Properties of Phases and Alloys of the Mo–Ni–B System in the Ni–MoNi–Mo2NiB2–Ni2B Region

Materials Science - For alloys of the Mo–Ni–B system annealed at subsolidus temperatures (and some as-cast alloys) in the Ni–MoNi–Mo2NiB2–Ni2B region, we study the...     

Structure of Mo2.0 – x Ni1.0 + x P (x = 0.2) and Some Crystal-Chemical Features of Ternary Phases in the Mo–Ni–P System

The crystal structure of Mo_{2.0 – x} Ni_{1.0 + x} P (x= 0.2) is determined by powder x-ray diffraction (monoclinic symmetry, new structure type, sp. gr. Im, a = 1.04036(5) nm, b= 0.84055(4) nm, c= 0.47357(2) nm, = 91.538(3)°; R _int = 0.094, R _prof = 0.197). The 850°C section of the Mo–Ni–P phase diagram is studied in detail, and the crystal-chemical features of molybdenum nickel phosphides are discussed.     

Thermophysical Properties of Ag and Ag–Cu Liquid Alloys at 1098K to 1573K

The surface tension and density of liquid Ag and Ag–Cu alloys were measured with the sessile drop method. The sessile drop tests were carried out at temperatures from 1098K to 1573 K, on cooling (temperature decreasing stepwise) under a protective atmosphere of high purity Ar (6N). The density of liquid Ag and Ag–Cu alloys decreases linearly with increasing temperature, and an increase in concentration of copper results in a lower density. The surface tension dependence on temperature can be described by linear equations, and the surface tension increases with increasing Cu content. The results of the measurements show good agreement with existing literature data and with thermodynamic calculations made using the Butler equation.     

Structure and Properties of Nanostructured Vacuum-Deposited Foils of Invar Fe–(35–38 wt%)Ni Alloys

The process of electron beam vacuum deposition of the Fe–(35–38 wt%)Ni alloys at substrate temperatures Ts from 300 to700 °C were used to produce vacuum-deposited foils with the FCC structure, differing by the size of characteristic microstructural elements(grains and subgrains). It was shown that refinement of foil microstructural elements to nanoscale is accompanied by their microhardness increase up to 4–5 GPa. The change of the thermal expansion coefficient(TEC) of the nanostructured(NS) foil of the Fe–35.1Ni alloy within the temperature range from-50 to 150 °C has some deviation from that observed for cast Invar alloy of the same composition. It has been found that the main factors affecting the peculiarities of thermal expansion of the NS foil can be related to the presence of small fraction of BCCphase in them, high level of crystalline lattice microstrains and inhomogeneous magnetic order in FCCphase. It was shown that as a result of additional thermal treatment of NS foils their invar properties become similar to that observed for cast Invar alloy but mechanical properties remain on the same level.     

Obtaining of Ni–P–TiO2 Composite Coatings with TiO2 Sol and Surfactants and Their Properties

The influence of surfactants and TiO₂ sol on mechanical, catalytic, and corrosive properties of electroless Ni–P coatings was investigated. Additives of the surfactants caused the decrease of internal stresses in the Ni–P coatings and smoothing of their surfaces. Incorporation of the TiO₂ particles facilitated the rise of microhardness of the Ni–P coatings from 545 ± 11 Hv up to 614 ± 17 Hv. Additives of the surfactants accelerated hydrogen evolution reaction on the composite Ni–P–TiO₂ coatings in acid and alkaline media, and increased photocatalytic activity in methylene blue decomposition. Incorporation of the TiO₂ particles and application of the surfactants resulted in an improvement in the corrosion resistance of original Ni–P coatings in 0.5 M H₂SO₄.     

Decomposition of Fe–(6–20) at.% Mo alloys

Binary iron alloys containing 6, 10, 15 and 20 at.% Mo were investigated. It was found that the “ordering–phase separation” transition is a time depending process: at the beginning of isothermal aging at 550 °C, a modulated structure is formed in the solid solution as a result of the tendency toward phase separation; with time, Fe₂Mo particles precipitate in the modulated structure dissolving as a result of the tendency toward ordering. Further aging at 550 °C leads to the complete dissolution of the modulated structure and Fe₂Mo particles remain the only phase precipitated in the solid solution.     

Properties and microstructure of WC–TiC–Co and WC–TiC–MO2C–Co(Ni) cemented carbides

Abstract

The present study is an attempt to observe the changes in microstructure and properties of modified WC–10Co cemented carbides from the viewpoint of the distinctive role played by modified binder phase. Introduction of TiC into WC–10Co cemented carbide results in microstructural non-uniformity, i.e. a wide range of grain size distribution, which in turn gives rise to a drastic drop in values of transverse rupture strength and toughness. The modification of binder and carbide phases by incorporating, respectively, nickel and M02C improves the microstructural uniformity, which ensures better mechanical properties. The present findings have been interpreted in terms of various quantitative microstructural parameters, with particular attention being given to the wettability factor.

