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Ultra-thin Fe-6.5 wt. % Si ribbons of 35 μm in thickness were prepared by melt-spinning. The magnetic properties were investigated before and after annealing at 1000 °C. The DC properties and low-frequency (400 Hz~10 kHz) iron losses significantly improved after heat treatment. A simplified formula— P t = k t B m N —based on the Steinmetz law, which can be used to predict the AC iron loss, is presented. The symbols “kt” and “N” are defined as functions of microstructure and frequency. According to the tested results of iron loss, the values of “kt” and “N” can be fitted and therefore the simplified formula can be determined. The extent of AC iron losses can be predicted according to the formula. The results obtained from the formula predict AC iron loss to a good degree. The method developed in this work could be extended to other magnetic materials for predicting AC iron loss with greater ease.

The flow behavior of Fe-6.5wt. %Si alloys during hot compression was investigated at temperatures 650–950 °C and strain rates 0.01–10 s−1. The results showed that the flow stress depended distinctly on the deformation temperatures and strain rates. The flow stress and work hardening rate increased with the decrease of temperature and the increase of strain rate. The activation energy under all the deformation conditions was calculated to be 410 kJ/mol. The constitutive equation with hyperbolic sine function and Zener–Hollomon parameter was developed. The peak stress, critical stress, and steady-state stress could be represented as σ = A + Bln(Z/A). Dynamic recrystallization occurred under the deformation conditions where the values of Z were lower than 1020. Processing maps were established to optimize the processing parameters. The power dissipation efficiency decreased in the high temperature and low strain rate region, increased in the high temperature and high strain rate region, and remained unchanged in other regions with the increase of true strain. Furthermore, the unstable area expanded. The true strain of 0.7 was the optimum reduction according to the processing map. Based on the analysis of surface quality, microstructures, and ordered structures, the optimized processing parameters for the Fe-6.5wt. %Si alloys were the temperature and strain rate of higher than 900 °C and 0.01–10 s−1, respectively, or 800–900 °C and lower than 0.4 s−1, respectively.

The flow behavior of Fe-6.5wt.%Si alloys during hot compression was investigated at temperatures 650–950 °C and strain rates 0.01–10 s-1. The results showed that the flow stress depended distinctly on the deformation temperatures and strain rates. The flow stress and work hardening rate increased with the decrease of temperature and the increase of strain rate. The activation energy under all the deformation conditions was calculated to be 410 kJ/mol. The constitutive equation with hyperbolic sine function and Zener–Hollomon parameter was developed. The peak stress, critical stress, and steady-state stress could be represented as σ=A+Bln(Z/A). Dynamic recrystallization occurred under the deformation conditions where the values of Z were lower than 1020. Processing maps were established to optimize the processing parameters. The power dissipation efficiency decreased in the high temperature and low strain rate region, increased in the high temperature and high strain rate region, and remained unchanged in other regions with the increase of true strain. Furthermore, the unstable area expanded. The true strain of 0.7 was the optimum reduction according to the processing map. Based on the analysis of surface quality, microstructures, and ordered structures, the optimized processing parameters for the Fe-6.5wt.%Si alloys were the temperature and strain rate of higher than 900 °C and 0.01–10 s-1, respectively, or 800–900 °C and lower than 0.4 s-1, respectively.

A series of β-γ Ti-44Al-8Nb-0.2B-0.2Y alloys have been modified with 0.5 to 2.0 at.% of the β-stabilizing elements Mn, Cr, Mo and V. Additions of Cr and Mo alone result in a decrease in the flow stress, whereas the opposite effect was observed for additions of V. For alloys with Mn additions, a minimum value of the flow stress was achieved in the alloy with 1.5% Mn. For alloys with combined additions, optimum hot deformation behavior was obtained for the alloy with 1.5% Mn and 1.0% Cr.

Fracture and deformation characteristics of the Ti-based metallic glass matrix composite have been studied by the tensile test and the in situ TEM tension test. Typically, the composite exhibits the high strength and considerable plasticity. Microscopically, it was found that shear deformation zone formed at the crack tip in glass phase, which can bring about quick propagation of shear bands. However, the plastic deformation zone nearby the crack tip in dendrites will postpone or retard the crack extension by dislocations. The attributions of micro-deformations to mechanical properties of composites were discussed.

Microstructural instability of fully lamellar Ti–45Al–8.5Nb–(W, B, Y) alloys during long-term thermal cycling (500 and 1000 cycles) between room temperature and 900 °C or 1000 °C was investigated. The coarsening of lamellar colony boundaries and precipitation of B2 particles are produced as a result of the microstructures degradation. The boundaries are coarsened by the precipitation of coarse γ grains. The width of the coarsened boundaries increases with increasing cycles and temperatures. Owing to the large interface energy, the coarsening of colony boundaries prefers to occur at boundaries with high misorientation angles. There is a coincidence-site lattice relationship between the precipitated γ grains and the lamellar colony at one side of the boundary. In addition, the precipitation of B2 phase occurs not only at lamellar colony boundaries by consuming (α2 + γ) lamellae but also at γ/γ interfaces via two possible mechanisms will be discussed in detail.

