Synthesis of FCC Mg–Zr and Mg–Hf hydrides using GPa hydrogen pressure method and their hydrogen-desorption properties

Magnesium-based hydrides with Zr or Hf have been synthesized by means of an ultra-high pressure technique. Powder mixtures of MgH₂ and ZrH₂ or HfH₂ have been heated up to 873 K under 4–8 GPa in a multi-anvil cell. New ternary phases (Mg–Zr–H and Mg–Hf–H) with a face centered cubic (FCC) structure have been formed. In the Mg–Zr hydride, the FCC phase with disordered metal–atom occupancy was observed, while a Ca₇Ge-type super-lattice structure was observed in the Mg–Hf hydride. By the temperature programmed desorption (TPD) measurements, these new hydrides exhibit the hydrogen-desorption at around 543–583 K, which were 130–70 K lower than that of MgH₂ at a heating rate of 10 K/min under vacuum. Desorbed hydrogen contents were estimated to be 4.2 and 3.0 mass% for Mg–Zr and Mg–Hf hydrides, respectively.     

Effects of small addition of In on the structure of the rapidly cooled Sn–Ag–Zn solder

The effect of small additions of In, up to 1 wt.%, on the microstructure of the eutectic Sn–3.7 wt.%Ag–0.9 wt.%Zn solder was investigated. As observed by microstructural analysis, the increase of In content made β-Sn easy to form but suppressed the formation of the AgZn phase in the Sn–3.7Ag–0.9Zn solder. After annealing at 473 K for 20 and 50 h, the microstructure varied a lot in the morphology of the investigated Sn–Ag–Zn–In solder. The β-Sn dendrites grew coarser but dimmer accompanied with the segregation of the intermetallic compounds (IMCs) along their boundaries. Furthermore, the suppressed Ag–Zn IMCs formed in the Sn–3.7Ag–0.9Zn–1In solder. And the coarsening of the β-Sn dendrites and the growth of IMCs particles in the microstructure of the samples brought a significant softening during annealing of the investigated Sn–Ag–Zn–In alloys.     

The Zn-rich corner of the 450 °C isothermal section of the Zn–Bi–Fe–Ni quaternary system

Following up on recent studies of the isothermal section of the Zn–Fe–Ni, Zn–Fe–Bi and Zn–Bi–Ni ternary systems at 450 °C, the Zn-rich corner of the 450 °C isothermal section of the Zn–Bi–Fe–Ni quaternary system with the Zn being fixed at 93 at.% was determined experimentally using the equilibrated alloys approach. The specimens were investigated by means of scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). It was found there exist 4 two-phase regions, 5 three-phase regions and 2 four-phase regions. Two liquid L (Zn) and L (Bi) can coexist with T, ζ and δ-Ni in this isothermal section, no new phase was found in this study.     

Mechanical properties of alloys of the Al−Si−Zn−Mg−Ti system unmodified and modified with strontium

Conclusion Modifying alloys of the Al–Si–Zn–Mg–Ti system with strontium promotes an increase in their strength and ductility by 10–20%. In the cast condition the greatest elongation is possessed by alloys containing 6–9% silicon and a small addition of zinc. After heat treatment, maximum values of strength and relative elongation are possessed by alloys containing 9–10% Si.V. I. Nikitin Institute of Chemistry, Academy of Sciences of the Tadzhik SSR. V. I. Lenin Chelyabinsk Tractor Factory Production Unit. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 58–62, September, 1985.     

The third-element effect in the oxidation of Ni–xCr–7Al (x = 0, 5, 10, 15 at.%) alloys in 1 atm O2 at 900–1000 °C

The oxidation in 1 atm of pure oxygen of Ni–Cr–Al alloys with a constant aluminum content of 7 at.% and containing 5, 10 and 15 at.% Cr was studied at 900 and 1000 °C and compared to the behavior of the corresponding binary Ni–Al alloy (Ni–7Al). A dense external scale of NiO overlying a zone of internal oxide precipitates formed on Ni–7Al and Ni–5Cr–7Al at both temperatures. Conversely, an external Al₂O₃ layer formed on Ni–10Cr–7Al at both temperatures and on Ni–15Cr–7Al at 900 °C, while the scales grown initially on Ni–15Cr–7Al at 1000 °C were more complex, but eventually developed an innermost protective alumina layer. Thus, the addition of sufficient chromium levels to Ni–7Al produced a classical third-element effect, inducing the transition between internal and external oxidation of aluminum. This effect is interpreted on the basis of an extension to ternary alloys of a criterion first proposed by Wagner for the transition between internal and external oxidation of the most reactive component in binary alloys.     

