Corrosion of Y, Fe and Fe-15Y in H_2-H_2S Mixture under 10~(-3) Pa S_2 at 600～800℃

The corrosion of an Fe-based alloy containing 15 wt pct Y in H2-H2S mixtures under 10-3 Pa S2 was studied at 600~800℃ in an attempt to find materials with improved sulphidation resistance with respect to pure Fe. The presence of Y has been shown to be beneflcial, but not sufficient to the level expected. In fact, the alloy is able to form at all tested temperatures an external FeS layer, beneath which a zone containing a mixture of the two sulphides is also present. Thus,Fe can still diffuse through this region to form the outer FeS layer with non-negligible rate. The corrosion rate of Fe is considerably reduced by the Y addition. but the alloy corrodes still much more rapidly than Y. The sulphidation kinetics is generally rather irregular for both the pure metals, while the corrosion rate of the alloy decreases with time and tends to become parabolic after an initial period of 12~17 h. The sulphidation behaviour of the alloys is discussed by taking into account the presence of an intermetallic compound Fe17Y2 and the limited solubility of Y in Fe     

Oxidation of NiAl-Ag Alloys at 1000℃ in 0.1 MPa O_2

Small amounts of silver have been added to the intermetallic compound NiAl with the purpose of improving its mechanical properties. Four ternary NiAI-Ag alloys containing 0.5, 1, 5 and 10 at. pct Ag, denoted as NiAI-0.5Ag, NiAI-1Ag, NiAI-5Ag and NiAI-10Ag, and the Ag-free NiAl have been oxidized at 1000℃for 24 h in 0.1 MPa O2 to study the effect of the presence of silver on the oxidation behavior of NiAl. All the NiAI-Ag alloys are composed of a matrix of β-NiAI containing a dispersion of isolated particles of a second silver-rich phase. A continuous external layer of AI2O3 formed on all the alloys. In addition, the scales formed on NiAI-5Ag contained a thin and discontinuous layer of pure silver located at the alloy/AI2O3 interface, while those formed on NiAI-10Ag contained isolated particles as well as discontinuous layers of silver at various locations in the scale extending up to the gas/scale interface. The kinetic curves of all the alloys were generally composed of two main parabolic stages with smaller parabolic rate constants for the final stage. The addition of silver does not significantly affect the oxidation behavior of the NiAl intermetallic compound in all cases, as expected because silver is essentially present only as a second phase due to its very small solubility in β-NiAI.     

Oxidation of NiAl-Ag Alloys at 1000℃ in 0.1 MPa O2

Small amounts of silver have been added to the intermetallic compound NiAl with the purpose of improving its mechanical properties. Four ternary NiAl-Ag alloys containing 0.5, 1, 5 and 10 at. pct Ag, denoted as NiAl-0.5Ag, NiAl-1Ag, NiAl-5Ag and NiAl-10Ag, and the Ag-free NiAl have been oxidized at 1000℃ for 24 h in 0.1 MPa O2 to study the effect of the presence of silver on the oxidation behavior of NiAl. All the NiAl-Ag alloys are composed of a matrix of β-NiAl containing a dispersion of isolated particles of a second silver-rich phase. A continuous external layer of Al2O3 formed on all the alloys. In addition, the scales formed on NiAl-5Ag contained a thin and discontinuous layer of pure silver located at the alloy/Al2O3 interface, while those formed on NiAl-10Ag contained isolated particles as well as discontinuous layers of silver at various locations in the scale extending up to the gas/scale interface. The kinetic curves of all the alloys were generally composed of two main parabolic stages with smaller parabolic rate constants for the final stage. The addition of silver does not significantly affect the oxidation behavior of the NiAl intermetallic compound in all cases, as expected because silver is essentially present only as a second phase due to its very small solubility in β-NiAl.     

