Self-propagating high-temperature synthesis of TiCxNy–TiB2 ceramics from a Ti–B4C–BN system

An experimental study on direct formation of TiC_xN_y–TiB₂ ceramics by self-propagating high-temperature synthesis (SHS) was conducted using a Ti–B₄C–BN system. The effects of the C/(C + N) ratio on the combustion behavior and reaction products were investigated. Experimental characterizations of quenched samples show that the combustion reaction started with the formation of highly substoichiometric TiN_y and TiB due to the solid-state reaction between Ti and BN; and then the TiN_y precursor and TiB dissolved back into the titanium melt, forming the Ti–B–N liquid, which in turn transformed to the Ti–B–N–C liquid due to the dissolution of the carbon atoms diffused away from B₄C. Finally, the TiC_xN_y and TiB₂ particles are formed from the melt through the dissolution-precipitation mechanism.     

Effect of nickel addition on the exothermic reaction of the Ti–C–BN system

The effect of Ni addition on the exothermic reaction in the Ti–C–BN system was investigated using differential thermal analysis (DTA). Based on DTA and X-ray diffraction (XRD) analyses, a reaction path for the formation of TiC_xN_y and TiB₂ in the Ni–Ti–C–BN system was proposed in which the reaction initiated with the solid-state diffusion between Ti and BN. The resultant TiN_x then reacted with Ni to form Ni–Ti compounds (e.g., Ti₂Ni). With increasing temperature, a Ni–Ti–N eutectic liquid phase formed between the Ni–Ti compounds and TiN_x at about 1110 °C, enabling the dissolution of C and B in the melt to form Ni–Ti–N–C–B liquid. Finally, TiC_xN_y and TiB₂ formed and precipitated out of the liquid.     

Microstructure and grain refining performance of a new Al–Ti–C–B master alloy

A kind of Al–Ti–C–B master alloy with a uniform microstructure is prepared using a melt reaction method. It is found that the average grain size of α-Al can be reduced from 3500 to 170 μm by the addition of 0.2 wt.% of the prepared Al–5Ti–0.3C–0.2B and the refining efficiency does not fade obviously within 60 min. It is considered that the TiC_xB_y and TiB_2−mC_n particles found at the grain center are the effective and stable nucleating substrates for α-Al during solidification, which accounts for the good grain refining performance.     

Combustion synthesis of TiC–TiB2 composites

An experimental study on formation of TiC–TiB₂ in situ composites with a broad range of compositions was conducted by self-propagating high-temperature synthesis (SHS) using the reactant compacts from different combinations of Ti, B₄C, C, and B powders. Direct reaction of Ti with B₄C at stoichiometry of Ti:B₄C = 3:1 yields a TiB₂-rich composite with TiC:TiB₂ = 1:2. Formation of the products containing 20, 33.3, and 50 mol% of TiB₂ was achieved by the Ti–B₄C–C reactants. In addition, the test specimen composed of Ti, B₄C, and B was employed for the synthesis of a composite with 80 mol% TiB₂. Among three different types of the powder compacts, the boron-containing sample was characterized by the fastest combustion wave and the highest reaction temperature. The lowest combustion temperature and wave velocity were observed in the Ti–B₄C compact. When fine Ni particles were added to the Ti–B₄C reactant, it was found that the propagation rate of the reaction front was increased and the densification of the end product was enhanced significantly. This was attributed to formation of the Ti–Ni eutectic liquid during the reaction. As a result, the relative density of a TiC + 2TiB₂ composite increases from 30 to 86% with the Ni content from 0 to 20 mol%. Based upon the XRD analysis, small amounts of TiNi₃ and TiB were detected in the Ni-reinforced TiC–TiB₂ composites.     

Wear-resistant Ti–B–N nanocomposite coatings synthesized by reactive cathodic arc evaporation

Wear-resistant Ti–B–N coatings have been synthesized by reactive arc evaporation of Ti–TiB₂ compound cathodes in a commercial Oerlikon Balzers Rapid Coating System. Owing to the strong non-equilibrium conditions of the deposition method, a TiN–TiB_x phase mixture is observed at low N₂ partial pressures, as determined by elastic recoil detection analysis, X-ray diffraction, X-ray spectroscopy, transmission electron microscopy and selected area electron diffraction. The indicated formation of a metastable solid solution of B in face-centered cubic TiN gives rise to a maximum in hardness (>40 GPa) and wear resistance on the expense of increased compressive stresses. A further saturation of the nitrogen content results in the formation of a TiN–BN nanocomposite, where the BN phase fraction was tailored by the target composition (Ti/B ratio of 5/3 and 5/1). However, the amorphous nature of the BN phase does not support self-lubricious properties, showing friction coefficients of 0.7 ± 0.1 against alumina. The effect of an increased bias voltage on structure and morphology was investigated from −20 to −140 V and the thermal stability assessed in Ar and air by simultaneous thermal analysis up to 1400 °C.     

