forming process through solid–liquid particle contact. In addition, solid–solid contacts were also observed (in 2D as well as 3D microstructural observation) and considered useful to provide structural integrity prior to forming. However, these contacts also must also be weak enough to be sheared easily. Compression test results for AISI M2 steel showed that thixotropic behaviour and complete mould filling were observed starting from 35 liquid percent. The same behaviour is also expected to occur for XW-42 steel due to its similarity in microstructural evolution with AISI M2 steel.     

Thermal Noise Sensor Insulation Using Ultra-thin Ceramic Coatings

The insulation resistance and interference rejection of several prototype thermal noise sensors were measured. It was found that twisting the connecting wires as a pair optimizes the magnetic interference rejection. High-temperature-resistant wire insulation was developed by vapor depositing a few micrometer thick ceramic coating. The best insulation was obtained with a coating of 1.25μm SiO₂ + 1.5μm TiO₂ + 0.25μm ZrO₂. The insulation of four such coated pairs reached stable levels of 18 ± 3kΩ during a testing period of 1 week at 950°C under atmospheric conditions.     

Formation of water-soluble and biocompatible TOPO-capped CdSe quantum dots with efficient photoluminescence

Hollow hydroxyapatite (HA) microspheres (diameter = 100–800 μm) were prepared by reacting solid Li₂O–CaO–B₂O₃ glass spheres in 0.25 M K₂HPO₄ solution at 37°C. The influence of subsequent heating on the microstructure, surface area, and compressive strength of the HA microspheres was evaluated using scanning electron microscopy, the BET method, and nano-mechanical testing. The surface area and rupture strength of the as-prepared microspheres were 135 m²/g and 1.6 ± 0.6 MPa, respectively. On heating for 8 h at 600°C, the surface area decreased to 27 m²/g, but there was no increase in the compressive strength (1.7 ± 0.4 MPa). Heating to 800°C (8 h) resulted in a marked decrease in the surface area (to 2.6 m²/g) and a sharp increase in the compressive strength (to >35 ± 8 MPa). These hollow HA microspheres may be useful as devices for drug or protein growth factor delivery or as scaffolds for engineered tissues.     

Fabrication and properties of a lubrication composite coating based on poly(<Emphasis Type="Italic">p</Emphasis>-hydroxybenzoic acid) (PHBA)

The present paper describes an approach for fabricating smooth, compact and homogeneous composite coatings of PHBA/PA/MoS₂ on test blocks. The tribological behaviors were tested on a ring-block machine. For the PHBA/PA 6,6/MoS₂ coating of 20 wt.% PA 6,6 and 30 wt.% MoS₂ with the thickness of 20–40 μm, the steady friction coefficient was approximately 0.04 with the lowest wear loss while sliding against AISI 1045 steel ring. The PHBA in coating was synthesized in situ at 200 °C for the first step and 260 °C for the second. The chemical structures and thermal properties of the obtained PHBA were characterized by means of Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry/thermogravimetry (DSC/TG). The results showed that the chemical structure of the obtained PHBA was identical to that of the commercial PHBA powder despite that the decomposition temperature and the crystal transition temperature of the former were approximately 10–20 °C lower than that of the latter. The influence of nominal pressure and sliding velocity on the friction coefficient (μ) and wear volume loss of the coatings was investigated. The results displayed that μ increased with the increase of sliding velocity, while it decreased when the nominal pressure was increased. For the volume loss, it increased with both the increase of speed and pressure.     

Study on NbC particulate-reinforced iron matrix composite produced in situ

In the infiltration casting process and heat treatment method, gray cast iron and niobium wires are compounded. The reinforcement phase NbC particles are synthesized in situ between niobium wires and graphite phases in the gray cast iron using heat treatment. The microstructure and micro-hardness of the compound region are observed and measured through X-ray diffraction, scanning electron microscopy, and micro-hardness testing. The results indicate that at 1172 °C for 25 min, the in situ reaction area is diffusely extended eight times larger than the original diameter of 0.7 mm. The NbC particles synthesized in situ are tiny square- or rectangle-like particles that are evenly distributed in the gray cast iron. The highest micro-hardness value of the composite region is 1988 HV_0.05, and the average micro-hardness value of the composite region after 20 min heat treatment is 953 HV_0.05 or about five times larger than that of the matrix. After heat treatment at 1172 °C for 25 min, the average micro-hardness value of the composite was about 458 HV_0.05, and the average macro-hardness was 49.2 HRC.     