Microstructure and microsegregation of directionally solidified Ti–45Al–8Nb alloy were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe microanalyzer (EPMA). For the alloy solidified at the solidification rates (v) ranging from 10 to 400 μm·s−1, the microstructure of the mushy zone exhibits a cellular-dendritic structure at lower growth rate (v = 10–50 μm·s−1) and a typical dendritic morphology at higher growth rate (v = 100–400 μm·s−1). The relationship between primary dendrite arm spacing (λ 1) and v is λ 1 = 1.08 × 103 v −0.35. Al and Nb elements segregate at interdendritic zone and in the dendritic core, respectively. In solid of mushy zone, a relatively flat concentration profile is observed for the typical dendrite structure, and Nb enriches in B2 phase induced by β → α + β transformation. The content of B2 phase is hardly affected by v. The extent of microsegregation in steady-state zone decreases at a lower growth rate because holding the samples at higher temperature after solidification for a long time can homogenize the solid effectively.

Intermetallic Ti–xAl–8Nb (x = 41, 43, 45, 47, 49; at%) alloys were solidified unidirectionally upwards with a constant temperature gradient of G = 3.8 K·mm−1 at wide range of growth rates of v = 10–400 μm·s−1 using a Bridgman directional solidification (DS) furnace. Microstructural parameters including the primary dendrite arm spacing (λ 1), secondary dendrite arm spacing (λ 2), dendrite tip radius (R) and mushy zone depth (d) were measured statistically. The values of λ 1, λ 2, R and d decrease as the growth rate increases for a given composition (x). The values of λ 1, λ 2, R and v increase with the increase in x value, while the value of d firstly increases and then decreases with the increase in x value for a given v. The relationships between λ 1, λ 2 and R were analyzed by the linear regression. The average growth rate exponent of λ 1 is 0.29, which is in accordance with the previous experimental observations, and that of λ 2 is close to the previous experimental results, while those of R and d are lower than the results in other alloy systems. In addition, theoretical models for λ 1, λ 2 and R were compared with the experimental observations, and a comparison of the present experimental results with the theoretical models and previous experimental results was also made.

The ordered ω phase in as-cast Ti-45Al-8.5Nb-0.2B alloy and its phase transformation during heat treatment are investigated. Ordered ω variants are observed to uniformly precipitate within the βo area in as-cast Ti-45Al-8.5Nb-0.2B alloy. After annealing at 850 °C for 500 h, the βo areas are replaced by large B82-ωo grains. Small γ precipitates are observed at the grain boundaries of the ωo phase and are thought to be transformed from the βo phase. Moreover, the ωo precipitates directly transformed from the parent α2 laths are found within the lamellar colonies. The orientation relationship between the ωo phase and the lamellar structure is 2 ¯ 0]α2; (111)γ//(11 2 ¯ 0)ωo//(0001)α2. The interfaces between the ωo and γ are semi-coherent. The ωo phase is an equilibrium phase at 850 °C in high Nb-containing TiAl alloys. When annealed at 1250 °C, the ordered ω is eliminated in a short time, and the βo phase is substituted by the coarsened α2 laths in the lamellar colonies after 12 h annealing.

Ti–48Al–6Nb porous alloys were synthesized by the powder metallurgy (PM) method, and the associated phase transformation and pore parameter were investigated in order to reveal the pore-formation mechanism. The present results indicate that the Nb–Al and Ti–Al phase transformations contribute to the pore-formation. It was found that the five-step phase transformations for the Ti–48Al–6Nb porous alloys occur as follows: (1) Ti + Al → TiAl3 at 600–700 °C; (2) Nb + Al → NbAl3 at 700–900 °C; (3) TiAl3 + Ti → TiAl at 900–1100 °C; (4) TiAl + Ti → Ti3Al/TiAl at 1100–1350 °C; (5) NbAl3 + Nb → Nb2Al and the Ti3Al turns to the major phase at 1350 °C. These phase transformations made the pore-diameter increasing continuously from 1.71 μm to 12.10 μm and also made the pore volume distributing widely. At the second step of 700–900 °C, the Nb–Al phase transformation leads to 5% more volume expansion compared to the Ti–Al based porous alloys. Meanwhile, the porosity and total pore area initially increase and then decrease at this step, but they increase intensely at the final step, which is needed as a catalytic carrier. Keywords: Porous materials, Phase transformation, Heat treatment, Powder metallurgy, Microstructure

The precipitated silicide phase in a high-Nb TiAl alloyed with Si addition was studied. Unlike the Ti5Si3 precipitates formed in Ti–Al–Si ternary system, the silicide particles formed in this study consisted of a Nb5Si3 (designated as e) phase and had a hexagonal D88 crystal structure. The volume fraction of Nb5Si3 phase increased after heat treatment at 1473 K for 30 min as the B2 phase decomposed. A large number of Nb5Si3 precipitated on lamellar boundaries and had a specific orientation relationship (OR) with α2 and γ: (1 1 ¯ 0 0)e//(1 1 ¯ 0 0)α2 and [1 1 2 ¯ 3]e//[1 1 2 ¯ 0]α2; (1 1 ¯ 0 0)e// ( 1 1 ¯ 2 ¯ ) γ and [1 1 2 ¯ 3]e//[1 1 0]γ. The semi-coherent interfaces of Nb5Si3 with the matrix resulted in regular interface dislocations.

