Mechanical properties of austenitic stainless steel with high niobium contents

To better understand the influence of the microstructural characteristics on the mechanical properties of Fe-Cr₂₂-Ni₂₅-Nb_x austenitic stainless steel (ASS-Nb_x), the mechanical properties were investigated. Nb addition was conducted with four different amounts: 0, 0.29, 0.58 and 0.86%. With the increasing Nb content, the mean grain size for the Fe-Cr-Ni-based alloys decreased, while the size of Nb precipitate increased. Owing to the different microstructural characteristics, their mechanical properties were altered. The highest tensile strength was obtained for ASS-Nb_0.29 alloy. However, with the increasing Nb content in ASS-Nb_0.29–0.86 alloys, the tensile strength decreases despite the grain refinement. The mechanical properties of the ASS-Nb alloys were influenced by the Nb precipitation hardening and the grain boundary cohesive strength, arising from the size of Nb precipitations.     

Effect of composition on the crystallization and magnetic properties of Fe–Co–Si–B–Nb amorphous alloys

The crystallization behavior and magnetic properties of Fe₆₂Co₁₀Si_15−x B_18−y Nb_{(x + y)−5} amorphous alloys with x = 0–5 and y = 0–5 were examined. Primary crystallization temperature of Fe₆₂Co₁₀Si_15−x B₁₃Nb _x and Fe₆₂Co₁₀Si₁₀B_18−y Nb _y alloys increased with the addition of Nb. The primary and secondary crystallization temperatures were well separated when the Nb content is above 4 at%. The alloys with 15–18 at% B showed a distinct supercooled region. The Nb addition decreased the Curie temperature as well as room temperature saturation magnetization. The glassy-type Fe₆₂Co₁₀Si₁₀B₁₈ alloy exhibited good soft magnetic properties as well as a supercooled liquid region of 39 K. The finding of the glassy-type Fe-based alloy without Nb element exhibiting high Bs above 1.4 T is promising for future use as a soft magnetic glass material.     

Crystallization characteristics of an amorphous Nb81Si19 alloy under high pressure and formation of the A15 phase

Amorphous Nb-19 at% Si alloy, prepared by rapid quenching from the molten state, was annealed while being subjected to a pressure of 10 GPA. X-ray diffraction investigations on the alloy specimens quenched to ambient conditions have shown that pressure greatly alters the crystallization characteristics and the cubic A15 (Nb₃Si)-phase forms in preference to the tetragonal Nb₃Si-phase at temperatures in the range from 710° C to 800° C. Up to 680° C, the component atoms do not show any tendency towards ordering upon crystallization and the body-centred tetragonal solid solution forms; while, at 830° C, niobium atoms diffuse to form the body-centred cubic Nb precipitates. Superconducting properties have been measured for the single-phase A15 structure with the lattice parametera=0.5155 nm with the results that the transition temperature,T _C, is 3.4 K and the temperature coefficient of the upper critical field,H _C2, is 1.2 MA m^–1 K^–1 (15 kOe K^–1).     

Microstructure evolution and mechanical properties of Nb-alloyed Cu–Zr–Al–Ni large-sized metallic glass composites

The effects of Nb on the microstructures and mechanical properties of large-sized (Cu_0.47Zr_0.47Al_0.06)_99???xNi₁Nb_x (x?=?0, 0.5, 1, 2?at.-%) bulk metallic glass composites were investigated. It is verified that the liquidus temperature (T_l) of the Nb-added alloys decreases to cause the increase of glass-forming ability (GFA). The addition of Nb adjusts the distribution and the volume fraction of B2-CuZr phase in the Cu–Zr–Al–Ni large-sized composites by changing the GFA of the alloys. The mechanical properties of the composites strongly depend on the volume fraction and distribution of B2-CuZr phase in the glassy matrix. The alloy with 0.5?at.-% Nb addition exhibits the high mechanical properties, which should be attributed to the uniform distribution and the proper volume fraction of B2-CuZr phase in the glassy matrix.     