Effects of the high temperature plasma immersion ion implantation (PIII) of nitrogen in AISI H13 steel

In this paper we report the effect of high temperature PIII of nitrogen on the chemical and physical properties of AISI H13 steel. The implantation of H13 steels was carried out at different temperatures ranging between 300 °C and 720 °C. After the treatment, the surface morphology was drastically changed as observed by SEM analysis. Nitrogen penetration depth reaching up to 12 μm was achieved at 620 °C and 720 °C. The maximum hardness of about 592 HV was obtained for the sample treated at 470 °C that is 17% higher than for untreated specimen. There was a decrease of the hardness values for temperatures above 470 °C. The same hardness behavior with the temperature was confirmed by nanoindentation testing. Although an enriched nitrogen layer was obtained, no evidence of nitride compounds was detected by XRD analyses. On the other hand, improvements of the H13 steel tribological properties and corrosion resistance were obtained. The wear tests were conducted by pin-on-disk tribometer (rotating mode). The wear volume decreased by factor of 4.5 compared to the standard tempered and annealed H13 steel and 2.6 times reduction of the coefficient of friction was achieved. The electrochemical measurements were performed in 3.5% NaCl solution, pH = 6. Open circuit potential curves showed that the potentials are nobler for the PIII treated samples than for untreated specimen. In addition, the corrosion current density of the samples treated at 620 °C and 720 °C diminished to 3 × 10⁻⁸ A/cm².     

Tribological properties of oxidised boride coatings grown on AISI 4140 steel

In this study, we investigated the wear behaviour of borided and borided + short-duration oxidized AISI 4140 steel. Boronizing was carried out in a slurry salt bath consisting of borax, boric acid and ferro silicon. Also, short-duration oxidizing treatment was applied to borided steel to produce glass-like boron oxide layer. The short-duration oxidizing was performed at 750 °C for 3 min. Optical and scanning electron microscope (SEM) cross-sectional examinations of borided layer revealed a needle-shaped morphology. The presence of non-oxide boride type ceramics FeB and Fe₂B formed on the surface of steel substrate was confirmed by classical metallographic technique and X-ray diffraction (XRD) analysis. The hardness of borides formed on the surface of steel substrate and unborided steel substrate were 1446–1690 HV_0.1 and 280 HV_0.1, respectively. The wear behaviour of borided steel were characterised by using a pin-on-disc technique. The borided and short-duration oxidized steels, in the form of pins were allowed to slide against a hard AISI 440C stainless steel disc (63 HRc). The sliding velocity of 1 m s^− 1 for borided and short-duration oxidized steel and the nominal load on the pin was 20 N. The highest wear rates were observed on disc slide against the base steel, whilst the lowest wear rates occurred during sliding against the borided and short-duration oxidized steel surfaces. It was observed that the friction coefficient of unborided (hardened + tempered) and borided steels ranged from 0.50 to 0.60, but after short-duration oxidizing, the friction coefficient of borided steel was dropped to 0.12.     

An analysis of the error in measuring the field of the maximum magnetic permeability of steels

The error δ in measuring the parameters of the field Hμ _m of the maximum magnetic permeability μ _m of steels is estimated. It is established that δ is 5–10 times greater than the error of ±5% in measuring μ _m . It is shown that not all the reference data on μ _m and Hμ _m of steels are reliable. The inadvisability of using Hμ_m in magnetic structural analysis is demonstrated.     

Nitridation of the sol-gel derived TiO2 coating films and the infrared ray reflection

The titanium nitride coating film was prepared on the SiO₂ glass substrate by ammonolysis of titanium dioxide coating film formed by sol-gel method. The X-ray diffraction (XRD) pattern indicated that it is cubic titanium nitride with a lattice parameter,a _o, of 0.4231 nm. The obtained titanium nitride is non-stoichiometric (TiN _x x≤ 1) because the value, 0.4231 nm, is smaller than the stoichiometric one (0.4240 nm). The coating film show very high infrared (i.r.) reflectance in the wavelength region of 2–8 μm.     