Phase Relations in TiAl+Nb System

The microstructures and phases of ternary TiAl+Nb alloys containing 50-60 at.-%Al, 0-21 at.-%Nb have been studied using transmission electron microscopy (TEM) and X-ray powder diffraction. The phases present in the alloys and their distribution were found to be a sensitive function of composition. The phase relations between γ-TiAl and γ1 (a new ordered ternary intermetallic compound based on γ-TiAl) were determined. Essentially single γ phase was determined for alloys with relativety low Nb content (≤10 at.-%Nb). the γ1 phase was determined to exist in the composition range containing higher Nb contents (15-21 at.-%Nb). Between γ and γ1 phases, with intermediate Nb contents there is a transitional phase γ1 (a superstructure of γ-TiAl). As for the influence of Al concentration on the phase relations. the γ1 phase was inclined to form in the alloys with relatively high Al contents. The ordering transformation of γ, to γ1 is a continuous ordering process and the transition may be second order.     

Solderability of Electrodeposited Fe-Ni Alloys with Eutectic SnAgCu Solder

Solderabilities of electrodeposited Fe-Ni alloys with SnAgCu solder were examined by wetting balance measurements and compared to those of pure Ni and pure Fe platings. Excellent solderability was found on the Ni-52Fe plating as both the wetting force and kinetics approached or exceeded those on the pure Ni. However, upon further increase in Fe content to 75 at. pct, the solderability of the alloy was severely degraded even though it was still better than that of the pure Fe plating. X-ray photoelectron spectroscopy showed that such a strong dependence of solderability on Fe content is related to the much thinner, incomplete oxide coverage of Ni-rich plating surface.     

Accelerated Corrosion of Pure Fe Induced by Gaseous ZnC12 at High Tempreratures

ZnCl2 is one of the dominant aggressive species in waste incinerators or other advanced combustion power generation systems. In this study, the influence of minor amount of gaseous ZnCl2 on the corrosion behavior of pure iron was examined at 600--800℃ in a pure oxygen environment. The corrosion rate usually increased markedly with increasing temperatures at a fixed ZnCl2 content or with increased ZnCl2 contents at a constant temperature. The corrosion products were composed of a thin outer layer of ZnFe2O4 spinel and an inner zone with a much thicker layer of Fe2O3, which exhibited a serious separation from the matrix. Moreover, a molten FeCI2 layer was observed at the scale substrate interface. The accelerated corrosion of pure iron was attributed to the existence of FeCl2 with low melting point on the metal surface, which destroyed the cohesion and adhesion of the oxide scale. The results are discussed in relation to the thermodynamic factors and the presence of volatile compounds in the reaction system.     

Calculation of Surface Energy of Metals and Alloys by theElectron Density Functional Method

The surface energy values of (100), (110), (111) surfaces in Ni. Al and ordered alloys NiAl and Ni3Al have been calculated within the framework of methodology based upon the electron density functional method. The results of calculations are in good agreement with the known for pure metals experimental data and in case of Ni3Al allop There is also a good agreement with the results obtained by calculation using the embedded atom method. The investigation has been carried out in this work to show that the surface energy σ of alloys can not be interpreted as an averaged concentration σ of pure metals. For NiAl, the obtained resulsts reveal considerable distinctions in anisotropy of a in comparison to the anisotropy of surface energy in pure matals.     

Growth of carbon nanotube arrays on various CtxMey alloy films by chemical vapour deposition method

Carbon nanotube(CNT) arrays were fabricated on Ct-Me-N-(O) alloys with content of Ct in the range of 6–40 at.% by chemical vapour deposition. The Ct was a catalytic metal from the group of the following elements: Ni, Co, Fe, Pd, while Me was a transition metal from the group of Ⅳ–Ⅶ of the periodic table(where Me = Ti, V, Cr, Zr, Nb, Mo, Ta, W, Re). Carbon nanotubes were found to grow efficiently on the alloy surface with its composition containing Ti, V, Cr, Zr, Hf, Nb or Ta. The growth of CNTs was not observed when the alloy contained W or Re. Additions of oxygen and nitrogen in the alloy facilitated the formation of oxynitrides and catalyst extrusion on the alloy surface. Replacement of the metals in alloy composition affected the diameter of the resulting CNTs. The obtained results showed that the alloy films of varying thickness(10–500 nm) may be used for the CNTs growth. The resulting CNT material was highly homogenous and its synthesis reproducible.     

