TiN Phase Research Articles

Hot-Pressing of Ti-Al-N Multiphase Composite: Microstructure and Properties

This study focuses on the development and characterization of a bulk Ti-Al-N multiphase composite enriched with BN addition and sintered through hot pressing. The research aimed to create a material with optimized mechanical and corrosion-resistant properties suitable for demanding industrial applications. The composite was synthesized using a powder metallurgy approach with a mixture of AlN, TiN, and BN powders, processed under a high temperature and pressure. Comprehensive analyses, including microstructural evaluation, hardness testing, X-ray tomography, and electrochemical corrosion assessments, were conducted. The results confirmed the formation of a multiphase microstructure consisting of TiN, Ti₂AlN and Ti₃AlN phases. The microstructure was uniform with minimal porosity, achieving a hardness within the range of 500–540 HV2. Electrochemical tests revealed the formation of a passive oxide layer that provided moderate corrosion resistance in chloride-rich environment. However, localized pitting corrosion was observed under extreme conditions. The study highlights the potential of a BN admixture to enhance mechanical and corrosion-resistant properties and suggests directions for further optimization in sintering processes and material formulations.

Suitability of Available Interatomic Potentials for Sn to Model Its 2D Allotropes.

The suitability of a range of interatomic potentials for elemental tin was evaluated in order to identify an appropriate potential for modeling the stanene (2D tin) allotropes. Structural and mechanical features of the flat (F), low-buckled (LB), high-buckled (HB), full dumbbell (FD), trigonal dumbbell (TD), honeycomb dumbbell (HD), and large honeycomb dumbbell (LHD) monolayer tin (stanene) phases, were gained by means of the density functional theory (DFT) and molecular statics (MS) calculations with ten different Tersoff, modified embedded atom method (MEAM), and machine-learning-based (ML-IAP) interatomic potentials. A systematic quantitative comparison and discussion of the results is reported.

Evolution of Ductile L12 Phase in (FeCoNi)86-Al7Ti7 High-Entropy Alloy Aging at Various Temperatures and Its Strengthening Mechanism

Ductile participation with small lattice misfit against matrix has been a long-sought-after character in toughening alloys, and recently multicomponent intermetallic nanoparticle L12 phase was explored by compositional modification in FeCoNi-based alloys and reported its benefits on strength and ductility through 780 °C for 4h aging treatment. However, the L12 (A3B: Ni3Al) evolution in (FeCoNi)86-Al7Ti7 at a wide range of aging temperatures still lacks of comprehensive investigations. Herein, a series of aging temperatures (580 °C, 650 °C, 690 °C, 720 °C, 780 °C, and 820 °C) were carried out based on the synchrotron in-situ variable temperature XRD of the alloy. Results showed that both the composition and morphology of the L12 phase are dramatically dependent on the aging temperatures. Specifically, with aging temperature increased from 580 °C to 820 °C, A sites preferentially incorporated by more Co and Fe gradually turn into B sites partially substituted by Fe and Ti in the L12 phase, together with its morphology transforming from spherical to cuboidal. Meanwhile, the hierarchical microstructure induced by the precipitates of the tiny L12 phase at the aging temperature of 780 °C compensated the size departure of the primary L12 phase against the critical size to enhance the strength by enhancing its dislocation storage capacity. These hierarchical L12 phases strengthen the strong pair-coupling mechanism, ultimately illustrating its excellent strength-ductility balance aging at 780 °C against other aging temperatures.

Microstructure, precipitates and mechanical properties of Cu-3Ni-1Ti alloy by two-stage cold rolling and aging treatment

The effects of two-stage cold rolling and aging treatment on the mechanical and electrical properties of Cu-Ni-Ti alloy were investigated. The microstructure evolution, precipitation behavior, and strengthening mechanism of the alloy after two-stage cold rolling and aging treatment were analyzed using microhardness, tensile strength, and electrical performance tests, combined with transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques. The research results show that the alloy after two-stage cold rolling and aging treatment exhibits excellent comprehensive properties, tensile strength reaches 635 MPa, yield strength is 597 MPa, hardness is 182 HV, conductivity is 62.1 % IACS, and elongation is 14.5 %. This processing method facilitates the precipitation of more nanoscale Ni3Ti phases and the formation of smaller cellular substructures. Consequently, the alloy maintains its exceptional mechanical properties through the combined effects of dislocation and precipitation strengthening. This study provides a novel preparation process and a solid theoretical foundation for enhancing the mechanical and electrical properties of Cu-Ni-Ti alloys.