Directional solidification (DS) experiments with thermal stabilization (TS) treatments were performed on Ti–46Al–5Nb (at.%) alloys in a Bridgman-type furnace using a quenching technology. Influence of the TS treatment on mushy zone and directional growth afterwards were investigated. The results show that the length of the mushy zone decreases but the β dendrite spacing in directional growth significantly increases with increasing TS time. During the DS process, β dendrite spacing is more homogeneous and its growth direction is more inclined to parallel to the axial direction with increase of the TS time. Al solute concentration in the mushy zone in a steady-state is always lower than that in original as-cast alloys. The mushy zone with the columnar β and α grains is easily produced after TS treatment on the alloys with microstructures of the directional dendrite segregation morphology before DS starting. TS treatment results in the redistribute of solute Al thus changes the phase constituent in the mushy zone. An appropriate TS is necessary to produce the L + β + α region in the mushy zone, which is of great benefit to control DS microstructures of TiAl peritectic alloys.

The transformation of the D019-α2 phase to the B82-ωo phase is a new type of phase transformation in high Nb-containing TiAl alloys; experimental results concerning this phase transformation are still lacking. Moreover, studies on the orientation relationships (ORs) between these two phases are scarce compared with those reported between the disordered ω and α phases, which can be more complicated due to their ordered structures. In this study, the direct α2 to ωo phase transformation is observed by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The ωo phase is transformed from the α2 laths in the lamellar structure after annealing over long periods at 850 °C. The various ORs observed between these two phases can be merged into two typical ORs: [ 1 1 2 ¯ 0 ] α 2 / / [ 0 0 0 1 ] ω o , ( 0 0 0 2 ) α 2 / / ( 1 1 2 ¯ 0 ) ω o and [ 1 1 ¯ 0 0 ] α 2 / / [ 2 2 4 ¯ 3 ¯ ] ω o , ( 0 0 0 2 ) α 2 / / ( 0 1 1 ¯ 2 ) ω o . The other ORs observed are subsets of these two ORs. The edge-to-edge matching model is applied to predict the possible ORs between the ordered α2 and ωo phases based on the calculated close-packed planes of the two phases. The simulation results agree well with the experimental results.

Compressive tests were conducted on metallic glass matrix composites at a series loading rates. It was found that mechanical properties of the composite, e.g. yielding stress and plasticity, have a week dependence on strain rates of 4.0 × 10 −4 s −1 –4.0 × 10 −1 s −1 . Four composites were tested at a constant strain rate of 2.3 × 10 s −1 to uncover the dynamic deformation behaviors. Compared with the quasi-static case, the yielding strength increased under dynamic loading rate, but the plasticity decreased significantly. On the other hand, the dynamic compressive has closely relation with the dendrite size and volume fraction. The decreasing of the dendrite size and volume fraction leaded to the dynamic yielding strength increased but the plasticity decreased. For a same composite, e.g. T1 alloy, the yielding strengths increased slightly but fracture strain decreased with increasing of dynamic strain rates.

In this work, low-cost titanium was fabricated by gelcasting of titanium hydride powder. The effects of morphology and grain composition of powder raw material and solid loading on the rheological behavior of gelcasting slurry were studied. The degreasing, dehydriding and sintering behaviors of gelcasted green body were investigated by differential thermal analysis (DTA) and dilatometer. The results show that the solid loading of titanium hydride slurry reaches 50 vol%. Combination of dehydriding and sintering in one process accelerates the densification, and the relative sintered density of the final part achieves 96.5 %. In order to test the ability of gelcasting process for fabricating structural materials, a resin handle produced by 3D printing technology was used as a model and a titanium handle was successfully fabricated. Higher solid loading and better sinterability of titanium hydride powder promote manufacture of bulk titanium with high relative density, complex shape and well-defined microstructure.

Ceramic nanoparticles were considered difficult to be dispersed well in liquid metal, especially in non-reactive systems, by stir mixing methods due to their high specific surface energy. In this paper, an electromagnetic stirring process was exploited to disperse ceramic nanoparticles in an active TiAl alloy melt. The results indicate that finely dispersed nanoparticles can be obtained by stir mixing with the aid of reactive wetting. The presence of nanoparticles during solidification can refine the primary dendrites dramatically, which was primarily determined by the extent of particle pushing at the liquid–solid interface. Among the studied particles, TiC can refine the (γ + α2) lamellar colonies, which is attributed to the dissolution of carbon and subsequent precipitation of Ti2AlC during L + β β + α. The Vickers hardness of the nanocomposites as a function of stirring time was tested, and the Ti–45Al/TiC nanocomposite produced by 10 min stir mixing has the highest value, measuring 450 HV.

