Effect of Heat Treatment Time on Dy–Cu Alloy Diffusion Process in Dy-Containing Commercial Nd–Fe–B Sintered Magnets

In this paper, the grain boundary diffusion process(GBDP) using a Dy_(70)Cu_(30)(at.%) alloy as the diffusion source was performed in a commercial sintered Nd–Fe–B magnet, and the effect of heat treatment time on the microstructure and magnetic properties of the magnet was investigated in detail. For the processed magnets heat-treated at 860℃, as heat treatment time increased, the coercivity and the depth of(Nd,Dy)_2Fe_(14)B core–shell structure increased first and then decreased. However, when the heat treatment time was more than 2 h, the diffusion path of Dy from the Dy-rich shell phase into the Nd_2Fe_(14)B grains was revealed, and a nearly homogeneous(Nd,Dy)_2Fe_(14)B phase was formed, which brought on the decrease in both the depth of visible core–shell structure and the coercivity of Nd–Fe–B magnet.     

Preparation and Characterization of Amorphous W–B–C Alloy and Solid Solutions of C in Tungsten Borides

Mixtures of W and B_(13) C_2 powders were mechanically milled and subsequently annealed at 900–1200 °C. It is found that amorphous W–B–C alloy formed as the mixtures were milled for 20–80 h. After annealing the 80 h-milled mixtures at 900–950 °C, solid solutions of C and/or B in tungsten [W(B, C)], C in tungsten boride [W_2 B(C) or WB(C)]formed by the crystallization of amorphous W–B–C. The formation temperature of W_2 B(C) and WB(C) is lower than that of W_2 B and WB reported previously. As the 80 h-milled mixtures were annealed at 1200 °C, W reacted with amorphous W–B–C completely to form WB and W_2B_5 or W_2B_5 instead of the solid solutions of C in tungsten borides, which is determined by the mole ratio of W to B_(13) C_2. The formation mechanisms of the W_2 B(C) and WB(C) solid solutions as well as phase transition rules of the mixtures at annealing temperature and mole ratio were also investigated using first-principle calculation.     

Characterization of planar features in Mg–Y–Zn alloys

The planar features in a Mg–8Y–2Zn–0.6Zr (wt.%) alloy solution-treated at 500 °C for 1 h have been examined using conventional transmission electron microscopy and atomic-resolution high-angle annular dark-field scanning transmission electron microscopy. Three types of planar features are detected in the microstructure. The first type, which was previously reported to be an intrinsic stacking fault I₁ bounded by a Frank partial dislocation, is shown to be the 14H precipitate phase that is associated with Shockley partial dislocations. The second type is also a precipitate phase that has a single unit cell height and is associated with Shockley partial dislocations. The third type of planar feature comprises small ribbon-like stacking faults. These stacking faults are determined as intrinsic I₂ type bounded by two Shockley partial dislocations, which is further confirmed by computer simulation. The stacking fault energy associated with the faults is much smaller than that of pure magnesium.     

Characterization and oxidation behavior of MTCVD Ti–B–N coatings

In this work, Ti–B–N coatings have been prepared by moderate temperature chemical vapor deposition (MTCVD). The effect of a varying boron concentrations (9.6 and 55.4 at.%) on the chemical composition and the oxidation behavior was investigated by XRD, SEM, WDS, XPS and Raman spectroscopy. The results clearly demonstrate a good correlation between the different techniques. The same transition trends were observed in the examined Ti–B–N system in the progression from TiN to TiB₂ by the addition of boron. At boron concentrations ≥ 18 at.%, the coatings reveal a two phase structure comprising a nanocrystalline TiN phase embedded in an amorphous TiB₂ matrix. In Ti–B–N coatings with boron concentrations ≤ 18 at.%, the high sensitivity of Raman spectroscopy enabled the identification of an amorphous TiB phase.The oxidation behavior of Ti–B–N coatings was found to be affected by the boron concentration as well. Boron concentrations ≤ 18 at.% improve the thermal stability compared to TiN, most likely due to the TiB phase present in these coatings. Ti–B–N coatings with a high boron concentration show a higher degree of oxidation compared to TiN manifested in a higher oxide layer thickness. In addition, these coatings tend to form boron oxides on their surface, which lead to the formation of metastable anatase rather than the thermodynamically stable rutile.     

Electrochemical and Spectroscopic Study on the Corrosion of Ti–5Al and Ti–5Al–5Cu in Chloride Solutions

Metals and Materials International - In this study, manufacturing of Ti–5Al and Ti–5Al–5Cu alloys were accomplished employing mechanical alloying technique. The corrosion...     