Effect of Ni content on the compression properties and abrasive wear behavior of the (TiB2–TiCxNy)/Ni composites

The (TiB₂–TiC_xN_y)/Ni composites were fabricated by the method of combustion synthesis and hot press consolidation in a Ni–Ti–B₄C–BN system. The effect of Ni content on the microstructure, hardness, compression properties and abrasive wear behavior of the composites has been investigated. The results indicate that with the increase in Ni content from 30 wt.% to 60 wt.%, the average size of the ceramic particles TiB₂ and TiC_xN_y decreases from 5 μm to ≤ 1 μm, while the hardness and the abrasive wear resistance of the composites decrease. The composite with the Ni content of 30 wt.% Ni possesses the highest hardness (1560.8 Hv) and the best abrasive wear resistance. On another hand, with the increase in the Ni content, the compression strength increases firstly, and then decreases. The composite with 50 wt.% Ni possesses the highest compression strength (3.3 GPa). The hardness and fracture strain of the composite with 50 wt.% Ni are 1251.2 Hv and 3.9%, respectively.     

Characterization and blood compatibility of TiCxN1 − x hard coating prepared by plasma electrolytic carbonitriding

A novel technique to form Ti(C, N) on titanium, named as plasma electrolytic carbonitriding (PEC/N) on cathode was successful used to prepare TiC_xN_1 − x coating. The structure, composition and morphology of the coating were characterized by XRD, XPS and SEM, respectively. The results indicated that TiC_0.3N_0.7 as a new species appears on the surface of the titanium plate, and the thickness of the coating with porous surface morphology increases with the treated time. The blood compatibility of the TiC_0.3N_0.7 coating was evaluated by haemolysis ratios, dynamic blood clotting test, plasma recalcification time and platelet adhesion. The results indicated that the blood compatibility of the plasma-treated titanium with TiC_xN_1 − x coating is significantly improved as compared to the original titanium. Additionally, the results derived from measurements of hardness and corrosion indicated that the coating has excellent mechanical and corrosion-resistant properties.     

Forming carbonitride coatings on titanium by thermochemical treatment with C-N-O-containing media

The formation of TiC_xN_y coatings on titanium alloys through thermochemical treatment of graphite in nitrogen was investigated in this study. The presence of oxygen in saturating media was found to lower the nitrocarburizing temperature from 1,100°C to 850°C. Two methods to accumulate oxygen in a saturating medium have been proposed: using oxygen-containing nitrogen or oxygensaturated graphite. The sequence of stages of carbonitride formation in the Ti-C-N-O system is explained in this paper.     

Corrosion behaviour of laser gas nitrided Ti–6Al–4V in HCl solution

Laser surface nitriding of Ti–6Al–4V alloy was carried out with a Nd:YAG pulsed laser. The microstructure and corrosion behaviour of the nitrided samples were examined, using SEM, XRD, XPS, and anodic polarization tests in 2 M HCl solution. Laser nitriding produced a thin continuous TiN layer followed by TiN dendrites and TiN_0.3 needles. The laser nitrided specimen exhibited less corrosion current density, passivated more readily and also, maintained a lower current density over the duration of the experiment. This was correlated with the formation of very thin, continuous TiN_xO_y film, which could retard chloride ions ingress into the substrate.     

