JOM

Activation energies for creep of copper at intermediate temperatures, where crystal recovery was negligible, were determined by the simple technique of rapidly alternating the test temperature between T1 and T2 (T2= T1 + about 10°K) throughout a constant stress creep test. The activation energy for creep ΔH was found to be 37,000 ± 3,000 cal per mol, independent of stress and strain. The same creep laws as have been previously established for high temperature creep were found to be valid for creep at intermediate temperatures. But the ΔH was found to be lower than that for self-diffusion in the intermediate temperature range whereas it is known to be equal to that for self-diffusion at high temperatures.

Nitrogen is added to stainless steels to improve their toughness and corrosion resistance. However, it is not well understood how nitrogen may impact the precipitate/matrix interfacial properties. In this work, we consider the (FCC) Fe (001)/NbC (001) interface as a model system to study how interfacial structure, energy, and electron charge are affected by nitrogen using DFT calculations. We compare the structures and energetics of coherent and semi-coherent interfaces by including the elastic contribution component. It is found that nitrogen does not have a significant effect on either the interfacial energy or the atomic arrangement near the interface region. A highly intricate bonding feature is revealed near heterophase interfaces between alloy elements, in which metallic and covalent features are present together with charge transfer. Additionally, the work on determining accurate interfacial energies is at the core of all quantitative precipitation modeling efforts (in particular, in the XMAT Program). In turn, nucleation, growth/dissolution, and coarsening of precipitates contribute critically to the material’s ability to withstand creep, creep fatigue, and other detrimental processes reducing its service life. It is for this reason that developing quantitative understanding of interfaces and their energetics in materials is so important for their development and further improvement.

A hydrometallurgical process for the recovery of pure copper from an intimate mixture of chalcocite and pyrite is discussed. The dissolution of the copper can be accomplished by pressure leaching in an ammoniacal ammonium sulfate solution which results in the production of byproduct ammonium sulfate. In some locations this byproduct is undesirable, and an alternative process has been developed in which the chalcocite concentrate is leached directly in dilute sulfuric acid under an overpressure of air. This procedure converts the sulfide sulfur in the chalcocite to elemental sulfur and gives copper extractions of up to 98%. Any pyrite in the chalcocite concentrate is only slightly attacked during the leach and can thus be conveniently separated from the copper bearing solution together with the elemental sulfur. Sulfuric acid and ferric sulfate which are produced by the oxidation of a small portion of the pyrite, are removed from the leach solution by the addition of limestone. The copper is then recovered from the neutralized solution either by electrolysis or by reduction with hydrogen under pressure. The sulfuric acid which is regenerated in the copper winning operation is recirculated to the leaching step. The principal advantage of the process is that the bulk of the sulfide sulfur in the concentrate remains as unattacked pyrite or is converted to the elemental form, avoiding the need for a sulfuric acid plant to be integrated with the copper refining operation or discharge of sulfur dioxide to the atmosphere.

Discontinuously reinforced titanium alloys have been produced by gasatomizing Ti-6Al-4V (in weight percent) with additions of boron and/or carbon to make a pre-alloyed, in-situ reinforced titanium-alloy powder. The rapid cooling that takes place during atomization results in a fine and uniform dispersion of titanium carbide and titanium boride. The atomized powder can be consolidated using standard titanium powder consolidation methods such as hot isostatic pressing or extrusion and further processed to produce standard mill forms. Mechanical properties of the consolidated product show room-temperature tensile strengths up to 1,470 MPa with an elastic modulus of approximately 140 GPa.

The Ti-Mo-0 system was investigated in the region 0 to 45 wt pet Mo and 0 to 10 wt pet 0, from 600° to 1400°C. Solidus data are also presented. Isothermal sections at 700°, 900°, 1100°, and 1300°C, and vertical sections at 1 and 28 wt pet Mo, and 1 and 10 wt pet O are included.

Porous Fe3O4 scaffolds were fabricated while subject to a low (7.8 mT) magnetic field applied in helical and Bouligand motions using a custom-built tri-axial nested Helmholtz coils-based freeze-casting setup. This setup allowed for the control of a dynamic, uniform low-strength magnetic field to align particles during the freezing process, resulting in the majority of lamellar walls aligning within ± 30° of the magnetic field direction and a decrease in porosity by up to 42%. Similar to how helical and Bouligand structures in nature promote impact resistance, these magnetic field motions produced structures with improved high strain rate mechanical properties. Strain at failure was increased by up to 2 times as cracks deflected to match the applied angles of rotation of the magnetic field.