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Hierarchical iron–nickel oxyhydroxide nanosheets directly grown on porous TiFe2-based intermetallics exhibit ideal activity and stability at a large current density.

This study investigates the phase transformation and microstructure of porous FeAl parts sintered from elemental powder mixtures using in-situ neutron diffraction and in-situ thermal dilatometry. A single B2 structured FeAl phase was determined in the sintered FeAl alloy. The combined effects of the Kirkendall porosity, transient liquid phase, and phase transformations associated with powder sintering all contribute to the swelling phenomenon of the final sintered part. The aqueous corrosion test indicates that the corrosion products include iron oxides in the porous FeAl parts. The accumulation of corrosion products blocks the pore channel and decreases pore size and permeability over the soaking time.

Ti(C,N)-WC-Mo2C-TaC-Co-Ni cermets with various content of La2O3 were prepared by gas-pressure sintering at 1450 °C. The effects of ultrafine La2O3 additions (0, 0.05, 0.1 and 0.2 wt%) on the microstructure, mechanical properties, wear resistance and cutting performance of cermets were explored. In the microstructure of cermets, the La2O3 particles and dissolved La element in binder phases were observed, which could inhibit the dissolution-precipitation process of ceramics phases during liquid-sintering. Furthermore, the La2O3 could absorb and react with the impurity Al element with low melting point from raw powders, avoiding the appearance of liquid phase at the low temperature and partial overheating during sintering process. These mechanisms could inhibit the abnormal growth of Ti(C,N) core-(Ti,W,Mo,Ta)(C,N) rim structures effectively, leading to the thinning of brittle rim phases and coarsening of wear-proof Ti(C,N) particles. The decrease of proportion of brittle rim phase and ultrafine Ti(C,N) particles promoted the fracture toughness. The increase of proportion and grain size of Ti(C,N) improved the hardness, wear resistance and cutting performance significantly. However, the excessive addition of La2O3 would result in the agglomeration of La2O3, causing the sharp decline of mechanical properties and cutting performance. The cermet with 0.1 wt% La2O3 addition possessed the optimal mechanical properties with Vickers hardness, transverse rupture strength and fracture toughness of 1710 (HV30) Kgf/mm2, 2480 MPa and 11.7 MPa m1/2, respectively.

Intermetallic compounds have the characteristics of long-range ordered structure and combination of metallic and covalent bonds, showing intrinsic brittleness and outstanding performance stability. The synthesis mechanism, pore structure characterization and material properties of powder metallurgy porous intermetallics are reviewed in this paper. Compared with traditional porous materials, porous intermetallics have good thermal impact resistance, machinability, thermal and electrical conductivity similar to metals, as well as good chemical corrosion resistance, rigidity and high-temperature property similar to ceramics. The mechanisms of preparation and pore formation of porous intermetallics mainly include four aspects: (1) the physical process based on the interstitial space between the initial particles and its evolution in the subsequent procedures; (2) the chemical combustion process based on the violent reaction between the initial powder components; (3) the reaction kinetics process based on the difference between the diffusion rates of elements; (4) the phase transition process based on the difference between the phase densities. The characterization parameters to the pore structure description for porous intermetallics include mainly overall porosity, open porosity, permeability, maximum pore size, pore size distribution and tortuosity factor. In terms of microstructure characterization of porous intermetallics, three-dimensional pore morphology scanning technology has the potential to reveal the internal characteristics of pore structures. The research on material properties of porous intermetallics mainly focuses on electrochemical catalytic activity, generalized oxidation resistivity at high temperature, resistance against chemical corrosion and mechanical properties, which have obvious advantages over traditional porous materials. In the field of the development of porous intermetallics, it is expected to expand their applications by further reducing the pore size to the nanoscale level to improve the filtration accuracy or increase the specific surface area, as well as introducing the high entropy design on the composition to improve the brittleness and enhance their material performance.

The oxidation behavior of porous Ni-Cr-Fe materials prepared by reactive powder synthesis with different open porosity was studied in air at 6008C, 800 8C and 1 0008C. The differences in surface morphology, phase and pore structure parameters between material oxidized and non-oxidized were characterized by means of scanning electron microscopy, X-ray diffraction analysis and mercury intrusion. The results show that the oxidation rate of the samples which were oxidized at 600 8C for 340 h, for 560 h at 800 8C and for 560 h at 1 000 8C were 0.00027%2 h-1, 0.0558%2 h-1, and 0.64412%2 h-1, respectively. All the oxidation kinetics curves obeyed the parabolic law, exhibiting excellent high temperature oxidation resistance.

