Microstructure and Phase Equilibria in BCC-B2 Nb-Ti-Ru Refractory Superalloys.

Refractory superalloys (RSAs) are promising candidates for high-temperature, high-strength applications. Two-phase RSAs containing body-centered cubic (BCC) and ordered B2 phases are among the more promising candidates. Systems containing Ru-based B2 precipitates exhibit stable two-phase microstructures at temperatures in excess of 1600 °C.

Antimicrobial properties of a multi-component alloy.

High traffic touch surfaces such as doorknobs, countertops, and handrails can be transmission points for the spread of pathogens, emphasizing the need to develop materials that actively self-sanitize. Metals are frequently used for these surfaces due to their durability, but many metals also possess antimicrobial properties which function through a variety of mechanisms. This work investigates metallic alloys comprised of several metals which individually possess antimicrobial properties, with the target of achieving broad-spectrum, rapid sanitation through synergistic activity.

Nitrogen Effects in Additively Manufactured Martensitic Stainless Steels: Conventional Thermal Processing and Comparison with Wrought.

The microstructures of additively manufactured (AM) precipitation-hardenable stainless steels 17-4 and 15-5 were investigated and compared to those of conventionally produced materials. The residual N found in N-atomized 17-4 powder feedstock is inherited by the additively produced material, and has dramatic effects on phase stability, microstructure, and microstructural evolution. Nitrogen is a known austenite stabilizing element, and the as-built microstructure of AM 17-4 can contain up to 90 pct or more retained austenite, compared to the nearly 100 pct martensite structure of wrought 17-4.

Precipitation and dissolution of and during heat treatment of a laser powder-bed fusion produced Ni-based superalloy.

One drawback of the laser powder-bed fusion additive manufacturing (AM) technique is the build-up of residual stresses during processing that require a stress-relief heat treatment prior to components being removed from the build plate. Here, we demonstrate the coprecipitation of the -phase alongside the known -phase, during stress-relief annealing of AM Inconel 625 at 870 °C. The unexpected precipitation of in the AM material is attributed to the local solute enrichment to the interdendritic regions of the as-built solidification microstructure.

Systems Design Approach to Low-Cost Coinage Materials.

A systems approach within an Integrated Computational Materials Engineering framework was used to design three new low-cost seamless replacement coinage alloys to reduce the raw material of the current US coinage alloys. Maintaining compatibility with current coinage materials required matching the currently used alloy properties of yield strength, work-hardening behavior, electrical conductivity, color, corrosion resistance and wear resistance. In addition, the design alloys were required to use current production processes.

Homogenization Kinetics of a Nickel-based Superalloy Produced by Powder Bed Fusion Laser Sintering.

Additively manufactured (AM) metal components often exhibit fine dendritic microstructures and elemental segregation due to the initial rapid solidification and subsequent melting and cooling during the build process, which without homogenization would adversely affect materials performance. In this letter, we report observation of the homogenization kinetics of an AM nickel-based superalloy using synchrotron small angle X-ray scattering. The identified kinetic time scale is in good agreement with thermodynamic diffusion simulation predictions using microstructural dimensions acquired by scanning electron microscopy.

Rafting and Elastoplastic Deformation of Superalloys Studied by Neutron Diffraction.

The rafting of monocrystalline Ni- and Co-based superalloys has been studied by neutron diffractometry. Lattice parameter misfit values and the difference in phase stiffnesses at room temperature, , and are presented. These microstructural parameters should assist in refining computer models that aim to predict precipitate evolution in superalloys and aid future alloy design.

Application of computational thermodynamics to the design of a Co-Ni-based γ'-strengthened superalloy.

A currently available commercial Calphad thermodynamic database was utilized to investigate its applicability to alloy design in the new class of Co-Ni-based γ'-strengthened high temperature alloys. A simple primary design criterion was chosen: maximize the γ' solvus temperature in the six-component Co-Ni-Al-Ti-W-Ta system while ensuring no formation of secondary, potentially deleterious phases. Secondary design considerations included the effects of alloying elements on equilibrium γ' volume fraction and on solidus and liquidus temperatures.

Formation of the NiNb δ-phase in stress-relieved Inconel 625 produced via laser powder-bed fusion additive manufacturing.

The microstructural evolution of laser powder-bed additively manufactured Inconel 625 during a post-build stress-relief anneal of 1 h at 1143 K (870 °C) is investigated. It is found that this industry-recommended heat treatment promotes the formation of a significant fraction of the orthorhombic D0 NiNb δ-phase. This phase is known to have a deleterious influence on fracture toughness, ductility, and other mechanical properties in conventional, wrought Inconel 625; and is generally considered detrimental to materials' performance in service.

Phase equilibria and microstructural evolution in ternary Co-Al-W between 750 °C and 1100 °C.

Phase equilibria between 750 °C and 1100 °C in the Co-rich portion of the Co-Al-W ternary system are investigated via isothermal annealing of five ternary alloy compositions. At temperatures of 900 °C and below, the phase diagram is dominated by a three-phase tie-triangle between γ, D0, and B2. The 1000 °C section contains two three-phase tie-triangles, γ+D0+μ and γ+B2+μ; while only one, γ+B2+μ, exists at 1100 °C.

Additive Manufacturing of 17-4 PH Stainless Steel: Post Processing Heat Treatment to Achieve Uniform Reproducible Microstructure.

17-4 precipitation hardenable (PH) stainless steel is a useful material when a combination of high strength and good corrosion resistance up to about 315 °C is required. In the wrought form this steel has a fully martensitic structure that can be strengthened by precipitation of fine Cu-rich FCC precipitates upon aging. When fabricated via additive manufacturing (AM), specifically laser powder-bed fusion, 17-4 PH exhibits a dendritic structure containing a substantial fraction of nearly 50 % of retained austenite along with BCC/martensite and fine niobium carbides preferentially aligned along interdendritic boundaries.