The ordered ω phases in high Nb containing TiAl (Nb-TiAl) alloys have been garnering increasing attention in the recent years. However, the investigations on the Nb dependence on the ω o precipitation are scarce. In this study, the effect of Nb content on the ω o precipitation in high Nb (6–10 at%) containing TiAl alloys after long-time annealing at 850 °C has been studied. The results show that small ordered ω particles in the retained β o phase cannot be discerned under scanning electron microscope (SEM) but can be observed using transmission electron microscopy (TEM). Although the Nb segregation can be eliminated after the homogenization heat treatment, the ω o phase precipitated in all the alloys studied after annealing at 850 °C. TEM examination reveals that the orientation relationship between the ω o and α 2 phases can be derived as: [0001] ω o //[1120] α 2 ; (1120) ω o //(0001) α 2 , which indicates that the ω o phase is directly transformed from the parent α 2 phase. Small γ particles are also observed within the ω o areas. The α 2 → ω o + γ decomposition process is expected during annealing. It is concluded that ω o phase is an equilibrium phase in high Nb-TiAl alloys at 850 °C.

Microstructure and deformation mechanisms at a nanoindentation in the lamellar colony of high Nb containing TiAl alloy have been studied using the focused ion beam and the transmission electron microscopy. Considerable deformation twins are observed around the nanoindentation, and a strain gradient is generated. A continuous change in the bending angle of the lamellar structure can be derived, and a strain-induced grain refinement process is observed as various active deformations split the γ grains into subgrains. In addition to all possible deformation mechanisms (ordinary dislocation, super-dislocation and deformation twining) activated due to the heavy plastic deformation, a 6-layer hexagonal (6H) long-period stacking ordered structure is identified for the first time near the contact zone and is thought to be closely related to the glide of partial dislocations.

The B19 phase is widely observed in the α2 laths in Ti–45Al–8.5Nb–0.2W–0.2B–0.02Y alloy, forming a modulated structure together with the α2 phase. The distortion between the α2 and B19 phases exists only along the [ 1 1 ¯ 0 0 ] α 2 direction and is very difficult to detect. Thin γ laths precipitate regularly within the α2 + B19 structure to accommodate the lattice misfit, whereas the sizes of the γ laths are limited to a small scale. The B19 phase, however, is unstable and was eliminated after annealing at 900 °C for 30 min, followed by air-cooling. The pure α2 phase observed in the air-cooled sample is not in the equilibrium state. The B19 phase can be a stable phase in some temperatures below 900 °C but be repressed under rapid cooling.

During high-temperature compression tests on Mo 5 SiB 2 , the deformed microstructure varies with the temperature, strain rate and strain, and their changes have profound effects on the deformation behavior. At 1200 °C, the plastic deformation is provided by dislocation glide on potential slip planes, such as {1 1 0} and {0 0 1}. Due to the limitation of less activated slip systems, the specimens rupture when compressed to the strain of ~3% at 1200 °C and 1.67×10 −4 s −1 . With temperature increasing to 1400 °C, the activation of more independent slip systems increases the deformation capability of the alloy. However, there is an increasing tendency for slip planes to be of an unexpected type (e.g. {1 4 3} and {5 2 3}) as a function of decreasing strain rate and increasing temperature, which is related to dislocation climb. Moreover, dynamic recovery or recrystallization is easy to occur under the conditions of heavy deformation (like 25% strain) and slow strain rate (like 1.67×10 −4 s −1 ), showing the decrease in the dislocation density and flow stress.

Ternary composites of polyaniline/graphene oxide/Fe3O4 (PANI/GO/Fe3O4) were synthesized by a simple method and the electromagnetic absorption properties of the composites were investigated in the paper. The structures of the composites were characterized with Fourier-transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. It can be found that the maximum reflection loss of PANI/GO/Fe3O4 can reach −53.5 dB at 7.5 GHz, and the bandwidth exceeds −10 dB is 2.8 GHz with absorber thickness of 3.91 mm. The electromagnetic parameters indicated enhanced electromagnetic absorption properties of the nanocomposites, which was attributed to the better impedance matching. On the basis of the above characterization, an electromagnetic complementary theory was proposed to explain the impedance matching.

High Nb containing TiAl porous alloys were synthesised by powder metallurgy (PM). In order to reveal reaction mechanism of Nb in preparation of the porous alloys, Nb–Al diffusion reaction was investigated using diffusion couples at relatively low temperatures of 600–800°C. The porous Nb–Al diffusion layer was identified as NbAl3 phase and the thickness of diffusion layer indicated that the Nb–Al diffusion mainly occurred at 800°C. In addition, the pore diameter distribution indicated that Nb–Al diffusion also contributed to the increase in pore diameter. According to these results, the diffusion reaction model was established for high Nb containing TiAl porous alloys.