Raman spectroscopy investigations of TiBxCyNz coatings deposited by low pressure chemical vapor deposition

TiB_xC_yN_z coatings have been prepared applying LPCVD and characterized using SEM/EDX, XRD, and Raman micro-spectroscopy. It has been shown that first-order, defect-induced Raman spectra of good quality can be obtained from TiB_xC_yN_z coatings, even if buried within a multilayer stack. The Raman peak assignments fit well with previous work on TiC_1 − xN_x. Even small changes in the B:C:N ratio result in systematical shifts of the Raman peaks. With increasing nitrogen content, the acoustical phonons shift to lower frequencies. A high correlation of the Raman shifts with lattice constants derived from XRD has also been found. Additionally, intensity and FWHM of the Raman peaks also change going from carbon- to nitrogen-rich coatings. The sensitivity of the TA peak Raman shifts to changes of the investigated basic coating properties is largest for N-rich coatings. Looking at the full range of coatings the dependence of the Raman shifts is slightly nonlinear.The present work establishes Raman microscopy as a complementary non-destructive technique compared to XRD for studying coatings like TiB_xC_yN_z. Structural, optical and chemical properties can be determined with considerably higher spatial resolution.     

Magnetic anisotropy of Ho–Fe–Co–Cr intermetallic compounds

Starting with a Ho₃(Fe_1−xCo_x)_29−yCr_y, (x,y) = (0.6,4.5) and (0.8,5.5) nominal stoichiometry, a disordered variant of the hexagonal 2:17 phase (Th₂Ni₁₇-type, S.G. P6₃/mmc) occurs, since both the monoclinic 3:29 and the transition-metal-rich disordered Th₂Ni₁₇-type hexagonal compounds have the same rare earth to transition metal ratio, 1:9.7. The magnetic properties and the magnetocrystalline anisotropy of these compounds have been investigated. The anisotropy constant, K's, and the anisotropy field, μ₀H_A, values have been deduced from the magnetization curves measured on powder samples magnetically aligned in a rotating magnetic field. The compound with (x,y) = (0.8,5.5) shows a compensation point at about 55 K. The magnetic anisotropy of both compounds is that of easy-plane from room temperature to low temperatures down to 5 K.     

Titanium carbonitrides in steels alloyed with tungsten and molybdenum

Conclusions The possibility of tungsten dissolving in titanium carbonitride present in the steel is confirmed by two factors: 1) the solubility of tungsten in titanium carbide, established in the binary WC-TiC system [4–7]; 2) the existence of four phases with the same type of structure and similar lattice constants in the Ti–W–C–N system (a=4.33 Å for TiC,a=4.24 Å for TiN,a=4.27 Å for W₂C,a=4.126 Å for W₂N [7]).Considering the affinity of tungsten and molybdenum and their interchangeability in carbides of other types, one would expect partial replacement of titanium, with molybdenum in carbonitrides. The solubility of tungsten and molybdenum in titanium carbonitride was demonstrated in two steels of different types — austenitic steel 417455 and pearlitic steel T 67. In steel T60 with 13% Cr, however, neither tungsten nor molybdenum was found in the carbonitride. Consequently, it can be assumed that the solution of tungsten and molybdenum in Ti(C, N) is also determined by the properties of the metallic matrix and the treatment or primary cooling conditions of the steel. This determines whether or not tungsten or molybdenum partially replaces titanium in carbonitride.Skoda, Pilsen, Czechoslovakia. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 60–62, September, 1978.     

Niobium–aluminum oxynitride prepared by ammonolysis of oxide precursor obtained through the citrate route

Oxynitrides in the (Nb_1−xAl_x)(O,N) quaternary system were prepared by ammonolysis of oxide precursor obtained through the citrate route. The products at 1000 °C were a mixture of Nb(N,O) and NbN_0.95 at the niobium end (x = 0) and amorphous Al(O,N) at the aluminum end (x = 1). A new cubic compound (A) appeared mixed with Nb(N,O) in the compositional range 0.1 ≤ x ≤ 0.4. Its almost pure product was obtained at x = 0.5. The X-ray diffraction pattern was rock salt type (Nb_0.56Al_0.44)(O_0.38N_0.37□₀₂₅) in F_m−3m with a = 0.43481(1) nm. The product showed superconductivity with T_c = 15 K. Its crystallinity was much improved and its superconducting volume fraction increased to 32% after its thermal annealing at 1100 °C in evacuated sealed tube. A second cubic compound (B), rock salt type Nb[(O,N)_0.85□_0.15] with a = 0.434 nm, was observed mixed with amorphous Al(O,N) in the as-prepared products of the range 0.6 ≤ x ≤ 0.9.     

