Push-pull fatigue of LiF at elevated temperatures—II. Microstructures

Microstructural features associated with elevated-temperature fatigue of LiF single crystals is discussed. Debris structure predominates at 200°C. At 250°C and low strain rates, fatigue wall domains of the ‘labyrinth type’ are observed. Persistent slip bands (PSB's) are found in crystals cycled at 300°C, and typical ladder-like PSB structures are prominent at low strain rates. Cellular structures are observed at 365°C at high strain amplitudes. Cracks are found to nucleate at the intersection of slip bands, PSB's are not found at temperatures of 400°C and above. Rather elongated cellular structures are formed at high strain amplitudes. At low strain amplitude at 400°C, fatigue wall domains of the ‘block type’ are observed. Such a structure has not been observed previously. A dislocation model is proposed for the domain structure.     

Characterisation of solid phases in the iron–sulphate–water system where silver is present

A pressure oxidation (POX)-hot cure (HC)-lime boil (LB) process is used in industry to recover silver from refractory gold sulphide ores containing minerals such as pyrite and arsenopyrite. Pressure oxidation is used to oxidise minerals and liberate occluded gold particles. As such, iron goes into solution and under acidic and high-temperature conditions often precipitates as basic iron sulphate (BFS). BFS consumes excess lime during neutralisation before cyanidation. Therefore, a hot cure stage is required to re-dissolve BFS back into solution. BFS re-dissolution consumes acid and produces ferric sulphate. In the presence of silver, these conditions favour the slow formation of silver jarosite. Silver jarosite is refractory to cyanidation and must be broken down before cyanidation. This is done in the lime boil to produce a cyanide-soluble silver hydroxide. A study was conducted to investigate parameters that affect the precipitates that form in each stage of the POX-HC-LB process.     

Transient creep in iron at low stresses and homologous temperatures 0.40–0.54

Transient creep of high purity iron was investigated at low stresses and homologous temperatures 0.40–0.54 using the technique of helicoid specimens. At the intercept grain sizes less than ~ 123 μm, Coble creep operates and the transient creep strain ϵ_i increases linearly with applied stress and systematically with temperature. The duration of the transient creep period t_i is independent of applied stress and increases exponentially with decreasing temperature. The transient creep strain is caused primarily by bowing out of links of the three-dimensional dislocation network accompanied by releasing and moving of some of these links. The relative importance of the latter of these processes increases with temperature. The climb of the links is most probably controlled by dislocation core diffusion. At the intercept grain sizes greater than ~123 μm, Harper-Dorn creep operates. In this region, the transient creep strain ϵ_i increases linearly with applied stress. The influence of temperature on t_i and also the transition strain ϵ_i, is eventually dominated by the effects of mechanical and thermal treatment before creep exposure. Identical processes are suggested to be responsible for transient creep in Regions 1 and 2.     

Influence of sintering conditions on tensile and high cycle fatigue behaviour of powder injection moulded Ti–6Al–4V at ambient and elevated temperatures

Abstract

Tensile and high cycle fatigue properties of Ti–6Al–4V samples fabricated by powder injection moulding (PIM) are examined at room temperature and elevated temperatures. Standard wrought Ti–6Al–4V material is used for comparison. The tensile and the fatigue strength of samples fabricated by powder injection moulding are found to be significantly lower than conventional wrought material. On the other hand, strength and ductility of metal injection moulded (MIM) samples are high enough to be of large practical interest, in particular if the low processing costs for intricate shapes are taken into account. The inferior properties of the MIM material are caused by considerable remaining porosity, enlarged grain size and increased interstitial content. Prolonged sintering times lead to improved density and strength. At the same time, the room temperature ductility is observed to drop to very low levels, presumably because of additional grain growth.     

Stacking fault formation in γ′ phase during monotonic deformation of IN738LC at elevated temperatures

Deformation behaviour of IN738LC in two γ′ morphologies under monotonic loading at elevated temperatures has been studied. Mechanisms of dislocation-γ′ precipitate interaction have been identified. Dislocation reactions leading to stacking fault formation within γ′ have been characterized.     

Deformation mechanisms in h.c.p. metals at elevated temperatures—I. Creep behavior of magnesium

Experiments were conducted to determine the creep behavior of polycrystalline magnesium over the temperature range from 473 to 820 K. The results show the occurrence of three different mechanisms, with the creep process depending on the testing temperature and stress level. At lower temperatures, up to ~600–750 K, the activation energy for creep is equal to ~ 135 ± 10 kJ mole⁻¹. there is normal primary and secondary creep, the stress exponent is close to ~ 5.2. and there is extensive basal slip. This behavior is consistent with control by dislocation climb, with a breakdown in power-law creep at normalized stresses above ~ 1.3 × 10⁻¹. At higher temperatures, above ~600–750 K. and at stresses above ~2.5 MPa, the activation energy for creep. Q. depends on stress, σ, through the relationship Q = (140 ± 10) + (295 σ) kJ mole⁻¹ where σ is in MPa. Under these conditions, there is normal primary and secondary creep, the stress exponent is close to ~ 6.0. and there is extensive non-basal slip. This behavior is consistent with the cross-slip of dislocations from the basal to the prismatic planes, and the constriction energy in magnesium is estimated as ~ 135 ± 10 kJ mole⁻¹. Finally, at high temperatures and stresses below ~ 2.5 MPa, the activation energy is equal to ~ 139 kJ mole⁻¹. there is little or no primary creep, the stress exponent is close to 1.0. and there is an absence of visible surface slip lines. This behavior is attributed to a transition to lattice diffusion creep at these very low stress levels.     