Characterization and Diffusion Kinetics of borided Ni–Mg Alloys

Protection of Metals and Physical Chemistry of Surfaces - In this study, a mixture of 93% Ni–7% Mg and 97% Ni–3% Mg powders were produced by the TM method and the diffusion kinetics,...     

Formation and Evolution of Microstructures in Fe–9%Cr Heat-Resistant Steel

Microstructures of casting samples of Fe–9%Cr steel and samples subjected to different heat treatments were investigated to determine their formation and evolution mechanism. The results show that there is no macroscopic segregation in the casting Fe–9%Cr steel. During cooling from solidification temperature to room temperature, d-ferrite→austenite transformation is obviously influenced by cooling rate, while subsequent transformation of austenite does not obviously depend on the cooling rate. In the casting samples, a great number of precipitates distribute inside martensitic laths while there are almost no precipitates inside d-ferrite. When the casting samples were reheated to and isothermally held at 800 °C, the original precipitates and the lath boundaries disappeared gradually. Meanwhile, new precipitates nucleate and grow at the prior lath boundaries.     

Characterization of irradiated single crystals of Fe and Fe–15Cr

Pure Fe and Fe–15Cr single crystals with three different orientations, [1 0 0], [1 1 0] and [1 1 1], were irradiated in the BR2 reactor of SCK-CEN, at a temperature of 300 °C to a dose of 0.2 displacements per atom. Irradiation-induced microstructure changes were studied by transmission electron microscopy. The size distribution and defect densities were measured and the Burgers vectors and the nature of the loops were determined in detail. In the pure Fe specimens, mainly a〈1 0 0〉 edge-type interstitial dislocations loops could be identified. Their average density and size were (4.1 ± 0.4) × 10²¹ m^?3 and (8 ± 2) nm, respectively. In Fe–15Cr, on the other hand, no defects could be observed.     

Characterization of α_2 Precipitates in Ti–6Al and Ti–8Al Binary Alloys: A Comparative Investigation

Transmission electron microscopy (TEM) and atom probe tomography (APT) techniques were used to investigate the nanoscale orderedα_2 (Ti _(3 )Al) precipitates in Ti–Al binary alloys.Ti–6Al and Ti–8Al binary alloys were solution treated and aged to obtain Widmanstatten microstructure and promoteα_(2 )precipitates.The TEM results displayed strong short-range ordering ofα_(2 )precipitates in Ti–8Al alloy,while no evidence of the superlattice reflections ofα_(2 )in Ti–6Al alloy.The results acquired from APT showed theα_(2 )clusters and atoms distribution at the interface between the matrix andα_(2 )precipitates.The size and morphology ofα_(2 )particles in Ti–8Al alloy,respectively,obtained by TEM and APT are closely consistent.Meanwhile,the APT results displayed tiny size clusters in Ti–6Al alloy,which supposed to give evidence of the initial ordering process ofα_(2 )precipitates in the absence of correlative results from TEM.     

Effects of Sb Addition on Microstructural Evolution and Mechanical Properties of Mg–9Al–5Sn Alloy

The Mg–9Al–5Sn-xSb(x=0.0,0.3,0.6,1.0,1.5 wt%) alloys were prepared by a simple alloying process followed by hot extrusion with an extrusion ratio of 28.2. The effects of Sb additions on the microstructure and mechanical properties of the Mg–9 Al–5 Sn alloys were investigated by optical microscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy equipped with an energy-dispersive X-ray spectrometer. The results indicated that the phases α-Mg matrix, Mg_2_Sn, Mg_3Sb_2 and Mg_17 Al_12 exist in the as-cast Sb-containing alloys. Sb addition results in the precipitation of Mg_3Sb_2. The dendritic size of these alloys decreases with the addition of Sb. Both their ultimate tensile strength and yield strength of extruded alloys increase, and their elongation decreases gradually with increasing the content of Sb. The better mechanical properties of the as-extruded alloys were achieved due to the refined grains and the formation of dispersive second phases Mg_3Sb_2.     

Study of the effect of Ti and Ge in the microstructure of Nb–24Ti–18Si–5Ge in situ composite

