Comparison on Hot Tearing Behavior of Binary Mg–Al,Mg–Y,Mg–Gd,Mg–Zn,and Mg–Ca Alloys

Metallurgical and Materials Transactions A - Mg–1Al, Mg–0.9Y, Mg–2Gd, Mg–1.5Zn, and Mg–0.5Ca binary alloys were chosen to clarify the hot tearing mechanism since they...     

Phase composition,texture, and anisotropy of the properties of Al–Cu–Li–Mg alloy sheets

The formation of the anisotropy of the mechanical properties, the texture, and the phase composition of thin-sheet Al–4.3Cu–1.4Li–0.4Mg and Al–1.8Li–1.8Cu–0.9 Mg alloys have been studied by X-ray diffraction and tensile tests. Various types of anisotropy of the strength properties of the alloys have been revealed: normal anisotropy (strength in the longitudinal direction is higher than that in the transverse direction) in the Al–4.3Cu–1.4Li–0.4Mg alloy and inverse anisotropy in the Al–1.8Li–1.8Cu–0.9Mg alloy. It is shown that the anisotropy of the strength properties is dependent not only on the texture of a solid solution, but also on the content and the texture of the δ' (Al₃Li) and T1 (Al₂CuLi) phases and their coherency and compatibility of deformation with the matrix.     

A Study on Hot Tearing Susceptibility of Al–Cu,Al–Mg,and Al–Zn alloys

The present investigation deals with the hot tearing susceptibility of A206, A518, and A713 alloys. The hot tearing tests of the mentioned alloys were conducted at three different pouring temperatures using sand mold casting. Metallic cores designed to facilitate constrained radial contraction of the aforementioned alloys were used for casting. Macroscopic cracks were found in all the samples except in A518 alloy. It was observed that pouring temperatural and grain size have significant effect on crack susceptibility. Among the investigated alloys, A713 was found to be extremely prone to hot tearing. The microstructure characteristics of the alloys were studied using optical and scanning electron microscopy. Relationships between the pouring temperature, grain size and crack lengths of the alloys were also established.     

Density and Dynamic Viscosity of Sn,Sn–Ag,and Sn–Ag–Cu Liquid Lead-Free Solder Alloys

Powder Metallurgy and Metal Ceramics - Traditionally, the soldering process was carried out, applying mainly lead-based solder materials. However, the prohibition against using lead (Pb) in...     

The Influence of Synthesis Conditions on the Phase Composition,Structure, and Properties of the High-Entropy Ti–Cr–Fe–Ni–Cu Alloy

Powder Metallurgy and Metal Ceramics - The influence of production conditions on the structure, phase composition, and properties of the high-entropy Ti–Cr–Fe–Ni–Cu alloy...     

Phase Composition,Texture, and Residual Stresses in Al–Cu–Li Friction Stir Welds

The formation of the phase composition, the texture, and the residual stresses in the V-1469 alloy joint (Al–Cu–Li system) fabricated by friction stir welding is studied. A numerical correlation between the phase composition, the hardness, and the residual stresses in various zones and sections of the welded joint is found     

Role of Ti on Phase Evolution,Oxidation and Nitridation of Co–30Ni–10Al–8Cr–5Mo–2Nb–(0, 2 & 4) Ti Cobalt Base Superalloys at Elevated Temperature

Titanium is an important alloying addition to γ/γ′ cobalt-based superalloys that enhances the high temperature microstructural stability and make the alloys lighter. In this work, we probe the role of Ti composition on the phase stability and oxidation behavior of Co–30Ni–10Al–8Cr–5Mo–2Nb superalloys. With Ti addition, the γ′-solvus temperature is enhanced and the γ′-precipitate shape changes from spherical to rounded cuboids. Addition of 4 at. pct Ti to the alloy promotes topologically-close-packed (TCP) phase formation that are rich in Co, Cr, and Mo. During oxidation at 900 °C, Ti was found to facilitate the early formation of passivating oxide layers (spinel CoCr₂O₄/CoAl₂O₄) on the exposed surfaces, however, it was not effective in reducing the oxidation-induced mass gain. Microstructural analysis reveals that Ti delays the Al₂O₃ layer formation eventually leading to faster oxidation kinetics. Additionally, we also found formation of (Ti,Nb)N in the γ′ denuded zones near the alloy-oxide interface.