Study on crystallization behavior and microstructure of melt-spun Nd2(Fe,Nb)14B/α-Fe alloys

The effects of Nb addition on the crystallization behavior, microstructure, and magnetic properties of melt-spun Nd₂Fe₁₄B/α-Fe nanocomposite magnets have been studied. The addition of Nb can significantly improve the thermal stability of amorphous phase in as-spun alloys, narrow the range between the onset crystallization temperature and the optimal annealing temperature, restrain the initial formation and growth of α-Fe and Nd₂Fe₁₄B. A finer and more homogeneous microstructure can be obtained in the Nb-doped alloy than in the Nb-free alloy. And the Nb addition makes the grains more equiaxed shape. The Nd₁₀Fe₈₃Nb₁B₆ alloy annealed at 715 °C for 10 min exhibits the improved magnetic properties, B _r = 0.90 T, _i H _c = 750 kA/m, (BH)_max = 120 kJ/m³, the intrinsic coercivity and the maximum energy product increase by 25% and 14%, compared with the Nd₁₀Fe₈₄B₆ alloy.     

Effect of addition of Al and Cu on the properties of Sn–20Bi solder alloy

This study investigates the effect of the composite addition of Al and Cu on the microstructure, physical properties, wettability, and corrosion properties of Sn–20Bi solder alloy. Scanning electron microscopy and X-ray diffraction were used to identify the microstructure morphology and composition. The spreading area and contact angle of the Sn–20Bi–x (x?=?0, 0.1 wt% Al, 0.5 wt% Cu, and 0.1 wt% Al–0.5 wt% Cu) alloys on Cu substrates were used to measure the wettability of solder alloys. The results indicate that the alloy with 0.1 wt% Al produces the largest dendrite and the composite addition of 0.1 wt% Al and 0.5 wt% Cu formed Cu₆Sn₅ and CuAl₂ intermetallic compounds in the alloy structure. And the electrical conductivity of Sn–20Bi–0.1Al is the best, which reaches 5.32 MS/m. The spread area of the solder alloy is reduced by the addition of 0.1 wt% Al and 0.5 wt% Cu, which is 80.7 mm². The corrosion products of Sn–20Bi–x solder alloys are mainly lamellar Sn₃O(OH)₂Cl₂ and the corrosion resistance of 0.1 wt% Al solder alloy alone is the best. The overall corrosion resistance of Sn–20Bi–0.1Al–0.5Cu is weakened and the corrosion of solder alloy is not uniform.

     

Optimization of annealing treatment and comprehensive properties of Cu-containing Ti6Al4V-xCu alloys

The Ti6Al4V-Cu alloy was reported to show good antibacterial properties, which was promising to reduce the hazard of the bacterial infection problem. For the purpose of preparing Ti6Al4V-Cu alloy with satisfied comprehensive properties, it’s important to study the heat treatment and the appropriate Cu content of the alloy. In this study, high Cu content Ti6Al4V-xCu (x = 4.5, 6, 7.5 wt%) alloys were prepared, and firstly the annealing heat treatments were optimized in the α+β+Ti₂Cu triple phase region to obtain satisfied tensile mechanical properties. Then the effect of Cu content on the tribological property, corrosion resistance, antibacterial activity and cytotoxicity of the Ti6Al4V-xCu alloys were systematically studied to obtain the appropriate Cu content. The results showed that the optimal annealing temperatures for Ti6Al4V-xCu (x = 4.5, 6, 7.5 wt%) alloys were 720, 740 and 760 °C, respectively, which was resulted from the proper volume fractions of α, β and Ti₂Cu phases in the microstructure. The additions of 4.5 wt% and 6 wt% Cu into the medical Ti6Al4V alloy could enhance the wear resistance and corrosion resistance of the alloy, but the addition of 7.5 wt% Cu showed an opposite effect. With the increase of the Cu content, the antibacterial property was enhanced due to the increased volume fraction of Ti₂Cu phase in the microstructure, but when the Cu content was increased to 7.5 wt%, cytotoxicity was presented. A medium Cu content of 6 wt%, with annealing temperature of 740 °C make the alloy possesses the best comprehensive properties of tensile properties, wear resistance, corrosion resistance, antibacterial property and biocompatibility, which is promising for future medical applications.     

Effects of Nb doping on microstructure and properties of Bi4Ti3?xNbxO12 thin films prepared by magnetron sputtering

Bi₄Ti_3−xNb_xO₁₂ ferroelectric thin films were fabricated on p-Si substrates by magnetron sputtering. The effects of Nb doping on microstructure and properties of Bi₄Ti_3−xNb_xO₁₂ films were investigated. Bi₄Ti_3−xNb_xO₁₂ films had the same structure as Bi₄Ti₃O₁₂ with smaller and more uniform grains. The dielectric and ferroelectric properties of Bi₄Ti_3−xNb_xO₁₂ films were improved by Nb doping. Bi₄Ti_3−xNb_xO₁₂ films have better dielectric and ferroelectric properties with P _r = 16.5 μC/cm², E _C < 100 kV/cm, ε _r > 290, low dielectric loss (<0.9%) and clockwise C–V curves with a memory window of 0.9 V when x = 0.03–0.045, while an excessive Nb doping would lead to bad dielectric and ferroelectric properties.     