MST/1363     

Microstructure and strengthening mechanisms of a cast Mg–1.48Gd–1.13Y–0.16Zr (at.%) alloy

The microstructure and mechanical properties of a Mg–1.48Gd–1.13Y–0.16Zr (at.%) alloy in the as-cast, solution-treated, peak-aged and over-aged conditions have been investigated by a combination of thermodynamic calculations and experimental approaches. It is shown that both the Mg₂₄(Gd,Y)₅ and cuboid-shaped Mg₅(Gd,Y) phases exist in the as-cast sample, which is in good agreement with the Scheil solidification model. The former is dissolved during solution treatment, while the latter persists and coarsens. Subsequent artificial ageing results in the formation of metastable β′ precipitates within the α-Mg matrix and along the grain boundaries. The peak-aged alloy exhibits maximum ultimate tensile strength and tensile yield strength of 370 and 277 MPa, respectively, at room temperature. Moreover, the strengths decrease gently from room temperature to 250 °C with a gradual increase of elongation. The strengthening contributions to the yield strength are quantitatively evaluated from individual strengthening mechanisms by using measured microstructural parameters. The modelled yield strengths are compared with the experimental results and a reasonable agreement is reached.     

Tensile properties and fracture behaviour of an ultrafine grained Ti–47Al–2Cr (at.%) alloy at room and elevated temperatures

An ultrafine grained (UFG) Ti–47Al–2Cr (at.%) alloy has been synthesized using a combination of high energy mechanical milling and hot isostatic pressing (HIP) of a Ti/Al/Cr composite powder compact. The material produced has been tensile tested at room temperature, 700 and 800 °C, respectively, and the microstructure of the as-HIPed material and the microstructure and fracture surfaces of the tensile tested specimens have been examined using X-ray diffractometry, optical microscopy, scanning electron microscopy and transmission electron microscopy. The alloy shows no ductility during tensile testing at room temperature and 700 °C, respectively, but very high ductility (elongation to fracture 70–100%) when tensile tested 800 °C, indicating that its brittle to ductile transition temperature (BDTT) falls within the temperature range of 700–800 °C. The retaining of ultrafine fine equiaxed grain morphology after the large amount of plastic deformation of the specimens tensile tested at 800 °C and the clear morphology of individual grains in the fractured surface indicate that grain boundary sliding is the predominant deformation mechanism of plastic deformation of the UFG TiAl based alloy at 800 °C. Cavitation occurs at locations fairly uniformly distributed throughout the gauge length sections of the specimens tensile tested at 800 °C, again supporting the postulation that grain boundary sliding is the dominant mechanism of the plastic deformation of the UFG TiAl alloys at temperatures above their BDTT. The high ductility of the UFG alloy at 800 °C and its fairly low BDTT indicates that the material a highly favourable precursor for secondary thermomechanical processing.     

Fabrication and Properties of Ag–Ni Bimetallic Sheathed (Bi,Pb)-2223 Tapes

10-meter-long Ag?CNi bimetallic sheathed (Bi,Pb)-2223 tapes with outer nickel sheath and inner silver sheath have been successfully fabricated by the ??Powder in tube?? technique. Microstructure and phase evolution studies by means of SEM and XRD, as well as critical current density (J _c ) measurements have been performed. It is found that the nickel sheath and dwell time in the first sintering process have great influences on the texture evolution, phase transformation and J _c of the Bi-2223/Ag/Ni tapes. Mono-filament (Bi,Pb)-2223 tape with a J _c of 6656?A?cm^?2 and 61-filament tape with a J _c of 12420?A?cm^?2 are obtained. Although using composite bimetallic sheaths can reduce production costs and improve mechanical properties of the Bi-2223 tapes, the Bi-2223 content and J _c of Bi-2223/Ag/Ni tapes are relatively lower than that of traditional Bi-2223/Ag tapes. Meanwhile, due to higher Bi-2223 content and better alignment of Bi-2223 grains, tapes with 61-filament have higher J _c than mono-filament tapes.     

Effects of Cr Content on the Microstructure and Properties of 26Cr–3.5Mo–2Ni and 29Cr–3.5Mo–2Ni Super Ferritic Stainless Steels

By using scanning electron microscopy,energy-dispersive spectrometry,X-ray diffraction,strength and hardness measurements,the microstructure,precipitation,mechanical properties,and corrosion resistance have been investigated for two super ferritic stainless steels,26Cr–3.5Mo–2Ni and 29Cr–3.5Mo–2Ni,with the aim to consider the effect of Cr content.The results showed that with the addition of Cr content,the recrystallization temperature was increased;the precipitation of Laves and Sigma(σ)phases was promoted and the mechanical properties of super ferritic stainless steel were modified.Furthermore,the pitting corrosion resistance and corrosion resistance to H_2SO_4 of the two super ferritic stainless steels were improved.In addition,suitable annealing processing is a key factor to maintain integrated performance by optimizing microstructure and removing detrimental precipitation phases.     