     

Sintering,microstructure, and mechanical properties of PM manganese–molybdenum steels

Abstract

The effects of 0·5 wt-%Mo addition on the processing, microstructure, and strength of PM Fe–3·5Mn–0·7C steel are described. Water atomised and sponge irons, Astaloy 1·5Mo, milled ferromanganese, and graphite were the starting powders. During sintering in 75H₂ /25N₂ or pure hydrogen the dewpoint was controlled and monitored; in particular the effects of improving it from -35 to -60°C were investigated. Faster heating rates (≥20 K min^-1), sufficient gas flowrates, milling the ferro alloy under nitrogen, a low dewpoint (<-60°C), and a getter powder can all contribute to the reduction or prevention of oxidation of the manganese, in particular formation of oxide networks in the sintered steels. For 600 MPa compaction pressure densities up to 7·1 g cm^-3 were obtained; these were not significantly affected by sintering at temperatures up to 1180°C. The sintered microstructures were sensitively dependent on the cooling rate. Irrespective of the presence of Mo, slow furnace cooling at ～4 K min^-1 resulted in mainly pearlitic structures with some ferrite and coarse bainite, whereas fast cooling at ～40 K min^-1 produced martensite and some retained austenite, very fine pearlite, bainite, and some ferrite. Young's modulus, determined by tensile and ultrasonic tests, was in the range 110–155 GPa. Sintering with -60°C dewpoint resulted in tensile and transverse rupture strengths of420 and 860 MPa for the Mn steel, rising to 530 and1130 MPa as a result of the Mo addition. This contrasts with strength decreases observed when processing included use of high oxygen containing ferromanganese and sintering with -35°C dewpoint.     

Industrial processing,microstructures and mechanical properties of Fe–(2–4)Mn (–0.85Mo)–(0.3–0.7)C sintered steels

Abstract

The potential of PM Mn steels has been established in laboratory experiments. This paper deals with sintering of Fe–(2–4)Mn–(0.3/0.7)C, also with 0˙85%Mo addition, in an industrial pusher furnace at 1180°C in an atmosphere of 25% hydrogen plus 75% nitrogen, obtained from a cryogenic liquid, giving an inlet dew-point of ?55 °C. Tensile, bend (including fatigue) and miniature Charpy specimens were sintered in flowing gases and in semiclosed containers with a getter of ferromanganese, carbon and alumina. The quenched and tem- pered state was investigated, as was sinter hardening (cooling rate of 55 K min ?1), simulated for comparison with slow cooling at 10 K min ?1. As there was no forma tion of oxide networks at the combination of sintering temperature and dewpoint, in accordance with the Ellingham–Richardson diagram for Mn oxidation/reduction, the use of semiclosed containers was superfluous. The quenched and tempered specimens were brittle. Sinter hardening lead to an improvement in mechanical properties. The reproducibility of tensile and TRS data was high for the sintered materials, characterised by Weibull moduli m of 12–41. All the alloy microstructures were complex and heterogeneous, consisting of, depending on the local manganese and carbon contents, the diffusive and non-diffusive transformation products (pearlite, bainite, martensite) and additionally ferrite and retained austenite. The highest mechanical properties in the entire range of compositions investigated in the furnace cooled state: yield, tensile and bend strengths of 499, 637 and 1280 MPa, respectively, with impact energy of 18 J, and tensile and bend strains of 1˙17 and 1.57%, were achieved for the Fe–2Mn–0.85Mo–0.5C alloy, marginally superior to Fe–2Mn–0.7C. For the sinter hardened Fe–4Mn–0.3C alloy yield, tensile and bend strengths were 570, 664 and 1263 MPa, respectively, at an acceptable impact energy of 14 J, with tensile and bend strains of 0.52% and 1.8%. Many of the results compare favourably with the requirements of MPIF standard 35. Mn is a more effective strengthening agent than either Ni or Cu, or their combination, though generally at reduced plasticity.     

Parental beliefs, infant temperament, and marital quality: Associations with infant–mother and infant–father attachment.

