The formation of martensite in splat-quenched Fe-Mn and Fe-Ni-C alloys

A two-piston splat-quenching technique has been used to prepare splat-quenched Fe-Mn alloys with 0 to 20 wt % Mn, and splat-quenched Fe-Ni-C alloys with a nominal carbon content of 0.1 wt % and 0 to 40 wt % Ni. The resulting alloy microstructures have been investigated by a combination of optical and scanning electron microscopy, X-ray diffractometry, and microhardness testing; and the splat-quenched structures have been compared with the microstructures of similar alloys prepared by conventional solid-state quenching. In both alloy systems, splat-quenching produces a very small as-solidified austenite grain size, and a depression of the martensite transformation temperature as shown by an increased tendency to retain austenite to low temperatures. Because of the combination of a small austenite grain size and, therefore, fine scale martensite structure, splat-quenched martensitic alloys of Fe-Mn and Fe-Ni-C exhibit very high microhardness values.     

Microstructural characteristics of splatquenched aluminium-copper alloys

The microstructural characteristics of a range of splat-quenched aluminium-copper alloys are described. The variation of the microstructure as a function of thickness and composition has been determined, by use of conventional 100 kV and high-voltage electron microscopy, and also by ion-beam thinning techniques. With increasing thickness alloys containing < 13 at. % Cu undergo the coventional aluminium-copper precipitation sequence, but alloys of > 13 at.%Cu exhibit a range of degenerate, radial and parallel eutectic structures. Restriction of examination to standard areas, undergoing similar cooling paths, has enabled valid comparison to be made between specimens of different composition.     

XPS characterization of surface modified titanium alloys for use as biomaterials

Three different Ti alloys of biomedical interest have been studied by means of X-ray photoelectron spectroscopy (XPS) to determine their surface chemical composition in both as-received condition and after oxidation at 750 °C in air for different times. Compositions of the investigated alloys were, in wt.%, Ti-7Nb-6Al, Ti-13Nb-13Zr and Ti-15Zr-4Nb. XPS analyses showed a behaviour of the Ti-7Nb-6Al alloy different from that of the two TiNbZr alloys, evidencing the role of the chemical composition of the alloys on the oxidation mechanisms. The oxidation process generates an aluminium-oxide rich surface on the Ti-7Nb-6Al, while in the case of the TiNbZr alloys a titanium-oxide rich layer is formed. The effect of the heat treatment on the contribution of the minority elements at the surface is also discussed.     

Nanostructured Composite Materials with Improved Deformation Behavior

The recent progress in the development of nanostructured composites is described for Zr‐base multicomponent alloys as a typical example for such materials. These advanced composite materials are attractive candidates for structural as well as functional applications. The combination of high strength with high elastic strain of fully nanocrystalline and glassy alloys renders them quite unique in comparison to conventional (micro‐)crystalline materials. However, one major drawback for their use in engineering applications is the often limited macroscopic plastic deformability, despite the fact that some of these alloys show perfectly elastic‐plastic deformation behavior. To improve the room temperature ductility of either fully nanocrystalline or amorphous alloys, the concept of developing a heterogeneous microstructure combining a glassy or nanostructured matrix with second‐phase particles with a different length‐scale, has recently been employed. This review describes the composition dependent metastable phase formation in the Zr‐(Ti/Nb)‐Cu‐Ni‐Al alloy system, which in turn alters the mechanical properties of the alloys. We emphasize the possibilities to manipulate such composite microstructures in favor of either strength or ductility, or a combination of both, and also discuss the acquired ability to synthesize such in‐situ high‐strength composite microstructures in bulk form through inexpensive processing routes.     

On the glass-forming ability of Ni–P binary alloys

The composition dependence of glass-forming ability (GFA) of Ni–P binary alloys was systematically examined by fabricating ribbons of different thicknesses, and the microhardness of the glassy ribbon was measured. The eutectic alloy Ni_80.4P_19.6 has the best GFA and the highest microhardness in glassy state. As the alloy composition is deviated from the eutectic composition, both GFA and microhardness decrease, accompanied with an increasing full width at half maximum of the main broad peak in the X-ray diffraction spectrum of the glassy ribbon. All these results indicate a close correlation among microstructure, GFA and microhardness for the metallic glass.     

