A Comparison of the Plastic-Flow Response of a Powder-Metallurgy Nickel-Base Superalloy Under Nominally-Isothermal and T
- PDF / 2,484,870 Bytes
- 16 Pages / 593.972 x 792 pts Page_size
- 82 Downloads / 155 Views
DURING the last 40 years, the computer simulation of metal flow and microstructure evolution during metalworking operations has become a mature technology used widely in industry for selecting processing conditions, die and preform design, lubrication requirements, etc.[1–5] The application of such methods typically requires an extensive database of material properties, the description of friction and heat transfer phenomena at the workpiece-tooling interface, and the characteristics of the forming equipment itself. Key material characteristics include thermophysical properties (such as thermal conductivity/diffusivity and specific heat) and mechanical properties (such as the flow stress
S.L. SEMIATIN and D.W. MAHAFFEY are with the AFRL/ RXCM, Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, OH 45433. Contact e-mail: [email protected] D.J. TUNG and W. ZHANG are with the Materials Science and Engineering Department, The Ohio State University, Columbus, OH 43210. O.N. SENKOV is with the AFRL/RXCM, Air Force Research Laboratory, Materials and Manufacturing Directorate, and also with UES, Inc., 4401 DaytonXenia Road, Dayton, OH 45432. Manuscript submitted September 21, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
as function of strain, strain rate, temperature, and instantaneous microstructure/dislocation substructure). A plethora of laboratory test techniques has been developed to gather flow-stress data. These include the simple compression, uniaxial-tension, and torsion tests.[6] For the simulation of hot-working processes at strain rates of the order of 0.1 to 100 s1, such tests are typically performed under nominally-isothermal conditions in which deviations from the initial test temperature arise primarily from deformation-induced heating that cannot be dissipated rapidly enough into the dies (as in compression tests) or sample shoulders (in tension and torsion tests) to maintain a uniform, constant temperature. These temperature increases can be taken into account when analyzing the flow response in an attempt to describe plastic-flow behavior that would pertain to an idealized, truly-isothermal condition. On the other hand, the neglect of such corrections can provide insight into the deformation resistance of material elements within very large workpieces (e.g., billets, slabs, large open-die forgings) for which deformation heating gives rise to substantial temperature increases and concomitant changes in microstructure evolution. Despite the utility of nominally-isothermal tests to characterize the flow behavior of metallic materials, many metalworking processes involve marked
temperature changes that greatly exceed those associated with deformation-heating alone. Examples include conventional hot forging and extrusion in which heat transfer between a hot workpiece and cold tooling (i.e., so-called ‘‘die chill’’) can produce temperature drops of tens to hundreds of Kelvins per second in local regions near the interface. During such transients, a
Data Loading...