Ti3SiC2 has the unique properties integrating the advantages of metals and ceramics, and good open pore structure when alloyed with Al. In this work, porous Ti3SiC2 compounds with different Al/Si atom ratios were prepared through the reactive synthesis of elemental powders at 1300 °C. The results indicate that the phase compositions are determined by Al element mole number, and that the pore structure can be controlled through varying Ti particle size. The MAX phase transits from Ti3SiC2 with Al element mole number no more than 0.6 to Ti3AlC2 with Al element mole number in the range of 0.8–1.2. When Al element mole number is 0.6, the porous compound has a single MAX phase of Ti3SiC2 with uniform microporous structure and high bending strength. Porous Ti3SiC2 alloyed with 0.6Al has a slow linear increase rate of 0.0083%/μm in open porosity with increasing Ti particle size, and a strict linear relationship between the maximum aperture and Ti particle size with the increase rate of 0.0342 μm/μm. The pore structure formed by the phase transition mechanism for porous MAX phase has the smallest tortuosity factor compared with that formed by the clearance mechanism and the Kirkendall effect.

The oxidation behavior of porous Ni-16Cr-9Al alloys at 800 and 1 000 °C was studied using the isothermal temperature oxidation method. The differences in surface morphology, phase and pore structure between oxidized and non-oxidized materials were characterized by means of scanning electron microscopy, X-ray diffraction analysis and mercury intrusion porosimetry. The results revealed that the oxidation rate of the samples which were oxidized for 420 h at 800 °C was 0.012%2 h−1 and the oxidation products were Al2O3 and Cr2O3. The oxidation rate of the samples which were oxidized for 390 h at 1 000 °C was 0.415%2 h−1 and the oxidation products were Al2O3, Cr2O3 and Ni(Cr, Al)2O4. All the oxidation kinetics curves obeyed the parabolic law, exhibiting excellent high temperature oxidation resistance.

In this work, the effects of chromium doping methods on the microstructures and properties of Ti(C,N)-based cermets were investigated systematically. The results showed that the existence state of Cr element in the cermet was influenced by the different doping methods. The additive pure Cr powders might cause the appearance of Cr particles and solutions in the binder phase of cermets. However, with the addition of NiCr powders, the Cr element might distribute in the binder phase of cermet. The Cr3C2 addition could make Cr element disperse in the rim and binder phase. Moreover, the Cr atoms dissolved into binder phase might have the solid solution strengthening effect on the binder phase, which increased the hardness of cermets. The Cr element in binder phase could improve the oxidation resistance of cermets owing to the existence of chromium oxide layer in the internal oxidation region. Furthermore, the diffusion process of Mo atoms to the surface during oxidation was prevented by the dissolved Cr element in the binder phase, which led to the increased bonding strength between oxidation layer and unoxidized substrate. In addition, a larger amount NiCr powder addition had the excellent reinforcing effect on the corrosion resistance of cermets due to the appearance of stable chromium oxide film on the binder phase.

Porous MAX compound combines the advantages of metals and ceramics, and has great filtration application prospects in harsh environments. In this work, porous Ti3(Si,Al)C2 was prepared by reaction synthesis of elemental powders, and its cyclic oxidation resistance at 800 °C for 100 h was studied. The synthesized Ti3(Si,Al)C2 has the MAX phase purity above 99 vol% with the maximum aperture, open porosity and permeability of 5.3 μm, 42.9% and 16.27 m3·m−2·kPa−1·h−1, respectively. The oxidation kinetics of porous Ti3(Si,Al)C2 is divided into two stages, which includes the linear law for the initial period within the first 10 h and the parabolic law for the subsequent stable period with their oxidation rate constants of 1.37 × 10−2 h−1 and 4.76 × 10−4 h−1, respectively. The final oxide layer is composed of rutile TiO2 and Al3Ti5O2 phases. In the stable stage, the maximum aperture and open porosity remain nearly constant with slight linear reduction rates of 4.32 × 10−3 μm·h−1 and 5.58 × 10−2%·h−1, which are 2.1% and 3.6% of those in the initial stage, respectively. In the last oxidation procedure of 40 h, the permeability decreases by 2.8%, showing a high stability. The high-temperature oxidation process for porous Ti3(Si,Al)C2 maintains a high and stable permeability and enhances the filtration accuracy by 96.3%, which improves the filtration performance.

(Ti1-x,Zrx)(C0.5,N0.5)-Co cermets doped with various zirconium (x = 0, 0.05, 0.1, 0.15) were fabricated by in-situ carbothermal reduction-nitridation and liquid phase sintering-HIP treatment at 1500 °C. The microstructure, mechanical properties and oxidation resistance of (Ti1-x,Zrx)(C0.5,N0.5)-Co cermets were characterized by scanning electron microscope, X-ray diffraction, mechanical properties tests and high temperature oxidation experiment. The results showed that the existence of zirconium in cermets could refine the hard phase grain and improve the mechanical properties of cermets. The proper zirconium addition promoted the formation of a dense protective layer on the surface of cermets at the high temperature, which might reduce the diffusion rate of the oxygen atom and enhance the oxidation resistance of cermets.

Ni–Cr–Fe alloy samples with different porosities were prepared via the Kirkendall effect, with a reactive synthesis of Ni, Cr, and Fe elemental powders. The microstructure, surface morphology and the compositions were analyzed with X-ray diffraction and scanning electron microscopy. The corrosion behavior was explored in a 2 mol L−1 KOH solution using electrochemical methods and an immersion test. The polarization resistance indicated that the free corrosion potential and the lower corrosion current of the porous Ni–Cr–Fe alloy were −0.18528 V and 3.5998 × 10−7 A cm−2. The immersion test showed that after 25 days of immersion, the weight change of porous Ni–Cr–Fe alloy was 0.132 %, which was less than the porous Ni (0.346 %). X-ray photoelectron spectroscopy results revealed the corrosion products of the porous Ni–Cr–Fe alloy and the porous Ni. The corrosion mechanism of the porous Ni–Cr–Fe alloy was discussed.