There is widespread attention to surface profile and modification of 304 stainless steel for research development and application. Here, a successful electrolytic plasma processing (EPP) technique has been developed for both surface pretreatment and coating deposition of 304 stainless steel. Representative images confirm that the number of the pits increases and the ravines gradually disappear on the steel pretreated by EPP with the increase of processing time and applied voltage. Moreover, there is an obvious enhancement in surface roughness of 304 stainless steel after EPP pretreatment. In the case of coating deposition, the further EPP modification conducted on the pretreated sample offers a simple and effective technique for the production of zinc coatings having the features of full coverage and homogeneous distribution. The results show that a zinc coating with a thickness of approximately 0.5 μm can be obtained on the 304 stainless steel by means of EPP for only 60 s.

Microstructure instabilities of the fully lamellar Ti–45Al–8.5Nb–(W,B,Y) alloy were investigated by SEM and TEM after long-term thermal cycling (500 and 1000 thermal cycles) at 900 °C. Two major categories of microstructure instability were produced in the alloy after the thermal cycling: 1) The discontinuous coarsening implies that grain boundary migrations are inclined to occur in the Al-segregation region after the long-term thermal cycling, especially after 1000 thermal cycles. Al-segregation can be reduced during the process of long-term thermal cycling as a result of element diffusion; 2) The α 2 lamellae become thinner and are broken after 1000 thermal cycles caused by the dissolution of a 2 lamellae through phase transformation of α 2 →γ. The γ grains nucleate within the α 2 lamellae or (α 2 +γ) lamellae in a random direction.

Low-molecular mass organic gelcasting is utilized to fabricate titanium structural materials. The aim is to find a low-residual gel system for the fabrication of titanium with good ductility. The thermally reversible gel system is composed of 1,3:2,4-dibenzylidene sorbitol (gelator) and 1-butanol (solvent). Titanium hydride powders are used as raw material and the solid loading of gelcasting slurry reaches 48 vol%. Combination of dehydriding and sintering in one process accelerate densification and the relative sintered density reaches up to 97.5%. The contents of oxygen and carbon contamination are 0.31 and 0.08 wt%, respectively, which contribute to a high-level of mechanical property with tensile strength of 580 MPa and elongation of 8%. To achieve the near-net shape forming capability of low-molecular mass organic gelcasting, rosin is used to increase the green strength. Eventually, titanium parts with complex shape are successfully prepared.

The ordered intermetallic Mo5SiB2 displays a ceramic-like brittleness at the ambient temperature. The state density, charge distribution and elastic parameters were calculated by first-principles, based on the density functional method. The results indicated that the two different kinds of covalent bonds were intricately woven into the refractory phase. The improved Peierls–Nabarro stress which is caused by this kind of distribution mode makes dislocations move difficultly, resulting in intrinsic brittleness. The effects of substitutional alloying on the ductility of Mo5SiB2 were also assessed by the calculations on the elastic properties and dislocation line energy. It was shown that the metal (Nb, Tc) alloying was not to enhance effectively its toughness, but to improve the brittle-to-ductile transition temperature.

The initiation and evolution behavior of the shear-bands and microcracks in a Ti-based metallic-glass–matrix composite (MGMC) were investigated by using an in-situ tensile test under transmission electron microscopy (TEM). It was found that the plastic deformation of the Ti-based MGMC related with the generation of the plastic deformation zone in crystalline and shear deformation zone in glass phase near the crack tip. The dendrites can suppress the propagation of the shear band effectively. Before the rapid propagation of cracks, the extending of plastic deformation zone and shear deformation zone ahead of crack tip is the main pattern in the composite. & 2014 Chinese Materials Research Society. Production and hosting by Elsevier B.V. All rights reserved.

Nb and Sn are major alloying elements in Zr alloys. In this study, the microstructure, mechanical properties, corrosion behavior, cytocompatibility and magnetic resonance imaging (MRI) compatibility of Zr–2.5X (X = Nb, Sn) alloys for biomedical application are comparatively investigated. It is found that Zr–2.5Nb alloy has a duplex structure of α and β phase and Zr–2.5Sn alloy is composed of α phase. Both separate addition of Nb and Sn can strengthen Zr but Nb is more effective in strengthening Zr than Sn. The studied Zr–2.5X (X = Nb, Sn) alloys show improved corrosion resistance compared to pure Zr as indicted by the decreased corrosion current density. The alloying addition of Nb enhances the pitting resistance of Zr, whereas the addition of Sn decreases the pitting resistance of Zr. The extracts of Zr–2.5X alloys produce no significant deleterious effect on fibroblast cells (L-929) and osteoblast-like cells (MG 63), indicating good in vitro cytocompatibility. The Zr–2.5X (X = Nb, Sn) alloys show decreased magnetic susceptibility compared to pure Zr and their magnetic susceptibility is far lower than that of pure Ti and Ti–6Al–4V alloy. Based on these facts, Zr–2.5Nb alloy is more suitable for implant material than Zr–2.5Sn alloy. Sn is not suitable as individual alloying addition for Zr because Sn addition decreases the pitting resistance in physiological solution.