The effect of annealing on the deformation behaviour and microstructure of crystallized Mg–23.5Ni (wt.%) alloy

Rapidly solidified amorphous Mg–23.5Ni (wt.%) ribbons were crystallized at 300 and 400 °C for 90 min. After annealing at 300 °C the microstructure was heterogeneous, consisting of rounded eutectic–lamellar domains, which contained magnesium grains smaller than 500 nm. In the case of ribbons annealed at 400 °C the microstructure, however, was homogenous, and composed of well-formed magnesium grains and Mg₂Ni particles. At room temperature both crystallized materials were brittle due to the high volume fraction of Mg₂Ni particles, but they exhibited some ductility with increasing test temperature. Above 200 °C, the microstructure of the ribbons annealed at 300 °C was characterised by the formation of particle free zones during the tensile test. This structure was not observed in the material annealed at 400 °C. Deformation behaviour and changes in the microstructure during plastic flow of both crystallized materials were explained according to grain boundary sliding mechanisms.     

Microstructure and wear performance of Ni–20 wt.% Pb hypomonotectic alloys

The tribological properties of Ni–20 wt.% Pb alloys were measured by using a ball-on-disc reciprocating tribo-tester. The effects of load, sliding speed and melt undercooling on wear rate of the sample were investigated. The worn surface of Ni–20 wt.% Pb was examined using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results show that the wear properties of the samples undercooled by 85 and 390 K are obviously superior, which is attributed to more efficient transfer of Pb from the bulk material to the worn surface. The lubricating film is identified as a mixture of Ni₂O₃ and lead oxide by XPS analysis. At the same load or sliding speed, the predominant wear mechanisms can be identified as oxidative wear for the lower and larger undercooling and plastic deformation for the medium undercooling.     

Monte Carlo Study of Magnetic and Thermodynamic Properties of a Ferrimagnetic Ising on the Bathroom Tile (4–8) Lattice

The magnetic properties of mixed spins-1 and 3 /2 Ising model on a bathroom tile (4–8) lattice are studied by Monte Carlo simulation. The total magnetization and the magnetization of each sub-lattice of the mixed-spin lattice have been studied. The reduced transition temperatures are deduced. The variation of the total magnetization with the exchange interactions and the crystal fields is given. Magnetic hysteresis cycle is deduced. Magnetization plateaus appear on the magnetization curves at low temperature.     

Development of high strength in Ni–42Cr–7·7Al (at.-%) alloy

Abstract

An investigation has been made of the aging of supersaturated nickel based solid solution in a Ni–42Cr–7·7 Al (at.-%) alloy. Solution treatment of the alloy in the range 1150–1300°Cfollowed by quenching and aging at ~550–750°C produces high values of hardness and strength, e.g. 835 HV on aging at 600°C. This hardening results from a discontinuous precipitation reaction producing a fine scale lamellar structure consisting of nickel based and chromium based solid solutions; interlamellar spacings of ~60 nm were obtained. The rate of precipitation is substantially greater than that in a binary Ni–42 at.-%Cr alloy.

MST/736     

Effect of Milling Time on the Microstructure and Tensile Properties of Ultrafine Grained Ni–SiC Composites at Room Temperature

Bulk metallic nickel–silicon carbide nano-particle(Ni–Si CNP) composites, with milling time ranged from8 to 48 h, were prepared in a planetary ball mill and sintered using a spark plasma sintering(SPS)furnace. The microstructure of the Ni–Si CNP composites was characterized by transmission electron microscopy(TEM) and their mechanical properties were investigated by tensile measurements. The TEM results showed well-dispersed Si CNP particles, either within the matrix, between twins or along grain boundaries(GB), as well as the presence of stacking faults and twin structures, characteristics of materials with low stacking fault energy. Dislocation lines were also observed to interact with the Si CNP which were plastically nondeformable. A synergistic relationship existed between Hall–Petch strengthening and dispersion strengthening mechanisms, which was shown to greatly influence the mechanical properties of the Ni–Si CNP composites. Both the maximum yield and tensile strengths were found in the Ni–Si CNP composite with a milling time of 48 h, whereas the increased rate of strengths drastically decreased in material milled above 8 h due to the significant Si CNP agglomeration. The ball milling process resulted in the formation of nano-scale, ultra-fine grained(UFG) Ni–Si CNP composites when the milling time was extended for longer periods, greatly strengthening these materials. The sharp decrease in elongation percentages, however, should be comprehensively considered before irreversible inelastic deformation.     

Dielectric and pyroelectric properties of P(VDF-TrFE) and PCLT–P(VDF-TrFE) 0–3 nanocomposite films

Nanocrystalline calcium and lanthanum modified lead titanate (PCLT) powder prepared by a sol–gel process was incorporated into a polyvinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] copolymer matrix to form PCLT–P(VDF-TrFE) nanocomposite thin films with 0.11 volume fraction of ceramic. The relative permittivity and pyroelectric coefficient of the P(VDF-TrFE) copolymer and nanocomposite films were measured as functions of the poling electric field. After poling under the same conditions, the nanocomposite film was found to have a higher pyroelectric coefficient (by ∼35%) and figures of merit than those of the P(VDF-TrFE) film of a similar thickness.