Formation of unidirectional nanoporous structures in thickly anodized aluminum oxide layer

A series of anodic aluminum oxide(AAO) was grown on the commercially pure 1050 aluminum sheet by controlling electrolyte temperature (2–15 °C) and an odizing time (0.5–6 h), using a fixed applied current density of 3 A/dm² in diluted sulfuric acid electrolyte. A crack-free thick AAO with the thickness of 105–120 μm and containing unidirectional nano sized pores (average pore diameter of 5–7 nm) is successfully achieved in the specimens anodized for 2 h, irrespective of electrolyte temperature. When anodizing time reaches 6 h, very thick AAO with the thickness of 230–284 μm is grown, and average diameter of unidirectional pores is in the range of 6–24 nm. The higher values in both the AAO thickness and pore diameter are attained for the specimens anodized at higher temperatures of 10–15 °C. A crack is observed to exist in the AAO after anodizing up to 4 h and more. A higher fraction (more than 9%) of the crack is shown in the specimens anodized at higher temperatures of 10–15 °C for 6 h and a considerable amount of giant cracks are contained.     

Die steels for high-speed automatic hot die forging machines

Conclusions Steel 3Kh3M3F produced by ESR has the best combination of strength, hardness, and toughness, and also resistance to crazing. The life of punches made of this steel was double that of standard steel 3Kh2V8F and considerably higher than that of steels with a higher carbon content (0.4–0.5%).The life of 3Kh3M3F punches (ESR) was three to four thousand bearing races higher than that of the same steel melted in an open furnace.These data lead us to recommend that punches for high-speed water-cooled presses be manufactured from steel 3Kh3M3F (ESR) with the following chemical composition: 0.26–0.34% C, 2.8–3.3% Cr, 2.5–2.9% Mo, 0.40–0.60% V (ChMTU-1-963-70).The following heat treatment is recommended: preliminary heating in an electric furnace at 500–510°, salt bath at 850–860°, and salt bath at 1040±10°. The parts should be quenched in oil with a temperature of 120–150°. The first tempering after quenching should be conducted in a salt bath at 600° for 2 h, with cooling in air. The second tempering should be conducted in a salt bath at 560° for 2 h, with cooling in air. The hardness of the parts after heat treatment is HRC 49–51.All-Union Scientific-Research Institute of the Bearing Industry. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 20–25, November, 1973.     

Electrochemical hydrogen storage of NdMg12–Ni composites modified with carbon nanotubes and BN particles

In this work, the electrochemical performance of NdMg₁₂–Ni composite electrode in alkaline solution and the effect of the surface modification with carbon nanotubes (CNTs) and boron nitride (BN) particles on the NdMg₁₂–Ni composite were investigated. The NdMg₁₂ alloy was synthesized by a salt-cover-melting and a subsequent quenching process. The NdMg₁₂–Ni–BN and NdMg₁₂–Ni–CNTs composites were prepared by ball-milling NdMg₁₂ alloy, Ni powders and CNTs or BN particles. It is found that CNTs or BN particles are mainly attached onto the surface of the NdMg₁₂–Ni composite after the ball-milling process. The electrochemical experiment results indicate that the NdMg₁₂–Ni composites modified with CNTs or BN particles have the improved electrochemical performance. In particular, the NdMg₁₂–Ni–5 wt.% CNTs and NdMg₁₂–Ni–3 wt.% BN composites have the higher initial discharge capacity of 416.6 mAh/g and 442.9 mAh/g, respectively, larger than the original NdMg₁₂–Ni composite. The large amount of grain boundaries and crystalline defects, induced during the ball-milling process, can accelerate the bulk hydrogen diffusion and provide more surface active sites for the electrochemical reaction of the composites. However, the cycle stability of the composites modified by CNTs or BN particles is still not satisfactory for the practical application.     

Scandium-alloyed aluminum alloys

Conclusion The basic principles of alloying of aluminum alloys with scandium are: it is desirable to add scandium to aluminum alloys in a quantity from 0.1 to 0.3% together with zirconium (0.05–0.15%), which strengthens the positive influence of scandium on the structure and properties of alloys;the greatest effect (that is, the positive influence on mechanical properties and other characteristics) from addition of scandium together with zirconium is observed for alloys not containing alloy elements combining scandium in insoluble phases, specifically the Al–Mg, Al–Zn–Mg, and Al–Mg–Li systems;with a limited copper content alloying with scandium together with zirconium of Al–Zn–Mg–Cu and Al–Cu–Li system alloys is possible.At present on the basis of or taking into consideration the principles developed of alloying of aluminum alloys with scandium commercial aluminum alloys based on the Al–Mg–Sc–Sr (01570, 01571, 01523, 01505), Al–Zn–Mg–Sc–Zr (01970, 01975), and Al–Li–Mg–Sc–Zr (10421, 01423) systems have been developed.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 24–28, January, 1992.     

