Exp-G27 is a new low-cost Ni base wroughtWrought alloy developed by Carpenter Technology Corporation for applications such as jet engineJet engines turbine casing and internal combustion engine exhaust valves. Mainly strengthened by γ’, Exp-G27 has higher temperature stability compared to alloy 718. Within the targeted service temperature range between 704 and 871 °C, Exp-G27 demonstrates comparable mechanical performance as WaspaloyWaspaloy but with a significantly lower raw material cost. However, the creepCreep and stress ruptureStress rupture of Exp-G27 is slightly lower than WaspaloyWaspaloy. In this study, a cost-performance tradeoff study was carried out to help make modification to the original Exp-G27 to achieve superior creepCreep/stress ruptureStress rupture performance than WaspaloyWaspaloy while still being cost competitive.

High performance powder-based Ni-based superalloys exhibit exceptional in-service properties at elevated temperature, however this leads to reduced machinability and the potential for significant machining induced damage. Field assisted sintering technology (FAST) is capable of consolidating powder rapidly and efficiently, allowing for precise control of the microstructure via the dissolution of strengthening phases. In this study, subsolvus and supersolvus dwell temperatures were utilised to produce fine and coarse grain forms of an advanced Ni-based disk alloy. Surface integrity and machining forces were then evaluated after single point turning for a range of surface speeds. Higher cutting forces and lower depths of subsurface damage were generated when machining the fine grain (subsolvus) material when compared to the coarser grained (supersolvus) material. For both material conditions tested, higher surface speeds led to a reduced depth of subsurface deformation due to increased local temperatures, promoting workpiece softening. In addition, at higher cutting speeds the deformation of near surface gamma' precipitates were observed to be greater. These results demonstrate that the FAST process can be utilised to control microstructure, and as a result, tailor the machinability of Ni-based superalloy material. (c) 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0)

Oak Ridge National Laboratory (ORNL) and Carpenter Technology Corporation (Carpenter) participated in an in-kind cost share cooperative research and development agreement (CRADA) effort under the auspices of the Energy Efficiency and Renewable Energy (EERE) Technology Maturation Program to assess material properties of several potential AFA family grades and explore the feasibility of producing alumina-forming austenitic (AFA) stainless steels in tubular form needed for many power generation and chemical process applications. Carpenter's Research Laboratory successfully vacuum melted 30 lb heats of seven candidate AFA alloy compositions representing a wide range of alloy content and intended application temperatures. These compositions were evaluated by ORNL and Carpenter R&D for microstructure, tensile properties, creep properties, and oxidation resistance. In parallel, additional work was directed toward an initial tube manufacture demonstration of a baseline AFA alloy. Carpenter successfully manufactured a 10,000 lb production heat and delivered appropriate billets to a partner for extrusion evaluation. Tube product was successfully manufactured from the baseline AFA alloy, indicating good potential for commercially produced AFA tubular form material.

Physical and Finite Element Modeling (FEM) approaches were used to understand and simulate the geometrical and microstructural development during the co-extrusion of stainless steel/plain carbon steel tubing. The FEM results were used to understand the bulk flow of the materials and the effect of billet geometry on final layer thickness distribution as well as to provide state variable results used in the physical modeling. Novel billet design using a shortened core was proposed in an effort to better control material flow during the co-extrusion of stainless steel/plain carbon steel tubes. In order to minimize the amount of material that is extruded "out of geometrical tolerance" as a result of non-concurrent material flow, the core length in the initial billet was shortened. Extrusion was simulated using DEFORM 2D T finite element modeling software and compared to actual extrusion experiments performed on the industrial press. FEM and industrial scale extrusion results are presented and compared for two different extrusion ratios. There is a strong agreement between the FEM and actual results when investigating the core material distribution throughout the extrudate. It is shown that by reducing the core length in the initial billet approximately 10% -20%, concurrent material flow is promoted during the early stage of extrusion and the amount of out of tolerance material is minimized. Physical modeling performed via isothermal compression tests was used to understand the development of the thermo-mechanically affected zone (TMAZ) in the final product. Due to diffusion of elements at the interface of the two materials, a unique layered microstructure develops, which was further characterized using electron microprobe analysis (EPMA). The approach presented here is sufficient to characterize the deformation behavior and microstructural development of different bi-material systems.

Abstract Precipitation reactions occur in many different alloy systems when one phase transforms into a mixed-phase system as a result of cooling from high temperatures. This article discusses the homogenous and heterogeneous nucleation and growth of coherent and semicoherent precipitates. It describes two precipitation modes, namely, general or continuous precipitation and cellular or discontinuous precipitation. The article also provides information on the precipitation sequences in aluminum alloys.