Nb添加对Ti基非晶合金腐蚀及力学性能的影响

为研究微量添加Nb元素对Ti_(40)Zr_(10)Cu_(34-x)Pd_(14)Sn_2Nb_x(x为原子数分数,x=0、1%、3%、5%)非晶合金的耐腐蚀性能及力学性能的影响,本文利用动态极化曲线,分析了在0.144 mol/L的NaCl溶液及0.2 mol/L的PBS溶液中非晶合金Ti_(40)Zr_(10)Cu_(34-x)Pd_(14)Sn_2Nb_x(x=0、1%、3%、5%)的电化学性能,并通过材料拉伸试验研究了非晶合金块状样品的室温压缩性能.结果表明:在0.144 mol/L的NaCl溶液中,非晶合金样品在阳极区出现了自发钝化的特征,钝化电流密度在10~(-7)～10~(-8) A/cm~2,钝化电流密度随着Nb的添加略有降低,且点蚀电位随Nb原子数分数的增加分别为200、340、400和490 mV,说明微量添加Nb元素能有效提高Ti基非晶合金的耐点蚀能力,即在0.144 mol/L的NaCl溶液中Ti基非晶合金的耐腐蚀性随着Nb含量的增加而增强;在0.2 mol/L的PBS溶液中,因磷酸根离子的缓蚀作用,Nb添加导致的成分变化对非晶合金的腐蚀行为影响不大;此外,添加了原子数分数为1%及3%Nb的非晶合金,其压缩强度及塑性变形能力变化不大,但添加5%Nb的非晶合金因较大体积分数纳米晶的存在导致其室温断裂强度及塑性变形能力有明显下降.     

TiH2-based Ti-1Al-8V-5Fe PM alloys with different addition methods of alloying elements

The powder metallurgy high-strength Ti-1Al-8V-5Fe alloy (Ti-185 alloy) was investigated in this paper with different addition methods of alloying elements, Al, V, Fe pure elements powder (EP) or 1Al-8V-5Fe ternary master alloy powder (MAP), based on TiH₂ powders at the sintering temperature from 1150 to 1350°C. The results indicate that the Ti-185 alloy with the 1Al-8V-5Fe master alloy (Ti-185 MAP alloy) possesses the higher relative sintered density, less oxygen content, and less α-phase volume fraction versus the Ti-185 alloy with Al, V, and Fe pure elements (Ti-185 EP alloy). No matter where the sintering temperature is 1150, 1250, or 1350°C, Ti-185 MAP alloy invariably has the higher yield strength and hardness which have a strong relationship to its higher density and less volume fraction of softer α-phase in comparison with Ti-185 EP alloy.     

Bistability of hydrogen donors in proton-implanted GeSi alloy

Shallow hydrogen donors (H-donors) were formed in a Ge_{1 − x} Si _x (x = 0.012) alloy by the implantation of low-energy protons followed by heat treatment at 275°C The electrical properties of these donors have been studied using the method of capacitance-voltage characteristics. It is established that a certain fraction of the H-donors exhibit bistability, whereby their concentration changes reversibly when the sample temperature is cycled within 100–200°C. The properties of reversible H-donors in germanium are analogous to those of the bistable H-donors in silicon.     

Creep behaviour of hot isostatically pressed niobium alloy powder compacts

A commercial (C103) niobium-base metal alloy (Nb + 10wt% Hf + 1 wt% Ti) has been successfully manufactured from powders by a duplex hipping process. The microstructure, room temperature tensile properties and creep properties of this powder-source alloy compare favourably with wrought material. At high temperatures the creep behaviour of the alloy was found to be typical of that of Class 1 solid solution alloys (glide controlled), and over the temperature range 1400 to 1700 C it can be described accurately using the measured values of stress dependence and activation energy. The large ductility exhibited by this alloy at high temperature is discussed in terms of its strain-rate sensitivity.     