Fine structure of deformed magnetic alloys

Conclusions Electron microscopic analysis of changes in the fine structure of Fe–Co–Ni–Al–Cu alloys showed that elastic—plastic deformation results in slip in two systems in accordance with the change in the structure in the single-phase solid solution with a bcc lattice. The results of determining the dimensions of deformed blocks by x-ray electron microscopic analysis agree satisfactorily with calculated data. With increasing force of deformation the block sizes decrease; the critical size of the blocks, corresponding to the formation of a crack and fracture, is (1–2)·10³ Å.Tomsk Polytechnical Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 33–35, May, 1974.     

Grain refinement of cast titanium alloys via trace boron addition

The grain size of as-cast Ti–6Al–4V is reduced by about an order of magnitude from 1700 to 200 μm with an addition of 0.1 wt.% boron. A much weaker dependence of reduction in grain size is obtained for boron additions from >0.1% to 1.0%. Similar trends were observed in boron-modified as-cast Ti–6Al–2Sn–4Zr–2Mo–0.1Si.     

Effect of manganese on the microstructure of Mg–3Al alloy

The effect of manganese on the microstructure of Mg–3Al alloy, especially the nucleation efficiency of Al–Mn particles on primary Mg, has been investigated in this paper. Mg–0.72Mn was used to fabricate Mg–3Al–xMn (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) alloys, and the grain sizes of these alloys fluctuate at 390 μm indicating addition of manganese does not evidently influence the grain size of Mg–3Al alloy. Through XRD, FESEM and TEM detection, it is found that Al_0.89Mn_1.11 compound is the dominant Al–Mn phase in Mg–3Al–0.3Mn, Mg–3Al–0.4Mn and Mg–3Al–0.5Mn, and distributes in primary Mg matrix and interdendritic regions with an angular blocky morphology. The number of Al_0.89Mn_1.11 increases gradually with increasing manganese content while the grain sizes of primary Mg are nearly the same in Mg–3Al, Mg–3Al–0.3Mn, Mg–3Al–0.4Mn and Mg–3Al–0.5Mn, indicating Al_0.89Mn_1.11 has low nucleation efficiency on primary Mg.     

Determination of phase equilibria in the Co-rich Co–Al–W ternary system with a diffusion-couple technique

Phase equilibria in the Co-rich Co–Al–W ternary system were determined with a unique diffusion-couple technique in which Co–27Al and Co–15W binary alloys (at. %) were first coupled for interdiffusion and then heat-treated for precipitation. After a diffusion process at 1300 °C for 20 h, concentration gradients of Al and W were formed in the γ-Co(A1) matrix in the vicinity of the coupled interface. After a heat treatment at 900 °C for 500 h the γ′-Co₃(Al,W)(L1₂) phase was formed with a coarsened shape in contact with the γ, CoAl(B2) and Co₃W(D0₁₉) phases. Additionally, it appeared with a submicron cuboidal shape within the γ matrix. After 2000 h, however, the coarsened γ′ phase became infrequent and the three phases of γ, CoAl and Co₃W came into frequent contact with each other. These results clearly demonstrate that the γ′ phase is metastable and the three phases of γ, CoAl and Co₃W are thermodynamically in equilibrium at 900 °C in the Co–Al–W ternary system.     

Oxidation of molybdenum-tungsten-chromium-silicon alloys

The oxidation kinetics of (50–60) wt.% Mo-(35–47) wt.% Cr-(2–5) wt.% Si and (30–40) wt.% Mo-(30–40) wt.% W-(27–37) wt.% Cr-(0–3) wt.% Si alloys were studied between 1000 and 1200°C in a pure oxygen atmosphere. The oxidation of Mo-W-Cr-Si alloys resembled that of Mo-Cr-Si alloys but was much more oxidation resistant. In general, oxidation resistance increased with increasing Cr and Si content. Alloys with good oxidation behavior had a thin outer Cr₂O₃ layer and an internal oxidation zone (in both Mo and Mo-W alloys). Alloys displaying poor oxidation behavior had a porous Cr₂O₃ layer (in Mo alloys) or layers of oxides of W and Cr (in Mo-W alloys). Although the alloy systems were not truly oxidation resistant, definite improvement in oxidation resistance was achieved.     

Effect of boron on ductility of austenitic Cr−Ni−Mn steel with nitrogen

Conclusions Microalloying of Cr–Ni–Mn steel with boron in amounts of 0.002–0.005% (nominal) increased the ductility at 900–1100° by 100–125%, making it insusceptible to hot shortness. This improves the deformability of the ingots and slabs. With an increase of the boron concentration from 0.005 to 0.10% the ductility of the steel is greatly impaired at temperatures above 1100°.In view of the susceptibility of the steel to overheating at temperatures above 1260°, the optimal temperature for heating the ingots is 1240–1260° on condition that they be held in the range of 1200–1220° in the first stage of heating.I. P. Bardin Central Scientific-Research Institute of Ferrous Metallurgy. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 67–69, August, 1975.     