On the metastable miscibility gap in liquid Cu–Cr alloys

Electromagnetically levitated Cu–Cr alloy melts containing 5–70 at.% Cr were splat-quenched onto a chill substrate. The microstructure of the solidified alloys was investigated by scanning electron microscopy. The alloys containing 5–60 at.% Cr showed a droplet-shaped microstructure consisting of Cr-rich spheroids or and dendrites in a Cu-rich matrix, whereas those containing 65 and 70 at.% Cr showed a banded microstructure consisting of alternative Cu-rich and Cr-rich bands. Both types of microstructure presented evidence for metastable phase separation in Cu–Cr alloy compositions, thus verifying the existence of a broad miscibility gap in the undercooled liquid. However, the results suggested that the miscibility gap has a Cr-rich critical composition and a skewed geometry.     

The use of NbTiTa as a high field superconducting alloy

NbTi-based alloys containing 8% and 25% tantalum have been studied for use at fields around 12 tesla and at temperatures between 2 K and 3 K. These materials have significantly higher current densities at reduced temperatures than other NbTi-based alloys. Using the results of these studies, a 10,000 A, nominal 12 tesla conductor has been designed and is presently being fabricated for use in a test coil for the Lawrence Livermore Laboratory HFTF. The alloy selected for that conductor is Nb-43% Ti-25% Ta.     

Fabrication and nano-imprintabilities of Zr-, Pd- and Cu-based glassy alloy thin films

With the aim of investigating nano-imprintability of glassy alloys in a film form, Zr(49)Al(11)Ni(8)Cu(32), Pd(39)Cu(29)Ni(13)P(19) and Cu(38)Zr(47)Al(9)Ag(6) glassy alloy thin films were fabricated on Si substrate by a magnetron sputtering method. These films exhibit a very smooth surface, a distinct glass transition phenomenon and a large supercooled liquid region of about 80 K, which are suitable for imprinting materials. Moreover, thermal nano-imprintability of these obtained films is demonstrated by using a dot array mold with a dot diameter of 90 nm. Surface observations revealed that periodic nano-hole arrays with a hole diameter of 90 nm were successfully imprinted on the surface of these films. Among them, Pd-based glassy alloy thin film indicated more precise pattern imprintability, namely, flatter residual surface plane and sharper hole edge. It is said that these glassy alloy thin films, especially Pd-based glassy alloy thin film, are one of the promising materials for fabricating micro-machines and nano-devices by thermal imprinting.     

Oxidation behaviors of Nb-15W and Nb-15W-10Cr alloys fabricated by vacuum hot-pressing sintering

Vacuum hot-pressing sintering (VHPS) was used for fabricating Nb-15W and Nb-15W-10Cr (at.%) alloys under 30 MPa for 60 min at 1800 °C in pure argon atmosphere. Microstructure and oxidation resistance of both materials were investigated. Microstructure analysis showed that the as-sintered Nb-15W alloy only consisted of α-Nb (W) solid solution and the as-sintered Nb-15W-10Cr alloy composed of α-Nb (W, Cr) solid solution and small amount cubic type NbCr₂ Laves phase due to addition of 10 at.% Cr. The oxidation at 1300 °C for 4 h exhibited that the addition of 10 at.% Cr increased the oxidation rate of Nb-15W alloy. The effects of Cr on the oxidation behaviors are discussed in detail.     

