M.L. Wayman

The thermodynamics of interactive co-segregation of phosphorus and alloying elements in iron and temper-brittle steels

The thermodynamics of co-segregation and precipitation of P and alloying elements (transition metals M and carbon) involved in temper embrittlement of steels are studied quantitatively on the basis of the regular solution model for co-segregation. The equations of this model are fitted to the available Auger data for grain boundary segregation in high purity iron-base alloys and commercial steels, allowing the determination of the intrinsic segregation energies ΔGio and of the binary βPgb, βcgb and ternary βPCgb, ßMPgb interaction coefficients in the grain boundaries. This analysis shows that Ni, Cr, and Mo do not segregateper se in iron whereas Mn does weakly, and that the segregation of these elements is essentially driven by that of P through the strongβMPgb attractive interaction energyat the boundaries. This energy, which increases in the order Ni, Mn, Cr, Mo, is remarkably close to the bulk values βMPB in the corresponding phosphides as calculated on the basis of solubility data. The scavenging of P by M elements with largebulk M-P interactions is shown to play a determining role in low Mo and high (12 pct) Cr steels. The beneficial role of carbon is complex since it drives Mo to the grain boundaries due to the large Mo-C attraction, but it also strongly opposes P segregation due to the large repulsive P-C interaction.

Development of plasma-sprayed bioceramic coatings with bond coats based on titania and zirconia

Bond coats for plasma-sprayed hydroxyapatite (HAp) coatings on Ti-6A1-4V hip endoprotheses are being developed for improved in vivo performance. Bond coat powders consisting of (i) CaO-stabilized zirconia, (ii) a eutectic composition of titania and non-stabilized zirconia, and (iii) titania were applied by atmospheric plasma spraying (APS) to Ti-6A1-4V-coupons and 100 microm-thick Ti-6A1-4V foils. Subsequently, a thick layer of HAp was sprayed onto the thin bond coats. Peel tests on Ti-6A1-4V foil/bond coat/HAp top coat assemblies revealed that titania and titania/ zirconia bond coats increased the peel adhesion strength in a statistically significant way from 22 N m(-1) (HAp without a bond coat) to >42 and 32 N m(-1), respectively. Microstructural investigations by SEM on cross-sections of coatings leached in simulated body fluid for up to 28 days led to the conclusion that the chemically very stable bond coats act as an improved chemical barrier against in vivo release of metal ions from the implant, as well as an improved adhesive bond by development of very thin well-adhering reaction layers, presumbly composed of perovskite, calcium dititanate, and/or calcium zirconate.

Role of molybdenum in phosphorus-induced temper embrittlement

AbstractThe influence of Mo on reversible temper embrittlement(RTE)of a low-alloy 2¼Cr-lNi steel with variableP and Mo contents was studied by establishing the relationships among the Charpy impact transition temperature shifts, the nominal P and Mo concentrations, and their intergranular concentrations as measured by Auger electron spectroscopy. Segregation was also studied in ternary Fe-Mo-P alloys.Embrittlement in the steels exhibits a deep minimum for a nominal Mo content of 0.7 wt-%,while at 1.1 wt-% it resumes its value in the Mo-free steel. The de-embrittling action of Mo has two distinct origins. When dissolved in the ferrite matrix, Mo decreases the segregation of P atoms by tying them up in the grain interior. When segregated at the boundaries, Mo counteracts the embrittling effect of segregated P atoms. The former effect is dominant in low-P steels and ternary Fe-Mo-P alloys, while the latter operates in higher-P steels where the segregation of Mo is enhanced by that of P due to the strongly at...

An investigation of small magnetic particles by means of electron microscopy

Abstract The size distribution of magnetite grains in a basic igneous intrusion has been investigated by means of electron microscopy. The distribution was found to peak at about 1/4 μm and to extend well into the “submicroscopic” region. Many of the smaller particles observed are expected on theoretical grounds to be single-domain grains, and these undoubtedly make a significant contribution to the stable thermoremanent magnetization.

