The Ni3Al-Ni3Cr-Ni3Ru section of the Ni-Cr-Al-Ru system

An investigation is reported of the 75 at% nickel section of the Ni-Cr-Al-Ru system at 1523 and 1273 K. Constitutional data obtained by electron probe microanalysis, X-ray diffraction and microscopical examination are presented as partial isothermal sections. At 1523 K, the major part of the section consists of phase, while the aluminium-rich region contains a and+ region; the extent of the solid solution of chromium and ruthenium in totals ~ 4 at%. The ruthenium-rich corner of the section shows a two-phase region consisting of + ruthenium-rich solid solution. At 1273 K the,+ and + ruthenium regions increase in extent. The/ mismatch values in the equilibrated alloys studied lie in the range ~ –0.08 to –0.39%. Constitutional features of as-cast alloys are also reported.     

Microstructural and dimensional stabilities of a potential γ/γ′-α(Mo) directionally solidified eutectic superalloy under cyclic thermal exposure to 1000° C

A potential heat-resistant ductile eutectic composite,/-, in the Ni-Al-Mo ternary system has been thermally cycled in the temperature range 200 to 1000° C for up to 1000 cycles in an attempt to examine dimensional as well as microstructural stability of the composite under thermal fatigue conditions. The composite examined has two types of initial microstructure; in one, blocky -Ni₃Al encircles individual-Mo fibres (as-grown condition) whereas in the other, is in the form of fine cuboidal particles uniformly distributed in an Ni-rich fcc matrix (heat-treated condition). Dilatometric measurements upon temperature cycling show that the composite is stable against thermal ratchetting irrespective of initial microstructural conditions. However, the cycling induces microstructural change, which is characterized by segmentation of-Mo fibres or formation of a detrimental brittle phase identified as an intermetallic-NiMo that consumes-Mo fibres whether the fibres are encircled by or not. Post-cycling tensile tests at room temperature show that the fibre damage in the former has no fatal effect on tensile strength and ductility. A beneficial effect of the-encircling configuration is discussed on the basis of the recognition of a peritecto-eutectoid reaction:++ that has been disregarded.     

Elevated temperature deformation behaviour of multi-phase Ni-20 at % Al-30 at % Fe and its constituent phases

The mechanical behaviour of the multi-phase ( + /) alloy Ni-20 at % Al-30 at % Fe and alloys similar to its constituent and / phases, Ni-30 at % Al-20 at % Fe and Ni-12 at % Al-40 at % Fe, respectively, were investigated. When tested in tension at 300 K, the alloys exhibited 20%, 2% and 28% elongation, respectively. At elevated test temperatures (700, 900 and 1100 K), the multi-phase alloy exhibited increased ductility, reaching an elongation in excess of 70% at 1100 K without necking or fracture. Similarly, the alloy demonstrated increased ductility with increasing test temperatures. In contrast, the / alloy showed greatly reduced ductility with increasing temperature and was quite brittle both at 900 and 1100 K. Thus, whilst at room temperature the / phase improved the ductility of the + / aggregate, at elevated temperatures the phase alleviated the brittleness of the / phase, thereby preventing any embrittlement of the multi-phase alloy over the temperature range 300–1100 K. Also, whilst the phase improved the room-temperature strength of the multi-phase alloy, at elevated temperatures where the phase is known to be weak, the / phase improved the strength of the multi-phase alloy up to 900 K, beyond which the strength deteriorated due to disordering and lack of anomalous strengthening in the / component.     

The effective surface energy of brittle materials

The effective surface energy of four brittle materials, alumina, poly(methylmethacrylate), glass, and graphite, is calculated from load/deflection curves of notched bars deformed in three-point bending. Two of the methods, which are commonly used in fracture mechanics studies,viz the modified Griffith treatment and the compliance analysis method, are concerned with the effective surface energy at the initiation of fracture, _I . The third method, the work of fracture test, is concerned with the mean effective surface energy over the whole fracture process, _F . The two estimates of _I give consistent values, and there is no systematic variation of _I with notch depth. Values of _F decrease with increasing notch depth as the fracture process becomes more controlled. For alumina _{I F} . For PMMA and glass _I > _F because of a multiplicity of crack sources during fracture initiation. For graphite _I < _F because of subsidiary cracking as fracture proceeds.     