Microstructure evolution and mechanical properties of TC4/Ni metallic-intermetallic laminated composites: Formation and strengthening effects of Ti₂Ni phases

TC4/Ni metallic-intermetallic laminated (TN-MIL) composites were prepared by hot pressing at different temperatures and with varying Ni foils thicknesses. The phase formation and Ti₂Ni microstructure evolution were analyzed in detail using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and x-ray diffraction (XRD). The mechanical properties were evaluated through nanoindentation, room-temperature compression, and tensile tests, while fracture morphology was examined by SEM. The results show that as the hot-pressing temperature increases, the Ni₃Ti and TiNi phases at the interface gradually transform into the Ti₂Ni phase. Once the Ni is fully dissolved in the TC4 matrix, the intermetallic compound layer disappears. This diffusion process creates a concentration gradient in TC4. As the Ni concentration increases, the Ti₂Ni phase transitions from an island-like structure to a network, and ultimately forms a lamellar or mixed morphology. The TN-MIL composite prepared at 800°C has three intermetallic compound layers of Ni₃Ti, TiNi and Ti₂Ni, as well as lamellar, network and island-like Ti₂Ni structures in the TC4 matrix. This composite demonstrates excellent mechanical performance, achieving a maximum compressive strength of 1580 MPa and an ultimate tensile strength of 1010 MPa. The Ti₂Ni phase improves the material's deformation resistance due to its high strength and hardness, thereby increasing the overall hardness and strength. However, the inherent brittleness of Ti₂Ni and its propensity to induce stress concentrations at grain boundaries under strain conditions significantly elevate the risk of material fracture.

Modification of Ti-Al-V Alloys with Layers Containing TiN Particles Obtained via the Electrophoretic Deposition Process: Surface and Structural Properties.

The aim of this work was to obtain homogenous coatings containing chitosan with different concentrations of titanium nitride particles (TiN). The coatings were deposited via an electrophoretic process on an etched medically pure Ti-6Al-4V alloy. As part of the study, the zeta potential of the suspensions used for EPD coating deposition was measured, allowing for the optimization of process parameters and the assessment of suspension stability. Subsequently, the research focused on evaluating the microstructure (SEM + EDS), structure (XRD), and surface characteristics (roughness, contact angle, surface energy, microhardness, coating adhesion) of the deposited layers. SEM microscopy confirmed the effective deposition of titanium nitride particles onto the titanium alloy surface. XRD analysis proved the assumed phase composition of the coating. The increase in TiN phase content in the individual layers was confirmed. The chitosan/TiN layer's introduction altered the alloy surface, increasing its roughness and static water contact angle. The highest roughness and hydrophobic properties were observed in the coating with a 2 wt.% concentration of titanium nitride particles. Additionally, the coating containing the highest concentration of ceramic particles (2 wt.%) exhibited the highest hardness (197 HV) among all the tested layers. However, the TiN particles incorporation in the layer decreased the adhesion strength, from 2.36 MPa (0.5 wt.% TiN) to 1.04 MPa (2 wt.% TiN). The coatings surface and structural properties demonstrate potential as protective layers for implants and are suitable for further biological studies to assess their applicability in medical and veterinary fields.

