Structure-property characterization of rheocast and VADER processed IN-100 superalloy

Two recent solidification processes have been applied in the production of IN-100 nickel-base superalloy: rheocasting and vacuum arc double electrode remelting (VADER). A detailed microstructural examination has been made of the products of these two processes; associated tensile strength and fatigue crack propagation (FCP) rate at an elevated temperature were evaluated. In rheocasting, processing variables that have been evaluated include stirring speed, isothermal stirring time and volume fraction solid during isothermal stirring. VADER processed IN-100 was purchased from Special Metals Corp., New Hartford, NY. As-cast ingots were subjected to hot isostatic pressing (HIP) and heat treatment. Both rheocasting and VADER processed materials yield fine and equiaxed spherical structures, with reduced macrosegregation in comparison to ingot materials. The rheocast structures are discussed on the basis of the Vogel-Doherty-Cantor model of dendrite arm fragmentation. The rheocast ingots evaluated were superior in yield strength to both VADER and commercially cast IN-100 alloy. Rheocast and VADER ingots may have higher crack propagation resistance than P/M processed material

Teaching sustainable development in materials science and engineering

Preparing the next generation of materials scientists and engineers requires more than teaching them knowledge of material properties and behaviors. Materials science and engineering must also take into account materials sustainability in the context of society and the environment, as discussed throughout this issue. Including topics such as sustainability in a materials curriculum is not new. Issues of ethics, costs, and so on have long been an integral part of our education. Although detailed treatment of all such topics cannot be included in a general materials education curriculum, the concepts of sustainable development and the role of materials in a sustainable future can be introduced. Indeed, many materials science programs are beginning to include these topics in their curricula. This article discusses three such programs that the authors have helped design and implement in the United States, each taking a different approach to engaging students in these topics. The intention is not to provide an exhaustive overview of education in sustainable development, but rather to describe a range of strategies that are currently being applied and to raise pertinent issues in materials science education

The continuous rheoconversion process (CRP™): optimization & industrial applications

Semi-solid metal (SSM) processing has emerged as a preferred manufacturing scheme due to the superior quality associated with semi-solid castings. In recent years, the driving force to reduce process cost requires the development of robust, commercially viable rheocasting (also termed slurry-on-demand (SoD)) processes. The continuous rheoconversion process (CRP™) is a novel SoD process that was developed at MPI/ WPI. The process is based on a passive liquid mixing technique in which the nucleation and growth of the primary phase are controlled using a specially designed "reactor". The reactor provides heat extraction, copious nucleation, and forced convection during the initial stage of solidification, thus leading to the formation of globular structures. This paper presents our recent work on the optimization of the CRPTM for industrial applications. Specifically, we will discuss critical issues of optimizing and simplifying the process to retrofit most die casting facilities. Salient results from simulations and several industrial trials that have been carried out with ACRC Consortium Members are reviewed and discussed

CASTABILITY MEASURES FOR DIECASTING ALLOYS: FLUIDITY, HOT TEARING, AND DIE SOLDERING

Tautologically, castability is a critical requirement in any casting process. Traditionally, castability in sandand permanent mold applications is thought to depend heavily on fluidity and hot tearing. Givencapital investments in dies, die soldering is a critical parameter to consider for diecasting. We discussquantitative and robust methods to insure repeatable metal casting for diecasting applications by investigatingthese three areas. Weight reduction initiatives call for progressively thinner sections, which in turnare dependent on reliable fluidity. Quantitative investigation of hot tearing is revealing how stress developsand yields as alloys solidify, and this has implications on part distortion even when pressure-castingmethodologies preclude hot tearing failures.Understanding the underlying mechanism of die soldering presents opportunities to develop methodsto avoid costly downtime and extend die life. Through an understanding of castability parameters,greater control over the diecasting process can be achieved

Predicting compositions and properties of aluminum die casting alloys using artificial neural network