Formation and thermal stability of new Zr–Cu-based bulk glassy alloys with unusual glass-forming ability

The simultaneous addition of Al and Ag to Zr–Cu binary alloys increased in the stabilization of supercooled liquid, the reduced glass transition temperature and γ value, leading to greatly enhance the glass-forming ability (GFA). The Zr–Cu–Ag–Al glassy alloy samples with diameters above 15 mm were obtained in the wide composition range of 42–50 at% Zr, 32–42 at% Cu, 5–10 at% Ag, and 5–12 at% Al. The best GFA was obtained for Zr₄₈Cu₃₆Ag₈Al₈ alloy, and the glassy samples with diameters up to 25 mm were fabricated by an injection copper mold casting. The Zr₄₈Cu₃₆Ag₈Al₈ glassy alloy exhibited high tensile and compressive fracture strength of over 1800 MPa.     

Microstructure and martensitic transformation of Ni–Fe–Ga–Si ferromagnetic shape memory alloys

The effects of the fourth element Si on the martensitic transformation and magnetic properties of Ni–Fe–Ga magnetic shape memory alloys were investigated. A complete thermoelastic martensitic transformation in Ni–Fe–Ga–Si alloys was observed in the temperature range of 218–285 K. The martensitic transformation temperatures of Ni–Fe–Ga alloys are obviously decreased by the substitution of Si for Ga element, that is, the substitution of 1 at.% Si for Ga leads to a decrease of martensitic transformation temperature of about 39.6 K. Moreover, the substitution of Si for Ga leads to a decrease of the saturation magnetic field and the magnetic anisotropy constant K₁ obviously.     

Mixed Sulfidation/Carburization Attack on Several Heat-Resistant Alloys at 900°C

A sulfidation/carburization study of seven commercial heat-resistant alloyswas carried out at 900°C in a H₂–25 vol.%CH₄–14.8N₂–4CO–0.6CO₂–0.6H₂Satmosphere. The equilibrium partial pressures for oxygen (O₂) andsulfur (S₂) were 1.1×10^–22 and 4.1×10^–8 atm,respectively, and the carbon activity for this system was unity. The time ofexposure was 500 hr. Relatively thick, mixed sulfide scales were formed onall of the alloys tested. In addition, internal carburization occurred inall of the alloys. Using metal loss (i.e., the reduction in samplethickness) plus internal attack (internal sulfidation plus internalcarburization) as a performance criterion, an alloy with a nominalcomposition of Ni–29 wt.% Co–28Cr–2.75Si performed thebest, showing 0.71 mm of attack. An alloy with a nominal composition ofFe–20 wt.% Ni–25Cr performed the worst, being totally consumedby the test (>3.18 mm of attack). Alloys containing relatively highamounts of silicon (>2.5%) showed a dramatic increase in theirsulfidation resistance compared to the other alloys containing lowersilicon contents. The amount of iron present within a given material playeda dominant role in the carburization attack that occurred, with as expected,high-iron alloys showing significant internal carburization because of ahigh solubility and diffusivity of carbon in the matrix. The importance ofthe various alloying elements with respect to sulfidation and carburizationresistance is discussed.     

High-temperature oxidation of Fe-Cr-Al-Si alloys extruded into honeycomb structures

The oxidation behavior of Fe–20Cr–5Al–(0.5–5)Si and Fe–(12–20)Cr–(5–7)Al–(1–2)Si alloys extruded into honeycomb structures has been investigated at 1150°C in air for up to 500 hr. The oxidation weight gains decrease with increasing Si and Cr contents in the 5-Al alloys. Si additions are more efficient than Cr additions to reduce the weight gain. Increasing Si content in the 5-Al alloys suppresses the formation of an iron-chromium complex oxide, forming mullite and vitreous silica in the scale, although the location is not clearly indicated. The 5-Si alloy shows anisotropy in elongation of the honeycomb specimen during oxidation in the Fe–20Cr–5Al–xSi alloys, whereas alloying with Si and Cr does not improve the oxidation resistance of the 7-Al alloys significantly. These results are explained by Wagner's theory of a secondary getter. However, we point out additionally that the difference between Si and Cr in the Pilling-Bedworth ratio and the solubility of their oxides in the Al₂O₃ scale may contribute to the significant effect of Si additions. Finally, this paper demonstrates that the selected Fe–Cr–Al–Si honeycombs having walls 200 m thick show excellent oxidation resistance over 500 hr at 1150°C in air. The time to catastrophic oxidation is roughly proportional to the wall thickness in extruded honeycombs.