Effect of grain size on precipitation and microstrain of nanocrystalline NiTi alloys

The effect of aging treatment on the microstructure, phase transformation behavior and mechanical properties of nanocrystalline NiTi alloy was studied. The nanocrystalline NiTi alloys with different grain sizes were acquired by cold drawing followed by annealing at 350–500 °C for 10 min. The annealed samples were aged at 250–400 °C for 48 h. The Ti3Ni4 precipitates were found in aged nanocrystalline NiTi alloys. In the sample with smaller average nanograin size, the precipitates were found at the edge of grain boundaries and little lattice strain was shown in R phase matrix. In the sample with larger average grain size, the precipitates were found in the nanograins and exhibited a coherent interface with the matrix. The nanocrystalline R phase NiTi matrix exhibited a significant compressive stress at the end of the coherent precipitate. The coherent precipitates in sample aged at 250 °C after annealing at 500 °C suppress the stress-induced R → B19′ phase transformation and increased the upper plateau stress. The precipitation in sample aged at 250 °C after annealing at 350 °C unable to suppress the martensitic transformation effectively.

Precipitation strengthening behavior of Custom 455 stainless steel during tempering at 420 °C

After solid solution at 850 °C, the Custom 455 was aged at 420 °C for different times. The hardness changes were measured using a Vickers hardness tester, and the microstructure and composition of the second phase were studied using atom probe tomography (APT) and high-resolution transmission electron microscopy (HRTEM). The APT results indicate that in the early stage of aging, Cu atoms first segregate and attract Ti to form CuTi clusters; As the aging time increases, Ti atoms in CuTi clusters attract Ni and form CuTiNi clusters, resulting in a rapid increase in sample hardness; Subsequently, CuNiTi clusters grew and gradually separated into Cu-rich and NiTi-rich particles; As the aging time further increases, some NiTi-rich particles grow into rod-shaped Ni3Ti precipitates, while others have Si atoms and grow into spherical G phase particles. The orientation relationship between Cu-rich phase, Ni3Ti phase, and G phase is: [100]M//[0–11]Cu//[-12–10]Ni3Ti//[100]G, (011)M//(111)Cu//(0004)Ni3Ti//(022)G. The formation of the Cu-rich, Ni3Ti, and G phase resulted in a hardness peak of 538 HV after 16 h of aging. Subsequently, the decrease in hardness caused by the coarsening of the Cu-rich and Ni3Ti particles was offset by the newly formed G phase, resulting in a slow decrease in hardness.

Hot isostatic pressing of ball milled novel grade high entropy alloys at different sintering time and the investigation of their mechanical and corrosion resistance properties

Abstract With the discovery of high entropy alloys, new materials with superior properties have emerged. According to recent research, high-entropy alloys’ multi-component structure and mixing entropy have made them more prominent than other alloys. Because of their excellent chemical and mechanical properties—such as high hardness, high-temperature resistance, high wear resistance, chemical stability, and high corrosion resistance—high entropy alloys outperform other material types in various applications. A new grade of mechanically alloyed high entropy alloy (HEA) of composition 23Fe-21Cr-18Ni-20Ti-18Mn was consolidated by a hot isostatic pressing (HIP) at a temperature of 1000 °C, at different sintering time of 30, 60, and 90 min respectively. We have investigated the impact of sintering time on the microstructure, mechanical, corrosion, and wear-resistance properties. The x-ray diffraction (XRD) spectra of the 30 min HIPed HEA sample showed dominant s-FeCr phases and traces of γ-Fe, and the Ni-Ti phases. Whereas, the 90 min HIPed HEA samples showed more dominant Ni-Ti and traces of γ-Fe, and β-Mn phases. There is a phase transformation from BCC to HCP of consolidated HEA at increased holding time. The density of the samples increases from 5.882 to 6.327 g cm−3 and the porosity percentage decreases from 12.93 to 6.35% with the increase in the holding time. The Vickers microhardness value for 30, 60, and 90 min HIPed 23Fe-21Cr-18Ni-20Ti-18Mn HEA at 1000 °C was found to be 433, 513, and 793 HV respectively at an indentation load of 0.1 kgf. The consolidated HEA sample undergoes an abrasive and oxidative wear mechanism with ploughing and plastic deformation modes. The morphology of the wear debris was investigated using SEM. The 90 min sintered sample showed an excellent corrosion resistance due to the high rate of material densification and minimum surface flaws.