The present research examined parental beliefs about the importance of the paternal caregiving role, mothers’ and fathers’ reports of infant temperament, and observed marital quality as predictors of infant–mother and infant–father attachment security, over and above the effects of parental sensitivity. Infants’ attachment security to mothers and fathers were observed in the Strange Situation at 12 and 13 months, respectively (N = 62 two-parent families). Hierarchical regression models revealed that mothers who viewed the paternal caregiving role as important were less likely to have securely attached infants, but only when infant fussiness was high. In addition, fathers who viewed the paternal caregiving role as important were more likely to have securely attached infants, but only when infants’ fussiness or marital quality was high. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Phase Transformation Temperatures, γ–γ′ Lattice Parameter Misfit,and γ′ Precipitate Morphology in Co–Ti–V Alloys

In the context of developing tungsten free cobalt alloys, the physical metallurgical properties of γ′ precipitate strengthened Co–Ti–V alloys were investigated. In this study, few alloys were cast and heat treated to study systematic effects on the properties. The addition of V to the Co–Ti system decreases γ′ solvus temperature, whereas it increases solidus temperature. The γ–γ′ lattice parameter misfit decreases with V addition. The γ′ precipitates have cuboidal with round corners morphology, and the extent of roundedness of corners increases with V addition. Density functional theory calculations were performed to understand the experimental observation of phase transformation temperatures, lattice misfit, and γ′ precipitate morphology. The calculations indicate that magnitude of the heat of formation of Co₃(Ti,V) in the L1₂ crystal structure decreases with V addition. The γ–γ′ interfacial energy at 0 K is predicted to increase with V addition to the Co–Ti system.

     

Deposition,Characterization and Evaluation of Monolayer and Multilayer Ni,Ni–P and Ni–P–Nano ZnO<Subscript>p</Subscript> Coatings

Ni, Ni–P and Ni–P–ZnO_p monolayer films along with multilayer coatings containing different arrangements of these layers were produced on steel substrates by electrodeposition and electroless deposition techniques. Co-deposition of ZnO nano-particles, as well as morphology, cross-section, microstructure and microhardness of coatings were investigated. Corrosion behaviors of monolayer coatings were studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques, and the results were compared to multilayer films. Results revealed that, Ni–P–1.5 vol% ZnO_p monolayer film obtained from a bath with 4 g L^?1 of these particles had the highest hardness between all samples. Further addition of nano-particles to the bath lead to the formation of discontinuous films. Most of the multilayer coatings with different arrangements exhibited higher corrosion resistance as compared to monolayer films. Corrosion current density of three-layer Ni–P–ZnO_p/Ni/Ni–P coating, considered as the most corrosion resistant film, was about 538 times lower than monolayer Ni–P coating.     

Mother–infant responsiveness: Timing, mutual regulation, and interactional context.

Mutual regulation during the naturalistic interaction of 150 mothers and their 4-month-old infants was investigated from a dynamic systems perspective. Microanalyses of a wide range of behaviors and analysis of contingencies indicated that a 3-sec time period best captured contingencies. Both mothers and infants communicated primarily through vocal signals and responses, although maternal touches and infant looks also elicited responses. Although more expressive mothers did not have infants who behaved similarly, levels of contingent responsiveness between partners were significantly associated and occurred within distinct behavioral channels, suggesting coregulated interactional processes in which contingently responsive mothers shape their infants' communications toward mutual similarity. Mothers were more influential than infants over object play, whereas infants were more influential than mothers over expressive behavior. Interactional context consistently influenced contingent responsiveness; there was less mutual responsiveness when the infant was exploring, being held, or looking. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of oxygen atmosphere,FeOx and basicity on mineralogical phases of CaO–SiO2–MgO–Al2O3–FetO–P2O5 steelmaking slag

ABSTRACT

The mineralogical phase of slag after crystallisation is essential to utilisation of steelmaking slag. The mineralogical phases of cooled multicomponent CaO–SiO₂–MgO–Al₂O₃–Fe_tO–P₂O₅ slag with different iron oxide contents and basicities (defined as the ratio of mass percentage of CaO to mass percentage of SiO₂ (w(CaO)/w(SiO₂))) in different atmospheres were investigated in the present work by scanning electronic microscopy and energy dispersed spectroscopy analysis and X-ray diffraction. The mineralogical phases in steelmaking slag cooled in argon are mainly nCa₂SiO₄-Ca₃(PO₄)₂ (thereafter nC₂S-C₃P) solid solution, (Fe, Mn, Mg)O (RO) phase. Some CaMgSiO₄ phases could be found in slag with lower basicity. The mineralogical phases in steelmaking slag cooled in air are mainly nC₂S-C₃P solid solution, spinel phase. The overall crystallisation of slag cooled in both argon and air was enhanced with increasing basicity. However, the crystal sizes become smaller in sample with high basicity. The Fe-enriched phases were transformed from non-faceted RO phase in sample cooled in argon to faceted spinel phases in sample cooled in air. The crystallisation of slag cooled in both argon and air was promoted with increasing FeO_x content. The phosphorus content in solid solution was elevated with decreasing basicity and increasing FeO_x content. It was implied by the present work that appropriate basicity and air oxidation would be beneficial to magnetic separation and phosphorus utilisation.     

