Systematic Approach to Microstructure Design of Ni-Base Alloys Using Classical Nucleation and Growth Relations Coupled w
- PDF / 582,788 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 39 Downloads / 146 Views
NTRODUCTION
THE advance of physics-based modeling allows microstructure design through processing to produce desired property blends. In Ni-base superalloys, for example, the bimodal particle size distribution (PSD) is believed to have a beneficial set of properties. Recent studies[1] have shown that deformation response of Ni-base disk alloys is governed by the detailed microstructural features of the bimodal c¢ microstructure. These features include the average particle sizes, size distributions, and volume fractions of the secondary (large) and tertiary (small) c¢ precipitates. A typical example of the bimodal microstructure observed in the disk alloys is shown in Figure 1. Optimizing the creep response of these alloys requires a close control of the microstructural features of both the secondary and tertiary particles as a function of alloy composition and heat treatment schedule. Traditionally, controlling microstructural features has been an empirical effort, which is becoming both too costly and too slow for modern engine development cycles. Physics-based modeling promises to give a much tighter control of the microstructure and to make the BILLIE WANG, GK-12 Fellow and YUNZHI WANG, Professor, are with the Department of Material Science and Engineering, The Ohio State University, Columbus, OH, 43210. Y.H. WEN, Research Scientist, is with UES, Inc., Dayton, OH 45432. JEFF SIMMONS, Research Scientist, is with the Air Force Research Laboratory, AFRL, MLLM, Wright Patterson AFB, Dayton, OH 45433. Contact e-mail: jeff[email protected] This article is based on a presentation given in the symposium entitled ‘‘Solid-State Nucleation and Critical Nuclei during First Order Diffusional Phase Transformations’’ which occurred October 15–19, 2006 during the MS&T meeting in Cincinnati, OH, under the auspices of the TMS/ASMI Phase Transformations Committee. Article published online March 29, 2008 984—VOLUME 39A, MAY 2008
most efficient use of experimentalist time by identifying processing windows for the formation of desired microstructures. This work presents a method by which processing conditions favorable for the formation of a desired microstructure may be systematically identified by using a combination of an analysis of nucleation and growth processes and phase field modeling. It is expected that, using approaches such as this, the process of microstructural design can be optimized by replacing the traditional approach of analysis, followed by experimentation, with analysis, followed by modeling, and then followed by experimentation. Bimodal PSDs can develop through a variety of heat treatments. In the many superalloys, such as IN100, microstructure control is achieved by a series of step quenches, where the length and temperature of each isothermal hold controls the size and density of the particle populations. In another class of superalloys, such as Rene88DT, a simpler continuous cool process is employed. It is clear how a step quench could be used to produce a bimodal PSD, because nucleation rates can be controlled d
Data Loading...