Despite the large number of existing alloys and alloy databases, identifying proper alloys for specific applications still remains a challenge. In order to facilitate the selection and prediction of aluminum die casting alloys and their properties, an electronic database - ?i-Select-Al? - has been developed by the Advanced Casting Research Center (ACRC) and the North American Die Casting Association (NADCA). The key to the predictions is the determination of a relationship between alloy properties, chemical composition, and processing variables. Theoretically, these relationships can be ?accurately? determined using fundamental physical principles. However, in practice, the underlying mechanisms are not fully understood and difficult to be utilized. In this case, approximate empirical models are considered. In version 1.0 of the software trend equations have been generated. The nature of these trend equations limits the applicability and prediction ability of the software. In order to improve the prediction power; relationships based on an artificial neural network (ANN) were exploited in version 2.0. ANN has proven to be a highly flexible tool, suitable to treat multiple-input conditions and nonlinear phenomena with complex relationships between input and output variables. This article presents the working mechanisms, the programming, and the application of ANN in this project. The results show that ANN is a valuable modelling tool for predicting properties- fromcomposition and composition- from-properties for aluminum die casting alloys

Effects of Rapid Heating on Solutionizing Characteristics of Al-Si-Mg Alloys Using a Fluidized Bed

Effects of rapid heat transfer using a fluidized bed on the heat-treating response of Al-Si-Mg alloys (both unmodified and Sr modified) were investigated. The heating rate in the fluidized bed is greater than in conventional air convective furnaces. Particle size analyses of eutectic Si showed that the high heating rate during fluidized bed solution heat treatment causes faster fragmentation and spherodization of Si particles compared to conventional air convective furnaces. The mechanism of Si fragmentation through fluidized bed processing is through both brittle fracture and neck formation and its propagation. In contrast to this, the mechanism of Si fragmentation using a conventional air convective furnace is through neck formation and propagation. The Sr-modified D357 alloy showed a faster spherodizing rate than the unmodified alloy. Thermal analyses showed an exothermic reaction during solution heat treatment using a fluidized bed due to recrystallization, and coarsening of eutectic Al grains. Whereas the alloy solutionized using a conventional air convective furnace showed two exothermic reactions, one due to annihilation of point defects and the other due to recrystallization, and coarsening of the eutectic grains in the aluminum matrix. The recrystallization temperature of the alloy solutionized in the fluidized bed is lower than those in the conventional air convective furnace. Both tensile strength and elongation of fluidized bed solutionized alloys are greater than those solutionized using the air convective furnace. The optimum heat-treatment time for T4 temper using a fluidized bed for unmodified and Sr-modified alloy was reduced to 60 and 30 minutes, respectively

Relationship between casting modulus and grain size in cast A356 aluminium alloys

Microstructure of Al-Si alloy castings depends most generally on melt preparation and on the cooling rate imposed by the thermal modulus of the component. In the case of Al-Si alloys, emphasis is put during melt preparation on refinement of pro-eutectic (Al) grains and on modification of the Al-Si eutectic. Thermal analysis has been used since long to check melt preparation before casting, i.e. by analysis of the cooling curve during solidification of a sample cast in an instrumented cup. The conclusions drawn from such analysis are however valid for the particular cooling conditions of the cups. It thus appeared of interest to investigate how these conclusions could extrapolate to predict microstructure in complicated cast parts showing local changes in the solidification conditions. For that purpose, thermal analysis cups and instrumented sand and die castings with different thermal moduli and thus cooling rates have been made, and the whole set of cooling curves thus recorded has been analysed. A statistical analysis of the characteristic features of the cooling curves related to grain refinement in sand and die castings allowed determining the most significant parameters and expressing the cube of grain size as a polynomial of these parameters. After introduction of a further parameter quantifying melt refining an excellent correlation, with a R2 factor of 0.99 was obtained

Ultrasonic Sensing of Porous Granular Media

Emerging high temperature materials such as intermetallic alloys and composites are intrinsically brittle and cannot be either processed or machined by conventional methods. Near net shape processing (of rapidly solidified powders and plasma sprayed foils) using hot isostatic or vacuum hot pressing has recently emerged as a promising method for overcoming these problems. Interestingly, these consolidation processes determine both the component’s final shape and its mechanical properties (which depend on relative density, grain size, etc.). Thus a need has emerged for the control of mechanical properties (1,2)