Study on the effect of TiC/B on the performance of laser cladding in-situ fabricating wear-resistant self-lubricating coatings

To improve the wear resistance of IN718, coatings containing the self-lubricating phase h-BN were prepared and the coating properties were analyzed in relation to the variation of laser power. The results show the TiC added to the cladding powder partially decomposes and in-situ fabricates new reinforcing phases TiN, B4C, etc. The lubricating phase h-BN was in-situ fabricated by adding B into the powder. As the laser power increased from 1.6 kW to 2 kW and 2.5 kW, eutectic microstructures of high melting point reinforcing and lubricating phases were observed. Due to the decomposition of TiC and in-situ fabricated of TiC2, TiN and B4C concentrations changing with the laser power, the surface hardness of the coatings prepared at 2.5 kW was the highest at 391.03HV0.5. Which is 1.096 and 1.108 times of 1.6 kW and 2 kW. At room temperature, the coating fabricated by 2 kW has the highest average friction coefficient of 0.537. This is because the self-lubricating phase h-BN is a high-temperature lubricating phase and the wear surface has a low oxide content, and is influenced by the hardness of the coating. At 500°C, the coating fabricated with 2.5 kW has the lowest average friction coefficient due to the best synergistic effect of the lubricating and reinforcing phases at 0.376. The 2.5 kW coating has the best wear resistance, with wear rates 0.69 and 0.54 times at room temperature and 0.82 and 0.8 times at 500°C of 1.6 kW and 2 kW. The wear mechanism at room temperature is abrasive wear, and at 500°C is mainly a combination of h-BN and oxide synergistic lubrication.

Dendrite growth kinetics and microstructure evolution mechanism of Ni2TiAl intermetallic compound within substantially undercooled liquid Ni64Al19Ti17 alloy

The dendrite growth kinetics and microstructure evolution mechanism of the Ni2TiAl intermetallic compound within substantially undercooled liquid Ni64Al19Ti17 alloy were investigated using electrostatic levitation (ESL) and drop tube (DT) techniques. The growth velocity of primary Ni2TiAl dendrites displayed a power-law relation with liquid undercooling, achieving a maximum of 80 mm/s at the undercooling of 254 K (0.16 TL). The solidification pathway transformed from primary Ni2TiAl growth plus subsequent (Ni3Ti+Ni2TiAl) eutectic growth into the successive growth of Ni2TiAl and Ni3Ti phases as the alloy undercooling increased sufficiently. The high cooling rates of freely falling alloy droplets effectively suppressed the martensitic transformation observed for primary Ni2TiAl intermetallic compound under typical ESL radiative cooling condition. Both nanoindentation and Vickers hardness performances of the Ni2TiAl phase formed under these two conditions exhibited conspicuous enhancement due to grain refinement effects. The microstructures with martensitic transformation under ESL condition showed higher hardness than those under DT condition despite their larger grain size.

Enhancing sapphire/Kovar alloy brazed joint through combined effect of TiB whisker reinforcement and surface micro-nano structures

The brazed joining between Kovar alloy and sapphire was successfully achieved by using TiB whisker reinforcement and applying the surface micro-nano structure. We systematically studied the composition and mechanical properties of Kovar/Sapphire joint. The typical interfacial structure of the joint brazed at 825 °C for 10 min was determined as Sapphire/ γ-TiO/ Ti3(Cu,Al)3O/ Ag(s,s) + Cu(s,s) + TiB/ Ti2Cu + TiFe2 + TiNi3/ Kovar alloy. The addition of B forms tiny TiB whisker reinforcement phase in situ, which refines the interface structure. The presence of micro-nano structures improves the interface products on the sapphire side: reducing the generation of Ti3(Cu,Al)3O and replacing it with γ-TiO. This makes the phase transition on the sapphire side smoother and reduces thermal expansion coefficient mismatch, thereby enhancing joint strength. Under suitable brazing parameters, the maximum shear strength of the joint is 137 MPa. This study provides new insights for optimizing and improving connections between sapphire ceramics and metals, with potential applications in more ceramic/metal joining.