Pressure–composition–temperature hysteresis in C14 Laves phase alloys: Part 2. Applications in NiMH batteries

This part of our series of papers reports our efforts to predict sealed cell cycle life from lattice constant a/c ratio and/or PCT hysteresis based on correlations established from our previous studies reported in Part 1. In the case of Ti₂₁Zr_12.5V₁₄Ni_21.5−xCr₁₀Mn₂₁Sn_x alloys, as x is increased the a/c ratio increases and the PCT hysteresis decreases resulting in extended cycle life for the battery. This is in agreement with the results from Part 1. In the case of Ti₁₈Zr_15.5V₁₄Ni_24.2−xCr₁₀Mn_18−ySn_0.3Co_xAl_y alloys, the a/c ratio trend was not observed due to existence of more than one C14 phase, but the correlation between PCT hysteresis and cycle life was maintained. In the case of Ti₂₁Zr_12.5V₁₀Ni_40.2Cr_8.5−xMn_5.6−yCo_1.5+x+yAl_0.4Sn_0.3 alloys, the cycle life was dominated by the corrosive nature of the alloy affected by the Cr content. As a consequence, predictions from a/c ratio and PCT hysteresis can only be applied to the degree of pulverization in gas phase cycling and not to the sealed cell cycle life.     

Mechanical alloyed Ti–Cu–Ni–Si–B amorphous alloys with significant supercooled liquid region

This study examined the glass formation range of Ti_94–x–yCu_xNi_ySi₄B₂ alloy powders synthesized by mechanical alloying technique. According to the results, after 5–7 h of milling, the mechanically alloyed powders were amorphous at compositions with (x+y) equal to 20–40%. For the compositions with (x+y) larger than 45% or smaller than 10%, the structure of ball-milled powders is a partial amorphous single phase or coexistent partial amorphous and crystalline phases, respectively. The thermal stability of the amorphous powders was also investigated by differential thermal analysis. As the results demonstrated, several amorphous powders were found to exhibit a wide supercooled liquid region before crystallization. The temperature interval of the supercooled liquid region defined by the difference between T_g and T_x, i.e. ΔT(=T_x–T_g), are 52 K for Ti₇₄Ni₂₀Si₄B₂, 74 K for Ti₆₄Ni₃₀Si₄B₂, 58 K for Ti₆₄Cu₂₀Ni₁₀Si₄B₂, and 61 K for Ti₇₄Cu₁₀Ni₁₀Si₄B₂.     

Structural and magnetic susceptibility studies of samarium substituted magnesium–zinc ferrites

Polycrystalline soft ferrites Mg_1−x–Zn_x–Fe_2−y–Sm_y–O₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0; y = 0.0, 0.05 and 0.1) were prepared by usual ceramic method. The samples were characterized by X-ray diffraction and IR techniques. Magnetic properties have been studied from magnetization and (a)–(c) susceptibility measurements. The XRD patterns of all the samples reveal the formation of single-phase cubic spinel. The IR spectra show two strong absorption bands in the frequency range 300–800 cm⁻¹. The magnetization measurements exhibit the Neel's collinear ferrimagnetic behavior for x ≤ 0.2 and suggest non-collinear Y–K (Yaffet–Kittel) type magnetic ordering for x ≥ 0.4. The samples with x ≥ 0.8 are paramagnetic at and above the room temperature. Variation of ac susceptibility with temperature exhibit the single domain structure (SD) with x = 0.0 and multi-domain (MD) structure with x ≥ 0.2 on substitution of Zn²⁺ content. On substitution of Sm³⁺ content, the samples exhibit SD for x = 0.0, MD for x = 0.2 and MD to SP transition for x ≥ 0.4.     

Structure, microstructure and electrical properties of (1 − x − y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBi0.5Li0.5TiO3 lead-free piezoelectric ceramics

The ternary system (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBi_0.5Li_0.5TiO₃ (abbreviated to BNKLT-x/y) was synthesized by conventional oxide-mixed method. The phase structure, microstructure, and dielectric, ferroelectric and piezoelectric properties of the ceramics were investigated. The X-ray diffraction patterns showed that pure perovskite phase with rhombohedral structure can be obtained in all the ceramics. The grain size varied with x and y. The temperature dependence of dielectric constant and dielectric loss revealed there were two phase transitions which were from ferroelectric (tetragonal) to anti-ferroelectric (rhombohedral) and anti-ferroelectric to paraelectric (cubic). Either increasing x or y content can make T_m (the temperature at which dielectric constant _r reaches the maximum) increase. With the addition of Bi_0.5K_0.5TiO₃, the remanent polarization P_r increased but the coercive field E_c decreased. With the addition of Bi_0.5Li_0.5TiO₃, P_r increased obviously and E_c increased slightly. Due to the stronger ferroelectricity by modifying Bi_0.5K_0.5TiO₃ and Bi_0.5Li_0.5TiO₃, the piezoelectric properties were enhanced at x = 0.22 and y = 0.10, which were as follows: P_r = 31.92 μC/cm², E_c = 32.40 kV/cm, _r = 1118, tan δ = 0.041, d₃₃ = 203 pC/N and K_p = 0.31. The results show that the BNKLT-x/y ceramics are promising candidates for the lead-free materials.     