In Vivo and In Vitro Degradation Behavior of Magnesium Alloys as Biomaterials

The corrosion behavior of pure Mg,AZ31,and AZ91D were evaluated in various in vitro and in vivo environments to investigate the potential application of these metals as biodegradable implant materials.DC polarization tests and immersion tests were performed in different simulated body solutions,such as distilled(DI) water,simulated body fluid(SBF) and phosphate buffered solution(PBS).Mg/Mg alloys were also implanted in different places in a mouse for in vivo weight loss and biocompatibility investigations.The in vivo subcutis bio-corrosion rate was lower than the corrosion rate for all of the in vitro simulated corrosive environments.The Mg/Mg alloys were biocompatible based on histology results for the liver,heart,kidney,skin and lung of the mouse during the two months implantation.Optical microscopy and scanning electron microscopy were carried out to investigate the morphology and topography of Mg/Mg alloys after immersion testing and implantation to understand the corrosion mechanisms.     

Processing of Ceramic Based Nanocomposite Using α-Al2O3 Powder and FeCl2 Solution as Starting Materials

Alumina-iron nanocomposite powders were prepared by a two-step process. In the first step, α-Al2O3-FeCl2 powder mixture was formed by mixing α-Al2O3 powders with FeCl2 solution followed by drying. In the second step, the FeCl2 in the dry power mixture was selectively reduced to iron particles. A reduction temperature of 750℃ for 15 min in dry H2 was chosen based on the thermodynamic calculations. The concentration of iron in FeCl2 solution was calculated to be 20 vol. pct in the final composite. Two techniques were used to produce composite bulk materials. The Al2O3 nanocomposite powders were divided to two batches. The first batch of the produced mixture was hot pressed at 1400℃ and 27 MPa for 30 min in a graphite die. To study the effect of oxygen on the Al2O3/Fe interface bonding and mechanical properties of the composite, the second batch was heat treated in air at 700℃ for 20 min to partially oxidize the iron particles before hot pressing. Characterization of the composites was undertaken by conventional density measurements, X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and electron probe micro analysis （EPMA）. The suggested processing route （mixing, reduction and hot pressing） produces ceramic-metal nanocomposite much tougher than the pure Al2O3. The fracture strength of the produced Al2O3/Fe nanocomposite is nearly twice that of the pure Al2O3. The presence of spinel phase, FeAl204, as thick layer around the Fe particles in the Al2O3 matrix has a detrimental effect on interfacial bonding between Fe and AI203 and the fracture properties of the composite.     

In Vitro Evaluation of the Feasibility of Commercial Zn Alloys as Biodegradable Metals

In this work, three widely used commercial Zn alloys(ZA4-1, ZA4-3, ZA6-1) were purchased and prepared by hot extrusion at 200 °C. The microstructure, mechanical properties, corrosion behaviors,biocompatibility and hemocompatibility of Zn alloys were studied with pure Zn as control. Commercial Zn alloys demonstrated increased strength and superb elongation compared with pure Zn. Accelerated corrosion rates and uniform corrosion morphologies were observed in terms of commercial Zn alloys due to galvanic effects between Zn matrix and α-Al phases. 100% extracts of ZA4-1 and ZA6-1 alloys showed mild cytotoxicity while 50% extracts of all samples displayed good biocompatibility. Retardant cell cycle and inhibited stress fibers expression were observed induced by high concentration of Zn~(2+) releasing during corrosion. The hemolysis ratios of Zn alloys were lower than 1% while the adhered platelets showed slightly activated morphologies. In general, commercial Zn alloys possess promising mechanical properties, appropriate corrosion rates, significantly improved biocompatibility and good hemocompatibility in comparison to pure Zn. It is feasible to develop biodegradable metals based on commercial Zn alloys.     