Chemical-bonding and lattice-deformation mechanisms unifying the stability and diffusion trends of hydrogen in TiN and AlN polymorphs

The continuous development of hydrogen-permeation barriers (HPB) based on metal nitrides highly desires a generic unification of the key thermodynamic and kinetic mechanisms therein. This work employs first-principles calculations to study the stability and diffusion trends of H impurity in the rock-salt, wurtzite, and sphalerite phases of the prototypical TiN and AlN. The formation energies (Ef) of H at various interstitial and vacant sites in these nitrides are calculated, and the underlying chemical-bonding and lattice-deformation mechanisms are self-consistently revealed by the systematic structual, energetic, and electronic-structure analyses. This leads to the discovery of a generic volcanic trend of Ef in terms of the electron number on H (QH), which well portrays how the covalent-ionic H–N and H–metal bondings determine its stability in different atomistic environments. Then, the kinetic properties (e.g., potential barriers, diffusion coefficients, and isotope effects) of interstitial H in these nitrides are calculated, where the volcanic Ef–QH relationship is applied to better understand the joint contributions of chemical bonding and lattice deformation. Finally, the revealed mechanisms and volcanic Ef–QH relationship are generalized to successfully describe the behaviors of H in some important grain boundaries of c-TiN and c-AlN, including the Σ3{112}〈110〉 twin frequently observed in c-TiN and the Σ5{210}〈001〉 twin prototypical to many rock-salt materials. The widely varying hydrogen permeabilities measured in experiment on many nitride coatings are successfully explained, inspiring more useful chemical principles to guide the design of HPB coatings facing harsh environments with long-term reliability.

Enhanced mechanical properties and structural stability of Hf-modified NiTi alloy for advanced bearing materials

Ni-rich NiTi alloys suitable for bearing materials exhibit excellent properties such as high hardness, low modulus, non-magnetic, and corrosion resistance. In this study, the addition of Hf elements enhanced the mechanical properties and improved the structural stability of the alloys. The results indicate that the aging-treated Ni55Ti37Hf8 alloy demonstrates outstanding properties, with a Vickers hardness of 738.7 ± 12.5 HV, a nano-hardness of 9.6 ± 0.3 GPa, and an elastic modulus of 106.1 ± 2.2 GPa. The microstructure is primarily composed of the NiTi, Ni4Ti3 phase, and the H-phase. The structural stability of Ni55Ti37Hf8 alloy reached unprecedented levels, with hardness remaining at 673.1 ± 4.6 HV after heat treatment at 600°C for 100 h, meeting the requirements for bearing materials (exceeding 58 HRC). The Ni55Ti37Hf8 alloy exhibits superior thermal stability, making it a revolutionary option for the development of next-generation wear-resistant materials.

Bonding mechanism of TC4 titanium alloy/T2 copper vacuum diffusion bonded joint with nickel as transition interlayer

Vacuum diffusion bonding of TC4 titanium alloy (TC4) to T2 copper (T2) using nickel foil as transition interlayer was explored. Ti3Ni, Ti2Ni, TiNi, AlNi2Ti and TiNi3 phases arose at the TC4/Ni bonded interface, and Cu-Ni solid solution appeared in the Ni/T2 interface. Thereinto, AlNi2Ti was a kind of discontinuous nano precipitated phase, which distributed between TiNi and TiNi3 phases. The crystallographic orientations of Ti2Ni, TiNi, AlNi2Ti and TiNi3 phases were (201), (020), (11¯1) and (031), respectively. The interplanar spacing of (031), (11¯1) and (020) was correspondingly d(031) = 0.144 nm, d11¯1 = 0.275 nm and d(020) = 0.137 nm. The lattice mismatch between TiNi3 and TiNi was calculated to be 2.5 %, with low strain energy. The order of effective formation enthalpies for TiNi3, TiNi and Ti2Ni phases formed between titanium and nickel was ∆H′NiTi2 > ∆H′NiTi > ∆H′Ni3Ti. The growth activation energy of TiNi3, TiNi and Ti2Ni phases was correspondingly 35.8 kJ/mol, 180.6 kJ/mol and 347.1 kJ/mol. When welding at 880 °C for 60 min, the highest shear strength of the joints could achieve 150 MPa. The joints fractured along the Ni/T2 interface, the fracture surface of joint was composed of elongated dimples and cellular pits, presenting a shear ductile fracture mode. FCC-Cu, FCC-Ni and (Ni, Cu)ss phases were detected on TC4 and T2 fracture surfaces by XRD. The interdiffusion coefficient ratio of (Ni in Cu)/(Cu in Ni) and (Ni in Ti)/(Ti in Ni) decreased gradually with increasing temperature.