Effects of Nb and C additions on the crystallization behavior, microstructure and magnetic properties of B-rich nanocrystalline Nd–Fe–B ribbons

The effects of Nb and C additions on the crystallization behavior, microstructure and magnetic properties of B-rich Nd_9.4Fe_79.6−xNb_xB_11−yC_y (x = 0, 2, and 4; y = 0, 0.5, and 1.5) alloy ribbons have been investigated. The results show that Nb and C additions change the crystallization behavior of Nd_9.4Fe_79.6B₁₁, avoid the formation of metastable Nd₂Fe₂₃B₃ phase, leading to the simultaneously precipitation of α-Fe and Nd₂Fe₁₄B phases. The results also show that Nb and C additions suppress the formation and growth of the soft α-Fe phases, leading to the presence of a large amount of Nd₂Fe₁₄B phases. Nb and C additions also refine the structure, and thus increase the exchange coupling interaction between the soft and hard phases. Excellent magnetic properties of B_r = 0.85 T, _iH_c = 1106 kA/m, and (BH)_max = 117 kJ/m³ have been achieved in Nd_9.4Fe_75.6Nb₄B_10.5C_0.5 alloy ribbons.     

Self-propagating high-temperature synthesis with post-heat treatment of La1−xSrxFeO3 (x = 0–1) perovskite as catalyst for soot combustion

La_1−xSr_xFeO₃ (x = 0–1) perovskite, Sr-substituted LaFeO₃, was prepared by Self-propagating high-temperature synthesis (SHS) and its catalytic activity for soot combustion was experimentally examined in comparison with that of a conventional Pt/Al₂O₃ catalyst. The products were also characterized by XRD, FE-SEM, and BET specific surface area. The XRD analysis revealed that all the products had a perovskite phase as the major compound, together with intermediate phases with higher x values (x = 0.7–1). The BET specific surface area of the products increased with x. Moreover, the catalytic activity for soot combustion also increased with x, wherein the BET specific surface area appeared an appropriate index for explaining the observed activity. The sample with x = 0.8 exhibited the highest activity for soot combustion among all the SHS products. The soot combustion temperature of this product was as much as 100 °C lower than that of non-catalytic soot combustion. In other words, it had the same activity as that at only 20 °C higher, in comparison to conventional Pt/Al₂O₃ catalyst. More significantly, average apparent activation energy of sample with x = 0.8 calculated by Friedman method using TG/DTA was approximately 15 kJ/mol lower than that of Pt/Al₂O₃ catalyst. This result suggested that La_1−xSr_xFeO₃ has the possibility to be an alternative catalyst to Pt/Al₂O₃ catalyst.     

Preparation of Ti–Al–Si alloys by reactive sintering

The isothermal section of the Dy–Co–Ti system at 500 °C has been investigated in the whole composition range by means of X-ray diffraction, thermal analysis, scanning electron microscopy and energy dispersive X-ray spectroscopy. The only ternary phase DyTi_xCo_12−x is of ThMn₁₂-type structure, space group I4/mmm, and shows a small homogeneity range of 1 ≤ x ≤ 1.6. The lattice parameters for DyTi_xCo_12−x with 1 ≤ x ≤ 1.56 are a = 0.8336(4)–0.8402(1) nm and c = 0.4691(3)–0.4727(1) nm. Along a constant Dy concentration, the solid solubilities of Ti in the compounds Dy₂Co₁₇, DyCo₃, DyCo₂ and Dy₃Co are about 2.0, 2.0, 3.0 and 4.0 at.%, respectively. The TiCo phase has a homogeneity range of 50–54 at.% Co at 500 °C and dissolves up to 2.0 at.% Dy.