Transfer of iron to Cu–Ni alloys from the lining of the vacuum induction furnace

In Ni–Cu alloys, iron must be excluded in many cases. Iron may enter the alloy from the batch or the furnace lining. Since the Fe₂O₃ content in refractories may be as much as 2.5%, it is important to assess the increase in iron content in alloys on account of interaction with the furnace lining. In the present work, the influence of the Fe₂O₃ content in the crucible and the volume of the crucible on the iron content in the final alloy is studied. Thermodynamic analysis and experimental data indicate that the nickel and copper in Ni–Cu alloys may reduce iron that is present in the lining. When using low-iron batch, iron from the crucible is transferred almost completely to the melt. The increase in iron content in Ni–Cu alloys is investigated as a function of the capacity of the vacuum induction furnace and the Fe₂O₃ content in the periclase crucibles, with complete transfer of the iron from the lining to the melt. With increase in furnace capacity, less iron enters the melt from the crucible. With more than 200 kg of metal, the increase in iron concentration mainly depends not on the furnace capacity but on the Fe₂O₃ content in the refractory. In order to produce Ni–Cu alloys with <0.01% Fe, refractories with Fe₂O₃ content no higher than 0.5% must be used. To produce Ni?Cu alloys with <0.05% Fe, the use of lining refractories with Fe₂O₃ content no higher than 2.5% is recommended.     

The influence of interactional semantic patterns on the interpretation of noun–noun compounds.

The CARIN theory (C. L. Gagné & E. J. Shoben, 1997) proposes that people use statistical knowledge about the relations with which modifiers are typically used to facilitate the interpretation of modifier–noun combinations. However, research on semantic patterns in compounding has suggested that regularities tend to be associated with pairings of semantic categories, rather than individual concepts (e.g., P. Maguire, E. J. Wisniewski, & G. Storms, in press; B. Warren, 1978). In the present study, the authors investigated whether people are sensitive to interactional semantic patterns in compounding. Experiment 1 demonstrated that the influence of a given modifier on ease of interpretation varies depending on the semantic category of the head. Experiment 2 demonstrated that the relation preference of the head noun influences ease of interpretation when the semantic category of the modifier is compatible with that preference. In light of these findings, the authors suggest that people are sensitive to how different semantic categories tend to be paired in combination and that this information is used to facilitate the interpretation process. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Factor analysis of iron–phosphorus PM steel

Abstract

Alloy design and choice of process parameters are often tasks where different investigations lead in different directions and the process of selecting the best parameter settings is difficult. Multivariate statistics are capable of bringing order in such situations, and here data from four different investigations on the Fe–P–C system are collected and evaluated. Effects of chemical composition, compaction pressure, sintering time, and sintering temperature on properties including density, tensile strength, impact energy, proof stress, and elongation are studied. The investigation is based on principal factor analysis. Dimensional reduction is presented and discussed. The study compares the different investigations and the results for the Fe–P–C system show how different properties interact.     

Hydrogen embrittlement of Nb I—Macroscopic behavior at low temperatures

The effect of hydrogen on the ductility of niobium was studied in the temperature range 77–300 K. Tension testing and detailed fractographic studies were used to establish the roles of hydrogen concentration, temperature, yield stress and strain rate in the fracture process. It was shown that two ductility minima can be observed in the temperature range examined and that these are related to the precipitation of hydrides during the deformation process. The fracture mode is cleavage in the temperature range of both ductility minima. The solid solution of H in Nb was shown to be a highly ductile alloy; the ductility being terminated by the formation of a stress induced hydride which exhibits cleavage.A mechanism based on the formation of stress induced hydrides was proposed to account for the embrittlement of Nb-H alloys. This mechanism can account for the observed phenomena and should be generally applicable to systems which form stable hydrides or in which hydrides can be stabilized by an applied stress. A qualitative discussion of stress effects on the equilibrium between solid solution and the hydride is given and is related to the observed fracture phenomena.     

Characterization of Fe–C–Cr Based Hardfacing Alloys

Hardfacing is one of the adaptable methods that can build up the hard and wear resistant surface layer of different materials on the surface of substrate material. It helps them withstand wear, as well as prevent corrosion and high temperature oxidation. In the present investigation three different types of Fe–C–Cr based hardfacing electrodes with varying chemical compositions were deposited on ASTM A36 steel substrate by using manual metal arc welding (MMAW) process. ASTM A36 steel was selected as a base material after consulting with Pressure and Process Boilers, Saharanpur (India), which is a leading manufacturer of boilers. ASTM A36 steel is mostly used by this company for the production of induced draft fans. MMAW process with direct current constant current type power source was used to deposit the hardfaced layers of uniform quality. Straight polarity was used for MMAW process so that more of the arc heat should be concentrated on the electrode. The hardfaced samples were characterized using various characterization techniques and the results of the same were also outlined in the present investigation.