The effects of additive Ru powders on the microstructure, mechanical properties, abrasion resistance and corrosion resistant of Ti(C,N)-based cermets manufactured by sinter-HIP treatment are investigated systematically by scanning electron microscope, transmission electron microscope, machining test and electrochemical method. The additive Ru elements in cermets can diffuse into the binder phase of cermets, which can refine Ti(C,N) grains, reinforce binder phase of cermets through solution strengthening mechanism, and improve the mechanical properties of cermet significantly. The Ti(C,N)-based cermets with 1.0 wt% Ruthenium addition can possess the excellent hardness of 92.6 HRA, fracture toughness of 9.11 MPa m 1/2 and transverse rupture strength of 2806 MPa. Moreover, the existence of Ruthenium in binder phase can enhance abrasion resistance of cermets, reduce wear rate of cermets cutting tools, and increase the lifetime of tools obviously. In addition, the addition of 0.5 wt% Ruthenium in cermets may inhibit the dissolution process of binder phase in hydrochloric acid solution and improve the corrosion resistant of cermets.

Porous Ni–Cr–Al alloy samples were fabricated by pressureless sintering of Ni, Cr, and Al elemental powders. The phase transformation, swelling behavior, pore structure parameters, microstructure, and pore formation mechanisms of porous Ni–Cr–Al alloys were systematically investigated. Results show that obvious swelling behavior occurs during sintering. The open porosity of the Ni–Cr–Al alloy increases as the sintering temperature increases below 920°C, followed by a relatively declining value for phase transformation beyond 920°C. The porous Ni–Cr–Al alloy samples exhibit an open porosity of 35.02% when sintered at 1200°C for 3 h. The main pore formation mechanisms are the Kirkendall effect and the development of interparticle pores.

In this study, Ti(C,N)-WC-NbC-ZrC-Co-Ni cermets were prepared by sintering-hip at 1450 °C. The effect of ZrC addition on the microstructure, mechanical properties, oxidation resistance and wear resistance of Ti(C,N)-WC-NbC-Co-Ni cermets were explored in detail. The results show that ZrC addition plays the role of inhibitor in the dissolution–reprecipitation process, which can increase the wear-resistant carbide phases and inhibit the precipitation of brittle (Ti,W,Nb)(C,N) rim phase. Therefore, the core-rim structures are refined and the Nb content in binder increases, which enhance mechanical properties and oxidation resistance of cermets. With the increasing ZrC content, the oxidation resistance of cermets can be improved constantly, while the transverse rupture strength, fracture toughness and wear resistance of these cermets increase first and then decrease. The cermet with 1 wt% ZrC exhibits the transverse rupture strength of 2549 MPa and highest fracture toughness of 13.0 MPa m1/2. The oxidation weight gain of cermets containing 5 wt% ZrC after holding 100 h at 750 °C in air is 2.8 × 10−6 g mm−2, which is only 22% of that in the cermets without ZrC addition.

A powder metallurgy route which is characterized by the vacuum solid state sintering is utilized to fabricate Fe-20Cr-3C and Fe-20Cr-3C-2Mo-3V-2Co ultra high-carbon martensitic stainless steels. A sintering window from 1190 °C to 1210 °C is chosen to obtain high density samples and avoid liquid phase simultaneously. The densification process is promoted by solubility effect during formation of M7C3 and grain boundary diffusion. TEM analysis demonstrates three types of reaction products: the La(BO2)3 phase, the La2O3 phase and the La(Fe0.5V0.5)O3 phase, after adding 0.1 wt% LaB6. The impurity elements such as S and O are absorbed following the LaB6 addition to form non-gaseous products, which promotes densification by decreasing the sintering resistance and thus contributes to the improvement of bending strength and hardness. Both of the electrochemical and immersion results lead to the fact that the corrosion resistance of the steels are improved by 0.1 wt% LaB6 addition, in 3.5 wt% NaCl solution. However, the corrosion resistance of Fe-20Cr-3C-0.1LaB6 still can not compete with that of 316L stainless steel. Nevertheless, Fe-20Cr-3C-2Mo-3V-2Co and Fe-20Cr-3C-2Mo-3V-2Co-0.1LaB6 after quenching at high temperature present comparable corrosion resistance with that of 316L in 3.5 wt% NaCl solution.

Porous intermetallic compounds fabricated by reactive synthesis of elemental powders exhibit good pore formation capability and unique properties integrating the advantages of both metals and ceramics. The following aspects for the reactively synthesized porous intermetallics are reviewed: (1) near-net shaping fabrication process of porous intermetallics through an elemental powder mixture, (2) theoretical basis of the reactive synthesis procedure, (3) the pore structure properties and their quantitative relations, (4) the material properties including the mechanical property, acid and alkali corrosion resistivity, high temperature oxidation and sulfuration resistance, machinability, weldability, thermal shock resistance, hydrogen evolution activity, etc. and (5) applications of porous intermetallics in industrial filtration fields.