The effects of Ti and Ge on the microstructure and hardness of the as cast and heat treated Nb-24Ti–18Si–5Ge (at.%) alloy (ZF3) were studied. There was macrosegregation of Si. The phases present in the as cast alloy (ZF3-AC) were the (Nb,Ti)_ss, and the (Nb,Ti)₃(Si,Ge), β(Nb,Ti)₅(Si,Ge)₃ and hexagonal (Ti,Nb)₅(Si,Ge)₃ silicides, with the latter forming a eutectic with the solid solution. The same phases were present after heat treatment at 1200 °C for 100 h (ZH3-HT12) but only the (Nb,Ti)_ss, and the (Nb,Ti)₃(Si,Ge) and (Nb,Ti)₅(Si,Ge)₃ silicides were present after 100 h at 1500 °C (ZF3-HT15) where TiO₂ was also formed. Alloying with Ti did not stabilise the (Nb,Ti)_ss + (Nb,Ti)₃Si eutectic. The formation of the eutectic in ZF3-AC was strongly influenced by the partitioning behaviour of Ti in the solidifying melt that was enhanced by the presence of Ge. There were Ti rich areas in the (Nb,Ti)_ss and the (Nb,Ti)₃(Si,Ge) silicide only in ZF3-AC. The solubility of Ge in (Nb,Ti)₃(Si,Ge) increased after heat treatment at 1500 °C. The transformation of β(Nb,Ti)₅(Si,Ge)₃ to α(Nb,Ti)₅(Si,Ge)₃ progressed from ZF3-HT12 to ZF3-HT15 but equilibrium was not reached in ZF3-HT15. The synergy of Ti with Ge resulted to a strong hardening effect and a remarkable retention of the hardness. Alloying with Ti led to a reduction of the hardness of Nb₅Si₃ and to an increase of the hardness of Nb₃Si. The synergy of Ti with Ge resulted to a strong hardening effect for the (Nb,Ti)_ss.     

Microstructure Characterization and Fracture Toughness of Laves Phase-Based Cr–Nb–Ti Alloys

Three Laves phase-based alloys with nominal compositions of Cr2Nb–x Ti(x = 20,30,40,in at%) have been prepared through vacuum non-consumable arc melting.The results show that the microstructures of Cr2Nb-(20,30) Ti alloys are composed of the primary Laves phase C15–Cr2(Nb,Ti) and bcc solid solution phase,while the microstructure of Cr2Nb–40Ti alloy is developed with the eutectic phases C15–Cr2(Nb,Ti)/bcc solid solution.The measured fracture toughness of ternary Laves phase C15–Cr2(Nb,Ti) is about 3.0 MPa m1/2,much larger than 1.4 MPa m1/2for binary Laves phase Cr2 Nb.Meanwhile,the fracture toughness of Cr2Nb–x Ti(x = 20,30,40) alloys increases with increasing Ti content and reaches 10.6 MPa m1/2in Cr2Nb–40Ti alloy.The eutectic microstructure and addition of Ti in Cr2 Nb are found to be effective in toughening Laves phase-based alloys.     

Characterization of deformation localization in cold-rolled metastable β-Ti–Nb–Ta–Zr alloy

The deformation-induced microstructural variation in the metastable β-type biomedical Ti–35Nb–5Ta–7Zr (wt.%) alloy subjected to multi-pass cold-rolling to 90% reduction has been investigated by a combination of X-ray diffraction, optical microscopy, conventional transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) techniques. Multi-pass cold rolling for the Ti–35Nb–5Ta–7Zr alloy includes various localized deformation processes which can result in dislocation tangle, stress-induced ω-phase transformation and deformation-band formation. Deformation-induced amorphization caused by high-density defect accumulation in deformation bands has been identified. By means of TEM and HRTEM observations, distributional, morphological and structural features for deformation bands have been clearly revealed.     

Characterization of the redox processes in polyaniline using capacitance–potential curves

A systematic investigation of the redox properties of polyaniline in aqueous solutions using the capacitance–potential curves was done. The variation of the capacitance values in different regions of the sweep potentials was associated with the charge transport and the capacitive processes in the polymeric film. An increase in the capacitance was observed in the region of the first redox process (0.1 to 0.6 V), which is associated with the charge accumulation in the film due to the polymer oxidation and the Cl⁻ intercalation. In the third redox process in the voltammograms (0.85 to 1.2 V), a decrease in capacitance was observed which could be related to the H⁺ deintercalation and the formation of the pernigraniline state.     

Simulation of nitrogen transport and desorption in laser welds of 21Cr–6Ni–9Mn stainless steel

Loss of nitrogen is a concern when welding nitrogen strengthened stainless steel alloys. Building on the current understanding of the underlying mechanisms, a three-dimensional simulation of conduction mode laser weld pool development using the volume of fluid technique was developed. Weld pools formed by a moving Gaussian heat input for two different laser power densities were simulated and the transport and surface desorption of nitrogen was tracked using nitrogen macroparticles. The penetration depth and width of the weld pool predicted by the simulation was comparable to the data derived from macrographs of welds made on nitronic 40 alloy. Additionally, the 25–32% predicted decrease in nitrogen composition of the weld fusion zone by the new rate law is comparable to the literature.