Microstructural and in vitro chemical investigations into plasma-sprayed bioceramic coatings

Hydroxyapatite (HA) coatings plasma sprayed without and with bond coats (titania, zirconia) onto titanium alloy (Ti6A14V) substrates under both atmospheric and low pressure plasma spray conditions were investigated in terms of their microstructure and their resorption resistance during immersion in simulated body fluid (Hanks balanced salt solution). The microstructures of test samples were characterized using SEM on as-sprayed and leached surfaces and on the corresponding cross sections. Selected coating systems were studied by 2-dimensional secondary ion mass spectroscopy imaging to obtain information on plasma spray induced diffusional processes at the coating interfaces, as well as the spatial distribution of minor and trace elements. Coatings consisting of thin (10-15 microm) titania/zirconia (eutectic ratio) and titania bond coats, combined with a 150- to 180-microm thick HA top coat, yielded peel strengths in excess of 32 N/m, as well as sufficient resorption resistance.

The analysis of copper artifacts of the copper inuit

Abstract Metallography and neutron activation analysis have been used to investigate copper artifacts from 19th century archaeological sites associated with the “Copper Inuit” of the west-central Canadian Arctic. A knowledge of the source of the copper from which the artifacts were manufactured - native (local) copper or European (exotic) copper - is important, for example, to studies of the effects of European contact on utilization of native copper and on the general lifestyle of the Copper Inuit. Trace element analysis by neutron activation using the SLOWPOKE reactor has allowed local native copper, from the Coppermine River and Victoria Island, NW Territories, to be clearly distinguished from 19th century European smelted copper, which was found to contain higher concentrations of arsenic, antimony, nickel and selenium. Moreover, optical and scanning electron metallography revealed significant microstructural differences between native copper and the 19th century smelted copper. As a consequence it was possible to differentiate between native copper archaeological artifacts and those produced from smelted copper.

The effects of hydrogen on the deformation and fracture of nickel-iron alloys

Slow strain-rate tensile tests have been performed on hydrogen-charged f.c.c. nickel-iron alloys. The hydrogen embrittlement observed in pure nickel is suppressed by alloying with iron so that the deformation and fracture behaviour of alloys containing 50 and 60 % of iron is unaffected by the presence of hydrogen at levels in the order of 3 cm3/100 g. These and other results indicate that the hydrogen embrittlement of nickel and nickel-iron alloys is associated with the grain boundary precipitation of a hydride which decomposes during or after fracture. As nickel is alloyed with iron the tendency for hydride formation decreases and the hydrogen embrittlement is correspondingly reduced.

Archaeometallurgical contributions to a better understanding of the past

Abstract Archaeometallurgical investigations, and in particular those employing metallographic techniques, have greatly increased our understanding of the past, primarily by improving our knowledge of the histories of technological developments. However, these studies have potential for contributing to our comprehension of many more aspects of life in the past. The series of case studies presented here illustrate the application of metallography not only in elucidating the history of technology but also in areas such as the dating of objects, the determination of the spread of technologies and the nature and implications of the contact of cultures with the ‘outside’ world.

The radiocarbon dating and authentication of iron artifacts.

The continuing improvements in accelerator mass spectrometry (AMS) dating technology mean that it is possible to work on ever smaller samples, which in turn, make an ever wider range of sample potentially available for dating. This paper discusses some of the difficulties arising with the interpretation of AMS dates obtained from carbon in iron. The overriding problem is that the carbon, now in chemical combination with the iron, could have come from a variety of sources with very different origins. These are now potentially an iressolvable mixture in the iron. For iron made over the last millennium, there are the additional problems associated with the use of both fossil fuel and biomass fuel in different stages of the iron making, leading to great confusion, especially with authenticity studies.

The surface segregation behavior of manganese and nickel in iron

Abstract Electron probe micro-analysis and an electrolytic sectioning technique have been used to study the surface segregation of manganese and nickel in Fe-1% Mn, Fe-1% Ni and Fe-1% Mn-1% Ni alloys during annealing in the temperature range 260–760°C. Annealing at and above 590°C causes Mn, but not Ni, to segregate into an enriched surface zone typically 1–2 μm thick underlain by an Mn-depleted zone. The characteristics of the segregation are consistent with a non-equilibrium segregation model which predicts that when solute-vacancy binding energy is low and solute diffusivity is higher than solvent diffusivity, then solute enrichment occurs in the vicinity of vacancy sources. In the case of these alloys it is believed that during annealing in the temperature range where FeO is the predominant oxide, the occurrence of oxidation creates a vacancy flux inward from the surface, thereby allowing high diffusivity solute such as Mn to segregate to the surface. Since Ni diffusion occurs at about the same rate as does Fe self-diffusion, the surface segregation of Ni does not occur.