A novel method for suppressing the Selfpropagating High-temperature Synthesis (SHS) reactions during synthesis of porous FeAl intermetallics by introducing silicon (Si) was proposed. The exothermic behaviors, microstructures and phase compositions of Fe/Al/Si compacts with a content of 1–5 wt% Si were investigated to gain an insight into the mechanism of Si for influencing the diffusion reactions in Fe-Al system. The results showed that the interdiffusion and reaction velocities of Fe/Al/Si compacts were restrained due to the segregation of Si in the Fe-Al interface, which could avoid the intensive heat release from Fe-Al reactions. After final sintering, diffusional homogenization of porous FeAl intermetallics could be achieved. The beneficial effect of Si in preventing SHS reactions has been further verified in the industrial manufacturing of FeAl filter elements.

Sintering behavior of TiC-Fe-Co-Ni-Cr-Mo cermets with excellent mechanical properties and corrosion resistance was researched systematically by measurements of hardness, transverse rupture strength, scanning electron microscopy, X-ray diffraction and Tafel extrapolation. Results showed that with increase in sintering temperature, the hardness of sintered cermets increased constantly, while the transverse rupture strength initially increased and then decreased. Transverse rupture strength of cermets sintered at 1290 °C reached peak value of 2358.1 MPa. Moreover, cermets sintered at 1370 °C with transverse rupture strength of 1514 MPa and hardness of 67.6 HRC showed the best abrasive resistance and Icorr values of 1.611×e −7 .

A novel technology which was characterized by the vacuum solid state sintering was developed for powder metallurgy high speed steels production. During sintering, both the WC and Mo2C reacted with Fe and transformed to W and Mo rich M6C carbides which were the common hard phases in high speed steels. Also, a high number of W, Mo and Fe were dissolved in VC, forming the MC carbides. The densification of the material mainly relied on the solubility effect during the M6C and MC carbides formation. By alloying with a 0.1 wt% of LaB6 to the steel, the bending strength and the fracture toughness were improved from 3290 MPa and 25.6 MPam1/2 to 4018 MPa and 29.4 MPam1/2, respectively. The TEM analysis demonstrated three types of reaction products by the LaB6 addition: the amorphous phase, the core-shell structure and the La2O3 phase. The impurity elements such as the Mg, Al, Si, S, Ca, and O were absorbed following the LaB6 addition. Moreover, the deoxidization effect caused by the LaB6 addition promoted the sintering at a high-temperature period which contributed to the bending strength and fracture toughness improvement.

Tungsten carbide-cobalt cermets respectively doped with 0, 0.5, 1.0, 1.5 and 2. wt% aluminum nitride were fabricated by the sintering process at 1400. °C. The existence of aluminum nitride in the binder phase could refine tungsten carbide grains and reinforce the obtained cermets. The cermets with 1.0. wt% aluminum nitride exhibited the higher hardness of 17.1. GPa and transverse rupture strength of 3120. MPa, compared with 15.6. GPa and 2500. MPa of the pure cermets. Owing to the addition of aluminum nitride, a high oxidation resistance was measured in cermets with 2.0. wt% aluminum nitride, which is nearly 1.9 times than that in the pure cermets.

In this study, the effects of carbon additions on the microstructure, hardness, transverse rupture strength and abrasion resistance of Ti(C,N)-Fe cermets manufactured by powder metallurgy method were investigated by scanning electron microscopy, X-ray diffraction and mechanical properties tests. The results show that the microstructure of sintered Ti(C,N)-Fe cermets exhibits the homogeneous distribution of Ti(C,N) hard phase when 1.0 wt% carbon was added into the cermets. The transverse rupture strength of cermet can reach the peak of 2435 MPa and the fracture morphology can include a vast of transgranular fracture. Moreover, the comprehensive performance of Ti(C,N)-Fe cermets can improve significantly through the heat-treatment process. The hardness and transverse rupture strength of cermets after heat-treatment are 70.0HRC and 2483.2 MPa. The Ti(C,N)-Fe cermets have a potential application in machining.

Using hexa(4-carboxylphenoxy)cyclotriphosphazene (HCPCP) with six carboxyl groups as the core, a new kind of star-branched PA12 with hexafunctional cyclotriphosphazene core was prepared in the ring-opening polymerization of ω-laurolactam. The relationship between the structure and properties of star-branched PA12 had been systematically investigated. Compared with linear PA12, star-branched PA12 has lower relative viscosity and higher melt flow rate while its mechanical properties can be almost retained by the use of star-branching and an appropriate molecular weight. Research on crystallization and rheological behaviors indicate that star-branched PA12 with appropriate molecular weight has the faster crystallization rate, the higher flowability and the lower processing temperature and pressure than linear PA12, which could be used as the easy processing polyamide resin for the rapid molding process.