Influence of isochronal heat treatment on spray-deposited mixed phase tin based thin films for ammonia gas sensor applications

The current work applied the spray pyrolysis (SP) approach to coat mixed-phase SnS thin films at 350 °C, and then air annealed at 400,450,500 °C for use in sensor and solar cells applications. A variety of methods were employed to evaluate the structural, morphological, compositional, optical, and electrical characteristics of synthesised mixed-phase films. Films annealed at 500 °C are reported to have bigger crystal sizes, and all deposited SnS films exhibit the orthorhombic phase in addition to tetragonal phase of SnO2, with other visible secondary phases like SnS2,Sn2S3. Fourier transform infrared spectroscopy and Raman analyses verified the molecular structure and vibrational mode of SnS films. The Scanning electron microscopy tests reveal a consistent, size-varying two-dimensional flake like grain structure, while the optical studies show a variation in optical direct band-gap from 1.79 to 2.75eV. The Hall-effect shows that films subsequently annealed at 400 °C have improved electrical properties. An efficient metal oxide semiconductor gas sensor was developed by applying mixed-SnS film on the conducting side of an indium tin oxide coated glass plate. To examine the sensor selectivity at room temperature, a variety of test gases, such as NO2, H2S, C2H5OH, NH3, were purged at different concentrations. The optimum working temperature and concentration for NH3 selective gas have been determined to be 350 °C and 5 ppm. The sensor sensitivity is found to be maximum at operating temperature of 200 °C towards NH3 gas. An inexpensive, fabricated MOS-gas sensor based on mixed-phase SnS can be easily mass produced and may find potential applications in industrial and environmental monitoring.

Strengthening Cu-containing high entropy alloys through ultrasonic solidification constructed heterostructures

The solidification process of FeCoNiCu1.5Al0.2 high-entropy alloy (HEA) with two FCC phases was modulated by three-dimensional (3D) ultrasounds with 20 kHz frequency and 22 μm amplitude. The statically solidified alloy was composed of a primary γ1 phase growing into coarse dendrites and a Cu-rich γ2 phase dispersed in interdendritic spacings. Once 3D ultrasounds were applied, the primary γ1 phase was refined into small equiaxed grains and the secondary γ2 phase was distributed around their grain boundaries. Based on the estimation of local sound pressure and undercooling, as well as acoustic spectra examination, it is concluded that transient cavitation was the dominant reason for the formation of tiny equiaxed γ1 phase by remarkably increasing local nucleation rate, which also promoted the generation of connected γ2 phase together with acoustic streaming effect. The yield strength, ultimate strength and total elongation for ultrasonically solidified alloy sample were simultaneously enhanced by 73 %, 54 % and 13 %, which were up to 605 MPa, 845 MPa and 35 % respectively. According to LUR tests and dislocation characterization, both hetero-deformation induced (HDI) strengthening and grain refinement strengthening contributed to the increase of yield strength, while the former mainly enhanced ultimate strength and ductility synergistically. This indicates that 3D ultrasonic solidification provides an effective approach to overcoming the strength-ductility trade-off for Cu-containing HEAs.