Stress-induced phase transformations in a hot-deformed two-phase (α2+γ) TiAl alloy

Stress-induced 2, 2 and 9R phase transformations in a hot-deformed Ti–45 at% Al–10 at% Nb alloy have been investigated using high-resolution transmission electron microscopy. The 2 phase transformation is an interface-related process. The interfacial superdislocations emitted from the misoriented semicoherent 2– interface react with each other or with the moving dislocations in the phase, resulting in the formation of the 2 phase. The nucleation of the 2 phase transformation takes place either at the 2– interfaces or at the stacking faults on the basal plane of 2 phase, and the growth of plate is accomplished by the moving of a/61 0 1 0 Shockley partials on alternate basal plane (0 0 0 1)2. The 9R structure was usually found to form at incoherent twin or pseudotwin boundaries. During deformation the interfacial Shockley partial dislocations of these incoherent twin and pseudotwin boundaries may glide on (1 1 1) planes into the matrix, resulting in the formation of 9R structure. The interfaces (including 2– and – interfaces) as well as the crystallographic orientation relationship between the as-received or stress-induced 2, and 9R phase have been analysed. The mechanisms for the stress-induced 2, 2 and 9R phase transformations were also discussed. © 1998 Chapman & Hall     

Effect of retained austenite on the microstructure and mechanical properties of martensitic precipitation hardening stainless steel

The effect of retained austenite () on the microstructure and mechanical properties of a martensitic precipitation hardening stainless steel was experimentally investigated, whose chemical composition was Fe-1.8Cu-15.9Cr-7.3Ni-1.2Mo-0.08Nb-low C, N (mass%). The microstructures of all specimens consist of a typical lath martensite with interlath films of the retained , which is not reverted with aging. Cu-rich precipitates which may contribute to precipitation hardening can not clearly be observed. The tensile properties and Charpy absorbed energy are linearly approximated to the amount of retained as follows: 0.2% Y.S. (MPa) = 1192.3 – 13.6 × %, T.S. (MPa) = 1250.1 – 9.3 × %, El. (%) = 12.16 + 0.43 × %, R.A. (%) = 64.25 + 0.14 × %, and A.E. (J) = 72.5 + 0.8 × %. The introduction of retained is not beneficial to the fatigue limit. An excellent combinations of strength, ductility and toughness obtained in the present work is attributed to the introduction of retained and also to the chemical composition of the specimen used.     

The influence of interfacial dislocation arrangements in a fourth generation single crystal TMS-138 superalloy on creep properties

The morphologies of (001) / interfacial dislocation networks are studied through TEM observations. The lattice misfit has an important relation with creep property for superalloy during high temperature creep deformation. The fourth generation superalloy TMS-138 possesses superior creep properties based on its fine interfacial dislocation networks. The networks have two typical characteristics: closely spaced dislocations and stable square morphology during creep deformation. Such arranged dislocations can effectively prevent the slipping dislocations in the phase from moving through the / interface and improve drastically the creep resistance in the fourth generation superalloy TMS-138.     

Heat Inputs to Sub-mK Temperature Cryostats and Experiments from γ-Radiation and Cosmic Ray Muons

We measured the spectrum of energies deposited by -radiation, emanating from radioactive materials in the laboratory that houses our mK cryostat, and by cosmic ray muons. This allows us to quantify the heat input that adversely affects the lowest temperature accessible in sub-mK experiments. We use our nuclear stage, stage plate and experimental cell as a prototype model system, and calculate the power deposited due to low energy (below 2.65 MeV) background radiation quanta (~20 pW). This is significantly less than the power (~120 pW) deposited in the nuclear and experimental stages by muons. Installation of a 5 cm thick lead wall around the cryostat reduced the energy due to the flux of quanta by a factor of ~10 to ~2 pW, and the number of quanta by a factor of ~20. The lower energy, soft cosmic ray component was also affected by introducing the same thickness of lead, reducing the overall count of cosmic ray derived particles by ~15% and the heat leak to ~100 pW.     

Thermodynamic and structural factors determining the wear resistance of aluminum cast irons

When the carbon content in aluminum cast iron containing about 2.5% Al is reduced (to about 2.5%),. carbon is concentrated near the dendritic branches where a specific variety of pearlite (containing a finely dispersed carbon-rich -phase) is formed, the interdendritic regions remaining ferritic. Modifying cast irons of this kind with cerium leads not only to spherodization of graphite but also to the formation of -phase dendrites with a corresponding reduction in the carbon content in the ferritic matrix surrounding -phase dendrites and pearlite. This has a beneficial effect on the wear resistance of cast iron.     