Ordered porous polymer membranes can be facilely prepared by breath figures. Previous studies have confirmed that the solidifying of polymer is crucial for the formation of ordered porous structures, which directly depends on the hydrophobicity of polymer. However, it is still unknown how strong hydrophobicity is required. Here, cellulose acetate derivatives (CADs) were used to investigate the effect of hydrophobicity on ordered porous structures. The CADs with different hydrophobicity were firstly synthesized via simple reactions, and then the porous membranes were fabricated by the breath figure method. It was found that the pore size showed a decreasing trend with hydrophobicity, and the degree of order of porous structures firstly increased and then dropped, showing a critical hydrophobicity value for the transition of the degree of order. Therefore, it was confirmed that suitable hydrophobicity is critical for ordered porous structures of CADs while excessive hydrophobicity may impair the ordered structures.

In this study, the surface oxidation phenomenon of raw powders in the preparation of binderless titanium carbonitride-based ceramics was investigated, which might hinder the densification process. In order to reduce the oxidation and strengthen mutual diffusion, the micrometer-sized powder mixtures of Ti(C,N) and carbides additives, pre-alloyed (Ti,W,Mo,Ta)(C,N) solid solution powders were used. The utilization of solid solution raw powders can reduce the oxidation and promote densification effectively. In this way, the binderless ceramics with high relative density and great mechanical properties were fabricated. The hardness, transverse rapture strength and fracture toughness of materials prepared by solid solution powders were 2030 HV, 1280 MPa and 7.8 MPa m1/2, respectively. Moreover, the obtained binderless titanium carbonitride-based ceramics were found with low friction coefficient, excellent wear and oxidation resistance. The great oxidation resistance was attributed to the formation of rutile-type oxidation products facilitated by the existence of other metal elements in the ceramics.

Porous FeSi intermetallic compound was prepared by reactive synthesis of elemental powders. The evolutions of phase composition, microstructure and pore structure of Fe–Si compacts during the synthesis procedure were investigated, as well as the corrosion resistivity of the porous material against sulfuric acid solution. The results show that the major phases are generated in the order of α-Fe, Fe3Si, η-Fe5Si3 and e-FeSi during the sintering process. The skeletons of Fe5Si3 and FeSi phases are formed successively, resulting in a large number of connected pores in the compact. The final synthesized porous compound has the FeSi phase purity of 95.4 wt%. The open porosity, maximum pore size and gas permeability of porous FeSi are 53.8%, 14.1 μm and 92.20 m3 m−2 kPa−1·h−1, respectively. The radial dimension variation ratio, pore size and permeability show the linear change regulation with the sintering temperature with the change rate constants being 1.51 × 10−2%·°C−1, 5.3 × 10−2 μm·°C−1, 1.45 × 10−1 m3·m−2·kPa−1·h−1·°C−1, respectively. The pore size and permeability show the linear change law with the initial Fe powder size with the change rate constants being 5.4 × 10−2 μm·μm−1 and 3.05 × 10−1 m3·m−2·kPa−1·h−1·μm−1, respectively. The corrosion kinetics of the synthesized porous FeSi compound in 160 g·L−1 sulfuric acid solution shows a characteristic of two stages with the average corrosion rates being 2.11 × 10−3%·h−1 and 1.18 × 10−4%·h−1, respectively, in which porous FeSi shows good pore structure and microstructure stability.

Because of the poor performance of starch-based composites, we prepared the starch-based composites with good mechanical properties by a simple two-step melt-blending extrusion. Glycerol and nano-SiO2 were firstly introduced into starch to prepare the TPS/nano-SiO2 composite by the first extrusion, and poly(butylene adipate-co-terephthalate) (PBAT) and the compatibilizers were then incorporated to obtain the improved composites by the second extrusion. The mechanical properties, thermal properties, morphology, and structure of the composites were characterized. The results showed that the strength dramatically increased after the addition of nano-SiO2 into starch, and the elongation at break was significantly improved by the incorporation of PBAT. The tensile strength was increased distinctly after the addition of the compatibilizers. All the composites exhibited good mechanical properties. The melting transition, the thermal stability, and the crystalline structure did not change with the additives, whereas the glass transition of the starch-rich phase shifted to a lower temperature. The results indicated that the combined compatibilizers had better compatibilization than each one alone.

In this work, surface carburization has been performed on Ti–45Al–7Nb–0.3W alloy. The isothermal oxidation behavior of the alloy has been investigated in static air at 950 °C for 100 h. X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied to study the microstructural evolution. The results reveal that the carburized layer, with a thickness of 7.4 μm, is composed of nano-structured Ti 2 AlC and Ti 3 AlC phases. The oxidation weight gain of the carburized TiAl is half of that of the bare TiAl. The oxide scale of the carburized TiAl is compact without delamination and spallation. The inward diffusion of oxygen atom was hindered due to the existence of the carburized layer. Therefore, the carburization process is an effective and feasible treatment to improve the oxidation resistance of high Nb contained TiAl alloys.