Study on fabrication of multi-phase reinforcement coatings on Ti6Al4V by laser cladding for enhanced tribological performance

In order to improve the wear resistance, the multi-phase reinforcements coating with high hardness were fabricated on the surface of Ti6Al4V by laser cladding. In this study, Cr3C2 and Ti6Al4V powders, along with continuous fiber laser cladding in a protective gas of N2 atmosphere, were used to prepare a stepwise-solidifying-point multiphase composite coating (TiC, TiN, and CrN) on the surface of Ti6Al4V. The results showed that the crack-free coating with a coating depth of 1.24 mm and a maximum hardness of 1155.52 HV can be prepared on laser power of 900 W. As the laser power increases from 900 W to 1400 W, the combined effect of the soft α-Ti phase and the in-situ synthesized hard TiN phase on hardness results in a decrease in the maximum surface hardness at 1400 `W. And the surface hardness of Ti6Al4V after laser cladding increased by 2.80–2.68 times, and the wear rate decreased by 0.74–0.86 times. Due to the soft phase α-Ti and in-situ synthesized TiC-TiN secondary dendrites serve as the hard phase, which also serve as the supporting skeleton of the oxide film, and the coatings is enriched with TiO2 oxide film. Additionally, the wear mechanisms of Ti6Al4V include abrasive wear, adhesive wear, and oxidation wear. In contrast, the coatings primarily exhibit abrasive wear and oxidation wear.

Microstructure and phase composition of Ti-coated cBN powders intended for active coating technology (ACT) processes

Development of an active coating technology (ACT) was aimed at fabricating high strength sinters using metallized powders like in case of titanium coated cubic boron nitride (cBN). It helps to avoid inhomogeneity in distribution of the binder phase during their mixing, being the main defects in such compacts. The information concerning phase composition of the coating formed over cBN during their metallization would be of much help as it concerns setting a proper sintering temperature securing both durable fusion of boride particles and elimination of porosity. Presently, two commercial Ti coated cBN powders are available, i.e. CBN-B-TA, 6–12 µm, from Van Moppes, Switzerland and CeraMicron CM-CBN 80 Ti, 20–30 µm, from Ceratonia, Germany (coded as cBN-VM and cBN-CM, respectively). The present investigation was aimed at characterization of the coatings microstructure and phase composition, being necessary for optimising sintering procedure. The scanning and transmission electron microscopy observations backed with energy dispersive X-ray microanalysis (SEM/TEM/EDS) showed that the cBN-VM particles carried a coating of thickness varying from 50 nm to 150 nm consisting of TiB and TiN phases, while the cBN-CM ones were covered by a much thicker (∼500 nm) coating built of mostly of TiB and TiN2-type crystallites. As the columnar nitride phases formed bulk of the coatings, though at the coating/cBN substrate boundary a nano-crystalline layer of TiB phase was documented in both powders. The crystallites of boride phase were accompanied by a strings of porosity. The XRD measurements indicated also presence of small amounts of the α-Ti(N) phase, which was probably intermixed with the other phases without forming a separate sub-layer. The thinner coating, i.e. one that formed over cBN-VM powder, was contaminated with Cl and K being a residue from the molten salts synthesis (MSS) deposition, as well as some surface oxides. The gathered information makes a basis for elaboration of new generation of cBN sinters of improved properties.

The effect of Nb additions on the passive behavior of NiTi shape memory alloys

This study explores the passivity and localized corrosion behavior of Ni(100-x)/2Ti(100-x)/2Nbx shape memory alloys (where x = 3, 6, and 9 at.%) through potentiodynamic and potentiostatic polarization tests in 3.5 wt% NaCl solution. The results reveal a significant dependence of the surface passive film’s stability on the Nb concentration. Using X-ray photoelectron spectroscopy (XPS), the chemical composition of the passive films formed on the NiTiNb alloys was characterized. Microstructural analysis showed that increasing Nb content affects the volume fraction of the eutectic microconstituent, leading to the suppression of martensite and secondary Ni-Ti phases in the microstructure with higher Nb additions. The findings demonstrate that localized corrosion resistance improves with Nb additions, attributed to the incorporation of Nb2O5 into the TiO2 passive film, enhancing its protective capacity. Remarkably, the NiTi shape memory alloy exhibits immunity to localized corrosion when 9 at.% Nb is added.