A novel spray pyrolysis with two-step cycles has been developed to fabricate (Al2O3–Y2O3)/(Y2O3-stabilized ZrO2) (YSZ) laminated coating on 8Nb–TiAl alloy for resisting high-temperature oxidation. And a crack-free structure, except in the top sub-layer, has been established ultimately, with interlocking adhesion between the layers of coating. It is shown, from cyclic oxidation at 1000 °C, that 8Nb–TiAl alloy with laminated coating exhibits superior oxidation and spallation resistance. These beneficial effects can be attributed to the compact structure, the suppression of oxygen diffusion in Al2O3–Y2O3 layers, the decrease of thermal stresses and the increase of fracture toughness in such laminated coating.

Ti–48Al–6Nb (at.%) porous alloys are fabricated by elemental powder metallurgy to study the pore formation and propagation mechanism. Reactive diffusion, pore formation process, and pore characteristics of the porous TiAl–Nb alloys are investigated at different temperatures. It is found that the porous alloys exhibit a uniform, maze-like network skeleton, viz., a typical α 2 -TiAl 3 /γ-TiAl fully lamellar microstructure. The reactive diffusivities between Ti and Al powders are dominant during the Ti–Al–Nb powder sintering. Gas release during sintering also plays an important role in the pore propagation and the compact expanding process. In addition, a pore-formation model is proposed to interpret the growth mechanism of pores and skeletons.

In this work, as-cast microstructure characteristics are identified for the TiAl–Nb alloys with four typical solidification modes, namely, single β (B mode), hypo-peritectic (BA mode), hyper-peritectic (BAA mode) and single α (A mode) solidification. B mode alloys are chemically more homogeneous, and they show netty white ridge β-segregation and fine equiaxed lamellar grains compared to the other three mode alloys due to the β→α solid-phase transformation. Increasing Nb addition decreases the size of primary β dendrite and thus decreases the lamellar colony size of the B mode alloy. In BA and BAA mode alloys, much higher Al-segregation and worm-like β-segregation are formed in the interdendritic and dendritic regions, respectively. The low fraction and rapid growth of primary β dendrite in liquid and the subsequent peritectic α growth are responsible for the sharp casting texture and coarse lamellar colonies. A mode alloy is characterized by the columnar colony and weak casting texture due to the rapid growth of primary α dendrite accompanied by the lack of solid-state transformation refinement. As-cast microstructure evolution during cooling that depends on the phase transition sequence in the TiAl–Nb alloys with different solidification modes will also be proposed.

It is shown that a uniform and refined fully lamellar microstructure can be generated by tempering the quenched samples in the single α region of as-forged Ti–43Al–9V–Y alloy. The refining effect was mainly connected with the quenched microstructures especially for their substructure, grain size and the residual β particles after the quenching. A series of β-decomposed products: martensite plate, massive α and coarsened α lath with increasing grain size were produced due to the decreasing cooling rate during the wedge-shaped sample quenched into iced brine. In addition, the decomposition of β directly to γ has also been observed during the quenching with different cooling rate. The lamellar colony size can be controlled in the range of 25–50 μm after tempering.

Journal of alloys and compounds 807, 151649 - (2019). doi:10.1016/j.jallcom.2019.151649, The microstructure evolution and carbide precipitation in a Ti-46Al-8Nb-0.7C alloy as well as its creep properties at intermediate temperatures are investigated by high-energy X-ray diffraction and electron microscopy. The alloy with a nearly fully lamellar microstructure exhibits excellent creep resistance, which could be attributed to the good microstructural stability and strengthening effects from both P- and H-carbides. It is also found that the creep parameters have different effects on the precipitation of the carbides. The overall volume fraction of the carbides shows a positive correlation with the creep temperature and time. However, the thermal stability of P-carbides in the γ grain interior decreases at a higher creep temperature. The creep stress hardly affects the precipitation and morphology development of the P-carbides. On the contrary, a higher stress can promote the H-carbide formation at the γ/α2 interfaces via α2 lath decomposition in lamellar colonies., Published by ScienceDirect, Amsterdam [u.a.]

High Nb containing TiAl alloys have prospect to be used for turbo wheel and exhaust valve for vehicle engine. Friction welding is a suitable process for fabricating these components. For investigating the weldability of these alloys, cylindrical samples of Ti–45Al-8.5Nb-0.2W-0.2B-0.02Y (in at%) alloy with a diameter of 10 mm were welded by continuous drive friction welding process, and the microstructures and the mechanical properties of the joints were analyzed in this paper. The results showed that the weldability of the present alloy was very good. At parameters of rotational speed of 2400 r/min, friction pressure of 320 MPa, burn-off distance of 3 mm and upset pressure of 360 MPa, completely metallurgical bonding interfaces were obtained. The joint had a severely plastic deformation zone (SPDZ) with a biconcave lens geometry. The thicknesses of the center and periphery of SPDZ were about 40 μm and 800 μm, respectively. There existed a transition zone (TZ) between parent metal (PM) and SPDZ. SPDZ exhibited the deformation flow lines and had a randomly-oriented recrystallized duplex (DP) microstructure with the average grain size of 2.5 μm, in contrast, PM presented a nearly lamellar (NL) microstructure with a colony size of 150 μm. TZ showed a mixture microstructure combining deformed lamellar colonies and partially recrystallized grains. At room temperature, 750 °C and 800 °C, welding joints had better tensile properties than PM.