Ferroelectric and dielectric properties of Bi4-xNdxTi3O12 thin films prepared by sol–gel method

Bi_4-xNd_xTi₃O₁₂ (BNT-x, x = 0, 0.25, 0.50, 0.75 and 1.0) thin films were prepared on Pt/Ti/SiO₂/Si substrates by a sol–gel method. The microstructure, ferroelectric and dielectric properties of BNT-x thin films were investigated. The single-phase BNT-x thin films were obtained. With increasing Nd content, the preferred orientation changed from random to (117) and surface morphologies changed from the mixture of rod- and plate-like grains to rod-like grains. The Nd substitution improved the ferroelectric and dielectric properties of BTO films. BNT-x films showed better electrical properties at x = 0.50—1.0. BNT-0.75 film exhibited the best electrical properties with remanent polarization (2P _r) of 26.6 μC/cm², dielectric constant (ε _r) of 366 (at 1 MHz), dielectric loss (tanδ) of 0.034 (at 1 MHz), leakage current density (J) of ±3.0 × 10⁻⁶ A/cm² (at ± 5 V) and fatigue-free characteristics.     

Morphology and composition of nickel–boron nanolayer coating on boron carbide particles

This work is focused on electroless coating of Ni–B nanolayer on B₄C particle surfaces. The B₄C particles used are approximately 2 μm in average size. Effects of activation agent PdCl₂, complexing agent C₂H₈N₂, and reducing agent NaBH₄ addition rate are studied. The solids loading of B₄C is 0.625 g/L and the concentration of Ni²⁺ ions is 0.004 mol/L in the electroless coating solution. Scanning electron microscopy (SEM) shows that when B₄C:Pd²⁺ molar ratio is 1:0.005, a Ni–B nanolayer with the smallest Ni–B nodule size covers the B₄C particle surfaces. Complexing agent C₂H₈N₂ decreases Ni²⁺ ion release rate. Ni:C₂H₈N₂ ratio of 1:6 is the preferred complexing agent amount for achieving a continuous Ni–B nanolayer. The Ni–B nanolayer formation is also strongly dependent on the rate that Ni²⁺ ions are reduced. Slow Ni²⁺ reduction leads to increased Ni content in the Ni–B nanolayer. When the above three factors are combined at the optimal values for the electroless coating process, well-defined Ni–B nanolayer is obtained. SEM cross section analysis shows the Ni–B nanolayer completely covers the B₄C particles with less than 55 nm thickness.     

Laser surface modification of 316 L stainless steel with bioactive hydroxyapatite

Laser-engineered net shaping (LENS?), a commercial additive manufacturing process, was used to modify the surfaces of 316 L stainless steel with bioactive hydroxyapatite (HAP). The modified surfaces were characterized in terms of their microstructure, hardness and apatite forming ability. The results showed that with increase in laser energy input from 32 J/mm² to 59 J/mm² the thickness of the modified surface increased from 222 ± 12 μm to 355 ± 6 μm, while the average surface hardness decreased marginally from 403 ± 18 HV_0.3 to 372 ± 8 HV_0.3. Microstructural studies showed that the modified surface consisted of austenite dendrites with HAP and some reaction products primarily occurring in the inter-dendritic regions. Finally, the surface-modified 316 L samples immersed in simulated body fluids showed significantly higher apatite precipitation compared to unmodified 316 L samples.     