Precipitation of β particles in a fully lamellar Ti-47Al-2Nb-1Mn-0.5W-0.5Mo-0.2Si (at.%) alloy

The precipitation of (B2) particles at intermediate temperatures, between 760°C and 1050°C, is investigated in a fully lamellar TiAl-WMoSi alloy. The particles, having a thin-plate shape, usually precipitate on the ₂ side of ₂/ interfaces at low aging temperatures in an uneven two-dimensional growth mode. While those formed at higher aging temperatures, growing extensively within the ₂ plate and into the adjacent lamellae, have an ellipsoid shape. The growth of particles at low aging temperatures yields an activation energy of about 366 kJ/mol. It is suggested that at low aging temperatures the growth of particles proceeds via an ₂ precipitation process controlled by diffusion of W and Mo along the /₂ and / interfaces.     

Size-strength effects in sapphire and silicon nitride whiskers at 20° C

Tensile tests at 20° C have been carried out on seventy-three sapphire whiskers and on seventeen silicon nitride whiskers. The sapphire whiskers were of 0001, 1¯120, 10¯10, and 10¯11 orientations, while the silicon nitride whiskers were 0001, 11¯20, and 10¯13. Tensile strengths were in the range 45 to 1500 kg/mm², and deformation was found to be purely elastic. The tensile strength data have been analysed and fitted to empirical equations describing the effect of size on strength for different orientations. These empirical equations have been used to deduce possible fracture nucleation mechanisms. It is concluded that, in the case of 0001 sapphire whiskers, fracture nucleation may be due to dislocation pile-ups or interactions, while in the other cases a Griffith flaw mechanism is probably applicable.     

Phase Transitions in Solid Oxygen as Thermometric Fixed Points

For more than thirty years behaviour of phase transitions in solid oxygen has been the subject of an interest to thermometry because oxygen is one of few substances having three phase transitions in the low temperature range. The triple point of oxygen is the primary fixed point of the International Temperature Scale of 1990 and – and – phase transitions are recommended as secondary fixed points. In this paper heat capacity of oxygen in the region of the – transition is investigated. The heat capacity peak, which has the total width of about 50 mK, has been observed to be composed, in reality, of two sharper peaks separeted by 20 mK. Some preliminary results of the – transition investigation are also reported.     

A generalized model for the uniaxial isothermal deformation of a viscoelastic body

Summary Using the notion of a fractional derivative we formulate a new model for a uniaxial deformation of a visco-elastic body. The basic assumption is that all derivatives ₍₎ with respect to time of the stress depend (with specified weighting factor) on all derivatives ₍₎ with respect to time of the strain (multiplied with another weighting factor), for 01. In this respect our model is a generalization of the Zener model, i.e., it is a Zener fractional model with infinitely many terms. The relation between stress and strain is given in explicit form. For two specific choices of parameters the behavior of the model under suddenly applied stress (creep) and suddenly applied strain (stress relaxation) are examined.     

On the dispersion of gases under the action of the medium

Some general regularities of dispersion of a gas emerging from a nozzle submerged in a liquid are considered. A condition for establishment of the so-called maximum dispersion state is formulated.Notation ₀ coefficient of surface tension at the liquidgas boundary - contact angle of wetting of the nozzle material surface by the liquid - p_at atmospheric pressure - p air pressure - density of the liquid - g gravitational acceleration - h height of the liquid column - ₁, and _g dynamic viscosity coefficients of the liquid and gas, respectively - R and r radii of the bubble and nozzle, respectively - Q and F dimensionless criteria - , , , , and undetermined coefficients - ratio of the circumference of a circle to its diameter     

Microstructural development in cast and aged Ni–Al–Cr-based alloys derived from the B2 type β-NiAl structure

The formation of intermetallic compounds consisting of nickel-rich B2-type NiAl (-phase) ductilized by two-phase A1 ()/L12 () regions provides the possibility of combining ductility and high-temperature performance. Similar microstructures can also form the basis of high-temperature shape memory alloys, due to martensitic transformation of the -phase to an L10-type product. One route by which –/ microstructures can be produced involves the use of chromium as a -stabilizer. However, microstructural development in such a case is complicated by the formation of -Cr precipitates.This paper examines microstructural development and stability in cast Ni-25 at % Al-14 at % Cr, Ni-29 at % Al-22 at % Cr and Ni-27 at % Al-8 at % Cr alloys, together with a more complex material, namely, Ni-20 at % Al-13 at % Co-9 at % Cr-4 at % Ti-1 at % Mo-1 at % V. Both the as-cast condition and samples aged at 850 and 1100 °C for 140 h are examined using transmission electron microscopy. The paper discusses the formation of L10 martensite, intradendritic ', interdendritic /' and -Cr precipitation.     