Speech perception, metalinguistic awareness, reading, and vocabulary in Chinese–English bilingual children.

In this study, we examined the intercorrelations among speech perception, metalinguistic (i.e., phonological and morphological) awareness, word reading, and vocabulary in a 1st language (L1) and a 2nd language (L2). Results from 3 age groups of Chinese–English bilingual children showed that speech perception was more predictive of reading and vocabulary in the L1 than L2. While morphological awareness uniquely predicted reading and vocabulary in both languages, phonological awareness played such a role after we controlled for morphological awareness only in the L2, which was alphabetic. L1 speech perception and metalinguistic awareness predicted L2 word reading but not vocabulary, after we controlled for the corresponding L2 variables. Hence, there are both similarities and differences between the 2 languages in how the constructs are related. The differences are attributable to variations in language properties and learning contexts. Implications of the present results for an effective L2 learning program are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of air atomisation,spray deposition and melt overflow techniques on microstructural features of Al–Fe–V–Si alloy

Abstract

Microstructural features of atomised powders, spray deposited preforms and melt overflow strips of 8009 series AlFeVSi alloy were investigated to reveal the microstructural evolution associated with the processing condition variations. X-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM) techniques were used to identify the crystal structures of dispersoid phases in the specimens. The primary intermetallic phase was characterised as bcc α-Al(Fe,V)Si having a lattice parameter in the range 12·51–12·53 Å, other phases are identified as icosahedral, Al₃Fe and Al₁₃(Fe,V)₄ by XRD. SEM was used to examine the morphological changes and quantitative element analysis to reveal the chemical composition of these phases in specimens. Various phase morphologies such as starlike, band shape and needlelike intermetallics were observed in these products, whereas the primary phase crystal structure is cubic and stable.     

Effects of basicity,MgO and MnO on mineralogical phases of CaO–FeOx–SiO2–P2O5 slag

The selective separation phosphorous rich phase from steel slag could be an effective way to utilise the steel slag. The mineralogical phase after cooling of steel slag is essential to selective separation of steel slag. In the present work, the mineralogical phases of CaO–FeO_x–SiO₂–P₂O₅ slag after controlled cooling were investigated by X-ray diffraction and scanning electronic microscopy and energy dispersed spectroscopy technique. It was found that the heat treatment at 1573?K would lead to the precipitation of Ca₂SiO₄–Ca₃P₂O₈ (C2S-C3P) solid solution for all samples. The heat treatment at 1273?K would lead to the precipitation of C2S-C3P, CaSiO₃ and Fe₂O₃. The increase of basicity would promote the crystallisation of CaO–FeO_x–SiO₂–P₂O₅ slag. The Effects of additions of MgO and MnO on phase formations of CaO–FeO_x–SiO₂–P₂O₅ slag were also studied. Fe₂O₃ gradually transformed into MgFe₂O₄ and MnFe₂O₄ in slag after crystallisation with addition of MgO and MnO, respectively. The sizes of MgFe₂O₄ and MnFe₂O₄ crystals increased with increases of MgO and MnO content. The increase of MgO and MnO content would promote the precipitation of MgFe₂O₄ phase and MnFe₂O_4, respectively. The precipitation of crystals from slag during cooling was interpreted by the kinetic and thermodynamic factors. It was proposed that addition of MgO and MnO in slag would be beneficial to magnetic separation of steel slag.     

Instruction, teacher–student relations, and math achievement trajectories in elementary school.

Children enter elementary school with widely different skill levels in core subjects. Whether because of differences in aptitude or in preparedness, these initial skill differences often translate into systematic disparities in achievement over time. How can teachers reduce these disparities? Three possibilities are to offer basic skills training, to expose students to higher order instruction, or to provide socioemotional support. Repeated measures analyses of longitudinal data from the Eunice Kennedy Shriver National Institute of Child Health and Human Development Study of Early Child Care and Youth Development revealed that children with low, average, or high math skills prior to elementary school followed different but parallel trajectories of math achievement up through fifth grade. When enrolled in classes with inference-based instruction, however, the initially least skilled children narrowed the achievement gap as long as they did not have conflictual relations with their teachers. They did not make this kind of progress if they were in classes focused exclusively on basic skills instruction or if they were in inference-focused classes but had conflictual relations with teachers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)