For titanium aluminide (TiAl) alloys, the high cost mainly comes from the forming process since the workability of TiAl alloys is quite low. To optimize the workability, introduction of β phase is an effective way. In the present study, a novel TiAl material alloyed with cheap β-stabilizing elements, Mo and Fe, was developed. The deformation behavior of the new alloy was characterized, and further alloying with interstitial elements to improve the high temperature properties was explored. Results show that the designed Ti–45Al–3Fe–2Mo at.% alloy has a fine grain β-stabilized microstructure. It shows a wide forging window, providing the foundation for an industrial forging process. The good deformability is derived from dynamic recrystallization of β phase and deformation-induced β → α 2 + γ transformation. With the addition of 0.5% C, the creep properties can be significantly improved, which is mainly caused by the decrease in the amount of β phase and the precipitation of P-type carbides.

We have designed and synthesized two low bandgap conjugated copolymers containing alternating meta-fluoro-p-alkoxyphenyl- (m-FPO-) or p-fluoro-m-alkoxyphenyl- (p-FPO-) substituted benzodithiophenes-co-benzooxadiazole (BO), named PBO-m-FPO and PBO-p-FPO. The properties, including UV–vis absorption, charge mobility and photovoltaic performance of the two polymers have been intensively investigated. The results indicated that the introduction of fluorine atom at m, p positions of phenyl substituted benzodithiophene unit hardly affected their absorption spectra and highest occupied molecular orbital (HOMO) level. However, the two polymers showed different photovoltaic properties. Power conversion efficiencies (PCEs) based on the device structure of ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al demonstrated a large distinction (5.9% for PBO-m-FPO vs 2.8% for PBO-p-FPO) at optimal weight ratio. When replacing the Ca layer with zirconium acetylacetonate (ZrAcac), using 3% 1,8-diiodooctane (DIO) as the active layer additive...

The porous Ni–Cu alloy with different porosity was fabricated through mixed elemental powders reaction synthesis by step sintering in vacuum furnace. The corrosion resistance and corrosion mechanism of the sintered porous Ni–Cu alloy in hydrofluoric acid (HF) were investigated by the immersion test, the potentiodynamic polarization and the electrochemical impedance spectroscopy (EIS) techniques. Results show that the sintered porous Ni–Cu alloy exhibits good corrosion resistance in hydrofluoric acid solution, compared with porous Ni. The corrosion rate of the sintered porous Ni–Cu is dependent upon the concentration of hydrofluoric acid solution, no passive phenomenon is found in potentiodynamic polarization curve in any concentration. Double capacitive loops for the porous Ni–Cu alloy in EIS results show that the corrosion process is controlled by electrochemical reaction. Moreover, the porosity has little influence on the corrosion resistance of the sintered porous Ni–Cu alloy in hydrofluoric acid solution, which is most likely due to the homogenous pore structure and chemical composition of the material, as well as the chemical stability of the bulk alloy itself.

A novel porous material Ti3SiC2 is synthesized using reactive synthesis of mixed elemental powders. The synthesized porous Ti3SiC2 has high purity more than 99.0%. By adjusting the fabrication parameters, porous Ti3SiC2 can be synthesized with average pore diameters ranging from ∼200 nm to over ∼40 μm and open porosity ranging from ∼19.5% to ∼53.2%. The pore formation mechanism has been studied. Also, the synthesized porous Ti3SiC2 material presents promising mechanical properties. This novel porous material has the potential to replace the traditional inorganic porous material.

Carburization was carried out to improve corrosion resistance of porous Ti–46.5 Al (at.%) intermetallic compound. X-ray diffractometry (XRD) and scanning electron microscopy (SEM) were applied to analyze the carburized layers. Electrochemical corrosion behavior of the untreated and the carburized samples were investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and open circuit potential. The results reveal that the continuous and thick carburized layers form after carburization treatment at 1203 K for 10 h, whose main phase is a functional complex ceramic phase, Ti 2 AlC. Carburization can improve corrosion resistance of the porous TiAl alloy. Among the carburized samples, the carburized one at 1203 K for 10 h presents the highest corrosion resistance and has the most stable oxide film.

In this work, high Nb-containing TiAl alloy sheets were hot rolled starting from powder metallurgical billets. The prealloyed powder prepared by the plasma rotation electrode process (PREP) was characterized. Results show that there are two typical morphologies of powders: martensitic (M) and dendritic (D) powders, which are formed due to different local cooling conditions. The two PREPed powders lead to the formation of different microstructures in HIPing. The coarse D powder will introduce defects, such as residual primary particle boundaries and interfacial porosity in the as-HIPed microstructures. The deformation behavior of PM high-Nb TiAl alloys largely depends on γ phase. Besides the dynamic recrystallization and the superplastic deformation, due to the large amount of the γ phase in PM high-Nb TiAl alloy and the high rolling rate, the mechanical twinning in γ phase plays a critical role in the hot rolling process. The mechanical properties of high-Nb TiAl alloys can be significantly improved by the hot rolling, through the refinement of microstructures and the elimination of primary particle boundaries. However, a large deformation may introduce defects and coarsened microstructures, and thus 60% deformation may be suitable for the purpose of improving mechanical properties.