Effects of Solid Solution Treating on the Microstructureand Damping Behaviour of MnCuNiFe Alloys

A high damping condition is easily obtained in Mn-(16~24)Cu-(4~6)Ni-2Fe (at. pct) alloys,when cooling rate is controlled after the solid solution treatment at 1173 K. It is observed that the temperature dependent changes of Iogarithmic decrement in 10 h cooled samples are sensitive to the alloy composition. As compared with water quenching treatment, controlled 10 h cooling improves TN temperature of the alloys extensively by producing a Mn-enriched matrix portion in the alloys. Calcuiations suggest that the relative decreases of Cu and Ni content in the matrix portion be dominated by the Ni content in the original alloys, and therefore, the volume fraction of the Cu, Ni-enriched precipitates is estimated to be about 20% and 10% in the 4Ni and 6Ni alloys, respectively. As a result, the TN temperature fOr each alloy, corresponding to the rising temperature of logarithmic decrement, has been related to the Cu, and Ni content in the Mnenriched matrix. The existence of {110} twinning boundaries is confirmed in the microstructure of both 4Ni and 6Ni alloys. However, the relative lattice strains, which the twinning boundaries act to accommodate, are found largely different in the two alloys. It is considered that boundaries with smaller orientation deviation could coordinate the external Stresses easily by cyclic moving, and therefore, the broader damping peak which occurs in the 10 h cooled 6Ni alloy becomes feasible. Electron diffraction results also indicate possible for mation of many sub-crystals in the matrix phase, which are relatively rotated on some invariant planes. Those sub-crystal boundaries might play some attenuation roles in the temperature range between TN and room temperature.     

Amorphization behaviour in mechanically alloyed Ni—Ta powders

Amorphization behaviour of NixTa100–x alloy powders synthesized by mechanical alloying mixtures of pure crystalline Ni and Ta powders with a Spex high energy ball mill was studied. The mechanically alloyed powders were amorphous for the composition range between Ni10Ta90 and Ni80Ta20. This range is larger than amorphous alloys prepared by the rapid-quenching process or by electron-gun deposition technique. A supersaturated nickel solid solution formed for Ni-rich composition. The thermal stability has been investigated by differential thermal analysis. The crystallization temperature of amorphous Ni—Ta powders was proportional to the Ta content, and the activation energy of amorphous Ni—Ta powders exhibited a maximum near the eutectic composition. It is found that the amorphization rate at the early stage of the mechanical alloying process was faster in the intermediate compositions than those at both Ni- and Ta-rich compositions.     

Quaternary Ti–Zr–Be–Ni bulk metallic glasses with large glass-forming ability

The glass-forming ability (GFA) of Ti–Zr–Be ternary alloys is dramatically improved by partially replacing Be with Ni. Centimeter-scale fully amorphous samples can be obtained in a wide Ni content range of 4 at.%–12 at.%. In particular, some of the developed Ti–Zr–Be–Ni alloys exhibit a critical diameter up to 20 mm, which is larger than that of other quaternary Ti-based bulk metallic glasses (BMGs). Moreover, Ni addition also enhances the yield strength and compressive plastic strain of Ti–Zr–Be alloys obviously. Based on the experimental results, the effect of substituting elements addition on the glass-forming ability of Ti–Zr–Be alloys has been systematically investigated and an empirical composition design method for the development of novel Ti-based BMGs with large GFA has been proposed.     

Thermodynamic properties of silver–palladium alloys determined by a solid state electrochemical method

Silver–palladium alloys have various industrial applications, such as in hydrogen permeation and hydrogen storage materials. The objective of the present study is to determine experimentally the thermodynamic properties of solid state silver–palladium alloys in low temperatures. Thermodynamic measurements of silver–palladium alloys have been performed over a temperature range of 450–750 K by the electromotive force method with superionic conductor AgI as the solid electrolyte. The activity and partial molar Gibbs energy of silver were obtained for Ag–Pd alloys over the whole composition range, and the thermodynamic properties of palladium were calculated using the Gibbs–Duhem equation. The results show that activities of silver exhibit fairly large negative deviations over most of the composition range, and the activities of palladium are characterized by both negative and positive deviations from the ideal Raoultian behavior. The results also show the minimum integral enthalpy of mixing of Ag–Pd alloys to locate at around 60 at.% Ag.     