Creep behaviour and microstructural evolution in AISI 316LN + Nb steels at 650 °C

The paper deals with the effect of niobium in the wrought AISI 316LN steels on the long-term creep characteristics at 650 °C. Casts B and C contained 0.1 and 0.3 wt.%Nb, respectively. As a reference material the niobium free Cast A was used. Small additions of niobium to the AISI 316LN steel resulted in a significant reduction of the minimum creep rate and shortening of the tertiary creep stage. At time to rupture exceeding 10⁴ h the creep rupture strength of the niobium-bearing Casts B and C was slightly inferior to the Cast A. Two nitrides formed in the Casts B and C: Z-phase and M₆X. The minimum creep rate in niobium-bearing casts was favourably affected by precipitation of the Z-phase. The dimensional stability of Z-phase particles was very high, but niobium additions also accelerated the formation and coarsening of η-Laves and σ-phase. Coarse σ-phase particles at grain boundaries contributed significantly to the shortening of the tertiary creep stage.     

High thermal conductivity composites consisting of diamond filler with tungsten coating and copper (silver) matrix

Tungsten coatings with thickness of 5–500 nm are applied onto plane-faced synthetic diamonds with particle sizes of about 430 and 180 μm. The composition and structure of the coatings are investigated using scanning electron microscopy, X-ray spectral analysis, X-ray diffraction, and atomic force microscopy. The composition of the coatings varies within the range W–W₂C–WC. The average roughness, R _a, of the coatings’ surfaces (20–100 nm) increases with the weight–average thickness of the coating. Composites with a thermal conductivity (TC) as high as 900 W m⁻¹ K⁻¹ are obtained by spontaneous infiltration, without the aid of pressure, using the coated diamond grains as a filler, and copper or silver as a binder. The optimal coating thickness for producing a composite with maximal TC is 100–250 nm. For this thickness the heat conductance of coatings as a filler/matrix interface is calculated as G = (2–10) × 10⁷ W m⁻² K⁻¹. The effects of coating composition, thickness and roughness, as well as of impurities, on wettability during the metal impregnation process and on the TC of the composites are considered.     

Silver coated bioactive glass particles for wound healing applications

Bioactive glass particles (0.42SiO₂–0.15CaO–0.23Na₂O–0.20ZnO) of varying size (<90 μm and 425–850 μm) were synthesized and coated with silver (Ag) to produce Ag coated particles (PAg). These were compared against the uncoated analogous particles (Pcon.). Surface area analysis determined that Ag coating of the glass particles resulted in increased the surface area from 2.90 to 9.12 m²/g (90 μm) and 1.09–7.71 m²/g (425–850 μm). Scanning electron microscopy determined that the Ag coating remained at the surface and there was little diffusion through the bulk. Antibacterial (Escherichia coli—13 mm and Staphylococcus epidermidis—12 mm) and antifungal testing (Candida albicans—7.7 mm) determined that small Ag-coated glass particles exhibited the largest inhibition zones compared to uncoated particles. pH analysis determined an overall higher pH consider in the smaller particles, where after 24 h the large uncoated and Ag coated particles were 8.27 and 8.74 respectively, while the smaller uncoated and Ag coated particles attained pH values of 9.63 and 9.35 respectively.     

Kinetics of borided gear steels

In this study, the case properties and diffusion kinetics of GS18NiMoCr36 (GS18), GS22NiMoCr56 (GS22) and GS32NiCrMo6.4 (GS32) gear steels borided in Ekabor-II powder were investigated by conducting a series of experiments at temperatures of 1123, 1173 and 1223 K for 2, 4 and 6 h. The boride layer was characterized by optical microscopy, X-ray diffraction technique and micro-Vickers hardness tester. X-ray diffraction analysis of boride layers on the surface of the steels revealed the existence of FeB, Fe₂B, CrB and Cr₂B compounds. The thickness of the boride layer increases by increasing boriding time and temperature for all steels. The hardness of the boride compounds formed on the surface of the steels GS18, GS22 and GS32 ranged from 1624 to 1905 HV_0,05, 1702 to 1948 HV_0,05, and 1745 to 2034 HV_0,05 respectively, whereas Vickers hardness values of the untreated steels GS18, GS22 and GS32 were 335 HV_0,05, 358 HV_0,05 and 411 HV_0,05, respectively. The activation energies (Q) of borided steels were 228.644 kJ/mol for GS18, 280.609 kJ/mol for GS22 and 294.359 kJ/mol for GS32. The growth kinetics of the boride layers forming on the GS18, GS22 and GS32 steels and the thickness of boride layers were also investigated.