Microstructural Evolution of Nb–V–Mo and V Containing TRIP-assisted Steels during Thermomechanical Processing

The microstructural evolution and precipitation behaviour of Nb–V–Mo and single V containing transformation induced plasticity assisted steels were investigated during thermomechanical processing. A plane strain compression testing machine was used to simulate the thermomechanical processing. Microstructures were characterised by optical microscopy, scanning-transmission electron microscopy and microanalysis, and X-ray diffraction analysis, and Vickers hardness was obtained from the deformed specimens. The resulting microstructure of both Nb–V–Mo and V steels at room temperature primarily consisted of an acicular/bainitic ferrite, retained austenite and martensite surrounded by allotriomorphic ferrite.The TEM analysis showed that a signi?cant number of Nb(V,Mo)(C,N) precipitates were formed in the microstructure down to the ?nishing stage in Nb–V–Mo steel(i.e. 830 °C). It was also found that the V(C,N)precipitation primarily occurred in both ferrite and deformed austenite below the ?nishing stage. The results suggested that Nb–Mo additions considerably increased the temperature stability of microalloy precipitates and controlled the microstructural evolution of austenite. However, the microalloy precipitation did not cause a signi?cant precipitation strengthening in both Nb–V–Mo and V steels at room temperature.     

Mechanisms of Solidification Structure Improvement of Ultra Pure 17 wt% Cr Ferritic Stainless Steel by Ti,Nb Addition

The grain structures and the precipitates in the solidification microstructure of the ultra pure 17 wt% Cr ferritic stainless steels with different Ti and/or Nb micro-alloying were investigated both experimentally and theoretically.It was found by the grain structure observation that the addition of Ti or Nb to the steel reduced the grain size (D) and elongation factor (E),and improved the equiaxed grain proportion (P) and globularity factor (ξ).Among the four steels studied,the minimum grain size and maximum equiaxed grain proportion were obtained by jointly adding both Ti and Nb to the steel.The SEM observation indicated that several kinds of precipitations,such as TiN,MC (rich in Nb),Laves phase (Fe2Nb) and so on,formed in the corresponding steels.In addition,the results calculated using the Thermo-Calc software illustrated that TiN precipitates in the liquid at proper Ti and N contents.Meanwhile,the solidification interval (△T) was enlarged by the addition of Ti or Nb,and the effectiveness of Nb was stronger than Ti.Based on the experimental and calculation results,the mechanisms of grain refinement and increment in equiaxed grain proportion were discussed.     

SiCp/Al Composites Fabricated by Modified Squeeze Casting Technique

A cost effective method was introduced to fabricate pure aluminum matrix composites reinforced with 20% volume fraction of 3.5 μm SiC particles by squeeze casting followed by hot extrusion. In order to lower volume fraction of the composites, a mixed preform containing pure aluminum powder and the SiC particles was used. The suitable processing parameters for the infiltration of pure aluminum melt into the mixed preform are： melt temperature 800℃, preform temperature 500℃, infiltration pressure 5 MPa, and solidification pressure 50 MPa. Microstructure and properties of the composites in both as-cast and hot extruded states were investigated. The results indicate that hot extrusion can obviously improve the mechanical properties of the composite.     

Preparation of DyFe_2 and TbFe_2 by Reduction-Diffusion Process

The pure intermetallic compounds (Tb1-x;Dyx)Fe2 are super-magnetostriction materials, which were produced from DyFe2 and TbFe2 in this paper. The thermodynamic possibility and kinetic feasible conditions for DyFe2 and TbFe2 preparation by reduction-diffusion in Ca-Dy2O3-Fe and Ca-Tb4O7-Fe systems were analyzed and the products of DyFe2 and TbFe2 were confirmed by XRD. The contracting core model was applied to describe the reduction-diffusion process in which the diffusion is a rate-controlled step. The apparent activation energies of DyFe2 and TbFe2 processes are 45 and 39 kJ/mol respectively.     