In situ Ti-based metallic glass matrix composites are fabricated by the Bridgman solidification, and the mechanical properties are investigated. The fine dendrites about 2 to 10 μm are uniformly distributed in the glass matrix. The compressive results show that the composites have high strength and large plasticity. The fracture strength for the composite at the withdrawal velocity of 1.6 mm/s is as high as 3000 MPa and the total fracture strain is up to 31.5 pct. Particularly, the dendrite size of the current composite would decrease with the increasing of the withdrawal velocity, which leads to the higher yield strength.

The resistivity and mechanical properties of Cu–Sn alloys with different compositions were explored by casting, normalising, cold work and subsequent annealing treatment. Results indicated that the Cu–Sn alloy had the characteristics of ultrahigh electrical conductivity, when the Sn content was ∼0·5 wt-%. Note that the resistivity of the as cast and annealed Cu–0·5 wt-%Sn alloys is 1·55 and 1·26 μΩ cm respectively.

Mo 5 SiB 2 (T2) was synthesized by sparking plasma sintering (SPS) under different heating rates and sintering temperatures. The powder mixture with a T2 composition (Mo–12.5Si–25B (at.%)) failed to produce the T2 single-phase alloy due to the volatilization of Si during SPS process. Extra 0.5 at.% Si added to this mixture offset the volatilization loss. It has been found that heating of the mixture at low heating rates favored the formation of binary phases in the solid state at medium temperatures. In this work, the T2 alloy with a fine-grained microstructure was obtained via a liquid–solid reaction when the mixture was heated fleetly to the temperatures above the silicon melting point at the rapid heating rate of 200 °C/min. The sintering temperature at 1500 °C for T2 synthesis is beneficial to enhance further densification, as well as to avoid abnormal grain growth at higher temperatures.

Porous Ti–xAl–8Nb (x = 45, 48, and 49 at%) alloys (i.e., intermetallic TiAl–Nb compounds) with cylindrical pores oriented along a single direction were prepared via unidirectional solidification in a hydrogen and helium gas atmosphere, while making use of the differences in the hydrogen solubilities of the liquid and solid phases of the alloys. The microstructures and pore morphologies of the alloys revealed that pore formation in the alloys was closely related to their solidification processes. In the case of the alloy with x = 45 at%, a primary solidified β (bcc) phase with high hydrogen solubility suppressed the formation of pores during solidification. On the other hand, in the case of the alloy with x = 49 at%, the formation of the primary β phase was suppressed, leading to the formation of elongated pores along the solidification direction. After being heat treated, the porous TiAl–Nb alloys exhibited a fully lamellar structure composed of α2-Ti3Al and γ-TiAl phases. These porous TiAl–Nb alloys with lamellar structures and directional pores exhibited superior compressive properties parallel to the direction of the pores.

The fracture behavior of the polycrystalline Mo5SiB2 alloy was investigated by three-point bending tests, in vacuum, in the range of 25–1400 °C at a crosshead speed of 10−3 mm/s. At room temperature (RT), the alloy exhibited a higher fracture toughness of 3.34 MPa m1/2 compared to single crystalline Mo5SiB2 with a value of ∼1.8 MPa m1/2. The improved toughness is attributed to crack overcoming the barrier effects of grain boundaries. With increasing temperature, the fracture mode underwent a conversion from transgranular cleavage at RT to a mix of transgranular cleavage and intergranular failure at elevated temperatures. At 1000 °C, the maximum increment (∼3.4 MPa m1/2) in toughness was found to be related to the brittle-to-ductile transition (BDT). At 1200 °C, the effects of extrinsic toughening mechanisms (microcracking, etc.) are limited, i.e. its toughness only increasing by ∼1.1 MPa m1/2. However, the cavities formed at triple junctions degraded toughness at 1400 °C.

Several methods were introduced for practicing and studying the method of TTT curve digitization by using Plot Digitizer (version 1.9) and OriginPro (version 8.0724). After digitizing, original TTT images, which can not be inquired in computer procedures, were transformed into the data series and digital patterns, providing a convenient way for inquiring the data points from TTT curves. It offers a handy tool for studying the relationship among the time, temperature and transformation. Furthermore, it provides a convenient method for thermal treatment teaching through courseware. It is believe that, after a systemic data processing, we can obtain a digitizing TTT data base, which can be inquired automatically by PC procedures, promoting the automatic level of the thermal treatment for industrial applications.

The omega phase in as-cast high-Nb-containing TiAl alloy exhibits particles with sizes on the nano- or microscale within the B2 matrix. Omega particles are transformed from the B2 phase by heterogeneous nucleation on the B2/γ boundaries or homogeneous nucleation within the B2 phase. After annealing at 900 °C, the omega particles disappear and transform into B2 phase. The transformation is rapidly initiated, but is difficult to complete.