Hydroxyapatite coating on the Ti-35Nb-xZr alloy by electron beam-physical vapor deposition

The aim of this study was to investigate the hydroxyapatite coating on the Ti-35Nb-xZr alloy by electron beam-physical vapor deposition. The Ti-35Nb-xZr ternary alloys contained from 3 wt.% to 10 wt.% Zr content were manufactured by arc melting furnace. Hydroxyapatite (HA) coatings were prepared by electron-beam physical vapor deposition (EB-PVD) method, and crystallization treatment was performed in Ar atmosphere at 300 and 500 °C for 1 h. The coated surface morphology of Ti-35Nb-xZr alloy was examined by FE-SEM, EDX and XRD, respectively. In order to evaluate the corrosion behavior, the tests were performed by potentiodynamic, cyclic polarization and AC impedance test. All the electrochemical data were obtained using a potentiostat. The Ti-35Nb-xZr alloys exhibited equiaxed structure with β phase, the peak of β phase increased with Zr contents. The hardness and elastic modulus of Ti-35Nb-xZr alloys decreased as Zr content increased. The HA coated layer was approximately 150 nm and Ca/P ratio of HA coated surface after heat treatment at 500 °C was around 1.67. The HA thin film consisted of small droplets with spherical shape by crystallization. From the anodic polarization curves, HA coated and heat treated Ti-35Nb-10Zr alloy showed higher corrosion potential than other samples. HA coated film on the Ti-35Nb-10Zr alloy can be shown high polarization resistance by crystallization.     

Comparison of Fe-Ni based alloys prepared by ball milling and rapid solidification

Mechanical alloying (MA) and rapid solidification (RS) are two important routes to obtain amorphous alloys. An Fe-Ni based metal-metalloid alloy (Fe₅₀Ni₃₀P₁₄Si₆) prepared by these two different processing routes was studied by differential scanning calorimetry, scanning electron microscopy with microanalysis, inductive coupled plasma, X-ray diffraction (XRD) and transmission Mössbauer spectroscopy (TMS). The results were compared with that obtained from other Fe-Ni based alloys of similar compositions. The structural analyses show that the materials obtained by mechanical alloying are not completely disordered after 40 h of milling whereas fully amorphous alloys were obtained by rapid solidification. TMS analyses show that, independent of the composition, after milling for 40 h, about 7% of the Fe remains unreacted. Furthermore, the thermal stability of mechanically alloyed samples is lower than that of the analogous material prepared by rapid solidification. In the MA alloys, a broad exothermic process associated to structural relaxation begins at low temperature. XRD patterns of crystallized alloys indicate that the crystallization products are bcc(Fe,Ni), fcc(Ni,Fe), and (Fe,Ni)-phosphides and -silicides.     

激光熔化沉积工艺对Nb-16Si二元合金显微组织的影响

以纯Nb粉末、纯Si粉末或Nb_5Si_3粉末为原料,采用预置粉末法和双通道同轴送粉法,通过激光熔化沉积(LMD)技术制备3种Nb-16Si二元合金。使用SEM,EDS和XRD等手段分析合金的显微组织特征。结果表明:LMD制备的Nb-16Si合金均由NbSS和Nb_3Si两相组成。原料粉末的堆叠方式和化学状态强烈影响合金的显微组织。以纯元素粉末为原料,预置粉末法制备的Nb-16Si合金,由尺寸约1~5μm的枝晶状初生NbSS和NbSS/Nb_3Si共晶组织组成,合金显微硬度约773HV;双通道同轴送粉法促使显微组织细小均匀化,合金中初生NbSS相呈近等轴状均匀分布,平均尺寸仅约2μm,合金硬度提高至817HV;以Nb+Nb_5Si_3粉末为原料,双通道同轴送粉法制备的Nb-16Si合金呈伪共晶组织,其显微硬度高达907HV。     

Evaluation of Mn substitution for Ni in alumina-forming austenitic stainless steels