High temperature compressive deformation behaviors of a high Nb-containing PM-TiAl alloy (Tie45Al e7Nb-0.3 W, at.%) were investigated at temperatures ranging from 1050 � C to 1200 � C, and strain rates from 0.001 s � 1 to 1 s � 1 . The microstructure mainly consists of g phase. The data obtained from the flow curves were employed to develop the constitutive equation, and the apparent activation energy (Q )w as determined to be 414 kJ mol � 1 . The size of the dynamically recrystallized grains (DRX) decreased with the increasing value of ZenereHollomon (Z) parameter. A processing map was constructed on the basis of the flow stress, and the condition of intermediate Z (1150 � C, 0.1 s � 1 ) was determined to be the optimum hot forging parameter for industrial productions. DRX was observed under all the deformation conditions. At high Z and intermediate Z condition, dislocation climbing and twinning accompanied by DRX can act as the main deformation mechanisms. At low Z condition, DRX becomes the dominant softening mechanism, accompanied by the bending of lamellar colonies as well as the broken of g grains and a2 grains.

Porous Ti 3 AlC 2 ceramics were fabricated by reactive synthesis. The process of fabrication involved five steps: (i) the pyrolysis of stearic acid at 450 °C; (ii) the decomposition of TiH 2 at 700 °C, which leads to the conversion of TiH 2 to Ti; (iii) the solid–liquid chemical reaction of solid Ti and molten Al at 800–1000 °C, which converts the mixture to Ti–Al compounds; (iv) the newly synthesized Ti–Al compounds that react with surplus Ti and graphite to form ternary carbides and TiC at 1100–1200 °C; and (v) reactive synthesized ternary carbides and TiC that yield porous Ti 3 AlC 2 at 1300 °C. The effects of sintering temperature and Al contents on porosity, pore size and permeability of porous Ti 3 AlC 2 ceramics were examined. The results revealed that the porosity and permeability tended to increase with reactive sintering temperature. The pore forming mechanism accompanying phase transformation was explored in this study.

In this work, the effects of micron grained WC additions on the microstructure and properties of ultrafine WC–(micron WC–Co) cemented carbides produced through low pressure sintering processes were investigated by scanning electron microscope and mechanical properties tests. The results show that the obvious crack deflection and transgranular fracture phenomenon could be observed with the addition of micron WC, which can resist the crack propagation and improve the toughness of cemented carbides. The sintered ultrafine WC–(micron WC–Co) hardmetals demonstrate excellent hardness and fracture toughness values (HV30: 1700 kg/mm2, KIC: 13.82 MPa m1/2). These inhomogeneous ultrafine WC–(micron WC–Co) cemented carbides have considerable potential for use in structural applications.

Porous Ti3AlC2 ceramics were fabricated through the reactive synthesis method with TiH2, Al and graphite powders. The effect of Al content on phase constitution, volume expansion, pore size and permeability were studied systematically. The experimental results showed that the Al content has a great affect on the properties and pore structures of porous Ti3AlC2 ceramics. When Al molar ratio was less than 1.2, the volume expansion ratio, the amount of Ti3AlC2 and porosity were improved with the increase in Al content. In contrary, these parameters of the porous Ti3AlC2 decreased while the Al molar ratio was more than 1.2. However, it was interesting to notice that the evolution of pore size and permeability was opposite to that of porosity. The fundamental reasons behind these phenomena have been explored. The pore structure forming mechanism by active sintering synthesis has also been proposed.

High temperature compressive deformation behaviors of PM-TiAl alloy containing Nb particles (Ti–45Al–5Nb–0.4W/2Nb (at. %)) were investigated at temperatures ranging from 1050 °C to 1200 °C, and strain rates from 0.001 s−1 to 1 s−1. The flow curves were employed to develop constitutive equations, and the apparent activation energy of deformation Q was determined as 447.35 kJ/mol. A revised processing map was constructed on the basis of the flow stress, which can accurately describe the deformation behaviors and predict the optimum hot forging condition. The addition of 2% Nb particles reduces the peak stress and increases the activation energy of TiAl-based intermetallic, however, it increases the instable domain in the processing map.

The phase equilibrium of the Al-Fe-Gd plays an important role of development of bulk amorphous alloys and magnetocaloric materials. The entire isothermal section of the phase diagram for Al-Fe-Gd ternary system at 773 K has been investigated by means of x-ray powder diffraction, scanning electron microscopy with energy dispersive analysis, and optical microscopy. The existences of 13 binary compounds for the Al-Fe, Al-Gd, and Fe-Gd binary systems were confirmed. The binary phases, i.e., Al2Gd, Fe2Gd, and α-Fe17Gd2 present appreciable ternary solubility. Three ternary compounds: τ1-Al10Fe2Gd, τ2-Al8+x Fe4-x Gd (0 ≤ x ≤ 2), and λ-Al2−x Fe x Gd (0.951 ≤ x ≤ 1.245) were determined. The isothermal section consists of 19 single-phase regions, 40 binary-phase regions, and 20 ternary-phase regions.