Effects of carbon content on microstructures and magnetic properties of annealed or solution treated Fe-Cr-Ni-C alloys

The correlations between microstructures and magnetic properties were studied in four Fe-17.5 mass%Cr-2.0 mass%Ni-Xmass%C (X = 0.3–0.6) alloys. Each alloy consisted of ferromagnetic and M₂₃C₆ carbide phases by step-annealing at 1053 K and 848 K. The number of the M₂₃C₆ carbide particles increased with the carbon content, and this microstructural variation caused a deterioration of the soft magnetic properties. On the other hand, the alloy with 0.3 mass% carbon content consisted of ferromagnetic and paramagnetic retained structures after solution treatment at 1473 K. The amount of the stable structure increased with the carbon content, while the amount of the structure decreased. This microstructural variation caused a decrease in the relative permeability, _r, and the stabilization of the paramagnetic property to low temperatures below room temperature. The temperature stability of the _r values was closely related to the martensite start temperature, M _s. From an equation for the estimation of M _s from the chemical compositions of the phase, the M _s's of the alloys with 0.3, 0.4, 0.5 and 0.6 mass%C were estimated to be 326, 289, 241 and 216 K respectively. These values were consistent with the M _s's expected from the microstructures and temperature dependences of the _r values.     

The influence of ageing on the stability of β-γ/γ′ derived microstructures in Ni-Al-Cr-(Co) alloys

Multiphase Ni-Al-(Fe)-(Cr)-(Co)-based intermetallics with (B2)- (A1)/(L1₂), - or - microstructures can exhibit significant room-temperature tensile ductility. In the case of Ni-Al-Cr-based alloys, microstructural development is complicated by the precipitation of -Cr, which can supplant the -phase during ageing of three-phase -/ microstructures. An investigation of the stability, during ageing, of cast Ni-Al-Cr-(Co) alloys with microstructures derived from -/ is reported. In the as-cast condition, the materials investigated consisted of a dendritic matrix containing L1₀ type martensite and interdendritic /. Extensive intra- and interdendritic -Cr precipitation was also observed. The stability during ageing of the interdendritic / microstructure is also considered and transformation of the L1₀ martensite is examined.     

The Ni3Al-Ni3Cr-Ni3Mo section of the Ni-Cr-Al-Mo system

An investigation is reported of the constitution of the 75 at % nickel section of the Ni-Cr-Al-Mo system in the temperature range 1523 to 1073 K. Alloys in the region 10 to 20 at % Al were annealed at 1523, 1273, and 1073 K, respectively, and subjected to electron microprobe analysis, X-ray diffraction, and microscopical and hardness examination. Constitutional data are presented as partial isothermal sections and as vertical sections. At 1523 K the section consists only of fields containing ,+ and , the last mentioned phase being predominant. With decreasing temperature the and + fields increase in extent. Also, the NiMo and Ni₃Mo phases were encountered in the ternary Ni-Al-Mo alloy studied. The quaternary + alloys showed small lattice mismatch values, i.e. up to 0.25%. Raft like morphologies of were found in the quaternary alloys, resulting from directional coarsening. Observations of as-cast structures are also reported.     

Temperature effects on the properties of Ge thin films

The effects of substrate temperature (T_s) on the properties of vacuum evaporated p-type Ge thin films have been investigated for 25s<400°C. Increase in the substrate temperature improves the crystallinity and increases the grain size resulting a gradual change from amorphous to polycrystalline structure which was attained above a substrate temperature of 225°C. Low resistive (1×10^–2 ohm-cm) and high mobility (280 cm²/V·s) films were obtained at T_s=400°C. It has been observed that the conduction mechanism in polycrystalline films was dominated successively by hopping, tunneling and thermionic emission as the sample temperature was increased from 40 to 400 K. In amorphous samples, conduction was described in terms of different hopping mechanisms.     

A novel X-ray technique for inspection of steel pipes

The corrosion-induced material loss in crude oil carrying steel pipelines was originally studied by making use of the backscatter X-ray technique. The steel thickness can be determined by studying the density profile of the backscatter intensity vs. the depth location of a voxel. There are, however, some practical limitations to the above method, and a new method for evaluating steel thickness, namely, the transcatter technique is described. This technique uses the intensity of the beam which is transmitted by the pipe wall and subsequently scattered by the hydrocarbon inside the pipeline. The thickness is evaluated using three techniques, namely, the sequential technique, the dual angle technique, and the reference technique. Of the three techniques, the sequential technique has been studied in detail. The mathematical equations and experimental results related to the transcatter technique show that the thickness can be measured with an accuracy of better than 10% for a nominal steel thickness of 8 mm with a measurement time of several minutes.