There has been increasing interest in the substitution of low-cost Mn for Ni in austenitic stainless steels due to the rising price of Ni. This paper investigates the possibility of such a substitution approach for the recently developed alumina (Al₂O₃)-forming austenitic (AFA) class of heat-resistant stainless steels. Computational thermodynamic tools were utilized to predict the alloy composition range to maintain an austenitic matrix microstructure when Mn is substituted for Ni in the presence of Al, which is a strong body-centered-cubic (BCC) phase stabilizer. Phase equilibria, oxidation behavior, and creep properties of Fe–(10–14)Cr–(5–15)Mn–(4–12)Ni–(2.5–3)Al–Cu–Nb–C–B (in weight percent) based alloys were studied. The alloys based on Fe–14Cr–2.5Al–(5–9)Mn–(10–12)Ni exhibited the best balance of oxidation and creep resistance, which represents approximately 50% reduction in Ni content compared to previously developed AFA alloys. These low-Ni, high-Mn AFA alloys formed protective Al₂O₃ scales up to 973–1073 K in air and at 923 K in air with 10% water vapor. Creep-rupture lives of the alloys under a severe screening condition of 1023 K and 100 MPa were in the 7.2 × 10⁵–1.8 × 10⁶ s (200–500 h) range, which is comparable to or somewhat improved over that of type 347 stainless steel (Fe–18Cr–11Ni base).     

Some aspects of splat-quenching in an inert atmosphere and of the formation of non-crystalline phases in Al-17.3 at. % Cu,germanium and tellurium

An apparatus for splat-quenching by the gun technique in a sealed, inert atmosphere is described. The importance of a low-oxygen quenching atmosphere in promoting efficient spreading of liquid particles and good thermal contact with the quenching surface is shown. A cooling rate of ～10¹⁰ K sec^?1 was estimated from the interlamellar spacing in a quenched Al-17.3 at. % Cu alloy. The process mechanisms of the gun technique are discussed with particular reference to the atomized droplet size and the effective specimen thickness for heat transfer. New non-crystalline phases are reported in electron-transparent areas of splat-quenched foils of Al-17.3 at. % Cu (eutectic composition) pure Ge and pure Te. The glassy Al-Cu phase was also observed in specimens which were chemically thinned from the thicker regions of foils; lattice image studies by high-resolution electron microscopy tentatively suggest that this phase has an amorphous, liquid-like atomic configuration. The peak positions in the electron diffraction patterns of the Ge and Te phases were compared, where possible, with those for the corresponding liquid and vapour-deposited phases. The results for Ge suggest that significant structural rearrangement took place during cooling and freezing from the liquid to give a paracrystalline, tetrahedral short-range order whereas, for Te, the liquid structure was probably largely preserved on freezing.     

具有大过冷液相温度区间的Cu基大块非晶合金的制备和机械性能

利用铜模铸造方法制备了具有大过冷液相温度区间的Cu-Zr-Ti-Ni系高强度Cu基大块非晶合金,对于Cu55Zr55Ti15Ni5合金,最大直径达5mm.过冷液相区温度范围ΔTx达45.48～70.98 K.Cu基玻璃合金棒表现出非常高的机械性能和明显的塑性,对于Cu50Zr25Ti15Ni10、Cu55Zr25Ti15Ni5和Cu54Zr22Ti18Ni6合金,压缩断裂强度分别达2155MPa、2026MPa和1904MPa,维氏硬度分别达674、678和685.加入Co元素扩大了CuZr-Ti-Ni系合金的ΔTx,Cu50Zr22Ti18Ni6Co4合金的ΔTx高达74.5K.     

A novel strategy for developing α+β dual-phase titanium alloys with low Young's modulus and high yield strength

In this study,a novel strategy for developing α+β dual-phase titanium alloys with low Young's modulus and high yield strength was proposed,and a Ti-15Nb-5Zr-4Sn-1Fe alloy was developed through theoret-ical composition design and microstructure manipulation.After hot-rolling and subsequent annealing,a high volume fraction of ultrafine grained α phase embedded in metastable β-matrix was formed in the microstructure as intended.Consequently,this alloy exhibits both low Young's modulus(61 GPa)and high yield strength(912 MPa).The experimental results prove that the proposed strategy is appropriate for developing titanium alloys with superior yield strength-to-modulus ratio than those of conven-tional metallic biomedical materials.Present study might shed light on the research and development of advanced biomedical titanium alloys with low Young's modulus and high yield strength.