Crystal growth and transport properties of α- and γ-phase NaxCoO2

The Na_xCoO₂ single crystals with γ- and α-phase structure were grown by an electro-crystallization of high temperature solution (EHTS) method. X-ray diffraction studies showed that γ-phase Na_xCoO₂ crystals were grown from a flux of pure NaOH, and α-phase Na_xCoO₂ crystals were grown from a mixed flux of NaOH with a small amount of SrCO₃. The in-plane electrical resistivity of γ-phase Na_xCoO₂ decreases with decreasing temperature (T), exhibiting the metal-like properties, while that of α-phase Na_xCoO₂ increases with decreasing temperature, exhibiting the semiconductor-like properties. The thermoelectric power S(T) at 300 K is 80 μV/K and 30 μV/K for γ- and α-phase Na_xCoO₂, respectively, and both decrease with decreasing temperature. R_H of γ-phase Na_xCoO₂ shows anomalous temperature dependence.     

Phase formation, sintering behavior and microwave dielectric properties of bismuth and manganese co-doped [(Pb, Ca) La](Fe, Nb)O3+δ solid solution

The phase formation, sintering behavior and microwave dielectric properties of Bi₂O₃ and MnO₂ co-doped [(Pb, Ca) La](Fe, Nb)O_3+δ (PCLFN) ceramics were investigated. The Bi₂O₃ and MnO₂ binary dopants formed stable and low melting temperature solubilities at grain boundary which resulted in an effectively lowered sintering temperature by about 140 °C a more rapid sintering process and enhanced bulk densities. Sintering procedure has significant effect on grain size and porosities in ceramics. With high sintering temperature and time, the evaporation of PbO scaled up from surface toward the bulk and resulted in a Pb²⁺ deficient layer up to 0.25 mm depth under ceramic surface. Investigation of sintering dynamic revealed that either volume diffusion or second-order interface mechanism controlled the grain growth in present system. An optimal microwave dielectric properties of ε_r = 91.1, Q _f = 4,870 GHz and τ _f = 18.5 ppm/°C could be obtained in Bi₂O₃ and MnO₂ co-doped [(Pb, Ca) La](Fe, Nb)O_3+δ ceramics sintered at 1,050 °C for 4 h when the quality ratio of Bi₂O₃/MnO₂ was 1 and the doping content w = 1 wt%.     

Tantalum influence on electrical properties of lead-free (K0.4425Na0.52Li0.0375)(Nb0.93?xTaxSb0.07) O3 piezoelectric ceramics

Lead-free (K_0.4425Na_0.52Li_0.0375)(Nb_0.93−x Sb_0.07Ta _x )O₃ (abbreviated as KNLNST _x ) piezoelectric ceramics with x = 0.045–0.075 have been prepared by an ordinary sintering technique with sintering temperature at 1,120 °C. The results of X-ray diffraction reveal that Ta⁵⁺ has diffused into the perovskite lattice to form a solid solution. The grain growth of the ceramics was inhibited by substituting Ta⁵⁺ for Nb⁵⁺. It has been shown that the substitution of Ta decreases Curie temperature T _C and orthorhombic-tetragonal phase transition temperature T _O-T. Besides, the dependence of the ceramics with different Ta content on the dielectric, piezoelectric and ferroelectric properties has been investigated. The results indicate that Ta substitution provides “soft” piezoelectric characteristics, owing to improvements in d ₃₃, k _p and ε _r and a decease in Q _m. For the ceramics with x = 0.06, the piezoelectric coefficient d ₃₃ becomes maximum at a value of 270 pC/N, while the other electrical properties remain reasonably high: dielectric constant ε _r = 1,577, planar mode electromechanical coupling factors k _p = 0.4, Curie temperature T _C = 252 °C and the remanent polarization P _r = 16.03 μC/cm². These results show that (K, Na, Li) (Nb, Sb)O₃ ceramics with small amount of Ta (x <8 mol%) are good lead-free piezoelectric ceramic.     

Synthesis and Properties of La2(Mo1 – x M x )2O9 (M = Nb, Ta) Ionic Conductors

La₂(Mo_{1 – x} M _x )₂O₉ (M = Nb, Ta; 0 < x 0.2) solid solutions were prepared, and their physicochemical and electrical properties were studied. Second harmonic generation measurements indicate that the solid solutions have a noncentrosymmetric structure and undergo a structural phase transition accompanied by a sharp increase in ionic conductivity, similar to that of La₂Mo₂O₉. The transition temperature is found to decrease with increasing Nb or Ta content. The introduction of 5 wt % Nb increases the 800°C conductivity of the material.     