High Nb-containing TiAl porous and gradient porous alloys were synthesized by elemental powder metallurgy (EPM). The effects of powder size on pore structure and gas permeability were investigated. It is found that pores are interconnected and skeletons consist of typical γ-TiAl/α 2 -Ti 3 Al fully lamellar microstructure for Ti–48Al–6Nb porous alloys. With the fining of particle size of Ti, Al and Nb powders, the pore size and porosity of Ti–48Al–6Nb porous alloys decrease. Otherwise, the gas permeability increases almost linearly when the porosity increases from 17% to 52% and the pore size increases from 3.18 μm to 26.69 μm. A good agreement is shown between the simulations by capillary permeability model and the results of the actual gas permeability. In addition, gradient porous alloys were fabricated using different powder sizes by constrained sintering process, and a prediction of the relationship between permeability and coating thickness was discussed. Results from this study indicate the potential applications in microfiltration development by tailoring porosity of the coating.

Pore structure control methods for porous FeAl intermetallics were studied in this paper based on pore formation mechanism. A large range of pore structure parameters can be obtained through fabrication parameter adjustment in porous FeAl preparation procedure. Open porosity and maximum pore size of porous FeAl have a direct proportional relationship to the powder size of raw materials and an inversely proportional relationship to the pressing pressure. The relationship between maximum pore size (dm) and raw material powder size (dp) can be determined as d m = 0.40 d P . Open porosity and maximum pore size decrease with increasing holding time at solid diffusion reactive procedure. The quantitative relationship between open porosity (θ) and holding time (t) at 600 °C is θ = 49.7 − 0.1 t ( 60 ≤ t ≤ 240 ) ; the quantitative relationship between maximum pore size (dm) and holding time (t) at 600 °C is d m = 20.3 − 0.065 t ( 60 ≤ t ≤ 240 ) .

A new tetrafluoridequinoxaline electron accepting block from a quinoxaline core, which is substituted with a fluorine atom onto its backbone and side chains, was designed. A new copolymer (PBDTT-ffQx) was synthesized from tetrafluoridequinoxaline and benzodithiophene. The copolymer was characterized in detail. The photovoltaic properties were well investigated. A high PCE of 8.6% based on the single junction device was obtained.

A new solution-processable organic small molecule, namely, TPA–DTBTz–TPA with triphenylamine (TPA) as electron donor and dithienylbenzotriazole (DTBTz) as electron acceptor was synthesized by a Heck cross-coupling reaction, and characterized by 1H NMR, TGA, UV–vis absorption, and cyclic voltammetry. The compound was found to be easily soluble in common organic solvents, such as chloroform, tetrahydrofuran and chlorobenzene with excellent film forming properties. TPA–DTBTz–TPA film exhibits an absorption band from 300 to 620 nm. The organic solar cells based on a blend of TPA–DTBTz–TPA and PC60BM (1:2, w/w) show a power conversion efficiency (PCE) of 0.93% with a short circuit current density of 4.43 mA/cm2 and an open circuit voltage of 0.74 V, under the illumination of AM 1.5, 100 mW/cm2.

The mechanical, electronic and thermodynamic properties of Al 12 X ( X = Mo, W, Re) compounds are investigated by means of density functional theory (DFT) based calculations. The calculated lattice constants of the compounds are in good agreement with the experimental data. Compared with the other theoretical data, the calculated formation enthalpy of Al 12 Mo is very accurate. The elastic constants of the three compounds have been calculated, and the bulk modulus, shear modulus, and Young’s modulus have been evaluated. The calculated results indicated that all three compounds show brittle behavior. The electronic density of states (DOS) and the bonding charge density have also been calculated to elucidate the bonding mechanism in these compounds and the results indicate that bonding characteristic is mostly of covalent nature. Finally, using a quasiharmonic Debye model, the Debye temperature, the heat capacity, the coefficient of thermal expansion and the Gruneisen parameter have also been obtained in the present work. The present calculations show that the Al 12 X (Mo, W and Re) intermetallics can enhance mechanical properties of the Al-matrix dramatically.

Tetragonal tungsten nanowire arrays were successfully fabricated on tungsten substrate using Ni catalysts by chemical vapor deposition (CVD) at 950 °C. The synthesized tungsten nanowires grew along [100] direction, with a high aspect ratio more than 50 and sharp tips. The Ni catalyst was found to be located at the wire's bottom and assisted the nucleation of the tungsten nanowire. Samples were characterized in detail by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) technologies. Based on the analysis of the experimental results, the possible formation mechanism of nanowires was proposed as well.

Porous Ni3Al alloys was prepared by cold pressing and reactive synthesis of Ni and Al elemental powders via the Kirkendall effect. Corrosion behavior of porous Ni3Al alloys was investigated by electrochemical tests and weight change measurements. Polarization resistance indicated that porous Ni3Al had more positive free corrosion potential and lower corrosion current than porous Ni and porous Ti and exhibited a wider passive region. The immersion test revealed that after 2000 h immersion, the weight change and pore structure of porous Ni3Al stayed stable in KOH solution. The influence of temperature on corrosion behavior and corrosion mechanism of porous Ni3Al were also discussed. (C) 2011 Elsevier Ltd. All rights reserved.