Modeling of crystal structure in material science curriculum was practiced and applied to keep it simple and understandable by using MS. The unit cells and atomic configurations are produced to show the theory system of geometry description of crystal structure. Many examples, as diamond, graphite, nanomaterial and advanced carbon materials, are employed to describe the main application of MS in material science teaching. According to these atomic modeling configurations, crystal structures exhibit a clearly and understandable appearance for us. So, the meaning of learning and understanding the related parameters of geometry description of crystal structure was explored with the point which helped students to realize and master the abstract concepts of crystal structure.

This article focuses on the tensile and compressive characteristics of a Ti-based bulk metallic glass composite (BMGC). It is found that the yield stress, maximum strength, and fracture strain are 1380 MPa, 1516 MPa, and 4.3% for uniaxial tension, but 1580 MPa, 4010 MPa, and 29% for uniaxial compression, respectively. The composite displays a linear “work hardening” capacity under compression; however, the “work softening” behavior is observed in the true engineering stress-strain curve upon tensile loading. The fracture surfaces of specimens also exhibit dissimilar properties under the different loadings.

Digitization of CCT curves by systemically using common softwares was studied and practiced to rebuild the digital patterns for teaching purpose. As treated in PC procedure, the CCT images printed in books were transformed into the digital data points, which can be read and record clearly and precisely in computer, extremely changing the appearance and precision of raw images. As the digital data, this digitized CCT curves can be conveniently introduced into the courseware, drawing more attendance and interesting from students than raw images. On the other hand, these digitized data also can be used as the CCT database for industrial applications, which can introduce automation into the thermal treatment industry. That is, the digitization of CCT curves will take great advantage of the improvement of teaching and promote the producing depth.

The objective of this study is to investigate the effect of alloying element indium on the microstructure, mechanical properties, corrosion behavior and in vitro cytotoxicity of Ti–In binary alloys, with the addition of 1, 5, 10 and 15 at.% indium. The phase constitution was studied by optical microscopic observation and X-ray diffraction measurements. The mechanical properties were characterized by tension and microhardness tests. Potentiodynamic polarization measurements were employed to investigate the corrosion behavior in artificial saliva solutions with and without fluoride. In vitro cytotoxicity was conducted by using L929 and NIH 3T3 mouse fibroblast cell lines, with commercially pure Ti (CP–Ti, ASTM grade 2) as negative control. All of the binary Ti–In alloys investigated in this work were found to have higher strength and microhardness than CP–Ti. Electrochemical results showed that Ti–In alloys exhibited the same order of magnitude of passivation current densities with CP–Ti in artificial saliva solutions. With the presence of NaF, Ti–10In and Ti–15In showed transpassive behavior and lower current densities at high potentials. All experimental Ti–In alloys showed good cytocompatibility, at the same level as CP–Ti. The addition of indium to titanium was effective on increasing the strength and microhardness, without impairing its good corrosion resistance and cytocompatibility.

t is well known that excellent soft magnetic properties are obtained in electrical steel with Si content of 6.5wt.%, such as high permeability, low coercive force, near zero magnetostriction, etc. However due to its poor ambient temperature ductility it is very hard to fabricate this material by conventional hot-cold rolling process. Meanwhile, high-density electropulsing treatment (EPT) attracts widespread applications as a new heat treatment approach. In this paper, heat treatment effect of high-density pulsing current on microstructure, micro-hardness and mechanical properties of as rolled Fe-6.5wt.%Si alloy sheet were investigated. The results showed that the microstructure and mechanical properties were closely related to the parameters of the pulses. Refined and uniform recrystallized grains were obtained by optimizing parameters of the high density pulses. Compared with the conventional heat treatment method, the time and temperature for heat treatment can be reduced dramatically. Therefore, it is considered that EPT is an efficient heat treatment approach for this rolled sheet. Mechanism of the effect of high-density pulsing current has been discussed also in this investigation.

The corrosion behavior of porous Nb-containing TiAl based alloys in HCl, NaOH and NH3H2O aqueous solutions with various concentrations has been studied simultaneously at room temperature. The results indicate that the porous alloys have good acidic resistance which is probably based on the combined work of Ti-Ti metallic bond and covalent bond. And pitting corrosion is the main corrosion behavior of Nb-free TiAl alloys during the first 40 hours, while intergranular corrosion is the main corrosion behavior later. Nb-containing alloys have better acid corrosion resistance due to inhibiting intergranular corrosion by Nb element. In addition, the porous TiAl based alloys are much more resistant to corrosion in alkaline solutions than in acidic solutions, owing to the different oxide films formed in alkalis solutions.

Compression and three-point bending tests were conducted at room temperature (RM) on the Mo5SiB2 (T2) alloy, which was prepared by sparking plasma sintering (SPS). It was found that almost no plastic deformation occured in the T2 alloy before failure but with a tremendous compressive strength of 2907 MPa. The fracture toughness determined from the single edge notch bend specimen is 3.34 MPa·m1/2, similar to the value of 3.5 MPa·m1/2 in ɑ-Al2O3. Once the cleavage crack initiated near the notch under continuous loads, it propagated on a certain plane (001) until the specimen completely fractured. In this work, the electronic structure was also calculated by the first-principles method, indicating that the contribution to RM brittleness is mainly caused by the covalent bonds which arrange alternately in the T2 phase.