An experimental investigation of phase transformation superplastic diffusion bonding of titanium alloy to stainless steel

The solid-state direct diffusion bonding of a near α-phase titanium alloy to an austenitic stainless steel by means of the phase transformation superplasticity (PTSP) caused by the cycles of heating and cooling has been carried out. The test results showed that, under the conditions of T_max = 890°C, T_min = 800°C, cyclic number of heating and cooling N = 10 cycles, specific pressure P = 5 MPa, heating rate V_h = 30°C/s and cooling rate V_c = 10°C/s, the ultimate tensile strength of the joint reached its maximum value (307 MPa), and the bonding time was only 120 s. In the phase transformation superplastic state, the deformation of titanium alloy has a character of ratcheting effect and it accumulates with the cycles of heating and cooling. The observations of tensile fracture interface showed that both the brittle intermetallic compound (FeTi) and the solid solution based on β-Ti were formed on the interface, and the more in quantity and the smaller in size the solid solutions are, the higher the ultimate tensile strength is.     

The effects of carbon on the magnetic properties of nanocrystalline Fe-based alloys

We investigate the magnetic properties of nanocrystalline Fe_73.5Cu₁M₃Si_13.5B₉ (M=Nb or Mo) alloys when C is substituted for B up to 2 at%. It is found that the permeability and coercivity deteriorate with the content of C in the case of both M=Nb and Mo. The saturation magnetization also deteriorates as C is substituted for B in the case of M=Mo but it improves linearly with the C content in the case of M=Nb. This increase in the saturation magnetization of the Fe-Cu-Nb-Si-B alloy with C addition can provide an opportunity to overcome one of the main disadvantages, low magnetic flux density, of the alloy. In the latter part of the work we also investigate the magnetic properties of Fe_76.5–y Cu₁Nb_y (Si_0.5B_0.4C_0.1)_22.5 (0y3) alloys, particular emphasis being given to the role of Nb in the presence of C. It is found that C may help Nb to suppress the growth of -Fe grains in the alloy.     

Effect of electropulsing on the precipitation of NbC x N1−x from austenite phase

The precipitation of NbC _x N_1?x significantly affects the high-temperature mechanical properties of Nb microalloyed steel. The control of the precipitation behaviour of NbC _x N_1?x is the key, especially the nucleation and precipitation from Nb solid solution. We explore to use electropulsing to promote the precipitation of NbC _x N_1?x through thermodynamic model, chemical phase analysis, XRD and TEM. The modelling research show that electropulsing intensity significantly promotes the nucleation of NbC _x N_1?x in austenite phase. The higher the electropulsing temperature is, the better the promotion effect is. The chemical phase analysis and XRD investigation results show that electropulsing can increase the amount of precipitation of NbC _x N_1?x by 50% at 950°C compared to the precipitation without electropulsing.     

Structure and dielectric properties of Ba1−xSrxCuSi2O6-Ba0.55Sr0.45TiO3 ferroelectric-dielectric composite ceramics

yBa_1?xSr_xCuSi₂O₆-(1?y) Ba_0.55Sr_0.45TiO₃ (x?=?0, 0.2 and y?=?10 wt%, 30 wt%) ferroelectric-dielectric composite ceramics were prepared by the solid-state sintering method. The relationship among phase composition, microstructures and dielectric properties has been investigated. By adjusting the content of the Ba_1?xSr_xCuSi₂O₆ and the content of Sr²⁺ in the Ba_1?xSr_xCuSi₂O₆, the effect of the dielectric material on BST was studied. With the increase of Ba_1?xSr_xCuSi₂O₆ content and the increase of the Sr²⁺ content, the dielectric peak of the composite material is gradually suppressed and broadened, and the Curie temperature (Tc) moves to the low temperature. The introduction of Ba_1?xSr_xCuSi₂O₆ reduced the permittivity of the composite material to a certain extent, at the same time, the dielectric tunability and quality factor (Q) value are maintained at a high level. The dielectric tunability of the four composite ceramics obtained is still higher than 10% under the applied electric field (at 30 kV/cm). The 30 wt% BCSO–70 wt% BST55 system and the 30 wt% BSCSO–70 wt% BST55 system has lower dielectric permittivity (830, 577), higher dielectric tunability (17.3%, 10.2% at 30 kV/cm) and a decent Q value (149 at 1.25 GHz, 168 at 1.31 GHz).