Cast AerMet100 exhibits mechanical properties comparable to the wrought properties of competing ultrahigh-strength steels; however, the segregation behavior had not been quantified under casting conditions. A microsegregation profile of the as-cast ingot was simulated and homogenization treatments were predicted using Thermo-Calc and DICTRA software. Experimental composition analysis confirmed the simulated microsegregation profile, and the homogenization process occurred at a slightly faster rate than predicted. The convergence of theory and experiment demonstrates the feasibility of designing cast alloy compositions assisted by computer simulation to minimize segregation without casting a large experimental matrix of test ingots.
This paper will describe the processing involved in the manufacture of low and high carbon grades of ASTM Wrought Cobalt-28 Chromium-6 Molybdenum Alloy for Surgical Implants (F 1537) as bar stock for use in a wide variety of biomedical applications. The effect of rolling temperature, annealing temperature, and cold drawing on the mechanical properties and grain size will be explored. Careful control of the thermomechanical working conditions is required to meet high strength requirements because age hardening and cold working of the alloy significantly degrade the ductility while producing the higher strength levels.
Technologies Company Sprayforming is a promising route for production of highly segregation prone alloys such as the high y' fraction nickel alloys that are finding increased usage in the hot stages of aircraft turbines. Conventional ingot metallurgy (IM) is experiencing increasing difficulties with segregation and segregation-related defects such as freckles and white spots with the highly alloyed materials and probably will not be able to produce the next generation of hot stage alloys. Powder metallurgy (PM) is an expensive production route and the oxide cleanliness is inferior to IM. Sprayforming offers the segregation free microstructure of PM with the oxide cleanliness of IM through the clean metal sprayforming (CMSF) technique at a production cost intermediate between IM and PM. Sprayformed Allvac@ 720 Alloy was produced by nitrogen gas atomization and collected as 325 mm diameter billets. The nitrogen atomization eliminated the thermal induced porosity typical of powder metallurgy production using argon atomization and refined the initial structure relative to conventional cast material. The as-sprayed grain size is an equiaxed ASTM 6-7 and the carbonitride particle distribution is l-2 urn. No segregation or segregation-related defects such as freckles or white spots were observed. The response of sprayformed material to thermomechanical processing (TMP) is demonstrated by an experimental forging matrix measuring the effects of heat treatment, strain, and strain rate. The sprayformed material exhibits a strong recrystallization response and the only unrecrystallized grains are observed in low strain rate deformation conditions. The deformation temperature and strain rate are the primary variables affecting the flow stress and the prior heat treatment has a minor effect at lower temperatures in the hot working range.
Dendritic segregation of alloying elements during solidification results in non-uniform chemical and mechanical properties of steels. Homogenization can reduce the composition imbalances and restore uniformnity of mechanical properties. AerMet100 is a high alloy steel produced in wrought forms by Carpenter Technology, Inc. for applications requiring a combination of high strength, high fracture toughness, and resistance to stress corrosion cracking. The nominal composition is (wt%) 13.4% Co, 11.1% Ni, 3.1% Cr, 1.2% Mo, 0.23% C, and the balance Fe. Recent studies of cast and homogenized AerMet100 have demonstrated the mechanical properties approaching the high levels of wrought AerMet100. Optimization of a homogenization treatment for elimination of the microsegregation developed during solidification was completed using thermodynamic/kinetic modeling and quantitative energy dispersive spectrometry (EDS) in scanning electron microscopy.The as-cast alloy has the classic fern-like dendritic structure shown in Figure 1. The primary dendrite arm spacing was 150-400 μm and the secondary arm spacing was 70-110μm.
Superior strength-toughness combinations can be obtained in Aermet 100 by an austenite→martensite phase transformation of small intralath austenite precipitates. The enhanced toughness in these alloys has been attributed to the presence of “metastable” austenite precipitates, the stability of which is intimately related to the size and composition. The austenite precipitates require high stability to resist transformation under all stress conditions except when in the triaxial stress field of a crack tip. The two primary factors determining austenite stability are size and composition. Thus the microstructureproperty correlations and further alloy development require quantitative microchemical analysis of the 50-150Å austenite precipitates.Of the two obvious analytical electron microscopy techniques, energy dispersive spectrometry (EDS) is superior for quantitative results. Several artifacts must be considered when performing quantitative EDS, for example; the continuum background, absorption/fluorescence effects, k-factor measurement and peak overlap. The continuum background fitting is elementary due to the high peak/background ratio and extensive research in this area.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.