In vitro and in vivo studies on pure Mg,Mg-1Ca and Mg-2Sr alloys processed by equal channel angular pressing

In the present work,the biomedical as-cast pure Mg,Mg–1 Ca and Mg–2 Sr alloys were processed with equal channel angular pressing(ECAP)technique to develop ultrafine microstructure within the materials,and their microstructures,mechanical properties,degradation behavior,cytocompatibility in vitro and biocompatibility in vivo were studied comprehensively.Finer-gained microstructures and improved mechanical properties of these three materials after ECAP were confirmed compared to their as-cast counterparts.Moreover,after ECAP the degradation rate of pure Mg was increased while that of Mg–1 Ca or Mg–2 Sr alloys decreased compared to the ascast counterparts.Additionally,good in vitro cytocompatibility and in vivo biocompatibility of these three materials were revealed by cell cultural tests using osteoblastic MC3 T3-E1 and human mesenchymal stem cells(h MSC)and in vivo animal tests at the lateral epicondyle of SD-rats’femur.This study offers an alternative powerful avenue to achieve good comprehensive properties of magnesium-based biodegradable metals.It might also help to extend the applied range of magnesium-based biodegradable metals in orthopedic field.     

Influence of Small Cr Addition on Thermal Stability and Magnetic Properties of Fe-Co-Zr-Nb-B Glassy Alloys

Fe62Cos-xCrxZr6Nb4B20 （x=0-4 at. pct） metallic glasses show high thermal stability with a maximum supercooled liquid region of about 84.8 K. The addition of 2 at. pct Cr causes the extension of the supercooled liquid region remarkably, leading to the enhancement of thermal stability and glass-forming ability. The crystallization of the Fe-based glassy alloys takes place through a single exothermic reaction, accompanying the precipitation of more than three kinds of crystallized phases such as α-Fe, Fe2Zr and ZrB2. The long-range atomic rearrangements required for the precipitation of the multiple crystalline phases seem to play an important role in the appearance of the large supercooled liquid region through the retardation of the crystallization reactions. The Fe-based alloys exhibit soft ferromagnetic properties. The saturation magnetization decreases with increasing Cr content while the saturated magnetostriction increases as a function of Cr content. There is no distinct change in the saturation magnetization and coercive force with annealing temperature below the crystallization temperature. The devitrification gives rise to a considerable enhancement in both as and He.     

Ultrafine-grained Nb-Cu immiscible alloy implants for hard tissue repair: Fabrication,characterization, and in vitro and in vivo evaluation

The biocompatible metallic implants with strong osteointegration often lack the ability of anti-infection.The biocompatible niobium(Nb) containing the antibacterial copper(Cu), the obtained Nb-Cu alloy, could be a potential candidate to solve this issue. To test this hypothesis, ultrafine-grained Nb-Cu immiscible alloys were fabricated via mechanical alloying and spark plasma sintering. The aim of this study was to investigate the microstructure, mechanical properties, magnetic susceptibility, c...     

A Comparative in vitro Study on Biomedical Zr-2.5X(X=Nb,Sn) Alloys

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 7.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—6AI—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.     

Microstructure Evolution and Tensile Properties of Ti3Al/Ni-based Superalloy Welded Joint

In the present work,the dissimilar joining of a Ti_3AI-based alloy to a Ni-based superalloy was attempted by gas tungsten arc(GTA) welding technology.Sound joints were successfully achieved by using a Cu—Ni alloy as filler material.According to X-ray energy dispersive spectroscopy and X-ray diffraction analysis results three transitional layers at the weld/Ti_3AI interface were verified as follows:Ti_2AINb phase dissolved with Cu and Ni;AI(Cu,Ni)_2Ti,(Cu,Ni)_2Ti and(Nb,Ti) solid solution;Cu-rich phase and a complex multi-element phase.The In718/weld interface is characterized by solid solutions of Ni,Cu,Cr,Fe and Nb.The average tensile strength of the as-welded joints at room temperature is 1 63 MPa,and after a post—weld heat treatment it is increased slightly to 177 MPa.The fracture occurred at the surfacial layer of the joined Ti_3AI base alloy,indicating that the Ti_2AINb layer dissolved with Cu and Ni is the weak link of the Ti_3AI/ln71 8 joint.